The correct option is D A is false and R is true
In marine ecosystems, phytoplankton carry out most of the photosynthesis that occurs. Phytoplankton are small organisms like diatoms with extremely simple structures, so most of their primary production or biomass is consumed by grazing organisms that feed on them. In contrast, a large fraction of the biomass that land plants produce, such as roots, trunks, are complex and cannot be consumed by herbivores for food, so proportionately less of the energy is fixed through primary production in terrestrial ecosystems. This is the reason why terrestrial ecosystems have smaller food chains or lesser trophic levels than marine ecosystems.