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UNIT
Chapters
7 Cell Structure and Function 8 Photosynthesis 9 Cellular Respiration and Fermentation 10 Cell Growth and Division
INTRODUCE the
Cells
Mr. Zong had promised it would be interest- ing. I put a cover glass on the drop of scummy pond water, and slipped the slide under my microscope. I was amazed. Creatures of every shape and description swam, slithered, and squirmed, every one of them, as my teacher explained, a single cell. I’ve never forgotten the spec- tacle of so much life packed into such tiny packages— or the wonder of what happens inside a living cell.
- Cellular Basis of Life
- (^) Homeostasis
- (^) Growth, Development, and Reproduction
187
Cell Structure
and Function
Cellular Basis of Life, Homeostasis Q: How are cell structures adapted to their functions?
Chapter 7 • Flash Cards
188
The Discovery of the Cell What is the cell theory? “Seeing is believing,” an old saying goes. It would be hard to find a bet- ter example of this than the discovery of the cell. Without the instru- ments to make them visible, cells remained out of sight and, therefore, out of mind for most of human history. All of this changed with a dramatic advance in technology—the invention of the microscope.
Early Microscopes In the late 1500s, eyeglass makers in Europe dis-
covered that using several glass lenses in combination could magnify even the smallest objects to make them easy to see. Before long, they had built the first true microscopes from these lenses, opening the door to the study of biology as we know it today. In 1665, Englishman Robert Hooke used an early compound micro- scope to look at a nonliving thin slice of cork, a plant material. Under the microscope, cork seemed to be made of thousands of tiny empty chambers. Hooke called these chambers “cells” because they reminded him of a monastery’s tiny rooms, which were called cells. The term cell is used in biology to this day. Today we know that living cells are not empty chambers, that in fact they contain a huge array of working parts, each with its own function. In Holland around the same time, Anton van Leeuwenhoek used a single-lens microscope to observe pond water and other things. To his amazement, the microscope revealed a fantastic world of tiny living organisms that seemed to be everywhere, in the water he and his neighbors drank, and even in his own mouth. Leeuwenhoek’s illustrations of the organisms he found in the human mouth—which today we call bacteria—are shown in Figure 7–1.
Life Is Cellular
Key Questions
What is the cell theory? How do microscopes work? How are prokaryotic and eukaryotic cells different?
Vocabulary
cell • cell theory • cell membrane • nucleus • eukaryote • prokaryote
Taking Notes
Outline Before you read, make an outline using the green and blue headings in the text. As you read, fill in notes under each heading.
FIGURE 7–1 Early Microscope Images Using a simple microscope, Anton van Leeuwenhoek was the first to observe living microorganisms. These drawings, taken from one of his letters, show bacteria in the human mouth.
190^ Lesson 7.1^ • Lesson Overview^ • Lesson Notes
THINK ABOUT IT What’s the smallest part of any living thing that
still counts as being “alive”? Is a leaf alive? How about your big toe? How about a drop of blood? Can we just keep dividing living things into smaller and smaller parts, or is there a point at which what’s left is no longer alive? As you will see, there is such a limit, the smallest living unit of any organism—the cell.
The Cell Theory Soon after van Leeuwenhoek, observations by
scientists made it clear that cellscells are the basic units of life. In 1838, German botanist Matthias Schleiden concluded that all plants are made of cells. The next year, German biologist Theodor Schwann stated that all animals are made of cells. In 1855, German physician Rudolf Virchow concluded that new cells can be produced only from the division of existing cells, confirming a suggestion made by German Lorenz Oken 50 years earlier. These discoveries, confirmed by many biologists, are summarized in the cell theory,cell theory, a fundamental concept of biology. The cell theory states:
- All living things are made up of cells.
- Cells are the basic units of structure and function in living things.
- New cells are produced from existing cells.
Exploring the Cell
How do microscopes work?
A microscope, as you know, produces an enlarged image of something very small. Most microscopes use lenses to magnify the image of an object by focusing light or electrons. Following in the footsteps of Hooke, Virchow, and others, modern biologists still use microscopes to explore the cell. But today’s researchers use technology more power- ful than the pioneers of biology could ever have imagined.
Light Microscopes and Cell Stains The type of microscope you
are probably most familiar with is the compound light microscope. A typical light microscope allows light to pass through a specimen and uses two lenses to form an image. The first lens, called the objective lens, is located just above the specimen. This lens enlarges the image of the specimen. Most light microscopes have several objective lenses so that the power of magnification can be varied. The second lens, called the ocular lens, magnifies this image still further. Unfortunately, light itself limits the detail, or resolution, of images in a microscope. Like all forms of radiation, lightwaves are diffracted, or scattered, as they pass through matter. Because of this, light microscopes can produce clear images of objects only to a magnification of about 1000 times. Another problem with light microscopy is that most living cells are nearly transparent. Using chemical stains or dyes, as in Figure 7–2, can usually solve this problem. Some of these stains are so specific that they reveal only certain compounds or structures within the cell. Many of the slides you’ll examine in your biology class laboratory will be stained this way. A powerful variation on these staining techniques uses dyes that give off light of a particular color when viewed under specific wave- lengths of light, a property called fluorescence. Fluorescent dyes can be attached to specific molecules and can then be made visible using a special fluorescence microscope. New techniques, in fact, enable scien- tists to engineer cells that attach fluorescent labels of different colors to specific molecules as they are produced. Fluorescence microscopy makes it possible to see and identify the locations of these molecules and even allows scientists to watch them move around in a living cell.
FIGURE 7–2 Light Microscope and Cell Stains This specimen of onion leaf skin has been stained with a compound called toluidine blue. The dye makes the cell boundaries and nuclei clearly visible.
Cell Structure and Function 191
LM 35
0 1 nm 1 μm 10 μm 100 μm 1 mm 1 cm
LIGHT MICROSCOPE UNAIDED HUMAN EYE
DNA 2 nm
Cold virus 25 nm
Typical prokaryotic cell 1– 5 μm
Mitochondrion 1– 5 μm
Typical eukaryotic cell 10 – 100 μm Chaos chaos 1 mm
Chicken egg 5 cm
5 cm ELECTRON MICROSCOPE
1 nm = 1/1,000,000,000 m 1 μm = 1/1,000,000 m 1 mm = 1/1000 m 1 cm = 1/100 m
What Is a Cell?
(^1) Look through a microscope at a slide of a plant leaf or stem cross section. Sketch one or more cells. Record a description of their shape and internal parts. (^2) Repeat step 1 with slides of nerve cells, bacteria, and paramecia.
3 Compare the cells by listing the characteristics they have in common and some of the differences among them. Analyze and Conclude
1. Classify Classify the cells you observed into two or more groups. Explain what characteristics you used to put each cell in a particular group.
FIGURE 7–4 Cell Size Is Relative The human eye can see objects larger than about 0.5 mm. Most of what interests cell biologists, however, is much smaller than that. Microscopes make seeing the cellular and subcellular world possible.
At the hospital, a sample of Michelle’s blood was drawn and examined. The red blood cells appeared swollen. What kind of microscope was most likely used to study the blood sample?
Prokaryotes and Eukaryotes
How are prokaryotic and eukaryotic cells different?
Cells come in an amazing variety of shapes and sizes, some of which are shown in Figure 7–4. Although typical cells range from 5 to 50 micrometers in diameter, the smallest Mycoplasma bacteria are only 0.2 micrometer across, so small that they are difficult to see under even the best light microscopes. In contrast, the giant amoeba Chaos chaos can be 1000 micrometers (1 millimeter) in diameter, large enough to be seen with the unaided eye as a tiny speck in pond water. Despite their differences, all cells, at some point in their lives, contain DNA, the molecule that carries biological information. In addition, all cells are surrounded by a thin flexible barrier called a cell membrane.cell membrane. (The cell membrane is sometimes called the plasma membrane because many cells in the body are in direct contact with the fluid portion of the blood—the plasma.) There are other similarities as well, as you will learn in the next lesson. Cells fall into two broad categories, depending on whether they contain a nucleus. The nucleusnucleus (plural: nuclei) is a large membrane- enclosed structure that contains genetic material in the form of DNA and controls many of the cell’s activities. EukaryotesEukaryotes (yoo kar ee ohts) are cells that enclose their DNA in nuclei. ProkaryotesProkaryotes (pro kar ee ohts) are cells that do not enclose DNA in nuclei.
Cell Structure and Function 193
Review Key Concepts
1. a. Review What is a cell? b. Explain What three statements make up the cell theory? c. Infer How did the invention of the micro- scope help the development of the cell theory? 2. a. Review How do microscopes work? b. Apply Concepts What does it mean if a micrograph is “false-colored?” 3. a. Review What features do all cells have? b. Summarize What is the main difference between prokaryotes and eukaryotes?
A light microscope can magnify images up to 1000 times. To calculate the total magnification of a specimen, multiply the magnification of the eyepiece lens by the magnification of the objective lens used. (For more information on microscopes, see Appendix B.)
4. Calculate What is the total magnification of a microscope that has an eyepiece magnification of 10× and an objective lens magnification of 50×. 5. Calculate A 10 micrometer cell is viewed through a 10× objective and a 10× eyepiece. How large will the cell appear to the microscope user?
PROKARYOTIC CELL EUKARYOTIC CELLS
Animal Cell Plant Cell
Lesson 7.1 • Self-Test • Lesson Assessment
Prokaryotes As seen in Figure 7–5, prokaryotic cells are generally
smaller and simpler than eukaryotic cells, although there are many excep- tions to this rule. Prokaryotic cells do not separate their genetic material within a nucleus. Despite their simplicity, prokaryotes carry out every activity associated with living things. They grow, reproduce, respond to the environment, and, in some cases, glide along surfaces or swim through liquids. The organisms we call bacteria are prokaryotes.
Eukaryotes Eukaryotic cells are generally larger and more com-
plex than prokaryotic cells. Most eukaryotic cells contain dozens of structures and internal membranes, and many are highly specialized. In eukaryotic cells, the nucleus separates the genetic material from the rest of the cell. Eukaryotes display great variety: some, like the ones commonly called “protists,” live solitary lives as unicellular organisms; others form large, multicellular organisms—plants, ani- FIGURE 7–5 Cell Types In general, mals, and fungi. eukaryotic cells (including plant and animal cells) are more complex than prokaryotic cells.
BUILD Vocabulary
WORD ORIGINS The noun prokaryote comes from the Greek word karyon , meaning “kernel,” or nucleus. The prefix pro- means “before.” Prokaryotic cells first evolved before nuclei developed.
194 Chapter 7 • Lesson 1
Cell Organization What is the role of the cell nucleus? The eukaryotic cell is a complex and busy place. But if you look closely at eukaryotic cells, patterns begin to emerge. For example, it’s easy to divide each cell into two major parts: the nucleus and the cytoplasm. The cytoplasmcytoplasm is the portion of the cell outside the nucleus. As you will see, the nucleus and cytoplasm work together in the business of life. Prokaryotic cells have cytoplasm too, even though they do not have a nucleus. In our discussion of cell structure, we consider each major com- ponent of plant and animal eukaryotic cells—some of which are also found in prokaryotic cells—one by one. Because many of these structures act like specialized organs, they are known as organelles,organelles, literally “little organs.” Understanding what each organelle does helps us understand the cell as a whole. A summary of cell structure can be found on pages 206–207.
Cell Structure
Key Questions
What is the role of the cell nucleus? What are the functions of vacuoles, lysosomes, and the cytoskeleton? What organelles help make and transport proteins? What are the functions of chloroplasts and mitochondria? What is the function of the cell membrane?
Vocabulary
cytoplasm • organelle • vacuole • lysosome • cytoskeleton • centriole • ribosome • endoplasmic reticulum • Golgi apparatus • chloroplast • mitochondrion • cell wall • lipid bilayer • selectively permeable
Taking Notes
Venn Diagram Create a Venn diagram that illustrates the simi- larities and differences between prokaryotes and eukaryotes.
THE CELL AS A
LIVING FACTORY
FIGURE 7–6 The specialization and organization of work and workers contribute to the productivity of a factory. In much the same way, the specialized parts in a cell contribute to the cell’s overall stability and survival.
196 Lesson 7.2^ • Lesson Overview^ • Lesson Notes^ • Visual Analogy
THINK ABOUT IT At first glance, a factory is a puzzling place.
Machines buzz and clatter; people move quickly in different direc- tions. So much activity can be confusing. However, if you take the time to watch carefully, what might at first seem like chaos begins to make sense. The same is true for the living cell.
Comparing the Cell to a Factory In some respects, the eukaryotic
cell is much like a living version of a modern factory (Figure 7–6). The different organelles of the cell can be compared to the specialized machines and assembly lines of the factory. In addition, cells, like factories, follow instructions and produce products. As we look through the organization of the cell, we’ll find plenty of places in which the comparison works so well that it will help us understand how cells work.
The Nucleus In the same way that the main office controls a large factory,
the nucleus is the control center of the cell. The nucleus contains nearly all the cell’s DNA and, with it, the coded instructions for making proteins and other important molecules. Prokaryotic cells lack a nucleus, but they do have DNA that contains the same kinds of instructions. The nucleus, shown in Figure 7–7, is surrounded by a nuclear envelope composed of two membranes. The nuclear envelope is dotted with thousands of nuclear pores, which allow material to move into and out of the nucleus. Like mes- sages, instructions, and blueprints moving in and out of a factory’s main office, a steady stream of proteins, RNA, and other molecules move through the nuclear pores to and from the rest of the cell. Chromosomes, which carry the cell’s genetic information, are also found in the nucleus. Most of the time, the threadlike chromosomes are spread throughout the nucleus in the form of chromatin—a complex of DNA bound to proteins. When a cell divides, its chromosomes con- dense and can be seen under a microscope. You will learn more about chromosomes in later chapters. Most nuclei also contain a small dense region known as the nucle- olus (noo klee uh lus). The nucleolus is where the assembly of ribo- somes begins.
In Your Notebook Describe the structure of the nucleus. Include the words nuclear envelope, nuclear pore, chromatin, chromosomes, and nucleolus in your description.
FIGURE 7–7 The Nucleus The nucleus controls most cell processes and contains DNA. The small, dense region in the nucleus is known as the nucleolus.
Nuclear envelope
Nuclear pores
Chromatin
Nucleolus
197
FIGURE 7–9 Cytoskeleton The cytoskeleton supports and gives shape to the cell, and is involved in many forms of cell movement. These connective tissue fibroblast cells have been treated with fluorescent tags that bind to certain elements. Microfilaments are pale purple, microtubules are yellow, and the nuclei are green.
The Cytoskeleton As you know, a factory building is supported by
steel or cement beams and by columns that hold up its walls and roof. Eukaryotic cells are given their shape and internal organization by a network of protein filaments known as the cytoskeleton.cytoskeleton. Certain parts of the cytoskeleton also help transport materials between different parts of the cell, much like the conveyor belts that carry materials from one part of a factory to another. Cytoskeletal components may also be involved in moving the entire cell as in cell flagella and cilia. The cytoskeleton helps the cell maintain its shape and is also involved in movement. Fluorescence imaging, as seen in Figure 7–9, clearly shows the complexity of a cell’s cytoskeletal network. Microfilaments (pale purple) and microtubules (yellow) are two of the principal protein fi laments that make up the cytoskeleton.
(^) Microfi laments Microfilaments are threadlike structures made up of a protein called actin. They form extensive networks in some cells and produce a tough flexible framework that supports the cell. Micro- fi laments also help cells move. Microfilament assembly and disassem- bly are responsible for the cytoplasmic movements that allow amoebas and other cells to crawl along surfaces.
(^) Microtubules Microtubules are hollow structures made up of proteins known as tubulins. In many cells, they play critical roles in maintaining cell shape. Microtubules are also important in cell divi- sion, where they form a structure known as the mitotic spindle, which helps to separate chromosomes. In animal cells, organelles called centrioles are also formed from tubulins. CentriolesCentrioles are located near the nucleus and help organize cell division. Centrioles are not found in plant cells. Microtubules also help build projections from the cell surface— known as cilia (singular: cilium) and flagella (singular: flagellum)— that enable cells to swim rapidly through liquid. The microtubules in cilia and flagella are arranged in a “9 + 2” pattern, as shown in Figure 7–10. Small cross-bridges between the microtubules in these organelles use chemical energy to pull on, or slide along, the micro- tubles, producing controlled movements.
Cross Section
FIGURE 7–10 The “9 + 2” Pattern of Microtubules In this micrograph showing the cross section of a cilium, you can clearly see the 9 + 2 arrange- ment of the red microtubules. Apply Concepts What is the function of cilia?
LM 1175
TEM 110,000
Cell Structure and Function 199
Smooth endoplasmic reticulum
Vesicle
Rough endoplasmic reticulum
Nucleus
Ribosome
Protein
(^1) Proteins are assembled on ribosomes.
(^2) Proteins targeted for export to the cell membrane, or to specialized locations within the cell, complete their assembly on ribosomes bound to the rough endoplasmic reticulum.
3 Newly assembled proteins are carried from the rough endoplasmic reticulum to the Golgi apparatus in vesicles.
C Y T O P L A S M
Organelles That Build Proteins What organelles help make and transport proteins? Life is a dynamic process, and living things are always working, build- ing new molecules all the time, especially proteins, which catalyze chemical reactions and make up important structures in the cell. Because proteins carry out so many of the essential functions of living things, a big part of the cell is devoted to their production and distri- bution. Proteins are synthesized on ribosomes, sometimes in associa- tion with the rough endoplasmic reticulum in eukaryotes. The process of making proteins is summarized in Figure 7–11.
Ribosomes One of the most important jobs carried out in the cel-
lular “factory” is making proteins. Proteins are assembled on ribosomes. RibosomesRibosomes are small particles of RNA and protein found throughout the cytoplasm in all cells. Ribosomes produce proteins by following coded instructions that come from DNA. Each ribosome, in its own way, is like a small machine in a factory, turning out proteins on orders that come from its DNA “boss.” Cells that are especially active in protein synthesis often contain large numbers of ribosomes.
Endoplasmic Reticulum Eukaryotic cells contain an internal mem-
brane system known as the endoplasmic reticulumendoplasmic reticulum (en doh plaz mik rih tik yuh lum), or ER. The endoplasmic reticulum is where lipid components of the cell membrane are assembled, along with proteins and other materials that are exported from the cell. The portion of the ER involved in the synthesis of proteins is called rough endoplasmic reticulum, or rough ER. It is given this name because of the ribosomes found on its surface. Newly made proteins leave these ribosomes and are inserted into the rough ER, where they may be chemically modified.
Cellular Power Plants Mitochondria convert chemical energy stored in food into a form that can be used easily by the cell.
Cellular Solar Plants Chloroplasts, found in plants and some other organisms such as algae, convert energy from the sun into chemical energy that is stored as food.
Organelles That Capture
and Release Energy What are the functions of chloroplasts and mitochondria? All living things require a source of energy. Factories are hooked up to the local power company, but how do cells get energy? Most cells are powered by food molecules that are built using energy from the sun.
Chloroplasts Plants and some other organisms contain chloroplasts
(klawr uh plasts). ChloroplastsChloroplasts are the biological equivalents of solar power plants. Chloroplasts capture the energy from sunlight and convert it into food that contains chemical energy in a process called photosynthesis. Two membranes surround chloroplasts. Inside the organelle are large stacks of other membranes, which contain the green pigment chlorophyll.
Mitochondria Nearly all eukaryotic cells, including plants, contain
mitochondria (myt oh kahn dree uh; singular: mitochondrion). MitochondriaMitochondria are the power plants of the cell. Mitochondria convert the chemical energy stored in food into compounds that are more convenient for the cell to use. Like chloroplasts, two membranes—an outer membrane and an inner membrane—enclose mitochondria. The inner membrane is folded up inside the organelle, as shown in Figure 7–12. One of the most interesting aspects of mitochondria is the way in which they are inherited. In humans, all or nearly all of our mitochon- dria come from the cytoplasm of the ovum, or egg cell. This means that when your relatives are discussing which side of the family should take credit for your best characteristics, you can tell them that you got your mitochondria from Mom! Another interesting point: Chloroplasts and mitochondria contain their own genetic information in the form of small DNA molecules. This observation has led to the idea that they may be descended from independent microorganisms. This idea, called the endosymbiotic theory, is discussed in Chapter 19.
FIGURE 7–12 Cellular Powerhouses Chloroplasts and mitochondria are both involved in energy conversion processes within the cell. Infer What kind of cell—plant or animal—is shown in the micrograph? How do you know?
TEM 4500
202 Chapter 7 • Lesson 2
Cellular Boundaries
What is the function of the cell membrane?
A working factory needs walls and a roof to protect it from the environment outside, and also to serve as a barrier that keeps its products safe and secure until they are ready to be shipped out. Cells have similar needs, and they meet them in a similar way. As you have learned, all cells are surrounded by a barrier known as the cell membrane. Many cells, including most prokaryotes, also produce a strong supporting layer around the membrane known as a cell wall.cell wall.
Cell Walls Many organisms have cell walls in addition to cell
membranes. The main function of the cell wall is to support, shape, and protect the cell. Most prokaryotes and many eukary- otes have cell walls. Animal cells do not have cell walls. Cell walls lie outside the cell membrane. Most cell walls are porousporous enough to allow water, oxygen, carbon dioxide, and certain other sub- stances to pass through easily. Cell walls provide much of the strength needed for plants to stand against the force of gravity. In trees and other large plants, nearly all of the tissue we call wood is made up of cell walls. The cellulose fiber used for paper as well as the lumber used for build- ing comes from these walls. So if you are reading these words off a sheet of paper from a book resting on a wooden desk, you’ve got cell walls all around you.
Making a Model of a Cell
(^1) Your class is going to make a model of a plant cell using the whole classroom. Work with a partner or in a small group to decide what cell part or organelle you would like to model. (Use Figure 7–14 on pages 206–207 as a starting point. It gives you an idea of the relative sizes of various cell parts and their possible positions.) (^2) Using materials of your choice, make a three- dimensional model of the cell part or organelle you chose. Make the model as complete and as accurate as you can. 3 Label an index card with the name of your cell part or organelle, and list its main features and functions. Attach the card to your model.
(^4) Attach your model to an appropriate place in the room. If possible, attach your model to another related cell part or organelle. Analyze and Conclude
1. Calculate Assume that a typical plant cell is 50 micrometers wide (50 × 10–6^ m). Calculate the scale of your classroom cell model. ( Hint: Divide the width of the classroom by the width of a cell, making sure to use the same units.) 2. Compare and Contrast How is your model cell part or organelle similar to the real cell part or organelle? How is it different? 3. Evaluate Based on your work with this model, describe how you could make a better model. What new information would your improved model demonstrate?
BUILD Vocabulary
ACADEMIC WORDS The adjective porousporous means “allowing materials to pass through.” A porous cell wall allows substances like water and oxygen to pass through it.
Cell Structure and Function 203
(^) The Fluid Mosaic Model Embedded in the lipid bilayer of most cell membranes are protein molecules. Carbohydrate molecules are attached to many of these proteins. Because the proteins embedded in the lipid bilayer can move around and “float” among the lipids, and because so many different kinds of molecules make up the cell mem- brane, scientists describe the cell membrane as a “fluid mosaic.” A mosaic is a kind of art that involves bits and pieces of different colors or materials. What are all these different molecules doing? As you will see, some of the proteins form channels and pumps that help to move material across the cell membrane. Many of the carbohydrate mol- ecules act like chemical identification cards, allowing individual cells to identify one another. Some proteins attach directly to the cytoskel- eton, enabling cells to respond to their environment by using their membranes to help move or change shape. As you know, some things are allowed to enter and leave a factory, and some are not. The same is true for living cells. Although many substances can cross biological membranes, some are too large or too strongly charged to cross the lipid bilayer. If a substance is able to cross a membrane, the membrane is said to be permeable to it. A membrane is impermeable to substances that cannot pass across it. Most biologi- cal membranes are selectively permeable,selectively permeable, meaning that some sub- stances can pass across them and others cannot. Selectively permeable membranes are also called semipermeable membranes.
Review Key Concepts
1. a. Review What are the two major parts of the cell? b. Use Analogies How is the role of the nucleus in a cell similar to the role of the cap- tain on a sports team? 2. a. Review What is the function of lysosomes? b. Apply Concepts How do contractile vacuoles help maintain water balance? 3. a. Review What is the difference between rough and smooth ER? b. Sequence Describe the steps involved in the synthesis, packaging, and export of a protein from a cell. 4. a. Review What is the function of mitochondria? b. Infer You examine an unknown cell under a microscope and discover that the cell contains chloroplasts. From what type of organism does the cell likely come? 5. a. Review Why is the cell membrane some- times referred to as a fluid mosaic? What part of the cell membrane acts like a fluid? And what makes it like a mosaic? b. Explain How do the properties of lipids help explain the structure of a cell membrane? c. Infer Why do you think it’s important that cell membranes are selectively permeable? 6. Using the cells on the next page as a guide, draw your own models of a prokaryotic cell, a plant cell, and an animal cell. Then use each of the vocabulary words from this lesson to label your cells.
Lesson 7.
Cell Structure and Function 205
- Self-Test • Lesson Assessment
ANIMAL CELL Cell membrane
Centrioles
Vesicle
Rough endoplasmic reticulum Ribosomes (attached) Ribosomes (free)
Golgi apparatus
Mitochondrion
Lysosome
Cytoskeleton
Smooth endoplasmic reticulum
Nucleus (contains DNA)
Vacuole
Cell wall
Cell membrane
PROKARYOTIC CELL DNA
Ribosomes
PLANT CELL
Cell wall
Cell membrane
Vesicle
Golgi apparatus
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Ribosomes (attached) Ribosomes (free)
Mitochondrion
Cytoskeleton
Chloroplast
Central vacuole
Nucleus (contains DNA)
Vacuole
TYPICAL CELLS
FIGURE 7–14 Eukaryotic cells contain a variety of organelles, a few of which they have in common with prokaryotic cells. Note in the table on the facing page that while prokaryotic cells lack cytoskeleton and chloroplasts, they accomplish their functions in other ways as described. Interpret Visuals What structures do prokaryotic cells have in common with animal cells? With plant cells?
206 Lesson 7.2^ • Art Review • Tutor Tube
