Chapter 2, Problem 30A

Summary Introduction

Introduction : The exchange of matter through the biosphere is called biogeochemical cycle. Nitrogen cycle is one such biogeochemical cycle in which nitrogen is recycled from atmosphere into compounds that can be used by plants.

Answer to Problem 30A

Correct answer :

The correct answer is option D. Nitrogen fixation

Explanation of Solution

Explanation for incorrect answer:

Option D. Nitrogen fixation- Plants and animals cannot use nitrogen directly from the atmosphere. Some bacteria that live in soil, water and in plant root nodules capture the nitrogen from air and convert it to compounds that are useful to plants. This process is called nitrogen fixation. Some nitrogen is also fixed during lightning when the energy from lightning, convert nitrogen to nitrates. Hence this is the correct option.

Explanation for incorrect answer:

Option A. Ammonification- It is a process during which the soil bacteria and decomposers decompose the dead organisms and transform the nitrogen in proteins and other compounds into ammonia. Hence this is not a correct option.

Option B. Nitrate cycling- This is a continuous process during which nitrogen is converted to nitrates and other compounds and is used and reused by plants and animals. Nitrogen is cycled continuously through the biosphere. It involves nitrogen fixation, ammonification and denitrification. Hence, this is an incorrect option.

Option C. Denitrification- This is the end process in nitrogen cycle. Organisms present in soil convert fixed nitrogen compounds back into nitrogen gas which escapes into the atmosphere. This process is called denitrification. Hence, this option is incorrect.