Food Chain and Food Web

Food Chain and Food Web

Living organisms need food to perform their life processes. Some organisms can produce their own food, such as plants, while other organisms cannot do this and need to feed on other organisms to obtain their energy.

We can therefore identify different feeding types in an ecosystem, based on how the organism obtain (gets) its food. They are producers and consumers.

Producers

Producers are organisms that are able to produce their own organic food. They do not need to eat other organisms to do this. Producers are also called autotrophs. Can you name an organism that prepare it’s own food?

Plants are producers because they make their own food by photosynthesis.

What do plants need in order to photosynthesis?

Consumers

Organisms which cannot produce their own food, need to eat other organisms as food. These organisms are called consumers. All animals are consumers as they cannot produce their own food. Consumers are also called heterotrophs.

There are many types of consumers and we can classify them into specific groups depending on the food that they consume. These are:

* herbivores

Animals which eat plants or plant products e.g: cattle, deer, goat and rat.

* carnivores

Animals that eat other animals e.g: Lion, tiger, frog and owl.

* omnivores

Animals that eat both plants and animals e.g: Humans, dog and crow

* decomposers

Micro-organisms that obtain energy from the chemical breakdown of dead organisms (both plants and animals). They break complex organic substances into simple organic substances that goes into the soil and are used by plants. (e.g) Bacterium, Fungi

Food chain

In a forest, deer eats grass; and in turn we know tiger eats deers. In any ecosystem there is a chain like relationship between the organisms that live there. This sequence of who eats whom in an ecosystem is called as food chain.

It describes how organisms get energy and nutrients by eating other organisms.

A food chain shows the relationship between producers (e.g. grass) and consumers (e.g. deer, goats, cows and tiger).

E.g. Food chain in a terrestrial (grassland) ecosystem

E.g. Food chain in an aquatic (lake) ecosystem

Energy flow

The food chain begins with the energy given by the Sun. Sunlight triggers photosynthesis in plants. The energy from the Sun is stored in the plant parts. When the grasshopper eats the grass, the energy flows from grass to grasshopper. Frog gets energy by eating grasshopper. This energy is transferred to a crow, when the frog is eaten by a crow. Thus we conclude the primary energy production in the world of living things is made by plants; that is by photosynthesis.

The micro organism reduce the excreata and the dead bodies of animals into primary simple components and puts them back into soil. It is this material that help the plants to grow. Thus we can see that there is a cycle of materials from primary producers to highest level predators, then back to soil.

Trophic levels

We see that the energy is passed along from the producer to the consumers. But, there are three different consumers in any food chain. How can we distinguish different consumers?

Animals that eat plants are primary consumers.

Animals that eat primary consumers are called secondary consumers.

Animals that eat the secondary consumers (mostly predators) are the tertiary consumers.

There may even be large predators that eat tertiary consumers. They are called as quaternary consumers.

Each of these levels in the food chain is called a trophic level.

Organism uses up to 90% of its food energy for its life processes. Only about 10% of energy goes into new body cells and will be available to the next animal when it gets eaten. This loss of energy at each trophic level can be shown by an energy pyramid.

A rat eats grains; and in turn we know snake eats rat. Now snake is a prey for peacock and in turn peacocks are easy prey for tigers and leopards. Now think? Do tigers have any natural predators?

In all food chain there is a top level predator that has no natural predators. In an aquatic ecosystem there are no natural predator for alligator; in a forest there are no natural predators for tigers.

Importance of food chain

1 .Learning food chain help us to understand the feeding relationship and interaction between organisms in any ecosystem.

2. Understanding the food chain also helps us to appreciate the energy flow and nutrient circulation in an ecosystem. This is important because pollution impacts the ecosystem. The food chain can be used to understand the movement of toxic substances and their impacts.

Food web

Consumers have different sources of food in an ecosystem and do not rely on only one species for their food. If we put all the food chains within an ecosystem together, then we end up with many interconnected food chains. This is called a food web.

A food web is very useful to show the many different feeding relationships between different species within an ecosystem.

Activity 2: Take a square paper. Fold its diagonals. Draw three lines in three triangles as shown in the picture.  

Cut from the edge of the diagonal to the center as shown in the picture.

If you fold this triangle and paste behind the third triangle you get a pyramidal shape.

In one of the triangles, draw images of each of the organisms in the different levels.

In another triangle write the names of the organisms. In the last triangle, write the energy level of the organism. Have a look at the following example. You must come up with different organisms!.