Answer: unidirectional.
- A unidirectional
- B cyclic
- C fully reversible
- D always zero
Correct answer: A. unidirectional
Explanation: Energy flows one way, from the sun through producers to consumers, and is lost as heat.
Energy pyramid showing a simple food chain (producer to herbivore to carnivore) with energy decreasing roughly tenfold at each trophic level.
Concept context
Ecosystems, food chains, energy flow, nutrient cycles, biodiversity, and conservation.