When is an ecosystem said to have high net primary productivity (NPP)?

• A. When there are more consumers than producers in the ecosystem.
• B. When the rate of respiration in producers is greater than the rate of photosynthesis.
• C. When all energy produced by autotrophs is immediately consumed by herbivores.
• D. When the rate of photosynthesis exceeds the rate of respiration in producers, resulting in a large accumulation of biomass.

Answer: (D)

Verified step by step guidance

1. Understand the concept of Net Primary Productivity (NPP): NPP is the amount of energy that remains in an ecosystem after autotrophs (producers) have used some of the energy they captured during photosynthesis for their own respiration. It represents the energy available for growth, reproduction, and consumption by herbivores and other consumers.
2. Recall the relationship between photosynthesis and respiration: Photosynthesis is the process by which producers convert light energy into chemical energy stored in glucose, while respiration is the process of breaking down glucose to release energy for cellular activities. NPP is calculated as the difference between the energy captured during photosynthesis and the energy used during respiration.
3. Analyze the conditions for high NPP: High NPP occurs when the rate of photosynthesis significantly exceeds the rate of respiration in producers. This means that more energy is being stored as biomass than is being used for metabolic processes.
4. Evaluate the incorrect options: (1) More consumers than producers do not directly affect NPP, as NPP is determined by producer activity. (2) If respiration exceeds photosynthesis, there would be a net loss of energy, leading to low or negative NPP. (3) If all energy is immediately consumed by herbivores, there would be no accumulation of biomass, which contradicts the definition of NPP.
5. Conclude with the correct condition: The ecosystem has high NPP when the rate of photosynthesis exceeds the rate of respiration in producers, resulting in a large accumulation of biomass. This stored energy supports the growth of the ecosystem and provides energy for higher trophic levels.