Ecosystems

Imagine a frog. Where does it live? In a pond. That pond is the frog's habitat — the place where a living thing finds everything it needs to survive: food, water, shelter and a place to reproduce.

But the pond is not just frogs. It also has fish, insects, water plants, mud, water and sunlight. All of these together make up an ecosystem.

An ecosystem has two parts:

• Living parts — every plant, animal and microorganism in the area.
• Non-living parts — the water, soil, air, sunlight and temperature.

Ecosystems come in every size — a single rotting log, a whole desert, or an entire ocean.

In any ecosystem, living things get food in different ways. We sort them into three groups.

• Producers — they make their own food. Almost all producers are green plants, which make food from sunlight by photosynthesis. They are the start of every food chain.
• Consumers — they cannot make food, so they eat other living things. A rabbit, a lion and you are all consumers.
• Decomposers — they feed on dead plants and animals, breaking them down. Fungi (like mushrooms) and many bacteria are decomposers.

Decomposers do a vital job: they recycle nutrients back into the soil, so producers can use them to grow again.

A food chain is a simple diagram that shows what eats what. It traces the path of food energy through an ecosystem.

Two things to notice:

• The chain almost always begins with the Sun. The Sun's light energy is captured by green plants in photosynthesis.
• Each arrow points from the food to the eater — it shows which way the energy flows. The arrow means "is eaten by".

So in grass → rabbit → fox, the grass is eaten by the rabbit, and the rabbit is eaten by the fox.

In real life, most animals eat more than one kind of food, and most living things are eaten by more than one kind of animal. A single food chain cannot show all of this.

A food web joins lots of food chains together. It gives a much fuller picture of the feeding relationships in an ecosystem.

Food webs help us see how everything is connected. If one living thing disappears, you can trace the arrows to predict which others might be affected.

Living things in an ecosystem do not survive alone — they depend on each other. This is called interdependence.

• A bee depends on flowers for food; the flower depends on the bee to spread its pollen.
• A rabbit depends on grass to eat; a fox depends on rabbits.
• Every consumer depends, in the end, on producers.

Living things also have features that help them survive in their own habitat. These features are called adaptations.

• A camel in the desert has thick eyelashes and stores fat in its hump for the long times between meals.
• A polar bear has thick fur and a layer of fat to stay warm in the freezing Arctic.
• A cactus has a thick stem to store water and spines instead of leaves to lose less water.

An adaptation is a perfect example of the big biology idea: a living thing's features are suited to its way of life. Whenever you meet a new living thing, ask: what features does it have, and how do they help it survive where it lives?

Understanding ecosystems now opens the door to many later topics:

• Photosynthesis — you will study in detail how producers capture the Sun's energy.
• Adaptation and variation — you will explore why living things differ and how they suit their habitats.
• Human impact — you will see how pollution and habitat loss can damage food webs.
• Energy in science — the idea of energy flowing along a chain links to energy topics in physics.

Whenever a later topic feels tricky, picture a food chain and ask where the energy is going. Take your time — really understanding how living things connect is worth far more than rushing through it.