What would happen in an ecosystem without primary consumers

Ecosystem will collapse

Explanation:

In an Ecosystem food chain consists of producers, primary consumers, secondary consumers etc.

During energy transfer energy is transferred from producers to primary consumers.

From primary producers to secondary consumers.

Primary consumers feed on producers.

Secondary consumers feed on primary producers.

Secondary consumers cannot feed directly on producers.

An ecosystem without primary consumers will leads to zero energy transfer in which secondary consumers cannot survive without primary consumers.

This leads to decrease in secondary consumers which effect tertiary consumers.