CLEP Biology Ecosystems and Energy Flow 4

Question 1

In the carbon cycle, which process is responsible for transferring carbon from the atmosphere into marine organisms?

Accepted Answer

Photosynthesis by marine phytoplankton

Answer

Marine phytoplankton fix atmospheric CO₂ dissolved in seawater through photosynthesis, forming the base of marine food webs.

Question 2

Eutrophication of a lake following nutrient runoff leads to fish kills primarily because:

Accepted Answer

Decomposition of dying algae depletes dissolved oxygen

Answer

Massive algal blooms die and sink; aerobic decomposition of this organic matter consumes most dissolved oxygen, creating hypoxic conditions that kill fish.

Question 3

Which of the following is an example of a keystone species exerting top-down control on an ecosystem?

Accepted Answer

Sea otters limiting sea urchin populations, preserving kelp forests

Answer

Sea otters are a classic keystone predator; by controlling sea urchin numbers, they prevent overgrazing of kelp, maintaining entire kelp forest ecosystems.

Question 4

In comparing aquatic and terrestrial ecosystems, which statement is generally true about energy pyramids?

Accepted Answer

In aquatic ecosystems, biomass of producers often equals or is less than that of consumers

Answer

In many aquatic ecosystems, especially open oceans, phytoplankton reproduce so rapidly that consumers (zooplankton) can maintain biomass equal to or greater than producers.

Question 5

Sulfur enters the biotic component of an ecosystem primarily through:

Accepted Answer

Plant uptake of sulfate (SO₄²⁻) ions from soil solution

Answer

Plants absorb sulfate ions dissolved in soil water and incorporate sulfur into amino acids such as cysteine and methionine, entering the food web.

CLEP Practice Test

CLEP Practice Test

CLEP Biology Ecosystems and Energy Flow 4