Question

Assertion: In tropical rainforest O horizon and A horizon of soil profile are shallow and nutrient-poor.
Reason: Excessive growth of microorganisms in soil depletes its organic content.
(a) Both assertion and reason are correct and the region is the correct explanation of assertion.
(b) Both assertion and reason are correct but the reason is not the correct explanation for the assertion.
(c) Assertion is correct but the reason is incorrect.
(d) Both assertion and reason are incorrect.

Answer 1

Hint: In the tropical rainforest, the nutrient content of the soil is very poor because of heavy rain that flushes out the nutrient on top of the soil as water is a great solvent.

Complete answer:
O horizon is the topmost layer of soil and a horizontal comes below zero horizontal. Vegetation grows and various biological activities take place in this topmost layer. In a tropical rainforest, the temperature is very high as well as the humidity because of the high rainfall rate in this area. The soil in this area is red latosols and is very thick. Leaching of minerals from the topsoil occurs rapidly. Leaching is the process through which water is caring for soluble substances and small particles’ true soil or rock. In the leaching process as the water passes through the rock and soil it interacts with the surface minerals as the result the compounds on the minerals can get dissolved in the water. As well as the cycling of nutrients occurs very rapidly. So the nutrient content isn't low thanks to bacteria but is low thanks to leaching.

So the correct answer is 'Assertion and Reason are true but Reason is not the correct explanation of Assertion'.

Note:
- Vegetation grows and various biological activities take place in this topmost layer of the soil.
- In a tropical rainforest, the temperature is very high, and also the rate of rainfall is high too.
- Leaching is the process through which nutrients of the top layer of soil get dissolved in the water and make it less fertile.