Question 1

Imagine that a coyote tobacco plant is being eaten by M. sexta caterpillars. In response to these specific herbivores, the tobacco produces volatile chemicals that can travel through the air. Why?

Accepted Answer

The volatile chemicals are released to attract insect predators that will prey on the caterpillars, thus protecting the plant from further damage.

Question 2

Which of the following is TRUE of protein-based plant chemical defenses?

Accepted Answer

Plants and animals use the same 20 amino acids to construct proteins, but some plants have additional amino acids that can act as defenses.

Question 3

Consider an experiment in which two species of plants, A and B, are grown in separate pots in the same enclosure, either with an herbivorous insect that eats only plant A (treatment) or with no herbivores (control). How do you expect growth for species B will differ between the two treatments?

Accepted Answer

The answer of Consider an experiment in which two species...

Question 4

In what type of environment would you expect to find a plant that spends most of its resources on defenses, rather than growth?

Accepted Answer

The answer of In what type of environment would you...

Question 5

A researcher notices that in a given environment, plants tend to grow rapidly and produce few chemical and mechanical defenses. What can she deduce about this environment?

Accepted Answer

Rapid growth and low production of defenses suggest that the environment is likely to be nutrient-rich, as the plants do not require a lot of resources to allocate toward defenses.

Question 6

One of the first chemotherapy drugs, vincristine, was discovered in the Madagascar periwinkle and is a(n):

Accepted Answer

Vincristine is an alkaloid, which is a naturally occurring compound with a nitrogen-containing ring structure. The Madagascar periwinkle is one of the primary sources of this compound, which has been used as a chemotherapeutic agent since the 1960s.

Question 7

Because ant-plants must continually provide sugars, protein, and fats to ensure a large enough population of defending ants when herbivores attack, ant defense could be considered a(n) _____ form of defense.

Accepted Answer

Constitutive defenses are those that are always present in the plant, regardless of whether there is a threat present. Since ant-plants must continually provide for their defending ants to maintain a ready defense against herbivores, this type of defense is considered constitutive, as it is not induced by the presence of a threat but is a constant feature of the plant.

Question 8

Nicotiana attenuata is subject to damage by both generalist and specialist herbivores. The production of nicotine is not effective against one specialist, M. sexta. If an individual of N. attenuata is being eaten by both M. sexta and a generalist herbivore, what would you expect to happen?

Accepted Answer

The production of nicotine is not effective against M. sexta, so its production would not be stimulated by the presence of the specialist herbivore. However, the presence of a generalist herbivore would likely stimulate the production of nicotine as a defense mechanism. Additionally, the individual may also produce chemicals that attract insects that prey on different life stages of M. sexta. This would provide a double defense strategy against both specialist and generalist herbivores.

Question 9

Which of the following is NOT analogous to a sensory pathway by which plants can detect herbivores?

Accepted Answer

Plants do not have visual sensory pathways, so sight is not analogous to the sensory pathways they use to detect herbivores. However, they do have taste (chemical receptors on leaf surfaces), smell (volatile compounds released in response to damage), and sound (vibrations caused by feeding or movement of herbivores).

Question 10

When a coyote tobacco plant releases volatile signals in response to M. sexta caterpillars, this is an example of a(n) _____. The presence of hairs on the leaf of a milkweed plant is an example of a(n) _____.

Accepted Answer

The release of volatile signals by the coyote tobacco plant is an example of an inducible defense, as it is induced in response to the presence of M. sexta caterpillars. On the other hand, the presence of hairs on the leaf of a milkweed plant is an example of a constitutive defense, as it is always present on the plant and does not require induction. Therefore, the best choice is D - inducible defense for the coyote tobacco plant and constitutive defense for the milkweed plant.

Question 11

Consider this figure from your text.  How do you think the daily increase in leaf area of the clay-origin and sand-origin species, when growing in the unprotected clay and sandy habitats, would change in response to a large increase in far-red light?

Accepted Answer

The graph shows that an increase in far-red light leads to a decrease in daily leaf area increase for both clay-origin and sand-origin species when they are growing in unprotected clay and sandy habitats. Therefore, it is likely that a large increase in far-red light would result in a lower daily increase in leaf area for both species in both habitats.

Question 12

You are studying inducible defenses against herbivory in a plant by pretreating some of the plants with a small amount of simulated herbivory damage before exposing them to herbivores. You notice that in one of your experimental lineages the mature leaves, but not the developing leaves or meristematic tissues, receive just as much damage from insects whether they receive the pretreatment or not. You hypothesize that, in this lineage, _____ has been down-regulated.

Accepted Answer

The answer of You are studying inducible defenses against herbivory...

Question 13

A seed from a yew tree germinates on the forest floor. During the first few months of its life, the sapling dedicates most of its resources to increasing in height rather than producing the defensive compound taxol. What is this allocation of resources an example of?

Accepted Answer

The allocation of resources towards height growth instead of producing taxol is an example of a trade-off, as the plant is sacrificing one trait for another.

Question 14

Volatile chemicals that escape from plants into the air:

Accepted Answer

Volatile chemicals can assist parasitic plants in locating hosts, attract predators to herbivore-damaged plants, and play a role in systemic acquired resistance. However, they can sometimes be released due to tissue damage without an adaptive function.

Question 15

Consider an experiment in which two species of plants, A and B, are grown in separate pots in the same enclosure, either with an herbivorous insect that eats only plant A (treatment) or with no herbivores (control). How do you expect allocation to defense for species B will differ between the two treatments?

Accepted Answer

BSpecies B's allocation to defense will not differ in the presence of an herbivorous insect that only eats plant A if it relies on physical defenses like hairs or spines, as these are constitutive defenses not influenced by the presence of herbivores that do not target them. However, if species B relies on chemical defenses, which can be induced by the presence of herbivores or signals from other plants being attacked, its allocation to defense could be higher in the treatment due to the presence of the herbivorous insect attacking plant A, potentially triggering a defensive response in plant B.

Question 16

Many plants produce volatile (airborne) compounds when attacked by herbivores. In what ways do these compounds aid the plant in protecting itself?

Accepted Answer

The answer of Many plants produce volatile (airborne) compounds when...

Question 17

Cassava roots release the toxin hydrogen cyanide when their cells are damaged.

Accepted Answer

This is true. Cassava roots contain a compound called linamarin which, when the cassava is damaged, can be broken down into hydrogen cyanide. This is a natural defense mechanism of the cassava plant.

Question 18

The hard mineral silica plates found in some grasses is an effective defense because silica:

Accepted Answer

Silica plates are abrasive and can wear down the mouthparts of insects. This makes it more difficult for them to feed efficiently and may deter them from feeding on the grass altogether.

Question 19

Three isolated populations of a single species have different histories: population A recently suffered damage from a virus; population B was recently exposed to an herbivorous caterpillar, L. sexta; and population C had no recent exposure to pathogens or herbivores. All three populations are now free of pathogens and herbivores and have the same total biomass. You decide to do an experiment in which you introduce L. sexta into all three populations. How do you expect the three populations to respond?

Accepted Answer

Population B has recently been exposed to L. sexta and has therefore developed some resistance to it. Population C has had no recent exposure to pathogens or herbivores and is therefore likely to be the most susceptible to damage from L. sexta. Population A has recently suffered damage from a virus, which may have weakened the plants and made them more susceptible to damage from L. sexta. Therefore, we expect that plant biomass will be highest in B, then C, and lowest in A.

Question 20

One of the reasons that so many farmers spray pesticides on their crops is to decrease the amount of energy the crops need to invest in the production of hairs on leaves to deter insect herbivores.

Accepted Answer

Farmers spray pesticides on their crops primarily to protect them from pests and diseases, not to reduce the energy crops spend on developing physical deterrents like leaf hairs.

Quiz 32: Plant Defense: Keeping the World Green