CHAPTER 4 CELLS

LIVING ORGANISMS are HIGHLY ORGANIZED Cells, the simplest collection of matter that can live, were first observed by Robert Hooke in 1665 Antoni van Leeuwenhoek later described cells that could move He viewed bacteria with his own hand-crafted microscopes Leeuwenhoek was a haberdasher who developed the microscope to magnify the cloth he used to make clothing. His greatest contribution to science was his curiosity. As a result, he observed “animalcules” in a variety of liquids and reported his findings to the most prestigious science society of the day, the Royal Society of London. Copyright © 2009 Pearson Education, Inc.

The early microscopes provided data to establish the cell theory All living things are composed of cells All cells come from other cells (NO Spontaneous Generation) Life at the cellular level arises from structural order, reflecting emergent properties and the correlation between structure and function. Copyright © 2009 Pearson Education, Inc.

INTRODUCTION TO THE CELL Copyright © 2009 Pearson Education, Inc.

Microscopes reveal the world of the cell A variety of microscopes have been developed for a clearer view of cells and cellular structure The most frequently used microscope is the light microscope (LM)—like the one used in biology laboratories We will use a COMPOUND LIGHT MICROSCOPE Light passes through a specimen then through 2 glass lenses into the viewer’s eye Specimens can be magnified up to 400 times the actual size of the specimen With today’s modern light microscopes, images can be directed onto photographic film or a digital sensor, or onto a video screen. Student Misconceptions and Concerns 1. Students typically cannot distinguish between the concepts of resolution and magnification. However, pixels and resolution of digital images can help clarify the distinction. Consider printing the same image at high and low resolution and enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. Teaching Tips 1. Challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, etc. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a chance to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, etc. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes (they need not state their answers publicly, to avoid embarrassment). 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope, and a compound light microscope using microscope slides. The way these scopes function parallels the workings of electron microscopes. Dissection microscopes are like a SEM—both rely upon a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye . . . the same way a compound light microscope or TEM works! Copyright © 2009 Pearson Education, Inc.

Eyepiece Enlarges image formed by objective lens Ocular lens Magnifies specimen, forming primary image Objective lens Specimen Condenser lens Focuses light through specimen Figure 4.1A Light microscope (LM) Light source

Microscopes reveal the world of the cell Microscopes have limitations Both the human eye and the microscope have limits of RESOLUTION—the ability to distinguish between small structures Therefore, the light microscope cannot provide the details of a small cell’s structure SO…we can stain the specimen Can you think of a problem with this??? The human eye cannot resolve details finer than 0.1 mm. The light microscope can resolve objects as small as 0.2 micrometers. Student Misconceptions and Concerns 1. Students typically cannot distinguish between the concepts of resolution and magnification. However, pixels and resolution of digital images can help clarify the distinction. Consider printing the same image at high and low resolution and enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. Teaching Tips 1. Challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, etc. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a chance to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, etc. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes (they need not state their answers publicly, to avoid embarrassment). 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope, and a compound light microscope using microscope slides. The way these scopes function parallels the workings of electron microscopes. Dissection microscopes are like a SEM—both rely upon a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye . . . the same way a compound light microscope or TEM works! Copyright © 2009 Pearson Education, Inc.

Figure 4.1B Light micrograph of a protist, Paramecium.

Table 4.1 Measurement equivalents

10 m 1 m Unaided eye 100 mm (10 cm) 10 mm (1 cm) 1 mm 100 µm Human height 1 m Length of some nerve and muscle cells 100 mm (10 cm) Unaided eye Chicken egg 10 mm (1 cm) Frog egg 1 mm 100 µm Most plant and animal cells Light microscope 10 µm Nucleus Most bacteria Mitochondrion 1 µm Figure 4.2A The sizes of cells and related objects. Mycoplasmas (smallest bacteria) Electron microscope 100 nm Viruses Ribosome 10 nm Proteins Lipids 1 nm Small molecules 0.1 nm Atoms

Prokaryotic cells are structurally simpler than eukaryotic cells Bacteria and archaea are prokaryotic cells All other forms of life are eukaryotic cells Both prokaryotic and eukaryotic cells have a plasma membrane and one or more chromosomes (DNA) and ribosomes Eukaryotic cells have a membrane-bound nucleus and a number of other organelles, whereas prokaryotes have no nucleus and no true organelles Bacteria have a single chromosome that is found within the cell in the form of a circle (no free ends). They have extrachromosomal DNA called plasmids, but they are not necessary for viability of the cell. Students should be reminded that there are possible evolutionary relationships between prokaryotic and eukaryotic cells and questioned about these relationships. Did eukaryotic cells evolve from bacteria-like organisms or perhaps Archaea? For the BLAST Animation Prokaryotic Cell Size, go to Animation and Video Files. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. (For example, both membranes and our skin detect stimuli, engage in gas exchange, and serve as sites of excretion and absorption.) Teaching Tips 1. A visual comparison of prokaryotic and eukaryotic cells, such as that found in Figure 1.4, can be very helpful when discussing the key differences between these cell types. These cells are strikingly different in size and composition. Providing students with a visual reference point rather than simply listing these traits will help them better retain this information. 2. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter of a factor of ten translates into a much greater difference in volume. If students recall enough geometry, you may want to challenge them to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 3. Germs—here is a term that we learn early in our lives but that is rarely well-defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 4. Module 4.3 mentions how antibiotics can specifically target prokaryotic but not eukaryotic cells, providing a good segue into discussion of the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at http://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1.html. Copyright © 2009 Pearson Education, Inc.

Prokaryotic Cells Prokaryotic cells are like a studio (one-room) apartment All functions take place within the plasma membrane of the cell

A thin section through the bacterium Bacillus coagulans (TEM) Pili Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule Figure 4.3 A structural diagram (left) and electron micrograph (right) of a typical prokaryotic cell. Module 4.3 mentions how antibiotics can specifically target prokaryotic but not eukaryotic cells. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at http://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1.html. A thin section through the bacterium Bacillus coagulans (TEM) A typical rod-shaped bacterium Flagella

Eukaryotic cells are partitioned into functional compartments Eukaryotic cells are like a multiple room apartment Different functions take place in different organelles Teaching Tips 1. Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. Copyright © 2009 Pearson Education, Inc.

Eukaryotic cells are partitioned into functional compartments Manufacturing of protein molecules involves the nucleus, ribosomes, endoplasmic reticulum, and Golgi apparatus The nuclear DNA directs protein synthesis by first transcribing DNA into mRNA. The mRNA reaches the ribosomes, which translate the genetic message into a protein. The entire process of transcription and translation requires enzymes, whose synthesis was also directed by DNA. The endoplasmic reticulum and Golgi apparatus further process the proteins. Teaching Tips 1. Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. Copyright © 2009 Pearson Education, Inc.

The nucleus is the cell’s genetic control center It contains the information (DNA) to make protein molecules The nuclear envelope is a double membrane with pores that allow material (messenger RNA) to flow out of the nucleus It is attached to a network of cellular membranes called the endoplasmic reticulum Each of the membranes in the nuclear envelope (membrane) is a lipid bilayer separated by a space of 20–40 nm. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Noting the main flow of genetic information on the board as DNA → RNA → protein will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, rRNA, mRNA, ribosomes, and proteins are produced in a cell. 2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the door to the boss’s office. 3. Some of your more knowledgeable students may like to guess the exceptions to the rule of 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and adult red blood cells in mammals. 4. If you want to challenge your students further, ask them to consider the adaptive advantage of using mRNA to direct the production of proteins instead of using DNA directly. Some biologists suggest that DNA is better protected in the nucleus and that mRNA, exposed to more damaging cross-reactions in the cytosol, is the temporary working copy of the genetic material. In some ways, this is like making a working photocopy of an important document, keeping the original copy safely stored away. Copyright © 2009 Pearson Education, Inc.

Two membranes of nuclear envelope Nucleus Nucleolus Chromatin Pore Figure 4.6 TEM (left) and diagram (right) of the nucleus. Endoplasmic reticulum Ribosomes

Ribosomes make proteins for use in the cell and outside of the cell Ribosomes are involved in the cell’s protein synthesis Ribosomes are synthesized in the nucleolus, which is found in the nucleus An example of a cell that at times must make a large amount of protein is a lymphocyte, a white blood cell. Upon stimulation by infectious agents like bacteria, it pumps out a significant amount of antibody, a protein, to fight the infection. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Consider challenging your students to explain how we can have four main types of organic molecules functioning in specific roles in our cells, yet DNA and RNA only specifically dictate the generation of proteins (and more copies of DNA and RNA). How is the production of specific types of carbohydrates and lipids in cells controlled? (Answer: primarily by the specific properties of enzymes.) Copyright © 2009 Pearson Education, Inc.

Endoplasmic reticulum (ER) Ribosomes Cytoplasm ER Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit Figure 4.7 Ribosomes. Small subunit TEM showing ER and ribosomes Diagram of a ribosome

The endoplasmic reticulum is a biosynthetic factory There are two kinds of endoplasmic reticulum—smooth and rough Smooth ER lacks attached ribosomes Rough ER lines the outer surface of membranes They differ in structure and function However, they are connected Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. If you continue the factory analogy, the addition of a molecular tag by the Golgi apparatus is like adding address labels in the shipping department of a factory. Copyright © 2009 Pearson Education, Inc.

Nuclear envelope Ribosomes Smooth ER Rough ER Figure 4.9A Smooth and rough endoplasmic reticulum.

The endoplasmic reticulum is a biosynthetic factory Smooth ER is involved in a variety of diverse metabolic processes For example, enzymes produced by the smooth ER are involved in the synthesis of lipids, oils, phospholipids, and steroids Smooth ER processes include synthesis of lipids, metabolism of carbohydrates, and detoxification of drugs and poisons. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. If you continue the factory analogy, the addition of a molecular tag by the Golgi apparatus is like adding address labels in the shipping department of a factory. Copyright © 2009 Pearson Education, Inc.

The endoplasmic reticulum is a biosynthetic factory Rough ER makes proteins Once proteins are synthesized, they are transported in vesicles to other parts of the endomembrane system Secreted proteins are important to the multicellular individual. For example, hormones, antibodies, and enzymes are glycoproteins that have significant impacts on homeostasis, protection, or metabolism. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. If you continue the factory analogy, the addition of a molecular tag by the Golgi apparatus is like adding address labels in the shipping department of a factory. Copyright © 2009 Pearson Education, Inc.

The Golgi apparatus finishes, sorts, and ships cell products The Golgi apparatus functions in conjunction with the ER by modifying products of the ER Products travel in transport vesicles from the ER to the Golgi apparatus One side of the Golgi apparatus functions as a receiving dock for the product and the other as a shipping dock Products are modified as they go from one side of the Golgi apparatus to the other and travel in vesicles to other sites The finished product can become part of the plasma membrane or other organelle, or it may move to the plasma membrane for export from the cell. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Some people think the Golgi apparatus looks like a stack of pita bread. 2. If you continue the factory analogy, the addition of a molecular tag by the Golgi apparatus is like adding address labels in the shipping department of a factory. Copyright © 2009 Pearson Education, Inc.

4 3 1 2 Transport vesicle buds off Ribosome Secretory protein inside trans- port vesicle 3 Sugar chain 1 Figure 4.9B Synthesis and packaging of a secretory protein by the rough ER. Glycoprotein 2 Polypeptide Rough ER

Golgi apparatus “Receiving” side of Golgi Golgi apparatus apparatus Transport vesicle from ER New vesicle forming Figure 4.10 The Golgi apparatus. You might tell your students that the Golgi apparatus looks like a stack of pita bread. Transport vesicle from the Golgi “Shipping” side of Golgi apparatus

PROTEIN SYNTHESIS In the nucleus, DNA information for protein synthesis is copied into messenger RNA (mRNA) mRNA leaves the nucleus; goes to the ribosomes Proteins are synthesized at the ribosomes Proteins leave the ribosomes in transport vesicles headed for the Golgi apparatus Proteins are modified at the Golgi apparatus Modified proteins leave the Golgi apparatus in transport vesicles headed for their destination (inside or outside of the cell)

Nucleus Nuclear membrane Rough ER Smooth ER Transport vesicle Figure 4.13 Connections among the organelles of the endomembrane system. Golgi apparatus Lysosome Vacuole Plasma membrane

Lysosomes are digestive compartments within a cell A lysosome is a membranous sac containing digestive enzymes The enzymes and membrane are produced by the ER and transferred to the Golgi apparatus for processing The membrane serves to safely isolate these potent enzymes from the rest of the cell These enzymes can be used to: Digest dead cells Digest “food” for unicellular organisms Destroy pathogens (WHITE BLOOD CELLS) Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. As noted in Module 4.11, lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.” Copyright © 2009 Pearson Education, Inc.

Vacuoles function in the general maintenance of the cell Vacuoles are membranous sacs that are found in a variety of cells and possess an assortment of functions Examples are the central vacuole in plants Water is stored here For the BLAST Animation Vacuoles, go to Animation and Video Files. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Challenge your students to identify animal cell organelles other than mitochondria that are not involved in the synthesis of proteins. (Vacuoles and peroxisomes are not involved in protein synthesis). Copyright © 2009 Pearson Education, Inc.

Chloroplast Nucleus Central vacuole Figure 4.12A Central vacuole in a plant cell. Ask your students to identify organelles in animal cells that are not involved in the synthesis of proteins (other than mitochondria). (Vacuoles and peroxisomes are not involved in protein synthesis.)

Mitochondria harvest chemical energy from food Cellular respiration is accomplished in the mitochondria of eukaryotic cells Cellular respiration involves conversion of chemical energy in foods (GLUCOSE) to chemical energy in ATP (adenosine triphosphate) A cell may have thousands of mitochondria. For the BLAST Animation Mitochondria, go to Animation and Video Files. Student Misconceptions and Concerns 1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They might think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night. Teaching Tips 1. ATP functions in cells much like money functions in modern societies. Each holds value that can be generated in one place and spent in another. This analogy has been very helpful for many students. 2. Mitochondria and chloroplasts are each wrapped by multiple membranes. In both organelles, the innermost membranes are the sites of greatest molecular activity and the outer membranes have fewer significant functions. These outer membranes best correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. Copyright © 2009 Pearson Education, Inc.

Mitochondrion Outer membrane Intermembrane space Inner membrane Figure 4.14 The mitochondrion. Inner membrane Cristae Matrix

Chloroplasts convert solar (sunlight) energy to chemical energy Chloroplasts are the photosynthesizing organelles of plants Photosynthesis is the conversion of light energy to chemical energy of sugar molecules Chloroplasts contain the green pigment chlorophyll, along with enzymes and other molecules that function in the photosynthetic production of sugar. Student Misconceptions and Concerns 1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They might think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night. Teaching Tips 1. Mitochondria and chloroplasts are each wrapped by multiple membranes. In both organelles, the innermost membranes are the sites of greatest molecular activity and the outer membranes have fewer significant functions. These outer membranes best correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. Copyright © 2009 Pearson Education, Inc.

Chloroplast Stroma Inner and outer membranes Granum Intermembrane Figure 4.15 The chloroplast. Granum Intermembrane space

Cilia and flagella move when microtubules bend While some protists have flagella and cilia that are important in locomotion, some cells of multicellular organisms have them for different reasons Cells that sweep mucus out of our lungs have cilia Animal sperm are flagellated Student Misconceptions and Concerns 1. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed. Teaching Tips 1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach! Copyright © 2009 Pearson Education, Inc.

Cilia Figure 4.18A Cilia on cells lining the respiratory tract.

Flagellum Figure 4.18B Undulating flagellum on a sperm cell.

Eukaryotic cells are partitioned into functional compartments Although there are many similarities between animal and plant cells, differences exist Lysosomes and centrioles are not found in plant cells Plant cells have a rigid cell wall, chloroplasts, and a central vacuole not found in animal cells For the BLAST Animation Animal Cell Overview, go to Animation and Video Files. For the BLAST Animation Plant Cell Overview, go to Animation and Video Files. For the BioFlix Animation Tour of an Animal Cell, go to Animation and Video Files. For the BioFlix Animation Tour of a Plant Cell, go to Animation and Video Files. For the Discovery Video Cells, go to Animation and Video Files. Teaching Tips 1. Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. Copyright © 2009 Pearson Education, Inc.

NUCLEUS: Nuclear envelope Chromosomes Smooth endoplasmic reticulum Nucleolus Rough endoplasmic reticulum Lysosome Centriole Ribosomes Figure 4.4A An animal cell. Peroxisome Golgi apparatus CYTOSKELETON: Microtubule Plasma membrane Intermediate filament Mitochondrion Microfilament

Review of Cell Types Bacterial Cell Plant Cell Animal Cell Ten times smaller (1-10 micrometers) 10-100 micrometers One “Naked” Chromosome Multiple Chromosomes Cell Wall No Cell Wall No Nucleus Nucleus No Organelles Organelles Chloroplasts; Central Vacuoles No Chloroplasts or Central Vacuoles No Centrioles or Lysosomes Centrioles and Lysosomes