Cambridge O Level Biology · Syllabus 5090 · Relationships of Organisms with One Another and with the Environment
Food Chain
What is Food Chain?
A diagram showing the transfer of energy and materials from one organism to the next, beginning with a producer. Each arrow points from the organism being eaten to the organism eating it, because that is the direction in which chemical energy, biomass and nutrients are transferred. A food chain shows one feeding route only, so the same organism may appear in several different chains within one ecosystem.
This definition is part of the Relationships of Organisms with One Another and with the Environment chapter in Cambridge O Level Biology.
Food Chain in context
Ecosystems run on one input and two very different accounting systems. Light energy from the Sun enters through photosynthesis, passes along food chains by feeding, and is transferred to the environment as thermal energy at every step — so energy flows through an ecosystem and is never recycled. The atoms carried with it are different: carbon and nitrogen move from air to producer to consumer to decomposer and back to the air, so matter cycles and is used again. Everything else in this topic — short food chains, ecological pyramids, the carbon and nitrogen cycles, eutrophication, conservation — is a consequence of those two sentences.
Common mistakes with Food Chain
- “All pesticides build up through food chains.” Why it is wrong: persistence varies enormously, and many pesticides break down within days. Exam-safe: pesticides that are not broken down may accumulate within organisms and become more concentrated at successive trophic levels.
Questions students ask about Food Chain
Which way do food chain arrows point?
From the organism being eaten to the organism eating it. The arrow shows the transfer of energy, biomass and nutrients, and that transfer goes into the feeder. Reading it as “is eaten by” is a useful check, but if you are asked what the arrow represents, name the transfer and its direction.
Why are food chains usually shorter than five levels?
Because transfer is inefficient, so the energy available falls sharply at each level. After a few transfers there is too little energy arriving to support another population of predators large enough to survive and reproduce. Say usually: some marine chains are longer because their producers are highly productive.