Despite, being different from each other, plants and animals need each other. Neither plants nor animals can survive without the other. 

Animals Depend on Plants for Food 

Directly or indirectly all animals depend on plants for food. Herbivores, directly depend on plants for food, for example, Cows, Goats and Giraffe eats plants thus they are directly dependent on them. Carnivores such as tigers, lions, or wolves eat flesh of other animals, and thus depend indirectly on plants for their food. 

Animals Depend on Plants for Shelter 

Trees are the shelter for several animals such as birds, squirrels, monkeys, and insects. Birds build nests on trees, while squirrels, monkeys, and insects live on tree branches.

Animals Depend on Plants for Oxygen 

In the presence of sunlight, carbon dioxide, and water, plants produce their food. They give out oxygen during this process and in the course of respiration animals take in this oxygen. Plants also take in a small amount of oxygen during respiration.

Plants Use Carbon Dioxide Produced by Animals 

We are well aware that during respiration, animals take in oxygen and give out carbon dioxide. Plants use this carbon dioxide during photosynthesis.

Plants depend on Animals for reproduction

There are animals such as butterflies and honeybees, help plants to reproduce by germinating flowers. As birds and animals eat the fleshy fruits from the plants, and scatter their seeds, varieties of plants grow over a large area . 

Living Things Make the Soil fertile

Air is  required by the roots of plants to make food and grow, animals that live in the soil, like earthworms, help to loosen it so that air can travel in the soil. They also help to make the soil fertile. Thus, animals like the earthworm, bacteria and fungi help to decay waste, and dead living things. This helps the nutrients in their dead bodies to mix with soil, making it fertile.

All the living beings need energy for their survival. Plants rely on the soil, water, and the sun for energy, on the other hand, animals rely on plants as well as on other animals for energy. Within the ecosystem, plants and animals, count on each other for life. 

This interdependence has been described by the scientists, using a Food chain or a Food web. 

Food Chain 

A food chain expresses how different organisms eat each other for survival, starting with a plant and ending with an animal. 

For example, you could write the food chain for a lion-like this: 

Grass ---> zebra ---> lion 

The lion eats the zebra, which eats the grass. 

Let us comprehend this with another example. The grasshopper eats grass, the frog eats the grasshopper, the snake eats the frog, and the eagle eats the snake. 

Links of the Chain 

We can describe each link of the food chain with different names. The names mostly depend on what the organism eats, and on its contributions to the energy of the ecosystem. 

Producers 

As we are acquainted with the fact that plants produce energy for the ecosystem, they are the producer in the food chain. They do this because, they soak up energy from sunlight through photosynthesis. They also need water and nutrients from the soil, but plants are the only source of new energy. 

Consumers 

Animals are the consumers. This is because they don't produce energy, they just consume it up. The plant eating animals are called primary consumers or herbivores. Animals that eat other animals are called secondary consumers or carnivores. If a carnivore eats another carnivore, it is called a tertiary consumer. There are a few animals who eat both plants and animals. They are called omnivores. 

Decomposers 

The organisms that get energy from dead or waste organic materials are known as decomposers. This is the last stage in a food chain. As the decomposers, convert organic waste materials into inorganic materials like nutrient-rich soil or land, They become an integral part of a food chain. A few examples of decomposers are bacteria,worms,  and fungi. 

Decomposers complete a life cycle, as the nutrients provided by them to the soil, can be utilized by autotrophs or producers. Thus, starting a whole new food chain. 

NGSS