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Chapter 7: Cell Structure and Function Instructional Sequence Section 7.1: What are Cells? Four 45minute class periods Section 7.2: Cells, a Look Inside Four 45minute class periods 112 1. Complete Chapter 7 Pretest. 2. Complete Investigation 7A. 3. Read Section 7.1, pp. 136 to 140. 4. Complete Section Review, p. 141. 1. Read Section 7.2, pp. 142 to 148. 2. Complete Section Review, p. 149. 3. Complete Investigation 7B. 4. Complete Chapter Assessment, pp. 153 to 154. UNIT 3: CELL BIOLOGY Learning Goals Activities and Resources • Explain that cells are the basic unit of structure and function in all living organisms. • Explore cell theory and analyze similarities and differences among cells. • Differentiate between cell structure and function. • Classify living cells as prokaryotic or eukaryotic. Laboratory Investigation 7A: Examining Onion Tissue • Identify and describe parts of a cell and their functions. • Compare and contrast animal and plant cells. Laboratory Investigation 7B: Animal and Plant Cells Connection: Organ Transplants Chapter Activity: Building a Scale Model of a Cell Chapter Project: Cellular Song Teacher’s Resource CD: • Chapter 7 Pretest • Graphic Organizer: Prokaryotic and Eukaryotic Cells • Skill and Practice: Robert Hooke, Antonie van Leeuwenhoek Teaching Illustrations CD: • Cell Theory Teacher’s Resource CD: • Graphic Organizer: Plant vs. Animal Cells • Skill and Practice: Animal Cell Parts, Plant Cell Parts Teaching Illustrations CD: • Diagram of an Animal Cell, Diagram of a Plant Cell National Standards INQ.1.2 INQ.1.7 LS.C.1.2 LS.C.1.2 LS.C.1.3 LS.C.1.4 LS.C.2.1 LS.C.2.4 LS.C.3.1 LS.C.3.4 INQ.1.2 INQ.1.3 INQ.1.4 INQ.1.7 INQ.1.8 LS.C.1.1 LS.C.1.2 LS.C.1.3 LS.C.1.4 LS.C.1.5 LS.C.2.3 LS.C.2.4 CHAPTER 7 RESOURCES Language Tools Differentiated Strategies Literary Picks ELL Strategies: Listed in the ELL Ancillary Vocabulary: cell theory, cell membrane, organelle, cytoplasm, prokaryotic cell, eukaryotic cell Learning Strategies: • Active Learning - Motivate • Cooperative Learning - Investigation 5A • Active Research - Extend Word Origins: cytoplasm Materials Active Learning - Motivate: dropper bottles, pond water, distilled water, microscope, slides, coverslips Investigation 7A: microscope, slides, coverslips, tweezers, piece of onion, iodine stain Teaching Tip: Viewing Water Samples Vocabulary: mitochondria, vacuole, endoplasmic reticulum, ribosome, golgi body, lysosome, cytoskeleton, chloroplast, cell wall Word Origins: endoplasmic reticulum RAFT Writing Strategy Learning Strategies: • Active Learning - Motivate • Cooperative Learning - Investigation 5B • Graphic Organizer - Explain: Venn Diagram • Active Learning and Active Research - Extend Teaching Tip: Cell Concentration Cell Concentration: 10 microscopes, 5 pairs of prepared slides Investigation 7B: microscope, slides, coverslips, tweezers, flat toothpicks, prepared slides of muscle tissue, live Ulothrix, methylene blue stain, colored pencils, sanitizing beaker (bleach water) for disposal of toothpicks Chapter Activity: large sheets of construction paper, metric ruler, calculator Closure Cards 113 7.1 What Are Cells? Literary Picks... Reading Level About the Lesson In this lesson, students learn that cells are the basic units of structure and function in living organisms. They discover how the invention of the microscope helped scientists identify and learn more about cells. Students explore the cell theory and analyze similarities and differences among cells. They also differentiate prokaryotic and eukaryotic cells. Divide students into small groups. Provide each group with two dropper bottles: one with distilled water (labeled A) and one that contains pond water (labeled B). Do not tell students anything about the composition of either sample. Instead, have them make qualitative observations about the contents in each bottle before viewing them under the microscope. Then have them prepare a slide to observe each sample. Ask students to describe what they see. Without identifying the specific organisms, lead a discussion to help students conclude that these tiny organisms are made of cells. You may even want to have students create names for these “mystery creatures” based on their shape or patterns of movement. Students complete Investigation 7A before reading Section 7.1. The focus of this investigation is to familiarize students with general characteristics of cells; and how to prepare and view a microscope slide. 1. Allow one class period to complete the investigation. 2. Students work in groups of three to five. 3. Prepare dropper bottles of iodine and containers of sliced onion in advance. 4. Have students wear gloves, goggles, and an apron when preparing slides. 114 UNIT 3: CELL BIOLOGY Materials • • • • • • microscope slides coverslips tweezers piece of onion iodine stain The Cell Works: Microexplorers by Patrick Baeuerle An expedition into the world of cells. The author explores the different parts of cells, how they are made, and how they work together. 6-8 The Double Helix by James Watson and Lawrence Bragg A true story about the discovery of the DNA structure. This book explains the science process as it applies to the overall history of DNA. 9-12 Microbe Hunters by Paul de Kruif Explores the discovery of germs by providing a short biography of various scientists. Includes a chapter on Anton van Leeuwenhoek and the discovery of microbes. Teaching Tip . . . INVESTIGATION 7A: EXAMINING ONION TISSUE Setup 3-5 Title Vocabulary cell tissue cell wall nucleus cytoplasm Viewing Water Samples Be sure that you view the pond sample in advance, as it may not contain enough organisms. You can always add organisms to the pond water to make the viewing more interesting. Revisit this activity when teaching about protists so that students can observe variations in how these microorganisms move. 7.1 WHAT ARE CELLS? Word Origins . . . Prokaryotes vs. Eukaryotes Students often question how a prokaryotic cell is able to function since it does not have a nucleus. The answer lies in how students differentiate prokaryotic and eukaryotic cells. Although prokaryotic cells have no nucleus, they do have DNA. Prokaryotic DNA is much simpler than DNA found in eukaryotes. For example, prokaryotes usually have one large, round DNA molecule that has none of the proteins common to eukaryotic DNA. However, prokaryotes (like eukaryotes) do have ribosomes for protein synthesis and genes that function in heredity. Prokaryotes lack membrane-covered organelles, like vacuoles, lysosomes, and endoplasmic reticulum. They also have no mitochondria; but, they are able to use the inner surface of the cell membrane to make ATP. Many prokaryotes also have a cell wall. Unlike plant cell walls (made of cellulose), prokaryote cell walls get their shape and strength from peptidoglycan (or murein), a molecule made of amino acids and sugars. Cytoplasm (cyto-, from Greek kutos or kytos, meaning “hollow vessel”; -plasm, from Greek plasma, meaning to “form or shape”) The term cytoplasm is formed from the union of a prefix, cyto- and a suffix, -plasm. Cyto- means “cell” and -plasm means “substance or material that forms.” 1. Have students use the prefix, cyto- and suffix -plasm to define cytoplasm in their own words. 2. Ask students, What do you think a cytologist does? Note: Write the term on the board. Remind students that the suffix -ology means the “study of.” Prokaryotes have no microtubules. Therefore the structure of a prokaryotic flagellum is very different from that of a eukaryote. Prokaryotes move as the flagellum rotates. Eukaryotes are propelled by the whip-like motion of their flagella. 1. Have students guess how many microorganisms are present in one drop of pond water. Instruct small groups of students to prepare a slide and view it under low, medium, and high power. Each time, have students count the number of organisms they can see. Create a table (Figure 7.1) on the board for students to record their data and find the average number of organisms. 2. Students create closure cards and reflect on at least two new things they learned about cells. 3. Students use the Internet, encyclopedia, or other resources to research one specialized cell found in the human body. Draw the cell and describe its function. Label different organelles within the cell, like the cell membrane, cytoplasm, and nucleus. Display students’ work in your classroom. Number of Creatures medium low power high power power Group A Group B Average Figure 7.1: Sample table for counting the number of organisms in a drop of pond water. Students complete Section 7.1 review questions. 7.1 WHAT ARE CELLS? 115 Investigation 7A: Examining Onion Tissue Hold up an onion before students. What are some characteristics of this onion? Students make qualitative observations about the onion. For example, students may describe the shape or color of the onion. Divide students into their lab groups. Provide each group with a container of onion pieces. Look at the onion pieces in your container. How are these pieces different in appearance from the whole onion you viewed? Students offer comparisons of the onion pieces to the whole, such as differences in texture or color. Accept all reasonable responses. Let’s examine the onion in another way. Onions have many layers. Suppose you peel off a layer of onion and view it under a microscope. What do you think you will see? Gradually peel away thinner layers of onion. Then use tweezers to peel away a layer that is thin enough to examine under the microscope. Some practice is needed to get a layer that is thin enough to view. Encourage students to make predictions about what the onion tissue will look like when viewed under the microscope. Prepare a slide in order to view the tissue under the microscope. Place a drop of water on the slide. Use tweezers to remove a thin piece of onion tissue from the inside of a small piece of onion. Gently lower the onion tissue onto the slide. Be careful to not to crease the skin. Use the tweezers to place the coverslip over the onion skin. Tell students to place the coverslip over the onion skin slowly in order to avoid trapping air bubbles between the coverslip and the slide. Draw a picture to describe what you see. Students prepare an unstained slide of the onion tissue. Students should be able to see cells in orderly patterns, which may resemble white floor tiles or a brick wall. They may even be able to detect some motion in the cytoplasm. Doing this step before adding a stain gives students practice in preparing a slide and obtaining a thin layer of onion tissue. It also helps students to see why staining the tissue enhances viewing the components of the cell. A Preparing a slide of onion tissue Prepare another slide of onion tissue. This time, you will apply a stain. The stain that you will use is iodine. Be sure that you use only one drop of the iodine. Use the pictures shown in part one of your investigation handout as a guide. Inform students to be cautious as iodine can stain skin and clothing. It may also be harmful if ingested. Students prepare the slide of onion tissue with stain. Walk around and observe as students prepare the slides. Assist students as needed. Remind students to lower the coverslip slowly in order to reduce the probability of trapping air bubbles. 116 UNIT 3: CELL BIOLOGY 7A Examining Onion Tissue What is onion tissue made of? Do you think peeling an onion will make you cry? Well, here’s your chance to test your hypothesis. In this investigation, you will peel a thin layer from a piece of onion. You will stain that layer of tissue on a microscope slide. Then you will examine your slide under a microscope and make sketches of what you see. Materials • • • • • • Microscope Slides Coverslips Tweezers Piece of onion Iodine stain Safety tip: Wear gloves, goggles, and an apron while preparing the slides. A Preparing a slide of onion tissue Onions have many layers. The inner surface of each layer has a thin layer of tissue that’s easy to peel off. Since it is almost transparent, you will need to apply a stain so you can see things under a microscope. Follow the procedures below to make a slide of onion tissue. 1. Place a drop of iodine stain onto a slide. 2. Using the tweezers, gently peel the thin layer of tissue off the inside of a small piece of onion. 3. Using the tweezers, gently lower the onion skin onto the slide. Be careful not to crease the skin. 4. Use the tweezers to place a cover slip over the onion skin. B Stop and think a. What is the purpose of the iodine stain? b. What do you think you will see under the microscope? In your notebook, sketch what you think you will see. c. What is a tissue? What is the next level of organization above tissues? What is the level of organization below tissues? 38 7.1 INVESTIGATION 7A: EXAMINING ONION TISSUE Stop and think B Take a moment to think about the slides you have prepared. Then answer each question in part two of the investigation. Discuss students’ answers to each question. Walk around and check students’ sketches of what they predict they will see when viewing the stained onion tissue. Talk about the levels of organization of living organisms. This is a good time to revisit the vocabulary terms, cell, tissue, and organ. Observing onion tissue under a microscope C Now it is time to view the stained onion tissue. What should you do first? Students ensure that the stage is lowered to its lowest point. Good answer. Check your objectives. Are you at low power? Place your slide on the stage and secure it with the stage clips. Students set up the microscope and prepare to view the sample under low power. View the onion tissue at low, medium, and high power. Make a detailed sketch of what you see at each magnification. Also record any other observations beneath each sketch. Students view the slide at each magnification and record what they observe. Remind students to look at the microscope from the side when changing objectives to ensure that the slide is not hit, shifted, or damaged. Also, remind students not to use the coarse adjustment knob when viewing the slide at high power as this could also damage the slide. Thinking about what you observed D Examine each of your sketches closely. Do you notice any trends in what you observed as the power was changed? Students should note that they were able to see more detail of the onion tissue as the power was increased. Encourage students to discuss what they saw. Background Information... Why Onions Make You Cry Students know that onions have cells. Onion cells consist of enzymes and other sulfur-containing compounds. The membranes in whole onion cells keep these substances apart. When an onion is sliced, this barrier is broken and a chemical reaction between sulfur and enzymes is initiated. One of the products of this reaction is a gas. As this gas is released, it further interacts with the water that is already present in our eyes. The product of this interaction, sulfuric acid, irritates the nerve endings in the eye and creates a stinging sensation. The stinging is like a message being sent to the brain, telling it to “do something.” The brain’s response is to protect the eyes by attempting to dilute the acid. The brain directs the tear ducts to produce more water, which makes the eyes water, or “cry.” Enzymes are affected by temperature. If an onion is cooled before slicing, the effects are minimized. This is why it is often recommended to either peel and refrigerate an onion before cutting it, or to slice it under running water. Use your observations to help you answer each of the questions in part four. Discuss the answers to each question with the class. Review the visible organelles with the students and talk about their characteristics. As a result of completing this investigation, many students often question why onions make the eyes water. Use the information provided in Why Onions Make You Cry to explain the reasoning to your students. 7.1 WHAT ARE CELLS? 117 7.2 Cells: A Look Inside Teaching Tip . . . About the Lesson In this lesson students take an in-depth look at plant and animal cells. Students learn to identify organelles and describe how they function. Students also compare and contrast plant and animal cells. Show students pictures of different types of cells. For each picture, have students describe and identify familiar organelles, like the nucleus. Be sure to have a variety of cell types. Then have students group the cells based on their similarities. Students may begin to categorize cells by shape or size, or even by the presence (or absence) of certain organelles. See Teaching Tip (right) for an alternate activity. Students complete Investigation 7B after reading Section 5.2. Students will view and identify organelles that are common to plant and animal cells, and describe those that are unique to each cell type. It is important that students realize that not all animal cells (or plant cells) look and function exactly alike. INVESTIGATION 7B: ANIMAL AND PLANT CELLS Setup 1. Allow class period to complete the investigation. 2. Students work in groups of three to five. 3. Store the Ulothrix according the supplier’s recommendations. 4. Check the condition of prepared muscle tissue slides before the investigation. 5. Prepare a waste container for used toothpicks. 6. Caution students that methylene blue may stain skin and clothing and is harmful if ingested. 120 UNIT 3: CELL BIOLOGY Materials • • • • • • • • • • microscope slides coverslips tweezers flat toothpicks prepared slides of muscle tissue live Ulothrix methylene blue stain colored pencils Sanitizing beaker (bleach water) for disposal of toothpicks Vocabulary organelle epithelial cell chloroplast multicellular Cell Concentration Set up ten microscopes and number them one to 1en. Prepare ten slides, two each of five different cell types. Put one slide under each microscope. Have students work in pairs to view each slide. Don’t tell students that they are playing a game just yet. Simply instruct them to pay close attention to the details of each cell. Then have students try to remember which pairs of microscopes had similar cells. They can identify the matching microscopes by their numbers. Be sure to include at least one plant cell pair, as students should easily identify its unique cell wall. Word Origins . . . Endoplasmic reticulum (endo-, from Greek meaning “inside”; reticulum, from Latin meaning “little net”) The endoplasmic reticulum is “the little network located inside the cytoplasm of the cell.” Many organelles share common prefixes, suffixes, or roots. Here are a few to discuss with your students. 1. the suffix -some (from Greek, soma, meaning “body”) Examples: lysosomes, ribosomes 2. the prefix chloro- (from Greek khloros, meaning “green”) Examples: chlorophyll, chloroplast 7.2 CELLS: A LOOK INSIDE Using a Venn Diagram Students sometimes experience difficulty differentiating the cell wall and the cell membrane. In many instances, students are confused because both organelles have names beginning with the word cell. Others may forget that the plant cell has both a cell wall and a cell membrane, while animal cells have no cell wall. Instruct students to create a Venn diagram (Figure 7.2) to compare and contrast these structures. 1. Play a game of “Cell Charades.” Students work in groups to act out the role of organelles in cells while their classmates guess what they are. Encourage students to create visuals or other effects to make their acting more interesting. For example, the group representing the nucleus may create a sign for one of its members that says “I’m the boss!” Then that person could walk around the classroom telling other organelles (group members) what to do. 2. Plan a field trip for students to visit a local factory. Have students compare jobs of various factory workers with parts of the cell. 3. Students write a RAFT to demonstrate their knowledge of the structure, function, and other characteristics of organelles in the cell (see example, right). Students complete Section 7.2 review questions. 7.2 CELLS: A LOOK INSIDE 121 Investigation 7B: Animal and Plant Cells Guided Practice . . . What do you have in common with a rose, a tiger, an ant, a fungus, and a bacterium? Display pictures (or transparencies) of each of these objects before students. Students may make a variety of connections among these items. For example, like humans, these are all examples of living organisms. RAFT Writing Very good. Human beings, like each of these things, are examples of living organisms. What are some of the qualities of living things? Encourage students to recall what they learned about the characteristics of living things in Chapter 2. Acceptable responses are that all living things are able to grow, develop, respond to their surroundings, reproduce, use energy, and are made up of cells. Write these characteristics on the board as students name them. Audience: The cell membrane or cell wall You are correct. These are all qualities of living things. In today’s investigation, you will focus on one of the characteristics of living organisms: cells. All living things are made of cells. Do you think that your cells are like those of a rose? Students may have differences in opinion about whether human and rose cells are alike in any way. Encourage students to discuss how cells in the human body may be similar to or different from a rose plant’s cells. One feature that you have in common with the rose is that both you and the rose are multicellular. What does the term multicellular mean? Multicellular means having many cells. Talk about the prefix multi- and contrast it with the prefix uni- or the term unicellular. Good answer. Both plants and animals have different types of cells that allow them to perform different functions. Each of these functions, or jobs, is important to the cell’s survival. However, the types of structures found in plant and animal cells are different. A big factor in these differences is the way cells store materials and create the energy they need to stay alive. A Observing animal cells Today you will compare animal cells to plant cells. You will view two types of animal cells: epithelial cells and muscle cells. Epithelial cells are the cells that line your mouth. Write the term epithelial and its meaning on the board. The epithelial cells are your own cheek cells. You will prepare a slide of the cheek cells first. Students gather the materials they need to prepare the slides. Demonstrate the proper technique for scraping the cheek and preparing the slides. Instruct students to follow the visual steps provided to prepare the slide. Assist students as needed. Verify that each group has correctly prepared each slide. Follow each step outlined in part 1 of the investigation. Look at the cheek cells under low, medium, and high power. What do you see? Draw a picture of what you see at each magnification in Table 1. Make note of any structures that you are able to identify. Students view the stained cheek cells under low, medium, and high power. Some structures that students may identify include the cell membrane, nucleus, and cytoplasm. Direct 122 UNIT 3: CELL BIOLOGY Role: Any organelle in a cell, except the cell membrane or cell wall. Format: Student’s choice of a letter or advertisement placed in The Cellular Scoop Topic: You have not been performing your organelle duties up to the standards set by the cell wall or cell membrane (also known as the “Gatekeeper”). The local newspaper, The Cellular Scoop, has reported that you are about to be evicted from the cell. Convince the Gatekeeper that you are essential to the cell’s survival and should be allowed to stay. Ordering live organisms Be sure to order the Ulothrix 3 to 4 weeks in advance of the investigation. If the organisms arrive early, you may keep them in an aquarium with a bubbler. 7.2 INVESTIGATION 7B: ANIMAL AND PLANT CELLS students to properly dispose of the toothpicks (see Teaching Tip). It may also be helpful to have colored pencils available for students to complete their sketches. Look at the prepared slide of the muscle tissue cells under low, medium, and high power. Sketch what you see and record your observations in Table 1. Students record their observations. Students should note that they are able to see more details of the cells as the power is increased. Thinking about what you observed B Use your sketches and observations to help you answer each question in part 2. 7B Animal and Plant Cells What are the differences between animal and plant cells? In this investigation you will compare animal cells (your own epithelial cells and prepared slides) and plant cells (live Ulothrix - an algae that is closely related to plants, and the onion cells you observed in the last investigation). Materials • • • • • Microscope Slides Coverslips Tweezers Colored pencils • Flat toothpicks • Prepared slide of muscle tissue • Live Ulothrix • Methylene blue stain Safety tip: Wear gloves, goggles, and an apron when preparing slides. Allow time for students to complete the questions. Discuss their observations. Observing Ulothrix cells C Ulothrix is a filamentous and photosynthetic green algae. Therefore it is actually a protist, not a plant. However, it is beneficial to observe Ulothrix under the microscope because it has clearly defined organelles, like cell walls and chloroplasts, in common with plants. Prepare a wet mount of Ulothrix filaments. View this slide under the same magnifications that you used to look at the two animal cell samples. Sketch what you observe. Tell students not to clump too many filaments on the slide. Emphasize to students that this is not a case where more is better. Students record their observations of Ulothrix and create sketches. Students should clearly see organelles like the cell wall, nucleus, and chloroplasts. Thinking about what you observed D Think about the last investigation. Do you remember viewing the onion cells? What was different A Observing animal cells The cells that line the inside of your mouth are called epithelial cells. These cells are easy to collect and observe. Follow the procedures below. 1. Place a small drop of methylene blue stain onto a clean slide. 2. Remove a clean flat toothpick. Wet the wide end of the toothpick using tap water. 3. Gently scrape the inside of your cheek with the wide end of the toothpick. DO NOT USE FORCE! 4. Place the toothpick into the stain on the slide and gently swirl to mix the cheek cells with the stain. Dispose of the toothpick as directed by your teacher. DO NOT REUSE THE TOOTHPICK. 5. Using tweezers, gently place a coverslip on top of the methylene blue solution as shown. 6. Place the slide on the microscope stage and observe under low power, medium power, and high power. Sketch what you see and record your observations in Table 1. 7. Dispose of the cheek cell slide as directed by your teacher. 8. Obtain a prepared slide of muscle tissue cells. Place the slide on the microscope stage and observe under low power, medium power and high power. Sketch what you see and record your observations in Table 1. about the method you used to look at the onion cells compared to how you looked at the Ulothrix? Students needed a stain to see details of the onion cells but did not for the Ulothrix. How are onion and Ulothrix cells alike? How are they different? Students answer each question in part 4. Set up a few microscopes with prepared slides of stained onion cells, or you may have students prepare slides of onion tissue once more. Allow students to look at them again to make comparisons. Applying your knowledge E You have viewed both animal and plant cells under the microscope. Which structures are common to both plant and animal cells? Which are unique to plant cells? Students answer questions with members of their investigation group. Engage the class in a discussion to review their responses to the questions. Questions a and b require students to identify specific structures within the cell. Use this time to review the name, identifying characteristics, and function of each organelle. Point out each of these organelles to students as you name them. 40 Teaching Tip . . . Disposal of Used Toothpicks Prepare a beaker of water with a teaspoon of bleach added. Label the beaker Used Toothpicks. Instruct students to place their used toothpicks in the beaker. Dispose of the toothpicks at the end of the class period. 7.2 CELLS: A LOOK INSIDE 123