(a) Green plants contain cell organelles called chloroplast. Chloroplast contains green colour pigments called chlorophylls. Chlorophylls have ability to trap solar energy and this energy is used to fix carbon dioxide into food (glucose). Since green plants produce food, so they are called producers.

(b) The scientific term used for progressive accumulation of harmful chemicals at each trophic level of a food chain is “biological magnification”. It occurs when the number of chemicals and toxins increase and accumulate through the trophic levels of a food chain. Chemical substances from crop fields and industries are released into the environment, making their way toward food chains and food webs. Normally biological magnification doesn’t affect directly but exposure to these harmful chemicals may cause some long-term side effects.