Biology End of Course Assessment (E.C.A.) Review

SPEEDWAY HIGH SCHOOL

Biology

End of Course Assessment (E.C.A.) Review

Testing Tips

When answering a short answer/free response question, explain any major

vocabulary words that you use so that the reader knows that you know what it means.

BAD EXAMPLE: “First the cells do transcription then it does translation.” GOOD EXAMPLE: “First the cells make mRNA through the process of transcription, then the cell decodes that mRNA into protein through translation.”

Review each question and make sure that you understand what it is asking and that you answer all the parts.

HINT: If the test asks for 2 examples, give at least 2 examples. Be concise, but if in doubt, explain more than you feel that you need to.

NOTE: Points will not be deducted for too much information, but will be deducted if there is not enough. The grader wants to know that you UNDERSTAND the concept, so show them that you do.

Avoid using pronouns, like it and they. Instead, refer directly to the subject.

BAD EXAMPLE: “It eats the other one and gets energy from it.” GOOD EXAMPLE: “The consumer eats the producer to get energy.”

Do not assume that the reader “knows what you mean.” Study in shorter, frequent bursts instead of cramming.

HINT: You remember lyrics to a song because you hear it frequently, not because you sit for hours listening to it over and over again.

Relax before the test. Trust yourself.

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© Houghton Mifflin Harcourt Publishing Company

2 Indiana Science Standards Review

B.1.1 Indiana Biology

Describe the structure of the major categories of organic compounds which make up living organisms in terms of their building blocks and the small number of chemical elements (carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur) from which they are composed.

STANDARD REVIEW

Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen atoms in the proportion of 1:2:1. Carbohydrates are a key source of energy and are found in most foods. The building blocks of carbohydrates are single sugars, called monosaccharides, such as glucose, C6H12O6, and fructose. Disaccharides are double sugars formed when two monosaccharides are joined. Polysaccharides, such as starch, are chains of three or more monosaccharides.

Lipids are nonpolar molecules that are not soluble or mostly insoluble in water. They include fats, phospholipids, steroids, and waxes. Phospholipids make up the lipid bilayer of cell membranes. Steroids include cholesterol, which is found in animal cell membranes. Fats are lipids that store energy.

Proteins are usually large molecules formed by linked smaller molecules called amino acids. Amino acids are the building blocks of proteins. Some proteins are enzymes and promote chemical reactions. Other proteins have important structural functions.

Nucleic acids are long chains of smaller molecules called nucleotides. A nucleotide has three parts: a sugar, a base, and a phosphate group, which contains phosphorus and oxygen atoms. There are two types of nucleic acids—DNA and RNA—and each type contains four kinds of nucleotides. Chromosomes contain long strands of DNA, which stores hereditary information. RNA plays many key roles in the manufacture of proteins.

STANDARD PRACTICE 1 What are the subunits that make up complex carbohydrates?

A amino acids B fatty acids

C monosaccharides D nucleotides

2 Proteins are used to enable movement, provide structure and support, and carry out important chemical reactions inside the body. What is needed in order for the human body to synthesize proteins?

A a diet rich in amino acids

B sufficient sunlight and water

C 1,200 calories of nutrients per day

D minerals and fats in sufficient amounts

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3 Which type of organic compound is illustrated below?

A carbohydrate

B lipid

C nucleic acid

D protein

4 Phospholipids are a class of lipids that make up cell membranes. A. Describe the structure of phospholipids.

B. Describe how this structure relates to their function in cell membranes.

5 Two of the four principle classes of organic compounds are proteins and nucleic acids. Describe the relationship between proteins and nucleic acids.

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Understand that the shape of a molecule determines its role in the many different types of cellular processes including metabolism, homeostasis, growth and development, and heredity, and understand that the majority of these processes involve proteins that act as enzymes.

STANDARD REVIEW

The chemical reactions in cells occur quickly and at relatively low temperatures because of the action of many enzymes. Enzymes are substances that increase the speed of chemical reactions. Most enzymes are proteins. Enzymes are catalysts, or substances that reduce the activation energy of a chemical reaction. An enzyme increases the speed of a chemical reaction by reducing the activation energy of the reaction. Enzymes help organisms maintain homeostasis. Without enzymes, chemical reactions would not occur quickly enough to sustain life.

Enzymes assist biochemical reactions by bringing key molecules together. A substance on which an enzyme acts during a chemical reaction is called a substrate. Enzymes act only on specifi c substrates, and an enzyme’s shape determines its activity. Typically, an enzyme is a large protein with one or more deep folds on its surface. These folds form pockets called active sites. An enzyme’s substrate fi ts into the active site. An enzyme acts only on a specifi c substrate because only that substrate fi ts into its active site. Cells in the body contain many different enzymes, and each enzyme catalyzes a different chemical reaction.

Any factor that changes the shape of an enzyme can affect the enzyme’s activity. For example, enzymes operate most effi ciently within a certain range of temperatures. Temperatures outside this range can either break or strengthen some of the enzyme’s bonds, changing its shape. Moreover, each enzyme operates best within a certain range of pH values. A pH value outside this range can cause bonds in an enzyme to break, reducing the enzyme’s effectiveness.

STANDARD PRACTICE 1 Which characteristic of an enzyme is generally MOST important to its function?

A color of active site B shape of active site

C shape of overall protein D density of overall protein

2 Living things use enzymes in the chemical reactions of metabolism. When food is digested, it is metabolized to release energy. Which statement BEST describes the role of an enzyme in this process?

A Because enzymes are proteins, they react only with other protein molecules, resulting in the production of glucose.

B The active site of the enzyme attached to the substrate of a food molecule produces carbon molecules, the building blocks of cells.


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C The active site of an enzyme attached to a substrate prevents the chemical reactions involved in metabolism from happening too quickly.

D The active site of the enzyme binds to a substrate on a food molecule and the enzyme changes shape slightly, causing a chemical reaction to happen.

3 Many of the proteins in the human body are enzymes that catalyze chemical reactions. What is the relationship between enzymes and activation energy?

A When an enzyme catalyzes a reaction, it increases the activation energy of the reaction.

B When an enzyme catalyzes a reaction, it increases the activation energy of the product.

C When an enzyme catalyzes a reaction, it decreases the activation energy of the reaction.

D When an enzyme catalyzes a reaction, it does not affect the activation energy of the reaction.

4 Enzymes are specific. That is, each enzyme acts on only one type of substrate and catalyzes only one type of chemical reaction.

A. Describe what a substrate is.

B. Explain why one enzyme cannot act on more than one type of substrate.

5 Describe how changes in temperature or pH can cause an enzyme to stop functioning.

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Explain and give examples of how the function and differentiation of cells is infl uenced by their external environment, including temperature, acidity and the concentration of certain molecules, and that changes in these conditions may affect how a cell functions.

STANDARD REVIEW

Cells are affected by their external environments. One factor that can affect cells is the relative concentrations of dissolved particles on either side of the cell membrane. The direction of water movement across the cell membrane (by osmosis) depends on the rela-tive concentrations of free water molecules in the cytoplasm and in the fl uid outside the cell. There are three possibilities for the direction of water movement:

1. Water moves out. When water diffuses out of the cell, the cell shrinks. A solution that causes a cell to shrink because of osmosis is called a hypertonic solution. If the fl uid outside the cell has a higher concentration of dissolved particles than the cytoplasm has, then the outside fl uid also has a lower concentration of free water molecules than the cytoplasm.

2. Water moves in. When water diffuses into the cell, the cell swells. A solution that causes a cell to swell because of osmosis is called a hypotonic solution. If the fl uid outside the cell has a lower concentration of dissolved particles than the cytoplasm has, then the outside fl uid also has a higher concentration of free water molecules than the cytoplasm.

3. No net water movement. If the cytoplasm and the fl uid outside the cell have the same concentration of free water molecules, water diffuses into and out of the cell at equal rates. This results in no net movement of water across the cell membrane, and the cell stays the same size—a state of equilibrium. A solution that produces no change in cell volume because of osmosis is called an isotonic solution.

STANDARD PRACTICE 1 What will MOST LIKELY happen to a cell placed in an isotonic solution?

A It will burst. B It will shrink.

C It will lose water. D It will stay the same size.

2 A student places a bunch of grapes in a bowl of plain water and a second bunch of grapes in a bowl of salt water. After an hour, the grapes in the plain water are swollen, whereas the grapes in the salt water are shriveled. What cellular process caused the grapes to shrivel?

A active transport B diffusion

C exocytosis D osmosis

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3 Javier notices that one of his house plants has drooping leaves. Which description explains what happens when he waters the plant?

A The sudden movement of water by osmosis into the plant cells causes the cells to swell and burst.

B The environment changes from hypotonic to hypertonic, the central vacuole swells, and the leaves stop drooping.

C The environment changes from isotonic to hypertonic, mitochondria in the plant cells take up the additional water, and the leaves stop drooping.

D The environment changes from isotonic to hypotonic, water moves into cells by osmosis, vesicles in the plant cells swell, and the leaves stop drooping.

4 Imagine that a single-cell organism is adapted to live in ocean water. A. Describe what would likely happen if this cell were placed in a sample of fresh water

collected from a lake.

B. What term describes the sample of lake water relative to the cytosol within the cell?

5 Explain why placing a carrot in a bowl of salt water will eventually cause the carrot to shrink.

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Describe features common to all cells that are essential for growth and survival, and explain their functions.

STANDARD REVIEW

Within a cell’s cytoplasm are many structures, often suspended in a system of microscopic fi bers called the cytoskeleton. The cytoplasm also includes organelles that carry out various life processes. Organelles are structures that perform specifi c functions within the cell. Different types of cells have different organelles. The table below summarizes the functions of these organelles.

Table 1 Organelles and Their Functions

Nucleusthe organelle that contains the cell’s DNA and is the control center of the cell

Chloroplastthe organelle that uses the energy of sunlight to make food

Ribosomethe organelle in which amino acids are hooked together to make proteins

Endoplasmic reticulumthe organelle that makes lipids, breaks down drugs and other substances, and packages proteins for Golgi complex

Mitochondrionthe organelle that breaks down food molecules to make ATP

Lysosomethe organelle that digests food particles, wastes, cell parts, and foreign invaders

Large central vacuolethe organelle that stores water and other materi-als

Golgi complexthe organelle that processes and transports pro-teins and other materials out of cell

STANDARD PRACTICE 1 A city’s power plant generates energy in a form that can be distributed to homes and

businesses for use in carrying out work. What structure inside the cell is most similar to a city’s power plant?

A lysosome B mitochondrion

C nucleus D ribosome

2 Which structure encloses the cell’s genetic material?

A endoplasmic reticulum B Golgi apparatus


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3 How are the endoplasmic reticulum and Golgi apparatus similar?

A Both contain their own kind of DNA.

B Both are found only in plant cells and not in animals cells.

C Both are involved in producing chemical energy for the cell.

D Both are made up of membranes consisting of a lipid bilayer.

4 A vesicle is a small, membrane-bound sac that transports substances in cells. Lysosomes are small, spherical vesicles.

A. What kind of chemicals can be found in lysosomes?

B. Describe the function of lysosomes.

5 Plants that have plenty of water stand upright. Plants that do not have enough water will wilt. Explain the role that a plant cell’s central vacuole plays under these conditions.

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Describe the structure of a cell membrane and explain how it regulates the transport of materials into and out of the cell and prevents harmful materials from entering the cell.

STANDARD REVIEW

Cells share common structural features, including an outer boundary called the cell membrane. The cell membrane encloses the cell and separates the cell interior, called the cytoplasm, from its surroundings. The cell membrane also regulates what enters and leaves a cell—including gases, nutrients, and wastes.

Movement across the cell membrane that does not require energy from the cell is called passive transport. One kind of passive transport, diffusion, is the movement of a sub-stance from an area of high concentration to an area of lower concentration caused by the random motion of particles of the substance. The diffusion of water through a selectively permeable membrane is called osmosis. In facilitated diffusion, a carrier protein transports a substance across the cell membrane down the concentration gradient of the substance.

Active transport is the movement of a substance against the concentration gradient of the substance. Active transport requires cells to use energy. In animal cells, the sodium-potassium pump uses energy supplied by ATP to transport sodium ions out of the cell and potassium ions into the cell. During endocytosis, substances are moved into a cell by a vesicle that pinches off from the cell membrane. During exocytosis, substances inside a vesicle are released from a cell as the vesicle fuses with the cell membrane.

STANDARD PRACTICE 1 The diffusion of water through a selectively permeable membrane is called osmosis.

Which description represents the effects of osmosis on a plant cell when the concentration of sugar particles is greater inside the cell than outside?

A Water diffuses into the cell, and the cell swells.

B Water diffuses out of the cell, and the cell shrinks.

C Water moves into and out of the cell at equal rates, and cell size remains the same.

D Water is blocked from moving into or out of the cell, and cell size remains the same.

2 An oxygen molecule comes into contact with the outside of a cell’s lipid bilayer. What process would allow the molecule to move into the cell?

A osmosis B active transport

C simple diffusion D facilitated diffusion


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3 Sodium-potassium pumps, endocytosis, and exocytosis all involve active transport. Which of the following is a characteristic of active transport?

A It involves facilitated diffusion.

B It requires energy from the cell.

C It relies on vesicles that often function as pumps.

D It moves substances with a concentration gradient.

4 Glucose, a large sugar molecule, is transported across the cell membrane through facilitated diffusion. Sodium and potassium ions, on the other hand, cross the membrane through active transport.

A. How are facilitated diffusion and the active transport of sodium and potassium ions similar?

B. In what way are these two processes different?

5 Nerve cells and cells of various glands release proteins by exocytosis. Describe exocytosis.


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Explain that most cells contain mitochondria, the key sites of cellular respiration, where stored chemical energy is converted into useable energy for the cell, and some cells, includ-ing many plant cells, contain chloroplasts, the key sites of photosynthesis, where the energy of light is captured for use in chemical work.

STANDARD REVIEW

Photosynthesis, which takes place in chloroplasts, and cellular respiration, which takes place in mitochondria, are related processes. The table below shows the relationship be-tween these processes and what is needed for each to take place.

Light energy

ATP

↓

↓

Chloroplast(of plant cells)

Mitochondrion(of plant and animals cells)

← ←

→ →

CO2 + H2O

C6H12O6 + O2

STANDARD PRACTICE 1 Plants play an important role in the carbon cycle by producing carbohydrates. Which of

the following cell structures enables plants to make carbohydrates from carbon dioxide and water?

A cell wall

B central vacuole

C chloroplast

D nucleus

2 A cell contains both chloroplasts and mitochondria. Which conclusion can you draw about this organism?

A It is a heterotroph.

B It does not have a metabolism.

C It carries out photosynthesis and cellular respiration.

D It gets its energy by consuming other organisms as food.

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3 The flow chart below shows a process that generates ATP.

Pyruvate + O2 → Krebs cycle → Electron transport chain

Where does this process take place within a cell?

A chloroplast

B mitochondria

C nucleus

D ribosome

4 All cells require chemical energy in the form of sugars, such as glucose.

A. Which process produces glucose and which organelle carries out this process?

B. Which process requires glucose and which organelle carries out this process?

5 Animal cells do not contain chloroplasts. What does this indicate about how animals must get the sugars they need to produce chemical energy that their cells can use?

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Explain that all cells contain ribosomes, the key sites for protein synthesis, where genetic material is decoded in order to form unique proteins.

STANDARD REVIEW

Following the instructions encoded in nucleic acids (DNA and RNA), cells make proteins on cellular structures called ribosomes. Each ribosome is made of dozens of different proteins as well as RNA. Some of the ribosomes in a eukaryotic cell are suspended in the cytosol, as they are in prokaryotic cells. These “free” ribosomes make proteins that remain inside the cell, such as proteins used to build new organelles.

Proteins that are exported from the cell, such as some signal molecules, are made on the ribosomes that lie on the surface of the endoplasmic reticulum. The endoplasmic reticu-lum, or ER, is an extensive system of internal membranes that moves proteins and other substances through the cell. Like the cell membrane, the membranes of the ER are made of a lipid bilayer with embedded proteins.

The part of the ER with attached ribosomes is called rough ER because it has a rough appearance when viewed in the electron microscope. (The rest of the ER is called smooth ER because it lacks ribosomes and thus appears smooth when viewed in the electron microscope.) The rough ER helps transport the proteins that are made by its attached ribosomes. As each protein is made, it crosses the ER membrane and enters the ER. The portion of the ER that contains the completed protein then pinches off to form a vesicle. A vesicle is a small, membrane-bound sac that transports substances in cells. Because certain proteins are enclosed inside vesicles, these proteins are kept separate from proteins that are produced by free ribosomes in the cytoplasm.

STANDARD PRACTICE 1 Which cell structure is the site of protein synthesis?

A lysosome

B mitochondrion

C nucleus

D ribosome

2 Where are ribosomes found within a cell?

A only floating freely within the cytosol

B only on the surface of the endoplasmic reticulum

C embedded in the walls of the nucleus and in the endoplasmic reticulum

D floating freely within the cytosol and embedded in the endoplasmic reticulum

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3 Two cellular processes involving nucleic acids include transcription and translation. Transcription is the production of mRNA using DNA as a template. Translation is the production of proteins using mRNA as a template. Which is the site for translation?

A chloroplast B mitochondria


4 Many antibiotics work by targeting and disabling pathogenic bacterial ribosomes.

A. What would happen to a bacteria cell if its ribosomes no longer functioned?

B. Why is it important for antibiotics that target ribosomes to be specific to bacterial ribosomes?

5 Compare the smooth endoplasmic reticulum and the rough endoplasmic reticulum in terms of form and function.

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Explain that cells use proteins to form structures, including cilia, fl agella, which allow them to carry out specifi c functions, including movement, adhesion, and absorption.

STANDARD REVIEW

Many prokaryotes and single-celled eukaryotes have fl agella (singular, fl agellum). Flagella are long, threadlike structures that protrude from the cell’s surface. Bacterial fl agella are simple structures composed of a single fi ber of protein that spins like a corkscrew to move the cell. Eukaryotic fl agella are more-complex structures made of microtubules that whip back and forth rather than spin. When some prokaryotic fl agella rotate, they propel the organisms through their environment at speeds of up to 20 cell lengths per second.

Some bacteria also have shorter, thicker outgrowths called pili (singular, pilus). Pili enable bacteria to attach to surfaces or to other cells. For example, the pili of the Gram-negative bacteria E. coli has pili that can adhere to the surfaces of intestinal-lining cells. Pili also join bacterial cells prior to conjugation—the process in which two single-cell organisms can exchange genetic material.

Short, hair-like structures called cilia (singular, cilium) protrude from the surface of many kinds of cells. Like fl agella, cilia propel some cells through their environment. In other cells, cilia move substances across the cell’s surface. For example, cilia on cells lining the respiratory system remove debris from air passages. Cilia also help some organisms gather food. For example, cilia lining the oral groove of a paramecium create a “whirlpool” that helps capture small bits of food.

STANDARD PRACTICE 1 How does a flagellum help a cell achieve movement through its environment?

A by hopping along a surface like a leg

B by whipping back and forth within a fluid

C by coiling around nearby objects and pulling on them

D by shooting out a jet of fluid in the direction opposite of motion

2 Many organisms that are single cells use one or more of the following structures to move through fluids or adhere to surfaces. Which structures do bacterial cells use to connect together and exchange DNA?

A cilia

B flagella

C pili

D pseudopods

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3 The illustration below shows a type of protist called a euglena.

Chloroplast

Nucleus

Cell wall

FL_Biology_FCAT_WB_10-40.indd 26 2/24/05 11:13:16 AM

Which structure shown in the illustration does a euglena use to move around in its environment?

A cilium B flagellum

C pilus D pseudopod

4 Many single-cell organisms, such as bacteria and protists, are able to move around in their liquid environments.

A. Identify and describe two structures that single-cell organisms use for movement.

B. How do the two structures compare in size?

5 Multicellular organisms such as humans have some cells with structures called cilia. Describe an example of human body cells that have cilia and explain their function.

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Investigate a variety of different cell types and relate the proportion of different organelles within these cells to their functions.

STANDARD REVIEW

A prokaryote is a single-celled organism that lacks a nucleus and other internal compartments. Prokaryotic cells depend on a strong cell wall to give the cell shape. Some prokaryotic cell walls are surrounded by a structure called a capsule, which is also composed of polysaccharides. The capsule enables prokaryotes to cling to almost anything, including teeth, skin, and food.

A eukaryote, such as a plant or an animal, is an organism whose cells have a nucleus. The nucleus is an internal compartment that houses the cell’s DNA. Other internal compart-ments, or organelles, enable eukaryotic cells to function in ways different from prokaryotes. An organelle is a structure that carries out specifi c activities in the cell. Specialized cells within a multicellular organism may contain more of one kind of organelle than another, depending on their function.

Many organelles—such as the endoplasmic reticulum, vesicles, Golgi apparatus, lysosomes, and mitochondria—are found in both animal cells and plant cells. However, plant cells have three additional structures that are not found in animal cells:

• The cell wall—composed of proteins and carbohydrates, including the polysaccharide cellulose—surrounds the cell membrane of plant cells.

• Chloroplasts are organelles that use light energy to make carbohydrates from carbon dioxide and water.

• The central vacuole is a large membrane-bound space that stores water and may contain many substances, including ions, nutrients, and wastes; when full, it makes the cell rigid.

STANDARD PRACTICE 1 A cell has a cell wall. Which conclusion can you draw about the cell?

A It must be a prokaryote.

B It must not be a eukaryote.

C It must not be an animal cell.

D It must compose a single-cell organism.

2 Which could be found in a prokaryote?

A endoplasmic reticulum B flagellum

C mitochondrion D nucleus

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3 Cells may have different shapes and different amounts of organelles, depending on their function. Which features do plant cells have that animal cells lack?

A chloroplast, ribosome, and cell wall

B Golgi apparatus, cytoskeleton, and vesicle

C cell wall, chloroplast, and central vacuole

D central vacuole, chloroplast, and smooth ER

4 The diagram below shows a cell.

STRUCTURE OF A CELL


A. What type of organism (plant, animal, bacterium) might contain this type of cell?

B. Identify the structures that are either present or lacking in this cell that indicate what type of cell it is.

5 A certain type of cell contains an unusually large number of mitochondria. What can you infer about this cell? Explain.

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Describe how some organisms capture the sun’s energy through the process of photosynthesis by converting carbon dioxide and water into high energy compounds and releasing oxygen.

STANDARD REVIEW

Photosynthesis is the process that provides energy for almost all life forms. As described below, photosynthesis has three stages:

Stage 1: Energy is captured from sunlight. Pigments such as chlorophyll absorb light energy, which excites electrons.

Stage 2: Light energy is converted to chemical energy, which is temporarily stored in ATP and the energy carrier molecule NADPH. This stage occurs when the excited electrons are passed through a series of molecules—called an electron transport chain—along a thylakoid membrane.

Stage 3: The chemical energy stored in ATP and NADPH powers the formation of organic compounds, using carbon dioxide, CO2. The most common way that this happens is called the Calvin cycle.

Photosynthesis occurs in the chloroplasts of plant cells and algae and in the cell membrane of certain prokaryotes. Photosynthesis can be summarized by the following equation:

6CO2 + 6H2O C6H12O6 + 6O2carbondioxide

oxygengas

water sugars

light

STANDARD PRACTICE 1 Which is a product of photosynthesis?

A carbon dioxide

B protein

C sugar

D water

2 Autotrophs, such as plants, use light to make their own food. What happens to the light absorbed by a plant during photosynthesis?

A It is converted to kinetic energy.

B It is converted to chemical energy, which the plant stores.

C It powers a reaction that produces carbon dioxide and water.

D It powers a reaction that produces oxygen and carbon dioxide.

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3 Constance made the table below during a field investigation on ocean life.

Characteristics of Several Ocean Zones

Zones Description

Intertidal Air, sun, and water exposure; crashing waves

Neritic Water depth less than 200 m; lots of sunlight; relatively warm water

Benthic Very deep water; no light; cold except near thermal vents that emit heat and chemicals

Based on Constance’s table, which of the following is a valid conclusion?

A There are no producers in the benthic zone that rely on photosynthesis. B Organisms in the intertidal zone must be able to withstand very cold water. C Organisms in the benthic zone must be able to tolerate occasional air exposure. D The warm water and abundant sunlight in the neritic zone limits the plankton

population.

4 Latecia conducted an experimental investigation of the gas production of a water plant. She placed a beaker upside down over a water plant submerged in water and collected the gas that the water plant produced when kept in sunlight. After several days, a large bubble of gas collected in the upside-down beaker, as shown below.

hb07ca-srw_04-31.indd 15 4/20/06 10:48:28 AM

A. Given that the gas came from the water plant, what are the contents of the bubble of gas collected in the test tube?

B. What process produced this gas?

5 Identify the substances that are needed for photosynthesis and the substances that are produced by photosynthesis.

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Describe how most organisms can combine and recombine the elements contained in sugar molecules into a variety of biologically essential compounds by utilizing the energy from cellular respiration.

STANDARD REVIEW

Most of the foods we eat contain usable energy. Much of the energy in a banana, for example, is stored in proteins, carbohydrates, and fats. But before the energy can be used, it is transferred to ATP. As in most organisms, cells in the human body transfer the energy in organic compounds, especially glucose, to ATP through a process called cellular respira-tion. When a person breathes in oxygen, the production of ATP is more effi cient, although some ATP is made without oxygen. Metabolic processes that require oxygen are called aerobic. Metabolic processes that do not require oxygen are called anaerobic, meaning “without air.”

Cellular respiration is the process cells use to harvest the energy in organic compounds, particularly glucose. The breakdown of glucose during cellular respiration can be summa-rized by the following equation:

C6H12O6 + 6O2 6CO2 + 6H2O + energycarbondioxide

oxygengas

water ATPglucose

enzymes

As the fi gure below shows, cellular respiration occurs in two stages.

Stage 1: Glucose is converted to pyruvate, producing a small amount of ATP and NADH.

Stage 2: When oxygen is present, pyruvate and NADH are used to make a large amount of ATP. This process is called aerobic respiration. Aerobic respiration occurs in the mito-chondria of eukaryotic cells and in the cell membrane of prokaryotic cells. When oxygen is not present, pyruvate is converted to either lactate or ethanol and carbon dioxide through anaerobic processes called fermentation.


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STANDARD PRACTICE

1 Which statement is true of cellular respiration?

A Only plants carry out cellular respiration.

B Only animals carry out cellular respiration.

C Both plants and animals carry out cellular respiration.

D Neither plants or animals carry out cellular respiration.

2 Cells use sugars to produce energy through several different processes. Which process would provide the MOST energy for cell functions?

A glycolysis B aerobic respiration

C aerobic fermentation D anaerobic fermentation

3 Daphnia are small water invertebrates that are almost transparent. Like all animals, Daphnia require chemical energy to live. They use structures called gills to extract oxygen from the water to obtain chemical energy. Which statement below describes how they obtain chemical energy?

A Daphnia absorb glucose from algae and then use fermentation to release chemical energy in the form of ATP.

B Daphnia absorb pyruvate from algae and then use gluconeogenesis to release chemical energy in the form of ADP.

C Daphnia absorb glucose from algae and then use cellular respiration to release chemical energy in the form of ATP.

D Daphnia absorb glucose from algae and then use cellular respiration to release chemical energy in the form of NADP.

4 The many steps of cellular respiration can be summarized by a balanced chemical equation.

A. What are the reactants (starting substances) of cellular respiration?

B. What are the products of cellular respiration?

5 Cellular respiration generates chemical energy for a cell. What energy-storing molecule is generated through cellular respiration?

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Recognize and describe that metabolism consists of all of the biochemical reactions that occur inside cells, including the production, modifi cation, transport, and exchange of materials that are required for the maintenance of life.

STANDARD REVIEWLiving organisms carry out many different chemical reactions in order to obtain and then use energy to run the processes of life. All living things use energy to grow, to move, and to process information. Without energy, life soon stops. Metabolism is the sum of all of the chemical reactions carried out in an organism.

Almost all the energy used by living organisms is originally captured from sunlight. Plants, algae, and some bacteria capture this solar energy and use it to make complex molecules in a process called photosynthesis. These molecules then serve as the source of energy, or food, for other organisms. For example, some single-cell organisms called paramecia eat other single-cell organisms called bacteria. Many animals eat plants. Humans eat plants or animals that have eaten plants. Energy fl ows from the sun to plants, from these plants to plant-eating organisms, and from plant-eating organisms to meat-eating organisms. The process of eating food equates with extracting energy from that food. As the food is digested, chemical reactions convert the chemical energy in food molecules to forms of energy that can be used within the body’s cells. This process is called cellular respiration.

When a log burns, the energy stored in wood is released quickly as heat and light. But in cells, the chemical energy stored in food molecules is released gradually in a series of enzyme-assisted chemical reactions. The product of one chemical reaction becomes a reactant in the next reaction. In the breakdown of starch, for example, each reaction releases energy.

When cells break down food molecules, some of the energy in the molecules is released as heat. Much of the remaining energy is stored temporarily in molecules of ATP, or adenos-ine triphosphate. ATP is composed of a single nucleotide with two extra energy-storing phosphate groups. Like money, ATP is a portable form of energy “currency” inside cells. ATP delivers energy wherever that energy is needed in a cell.

Cells break down ATP to release the energy it stores. The energy released when ATP is broken down can be used to power other chemical reactions, such as those that build molecules. In cells, most chemical reactions require less energy than is released from the breakdown of ATP. Therefore, enough energy is released from ATP to drive most of a cell’s activities.

STANDARD PRACTICE 1 Which activity within a living thing is NOT part of metabolism?

A the production of proteins from amino acids

B the passing of hereditary information from parent to offspring

C the breakdown of food molecules to produce chemical energy

D the exchange of carbon dioxide and oxygen with the environment


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2 ATP is a cell’s main form of energy “currency.” Which of the following comprises an ATP molecule?

A adenine, the sugar ribose, and three phosphate groups

B adenine, the sugar deoxyribose, and two phosphate groups

C a nitrogenous base, a phosphate group, and the sugar ribose

D a complex molecule of amino acids surrounding an iron atom

3 ATP provides the energy needed to carry out many cell functions. Which of the following processes does NOT require ATP?

A making more ATP

B muscle contraction

C active transport of protein across a membrane

D passive transport of oxygen across a cell membrane

4 Humans and other heterotrophs get their energy from eating food. A. What process in human body cells transfers the energy stored in a grilled cheese

sandwich to ATP?

B. How is ATP used in cells?

5 What is metabolism?

Name Date



Describe how matter cycles through an ecosystem by way of food chains and food webs and how organisms convert that matter into a variety of organic molecules to be used in part in their own cellular structures.

STANDARD REVIEW

Everything that organisms do in ecosystems—running, breathing, burrowing, growing—requires matter and energy. The fl ow of matter and energy is the most important factor that controls what kinds of organisms live in an ecosystem and how many organisms the ecosystem can support.

Most life on Earth depends on photosynthetic organisms, which capture some of the Sun’s light energy and store it as chemical energy in organic molecules. These organic compounds are what we call food. The rate at which organic material is produced by photosynthetic organisms in an ecosystem is called primary productivity. Primary productivity determines the amount of energy available in an ecosystem. Most organisms in an ecosystem can be thought of as chemical machines driven by the energy captured in photosynthesis. Organisms that fi rst capture energy, the producers, include plants, some kinds of bacteria, and algae. Producers make energy-storing molecules. All other organisms in an ecosystem are consumers—those organisms that consume plants or other organisms to obtain the matter and energy necessary to build their molecules.

The path of matter and energy through the living components of an ecosystem is called a food chain. An example of a food chain is shown below. The arrows show the direction of matter and energy fl ow. That is, each arrow points to the organism that consumes the other organism as food.

plants → grasshoppers → rats → owls

In most ecosystems, matter and energy do not follow simple straight paths because individual animals often feed from different sources. This creates a complicated, interconnected group of food chains called a food web. The diagram below shows a simple food web.

FOOD WEB

Algae and phytoplankton

Shrew

Coyote

Mouse

Grasshopper

Plants

Hawk

Duck Heron

Fish

Crab

Brine shrimp

hb07ca-srw_32-67.indd 45 4/20/06 10:49:30 AM


Name Date




STANDARD PRACTICE

1 Grasses, hawks, mice, and snakes are all organisms that live in a prairie. In the prairie food chain, which is the correct arrangement according to matter and energy flow?

A hawk → snake → mouse → grass

B grass → snake → mouse → hawk

C grass → mouse → snake → hawk

D hawk → mouse → snake → grass

2 Which food chain is possible?

A consumer → consumer → producer

B consumer → producer → consumer

C producer → consumer → consumer

D producer → producer → consumer

3 The Yellowstone area contains a great variety of organisms, including plants, algae, moss, fungi, blue jays, fish, and grizzly bears. Which sequence BEST represents the transfer of matter and energy through the Yellowstone ecosystem?

A fungi to moss to algae to fish

B blue jay to moss to fungi to plant

C algae to fish to grizzly bear to fungi

D plant to blue jay to algae to grizzly bear

4 Examine the food web on the previous page. A. Identify all of the organisms in the food web that are producers.

B. Draw a food chain that includes four organisms included in the food web.

5 Teresa drew a food chain that included two producers, two consumers, and three arrows. Explain why Teresa’s food chain is inaccurate.

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Describe how energy from the sun fl ows through an ecosystem by way of food chains and food webs and only a small portion of that energy is used by individual organisms while the majority of energy is lost as heat.

STANDARD REVIEW

Ecologists study how energy moves through an ecosystem by assigning organisms in that ecosystem to a specifi c level, called a trophic level. Energy moves from one trophic level to another. The lowest trophic level of any ecosystem is occupied by the producers, such as plants, algae, and bacteria. Producers use carbon dioxide and energy from the Sun to build energy-rich carbohydrates.

At the second trophic level are herbivores, animals that eat plants or other primary producers. These primary consumers include cows, horses, caterpillars, and some ducks. The third trophic level includes secondary consumers, animals that eat other animals, or carnivores. Tigers, wolves, and snakes are carnivores. Some animals, such as bears and cranes, are omnivores, eating both plants and animals. Many ecosystems contain a fourth trophic level composed of carnivores that consume other carnivores. These are tertiary consumers, or top carnivores.

During every transfer of energy within an ecosystem, energy is lost as heat. Thus, the amount of useful energy available decreases as energy passes through an ecosystem, limit-ing the number of trophic levels an ecosystem can support. When a plant harvests energy from sunlight, photosynthesis captures only about one percent of the energy available to the leaves. When an herbivore uses plant molecules to make its own molecules, only about ten percent of the energy in the plant ends up in the herbivore’s molecules. Finally, when a carnivore eats the herbivore, about ninety percent of the energy is lost in making carnivore molecules. At each trophic level, the energy stored by the organisms is about one-tenth of that stored by the organisms in the level below.

Ecologists often illustrate the fl ow of energy through ecosystems with an energy pyramid, a diagram in which each trophic level is represented by a level within the pyramid, with the lowest trophic level on the bottom. The width of each level in the pyramid is determined by the amount of energy stored in the organisms at that trophic level. Because energy is lost at each trophic level, the amount of energy available at the top level is much smaller than the amount of energy available at the bottom level.

STANDARD PRACTICE 1 Which biological diagram shows the flow of energy within an ecosystem?

A cladogram

B dichotomous key

C food web

D Punnett square


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2 Kerry drew the following food chain in her science notebook. plants → grasshoppers → rats → owls

How would the grasshoppers be classified in this food chain?

A producer B primary consumer

C tertiary consumer D secondary consumer

3 Very rarely do ecosystems contain more than four trophic levels, because there is not enough energy to support more. In which trophic level is there the LEAST energy available?

A producer B tertiary consumer

C primary consumer D secondary consumer

4 The diagram below is an energy pyramid.

A. Draw a food chain that represents the flow of energy in this ecosystem.

B. Which organism represents the trophic level for which there is the LEAST energy available?

5 Explain why producers are represented in the widest part of an energy pyramid (at the base level).

Name Date




Explain that the amount of life an environment can support is limited by the available energy, water, oxygen, and minerals, and by the ability of ecosystems to recycle the remains of dead organisms.

STANDARD REVIEWThe physical parts of the ecosystems on Earth cycle constantly. The atoms that make up living things are passed from one organism to another in a great circle of use. Producers are eaten by herbivores, herbivores are eaten by carnivores, and carnivores are eaten by top carnivores.

In every ecosystem there is a special class of consumers called detrivores, which include worms and fungal and bacterial decomposers. Detrivores are organisms that obtain their matter and energy from the organic wastes and dead bodies that are produced at all trophic levels. Bacteria and fungi are known as decomposers because they cause decay. Decomposition of bodies and wastes releases nutrients back into the environment to be recycled by other organisms.

All materials that cycle through living organisms are important in maintaining the health of ecosystems, but four substances are particularly important: water, carbon, nitrogen, and phosphorus. The paths of water, carbon, nitrogen, and phosphorus pass from the nonliv-ing environment to living organisms and then back to the nonliving environment. These paths form closed circles, or cycles, called biogeochemical cycles. In each biogeochemical cycle, a pathway forms when a substance enters living organisms (such as trees) from the atmosphere, water, or soil; stays for a time in the living organism; then returns to the nonliving environment.

STANDARD PRACTICE 1 Through which process do plants release water vapor to the atmosphere as part of the

water cycle?

A nitrification B photosynthesis

C precipitation D transpiration

2 The food chain below represents the interactions between organisms in an old field ecosystem.

grass → grasshopper → shrew → coyote

Which of the following statements BEST characterizes this food chain?

A There are no producers in this food chain.

B There are no consumers in this food chain.

C There are no decomposers in this food chain.

D All the different types of organisms are included.

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3 Photosynthesis and cellular respiration are interrelated processes. During which biogeochemical cycle do the biological processes of photosynthesis and cellular respiration play key roles?

A carbon cycle B nitrogen cycle

C hydrogen cycle D phosphorus cycle

4 Every ecosystem includes organisms called detrivores.

A. What are detrivores?

B. What important role do detrivores play in an ecosystem?

5 Describe what would eventually happen if all of the decomposers in an ecosystem suddenly disappeared.

Name Date



Describe how human activities and natural phenomena can change the fl ow of matter and energy in an ecosystem and how those changes impact other species.

STANDARD REVIEW

The variety of organisms, their genetic differences, and the communities and ecosystems in which they occur is termed biodiversity. Biodiversity is a measure of both the number of different species in a community (species richness) and the relative numbers of each of the species (species diversity). Some of the most diverse communities are those living in tropi-cal rainforests.

Over the last 50 years, about half of the world’s tropical rainforests have been burned to make pasture and farmland or have been cut for timber. Many thousands of square miles more will be destroyed this year. The people responsible, often poor farmers, view the forest lands as a resource to be developed, much as Americans viewed North American forests a century ago.

The problem is that as the rainforests disappear, so do their inhabitants. No one knows how many species are being lost. To fi nd out, scientists carefully catalogue all of the resi-dents of one small segment of forest and then extrapolate their data. That is, scientists use what they know to predict what they do not know. The resulting estimates vary widely, but it is clear Earth is losing many species. Some ten percent of well-known species teeter on the brink of extinction. Worst-case estimates are that we will lose up to one-fi fth of the world’s species of plants and animals—about one million specie— during the next 50 years. An extinction of this size has not occurred in at least 65 million years, since the end of the age of dinosaurs.

The tragedy of extinction is that as species disappear, so do our chances to learn about them and their possible benefi ts. This situation is comparable to burning a library before reading the books—we lose forever the knowledge we might have gained. Also, experi-ments have clearly demonstrated that an ecosystem’s biodiversity and productivity are related. That is, increased species richness leads to greater productivity.

STANDARD PRACTICE 1 Acid rains form when air pollution combines with moisture in the atmosphere and falls

to Earth as precipitation that has a low pH. Which of the following effects CANNOT be attributed to acid rain?

A an increase in CO2 in Earth’s atmosphere

B damage to historic buildings and monuments

C death of aquatic organisms in lakes and streams

D damage to trees and a decline of forest communities


Name Date




2 Imagine that a city located in a desert environment has grown significantly over the last few decades. Which statement BEST describes how the growth of the metropolitan city would impact the desert environment in the area?

A Biodiversity would decrease in the area but increase in the desert beyond the city.

B By destroying habitat to build homes and highways, the growth of the city would decrease the biodiversity in the desert.

C The growth of the city would have little impact on the environment, because few animals likely lived there before growth happened.

D By bringing in water, the growth of the city would improve the entire desert environment and increase the biodiversity.

3 Tropical rain forests receive as much as 450 cm of rain per year. They are the richest biome in terms of number of species. Which statement BEST explains how destruction of tropical rain forests could affect the carbon cycle?

A Destroying rain forest trees would cause carbon dioxide levels in the atmosphere to drop dangerously low.

B A loss of rain forest trees would have only a small effect on the carbon cycle, because they are green all year long.

C Rain forest destruction would cause only a small increase in carbon dioxide levels if the roots were left to remove carbon dioxide from the air.

D Cutting down rain forests could increase atmospheric carbon dioxide levels, because trees that could take up carbon dioxide would be removed.

4 Many human activities threaten the biodiversity of ecosystems. A. What is biodiversity?

B. Describe one way that a decrease in species diversity can affect an ecosystem.

5 Imagine that a certain animal becomes extinct due to human activity. What effect, if any, would this have on the animal’s prey and on its predators?

Name Date



Describe the consequences of introducing non-native species into an ecosystem and identify the impact it may have on that ecosystem.

STANDARD REVIEW

An exotic species is a species that is not native to a particular region. Humans often accidentally introduce nonnative species from one ecosystem to another when they trans-port goods. For example, insects that live on crop plants are often transported along with fruits and vegetables imported from other countries. Some nonnative species are intro-duced to an ecosystem on purpose. For example, people often cultivate exotic plants for decoration or as crops. Other nonnative species may be introduced to a region as house-hold pets. These pets may later escape or be released into the wild. Still other exotic species might be introduced on purpose in an attempt to control native populations.

Exotic species can often thrive in their new homes and, thus, are often called invasive species. They may not have natural predators in their new environments. Or, they may out-compete native species for limited resources. They may even prey upon native organisms that did not have many native predators before the invasion. When these invaders thrive, they can often cause devastating problems for native species. For example, Burmese pythons brought to Florida as pets have invaded the Florida Everglades—a wetland region that is home to many threatened plant and animal species. The exotic pythons have few natural predators and are reproducing rapidly in their new home. Their presence is a nuisance in part because they have been known to prey upon native species, such as the endangered Key Largo wood rats.

STANDARD PRACTICE 1 Biologists speculate that in the mid-1980s a cargo ship from Eastern Europe dumped

ballast water containing a tiny clam-like organism called the zebra mussel into the Great Lakes. The zebra mussel is native to waters in Eastern Europe but had never lived in North America. The zebra mussels began to attach to piers, boat hulls, pipes, and any other available surface. Conditions in the Great Lakes were ideal for these filter feeders, which strain plankton out of lake water. Plankton is a food resource for other small aquatic animals and fish larvae. Zebra mussels can strain food from about one liter of water per day. These invaders thrived and spread throughout the Great Lakes. They now threaten other North American waterways. The presence of large quantities of plankton decreases water clarity. Since zebra mussels were introduced, the clarity of Lake Erie’s water has increased 600%. What does this MOST LIKELY indicate about zebra mussels?

A In clear water, it is easy to catch zebra mussels.

B Zebra mussels could be used to solve water pollution problems.

C There is not enough data given to infer a link between zebra mussels and water clarity.

D Zebra mussels are such efficient feeders that they have greatly reduced the amount of plankton in Lake Erie.


Name Date




2 Imagine that a nonnative bird species appears in an ecosystem. Which of the following will NOT be a likely change in the ecosystem?

A Native bird species will immediately migrate to another area.

B Bird predator species will temporarily have more available prey.

C Each food chain in the ecosystem will adjust over time to include the new species of bird.

D Birds that share the same niche as the new species will have more competition for food resources.

3 Noxious weeds are weeds that invade ecosystems and grow very quickly and aggressively. How do noxious weeds affect the biodiversity of an ecosystem?

A The biodiversity increases slightly because the weeds represent another species in the area.

B The weeds increase the biodiversity because they increase the total energy of the producers.

C The biodiversity usually decreases greatly as the noxious weeds out-compete the local plants.

D The biodiversity is not affected at all since the noxious weeds simply replace the dominant plant in the ecosystem.

4 The kudzu vine is a plant native to Japan. It was brought over to the United States in the late 1800s as a decorative plant that also helps prevent soil erosion. It has since spread throughout the southeastern United States, covering native shrubs and trees with its green, leafy vines.

A. What term describes such a species that is not native to a region?

B. How could the kudzu vine cause problems for native species in the US?

5 Some exotic species do not thrive in their new homes. How would such unsuccessful exotic species likely affect an ecosystem?

Name Date



Describe how climate, the pattern of matter and energy fl ow, the birth and death of new organisms, and the interaction between those organisms contribute to the long term stability of an ecosystem.

STANDARD REVIEW

A population consists of all the individuals of a species that live together in one place at one time. Every population tends to grow because individuals tend to have multiple offspring over their lifetime. A population grows when more individuals are born than die in a given period. But eventually, limited resources in an environment limit the growth of a population. The growth of a population is limited by predators, disease, and the availability of resources, such as food and water. Eventually, growth slows, and the population may stabilize. The population size that an environment can sustain is called the carrying capacity.

One way to model how populations change is to assume that birth and death rates vary with population size. When a population is below carrying capacity, the growth rate is rap-id. However, as the population approaches the carrying capacity, death rates begin to rise and birthrates begin to decline. Competition for food, shelter, mates, and limited resources tends to increase as a population approaches its carrying capacity. The accumulation of wastes also increases. As a result, the rate of growth slows. The population eventually stops growing when the death rate equals the birthrate.

STANDARD PRACTICE 1 Researchers have found that a local squirrel population fluctuates from year to year,

increasing one year and decreasing the next. Which of the following factors would cause the squirrel population to grow?

A the birth rate is equal to the death rate

B emigration is greater than immigration

C the death rate is higher than the birth rate

D the birth rate is greater than the death rate

2 All populations fluctuate in size. Which of the following is a nonenvironmental factor that might cause a population to be reduced in size?

A decreased predation

B increased competition

C emergence of disease resistance

D increased availability of a food source


Name Date




3 Your class has been observing the population growth of a species of Paramecium, a single-celled organism, for 18 days. Your data are shown in the graph below. Food was occasionally added to the test tube in which the paramecia were grown.

100

50

03 6 9 12 15 18

Days

Nu

mb

er o

fP

aram

eciu

m p

er m

L

hb07ca-srw_32-67.indd 43 4/20/06 10:49:29 AM

Look at the graph above. What is the carrying capacity of the test-tube environment as long as food is added?

A about 10 paramecia B about 50 paramecia

C about 75 paramecia D about 100 paramecia

4 Climate affects the long term stability of an ecosystem. A. What is climate?

B. Describe the role that climate plays in determining the types and numbers of organisms that live in an area.

5 How are birth rate and death rate related to the rate of population growth in an ecosystem?

Name Date




Describe the relationship between chromosomes and DNA along with their basic structure and function.

STANDARD REVIEW

Cell structures called chromosomes contain all of an organism’s genetic information. A chromosome consists of DNA tightly coiled around proteins. James Watson and Francis Crick were the fi rst to piece together a model of the structure of DNA. The discovery of DNA’s structure was important because it clarifi ed how DNA could serve as genetic material.

Watson and Crick determined that a DNA molecule is a double helix—two strands twisted around each other, like a winding staircase. Each strand is made of linked nucleotides. Nucleotides are the subunits that make up DNA. Each nucleotide is made of three parts: a phosphate group, a fi ve-carbon sugar molecule, and a nitrogen-containing base. The fi ve-carbon sugar in DNA nucleotides is called deoxyribose, from which DNA gets its full name, deoxyribonucleic acid. While the sugar molecule and the phosphate group are the same for each nucleotide in a molecule of DNA, the nitrogen base may be any one of four different kinds: adenine (A), guanine (G), thymine (T), and cytosine (C).

The overall shape of the DNA structure resembles a twisted ladder. The sugar-phosphate backbones are similar to the side rails of the ladder, while the paired nitrogen bases are similar to the rungs of the ladder. The nitrogen bases face each other. The double helix is held together by weak hydrogen bonds between the pairs of bases. The bases always pair in the same way: an adenine on one strand always pairs with a thymine on the opposite strand, and a guanine on one strand always pairs with a cytosine on the opposite strand.

STANDARD PRACTICE 1 Which structures make up the backbones of a DNA molecule?

A only nitrogen bases

B only sugars and phosphates

C only sugars and nitrogen bases

D only phosphates and nitrogen bases

2 What holds together the two strands of a molecule of DNA?

A single bonds between the paired bases

B hydrogen bonds between the paired bases

C double bonds between the phosphate groups

D hydrogen bonds between the phosphate groups

Name Date




3 The diagram below represents an incomplete model of the DNA molecule.

T

GC

AG

C

CG

A

AT

G C

T

C

G

TA

A

C A

T

G

Even though the model is not complete, what pattern is evident in this representation of the DNA molecule?

A Every third base pair has a mutation.

B Guanine is always paired with cytosine.

C The model has a repeating base sequence.

D There are two sugars between each phosphate.

4 Chromosomes are made up of long molecules of DNA coiled tightly with proteins. A. What do the letters DNA stand for?

B. What sugar does the D in DNA refer to?

5 Identify the four nitrogen bases found in DNA and how they pair with one another.

Name Date




Describe how hereditary information passed from parents to offspring is encoded in regions of DNA molecules called genes.

STANDARD REVIEW

The vast amount of information encoded in DNA is organized into units called genes. A gene is a segment of DNA that codes for a protein. A single molecule of DNA has thousands of genes lined up like train cars. Genes play an important role in determining how a person’s body develops and functions. The information contained in DNA is used to direct the synthesis of proteins.

The information in DNA is fi rst copied into a molecule of messenger RNA. Messenger RNA (mRNA) is the molecule that carries the instructions for making a protein from a gene and delivers it to the site in the cell where proteins are built. The information is translated from the language of RNA—nucleotides—to the language of proteins—amino acids. The RNA instructions are written on codons, a series of three-nucleotide sequences on the mRNA. Each codon along the mRNA strand corresponds to an amino acid or signifi es a start or stop signal for translation. The chart below shows the genetic code—the amino acids and “start” and “stop” signals that are coded for by each of the possible 64 mRNA codons.

Codons in mRNA

First base

Second baseThird base

UUUUUCUUAUUG

UCUUCCUCAUCG

UAUUACUAAUAG

UGUUGCUGA–StopUGG–Tryptophan

UCAG

CUUCUCCUACUG

CCUCCCCCACCG

CAUCACCAACAG

CGUCGCCGACGG

UCAG

AUUAUCAUAAUG–Start

ACUACCACAACG

AAUAACAAAAAG

AGUAGCAGAAGG

UCAG

GUUGUCGUAGUG

GCUGCCGCAGCG

GAUGACGAAGAG

GGUGGCGGAGGG

UCAG

Phenylalanine

Leucine

Leucine

Isoleucine

Valine

Serine

Proline

Threonine

Alanine

Tyrosine

Stop

Histidine

Glutamine

Asparagine

Lysine

Aspartic acid

Glutamic acid

Cysteine

Arginine

Serine

Arginine

Glycine

1 Find the first base of the mRNA codon in this column of the table.

CCCC

2 Follow that row to the column that matches the second base of the codon.

3 Move up or down in that box until you match the third base of the codon with this column of the chart.

U

U

C

A

C A G

G

Name Date




STANDARD PRACTICE 1 There are 64 possible mRNA codons that make up the genetic code. Which of the

following is true of the genetic code?

A Codons can be only three amino acids long.

B Codons can be one, two, or three bases long.

C Each codon is linked to only one amino acid.

D Each amino acid is linked to only one codon.

2 A strand of messenger RNA is attached to a ribosome and is directing protein synthesis. The next exposed codon of this messenger RNA has the code GAA. It is most likely to bond with a transfer RNA that has which amino acid?

A arginine B aspartic acid

C glutamic acid D glutamine

3 Mutations have various effects on the amino acid sequence that determines protein structure and function. A silent mutation has no effect on the protein’s function. Which mutation would result in a silent mutation?

A UAA to CAA B CCA to CCG

C AUA to AUG D GCU to GGU

4 During the formation of mRNA, the mRNA base uracil pairs with the DNA base adenine. The other bases—guanine, cytosine, and adenine—pair as they would during DNA replication. Imagine that a segment of a gene has the DNA base sequence: ATAGCGTAGCCC.

A. What is the mRNA base sequence produced by this DNA base sequence?

B. What is the sequence of amino acids produced by this mRNA base sequence?

5 The genetic code is nearly universal. That is, with few exceptions, the same codons code for the same amino acids in all organisms. What does the near universality of the genetic code suggest about the evolutionary ancestry of organisms?

Name Date




Describe the process by which DNA directs the production of protein within a cell.

STANDARD REVIEW

Traits, such as eye color, are determined by proteins that are built according to instructions coded in DNA. Recall that proteins have many functions, including acting as enzymes and cell membrane channels. Proteins, however, are not built directly from DNA. Ribonucleic acid (RNA) is also involved.

Like DNA, ribonucleic acid is a nucleic acid—a molecule made of nucleotides linked together. RNA differs from DNA in three ways. First, RNA consists of a single strand of nucleotides instead of the two strands found in DNA. Second, RNA nucleotides contain the fi ve-carbon sugar ribose rather than the sugar deoxyribose, which is found in DNA nucleotides. Ribose contains one more oxygen atom than deoxyribose. And third, in addition to the A, G, and C nitrogen bases found in DNA, RNA nucleotides can have a nitrogen base called uracil—abbreviated as U. No thymine (T) bases are found in RNA. Like thymine, uracil is complementary to adenine whenever RNA base pairs with another nucleic acid.

A gene’s instructions for making a protein are coded in the sequence of nucleotides in the gene. The instructions for making a protein are transferred from a gene to an RNA molecule (called messenger RNA) in a process called transcription. Cells then use two different types of RNA (transfer RNA and ribosomal RNA) to read the instructions on the messenger RNA molecule and put together the amino acids that make up the protein in a process called translation. The entire process by which proteins are made based on the information encoded in DNA is called gene expression, or protein synthesis.

STANDARD PRACTICE 1 Which of the following identifies the process of forming a nucleic acid by using another

molecule as a template and identifies its most common form?

A translation—the synthesis of RNA using one strand of DNA

B transcription—the synthesis of RNA using one strand of DNA

C replication—the synthesis of proteins using one strand of RNA

D protein synthesis—the synthesis of proteins using one strand of DNA

2 What DNA sequence complements the messenger RNA sequence ACUGACGUCGAA?

A ACTGACGTCGAA B ACUGACGUCGAA

C TGACTGCAGCTT D UGACUGCAGCUU

Name Date




3 The diagram below shows one process that occurs during gene expression.

G

R

G

R

A

R

A

R

A

R

A

R

C

R

C

R

C

R

U

R

T

R

T

R

DNA

mRNA


What process does the diagram represent?

A DNA replication B RNA replication

C transcription D translation

4 The diagram below shows the processes that occur during gene expression.

DNA RNA

A

B

C D

A. At which step would transfer RNA (tRNA) be necessary? What is the term that describes this step?

B. What kind of molecule is indicated by the box beneath letter D?

5 Describe the process by which a segment of DNA directs the production of a protein.

Name Date




Explain how the unique shape and activity of each protein is determined by the sequence of its amino acids.

STANDARD REVIEW

A protein is usually a large molecule formed by linked smaller molecules called amino acids. Amino acids are the building blocks of proteins. Twenty different amino acids are found in proteins. Some amino acids are polar; others are nonpolar. Besides being polar and nonpolar, some amino acids are electrically charged (positive or negative), and others are not charged.

Proteins fold into compact shapes, determined in part by how the protein’s amino acids interact with water and with one another. For example, polar amino acids tend to attract other polar amino acids and repel nonpolar amino acids. The chain of amino acids that forms a protein always folds into a shape that keeps these nonpolar amino acids near one another while also keeping the polar amino acids near one another. In this way, the specifi c sequence of amino acids determines the fi nal shape of the protein.

Both the shape of a protein and the chemistry of its amino acids determine its function. For example, proteins that act as enzymes have pockets called active sites (shown below) that accept substrates—the chemicals on which the protein acts. The shape of the active site matches the shape of the substrates very specifi cally. The polarity of the amino acids in the active site also matches the polarity of the substrates.

Activesite

Substrates

Enzyme

Product

STANDARD PRACTICE 1 Which characteristic in NOT important for determining how well a substrate and

enzyme bind together?

A charge

B color

C shape

D solubility

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2 Oppositely charged particles attract one another, while like charges repel one another. Imagine that a chemical causes the amino acids in an active site on an enzyme to change from a positive charge to a negative charge. How would this change MOST LIKELY affect the way this enzyme interacts with its negatively charged substrate?

A It would cause the substrate to be repelled by the active site.

B It would cause the substrate to bind more tightly with the active site.

C It would have no effect on the way the substrate and active site bind together.

D It would cause the active site to bind to twice the usual number of substrates at once.

3 Leucine, alanine, and tryptophan are amino acids that are hydrophobic. That is, they are nonpolar and do not dissolve well in water. Serine, threonine, and asparagine, on the other hand, are polar amino acids, which means that they do dissolve in water. Which pair of amino acids would MOST LIKELY come together in a folded protein?

A leucine and serine B alanine and threonine

C asparagine and alanine D alanine and tryptophan

4 The shape of a protein—particularly the active site of an enzyme—is often integral to its function.

A. How is the shape of a protein related to its amino acid sequence?

B. Imagine that a mutation in DNA produces a protein with a slightly different amino acid sequence. How would this mutation affect the protein’s function?

5 What characteristics of amino acids affect how they interact?

Name Date



Understand that proteins are responsible for the observable traits of an organism and for most of the functions within an organism.

STANDARD REVIEW

Proteins have many different roles in living things. Some proteins are enzymes that promote chemical reactions. Other proteins have important structural functions. For example, the protein collagen is found in skin, ligaments, tendons, and bones. Your hair and muscles contain structural proteins and so do the fi bers of a blood clot. Other proteins called anti-bodies help your body defend against infection. Specialized proteins in muscles enable your muscles to contract. In your blood, a protein called hemoglobin carries oxygen from your lungs to body tissues.

Inherited traits that can be observed in an organism are the result of proteins. Variations among individuals are due to differences in the specifi c sequence of amino acids that make up proteins. Differences in traits can be due to differences in protein shape that affect protein form or function. Or, they can be due to the inability of an individual to produce a certain protein. For example, in the genetic disorder albinism, the body is unable to pro-duce an enzyme necessary for the production of melanin. Melanin is a pigment that gives dark color to hair, skin, scales, eyes, and feathers. Without melanin, an organism’s surface coloration may be milky white and its eyes may be pink.

STANDARD PRACTICE 1 Some proteins serve important structural functions in living things. Which substance is a

structural protein?

A calcium

B chlorophyll

C cholesterol

D collagen

2 Which class of biological molecule includes enzymes and the structures that determine most observable traits in living things?

A carbohydrates

B lipids

C nucleic acids

D proteins


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3 Many animals that are albinos have white coloration and pink eyes. How is albinism related to protein production?

A Albinism is the result of a lack of melanin, which is a protein that is dark in color.

B Albinism is the result of an overproduction of melanin, which is a protein that is white in color.

C Albinism is the result of an overproduction of melanin, which is a protein that breaks down dark pigments.

D Albinism is the result of a lack of a protein that helps produce melanin, a pigment that is dark in color.

4 Proteins serve many roles in living things. A. Describe an example of a protein that helps the circulatory system function.

B. Describe an example of a protein that helps the immune system function.

5 Why is a diet high in amino acids important for building strong muscles?


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Recognize that traits can be structural, physiological or behavioral and can include readily observable characteristics at the organismal level or less recognizable features at the molecular and cellular level.

STANDARD REVIEW

Many of the heritable traits you are familiar with are physical. They account for the many different physical features that distinguish one individual from another. For example, in humans, the presence or absence of a cleft chin, dimples, and freckles are all physical characteristics that can be inherited through simple dominant or recessive traits. Other physical traits, such as height, hair color, eye color, and skin color, involve more complicated mechanisms of inheritance and are infl uenced by many different factors.

Biologists have learned that many kinds of behaviors are infl uenced by genes. Genetically programmed behavior is often called innate behavior, or more commonly, instinct. For example, an orb spider builds her web the same way every time. There is little or no varia-tion in what she does, and her female offspring will build their webs in the same manner without being taught.

STANDARD PRACTICE 1 Traits can be structural, physiological, or behavioral. Which is a behavioral trait?

A the color of a pigment B the shape of an enzyme

C the length of a thigh bone D the instinct to forage for food

2 A scientist wants to investigate a behavioral trait—specifically, how male guppies behave in the presence of female guppies. She puts two long-tailed guppies in the same fish tank. The male guppies appear to be indifferent to each other’s presence. However, when the scientist adds one female guppy to the tank, the male guppies become aggressive toward one another. Throughout the experiment, the scientist gives the fish enough food so that they do not need to compete for it. In the experiment, why does the scientist maintain the abundance of food before and during the presence of the female guppy?

A The scientist wants to see how the guppies react to various amounts of food.

B The scientist wants to see if the female is more interested in food than the male guppies.

C The scientist wants the guppies to have enough energy to display their natural behavior.

D The scientist must ensure that the guppy’s behavior is not affected by the need to compete for food.


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3 Behavioral adaptations often develop hand in hand with physical adaptations. For example, changes in the shape and orientation of pelvic and leg bones allowed early hominids to become bipedal—that is, they evolved to walk on two legs instead of four. What advantage did the development of bipedalism MOST LIKELY confer to early hominids?

A It allowed them to see with binocular vision.

B It allowed them to evolve an opposable thumb.

C It allowed them to evolve a complex social structure.

D It allowed them to move and hold objects at the same time.

4 Both physical traits and behavioral traits can be acted upon by natural selection. A. What must be true of a behavioral trait for it to have a selective advantage?

B. Male birds of paradise have extremely long, showy tail feathers. Describe a possible selective advantage for having this trait.

5 Differences in traits from one individual to the next are often determined by factors at the cellular level even though they may also be observable at the organismal level. That is, traits that are easily seen with the naked eye can often be due to physical characteristics of molecules. Give an example of such a trait.


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Describe the process of mitosis and explain that this process ordinarily results in daughter cells with a genetic make-up identical to the parent cells.

STANDARD REVIEW

Cells reproduce themselves through mitosis and cytokinesis. Mitosis is the process during cell division in which the nucleus of a cell is divided into two nuclei. Each nucleus ends up with the same number and kinds of chromosomes as the original cell. The process during cell division in which the cytoplasm divides is called cytokinesis.

Steps of Mitosis

Step 1: Prophase Chromosomes coil up and become visible during prophase. The nuclear envelope dissolves and a spindle forms.

Step 2: Metaphase During metaphase the chromosomes move to the center of the cell and line up along the equator. Spindle fi bers link the chromatids of each chromosome to opposite poles.

Step 3: Anaphase Centromeres divide during anaphase. The two chromatids (now called chromosomes) move toward opposite poles as the spindle fi bers attached to them shorten.

Step 4: Telophase A nuclear envelope forms around the chromosomes at each pole. Chromosomes, now at opposite poles, uncoil and the spindle dissolves. The spindle fi bers break down and disappear. Mitosis is complete.

Mitosis and cytokinesis produce new cells that are identical to the original cells and allow organisms to grow, replace damaged tissues, and, in some organisms, reproduce asexually.

STANDARD PRACTICE 1 The following diagrams show four stages of a cell dividing by mitosis.

1 2 3 4


Which list of numbers names the diagrams in the correct sequence as they occur in the cell cycle?

A 1, 3, 4, 2 B 2, 1, 3, 4

C 2, 4, 3, 1 D 4, 3, 2, 1

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2 The cell cycle is a repeating sequence of cellular growth and division during the life of an organism. Which of the following is NOT a true statement concerning cell division of body cells?

A Cells divide in a process called meiosis.

B Cells divide in order to maintain homeostasis.

C Cells divide when the parent cell gets too big.

D Cells divide in order to repair themselves when damaged.

3 Which of the following statements is true of mitosis?

A Two cells are produced, each containing half of the DNA of the parent cell.

B Four cells are produced, each containing half of the DNA of the parent cell.

C Two cells are produced, each containing a complete set of the parent cell’s DNA.

D Three cells are produced: one cell receives the entire DNA of the parent and the other two synthesize new DNA from spare nucleotides.

4 As part of the cell cycle, a cell produces new daughter cells that are identical to the original cell.

A. During which phase are the two daughter cells physically separated?

B. What would result if this phase did not occur?

5 Explain how mitosis relates to the asexual reproduction of single cells.

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Understand that most cells of a multicellular organism contain the same genes, but develop from a single cell (e.g., a fertilized egg) in different ways due to differential gene expression.

STANDARD REVIEW

A multicellular organism is an organism composed of many cells that are permanently associated with one another. Multicellularity occurs only in eukaryotes. While single cells cannot grow larger than a certain size, multicellular organisms can be large. True multicel-lularity occurs when individual cells are in contact with each other and when their activi-ties are coordinated.

Multicellularity enables cells to specialize in different functions. With this division of labor, a multicellular organism can have cells that protect it. Other cells help the organism move about, and still others play roles in reproduction and feeding. Cell specialization begins as a new organism develops. For example, as a chicken develops from an egg, new cells form by cell division. These cells grow and undergo differentiation, the process by which cells develop a specialized form and function.

All of the cells in an individual organism arise from the zygote, the single cell formed at fertilization. The DNA contained in this zygote codes for all of the proteins found in all of the different cell types in the adult organism. Cells differentiate by expressing only some of these genes and not others.

Plants and animals have complex multicellularity. The specialized cells of most plants and animals are organized into structures called tissues and organs. A tissue is a distinct group of cells with similar structure and function. Muscle, for example, is a tissue com-posed of many muscle cells that work together. Different tissues may be organized into an organ, which is a specialized structure with a specifi c function. An example of an organ is the heart, which is composed of muscle, nerve, and other tissues that work together as a pump. Various organs that carry out a major body function make up an organ system. The circulatory system, which is composed of the heart, the blood vessels, and the blood within them, is an example of an organ system.

STANDARD PRACTICE 1 Which series shows the different levels of cellular organization in order from least

complex to most complex?

A cell → tissue → organ → organ system

B tissue → cell → organ → organ system

C organ system → organ → cell → tissue

D organ system → organ → tissue → cell


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2 Which kingdom does NOT include organisms that are multicellular?

A Animalia B Eubacteria

C Fungi D Plantae

3 Which statement correctly compares the genomes of a fertilized egg and a differentiated cell that arose from that fertilized egg?

A The genomes are identical and every gene is expressed fully in each cell.

B The genomes are identical, but different genes are expressed in each cell.

C The genome of the fertilized egg is larger than the genome of the differentiated cell.

D The genome of the differentiated cell is larger than the genome of the fertilized egg.

4 The cells of developing multicellular organisms undergo cell differentiation.

A. What is cell differentiation?

B. How do the cells in an individual differentiate when they all have the same DNA?

5 Describe an advantage of multicellularity.

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Explain that in multicellular organisms the zygote produced during fertilization undergoes a series of cell divisions that lead to clusters of cells that go on to specialize and become the organism’s tissues and organs.

STANDARD REVIEW

In all animals except sponges, the zygote (fertilized egg cell) undergoes cell divisions that form a hollow ball of cells called a blastula. Cells within the blastula eventually develop into three distinct layers of cells—ectoderm, endoderm, and mesoderm. These layers are called the primary tissue layers because they give rise to all of the tissues and organs of the adult body. The table below lists the three primary tissue layers and summarizes the body tissues and organs to which they give rise. Note that the table includes some organs, such as the urinary bladder, found only in vertebrates. The organs of vertebrates are complex structures containing cells that arise from more than one primary tissue layer. For example, the digestive system is formed primarily from endoderm and mesoderm.

Origin of Animal Tissues and Organs

Primary tissue layer Gives rise toEctoderm Outer layer of skin; nervous system; sense organs, such as eyes

Endoderm Lining of digestive tract; respiratory system; urinary bladder; digestive organs; liver; many glands

Mesoderm Most of the skeleton; muscles; circulatory system; reproductive organs; excretory organs

The cells of all animals except sponges are organized into structural and functional units called tissues. Tissues are groups of cells with a common structure that work together to perform a specifi c function. For example, the cells of adipose tissue are specialized for stor-ing fat. The cells of muscle tissue are specialized to contract, producing movement. The cells of nerve tissue are specialized to conduct signals.

STANDARD PRACTICE 1 Which series lists the structures in order of their formation during embryonic

development?

A blastula → zygote → ectoderm layer

B zygote → blastula → mesoderm layer

C fertilized egg → ectoderm layer → zygote

D fertilized egg → endoderm layer → blastula


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2 What embryonic tissue layer gives rise to the small intestine?

A ectoderm B endoderm

C mesoderm D pachyderm

3 The blastula undergoes gastrulation to form the gastrula, which has the three primary tissue layers. The ectoderm layer makes up the outer part of the gastrula. Which organ results from ectoderm tissue layer?

A bladder B eye

C heart D stomach

4 Imagine that a mutation occurs in one of the mesoderm cells of a developing embryo. A. Will the mutation appear in all other cells of the body? Explain.

B. What kinds of tissues in the adult organism could be affected by such a mutation during development?

5 Embryonic stem cells are cells taken from an embryo that can divide endlessly and give rise to every type of tissue in the body. Embryonic stem cells must be harvested before the endoderm, ectoderm, and mesoderm tissue layers have formed. Explain why they cannot be harvested after this stage.

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Describe and model the process of meiosis and explain the relationship between the genetic make-up of the parent cell and the daughter cells (gametes).

STANDARD REVIEWSome organisms reproduce by joining gametes to form the fi rst cell of a new individual. The gametes are haploid—they contain one set of chromosomes. Meiosis is a form of cell division that halves the number of chromosomes when forming specialized reproductive cells, such as gametes or spores. Meiosis involves two divisions of the nucleus—meiosis I and meiosis II.Steps of MeiosisBefore meiosis begins, the DNA in the original cell is replicated. Thus, meiosis starts with homologous chromosomes. Recall that homologous chromosomes are similar in size, shape, and genetic content. The stages of meiosis are summarized below:Step 1: Prophase I The chromosomes condense, and the nuclear envelope breaks down. Homologous chromosomes pair along their length. Crossing-over occurs when portions of a chromatid on one homologous chromosome are broken and exchanged with the corresponding chromatid portions of the other homologous chromosome.Step 2: Metaphase I The pairs of homologous chromosomes are moved by the spindle to the equator of the cell. The homologous chromosomes remain together.Step 3: Anaphase I The homologous chromosomes separate. As in mitosis, the chromosomes of each pair are pulled to opposite poles of the cell by the spindle fi bers. But the chromatids do not separate at their centromeres—each chromosome is still composed of two chromatids. The genetic material, however, has recombined.Step 4: Telophase I Individual chromosomes gather at each of the poles. In most organisms, the cytoplasm divides (cytokinesis), forming two new cells. Both cells or poles contain one chromosome from each pair of homologous chromosomes. Chromosomes do not replicate between meiosis I and meiosis II.Step 5: Prophase II A new spindle forms around the chromosomes.Step 6: Metaphase II The chromosomes line up along the equator and are attached at their centromeres to spindle fi bers.Step 7: Anaphase II The centromeres divide, and the chromatids (now called chromosomes) move to opposite poles of the cell.Step 8: Telophase II A nuclear envelope forms around each set of chromosomes. The spindle breaks down, and the cell undergoes cytokinesis. The result of meiosis is four haploid cells.

STANDARD PRACTICE 1 Imagine that sex cells divided by mitosis instead of meiosis. What would then be the

result of fertilization of an ovum by a sperm cell?

A Fertilization would result in the formation of two identical cells. B The new individual would be identical to only one of the parents. C Fertilization would cause crossing-over and recombination of genes. D Cells of the new individual would have double the necessary number of

chromosomes.


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2 Which statement explains why approximately half of an individual’s DNA sequence comes from each parent?

A A cell from one parent undergoes meiosis, producing offspring cells that have both parents’ DNA.

B A cell from one parent undergoes mitotic cell division, producing offspring cells that have only half of that parent’s DNA.

C Cells in the parents undergo meiosis, producing haploid gametes that meet up during fertilization to produce a diploid individual.

D Cells in the parents undergo mitosis, producing offspring cells that meet up during fertilization to produce an individual with half of each parent’s DNA.

3 Meiosis is the form of cell division that produces gametes. Which of the following statements correctly describes gametes?

A In spermatogenesis, eight sperm cells are produced.

B Eggs are diploid and, when fertilized, give rise to haploid cells.

C In the formation of eggs, four identical haploid cells are produced.

D In oogenesis, the cytoplasm divides unequally, producing an ovum and three smaller polar bodies.

4 Gametes are haploid cells produced through meiosis. A. What does it mean to be haploid?

B. How does a haploid cell compare to a diploid cell?

5 Describe how anaphase I differs from anaphase II in meiosis.

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Explain how, in sexual reproduction, crossing-over, independent assortment, and random fertilization, result in offspring that are genetically different from the parents.

STANDARD REVIEW

Some organisms have two parents, while others have one. Some organisms look exactly like their parents and siblings. Others share traits with family members but are not identical to them. The amount of similarity among family members is determined by the type of reproduction—whether it is asexual or sexual.

In asexual reproduction a single parent passes copies of all of its genes to each of its offspring; there is no fusion of haploid cells such as gametes. Asexual reproduction involves only mitosis, not meiosis. An individual produced by asexual reproduction is a clone, an organism that is genetically identical to its parent. Prokaryotes, for example, reproduce asexually. In a stable environment, asexual reproduction allows organisms to produce many offspring in a short period of time without using energy to produce gametes or to fi nd a mate. However, the DNA of these organisms varies little among individuals.

In contrast, in sexual reproduction two parents each form reproductive cells through meiosis that have one-half the number of chromosomes. A diploid mother and father give rise to haploid gametes, which join to form diploid offspring. Because both parents con-tribute genetic material, the offspring have traits of both parents but are not exactly like either parent. Sexual reproduction, with the formation of haploid cells, occurs in eukaryotic organisms, including humans.

Sexual reproduction provides a powerful means of quickly making different combinations of genes among individuals. Such genetic diversity is the raw material for evolution. In hu-mans, for example, each gamete receives one chromosome from each of 23 pairs of homolo-gous chromosomes. Which of the two chromosomes that an offspring receives from each of the 23 pairs is a matter of chance. This random distribution of homologous chromosomes during meiosis is called independent assortment. Each of the 23 pairs of chromosomes segregates (separates) independently. Thus, 223 (about 8 million) gametes with different gene combinations can be produced from one original cell by this mechanism. Crossing-over adds even more recombination.

STANDARD PRACTICE 1 In asexual reproduction, a single parent passes copies of all of its genes to each of its

offspring. When is asexual reproduction in plants advantageous?

A when the environment is unstable

B when there is little competition for resources

C when plants are well adapted to the environment

D when there are multiple disease agents in the environment


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2 Cells and the organisms they make up reproduce through cell division. Some organisms reproduce through mitosis, while others reproduce through meiosis and fertilization. What advantage does meiosis give to organisms that reproduce sexually?

A Meiosis ensures that offspring inherit genes from their parents.

B Meiosis ensures that offspring will not inherit any genetic disorders.

C Meiosis ensures that offspring are genetically different from their parents.

D Meiosis ensures that offspring will have identical phenotypes to their parents.

3 Konesha’s eyes are brown, just like her mother’s eyes. Konesha has long fingers like her father, but her mother’s fingers are much shorter. What is the MOST LIKELY reason why Konesha’s appearance is similar to and different from that of her parents?

A All of her traits depended upon pure chance.

B Her eye color is an inherited trait, but finger length is a trait that evolved in Konesha.

C She inherited some traits, such as eye color, from her mother and others, such as finger length, from her father.

D She inherited her eye color from her mother but grew longer fingers because she had better nutrition as an infant.

4 Crossing-over contributes to the recombination of genetic material in offspring. A. When does crossing-over happen during meiosis?

B. How does crossing-over contribute additional variation in the DNA of the sex cells formed during meiosis?

5 Identify three ways that genes are recombined during sexual reproduction.

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Distinguish between dominant and recessive alleles and determine the phenotype that would result from the different possible combinations of alleles in an offspring.

STANDARD REVIEW

Modern genetics is based on Gregor Johann Mendel’s explanations for the patterns of heredity that he studied in garden pea plants. Mendel’s fi rst experiments used monohybrid crosses and were carried out in three steps that are described below.

1. He produced a true-breeding P generation by self-pollinating plants that produced only purple fl owers and by self-pollinating plants that produced only white fl owers.

2. He produced an F1 generation by cross pollinating the two varieties from the true-breeding P generation. He observed that this F1 generation had fl owers that were all purple.

3. He produced an F2 generation by self-pollinating plants from this F1 generation. He observed that three fourths of this F2 generation had fl owers that were purple, while one fourth had fl owers that were white.

For each of the seven characteristics that Mendel studied in this experiment, he found a similar 3-to-1 ratio of contrasting traits in the F2 generation. Mendel’s experiments showed that offspring do not show a trait for every allele they receive. Instead, combinations of alleles determine traits. When two different alleles occur together, one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance. Mendel described the expressed form of the character as dominant. The trait that was not expressed when the dominant form was present was described as recessive. For example, if a plant has both purple and white alleles for fl ower color but blooms purple fl owers, then purple is the dominant form; white is the recessive form.

The set of alleles that an individual has for a characteristic is called the genotype. The trait that results from a set of alleles is the phenotype. In other words, genotype determines phenotype. If an individual has two of the same alleles of a certain gene, the individual is homozygous for the related characteristic. On the other hand, if an individual has two dif-ferent alleles of a certain gene, the individual is heterozygous for the related characteristic. In the heterozygous case, the dominant allele is expressed.

STANDARD PRACTICE 1 A lily has one allele for spotted pink petals and one allele for solid pink petals. The

resulting flower has spotted pink petals. What must be true?

A The allele for spotted pink petals is recessive.

B The allele for spotted pink petals is dominant.

C The alleles for spotted and solid pink petals are both recessive.

D The alleles for spotted and solid pink petals are both dominant.

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2 In humans, having freckles (F ) is dominant to not having freckles (f ). Having a cleft chin (C ) is also dominant to not having a cleft chin (c). Which statement is true of the offspring of a cross between parents that are both heterozygous for both traits (FfCc)?

A Any offspring with freckles must also have a cleft chin.

B Any offspring who does not have freckles must have a cleft chin.

C All of the offspring will be heterozygous for both traits.

D The offspring could exhibit both traits, neither trait, or only one of the traits.

3 A parent that is heterozygous for two different traits (AaBb) can pass any combination of two alleles (AB, Ab, aB, or ab) to its offspring. Which statement explains why this is possible?

A There are alternative versions of genes.

B The two alleles for a single gene separate when gametes are formed.

C For each inherited characteristic, an individual has two copies of the gene.

D The alleles of different genes separate independently of one another during gamete formation.

4 For a certain plant, purple flowers (allele: P) are dominant, and white flowers (allele: p) are recessive. A purple plant carrying both types of alleles is crossed with a true-breeding white plant.

A. What are the possible genotypes of the offspring?

B. What are the possible phenotypes of the offspring?

5 Briefly describe Mendel’s experiments with pea plants and his observed results.

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Describe dominant, recessive, codominant, sex-linked, incompletely dominant, multiply allelic, and polygenic traits and illustrate their inheritance patterns over multiple generations.

STANDARD REVIEW

Most patterns of inheritance are more complex than the simple dominant and recessive patterns that Mendel identifi ed.

• Sex-Linked An autosome is a chromosome other than an X or Y sex chromosome. If a trait is sex-linked, its effects are usually seen only in males. A sex-linked gene’s allele is located only on the X or Y chromosome. Because males have only one X chromosome, a male who carries a recessive allele on the X chromosome will exhibit the sex-linked condition.

• Polygenic Inheritance When several genes infl uence a character, the character exhibits polygenic inheritance. The genes for a polygenic character may be scattered along the same chromosome or located on different chromosomes. Determining the effect of any one of these genes is diffi cult. Familiar examples of polygenic characters in humans include eye color, height, weight, and hair and skin color.

• Incomplete Dominance In some organisms, an individual displays a phenotype that is intermediate between the two parents, a condition known as incomplete domi-nance. For example, when a snapdragon with red fl owers is crossed with a snap-dragon with white fl owers, a snapdragon with pink fl owers is produced. Neither the red nor the white allele is completely dominant over the other allele. The fl owers appear pink.

• Multiple Alleles Genes with three or more alleles are said to have multiple alleles. For example, in the human population, the ABO blood groups (blood types) are determined by three alleles, IA, IB, and i. The letters A and B refer to two carbohy-drates on the surface of red blood cells. In the i allele, neither carbohydrate is present. The IA and IB alleles are both dominant over i. A person who inherits two i alleles has type O blood.

• Codominance For some characters, two dominant alleles are expressed at the same time. In this case, both forms of the character are displayed, a phenomenon called codominance. The situation of human ABO blood groups is an example of codominance. The genotype of a person who has blood type AB is IAIB, and neither allele is dominant over the other. Type AB blood cells carry both A- and B-types of carbohydrate molecules on their surfaces.

STANDARD PRACTICE 1 A gardener crossed a plant with red flowers with a plant that had white flowers. The

offspring plants had pink flowers. What is the MOST LIKELY genetic reason for these differences in color?

A codominance B recessive pink genes

C polygenic inheritance D incomplete dominance

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2 The diagram below shows a pedigree.


What can you conclude about the trait shown in this pedigree?

A The trait is autosomal and dominant.

B The trait is Y-linked and dominant.

C The trait is X-linked and dominant.

D The trait is X-linked and recessive.

3 A trait for flower color shows incomplete dominance, where heterozygous individuals have pink flowers. If a homozygous individual were crossed with a heterozygous individual, what percentage of their offspring would exhibit pink flowers?

A 0% B 50%

C 75% D 100%

4 In Caucasians, the child of a straight-haired parent and a curly-haired parent will have wavy hair. Straight hair and curly hair are homozygous dominant traits. Wavy hair is heterozygous and is intermediate between straight and curly hair.

A. What kind of inheritance pattern is this?

B. What is the expected phenotype of a child born to a mother with straight hair and a father with curly hair?

5 Explain how codominance differs from incomplete dominance.

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Determine the likelihood of the appearance of a specifi c trait in an offspring given the genetic make-up of the parents.

STANDARD REVIEW

One simple way of predicting the expected results (not necessarily the actual results) of the genotypes or phenotypes in a cross is to use a Punnett square. A Punnett square is a dia-gram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross. The simplest Punnett square consists of four boxes inside a square. The possible gametes that one parent can produce are written along the top of the square. The possible gametes the other parent can produce are written along the left side of the square. Each box inside the square contains two letters obtained by combining the allele along the top of the box with the allele along the side of the box. The letters in the boxes indicate the possible genotypes of the offspring.

Punnett squares can be used to predict the outcome of a monohybrid cross. For example, a Punnett square can be used to predict the outcome of a cross between a pea plant that is homozygous for yellow seed color (YY) and a pea plant that is homozygous for green seed color (yy). The Punnett square below left shows that 100 percent of the offspring in this type of cross are expected to be heterozygous (Yy), expressing the dominant trait of yellow seed color.

The Punnett square below right predicts the results of a monohybrid cross between two pea plants that are both heterozygous (Yy) for seed color. One-fourth of the offspring would be expected to have the genotype YY, two-fourths (or one-half) would be expected to have the genotype Yy, and one-fourth would be expected to have the genotype yy. Another way to express this is to say that the genotypic ratio is 1 YY : 2 Yy : 1 yy. Because the Y allele is dominant over the y allele, three-fourths of the offspring would be yellow, and one-fourth would be green. The phenotypic ratio is 3 yellow : 1 green.

Y Y

y Yy Yy

y Yy Yy

Y y

Y YY Yy

y Yy yy

STANDARD PRACTICE 1 Gregor Mendel crossed a true-breeding tall plant (TT ) with a true-breeding short plant

(tt). What are the predicted phenotypes for the offspring?

A all tall B all short

C ratio of 1 tall : 1 short D ratio of 3 tall : 1 short

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2 A population of crabs living on a sandy beach exhibits three colors: dark brown, light brown, and speckled. The genotypes for these colors are BB for dark brown, vbb for light brown, and Bb for speckled. If a dark brown crab were crossed with a light brown crab, what would be the predicted phenotypic ratio of their offspring?

A all speckled

B all dark brown

C 3 dark brown : 1 light brown

D 1 dark brown : 2 speckled : 1 light brown

3 In snap peas, yellow flowers (Y) are dominant to white flowers (y). In the cross YY × Yy, what would be the genotypic ratio of the F1 generation?

A 1:1 B 1:2

C 1:3 D 3:1

4 The Punnett square below shows a cross between two rabbits. Black fur (B) is dominant to brown fur (b).

B b

Bb � Bb

B 1 2

b 3 4

hb07ca-srw_04-31.indd 23 4/20/06 10:48:32 AM

A. What would be the phenotype of the offspring indicated by box 3?

B. If individuals from box 1 and box 4 were crossed, what would be the genotypes of the offspring?

5 Describe how you could determine whether a plant was heterozygous or homozygous for a certain trait.

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Explain the process by which a cell copies its DNA and identify factors that can damage DNA and cause changes in its nucleotide sequence.

STANDARD REVIEW

The process of making a copy of DNA is called DNA replication. DNA replication is summarized in the fi gure below. First, the two original strands separate. Then, proteins called DNA polymerases add complementary nucleotides to each strand. Bases always pair in the same way: an adenine (A) on one strand always pairs with a thymine (T) on the opposite strand, and a guanine (G) on one strand always pairs with a cytosine (C) on the opposite strand.

Replicationfork

DNAhelicase

DNA polymerases

NewDNA

NewDNA

OldDNA

OldDNA

Because of the strictness of base-pairing rules, the result of replication is always the formation of two DNA molecules that are identical to the original DNA molecule. Each resulting DNA molecule is composed of one of the original strands and one new strand.

STANDARD PRACTICE 1 James Watson and Francis Crick built a model showing that the structure of DNA is

like a twisted ladder called a double helix. What purpose does the double helix structure serve?

A The double helix shows that one strand of the DNA ladder is inherited from each parent.

B The sugars and phosphates that make up the sides of the DNA ladder twist and curve to conserve space in the cell.

C The double helix structure of DNA is a random occurrence, and DNA could just as easily be a straight, single-strand molecule.

D The pattern of complimentary bases on each side of the DNA ladder ensures that exact copies of the DNA are made during replication.

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2 The sequence of bases on one strand of a DNA molecule is AGCCTAG. After replication of the strand of DNA, what is the sequence of nitrogen bases on the complementary strand?

A AGCCTAG B CTAGGCA

C GATCCGA D TCGGATC

3 Imagine that a scientist placed a double-stranded molecule of DNA in a test tube along with the enzymes DNA helicase and DNA polymerase. He added great quantities of the four different types of nucleotides (A, T, G, and C) that had each been labeled with a radioactive marker. He then allowed the replication of DNA to take place in the test tube. The final result was two molecules of double-stranded DNA. What would be true of the two molecules of DNA?

A Both molecules of DNA would be made up of two strands that had the radioactive markers.

B Both molecules of DNA would be made up of two strands that did not have the radioactive markers.

C Both molecules of DNA would be made up of one strand that had the radioactive markers and one strand that did not have the radioactive markers.

D One molecule of DNA would be made up of two strands that had the radioactive markers, and the other would be made up of two strands that did not have the radioactive markers.

4 DNA helicase is an enzyme that opens up the double helix of DNA. A. What kind of bonds does DNA helicase break?

B. Explain why DNA helicase is needed during DNA replication.

5 Before replication, the sequence of nitrogen bases on one of the original strands of DNA is TAGCATACT. After replication of the strand of DNA, what is the sequence of nitrogen bases on the complementary strand?

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Explain and demonstrate how inserting, substituting or deleting segments of a DNA molecule can alter a gene, which is then passed to every cell that develops from it and that the results may be benefi cial, harmful or have little or no effect on the organism.

STANDARD REVIEW

Although changes in an organism’s hereditary information are relatively rare, they can occur. A change in the DNA of a gene is called a mutation. Mutations in gametes can be passed on to offspring of the affected individual, but mutations in body cells affect only the individual in which they occur.

Mutations that move an entire gene to a new location are called gene rearrangements. Changes in a gene’s position often disrupt the gene’s function because the gene is exposed to new regulatory controls in its new location.

Mutations that change a gene are called gene alterations. Gene alterations usually result in the placement of the wrong amino acid during protein assembly. This error will usually disrupt a protein’s function. In a point mutation, a single nucleotide changes. In an inser-tion mutation, a sizable length of DNA is inserted into a gene. In a deletion mutation, segments of a gene are lost, often during meiosis. A duplication mutation occurs when a chromosome fragment attaches to its homologous chromosome, which will then carry two copies of a certain set of genes. Another type of mutation is an inversion mutation, in which the chromosome piece reattaches to the original chromosome but in a reverse orientation. If the piece reattaches to a nonhomologous chromosome, a translocation mutation results.

Because the genetic message is read as a series of triplet nucleotides, insertions and dele-tions of one or two nucleotides can upset the triplet groupings. Imagine deleting the letter C from the sentence “THE CAT ATE.” Keeping the triplet groupings, the message would read “THE ATA TE,” which is meaningless. A mutation that causes a gene to be read in the wrong three-nucleotide sequence is called a frameshift mutation.

STANDARD PRACTICE 1 The base sequences below show two different sequences of the same gene. Wild Type: TTGACTCGGTATAC Mutant: TTGACTCGTATAC What type of mutation is illustrated?

A deletion

B insertion

C inversion

D substitution


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2 Errors sometimes happen during DNA replication. If a DNA nucleotide that contains guanine is accidentally substituted for a DNA nucleotide that contains thymine, which of the following will always happen because of the error in DNA replication?

A The cell will die when it divides.

B The cell will become a rapidly dividing cancer cell.

C The cell will produce mRNA with a mutated nucleotide sequence.

D The cell will have a better chance of surviving under different conditions.

3 A mutation in the DNA that produced the strand of messenger RNA shown in the chart below produced a new strand of mutant messenger RNA.

CODON AND ANTICODON PAIRING

Transfer RNA UGA CUG CAG CUU

Messenger RNA ACU GAC GUC GAA

If the mutation was a deletion, which strand of the following sequences would best represent the resulting mutant messenger RNA?

A ACGGACGUCGAA B ACUACGUCGAA

C ACUGACGUCCAA D ACUGCACGUCGAA

4 One kind of DNA mutation is called a frameshift mutation. A. What is a frameshift mutation?

B. Why do frameshift mutations more often result in a nonfunctioning protein than other kinds of mutations?

5 Explain how a mutation in a gene could have no effect on the organism that inherits the mutated gene.


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Explain how anatomical and molecular similarities among organisms suggest that life on earth began as simple, one-celled organisms about 4 billion years ago and multicellular organisms evolved later.

STANDARD REVIEW

In 1859, the English naturalist Charles Darwin published convincing evidence that species evolve, and he proposed a reasonable mechanism explaining how evolution occurs. Darwin suggested that individuals that have physical or behavioral traits that better suit their envi-ronment are more likely to survive and will reproduce more successfully than those that do not have such traits. Darwin called this differential rate of reproduction natural selection. In time, the number of individuals that carry favorable characteristics that are also inherit-ed will increase in a population. Thus, the nature of the population will change—a process he called evolution.

Darwin further suggested that organisms differ from place to place because their habitats present different challenges to, and opportunities for, survival and reproduction. Each species has evolved and has accumulated adaptations in response to its particular environ-ment. An adaptation is an inherited trait that has become common in a population because the trait provides a selective advantage.

Scientists have found many different kinds of evidence that support the theory of evolution. Fossils offer the most direct evidence that evolution takes place. Evidence of orderly change can be seen when fossils are arranged according to their age. The anatomy and development of living things also shows evidence of evolution. For example, the similarities of structures in different vertebrates provide evidence that all vertebrates share a common ancestor. Biological molecules also show evolutionary relationships. Differences in amino acid sequences and DNA sequences are greater between species that are more distantly related than between species that are more closely related.

STANDARD PRACTICE 1 Biologists look at how organisms are related and when they first appeared on Earth.

Which of the following is true about the organisms that live on Earth today?

A All organisms that have ever lived on Earth can still be found alive today.

B Some of the organisms alive today have been around for 4.6 billion years.

C The organisms alive today are the same as the ones that are found in fossils.

D The organisms alive today evolved from organisms that previously lived on Earth.

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2 A species of toad living in an area is similar in form to toad fossils found in very old rock. Which hypothesis does this observation support?

A Toads living near the area have evolved slowly over time.

B Toads evolved rapidly, because there are many variations in form.

C This species of toad burrowed into the rock and became fossilized.

D The toads living today migrated to the area from a different region.

3 Which observation is evidence that two organisms share a recent evolutionary ancestor?

A Both dragonflies and hummingbirds have wings and can fly.

B Both zebras and zebra fish have striped patterns and similar names.

C The mouth shapes of the duckbilled platypus and the duck are similar.

D The sequences of amino acids in chimpanzee and gorilla hemoglobin are similar.

4 Scientists hypothesize that single-cell organisms evolved first, and multicellular organisms evolved later from single-cell organisms.

A. What kind of fossil evidence would support this hypothesis?

B. Could you infer that a single-cell organism living today must have evolved before a multicellular organism living today? Explain.

5 Identify three kinds of evidence that support the theory that all organisms on Earth evolved from simple, single-cell organisms that lived long ago.

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Explain how organisms are classifi ed and named based on their evolutionary relationships into taxonomic categories.

STANDARD REVIEW

Modern classifi cation of living things is based on a system developed by the Swedish biologist Carl Linnaeus. It is organized into a ranked system of groups that increase in inclusiveness. Similar genera are grouped into a family. Similar families are combined into an order. Orders with common properties are united in a class. Classes with similar charac-teristics are assigned to a phylum. Similar phyla are collected into a kingdom. Similar king-doms are grouped into domains. All living things are grouped into one of three domains. Two domains, Archaea and Bacteria, are each composed of a single kingdom of prokary-otes. The third domain, Eukarya, contains all four kingdoms of eukaryotes.

Linnaeus’s classifi cation system was based on his observation that organisms have different degrees of similarity. For instance, a tiger resembles a gorilla more closely than either resembles a fi sh. According to Darwin’s views, organisms that are more similar to one another than they are to other organisms have descended from a more recent common ancestor. Therefore, classifi cation based on similarities should refl ect an organism’s phylog-eny, that is, its evolutionary history. Inferring evolutionary connections from similarities, however, can be misleading. Not all features, or characters, are inherited from a common ancestor. Consider the wings of a bird and the wings of an insect. Both enable fl ight, but the structures of the two kinds of wings differ.

Most biologists today analyze evolutionary relationships using cladistics. Cladistics is a method of analysis that reconstructs phylogenies by inferring relationships based on shared characters. Cladistics can be used to hypothesize the sequence in which different groups of organisms evolved. To do this, cladistics focuses on the nature of the characters in different groups of organisms.

STANDARD PRACTICE 1 Which series represents the correct order of levels of classification, from broadest

to narrowest?

A domain, kingdom, phylum, order, class, family, genus, species

B domain, kingdom, phylum, class, order, family, genus, species

C kingdom, phylum, domain, order, class, family, genus, species

D species, genus, family, class, order, phylum, kingdom, domain


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2 The following table classifies three different organisms.

CLASSIFICATION OF THREE DIFFERENT ORGANISMS

Organism Class A Family GenusBacterium Scotobacteria Spirochaetales Spirochaetaceae CristispiraBox elder Dicotyledones Sapindales Aceraceae AcerHuman Mammalia Primates Hominidae B

Which level of classification is represented by the box labeled A?

A division B kingdom

C order D phylum

3 The ancient Greeks grouped plants and animals according to their structural similarities. What are modern classification systems based on?

A. solely on structural characteristics of organisms

B. on similar behaviors as well as similar characteristics

C. solely on evolutionary relationships between organisms

D. on evolutionary relationships as well as similar characteristics

4 Early biologists thought that sponges were plants. Today, biologists classify sponges as animals rather than plants.

A. Describe a piece of evidence that supports the old classification of sponges as plants.

B. Describe a piece of evidence that supports today’s classification of sponges as animals.

5 Protists are classified using a different system than that used for most other types of organisms. Why does the system used to classify protists differ from other classification systems?

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Use anatomical and molecular evidence to establish evolutionary relationships between organisms.

STANDARD REVIEW

There are many kinds of evidence that support evolution. One kind of evidence can be found in fossils. A fossil is the preserved or mineralized remains or imprint of an organism that lived long ago. Fossils, therefore, provide an actual record of Earth’s past life-forms. Change over time (evolution) can be seen in the fossil record. Fossilized species found in older rocks are different from those found in newer rocks.

The anatomy of living organisms also provides evidence of evolution. Comparisons of the anatomy of different types of organisms often reveal basic similarities in body struc-tures even though the structure’s functions may differ between organisms. Both vestigial structures and homologous structures provide evidence of evolutionary relationships. A vestigial structure is a structure in an organism that is reduced in size and function but may have been complete and functional in the organism’s ancestors. A homologous structure is an anatomical structure found in two or more organisms that share a common ancestry though that structure may not share a common function.

The evolutionary history of organisms is also seen in the development of embryos. At some time in their development, all vertebrate embryos have a tail, buds that become limbs, and pharyngeal pouches. The tail remains in most adult vertebrates. Only adult fi sh and immature amphibians retain pharyngeal pouches (which contain their gills).

STANDARD PRACTICE

1 The diagram below shows the evolutionary relationships among five animals.

ANIMAL CLADOGRAM


What major characteristic is the same for all five animals?

A All are carnivores.

B All have backbones.

C All spend their entire lives on land.

D All maintain a constant body temperature.


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2 The pictures below show similarities among the forelimbs of three mammals.

These similarities provide evidence for which of the following hypotheses?

A Legs and wings may have evolved from flippers.

B All mammals have evolved from an ancestor that was a bat.

C A cat’s leg, a dolphin’s flipper, and a bat’s wing have identical functions.

D Cats, dolphins, and bats may have had the same ancestor millions of years ago.

3 Galápagos finches vary in beak size according to which island they inhabit. The evolution of beak sizes in Galápagos finches is a response to which of the following?

A. the color of their beaks

B the types of seeds available

C whether the populations interbreed

D the nutritional content of the seeds they eat

4 The hind limbs of whales are vestigial structures. A. What are vestigial structures?

B. How might a vestigial structure provide evidence of evolutionary relationships?

5 Describe an example of how the development of organisms can show evidence of evolution.

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Understand that molecular evidence supports the anatomical evidence for these evolutionary relationships and provides additional information about the order in which different lines of descent branched.

STANDARD REVIEW

The picture of successive change seen in the fossil record allows scientists to make a prediction that can be tested. If species have changed over time as the fossil record indi-cates, then the genes that determine the species’ characteristics should also have changed by mutation and selection. As species evolved, one change after another should have become part of their genetic instructions. Therefore, changes in a gene’s nucleotide sequence should build up over time.

This prediction was fi rst tested by analyzing the amino acid sequences of similar proteins found in several species. If evolution has taken place, then, in general, species that descended from a recent common ancestor should have fewer amino acid differences between their proteins than species that shared a common ancestor in the more distant past.

For example, comparing the same hemoglobin protein in several species reveals certain patterns. Species that are thought to have shared a common ancestor more recently (for example, humans and gorillas) have few amino acid sequence differences. However, those species that are thought to have shared a common ancestor in the more distant past (such as humans and mice) have many amino acid sequence differences.

More accurate hypotheses about evolutionary histories are based on large numbers of gene sequences. These evolutionary histories based on DNA sequences tend be very similar to evolutionary histories inferred by biologists based on comparative anatomy and on evidence from the fossil record.

STANDARD PRACTICE 1 When Darwin first proposed his theory of evolution by natural selection, the field of

genetics did not yet exist. In what way does genetic science now contribute to the study of evolution?

A Scientists can create organisms that were extinct using DNA from fossils and, thus, better understand how they evolved.

B Scientists can use genetic engineering to carry out the process of evolution over just months instead of millions of years.

C Scientists can compare the DNA from fossils in rock to determine evolutionary relationships among extinct species.

D Scientists can determine evolutionary relationships among living species by comparing amino acid sequences coded for by DNA.


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2 Which provides the STRONGEST evidence of recent common ancestry in two organisms?

A proteins with very similar shapes

B proteins with very similar functions

C proteins with very similar gene origins

D proteins with very similar amino acid sequences

3 Which type of biological molecule would NOT likely provide evidence of common ancestry among organisms?

A carbohydrate B DNA

C mRNA D protein

4 Modern scientists have observed that genetic changes happen over time in all natural populations. Therefore, by comparing amino acid sequences, scientists can determine how similar one species is to another. The table below compares amino acids in a number of species.

Hemoglobin Comparison

Animal with hemoglobin

Amino acids that differ from human hemoglobin

Gorilla 1

Rhesus monkey 8

Mouse 27

Chicken 45

Frog 67

Lamprey 125

A. Based on the information in the table, which animal in the table is LEAST closely related to humans?

B. Which animal in the table is MOST closely related to humans?

5 Why would two related organisms have similar DNA base sequences for a certain gene as well as similar amino acid sequences for a related protein?

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Describe how due to genetic variations, environmental forces, and reproductive pressures, organisms with benefi cial traits are more likely to survive, reproduce, and pass on their genetic information.

STANDARD REVIEW

Evolution is a change in the characteristics of a population from one generation to the next. Darwin proposed that evolution happened due to natural selection. Natural selection is the process by which individuals that have favorable variations and are better adapted to their environment survive and reproduce more successfully than less well adapted individu-als. Over many generations, natural selection can result in the evolution of new species, which is called speciation. The diagram below shows how natural selection changes populations.

1 OverproductionEach species producesmore individuals thancan survive to maturity.

2 Genetic VariationThe individuals of a population may differ in traits such as size, color, strength, speed, ability to find food, or resistance to certain diseases.

3 Struggle to SurviveIndividuals must compete with each other for limited resources. Also, some individuals will be harmed by predation, disease, or unfavorable conditions.

4 Differential ReproductionIndividuals that have certain traits are more likely to survive and reproduce than are individuals that lack those traits. Over time, those traits become more frequent in the population.

STANDARD PRACTICE 1 Speciation is the formation of new species as a result of evolution by natural selection.

What effect could separation of populations have on speciation?

A One half of the species will go extinct if the population is separated.

B The separated populations will always evolve into at least two different species.

C If the environments differ enough, the separated populations may evolve differently.

D By separating, the populations will no longer be able to interbreed and will die off.


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2 Evolution is a change in the characteristics of a population from one generation to the next. Which of the following is the correct order for the steps of evolution by natural selection?

A overproduction—selection—adaptation—variation

B. overproduction—selection—adaptation—evolution

C. overproduction—variation—selection—adaptation

D. selection—variation—adaptation—overproduction

3 Immigration to the United States in the 1800s from Eastern Europe is an example of which type of force for genetic change?

A increased birth rate

B genetic equilibrium

C gene flow through interbreeding

D increased chance of genetic mutation

4 In a population of clover flowers, there are both white and purple varieties. The cows that graze the field where the clover grows prefer the purple variety. Over time, the white clover flowers become much more numerous and the purple ones more scarce.

A. This is an example of which process that can cause evolutionary change?

B. Define this process.

5 Gene flow is one force that can cause evolutionary change. Give an example that illustrates gene flow.

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Explain how genetic variation within a population (a species) can be attributed to mutations as well as a random assortment of existing genes.

STANDARD REVIEW

Scientists now know that genes are responsible for inherited traits. Therefore, certain forms of a trait become more common in a population because more individuals in the popula-tion carry the alleles for those forms. In other words, natural selection causes the frequency of certain alleles in a population to increase or decrease over time. Mutations and the recombination of alleles that occur during sexual reproduction provide endless sources of new variations for natural selection.

Although mutation from one allele to another can eventually change allele frequencies, mutation rates in nature are very slow. Most genes mutate only about 1 to 10 times per 100,000 cell divisions, so mutation does not signifi cantly change allele frequencies, ex-cept over very long periods of time. Furthermore, not all mutations result in phenotypic changes. Recall that more than one codon—3-base DNA coding sequence—can code for the same amino acid. Therefore, some mutations may result in no change in the amino acid coded for in a protein, and other changes in an amino acid that do occur may not affect how that protein works. Mutation is, however, an important source of variation and also makes evolution possible.

Meiosis and the joining of gametes—processes that recombine alleles—are essential to evolution. No genetic process generates variation more quickly. In many cases, the pace of evolution appears to increase as the level of genetic variation increases. For example, when domesticated animals such as cattle and sheep are bred for large size, many large animals are produced at fi rst. But as the existing genetic combinations become used up, the ability to obtain larger and larger animals slows down. Further progress must then wait for the formation of new gene combinations.

The pace of evolution is sped up by genetic recombination. The combination of genes from two organisms results in a third type, not identical to either parent. Bear in mind that natural selection does not always favor genetic change. Indeed, many modern organisms are little changed from their ancestors of the distant past. Natural selection may favor existing combinations of genes, slowing the pace of evolution.

STANDARD PRACTICE 1 One way that populations can change is when new alleles appear. What is the major

source of new alleles in natural populations?

A mutations in sex cells

B mutations in somatic cells

C trait selection by natural selection

D adaptations in individual organisms


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2 Imagine that a mouse has white fur because of a mutation in its DNA. Which of the following conclusions can be drawn?

A The white mouse increases the diversity of the species.

B The white mouse decreases the diversity of the species.

C The internal organs of the white mouse must not function as well as those of other mice.

D The white mouse is more likely to survive than other mice because it is more visible to predators.

3 Sexual reproduction increases genetic variation in a population. Which is a way that meiosis and fertilization lead to genetic variation?

A Alleles are recombined when gametes from different parents join together.

B Mutations are usually repaired by cellular machinery before genes are expressed.

C DNA is replicated when a fertilized egg becomes a growing embryo through mitosis.

D Parents that are homozygous for the same trait will have offspring that are also homozygous for that trait.

4 During meiosis, homologous chromosomes line up next to each other. At this time, crossing over can occur

A. What is crossing over?

B. How does it increase genetic variation?

5 Describe an example of how genetic variation due to a mutation could help a population survive environmental change.

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Describe the modern scientifi c theory of the origins and history of life on earth, and evaluate the evidence that supports it.

STANDARD REVIEWScientists who study the origins of life think that the path to the development of living things began when molecules of nonliving matter reacted chemically during the fi rst billion years of Earth’s history. These chemical reactions, energized by the Sun and volcanic heat, produced simple, organic molecules that later formed more complex molecules that eventu-ally became the building blocks of the fi rst cells.

In the 1920s, the Russian scientist A. I. Oparin and the British scientist J.B.S. Haldane both suggested that Earth’s early oceans contained large amounts of organic molecules. This hypothesis became known as the primordial soup model. Oparin and Haldane hypothesized that the organic molecules in Earth’s vast oceans formed spontaneously through chemical reactions in the early atmosphere activated by energy from solar radia-tion, volcanic eruptions, and lightning.

In 1953, the primordial soup model was tested by Stanley Miller and Harold Urey. Miller placed the gases thought to have existed on early Earth into a device made up of glass tubes and vessels. To simulate lightning, he provided electrical sparks. After a few days, Miller found a complex collection of organic molecules, including some of life’s basic building blocks: amino acids, fatty acids, and other hydrocarbons. These results support the hypothesis that some basic chemicals of life could have formed spontaneously under conditions similar to those in the experiment.

Scientists have reevaluated the Miller-Urey experiment in light of the fact that we now know that four billion years ago, Earth did not have a protective layer of ozone gas, O3. Without ozone, ultraviolet radiation would have destroyed any ammonia and methane present in the atmosphere.

In 1986, the geophysicist Louis Lerman suggested that instead of a reaction in the atmosphere, the key processes that formed the chemicals needed for life took place within bubbles beneath the ocean’s surface. In this bubble model, he suggested that ammonia, methane, and other gases resulting from the numerous eruptions of undersea volcanoes were trapped in underwater bubbles. Inside the bubbles, these gases might have been pro-tected from damaging ultraviolet radiation and could have undergone chemical reactions. Eventually, the bubbles rose to the surface and burst, releasing simple organic molecules into the air. In the air, the simple organic molecules were exposed to ultraviolet radiation and lightning, which provided energy for further reactions. The more complex organic molecules that formed fell into the ocean with rain, starting another cycle.

STANDARD PRACTICE 1 Two models of the origin of life on Earth are the primordial soup model and the bubble

model. What do these two models of how life began on Earth have in common?

A Both explain how UV radiation produces ammonia and methane.

B Both involve only chemical reactions that take place within the ocean.

C Both include chemical reactions that take place when there is lightning.

D Both involve only chemical reactions that take place within the atmosphere.

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2 The bubble model states that the key processes that formed the chemicals needed for life took place within bubbles beneath the ocean’s surface. What important role did bubbles play according to the bubble model?

A They provided protection from damaging ultraviolet radiation.

B They allowed the reactions to take place in the presence of oxygen.

C They kept the chemical products from ever entering Earth’s atmosphere.

D They created the activation energy needed for spontaneous chemical reactions.

3 Which theory or model describes how eukaryotic organisms first developed mitochondria and chloroplasts?

A the bubble model

B the endosymbiotic theory

C the primordial soup model

D the formation of microspheres and coacervates

4 American scientists Stanley Miller and Harold Urey used an apparatus to simulate how life could have formed on Earth. The apparatus contained hydrogen gas, water vapor, ammonia, and methane. These gases were subjected to a spark, to simulate lightning. They found that organic molecules could form from the inorganic gases.

A. What did scientists conclude from this experiment?

B. Their theory of how life began, however, did not hold up under further testing. What crucial fact did they not have when they conducted their experiment?

5 Describe microspheres and what their formation suggests about the origin of life.

Documents

Biology End of Course Assessment (E.C.A.) Review