All living things must eat other living things to survive. You see a bird eating a worm. Or you see a lion preying on an innocent looking gazelle. You feel sad and sorry. But the truth is that one living thing must eat some other living thing to survive. Why is that? Because living things provide energy and we all need energy for survival.
The order where a small living thing is the food for a larger living thing which, in turn, is the food for an even larger living thing is called a food chain. Food chain usually begins with plant life and ends with an animal or a human. Lets look at an example. Plant leaves are eaten by caterpillar. A bird eats the caterpillar. Cat might eat the bird.
Plant -> Caterpillar -> Bird -> Cat (The arrow always points towards the eater)
Plants are called Producers because they produce their own food with the help of sunlight, water and nutrients from the soil. They aren’t dependent on any other living thing for food. They form basis of all food chains that occur on land. Animals and humans are called consumers as they can not produce their own food and are dependent on plants for their food. Living things that eat only plants are herbivores and ones that eat meat are carnivores. The ones that eat both are omnivores. An animal that naturally preys on others is called a predator. In a food chain there are many predators. Preys can be predators too! Can you figure out how?
The first consumer in the food chain that eats producers is called the primary consumer. The second consumer in the food chain that eat primary consumer are called secondary consumer. The third and subsequent consumer in the food chain that eat the secondary consumer are called tertiary consumer.
There are many food chains in an ecosystem. Member of one food chain can also belong to the other food chain. When we put all the food chains in the ecosystem together, we form a food web. Look at the picture below, doesn’t it look like a web?
Food chains exist not only on land but also under water. Underwater food chains start with microscopic organisms called Planktons. They are found on the upper sunlit layer of oceans and create their own food through photosynthesis. Planktons are the producers in the marine food chain. Planktons are eaten by small fish, which are then eaten by larger fishes like sharks. They are all consumers. Sharks are sometimes hunted by killer whales.
Position of each organism in the food chain is a Trophic level. Food chains on land have plants at first trophic level while food chains on water have phyto planktons at the first trophic level.
So each link of the chain is very important and you can imagine what will happen if they go missing. The whole balance would be lost.