1. The producers convert solar energy into chemical energy in the form of organic compounds .
2. The primary comsumers derive their nutrition from the producers . According to the energy tranfer law , only 10% of energy is transferred from one trophic level to the other level .
so, the energy that is captured by the producers does not revert back to the sun and the energy transferred to the herbivores does not come back to the producers. It just keeps on moving to the next trophic levels in a unidirectional way.
3. Thats why the flow of energy in the food chain is always unidirectional . A large no, of pesticides and chemicals are used to protect our crops from pests and diseases . Some of these chemicals are washed down from the soil , while some enter the water bodies . From the soil,they are absorbed by the plants along with water and minerals ;and from the water bodies . They are taken up by the aquatic plants and animals .As these chemicals cannot decompose ,they accumulate progessively at each trophic level . This increase in the concenteration of harmful chemicals with each step of food chain is called biomagnification . As human beings occupy the top level in food chain, These chemicals get accumulated in our bodies .