Ch 3 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
the toes through a process called apoptosis, or programmed cell death. This process is
controlled by the DNA found in the nucleus of the cell. The organelle inside the cell
responsible for the actual destruction of the cell is the lysosome. (p. 110)
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
plasma membrane made by microtubules from the centrioles. Cilia are used to move
mucus and trapped airborne debris up and out of the respiratory tract. (p. 90)
24. The three phases of interphase are: G1, during which the cell is metabolically active and
growing; S phase, when DNA is replicated; and G2, when final preparation for cell
division takes place. (p. 97)
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
transport of sodium and potassium ions so that with each “turn” of the pump, three
sodium ions are ejected out of the cell and two potassium ions are carried back into the
cell. (pp. 79–80)
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
transport, 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
take place during cell division, leaving the cell with a larger-than-normal cytoplasmic
mass to regulate. (p. 91)
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
cell walls of cellulose, water entry makes the cell “stiff” due to hydrostatic pressure. In
the case of skin cells, as water is absorbed, the cells swell, causing the skin to take an
undulating course to accommodate greater cell volume. (pp. 71–72)
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)
molecules in the intestines and the solute molecules within the cells. As a result of this
situation, the effect of the difference between the intestinal cells’ content osmolarity
(compartment 1) and the intestinal content osmolarity (compartment 2) will not only
prevent water reabsorption by the intestinal cell but will cause water to move rapidly
from compartment 1 into compartment 2, resulting in diarrhea. (pp. 71–72)
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.
Failure to do this will result in the cell being unable to complete its mitotic division
process, thus killing the cell. (p. 100)
b. By binding to DNA and blocking mRNA synthesis, Adriamycin effectively inhibits
protein synthesis. Cessation of this process prevents the cell from replacing enzymes
and other proteins required for cellular survival. (p. 102)
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 replicates itself in preparation for cell division. Without DNA replication, cells
would not have DNA for both daughter cells, and would not divide. (p. 97)
“G2 to M” represents the time frame between gap 2 (G2), which is the time needed for
synthesis of enzymes that are required for division, and visible mitosis (M1). In this
situation, cells would have duplicated DNA, and be prepared to divide, but could not go
into actual mitosis. Cells would be effectively “stuck” in prophase. (pp. 97–98)
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 both these structures dysfunctional. Hence the normal “sweeping out” of the
respiratory tract provided by the cilia lining the lumen of this system would be lost,
leading to increased respiratory problems. Loss of a functioning flagellum would render
the sperm immobile and lead to sterility in males. (p. 90)
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
more if the demand on the cell is greater. The high alcohol consumption typical of
alcoholics stimulates the production of smooth ER that contains enzymes involved in
elimination of alcohol, making the cells more efficient at this task. All other factors
being equal, people who consume little or no alcohol have much less smooth ER
because there is much less demand for its detoxification function. (p. 84)
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)