Chapter 3
Cells
3.1 Introduction
1. An adult human body consists of about ________ cells. (p. 76)
c. 50 to 100 trillion
2. Describe three types of differentiated cells. (p. 76)
Nerve cells are long with threadlike extensions that can be used to transmit motor or sensory information.
Muscle cells are slender and rod-like which contract to move parts of the body. Epithelial cells,
specifically simple squamous, are thin and flattened for gas exchange.
3.2 A Composite Cell
3. The three major parts of a cell are ______________________________. (p. 76)
b. the nucleus, cytoplasm, and the cell membrane
4. Distinguish between the cytoplasm and the cytosol of a cell. (p. 76)
The cytoplasm is composed of specialized structures called cytpolasmic organelles suspended in a liquid
called cytosol. The cytoplasm surrounds the nucleus and is contained by the cell membrane.
5. Explain the general function of organelles. (p. 76)
Organelles divide the labor in a cell by partitioning off certain areas or providing specific functions, such as
dismantling debris or packaging secretions.
6. Define selectively permeable. (p. 79)
Selectively permeable means that the cell membrane allows some substances to pass through easily, while
excluding other substances.
7. Describe the structure of a cell membrane and explain how this structural organization provides
the membrane’s function. (p. 79)
The basic structure of the cell membrane consists of a phospholipid bilayer. It contains embedded protein
molecules. It functions to keep the inner portion of the cell intact. It controls the entrance and exit of
substances.
8. List three functions of membrane proteins. (p. 80)
The functions of membrane proteins include acting as a receptor to combine with a specific substance such
as a hormone, while some form narrow passageways, or channels, through which various molecules and
ions can cross the cell membrane. Others function as enzymes in signal transduction.
9. State a way that cellular adhesion is essential to health; and a way that abnormal cellular adhesion
harms health. (p. 81)
Cellular adhesion enables cells to aggregate to form tissues. Certain cellular adhesion molecules also assist
the immune system in recognizing “self” and “non-self” cell surfaces. Abnormal cellular adhesion could
indicate a potential threat to health.
10. Match the following structures with their definitions: (pp. 82-89)
1. Golgi apparatus—e
2. Mitochondria—c
3. Peroxisomes—a
4. Cilia—h
5. Endoplasmic reticulum—g
6. Cytoskeleton—d
7. Vesicles—f
8. Ribosomes—b
11. Distinguish between organelles and inclusions. (p. 89)
An organelle is a structure within the cytoplasm that has a specific function. Inclusions are masses of
lifeless chemicals such as pigments or glycogen.
12. List the parts of the nucleus and explain why each is important. (p. 89)
Describe the structure of the nucleus and the functions of its contents.
The nucleus is a cellular organelle that is usually located near the center of the cell. It is a relatively large,
spherical structure enclosed in a double bilayered nuclear envelope, consisting of inner and outer
membranes.
This allows various substances to move between the nucleus and the cytoplasm. The nucleolus is a small,
dense body composed largely of RNA and protein. It assists in the production of ribosomes. Chromatin
consists of loosely coiled fibers composed of DNA molecules and protein that contain information for
synthesizing proteins that promote cellular life processes. These become chromosomes during cell
divisions.
3.3 Movements Into and Out of the Cell
13. Distinguish between active and passive mechanisms of movement across cell membranes. (p. 90)
Passive mechanisms do not require cellular energy. Active mechanisms use cellular energy.
14. Match the transport mechanisms on the left with their descriptions on the right. (pp. 90-98)
1. Diffusion—c
2. Facilitated diffusion—b
3. Filtration—f
4. Active transport—e
5. Endocytosis—a
6. Exocytosis—d
15. Define osmosis. (p. 93)
Osmosis is a special type of diffusion involving water. This is when water molecules diffuse from a region
of higher water concentration to a region of lower water concentration.
16. Distinguish between hypertonic, hypotonic, and isotonic solutions. (p. 94)
Hypertonic refers to a solution that has a higher osmotic pressure than that of the cell. This causes the cell
to shrink as water moves out of the cell. Hypotonic refers to a solution that has a lower osmotic pressure
than that of the cell. This causes the cell to swell and possibly burst as water moves into it. Isotonic refers
to a solution that has the same osmotic pressure as body fluids. This allows the cell size to remain
unchanged as water or solutes are not being pulled in any specific direction.
17. Explain how phagocytosis differs from receptor-mediated endocytosis. (p. 97)
Receptor-mediated endocytosis moves very specific kinds of particles into the cell. In this process, protein
molecules exit through a portion of the cell membrane to the outer surface, where they serve as receptors
for liquids. The proteins become binding sites for specific substances found in the interstitial fluid. These
are then allowed to enter the cell. It would be useful in the blood-brain barrier if there were a specific
receptor that could be triggered to allow substances, such as a drug, to cross the membrane.
18. Explain how transcytosis combines endocytosis and exocytosis. (p. 98)
Transcytosis is the selective and rapid transport of a substance or particle from one end of a cell to the
other. It also enables substances to cross barriers formed by tightly connected cells.
3.4 The Cell Cycle
19. The period of the cell cycle when DNA replicates is _________________. (Outcome 3.11)
c. S phase
20. Explain why interphase is not a period of rest for a cell. (p. 100)
Interphase is the stage in the life cycle of a cell where young cells grow, manufacture compounds, new
organelles are made and the chromosomes, and centrioles replicated.
21. Explain how meiosis differs from mitosis. (p. 100)
Mitosis is the division of somatic cells resulting in two identical daughter cells containing the diploid
number of chromosomes. Meiosis is the division of sex cells resulting in two, and then four, daughter cells
each containing the haploid number of chromosomes
22. ______________occur simultaneously. (p. 101)
c. Cytokinesis and telophase
23. Describe the events of mitosis in sequence. (p. 101)
Prophase is the first stage of mitosis where the chromosomes appear scattered throughout the nucleus. The
nuclear envelope dissolves and the sister chromatids are attached by the centromere. A spindle-shaped
group of microtubules forms between the centrioles as they move apart.
Metaphase is the second stage of mitosis. The chromosomes move along the spindle fibers and align
midway between the centrioles. Spindle fibers become attached to the centromere of the chromosomes.
Anaphase is where the centromere of the chromatids separate and the chromatids become individual
chromosomes. These are pulled apart toward the opposite sides of the cell.
Telophase is the final stage of mitosis where the chromosomes complete their migration toward the
centrioles.
It is much like prophase but with everything reversed. The nuclear envelope reforms and the chromosomes
become invisible.
3.5 Control of Cell Division
24. List five factors that control when and if a cell divides. (p. 103)
1. The DNA at the tips of chromosomes.
2. Kinases and cyclins.
3. Cell size
4. Hormones and growth factors
5. Space availability
25. Explain why it is important for the cell cycle to be highly regulated. (p. 104)
With too infrequent mitoses, an embryo could not develop, a child could not grow, and wounds would not
heal. Too frequent mitoses or those that continue unabated produce an abnormal growth, or neoplasm,
which may form a disorganized mass called a tumor.
.
26. Discuss the consequence of too little cell division and too much cell division. (p. 104)
With too infrequent mitoses, an embryo could not develop, a child could not grow, and wounds would not
heal. Too frequent mitoses or those that continue unabated produce an abnormal growth, or neoplasm,
which may form a disorganized mass called a tumor.
27. Distinguish between the ways that mutations in oncogenes and tumor suppressor genes cause
cancer. (p. 104)
Oncogenes are versions of genes that normally control the cell cycle, but are over expressed, increasing cell
division rate. Tumor suppressor genes, when removed or inactivated, lift control of the cell cycle, and
uncontrolled cell division results.
3.6 Stem and Progenitor Cells
28. Define differentiation. (p. 105)
Differentiation is the process by which cells develop different characteristics in structure and function.
29. A stem cell ____________. (p. 105)
a. self-renews.
30. Which of the following is true? (p. 105)
c. Differentiated cells are pluripotent until they specialize
31. Describe a general function of stem cells in the body. (p. 106)
Stem cells allow for continual growth and renewal by dividing repeatedly.
3.7 Cell Death
32. Explain how apoptosis (cell death) can be a normal part of development. (p. 106)
Apoptosis is programmed cell death which sculpts organs from tissues that naturally overgrow.
33. Provide an example of apoptosis. (p. 106)
Apoptosis carves away webbing between developing fingers and toes.
34. List the steps of apoptosis. (p. 106)
A receptor on the cell membrane receives a signal to die. Special enzymes are activated inside the cell.
These enzymes lead to cell destruction. The cell changes appearance. Finally, the cell shatters.
Phagocytes destroy the remains.
35. Distinguish between necrosis and apoptosis. (p. 106)
Apoptosis is fast, orderly, and contained destruction. Necrosis is a disordered form of cell death associated
with inflammation and injury.
36. Describe the relationship between apoptosis and mitosis. (p. 109)
Mitosis and apoptosis are synchronized throughout development, maturation, and aging.