Every plant and animal species, no matter how big or small, depends to some extent on another plant or animal species for its survival. It could be bees taking pollen from a flower, photosynthesis of plants, deer eating shrub leaves or lions eating the deer.
A food chain shows how energy is transferred from one living organism to another via food. It is important for us to understand how the food chain works so that we know what are the important living organisms that make up the food chain and how the ecology is balanced.
Photosynthesis is only the beginning of the food chain. There are many types of animals that will eat the products of the photosynthesis process. Examples are deer eating shrub leaves, rabbits eating carrots, or worms eating grass. When these animals eat these plant products, food energy and organic compounds are transferred from the plants to the animals.
These animals are in turn eaten by other animals, again transferring energy and organic compounds from one animal to another. So for how many levels does this go on? To follow the food chain to its different levels and know how it works go to this site.
The page also contains names and definitions of terms used to describe the 'players' in the food chain- producers, consumers, herbivores. You can also refer to the diagrammatic representations of food chains, food webs and ecological pyramids.
A food chain describes how energy and nutrients move through an ecosystem. At the basic level there are plants that produce the energy, then it moves up to higher-level organisms like herbivores. After that when carnivores eat the herbivores, energy is transferred from one to the other. To understand how this happens visit the link.
In the food chain, energy is transferred from one living organism through another in the form of food. There are primary producers, primary consumers, secondary consumers and decomposers- all part of the food chain. Follow this link for a good introduction to how food chains work. There are links to types of energy and also simple explanations to how photosynthesis is the starting point of the food chain. This site also tells us that because of our eating habits, we are in two food chains- marine and land.
Plants that have photosynthesis are supplying us with the first product of the food chain. Not only that, they are the source for oxygen, the food we eat, our clothes, and even our furniture, among other things. Plants also remove greenhouse gas from the air, provide habitat to many animals.
Therefore we should understand the ecology of the environment with respect to plants. What is their number in terms of individuals (the population), and with respect to other living beings in the environment. Go to this page to see where plants are placed with respect to other living organisms.
In typical grassland, for example, the plants outnumber all other levels in the pyramid combined. However in the forests, other living organisms compete for space with plants. But a balance is maintained in the ecosystem.
There may be special relationships that have evolved within the community in which one particular species grows in obligate association with one other particular species, upon which still others depend. This site explores such relationships.