Organisms in an ecosystem are usually grouped according to their trophic level into__________

Step 1: Analyze the question The question asks how organisms in an ecosystem are grouped by trophic level. "Trophic" refers to feeding, so the grouping is based on how an organism obtains its food and energy.

Step 2: The concept A trophic level is an organism's position in a food chain. At the broadest level, organisms fall into two main groups:

• Producers (autotrophs): make their own food, usually by photosynthesis (e.g. green plants, algae). They form the first trophic level.
• Consumers (heterotrophs): depend on other organisms for food. They include primary consumers (herbivores), secondary consumers (carnivores), and tertiary consumers. Decomposers and saprophytes feed on dead matter and are often treated as a special group of consumers.

Step 3: Check each option

• A. Carnivores and omnivores: These are only types of consumers. They leave out producers and herbivores, so the grouping is incomplete.
• B. Consumers and parasites: Parasites are themselves consumers, so this is not a proper division.
• C. Producers and saprophytes: This leaves out animals (herbivores and carnivores). Saprophytes are only one kind of consumer.
• D. Producers and consumers: This covers the two basic trophic groupings, those who make food and those who feed on others. ✔

Step 4: Answer The correct option is D, producers and consumers.

Exam tip: "Trophic level" means "feeding level". Always begin with producers at the base of the food chain, followed by the different levels of consumers. If an option names only a subtype (such as carnivores, parasites or saprophytes), it is probably too narrow to be the answer.