Desert plant populations have evolved sophisticated physiological

Question

Desert plant populations have evolved sophisticated physiological behavioral traits that aid survival in arid conditions. Some send out long, unusually deep taproots; others utilize shallow but widespread roots, which allow them to absorb large, intermittent flows of water. Certain plants protect their access to water. The creosote bush produces a potent root toxin which inhibits the growth of competing root systems. Daytime closure of stomata exemplifies a further genetic adaptation; guard cells work to minimize daytime water loss, later allowing the stomata to open when conditions are more favorable to gas exchange with the environment. Certain adaptations reflect the principle that a large surface area facilitates water and gas exchange. Most plants have small leaves, modified leaves (spines), or no leaves at all. The main food-producing organ is not the leaf but the stem, which is often green and non-woody. Thick, waxy stems and cuticles, seen in succulents such as cacti and agaves, also help conserve water. Spines and thorns (modified branches) protect against predators and also minimize water loss.   1 
 1. The passage refers to the spines and thorns of desert plants as

I. genetically evolved structural adaptations that protect against predation
II. genetic modifications that aid in the reduction of water loss
III. structures that do not participate directly in food production

(A) I only
(B) III only
(C) I and II only
(D) II and III only
(E) I, II and III

2 
 2. The author suggest that the guard cells of desert plants act to do which of the following?

I. Facilitate gas and water exchange between the plants and their surroundings
II. Cause the stomata of desert plants to remain closed during daytime hours
III. Respond to sudden, heavy rainfalls by forcing the plants’ stomata to open

(A) I only
(B) II only
(C) III only
(D) I and II only
(E) I, II, and III

3 
 3. The passage suggests that which of the following weather-related conditions would most benefit plants with shallow root systems?

(A) An unusually prolonged drought
(B) A windstorm
(C) A flash flood
(D) A light spring rain
(E) A winter snowfall

4 
 4. The adaptations of desert plants to their environment would tend to support the statement that

(A) the rate of genetic evolution is greater in the desert than in more temperate surroundings
(B) structures in a plant which usually perform one function may, under certain conditions, perform different functions
(C) while the amount of leaf surface area is critical for a desert plant, it is much less so for plants in most other environments
(D) desert plants do not have many physiological and behavioral traits in common with other plants
(E) desert plants could probably adapt to life in a variety of harsh ecosystems

Sajjad1994 · Accepted Answer

Official Explanation

Topic and Scope:    Desert plant adaptations and how aid in these plants’ survival.

Purpose and Main Idea:    The author is trying to describe the physiological traits that desert plants have adapted in order to survive in arid conditions.

Paragraph Structure:    The first paragraph describes some general adaptations. The second paragraph discusses adaptations based on the principle that a large surface area facilitates water and gas exchange.

1. The passage refers to the spines and thorns of desert plants as

Explanation

The whole passage focuses on structural and behavioral adaptations that desert plants have made in order to survive. While the word  “genetic”  is used only once (in the last sentence of paragraph 1), it’s clear that many of these modifications are genetic. Spines and thorns, which are identified in the second paragraph as modified leaves and branches, are inferably among these genetic adaptations. In the last sentence, it’s further stated that they protect against predation  (I)  and also that they help minimize water loss  (II) . Option  III  is confirmed in the third sentence of the second paragraph: most of a desert plant’s food is produced in its stem, not in its leaves, so it’s pretty clear that spines and thorns (again, modified leaves and branches) have little or nothing to do with food production.

ANSWER: E

2. The author suggest that the guard cells of desert plants act to do which of the following?

Explanation

Like question 1, this is another detail question, this time focusing on the functioning of guard cells, mentioned in the sentence that concludes paragraph 1. This sentence discusses two closely related plant features: the stomata and the guard cells. You read first that daytime closing of the stomata is an adaptation that helps to minimize daytime water loss. The second half of the sentence clearly implies that it’s the guard cells that control this opening and closing of the stomata. So, the guard cells force the stomata to close during the day, to minimize water loss, and then they later cause the stomata to open, when conditions for gas exchange between the plant and its environment are more favorable. The first two options are thus clearly suggested. The third option, however, is an unjustified inference. Nothing at all is stated to link the functioning of guard cells to sudden downpours.

ANSWER: D

3. The passage suggests that which of the following weather-related conditions would most benefit plants with shallow root systems?

Explanation

The stem is looking for the weather-related condition that would especially benefit plants with shallow root systems. Shallow root systems are mentioned up in the second sentence, and the point is that these specially adapted roots allow desert plants to take advantage of heavy, irregular flows of water. One example would be a very heavy, torrential downpour. The only choice that comes close to this is a flash flood. Flash floods result from unexpected, torrential rainfall.  (A) and (B)  are impossible; neither drought nor windstorms involve water.  (D)  won’t work because a light rain doesn’t fit with the idea of a large, sudden quantity of water.  (E) , finally, is pretty impossible , too. First, this choice doesn’t suggest a heavy, intermittent snowfall, and second, nothing is said in the passage to suggest snow would be of special benefit to shallow rooted plants.

ANSWER: C

Hope it helps

KarishmaB · Answer

2. The author suggest that the guard cells of desert plants act to do which of the following?

I. Facilitate gas and water exchange between the plants and their surroundings
II. Cause the stomata of desert plants to remain closed during daytime hours
III. Respond to sudden, heavy rainfalls by forcing the plants’ stomata to open

(A) I only
(B) II only
(C) III only
(D) I and II only
(E) I, II, and III

Facilitate is to assist. 
"Daytime closure of stomata exemplifies a further genetic adaptation; guard cells work to minimize daytime water loss, later allowing the stomata to open when conditions are more favorable to gas exchange with the environment."

Guard cells close and later allow the stomato to open. Hence they assist in the way gas and water exchange happens. 
Also, stomato are closed during daytime by guard cells (which later allow them to open)
We can imply both (I) and (II) from the passage.

Answer (D)

KarishmaB · Answer

4. The adaptations of desert plants to their environment would tend to support the statement that

(A) the rate of genetic evolution is greater in the desert than in more temperate surroundings
(B) structures in a plant which usually perform one function may, under certain conditions, perform different functions
(C) while the amount of leaf surface area is critical for a desert plant, it is much less so for plants in most other environments
(D) desert plants do not have many physiological and behavioral traits in common with other plants
(E) desert plants could probably adapt to life in a variety of harsh ecosystems

Note this:
Most plants have small leaves, modified leaves (spines), or no leaves at all. The main food-producing organ is not the leaf but the stem , which is often green and non-woody. Thick, waxy stems and cuticles, seen in succulents such as cacti and agaves, also help conserve water.  Spines (modified leaves) and thorns (modified branches) protect against predators and also minimize water loss .

Food is not produced by leaves but my stem. Modified leaves and branches serve other purposes - protect against predators and minimise water loss.

It is clear that (B) holds.

The other options are not implied.

Sajjad1994 · Answer

Official Explanation

4. The adaptations of desert plants to their environment would tend to support the statement that

Explanation

The second paragraph contains several examples of structures that in desert plants perform different functions than those they normally perform in plants in other environments. Spines and thorns in desert plants are modified leaves and branches, to reduce water loss. And as a result of their lack of normal leaves, most desert plants produce their food in their green, fleshy stems. As for the wrong choices, three of them— (A), (D), and (E)—simply can’t be answered.

There’s no information to support any of these statements. Finally, in choice  (C) , while the passage does indicate that a small leaf surface area is a critical factor for desert plants, nothing suggests that leaf surface area isn’t critical for plants in most other environments. Since the general principle is that a large surface area facilitates gas and water exchange one can infer that the larger leaf surface area of other plants helps in this process.

Answer: B

Hope it helps

ARSarkar · Answer

Sajjad1994  and  KarishmaB  ,

How can we say performing different action? We can say that some sophisticated work is done.

I think option D is correct - "desert plants do not have many physiological and behavioral traits in common with other plants" . The passage says -  Desert plant populations have evolved sophisticated physiological behavioral traits that aid survival in arid conditions . So, the traits of desert plants are dissimilar to those of non-arid region plants.
Please explain. 
Regards,
Ratan.

KarishmaB · Answer

We know that "Desert plant populations have evolved sophisticated physiological behavioral traits that aid survival in arid conditions" but that does not mean they don't have many common traits too. For example, they do have stomata (like other plants), they do exchange gases (like other plants) etc. 
Hence (D) is not correct. 
But (B) is because we are given that certain structures do perform functions different from what they usually perform.

manish8242 · Answer

Why E is not Correct in Q4?

manish8242 · Answer

Hi,sajjad

How can we determine that Branches doesn't take part in food production? In the passage it is just said that food is Produced MAINLY in Stem and not Leaves. So it might be possible leaves play a minor role in that. Also nothing is said about Branches. The option 3 in Q1 doesn't include the word 'LIKELY' it directly says a bold line so how can we say its right

Sajjad1994 · Answer

Read the text which is relevant to  III

"Most plants have small leaves, modified leaves (spines), or no leaves at all. The main food-producing organ is not the leaf but the stem, which is often green and non-woody."

and

"Spines and thorns (modified branches) protect against predators and also minimize water loss."

The passage says:  the main food-producing organ is the stem, not the leaf.
If the main organ is the stem, that means leaves are not the main site so leaves (and hence spines, which are modified leaves) do not play the main role, but could they still participate directly in food production?

For spines:  since they are modified leaves, they typically lack chlorophyll and do not perform photosynthesis so they indeed do not participate directly in food production.

For thorns (modified branches): branches in many plants can be photosynthetic if green, but the passage says the stem is the main food-producing organ, and these thorns are likely not green/photosynthetic (implied by their protective role and minimization of water loss). The passage does not explicitly say thorns are photosynthetic, so we can infer they do not participate directly in food production.

If you think maybe green branches could photosynthesize, so modified branches (thorns) might still do a bit of photosynthesis, then III might seem not necessarily true. But the passage’s wording suggests that in these desert plants, the stem is the primary photosynthetic organ, and spines/thorns are specialized for protection/water reduction, not food production.

Spines = modified leaves, hence not main food production (and since they’re spines, not green, no photosynthesis).
Thorns = modified branches, hence protective, water loss reduction, no mention of photosynthesis.

III can be inferred.

KarishmaB · Answer

Let's read the question stem carefully:

Question Stem: The adaptations of desert plants to their environment would tend to support the statement that

We are given that the desert plants have adapted to the lack of sufficient water (stems conserve water, spines and thorns minimize water loss and protect against predators).

Does this mean that they will adapt to life in a variety of harsh ecosystems?

We cannot say that. They have adapted to desert climate. Will they adapt to acidic environments? No info. Will they adapt to extremely cold environment? No info. There is nothing that says that they will adapt to a variety of harsh ecosystems. We just know that they have adapted to a desert life.

Hence (E) is not correct.

Desert plant populations have evolved sophisticated physiological

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Desert plant populations have evolved sophisticated physiological

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