Energy Flow

Organisms need energy for all life processes. The Sun is our main source of energy, providing us with light and heat. During the process of photosynthesis, light energy from the Sun is utilised by the plants and converted to chemical energy (food) which is stored. This chemical energy is utilised by plants for cellular respiration and growth and is also passed on to other organisms - herbivores, carnivores and decomposers. Thus, the Sun's energy is made available either directly or indirectly to all organisms as it flows through the biological ecosystem. Some useful energy is lost as heat at every step in a chain of events.

Food Chains and Energy Transfers along a food chain

The channels of constant flow of energy through the community are known as food chains. A food chain is defined as a sequence of organisms through which food energy is transferred as one organsim is eaten by the next in a sequence. This repeated cycle of eating and being eaten always starts with a plant or plant part as it receives energy from the Sun. At each transfer, a large amount of potential energy present in food is lost as heat. The amount of energy available at each step limits the number of links in the food chain.

As energy flows through a food chain, much of it is lost before it can be consumed by an organsim at the next level. Only 10% of the energy is converted into biomass(this is short for biological mass) and is made available to the next consumer in the food chain. Only 1 to 5 % of the sunlight is used by plants and about 95% or more of the incoming light energy from the Sun is sent back to the air, the water and the surrounding. Eventually this energy (heat energy now) is radiated back to space to warm the universe. The loss of energy limits the length of food chains. A short food chain provides more energy to consumers. Thus, a human obtains far more calories by eating vegetables and grains than by feeding cattle with the same amount of grain through another food chain and then consuming meat from these animals.