In a food chain, what is the key difference between primary consumers and secondary consumers in terms of what they eat?

Introduction / Context:
This question relates to ecology and the structure of food chains and food webs. Food chains describe how energy flows from one organism to another. Understanding which organisms are producers, primary consumers, and secondary consumers is fundamental to basic environmental science.

Given Data / Assumptions:

• Producers are green plants or algae that make their own food through photosynthesis.
• Primary consumers feed directly on producers.
• Secondary consumers feed on primary consumers.
• The question focuses on the difference in diet between these two consumer levels.

Concept / Approach:
In a typical simple food chain, energy begins with plants, passes to herbivores that eat plants, and then to carnivores that eat herbivores. Herbivores are primary consumers because they are the first level that consumes other organisms, and those organisms are plants. Secondary consumers eat primary consumers and are usually carnivores or omnivores. The correct option must capture that primary consumers feed on plants only, while secondary consumers feed on primary consumers.

Step-by-Step Solution:

Verification / Alternative check:
Textbook diagrams of food chains consistently show arrows from plants to herbivores and then from herbivores to carnivores. For example, grass to grasshopper to frog to snake. The grasshopper is a primary consumer because it eats plants alone, while the frog is a secondary consumer because it eats the grasshopper. This pattern confirms the wording given in option a.

Why Other Options Are Wrong:

• Option b is wrong because primary consumers do not usually eat other consumers, and secondary consumers do not mainly eat decomposed matter.
• Option c is wrong since it suggests secondary consumers eat plants as a main food and does not properly highlight their role as predators on primary consumers.
• Option d is wrong because it reverses the roles, claiming primary consumers eat other consumers and secondary consumers eat only plants, which is opposite to accepted ecological definitions.

Common Pitfalls:
Students sometimes confuse primary and secondary consumers when omnivores are present in examples, because omnivores eat both plants and animals. However, the core definition remains that primary consumers feed directly on producers, while secondary consumers feed on primary consumers. Keeping a simple food chain picture in mind helps avoid these confusions.

Final Answer:
Primary consumers eat only plants, secondary consumers eat primary consumers