Concept:Green plants prepare their own food by photosynthesis, so they act as primary producers in an ecosystem.Explanation:Photosynthesis converts light energy into chemical energy:6CO2+6H2Osunlight, chlorophyllC6H12O6+6O2The glucose formed stores energy that enters the food chain.Primary consumers, such as herbivores, eat green plants.Secondary consumers eat primary consumers.Decomposers break down dead organisms and recycle nutrients.Green plants do not consume other organisms, so they are not consumers or decomposers.They are autotrophs and occupy the first trophic level.Hence, they are called primary producers because they produce the initial organic matter for the ecosystem.Answer:Green plants in an ecosystem are Primary Producers.Option A: Primary Producer.