Microorganisms in the environment

The study of organisms in their environment is called ecology. All the different organisms that live together affect one another in some way. For example, one species of animal may eat another animal. A plant may provide shelter for an animal.

Microorganisms have important roles to play in the environment. In the rest of this Unit, we will look at how microorganisms affect other organisms in their environment, including their importance in food chains and food webs.

In this topic, you will look at how food chains and food webs describe how energy, in the form of food, is transferred between animals and plants. In the next topic, you will look at how microorganisms fit into food chains and food webs.

Food chains

Arun has chicken and rice for lunch. It gives him a lot of energy. The food you eat gives you energy.

How did the energy get into the food?

The energy in food begins in the Sun. Energy from the Sun reaches the Earth in sunlight.

Plants use energy from sunlight to make their own food. Some of the energy from the sunlight goes into the food that the plant stores in its roots, stems, fruits and leaves.

When an animal – such as Arun – eats part of the plant, it eats the food the plant made. This is how the animal gets energy. This is called energy transfer.

You can show how the energy passes from the Sun into the rice, and then into Arun’s body, by drawing a food chain.

The arrows in the food chain show how energy is passed from the Sun to the plant, and then is transferred to the rice, and then to Arun.

The first organism in a food chain is a producer. Plants use energy from the Sun to produce food.

All the other organisms in a food chain are consumers. Animals are always consumers. They have to eat ready-made food to get their energy. They consume (eat) plants or other animals.

Consumers that consume only plants are herbivores.

Consumers that consume other animals are carnivores.

Animals that catch, kill and eat other animals are predators. The animals they eat are their prey.

Food webs

Here are two more food chains. These food chains describe part of the feeding network of plants and animals on the African plains.

acacia tree → springbok → cheetah
grass → termite → aardvark → leopard

The diagram on the next page shows how the organisms in these two food chains, and some other organisms, are connected by their feeding habits. This diagram is a food web.

Put your finger on the acacia tree in the food web. Then move it to the springbok, then to the cheetah. You are tracing the path of the energy as it transfers along a food chain.

Now do the same for another food chain – the one that begins with grass and ends with a leopard.