Key Idea: Topic 2.4 explains how energy enters ecosystems (producers), how it moves through trophic levels (consumers), why food chains link into food webs, and how decomposers recycle nutrients to keep ecosystems running.
🌿 Producers (start of every food chain)
- Producers (plants/algae) make biomass using photosynthesis
- They convert light energy → chemical energy stored in glucose
- Biomass = stored energy available to the rest of the ecosystem
Without producers, no consumers can survive — they are the energy foundation.
🦊 Consumers and feeding types
- Herbivores eat producers; carnivores eat animals; omnivores eat both
- Scavengers eat dead animals; detritivores eat dead organic matter; saprotrophs digest dead matter externally
- Detritivores digest inside; saprotrophs digest outside using enzymes
🔗 Food chains and trophic levels
- Trophic level 1 = producers
- Trophic level 2 = primary consumers (herbivores)
- Trophic level 3 = secondary consumers; higher = tertiary/top predators
- Arrows show energy flow (from food → eater)
Exam rule: arrows in food chains show the direction of energy transfer, not “who eats who”.
🕸️ Food webs (real ecosystems)
- Food webs are interconnected food chains
- Most organisms have more than one food source
- More connections can increase stability if one species declines
♻️ Decomposers and nutrient recycling
- Energy flows one-way, but nutrients must be recycled
- Decomposers (mainly fungi/bacteria) break down dead matter and waste
- They release mineral nutrients back to soil/water for producers
- Prevents build-up of dead material and keeps soils fertile
High marks: link both ideas — energy flow (one-way) AND nutrient cycling (recycled by decomposers).
1) Define producer vs consumer. 2) What’s a trophic level? 3) What do arrows show? 4) Food chain vs food web? 5) Detritivores vs saprotrophs?