Problem 3 - AP Psychology Premium Prep 2021

Question

In a pond ecosystem, spring rains trigger an expansion of species at levels of the food chain. Runoff from nearby hills brings nutrients which, when combined with warming temperatures, trigger an algae bloom. The populations of small protozoans such as plankton expand by ingesting the algae. These plankton, subsequently, are consumed by small crustaceans such as crayfish, which ultimately become prey for fish such as catfish or carp. In this ecosystem, which of the following accurately describes the crayfish? (A) They are producers. (B) They are primary consumers. (C) They are secondary consumers. (D) They are tertiary consumers.

Step-by-Step Solution

Answer

In the given pond ecosystem, crayfish consume plankton, which are primary consumers. Therefore, crayfish are classified as secondary consumers. The correct answer is (C) They are secondary consumers.

Step 1: Understand the roles in the food chain

In the food chain, there are three main roles: 1. Producers: These are organisms that produce their own food through photosynthesis, such as plants and algae. 2. Consumers: These are organisms that consume other organisms to obtain their energy. Consumers can be further classified into primary, secondary, tertiary, and quaternary consumers. 3. Decomposers: These are organisms that break down dead organic matter and recycle nutrients into the ecosystem. Examples include fungi and bacteria.

Step 2: Determine the role of crayfish in the food chain

In the given ecosystem, crayfish are mentioned as eating small protozoans such as plankton. To classify crayfish in the food chain, we must identify what kind of consumer they are. We are given that: 1. Algae are producers. 2. Plankton feeds on algae, which makes them primary consumers. 3. Crayfish feeds on plankton, which makes them secondary consumers because they consume the primary consumers. Based on this information, the most fitting classification for crayfish in the ecosystem is secondary consumers.

Step 3: Select the correct answer choice

Based on our understanding of the food chain and the roles in it, we can now confidently choose the correct answer from the given options: (A) They are producers. (B) They are primary consumers. (C) They are secondary consumers. (D) They are tertiary consumers. The correct answer is (C) They are secondary consumers.