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CHAPTER
3
Cells: The Living Units
Objectives
The Cellular Basis of Life
1. Define cell.
The Plasma Membrane: Structure
3. Describe the chemical composition of the plasma membrane and relate it to membrane
functions.
The Plasma Membrane: Membrane Transport
5. Relate plasma membrane structure to active and passive transport processes.
6. Compare and contrast simple diffusion, facilitated diffusion, and osmosis relative to
substances transported, direction, and mechanism.
The Plasma Membrane: Generation of a Resting Membrane Potential
10. Define membrane potential and explain how the resting membrane potential is
established and maintained.
The Plasma Membrane: Cell-Environment Interactions
11. Describe the role of the glycocalyx when cells interact with their environment.
The Cytoplasm
13. Describe the composition of the cytosol.
14. Discuss the structure and function of mitochondria.
18. Describe the roles of centrioles in cell division and in formation of cilia and flagella.
19. Describe how the two main types of cell extensions, cilia and microvilli, differ in
structure and function.
The Nucleus
20. Outline the structure and function of the nuclear envelope, nucleolus, and chromatin.
Cell Growth and Reproduction
21. List the phases of the cell cycle and describe the key events of each phase.
22. Describe the process of DNA replication.
23. Define gene and genetic code and explain the function of genes.
Extracellular Materials
28. Name and describe the composition of extracellular materials.
Developmental Aspects of Cells
29. Discuss some theories of cell differentiation and aging.
Suggested Lecture Outline
I. The Cellular Basis of Life (p. 62; Figs. 3.1–3.2)
A. The four concepts of the cell theory state (p. 62; Figs. 3.1–3.2):
1. Cells are the basic structural and functional units of life.
4. The continuity of life has a cellular basis.
B. Cells have several basic characteristics (p. 62; Figs. 3.1–3.2):
1. Cells vary greatly in their size, shape, and function.
II. The Plasma Membrane: Structure (pp. 63–67; Figs. 3.3–3.5)
A. The Fluid Mosaic Model (pp. 63–65; Figs. 3.3–3.4)
1. The plasma membrane is composed of a double layer of lipid molecules, in which
proteins are embedded.
2. The lipid bilayer is composed of two layers of phospholipids with small amounts of
glycolipids, cholesterol, and lipid rafts.
3. There are two distinct populations of membrane proteins:
a. Integral proteins are transmembrane proteins that span the entire width of the
membrane and are involved with transport as channels or carriers.
B. The glycocalyx is the fuzzy, sticky, carbohydrate-rich area at a cell’s surface that acts as
a biological marker allowing cells to identify each other (pp. 65–66).
C. Cell Junctions (pp. 66–67; Fig. 3.5)
1. Most body cells are bound together using glycoproteins, specialized interlocking
regions, or specialized cell junctions.
III. The Plasma Membrane: Membrane Transport (pp. 67–79; Figs. 3.6–3.14;
Tables 3.1–3.2)
A. The cell membrane is selectively permeable: it allows nutrients to enter the cell and
waste to leave, but restricts movement of other substances in or out of the cell (p. 68).
B. Passive processes do not use energy (ATP) to move substances down their concentration
gradient (pp. 68–72; Figs. 3.7–3.9; Table 3.1).
3. In facilitated diffusion, sugars, amino acids, or ions are moved through the plasma
membrane by binding to protein carriers in the membrane or by moving through
channels.
4. Osmosis is the diffusion of water through a selectively permeable membrane.
a. Water will move into areas where the osmolarity, the total concentration of particles
in solution, is greater.
C. Active transport processes use energy contained in ATP to move substances across a
membrane (pp. 72–79; Figs. 3.10–3.14; Table 3.2).
1. Both primary active transport and secondary active transport uses solute pumps to
move substances against a concentration gradient.
a. In primary active transport, energy used to transport molecules is directly from
ATP.
2. Vesicular transport uses membranous sacs, called vesicles, to transport large particles,
macromolecules, and fluids across the plasma membrane, or within the cell.
3. Endocytosis, transcytosis, and vesicular trafficking are receptor-mediated vesicular
transport processes that move molecules into the cell.
IV. The Plasma Membrane: Generation of a Resting Membrane Potential
(pp. 79–80; Fig. 3.15)
A. A membrane potential is a voltage across the cell membrane that occurs due to a
separation of oppositely charged particles (ions) (p. 79).
V. The Plasma Membrane: Cell-Environment Interactions (pp. 80–81; Fig. 3.16)
A. Cells can interact directly with other cells, respond to extracellular chemicals, and inter-
act with molecules that direct migration (p. 80).
B. Roles of Cell Adhesion Molecules (CAMs) (p. 80)
1. Cell adhesion molecules (CAMs) are glycoproteins that act as attachment sites or
signals during embryonic development, wound repair, and immunity.
D. Role of Voltage-Gated Membrane Channel Proteins: Electrical Signaling (p. 81)
1. In excitable tissues, such as neurons or muscle cells, certain ion channels in the cell
membrane open or close in response to a change in membrane potential, allowing
electrical signaling between cells.
VI. The Cytoplasm (pp. 81–91; Figs. 3.17–3.28; Table 3.3)
A. The cytoplasm is the cellular material between the cell membrane and the nucleus and is
the site of most cellular activity (p. 81).
B. Cytoplasmic Organelles (pp. 83–91; Figs. 3.17–3.28; Table 3.3)
1. Mitochondria are membranous organelles that produce most of the ATP for a cell, by
breaking down food molecules and transferring the energy to the bonds of ATP.
2. Ribosomes are small, dark-staining granules consisting of protein and ribosomal RNA
that are the site of protein synthesis.
4. The Golgi apparatus is a series of stacked, flattened, membranous sacs associated with
groups of membranous vesicles.
a. The main function of the Golgi apparatus is to modify, concentrate, and package the
proteins and lipids made at the rough ER.
5. Lysosomes are spherical membranous organelles that contain digestive enzymes.
a. Lysosomes digest particles taken in by endocytosis, degrade worn-out organelles or
nonuseful tissues, and perform glycogen breakdown and release.
8. The cytoskeleton is a series of rods running through the cytosol, supporting cellular
structures and aiding in cell movement.
9. Centrosome and Centrioles
a. The centrosome is a region near the nucleus that functions to organize microtubules
and organize the mitotic spindle during cell division.
b. Centrioles are small, barrel-shaped organelles associated with the centrosome and
form the bases of cilia and flagella.
VII. The Nucleus (pp. 91–96; Figs. 3.29–3.30)
A. Basic Characteristics (p. 91; Fig. 3.29)
1. The nucleus contains the cellular DNA and determines the kinds and amounts of
proteins to be synthesized within a cell.
B. The Nuclear Envelope (pp. 92–93)
1. The nuclear envelope is a double-membrane barrier surrounding the nucleus.
a. The outer membrane is continuous with the rough ER, while the inner membrane is
2. The nuclear envelope encloses the fluid and solutes of the nucleus, the nucleoplasm.
C. Nucleoli (p. 93)
1. Nucleoli are dark-staining spherical bodies within the nucleus that are the sites of
assembly of ribosomal subunits, and are large in actively growing cells.
D. Chromatin (pp. 93–96; Fig. 3.30)
1. Chromatin is 30% DNA, the genetic material of the cell, 60% histone proteins, and
VIII. Cell Growth and Reproduction (pp. 96–110; Figs. 3.31–3.40)
A. The Cell Cycle (pp. 96–99; Figs. 3.31–3.33)
1. The cell cycle is a series of changes a cell goes through from the time it is formed to
the time it reproduces.
2. Interphase and cell division are the two main periods of the cell cycle.
3. Interphase is the period from cell formation to cell division and has three subphases.
a. During the G1, or gap 1, subphase, the cell is synthesizing proteins and actively
growing.
4. Cell division is a process necessary for growth and tissue repair. There are three main
events of cell division.
1. DNA specifies the structure of protein molecules that act as structural or functional
molecules.
2. Proteins are composed of polypeptide chains made up of amino acids.
3. Each gene is a segment of DNA that carries instructions for one polypetide chain.
4. There are four nucleotide bases, A, G, T, and C, that compose DNA, and each
5. The Role of RNA
a. RNA exists in three forms that decode and carry out the instructions of DNA in pro-
6. There are two main steps of protein synthesis: transcription and translation.
a. Transcription is the process of transferring information from a gene’s base sequence
to a complementary mRNA molecule.
1. DNA introns code for a variety of RNAs.
a. Antisense RNAs, made from the complementary DNA strand, can prevent mRNA
from being translated.
1. Autophagy is the process of degrading malfunctioning or obsolete organelles, to
prevent excessive accumulation of these structures.
IX. Extracellular Materials (p. 110)
A. Extracellular materials are substances contributing to body mass that are found outside
the cells (p. 110).
B. There are three classes of extracellular materials (p. 110):
1. Body fluids, consisting mainly of interstitial fluid, blood plasma, and cerebrospinal
fluid, are important for transport and solute dissolution.
X. Developmental Aspects of Cells (pp. 110–111)
A. Embryonic cells are exposed to different chemical signals that cause them to follow
different pathways in development (p. 110).
1. Chemical signals influence development by switching genes on and off.
B. Apoptosis and Modified Rates of Cell Division (p. 110)
1. Apoptosis is the programmed cell death of stressed, unneeded, injured, or aged cells.
a. In response to cellular damage or some extracellular signal, chemicals are released
to activate intracellular enzymes that digest cellular structures, killing the cell.
C. Cell Aging (p. 111)
1. The wear and tear theory considers the cumulative effect of slight chemical damage
and the production of free radicals.
Cross References
Additional information on topics covered in Chapter 3 can be found in the chapters listed below.
1. Chapter 2: Phospholipids; kinetic energy; ions; adenosine triphosphate; protein;
enzymes; deoxyribonucleic acid; ribonucleic acid; comparison of DNA and RNA;
hydrogen bond
5. Chapter 14: Membrane receptors and functions in the autonomic nervous system
6. Chapter 18: Cell junctions and cardiac function
7. Chapter 19: Cell junctions and movement of substances through capillary walls
8. Chapter 21: Function of lysozyme in protection of the body; function of cilia in innate
defense of the body
14. Chapter 27: Reproductive cell division and gamete production; tight junctions and the
blood testis barrier; functions of flagella and cilia; mitrochondria and energy production
in sperm cells
15. Chapter 29: Cell division in relation to the hereditary process
Lecture Hints
1. It is important to stress the distinction between passive and active processes.
2. Students will often equate bulk-phase endocytosis with “cell drinking” and forget that the
importance of the process is taking in the dissolved solutes in the fluid rather than the
solvent itself.
6. Clarify the distinction between centrioles and centromeres.
7. Clearly distinguish between mitosis and cytokinesis.
Activities/Demonstrations
1. Audiovisual materials are listed in the Multimedia in the Classroom and Lab section of
this Instructor Guide (p. 387).
7. Secure a glass funnel containing filter paper over a beaker. Illustrate how greater fluid
pressure (provided by more fluid in the funnel) leads to faster filtration.
8. Set up one or more of the following simple diffusion demonstrations:
a. Place a large histological dye crystal on the center of an agar plate a few hours before
lecture. A ring of color will appear radiating from the crystal. The plate can be
9. A simple osmometer: Place a glucose solution in a dialysis sac and tie securely to a
length of glass tubing. Secure the tubing with a stand and clamp so that the dialysis bag is
immersed in distilled water. Have students observe the fluid level in the tube over time.
10. If a microscope/TV camera system is available (or a microprojector), set it up to show
the effects of: (a) physiologic saline, (b) hypertonic saline, and (c) distilled water on red
blood cells.
Critical Thinking/Discussion Topics
1. Cells tend to have a relatively small and uniform size. Why aren’t cells larger? Discuss
your answer.
5. Why must each daughter cell produced by mitosis have mitochondria?
6. Use the mathematical equations for surface area and volume determination to show that
volume increases faster than surface area.
7. Why is damage to the heart more serious than damage to the liver (or other organ)?
8. Start with a cell containing 24 (or any hypothetical number you wish) chromosomes, and
in each stage of mitosis predict the number of chromosomes and chromatids present.
Library Research Topics
1. Receptor-mediated endocytosis is a highly selective mechanism of ingesting molecules.
How could it be used to kill cancer cells?
5. Many genetic diseases are caused by mutations that change the sequence of the nitrogen
bases in the DNA. How many codons are changed in the genetic disease sickle-cell
anemia? What amino acid is substituted in the hemoglobin because of this mutation?
6. During the past few years experimental implants of fetal tissue have been used for treat-
ment of brain disorders such as Parkinson’s disease. What is the current status of such
experimentation? What are some of the moral, ethical, and legal concerns involving such
experimentation?
List of Figures and Tables
All of the figures in the main text are available in JPEG format, PPT, and labeled & unlabeled
format on the Instructor Resource DVD. All of the figures and tables will also be available in
Transparency Acetate format. For more information, go to www.pearsonhighered.com/educator.
Figure 3.1 Cell diversity.
Figure 3.2 Structure of the generalized cell.
Figure 3.10 Primary Active Transport: The Na+-K+ Pump.
Figure 3.11 Secondary active transport is driven by the concentration gradient created by
primary active transport.
Figure 3.12 Events of endocytosis mediated by protein-coated pits.
Figure 3.13 Comparison of three types of endocytosis.
Figure 3.14 Exocytosis.
Figure 3.21 Electron micrograph of lysosomes (20,000X).
Figure 3.22 The endomembrane system.
Figure 3.23 Cytoskeletal elements support the cell and help to generate movement.
Figure 3.24 Microtubules and microfilaments function in cell motility by interacting with
motor molecules powered by ATP.
Figure 3.25 Centrioles.
Figure 3.26 Structure of a cilium.
Figure 3.27 Ciliary function.
Figure 3.35 Overview of stages of transcription.
Figure 3.36 The genetic code.
Answers to End-of-Chapter Questions
Multiple-Choice and Matching Question answers appear in Appendix H of the main text.
Short Answer Essay Questions
20. During embryonic development the embryo loses the webbing between the fingers and
21. Each daughter cell produced following mitosis is genetically identical to the mother cell.
Because each cell contains part of the original cell, a portion of the very first original cell
will always be found in each and every daughter cell. (p. 98)
22. The ER-bound ribosomes produce proteins that will be exported from the cell, while the
ribosomes found in the cytosol produce proteins used within the cell. (pp. 83–84)
23. The extensions found on the cells lining the trachea are cilia. Cilia are extensions of the
24. The three phases of interphase are: G1, during which the cell is metabolically active and
25. The sodium-potassium pump acts to maintain a polarized state of the membrane by
maintaining the diffusion gradient of sodium and potassium ions. The pump couples the
26. Primary active transport involves a change in the conformation of the transport protein,
which directly transports the bound solute across the membrane. Secondary active trans-
port, on the other hand, is an indirect transport in which the solute is “dragged along”
with another ion that is actively being pumped against its concentration gradient. This
pumped ion is usually transported by a primary active transport system. (p. 73)
27. The binucleate condition sometimes seen in liver cells occurs when cytokinesis does not
Critical Thinking and Clinical Application Questions
1. In each case, living cells have been immersed in a hypotonic solution, which will result
in water entry into the cells. In the case of celery, where the cells are also bounded by
2. By interfering with normal digestion and absorption of food material, the infectious
agents are causing the intestinal cell membrane to become impermeable to solute (food)
3. a. By damaging the mitotic spindle, Vincristine will inhibit the proper formation of the
microtubules used in pushing the centrioles toward the opposite poles of the cell.
4. “G1 to S” is the time between cell divisions, formerly referred to as the “resting stage,” to
differentiate it from cell division. The cell will stay in this phase until it is ready to
divide, at which time it moves into S, or the synthetic phase. In the synthetic phase, DNA
5. Peroxisomes are the cellular organelles that break down toxins. This organelle contains
oxidases and catalases. Oxidases use molecular oxygen to detoxify many substances,
such as alcohol and formaldehyde. (pp. 85–86)
6. Both cilia and flagella are involved in movement. Cilia propel other substances across the
cell’s surface, whereas the flagella propel the cell itself. Lack of dynein would render
7. One of the functions of the smooth ER is detoxification of drugs, such as alcohol.
Specific enzyme concentration on the smooth ER is need-based: the cell will produce
8. Salt water is a hypertonic fluid. The kidneys cannot make urine salty enough to remove
the excess salt you consume in the salt water. The kidneys instead make more urine by
removing needed water from your body, causing you to dehydrate. (p. 71)
Suggested Readings
Bartek, Jiri and Jiri Lukas. “Order from Destruction.” Science 294 (5540) (Oct. 2001): 66–67.
Dahlberg, Albert E. “The Ribosome in Action.” Science 292 (5518) (May 2001): 868–869.
Dickinson, Boonsri. “The Jiffy Lube of Genome Decoding.” Discover 29 (10)
(Oct. 2008): 48.
Finkel, Elizabeth. “The Mitochondrion: Is it Central to Apoptosis?” Science 292 (5516)
(April 2001): 624–626.
Hentze, Matthias W. “Believe It or Not—Translation in the Nucleus.” Science 293 (5532)
(Aug. 2001): 1058–1059.
Hughes, Julian R., et al. “A Microtubule Interactome: Complexes with Roles in Cell Cycle
and Mitosis.” PLoS Biology 6 (April 2008): 785–795.
Hunot, Stephane, and Richard A. Flavell. “Death of a Monopoly?” Science 292 (5518)
(May 2001): 865–866.
King, Ian F., and Robert E. Kingston. “Specifying Transcription.” Nature 414 (6866)
(Dec. 2001): 858–860.
Martinou, Jean-Claude, and Douglas R. Green. “Breaking the Mitochondrial Barrier.” Nature
Reviews: Molecular Cell Biology 2 (1) (Jan. 2001): 63–71.
Marx, Jean. “Caveolae: A Once-Elusive Structure Gets Some Respect.” Science 294 (5548)
(Nov. 2001): 1862–1865.
Nigg, Erich A. “Mitotic Kinases as Regulators of Cell Division and its Checkpoints.” Nature
Reviews: Molecular Cell Biology 2 (1) (Jan. 2001): 21–32.
Pennisi, Elizabeth. “Ribosome’s Inner Workings Come into Sharper View.” Science 291
(5513) (March 2001): 2526–2527.
Slepnev, Vladimir I., and Pietro De Camilli. “Accessory Factors in Clathrin-Dependent
Synaptic Vesicle Endocytosis.” Nature Reviews: Molecular Cell Biology 1 (3) (Dec.
2000): 187–198.
Sprong, H., et al. “How Proteins Move Lipids and Lipids Move Proteins.” Nature Reviews:
Molecular Cell Biology 2 (7) (July 2001): 504–513.
Van Meer, Gerrit. “The Different Hues of Lipid Rafts.” Science 296 (5569) (May 2002):
855–857.
