AP Biology : 8.2 Energy Flow Through Ecosystems – Exam Style questions with Answer- MCQ

Question

Refer to the following food web.

What is a role of the fox in this food web?
(A) producer
(B) primary consumer
(C) secondary consumer
(D) tertiary consumer

▶️Answer/Explanation

Ans:

(C) The fox is a secondary consumer because it gets its energy from a
primary consumer (the kangaroo rat). Choice (A) is incorrect because
the producer in this food web is grass; foxes are not photosynthetic and
cannot be producers. Since the fox shown in this food web does not
consume the producer, the fox cannot be a primary consumer, so choice
(B) is incorrect. Tertiary consumers get their energy from secondary
consumers. In the food web shown, the mountain lion and the eagle are
tertiary consumers; the fox is not a tertiary consumer, so choice (D) is
incorrect.

Question

Refer to the following food web.

The application of rat poison in the area results in the elimination of the kangaroo rat population. Which of the following is the most likely
effect of this event?
(A) The biomass of the producers will increase.
(B) The number of foxes in the ecosystem will likely increase.
(C) The amount of food available to the antelope will decrease.
(D) The mountain lions will eat fewer antelopes and more eagles.

▶️Answer/Explanation

Ans:

(A) Kangaroo rats eat grass. If the kangaroo rat population was
eliminated, less grass would be consumed, and the biomass of the
producers (the grass) would most likely increase. The foxes feed on the
kangaroo rats, so the elimination of the kangaroo rats would result in
less food for the foxes. In that case, the number of foxes would likely
decrease, not increase, so choice (B) is incorrect. Choice (C) is
incorrect because fewer kangaroo rats would mean more grass for the
antelopes, not less. Mountain lions do not eat eagles in this food web,
so choice (D) is incorrect.

Question

Why is it unlikely that a food web would contain more than five trophic levels?
(A) 90% of the nutrients are lost in each transfer to the next trophic level.
(B) 90% of the energy is lost in each transfer to the next trophic level.
(C) Decomposers can efficiently recycle nutrients for up to four trophic levels.
(D) The biomass at the producer level cannot exceed the biomass at the primary consumer level.

▶️Answer/Explanation

Ans:

(B) On average, 90% of the energy at a given trophic level is used in
metabolic processes at that level or is lost as heat and is not transferred
to the next trophic level. Choice (A) is incorrect because most nutrients
are transferred to the next trophic level when food is consumed.
Decomposers break down dead organic matter, regardless of the
number of trophic levels, so choice (C) is incorrect. The biomass at the
producer level must be larger than the biomass at the primary consumer
level, so choice (D) is incorrect.

Question

Why are the metabolic rates of smaller organisms generally higher than those of larger organisms?
(A) Smaller organisms have shorter life spans and therefore must accomplish more activities in less time. This requires a faster metabolic rate.
(B) Smaller organisms have a higher surface area to volume ratio than larger organisms and lose more heat to the environment.
(C) Smaller organisms are more likely to be ectothermic than larger organisms and therefore need a higher metabolic rate to compensate for this.
(D) Smaller organisms consume less food per gram of body weight than larger organisms and therefore need a higher metabolic rate to compensate for this.

▶️Answer/Explanation

Ans:

(B) Smaller organisms do have a greater surface area to volume ratio
than larger organisms and lose more heat to their environment per gram
of body weight, so smaller organisms need a higher metabolism to help
mitigate the heat loss. Not all small organisms have a shorter life span
than larger organisms, so choice (A) is incorrect. Choice (C) is
incorrect because not all small organisms are ectothermic. Also,
ectothermic animals cannot internally control their metabolic rate;
ectotherms are dependent upon environmental temperatures to
influence their metabolic rate. Smaller organisms do not necessarily
consume less food per gram of body weight; in fact, the higher
metabolic rate of smaller organisms may require that these small
organisms consume more food per gram of body weight, so choice (D)
is incorrect.

Question

Refer to the following food web. The arrows show the direction of the flow of energy, and species are represented by roman numerals.

Which species in this food web is most likely a producer?
(A) I
(B) II
(C) III
(D) IV

▶️Answer/Explanation

Ans:

(D) Producers transfer energy to other trophic levels and do not receive
energy from any trophic level. IV is the only member of this food web
that sends energy to other members but does not receive energy from
other members of the food web.

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