In the food pyramid, the greatest biomass appears at the level of:

a) birds and mammals
b) insects and zooplankton
c) phytoplankton and bacteria
d) small fish and other aquatic species

C) phytoplankton and bacteria

Explanation:

The biomass pyramid represents the amount of organic matter present in the body of organisms at each trophic level.

In an aquatic ecosystem, phytoplankton is the main producer of biomass, it reproduces quickly and has a short life cycle. At times, the biomass of phytoplankton may be smaller than the biomass of beings from other trophic levels, such as zooplankton and fish.

Bacteria are also major producers of biomass, in several different environments. For this reason, we can consider it, together with phytoplankton, the major biomass producers.

The biomass pyramid is a type of ecological pyramid. Ecological pyramids are graphical representations of trophic interactions between species in a community. They represent the flow of energy and matter between trophic levels, along the food chain.