Question

why is the number of producers usually much greater than the number of other organisms in an ecosystem?
a. producers have access to more nutrients than other organisms do.

b. competition for resources is greater for other organisms than for producers.

c. producers need to provide enough energy to satisfy the needs of other organisms.

d. available energy decreases as it is transferred from producers to other organisms.

Explanation:

In an ecosystem, energy transfer follows the 10% rule (only about 10% of energy is passed to the next trophic level). Producers (like plants) capture energy from the sun. As energy moves up (to herbivores, carnivores, etc.), available energy decreases. So, to support higher trophic levels (other organisms), there must be a larger number of producers to generate enough initial energy.

• Option A: Producers don't have "more nutrients"—nutrients cycle, and all organisms use them. Eliminate.
• Option B: Competition for resources is not the reason for producer numbers; producers are the base. Eliminate.
• Option C: Producers don't "need to provide energy" to satisfy others—energy transfer is passive (consumption), not intentional provision. Eliminate.
• Option D: Correct, as energy loss (decrease) in transfer means more producers are needed to sustain the energy requirements of higher trophic levels.

Answer:

D. Available energy decreases as it is transferred from producers to other organisms.