Chapter Two

Cell Processes and Energy

Lesson 2-1

Chemical Compounds in Cells

2-1

• An element is any substance that cannot be broken down into simpler substances. The smallest unit of an element is an atom. Elements found in living things are carbon, hydrogen, nitrogen, phosphorus, and sulfur.

• When two or more elements combine chemically, they form a compound. The smallest unit of most compounds is called a molecule.

2-1

• Most compounds that contain carbon are called organic compounds. The most important groups of organic compounds found in living things are carbohydrates, lipids, proteins, and nucleic acids.

• Compounds that do not contain carbon are called inorganic compounds.

2-1

• A carbohydrate is an energy-rich organic compound made of the elements carbon, hydrogen, and oxygen. Sugar and Starches are examples of carbohydrates – such as pasta. Carbohydrates provides energy to the cell.

• Proteins are large organic molecules made of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. Cells use proteins for cell membranes and many of the organelles within the cell.

– Protein molecules are made up of smaller molecules called amino acids.

• An enzyme is a type of protein that speeds up a chemical reaction in a living thing.

2-1

• Fats, oils, and waxes are lipids. Lipids are energy-rich organic compounds made of carbon, hydrogen, and oxygen.

• Nucleic acids are very large organic molecules made of carbon, oxygen, hydrogen, nitrogen, and phosphorus. Nucleic acids contain the instructions that cells need to carry out all the functions of life. There are two kinds of nucleic acids:– DNA – Deoxyribonucleic acid (DNA) is passed from parent to

offspring and directs all of the cell’s functions.– RNA – Ribonucleic acid (RNA) plays an important role in the

production of proteins.

DNA Model

2-1

• Water– Without water, most chemical reactions within

cells could not take place.– Water helps cells keep their size and shape.– Water also helps to keep the temperature of

cells from changing rapidly.

Image of Cells - Water

Image of Cells - Water

2-2

The Cell in Its Environment

The Cell Membrane

2-2

• The cell membrane is selectively permeable, which means that some substances can pass through it while others cannot.

• The cell membrane is usually permeable to substances such as oxygen, water, and carbon dioxide. The cell membrane is not permeable to salts and large molecules.

• Substances that can move into and out of a cell do so by one of three methods: diffusion, osmosis, or active transport.

2-2

1. Diffusion is the process by which molecules tend to move from an area of higher concentration to an area of lower concentration. Diffusion is caused by molecules moving and colliding. The collisions cause the molecules to push away from one another and spread out.

Diffusion

Molecules diffuse through the cell membrane into a cell when there is a higher concentration of the molecules outside the cell than inside the cell.

CELL

Diffusion

2-2

2. Osmosis – The diffusion of water molecules through a selectively permeable membrane.

– In osmosis, water molecules move from an area where they are highly concentrated through the cell membrane to an area where they are less concentrated.

Osmosis - Animation

• http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBooktransp.html

2-2

3. The movement of materials through a cell membrane without using energy is called passive transport. When a cell needs to take in materials that are in higher concentration inside the cell than outside the cell, the movement of the materials requires energy. Active transport is the movement of materials requires energy.

Active Transport

Passive Transport

2-2

• Most cells are very small. One reason is related to the fact that all materials move into and out of cells through the cell membrane.– When a cell reaches a certain size, it divides

into two new cells.

2-3

Photosynthesis

Photosynthesis

• Pea Pod

2-3

• The sun provides almost all the energy used by living on Earth.

• All cells need energy to carry out their functions. The process by which a cell captures the energy in sunlight and uses it to make food is called photosynthesis.

2-3

• During photosynthesis, plants and some other organisms use energy from the sun to convert carbon dioxide and water into oxygen and sugars, including glucose. There are two stages:

Photosynthesis

2-3

1. The first stage of photosynthesis involves capturing the energy in sunlight.

• In plants, this energy-capturing process occurs in the leaves and other green parts of the plant.

• The chloroplasts in plant cells give plants their green color. The green color comes from pigments, colored chemical compounds that absorb light.

• The main pigment found in the chloroplasts of plants is chlorophyll.

Image

Animation

• http://earthguide.ucsd.edu/earthguide/diagrams/photosynthesis/photosynthesis.html

2-3

2. In the second stage of photosynthesis, the cell uses captured energy to produce sugars.

– The cell needs two raw materials for this stage: water (H2O) and carbon dioxide (CO2). In plants, the roots absorb water from the soil. Carbon dioxide enters the plant through small openings on the undersides of the leaves called stomata.

2-3

• The events of photosynthesis can be summed up in a chemical equation:

Carbon Dioxide + Water Glucose + Oxygen

(sunlight)

Light Energy

6 CO2 + 6 H2O C6H12O6 + 6 O2

Image of Equation

2-3

• A plant is an autotroph, an organism that makes its own food.

• A heterotroph is an organism that cannot make its own food.– A caterpillar needs the energy in plant sugars. By eating plants

(autotroph), the caterpillar (heterotroph) gets their energy from the sun in an indirect way.

– Nearly all living things obtain energy either directly or indirectly from the energy of sunlight captured during photosynthesis. Photosynthesis is also essential to the air we breathe. Almost all the oxygen in Earth’s atmosphere was produced by living things through photosynthesis.

2-4

Respiration

2-4

• The process by which cells “withdraw” energy from glucose is called respiration.

• During respiration, cells break down simple food molecules such as glucose and release the energy they contain.– The term respiration is used to mean breathing.

This type of respiration is called cellular respiration, as not to confuse you with the respiration involving your lungs.

2-4

• In respiration, there are also two stages. You can view respiration as the exact opposite of photosynthesis:– Stage One: stage one takes place in the cytoplasm of the

organism’s cells. There, glucose molecules are broken down into smaller molecules. Oxygen is not involved in this stage of respiration – and only a small amount of energy is released.

– Stage two: The second stage of respiration takes place in the mitochondria. There, small molecules are broken down into even smaller molecules. These chemical reactions require oxygen, and a great deal of energy is released. Two other products of respiration are carbon dioxide and water.

2-4

Respiration Equation – the opposite of photosynthesis:

Glucose + Oxygen Carbon Dioxide +Water + Energy

C6H12O6 + 6 O2 6 CO2 + 6 H2O

2-4

• Together, photosynthesis and respiration form a cycle that keeps the levels of oxygen and carbon dioxide fairly constant in the atmosphere.– Some cells obtain their energy through fermentation,

and energy releasing process that does not require oxygen.

• (The making of some alcohols requires only the breaking down of sugars. The fermentation of grapes for wine, or the fermentation of yeast for beer).

2-5

Cell Division

Mitosis

• http://www.pbs.org/wgbh/nova/baby/divi_flash.html

2-5

• The regular sequence of growth and division that cells undergo is known as the cell cycle.

Diagram

Interphase

• The cell is engaged in metabolic activity as it prepares for mitosis (the next four phases that lead up to and include nuclear division). Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible.

Prophase

• Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes. The nucleolus disappears. Centrioles begin moving to opposite ends of the cell and fibers extend from the centromeres. Some fibers cross the cell to form the mitotic spindle.

Metaphase

• Spindle fibers align the chromosomes along the middle of the cell nucleus. This line is referred to as the metaphase plate. This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.

Anaphase

• The paired chromosomes separate and move to opposite sides of the cell.

Telephase

• Chromatids arrive at opposite poles of cell, and new membranes form around the daughter nuclei. The chromosomes disperse and are no longer visible under the light microscope. The spindle fibers disperse, and cytokinesis or the partitioning of the cell may also begin during this stage.

Cytokinesis

During cytokinesis, the cytoplasm divides, distributing the organelles into each of the two new cells.• Each daughter cell has the same number of

chromosomes as the original parent cell. • At the end of cytokinesis, each cells enters

Interphase, and the cycle begins again.

Animation

• http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells3.html

2-5

• A cell makes a copy of its DNA before mitosis occurs. DNA replication ensures that each daughter cell will have all of the genetic information it needs to carry out its activities.– The two sides of the DNA ladder are made up of

alternating sugar and phosphate molecules. Each rung of the DNA ladder is made up of a pair of molecules called nitrogen bases. There are four nitrogen bases: adenine, thymine, gaunine, and cytosine.

Plant Mitosis

Interphase Prophase Metaphase

Anaphase Telephase Interphase

Log-on (Game Time)

• Cell Cycle Game

• http://nobelprize.org/medicine/educational/2001/cellcycle.html