The transfer of energy between the food chains is inefficient because as the energy is transferred from one chain to another by consumption, energy is lost. In primary producers the main energy input is the sun. The green plants convert the energy in sunlight into the chemical bond energy of photosynthetic products although not all the energy from the sun reached the leaves. Energy is lost at many stages, some is reflected from the leaf and some is lost in transmission through the leaf. Energy is also lost during photosynthesis as heat loss during the chemical reactions. Energy is also used during respiration in plants and by this is stored for the next section of the chain.
Even more energy is lost when the consumer takes the energy from the producer. Energy is lost through the excretion of waste products, as well as heat loss and respiration. As so much energy is lost when transferred through food chains it is necessary that the transfers should remain as efficient as possible. This is necessary as it is thought that only around 10% of the energy gained from the previous tropic level is passed on the next level. This means that the energy from the sun is quickly reduced only allowing limited number of trophic levels in any food chain.
Food chains also depend on the nitrogen cycle as enzymes used during photosynthesis form amino acids. These in turn make protein, which involves nitrates. Plants cannot take the nitrogen that makes up 79% of the air; it has to be in the ‘fixed form’ in compounds such as NO3- and NH3. Four processes participate in the cycling of nitrogen through the biosphere. The first is nitrogen fixation, which is when the nitrogen molecules are broken apart so that its atoms can combine with other atoms, requires the input of substantial amounts of energy. This can be done by three methods, atmospheric fixation, biological fixation and industrial fixation.
The second stage is decay when proteins pass through plants just like carbohydrates and lipids in animals. At each level in a food chain the living organism’s metabolism produces organic nitrogen compounds that return to the environment, normally in excretions. Microorganisms then break down the molecules of the decay into ammonia.
The next stage is nitrification when the ammonia is taken up by plants through the roots and converted into nitrates in two steps. Firstly the bacteria of the genus Nitrosomonas oxidize NH3 to nitrates and then Nitrobacter oxidizes nitrites to nitrates. The bacteria is called nitrifying bacteria and makes nitrogen available in plant roots.
The finally stage is denitrification which reduces nitrates to nitrogen gas and returns it to the atmosphere. This is agented by anaerobic bacteria, which usually live in aquatic places. They use nitrates instead of oxygen for the final electron acceptor in their . This has then closed the nitrogen cycle; the first three processes get nitrogen from the atmosphere and the final process releases back into the air.
