1. If you were a plant pathogen, what would be the first obstacle to invading a host
plant that you would have to overcome?
a. Chemical toxins on the surface of a plant
b. Physical barriers on the exterior of a plant
c. Animal guardians of the host plant
d. Immune proteins in the plant tissue
The correct answer is b—
A. Answer a is incorrect. Although some plants may have toxins on their surface, the
majority of plants rely on an impermeable barrier to invasion.
The correct answer is b—Physical barriers on the exterior of a plant
B. Answer b is correct. The outside of most plants is covered by an impermeable
layer of bark. Furthermore, each plant cell has a rigid cell wall that can prevent
pathogen infection.
The correct answer is b—
C. Answer c is incorrect. Although some plants do have animal guardians (such as
ants protecting Acacia plants) this type of coevolution is rare and is unlikely to
protect a plant from an invading virus, bacterium, or fungus.
The correct answer is b—
D. Answer d is incorrect. Although most plants can produce immune proteins, they
are not the first line of defense to infection.
2. Plant dermal cells can secrete which of the following?
a. Suberin
b. Wax
c. Cutin
d. All of the above
The correct answer is d—
A. Answer a is correct. Plant root cells do secrete suberin, but it is not the only
answer.
The correct answer is d—
B. Answer b is correct. Plant root cells, primarily dermal cells, produce wax, but it is
not the only answer.
The correct answer is d—
C. Answer c is correct. Plant roots can produce cutin, but it is not the only answer.
The correct answer is d—All of the above
D. Answer d is correct. Answers a, b, and c are correct.
3. Some plants are recognized by fungal pathogens on the basis of their stomatal
pores. Which of the following would provide these plants immunity from fungal
infection?
a. Removing all of the stomata from the plant
b. Changing the spacing of stomatal pores in these plants
c. Reinforcing the cell wall in the guard cells of stomatal pores
d. Increasing the number of trichomes on the surfaces of these plants
The correct answer is b—
A. Answer a is incorrect. Removing the stomata from plants would kill the plant
regardless of fungal infection.
The correct answer is b—Changing the spacing of stomatal pores in these plants
B. Answer b is correct. Some fungal pathogens recognize host plants by the spacing
of their stomata. Altering this spacing, therefore, would prevent recognition by
the fungal pathogen.
The correct answer is b—
C. Answer c is incorrect. Reinforcing the guard cell wall would not prevent the
stomatal pore from allowing access to fungal pathogens. It may, however,
compromise guard cell function because the opening and closing of stomata
depends on asymmetrical thickening of the guard cell wall.
The correct answer is b—
D. Answer d is incorrect. Trichomes play a role in preventing predation by
herbivorous animals, but will not prevent fungal infection.
4. Your friend informs you that it is highly likely all of the plants in your yard are
“infected” with some kind of fungi or bacteria. The plants look perfectly healthy
to you at this time. The most prudent thing for you to do would be—
a. remove all your plants because they are likely to die
b. spray your plants with chemicals to remove all bacteria and fungi
c. remove all your plants and replace the soil
d. do nothing because many of these bacteria and fungi may be beneficial
The correct answer is d—
A. Answer a is incorrect. Many bacteria and fungi could be beneficial to the plants,
so ripping them up would not be prudent at this time.
The correct answer is d—
B. Answer b is incorrect. See the rationale for answer a.
The correct answer is d—
C. Answer c is incorrect. See the same rationale as for a and b.
The correct answer is d—do nothing because many of these bacteria and fungi may be
beneficial
D. Answer d is correct. Plants may be receiving benefits from these organisms.
5. Eating unscrubbed cassava root would likely—
a. lead to indigestion because the skin of the cassava plant is very difficult to
digest
b. make you sick because the soil on the surface may contain harmful
microbes
c. make you sick because the skin contains cyanogenic glycosides that would
produce cyanide in the digestive track
d. harm your teeth because of the small stones that would be on the surface
of the root
The correct answer is c—
A. Answer a is incorrect. The skin of the cassava plant is not difficult to digest.
The correct answer is c—
B. Answer b is incorrect. Although the soil does contain microbes, in small amounts
it is unlikely to make you sick.
The correct answer is c—make you sick because the skin contains cyanogenic glycosides
that would produce cyanide in the digestive track
C. Answer c is correct. The skin of the cassava plant contains high levels of
cyanogenic compounds that are converted to cyanide in the digestive track.
Cyanide is a poison that blocks electron transport.
The correct answer is c—
D. Answer d is incorrect. It is unlikely that you would hurt your teeth on stones in
soil.
6. You decide to plant a garden with a beautiful black walnut at one end and a
majestic white oak at the other end. You are quite disappointed, however, when
none of the seeds you plant around the walnut tree grow. What might explain this
observation?
a. The walnut tree filters out too much light, so the seeds fail to germinate
b. The roots of the walnut tree deplete all of the nutrients from the soil, so the
new seedlings starve
c. The walnut tree produces chemical toxins that prevent seed germination
d. The roots of the walnut tree deplete all of the water from the soil and
thereby prevent seed germination.
The correct answer is c—
A. Answer a is incorrect. Although dense forest canopies can filter enough light to
prevent seed germination, one tree would not preclude enough light to have this
effect. Moreover, the oak tree is filtering out light and is not affecting plant
growth.
The correct answer is c—
B. Answer b is incorrect. There are more than enough nutrient reserves in soil to
sustain many plants as is evidenced by the growth around the oak tree.
The correct answer is c—The walnut tree produces chemical toxins that prevent seed
germination.
C. Answer c is correct. Black walnut trees produce chemicals that diffuse throughout
the soil and prevent seed germination in a process called allelopathy.
The correct answer is c—
D. Answer d is incorrect. There is more than enough water in soil to sustain many
plants.
7. Vegetarians whose diet consists largely of soy are less likely to develop prostate
cancer because—
a. soy contains the anticancer drug taxol
b. eating meat increases the probability of developing prostate cancer, so
eliminating it from your diet reduces the chances of developing the disease
c. soy protein prevents accumulation of the prostate-specific antigen (PSA)
associated with prostate cancer
d. soy contains a phytoestrogen that may down-regulate estrogen and
androgen receptors in males who consume diets high in soy
The correct answer is d—
A. Answer a is incorrect. The anticancer drug taxol is isolated from yew trees.
The correct answer is d—
B. Answer b is incorrect. Meat does not have a known effect on the incidence of
prostate cancer.
The correct answer is d—
C. Answer c is incorrect. PSA is produced in prostate tumor cells and is not downregulated by soy proteins.
The correct answer is d—soy contains a phytoestrogens that may down-regulate estrogen
and androgen receptors in males who consume diets high in soy
D. Answer d is correct. It has been observed that in Asian males who eat diets high in
soy the incidence of prostate cancer is reduced. Soy contains a phytoestrogen that
may down-regulate estrogen and androgen receptors in these men.
8. Tonic water, containing quinine, was developed primarily—
a. as an enjoyable beverage
b. to help fight malaria
c. to reduce the risk of cancer
d. as a weak sedative
The correct answer is b—
A. Answer a is incorrect. Tonic water is actually quite bitter and was often mixed
with things like gin to make it more palatable.
The correct answer is b—to help fight malaria
B. Answer b is correct. Tonic water with quinine was developed to help fight
malaria.
The correct answer is b—
C. Answer c is incorrect. Quinine does not affect cancerous cells.
The correct answer is b—
D. Answer d is incorrect. Quinine does not have sedative properties.
9. Some plants have developed a mutualistic relationship with parasitoid wasps.
This mutualistic relationship would not occur if—
a. the plant quit producing nectar for the wasp
b. the wasp ceased to live on the plant
c. the plant quit producing volatile compounds that attract the wasp
d. the plant attracted too many caterpillars
The correct answer is c—
A. Answer a is incorrect. Parasitoid wasps are not attracted to the plants by nectar.
The correct answer is c—
B. Answer b is incorrect. The wasps do not live on the plants for this mutualistic
relationship to occur.
The correct answer is c—the plant quit producing volatile compounds that attract the
wasp
C. Answer c is correct. The volatile compounds produced in response to herbivory by
caterpillars attract the wasps to lay eggs inside the caterpillars.
The correct answer is c—
D. Answer d is incorrect. Having more caterpillars would actually aid the wasps.
10. Tomato leaves are not good to eat because—
a. when their tissue is damaged, it generates a foul odor that makes people
sick
b. they do not contain any useful nutrients for animals
c. they contain chemical toxins that will make animals sick
d. when their tissue is damaged, they produce proteinase inhibitors that will
prevent digestive enzyme function in animals
The correct answer is d—
A. Answer a is incorrect. Tomato plants do not produce a foul odor.
The correct answer is d—
B. Answer b is incorrect. They do contain macro- and micronutrients that would be
useful in animal diets.
The correct answer is d—
C. Answer c is incorrect. Tomato plants do not contain toxic chemicals.
The correct answer is d—when their tissue is damaged, they produce proteinase
inhibitors that will prevent digestive enzyme function in animals
D. Answer d is correct. Tomato plants do produce proteinase inhibitors in response to
tissue damage; these have adverse affects on the digestive tract of animals that eat
tomato plants. (The fruit, however, relies on predation by herbivores to disperse
its seed!).
11. A plant lacking R genes would likely—
a. be unable to carry out photosynthesis
b. be susceptible to infection by pathogens
c. be susceptible to predation by herbivores
d. paralyze animals who ingested it
The correct answer is b—
A. Answer a is incorrect. R genes have nothing to do with photosynthesis.
The correct answer is b—be susceptible to infection by pathogens
B. Answer b is correct. R genes confer resistance to pathogen infection; in their
absence the plant would be susceptible to infection.
The correct answer is b—
C. Answer c is incorrect. R genes do not affect animals, but rather target viral,
fungal, or microbial pathogens.
The correct answer is b—
D. Answer d is incorrect. R genes do not affect animals.
12. If a pathogen contains an avr gene not recognized by a plant, the plant will most
likely—
a. develop a disease
b. eliminate the pathogen because it is unrecognized
c. develop proteinase inhibitors
d. develop a different R gene
The correct answer is a—develop a disease
A. Answer a is correct. If the plant cannot recognize an avr gene, it won’t be able to
keep the pathogen in check, and will likely develop a disease.
The correct answer is a—
B. Answer b is incorrect. If the plant does not recognize the avr gene, it will not be
able to mount defenses against the pathogen and won’t be able to eliminate it.
The correct answer is a—
C. Answer c is incorrect. Proteinase inhibitors are not designed for pathogens.
The correct answer is a—
D. Answer d is incorrect. An individual plant is not capable of developing new R
genes in response to unidentified avr genes.
13. Both plant and animal immune systems can—
a. develop memory of past pathogens to more effectively deal with
subsequent infections
b. initiate expression of proteins to help fight the infection
c. kill their own cells to prevent spread of the infection
d. all of the above
The correct answer is d—
A. Answer a is incorrect. Although both plants and animals have a mechanism to
develop memory of past infectious agents, this is not the only answer.
The correct answer is d—
B. Answer b is incorrect. Although both plants and animals initiate new gene
expression to fight infection, this is not the only answer.
The correct answer is d—
C. Answer c is incorrect. Although both plants and animals can kill their own cells to
prevent spread of infection (for example, the hypersensitive response in plants and
the cellular immune response in animals), this is not the only answer.
The correct answer is d—all of the above
D. Answer d is correct. All of these are true: develop memory of past pathogens to
more effectively deal with subsequent infections, establish physical barriers to
infection, initiate expression of proteins to help fight the infection, and kill their
own cells to prevent spread of the infection.
14. In the hypersensitive response, plants might—
a. quickly kill their own cells at the site of infection
b. release hydrogen peroxide and nitric oxide
c. release antimicrobial chemicals
d. all of the above
The correct answer is d—
A. Answer a is incorrect. However, it is not the only one that is correct. In the
hypersensitive response, cells are quickly killed around the site of infection.
The correct answer is d—
B. Answer b is incorrect. However, it is not the only one that is correct. Hydrogen
peroxide and nitric oxide are often produced, largely with the purpose of killing
the plants own cells, but also potentially adversely affecting the pathogen.
The correct answer is d—
C. Answer c is incorrect. However, it is not the only one that is correct.
Antimicrobial chemicals are often produced to deal with the invading pathogen.
The correct answer is d—all of the above
D. Answer d is correct. Answers a, b, and c are all correct.
15. The primary difference between plant and animal long-term recognition of
pathogens is—
a. plants do not produce specific antibodies
b. animal recognition is usually not as long-lasting
c. plants cannot develop plant-wide recognition
d. all of the above
The correct answer is a—plants do not produce specific antibodies
A. Answer a is correct. Plants, unlike animals, are incapable of making antibodies.
The correct answer is a—
B. Answer b is incorrect. Animal recognition can be quite long-lasting, whereas plant
recognition is fairly short-lived.
The correct answer is a—
C. Answer c is incorrect. Plants can recognize pathogens beyond a point of
infection.
The correct answer is a—
D. Answer d is incorrect. Answers b and c are both incorrect.
Challenge Questions
1. Herbal medicine has long relied on plant extracts to cure human disease. Find
three examples of herbal remedies that have been exploited by the pharmaceutical
industry in modern drug production.
Answer—Quinine has been isolated from the bark of Cinchona trees for hundreds of
years to treat malaria.
The pharmaceutical industry found a way to make several synthetic forms of
quinine that are effective in treating some forms of malaria.
Breast cancer can be treated with taxol that is extracted from the Pacific yew.
When the Pacific yew population faced possible extinction, the pharmaceutical industry
found a way to synthesize taxol.
Opium poppies have long been used for their narcotic effect, both legally and
illegally. The active ingredient is morphine. Understanding the biochemical structure of
morphine and its affects on the human nervous system has lead to the synthesis of pain
killers for medicinal use.
2. Diagram the events surrounding infection of a plant by a fungal pathogen.
Include strategies used both by the pathogen and by the host plant.
Answer—Use Figure 40.4 as a sample diagram. Add the following information to the
labels that already occur on the diagram:
Plant epidermal cell—Layers of cutin make it difficult for fungi to get past the
plant’s surface.
Fungus entering stoma—Although essential for gas exchange and transpiration,
stoma are the weak link in the plant’s first line of defense. Fungi locate stoma and enter
through that opening.
Plant cell—Plant cells can sometimes recognize the fungus by proteins it releases.
This can trigger a hypersensitive response, which kills the fungus and prevents further
spread of the infection.
3. If you wanted to find new phytopharmaceuticals that could fight cancer, how
would you go about identifying new compounds?
Answer—If you were looking for a new phytopharmaceutical to fight cancer, you could
start by studying cultures that have reduced cancer rates. Try to find a correlation
between diet or herbal medicine used. You find a very promising species of plant and
determine how it is prepared as a food or remedy. Use this information to begin isolating
compounds from the plant and testing them in cultured cell lines. This is the approach
that an ethnobotanist would use. Ethnobotanists are trained in plant biology,
biochemistry, sociology, and anthropology.
4. Herbivory and infestation by pests and pathogens are detrimental to plants. Many
plants have developed toxins, or secondary compounds, to harm or deter these
activities. Why don’t all plants do this, and why don’t plants develop a whole
arsenal of defenses?
Answer—First of all, these chemical defenses are ultimately products of evolution,
namely through random mutations. The defenses a plant has, have been brought about by
favorable mutations and natural selection. Hence, a plant really has no way to decide
what compounds it wants to produce.
Second, these secondary compounds require energy to produce energy that comes
at a cost to overall productivity. A plant could produce a lot of toxic substances, but this
may lead to low levels of plant productivity. Although herbivory can be detrimental to
plant productivity, energetic balance is important when producing secondary compounds.