Food chain and food web

Every living thing needs food for energy. Plants make their food. A grasshopper eats grass, a frog eats the grasshopper, a snake eats the frog and an eagle eats the snake. When we write this as a line, we get a food chain. A food chain shows how food, and the energy in it, passes from one living thing to another.

Grass → Grasshopper → Frog → Snake → Eagle

The arrow means "is eaten by". It points in the direction in which energy flows.

The links of a food chain

• Producers are green plants. They produce food from sunlight, water and air. Every food chain starts with a producer.
• Consumers are animals. They cannot make food and must eat plants or other animals.
  • Herbivores eat only plants: cow, deer, rabbit, grasshopper.
  • Carnivores eat other animals: lion, tiger, snake, eagle.
  • Omnivores eat both plants and animals: human beings, bears, crows.
• Decomposers are bacteria and fungi. They break down dead plants and animals and return the nutrients to the soil, where plants use them again. Without decomposers, the earth would be covered with dead remains.

The sun is the source

All the energy in a food chain comes first from the sun. Plants trap it, a herbivore gets it by eating the plant, and a carnivore gets it by eating the herbivore. At each step, a large part of the energy is used up by the animal for moving, breathing and keeping warm. That is why food chains are short, usually four or five links, and why there are far fewer tigers than deer in a forest.

From food chain to food web

In nature, an animal rarely eats just one thing. A frog eats many kinds of insects. A snake may eat a frog, a rat or a bird's egg. So food chains cross and join one another like the threads of a net. This network is called a food web.

What happens if a link breaks

Suppose all the frogs in a pond die. The insects they used to eat will multiply and damage the crops, and the snakes that fed on frogs will go hungry. One missing link disturbs many others. This is why saving every kind of plant and animal, even the ones we do not like, keeps nature in balance.