Question 1

B. thuringiens bacteria is a remarkable resource for researchers and farmers alike when it comes to pest control. Why?

Accepted Answer

Bacillus thuringiensis (Bt) is known for producing insecticidal toxins (B) that are harmful to a variety of insect pests but are generally considered safe for humans and other non-target organisms. These toxins have been utilized in organic farming and in genetically engineered crops to provide resistance to pests (D), making Bt a valuable tool in agricultural biotechnology and pest management strategies.

Question 2

Consider the following situation: A tomato grower has heard that jasmonic acid can be used to stimulate plant defenses against herbivores. Because jasmonic acid is a naturally occurring compound, he decides he will expose his crops to it instead of using chemical pesticides to protect his crops. Which of the following is the MOST likely outcome of the grower's decision to use something other than traditional pesticides?

Accepted Answer

When exposed to jasmonic acid, plants typically allocate resources to defense rather than fruit production, which could result in fewer crops. This is especially true if the herbivores have a significant impact on the overall health and production of the plants. Option A is incorrect because methyl-jasmonic acid is simply a modified version of jasmonic acid, but both compounds are known to elicit plant defenses. Option C is incorrect because although plants may grow more slowly in the presence of jasmonic acid due to increased allocation of resources to defense, this does not necessarily mean that herbivores will have less to eat and will leave; they may simply consume the plants more slowly. Option D is also incorrect because herbivores are likely to consume more plant tissue if it is available, so increased tissue growth may actually attract more herbivores.

Question 3

A researcher has several N. attenuata plants growing in a field. He encloses one of these plants in an "airtight" and "sound-tight" plastic container, into which he constantly pumps air from a nearby canister. He then introduces M. sexta caterpillars into this container and assesses the expression of defensive compounds in the neighboring (nonenclosed) N. attenuata plants. What will he find?

Accepted Answer

The researcher has enclosed the N. attenuata plant in a container that is airtight and soundproof, which means that any signals produced by the plant will not be able to travel through the air to neighboring plants. Therefore, the plants surrounding the N. attenuata plant with the caterpillars will not demonstrate an increase in defensive compounds.

Question 4

Would a plant that is exposed first to a virus and then to an herbivore be expected to have more than, less than, or the same amount of damage from herbivory as a plant exposed to just the herbivore and why?

Accepted Answer

The answer of Would a plant that is exposed first...

Question 5

Imagine two different species of caterpillar are feeding on a N. attenuata plant. One of these species is M. sexta. How can this plant differentiate between M. sexta (which are unaffected by the plant's usual chemical defenses) and the other caterpillar species?

Accepted Answer

The saliva of M. sexta caterpillars has a distinct chemical composition which is recognized by N. attenuata plants, triggering the production of volatile chemical signals. This allows the plant to differentiate between M. sexta and other caterpillar species and mount a specific defense response.

Question 6

The observation that agricultural pests are evolving resistance to the Bt toxins suggests that farmers should plant _____ of their fields with non-Bt- producing varieties.
A)more
B)less

Accepted Answer

Planting more non-Bt-producing varieties can help reduce the selection pressure on pests to evolve resistance to Bt toxins.

Question 7

Which of the following would you expect to oppose density-dependent mortality in influencing the diversity of tropical forests?

Accepted Answer

Density-dependent mortality would be influenced by factors such as competition and predation, which would have greater impact for species that depend on specific types of pollinators or that cannot reproduce without a partner. Wind-pollinated species do not depend on specific pollinators, and therefore would not be as affected by density-dependent mortality as species with high species-specificity among pollinators.

Question 8

Which of the following statements is TRUE regarding plant defenses?

Accepted Answer

None of the statement is true.

A) This statement is not always true. Some plants may have trade-offs in allocating resources to different types of defenses, and may prioritize defense against one type of attacker over another. 
B) Plants allocate resources according to their specific growth conditions, and if a plant is in a competitive environment, it may allocate more resources to growth rather than defense. 
C) Plant resource allocation is complex and influenced by multiple factors, such as the type of attacker and the plant's own physiological state. 
D) Constitutive defenses are always present in a plant, even in the absence of predators or infection, while inducible defenses are only produced in response to a specific threat. Plants may still mount an inducible response even if they have constitutive defenses.

Question 9

You are studying a group of closely related plant species that are fed upon by numerous herbivores. One of these herbivores is a caterpillar species that has evolved the ability to sequester the alkaloid that is this plant group's principal defense against all herbivores. You then construct a phylogeny of the plant species. You expect to find that the most recently radiated species in the group that co-occur with the caterpillar:

Accepted Answer

The answer of You are studying a group of closely...

Question 10

The "escape and radiate" hypothesis predicts that rates of speciation would be higher in plant and insect groups that are engaged in a coevolutionary arms race. Assume that there is a plant species that evolves a new antiherbivore compound, and then an insect that evolves resistance. Which of the following graphs would you expect if the scenario above were to occur?

Accepted Answer

The answer of The "escape and radiate" hypothesis predicts that...

Question 11

The presence of herbivorous insects on plant populations is thought to contribute to the diversity of both plants and insects through both ecological and evolutionary processes. Which of the following statements describes a scenario in which plant diversity increases due to an evolutionary process involving natural selection by herbivorous insects?

Accepted Answer

In this scenario, a mutation arises in an insect subpopulation that allows them to tolerate or even metabolize the toxic alkaloids produced by the plant. This allows the insects to feed on a previously toxic plant, reducing the competition with other insect species and reducing the overall predation pressure on the plant. Over time, the plant may evolve to produce even more toxic alkaloids, leading to a continued cycle of coevolution and increasing diversity. This is an example of sympatric speciation through natural selection, as the plant and insect populations diverge due to their interactions with each other.

Question 12

Plants only produce defenses that are effective against a large array of herbivores; plants are not equipped to mount tailored defenses in response to specific predators.

Accepted Answer

Plants are able to mount tailored defenses in response to specific predators, such as producing chemicals that deter certain herbivores but not others. This is known as induced defense.

Question 13

You are studying an area of tropical forest containing a high density of rare tree species and a low density of common species. You find that wild pigs capable of eating all plant seeds indiscriminately have recently greatly increased in number and that these pigs are now the most important agents of seed mortality in this forest. How would you expect the diversity of tree species in the forest to respond in the future?

Accepted Answer

An increase in seed predation by generalists, like wild pigs, reduces the survival advantage of being a rare species because these predators do not discriminate between common and rare seeds. This indiscriminate predation tends to affect rare species disproportionately, as they have fewer seeds available to begin with, leading to a decline in tree diversity over time.

Question 14

Fractions of a field of Bt crops planted with non-Bt-expressing varieties:

Accepted Answer

The answer of Fractions of a field of Bt crops...

Question 15

Most plants produce nicotine constantly, as this compound deters most herbivores and is relatively "inexpensive" to make (given the abundance of nitrogen in the atmosphere).

Accepted Answer

Not all plants produce nicotine constantly. Nicotine production can vary depending on the plant species and environmental factors.

Question 16

Which of the following statements are consistent with the "escape and radiate hypothesis" of Ehrlich and Raven?

Accepted Answer

The answer of Which of the following statements are consistent...

Question 17

The phylogeny of a group of species you are studying shows that fast growth and low investment in defense is ancestral in the group, while a recently diverged subgroup containing 10% of the group's species is characterized by slow growth and epidermal hairs filled with a caustic agent. You hypothesize that:

Accepted Answer

The answer of The phylogeny of a group of species...

Question 18

If plant life was never subjected to herbivores/predators, how would plant diversity be affected?

Accepted Answer

Without herbivores/predators, there would be no pressure on plants to evolve defense mechanisms and adaptations, leading to less diversity among plant species.

Question 19

What are the components of the Janzen-Connell hypothesis?

Accepted Answer

The answer of What are the components of the Janzen-Connell...

Question 20

According to the Janzen-Connell hypothesis, for pathogens or herbivores to contribute to the maintenance of diversity requires that:

Accepted Answer

The answer of According to the Janzen-Connell hypothesis, for pathogens...

Quiz 32: Plant Defense: Keeping the World Green