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Lesson 2.1 Introduction to Cells Name Date Period

Key Terms

Prokaryote Eukaryote

Engage

1. What do you think this is a picture of? Explain your reasoning. 2. How large would you predict the small rod-shaped objects on the side of the slanted surface are? (use the scale below the photos)

A. B.

3. Compare the pictures of the cells on the left. What are the differences between the cells? 4. What are the similarities between the two cells?

Explore I The Cell: The Basic Unit of Life The cell is the basic unit of life - the smallest structure capable of basic life processes, such as taking in nutrients, getting rid of waste, and reproducing. All living things are made of cells. Some microscopic organisms, such as bacteria and protozoa, are unicellular, meaning they consist of a single cell. Animals, larger plants and many fungi are multicellular - composed of a great many cells working together. Cells carry out thousands of biochemical reactions each minute and reproduce new cells that continue life. Cells vary considerably in size. About 10,000 average-sized human cells can fit on the head of a pin. Despite their individuality, cells display a remarkable ability to physically join or associate, communicate, and coordinate with other cells.

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This photograph demonstrates the size of bacterial cells in relation to a pinpoint.

Explain I 1. What is the basic unit of life? 2. List three basic life processes. 3. Are bacteria and protozoa unicellular or multicellular?

Explore II Prokaryotes and Eukaryotes There are two general classes of cells, both of which clearly affect human health and are essential for maintaining life as we know it. Both types of cells have a cell membrane that surrounds the cytoplasm of a cell and physically separates the inner components from the outside environment. Prokaryotes Simple, smaller organisms. Bacteria are prokaryotes. They are found only in single-celled and colonial organisms. LACK A NUCLEUS

Eukaryotes Complex and larger organisms. They have organelles with their own membranes. Plants, animals, protists, and fungi are eukaryotes. Eukaryotic organisms can be either single-cellular or multicellular. HAVE A NUCLEUS

Prokaryotes and Eukaryotes: Key Differences The most important difference between prokaryotes and eukaryotes is that eukaryotes have:

Prokaryotes Eukaryotes A true nucleus Prokaryotes do not have a true nucleus.

DNA floats freely in the cytoplasm. Eukaryotes have a true nucleus. DNA is held within a membrane-bound nucleus.

Membrane-bound organelles

Prokaryotes do not have membrane-bound organelles, but do have ribosomes, which float freely.

Eukaryotes have membrane-bound organelles. These organelles are highly specialized structures that allow them to exhibit more sophisticated intracellular division of labor than is possible in prokaryotic cells.

Size

Small. Eukaryotic cells are, on average, ten times the size of prokaryotic cells.

DNA composition and length

Simple and circular. The DNA of eukaryotes is much more complex and therefore much more extensive than the DNA of prokaryotes.

Cytoskeleton Prokaryotes do not have a cytoskeleton as they are so small they do not need the extra support

Eukaryotes have a cytoskeleton which maintain the shape of the cell as well as anchoring organelles, moving the cell and controlling internal movement of structures.

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Explain II 4. The characteristics listed below describe either prokaryotic cells, eukaryotic cells, or both. Put a check in the side where the trait belongs. (Note: a trait can be check for both prokaryotes and eukaryotes)

Prokaryote Trait Eukaryote « usually smaller » « usually larger » « more complex » « simpler » « exist in multi-cellular forms » « either unicellular or colonial » « lacks a true nucleus » « has nucleus » « has ribosomes » « lacks organelles » « has DNA » « has a cell membrane » « has a cytoskeleton »

Explore III Cell Organelles: Eukaryotic Animal Cell

One of the defining characteristics of a eukaryote is that they have “membrane-bound organelles.” An organelle is a specialized subunit in the cell that has a specialized function. Both plant and animal cells are considered eukaryotes and have these organelles; they have some that are the same and some that are different. First, we will look at an animal cell. Below is a list of organelles that are found in both plant and animal cells.

Organelle (city analogy) Picture Description

Nucleus

(_____________________

_____________________)

The “control center” of a cell. Location for most of the nucleic acids a cell makes, such as DNA and RNA. The nucleus contains the nucleolus, which is responsible for making ribosomes.

Ribosome

(_____________________

_____________________)

Site of protein synthesis (where proteins are made).

Mitochondrion

(_____________________

_____________________)

Often described as "cellular power plants" because they generate most of the cell's supply chemical energy by breaking down sugar.

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Cell Organelles: Eukaryotic Animal and Plant Cell, continued.

Organelle Picture Description Rough Endoplasmic

Reticulum

(_____________________

_____________________)

A mesh of interconnected membranes that serve a function involving protein synthesis and transport. Rough endoplasmic reticulum (Rough ER) is so-named because of its rough appearance due to the numerous ribosomes that occur along the ER. Rough ER connects to the nuclear envelope through which the messenger RNA (mRNA) travels to the ribosomes.

Smooth Endoplasmic Reticulum

(_____________________

_____________________)

Smooth endoplasmic reticulum (Smooth ER) lacks the ribosomes characteristic of Rough ER. Smooth ER is thought to be involved in transport and other functions including helping to remove toxins.

Golgi Apparatus

(_____________________

_____________________)

Flattened stacks of membrane-bound sacs; functions as packaging plant. Macromolecules such as proteins, nucleic acids, lipids, and carbohydrates are moved to the Golgi for modification, packaged in vesicles, and transported to their destination.

Lysosome

(_____________________

_____________________)

Relatively large vesicles formed by the Golgi; they contain enzymes necessary for intracellular digestion. Lysosomes are more common in animal cells than plant cells.

Explain III 5. What is the primary structural difference between rough ER and smooth ER? 6. Which organelle’s function is to make energy for the cell? 7. Which part of the cell acts as a “boundary” between the inside and outside of all cells? 8. One of the organelles described can be found in eukaryotes and prokaryotes; which is it? 9. In which organelle is DNA located? 10. What occurs at ribosomes?

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Explore IV Cell Organelles: Eukaryotic Plant Cell Review the following structures that are found in plant cells but not animal cells.

Chloroplast

Site of photosynthesis in eukaryotes; they contain chlorophyll, the green pigment needed for plants to make sugar.

Cell Wall

A tough, flexible, and sometimes fairly rigid layer surrounding a cell, located outside the cell membrane, which provides the cell with structural support, protection, and acts as a filtering mechanism.

Central Vacuole

Central vacuoles are membrane-bound compartments that can serve a variety of secretory, excretory, and storage functions.

Explain IV 11. Which of the following correctly matches an organelle with its function?

a. mitochondrion . . . photosynthesis b. nucleus . . . making energy c. ribosome . . . manufactures lipids d. central vacuole . . . storage

12. I f chloroplasts carry out photosynthesis, which makes sugar, which organelle uses that sugar to make energy? 13. Identi f y the cell pictured to the right as a prokaryotic cell, a eukaryotic animal cell or a eukaryotic plant cell. Explain your choice. 14. Why would it be beneficial for a cell to have organelles (like eukaryotes), instead o f lacking them as in prokaryotes?

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CELL MODELS: Your teacher will give you three cell outlines and a collection of organelles. Using the information you have learned so far, use the organelles to create a prokaryotic cell, eukaryotic plant cell, and a eukaryotic animal cell. Not all of the organelles need to be used. Once your teacher has checked your cells, sketch all three cells you have created and label the structures and organelles found in each cell. When your sketches are finished, complete the table below.

Prokaryotic Cell:

Eukaryotic Animal Cell:

Eukaryotic Plant Cell:

Now that you have reviewed all of the cell parts for prokaryotes and eukaryotes, fill out the chart below by checking the appropriate box to indicate which structures are found in which organism(s). Use your cell sketches and this packet as a reference.

Structure/Organelle Prokaryotes? Eukaryotic Plant Cell? Eukaryotic Animal Cell? Cell membrane Cell wall Ribosome Mitochondrion Central Vacuole Chloroplast Golgi Apparatus Lysosome Rough ER Smooth ER Nucleus