CBSE Class 10 Science 2017 · Paper 31/2/1 · Question 18

(a) Pesticides are sprayed on crops, fruit trees included, to protect them from pests and diseases. Some of the pesticide stays on the fruits, and some is washed down into the soil and water bodies, from where plants absorb it along with water and minerals, so it also gets inside the fruits. Juice made from such fruits therefore contains the pesticide. Pesticide that seeps down through the soil can also contaminate ground water, and if such water is used in making the juice, it adds pesticide to the juice as well. Many pesticides are not biodegradable, so they are not broken down, and washing the fruit removes only part of what is on its skin. (b) The phenomenon is biological magnification. Non-biodegradable chemicals such as many pesticides enter a food chain through the plants. They are not broken down or excreted, so they get accumulated in each organism, and because an organism eats large amounts of food from the level below, their concentration increases progressively at each trophic level. Human beings are at the top of many food chains, so the maximum concentration of these chemicals can build up in our bodies, and beyond a limit it damages our organs.