Question

What would happen in an ecosystem without primary consumers?
The populations of producers would increase.
The populations of omnivores would increase.
The populations of carnivores would increase.
The populations of decomposers would decrease.

Answer 1

Think about what primary consumers do: they eat producers and are eaten by secondary consumers. You don't have any options involoving secondary consumers, so focus on the first.

What would happen if no animals were around which ate plants?