Key Idea: Topic 2.5 explains how energy flows through ecosystems, why energy transfer is inefficient, how energy enters via photosynthesis and is released by respiration, why food chains are short, and how energy is represented using biomass, pyramids, and productivity.
⚛️ Laws of thermodynamics
🌞 Energy input and release
📉 Energy loss in food chains
Only about 10% of energy is transferred to the next trophic level.
🏔️ Biomass and pyramids
⚡ Productivity
Net productivity = Gross productivity − Respiration
1️⃣ **Why is energy transfer inefficient?** Energy is lost as heat during respiration and not all biomass is eaten or digested. 2️⃣ **Why are food chains short?** Too much energy is lost at each trophic level. 3️⃣ **Which process brings energy in, and which releases it?** Photosynthesis brings energy in; respiration releases it. 4️⃣ **Why are pyramids of energy always upright?** Energy decreases at each trophic level. 5️⃣ **Net productivity formula?** NP = GP − respiration.