Question
Explain how harmful chemicals enter our bodies.
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Answer
Pesticides are poisonous chemical substances which are sprayed over crop plants to protect them from pests (harmful small animals) and diseases. These chemical pesticides mix up with soil and water. From soil and water, these pesticides are absorbed by the growing plants alongwith water and other minerals. When herbivorous animals eat plant food, then these poisonous chemical pesticides go into their bodies through the food chain. And when the carnivore animals eat herbivores, then the pesticides get transferred to their bodies. Man being an omnivore; eat plant food as well as herbivores. So the pesticides present in plant food and herbivores also get transferred to the man’s body through food. Thus, pesticides enter the food chain at the producer level (plant level) and in the process of transfer of food through food chains these harmful chemicals get concentrated at each trophic level.
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→The observations made by Swarali while doing the experiment are given below. Based on these write answers to the questions;
Swarali found that the light ray travelling from the denser medium to rarer medium goes away from the normal. If the angle of incidence (i) is raised by Swarali, the angle of refraction ( $r$ ) went on increasing. However, after certain value of the angle of incidence the light ray is seen to return back into the denser medium.
i. What is the specific value of $\angle i$ called?
ii. What is the process of reflection of incident ray into denser medium called?
iii. Draw the diagrams of three observations made by Swarali.
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