Who this is for: Cambridge IGCSE Coordinated Science (0654) students who confuse food chains with food webs, mislabel trophic levels, or cannot explain energy loss between levels.
What query it owns: how to understand and revise organisms and their environment in Cambridge IGCSE Coordinated Science.
Why this is safe: this page owns the organisms-and-their-environment revision-guide angle, while Tutopiya’s Organisms and Their Environment subtopic page owns the learning resource and the free Organisms and Their Environment quiz owns the practice.

Organisms and their environment covers how living things interact in ecosystems — food chains and webs, energy transfer, nutrient cycling and population changes. Cambridge IGCSE Coordinated Science (0654) tests whether you can name producers and consumers, assign trophic levels, explain energy loss, and describe the carbon and nitrogen cycles. This guide covers the syllabus definitions, diagram rules, and the question types that appear every year.

Key takeaways

• A food chain shows one feeding pathway; a food web shows many linked chains.
• Producers make food by photosynthesis; consumers eat other organisms; decomposers break down dead material.
• Trophic level = feeding level — producer is level 1, primary consumer level 2, and so on.
• Arrows in food chains point towards the eater (energy flow direction).
• Energy is lost at each trophic level (respiration, movement, heat) — typically only ~10% passes to the next level.

What are organisms and their environment in Cambridge IGCSE Coordinated Science?

An ecosystem includes all the living organisms in an area and the non-living factors they interact with. Food chains show how energy passes from producers through consumers; food webs show the full network of feeding relationships. Decomposers return nutrients to the soil so producers can reuse them. Population size is affected by food supply, predation, disease and competition.

You can read the full explanation, worked examples and notes on Tutopiya’s Organisms and Their Environment subtopic page before you attempt questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Producer	Organism that makes its own food (photosynthesis)	“Name the producer in this food chain”
Primary consumer	Herbivore eating producers	”State the trophic level”
Decomposer	Breaks down dead organic matter	”State the role of bacteria in a food web”
Food web	Several linked food chains	”Explain what happens if rabbits are removed”
Energy loss	Energy lost as heat at each level	”Explain why food chains are short”

Trophic levels — naming them correctly

Trophic level	Name	Example
1	Producer	Grass, algae, tree
2	Primary consumer	Rabbit, caterpillar
3	Secondary consumer	Fox, bird
4	Tertiary consumer	Hawk, owl
—	Decomposer	Bacteria, fungi

Energy transfer between trophic levels

Stage	What happens	Exam focus
Producer	Captures light energy by photosynthesis	”State the source of energy in ecosystems”
Consumer	Eats previous level; uses energy for life processes	”Explain energy loss between levels”
Respiration	Energy released as heat	”State why less energy reaches the next level”
Decomposer	Breaks down dead matter; returns nutrients	”Describe the role of decomposers”

Organisms and environment in past-paper wording

Command word	What the question wants	Typical stem
Define	Precise syllabus definition	”Define a food web.”
Name	Identify organisms or roles	”Name the secondary consumer.”
Draw	Labelled diagram with correct arrows	”Draw a food chain containing four organisms.”
Explain	Cause and effect	”Explain why removing wolves affects grass.”
Suggest	Apply to a new scenario	”Suggest what happens if pesticide kills insects.”

Worked exam-style stems

1. “Draw a food chain with grass, rabbit, fox and flea.” Grass → rabbit → fox → flea. Arrows point to the organism that eats the previous one. Reward: correct order + arrow direction.
2. “Explain why most food chains have fewer than five trophic levels.” Energy is lost at each level through respiration, movement and heat; insufficient energy remains to support more levels. Reward: energy loss + limited energy for next level.
3. “Explain why a pyramid of numbers for a tree ecosystem may be inverted.” One large tree supports many insects; the base (tree) has fewer individuals than the herbivores above it. Reward: link size/number to pyramid shape.

Practise on the Organisms and Their Environment quiz.

How organisms and their environment connect to the syllabus

This topic links to Human Influences on Ecosystems (pollution and habitat change) and Variation and Selection (adaptation to environment). The Cambridge IGCSE Coordinated Science resource hub links every ecology subtopic.

Common mistakes students make

• Drawing arrows away from the eater instead of towards the eater.
• Confusing food chain (one pathway) with food web (many pathways).
• Omitting decomposers when asked about nutrient return.
• Labelling trophic levels from zero instead of starting producers at level 1.
• Saying energy is recycled in ecosystems (energy flows through; nutrients are recycled).

When you need more support

If food-web knock-on effect questions keep costing marks, work through the Organisms and Their Environment quiz, then get help from a Cambridge IGCSE Coordinated Science tutor.

Frequently asked questions

What is the difference between a food chain and a food web? A food chain shows one feeding pathway; a food web shows many interconnected chains in a community.

Which way do arrows point in a food chain? Towards the organism that eats the previous one (energy flow direction).

Why are food chains usually short? Energy is lost at each trophic level, so insufficient energy remains to support many levels.

How do I revise organisms and their environment effectively? Learn trophic levels, arrow rules, energy loss, nutrient cycling, then take the quiz.

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