Food Chains and Food Webs

A food chain shows how energy flows from one living thing to another in an ecosystem — who eats what. Every food chain begins with a green plant (the producer) and ends with a top consumer that has no natural predator.

The roles in a food chain:

• Producers — green plants and algae. They MAKE their own food from sunlight, water and carbon dioxide through photosynthesis. They are always the first link in a food chain. Examples: grass, maize, sukuma wiki, water lilies, baobab.
• Primary consumers (herbivores) — animals that eat plants directly. Examples: cow, goat, antelope, zebra, rabbit, grasshopper.
• Secondary consumers (carnivores or omnivores) — animals that eat primary consumers. Examples: snake (eats rats), frog (eats grasshoppers), hawk (eats small birds).
• Tertiary consumers (top predators) — animals at the top of the chain with few or no natural predators. Examples: lion, leopard, eagle, shark, crocodile.
• Decomposers — bacteria and fungi that break down dead plants and animals into simple substances that go back into the soil for plants to use. They close the cycle.

Reading the arrows in a food chain:

The arrow points from the eaten TO the eater — that is, in the direction the energy flows. Example:

grass → grasshopper → frog → snake → eagle

This says: grass is eaten by grasshoppers; grasshoppers are eaten by frogs; frogs are eaten by snakes; snakes are eaten by eagles. The eagle is the top consumer.

Food webs:

In real ecosystems, animals rarely eat just one thing. A food web is many overlapping food chains in one ecosystem. For example, a rat is eaten by snakes, owls and cats; a frog is eaten by snakes, herons and big fish. Food webs show how complex and connected life in an ecosystem really is.

Energy loss along the chain:

Energy passes UP the chain but most is lost as heat, movement and waste at every step. Roughly only 10% of the energy at one level reaches the next. That's why a food chain rarely has more than four or five links — there isn't enough energy left for a sixth.

Examples of Kenyan food chains:

• Savannah: grass → zebra → lion.
• Pond: algae → small fish → larger fish → fish eagle.
• Farm: maize → rat → snake → mongoose.
• Forest: leaves → caterpillar → small bird → hawk.
• Soil cycle: dead leaves → earthworm → bird (and bacteria/fungi recycling the dead matter into soil nutrients).

What happens when a link is broken?

If one link in a food chain is removed (by hunting, pollution, drought, or disease), every other link is affected:

• Removing the top predator (e.g. lions) → primary consumers (zebras) increase → they overgraze the producers (grass) → ecosystem collapses.
• Removing producers (e.g. cutting down a forest) → primary consumers starve → secondary consumers starve → whole web collapses.
• Removing decomposers (e.g. with chemicals) → dead matter doesn't return to the soil → plants can't grow.

Common student mistakes to avoid:

• Drawing the arrows the wrong way. Arrows point from food TO eater, showing the direction of energy flow — not from predator to prey.
• Saying decomposers eat live things. Decomposers break down dead plants and animals.
• Calling humans always "top consumers". Humans are omnivores — we eat both plants AND animals, so we can sit at different levels in different chains.
• Putting two producers in a single chain. A chain has one producer at the start; it doesn't loop.
• Forgetting energy is lost at each level. Energy is NOT cycled — it dissipates as heat. Only nutrients (carbon, nitrogen, water) are cycled.

CBC Grade 4 introduces what plants and animals need to live; Grade 5 covers food chains, producers, consumers and decomposers; Grade 6 extends to food webs and the role of each living thing in an ecosystem; Grade 7–9 Integrated Science deepens this into energy pyramids, nutrient cycles, and the impact of human activity — material that appears in KPSEA and KJSEA.