The group of organisms at the base of the pyramid of numbers are

Analyze the question: It asks which group of organisms forms the base (the bottom level) of a pyramid of numbers.

Concept: A pyramid of numbers shows how many organisms exist at each trophic level in a food chain. Each level feeds on the one below it, so the bottom level supports all the others.

• Base: producers (green plants), which make their own food by photosynthesis
• Second level: primary consumers (herbivores)
• Third level: secondary consumers (carnivores that eat herbivores)
• Top: tertiary consumers (top carnivores)

Step-by-step solution:

1. Every food chain starts with an energy source, the sun.
2. Only producers can capture this energy and turn it into food.
3. Every other organism depends directly or indirectly on producers, so they must be at the bottom.
4. Producers are usually the most numerous (for example, many grass plants feeding fewer grasshoppers, which feed fewer lizards, which feed fewer hawks). This gives the broad base of the pyramid.
5. Decomposers act on dead matter from all levels. They are not placed as a level in the pyramid.

So the correct answer is C. producers.

Note: A pyramid of numbers can sometimes be inverted. For example, one large tree may support thousands of insects. Even then, the producers are still the base level.

Exam tip: Remember "P-P-S-T": Producers → Primary → Secondary → Tertiary. The first group in the list is always at the base.