Based on the energy pyramid seen here, which group of organisms is the primary consumer? a) predator fish b) birds and mammals c) insects and zooplankton d) phytoplankton and bacteria

The correct answer is-

C) insects and zooplankton.

Primary consumer are those organisms that consume producers ( autotrophs such as phytoplanktons and photosynthetic bacteria) that is they occupy the second trophic level ( the first being occupied by autotrophs) in a food chain within an ecosystem.

In an aquatic food chain, insects and zooplankton consume phytoplanktons ( autotrophs) and are considered as primary consumer.

Thus, option C) is the right answer.

they deliver oxygen to the blood