An inverted biomass pyramid refers to a situation where the biomass (amount of living organisms) in a particular trophic level is higher than the biomass in the trophic level below it. The correct answer is option 1, the marine ecosystem. In the marine ecosystem, phytoplankton, which are tiny aquatic plants, make up a large portion of the biomass in the primary producer level. These phytoplankton are consumed by zooplankton, which have a smaller biomass, creating an inverted pyramid. This is because the phytoplankton reproduce rapidly and are consumed quickly, while the zooplankton have a longer life cycle and lower reproductive rate. In contrast, in the grassland ecosystem (option 2), the biomass pyramid follows a traditional pattern with increasing biomass at higher trophic levels.