Chapter 2, Problem 3STP

Summary Introduction

Introduction : The exchange of matter through the biosphere is called biogeochemical cycle. Carbon cycle is one such biogeochemical cycle in which carbon is recycled as carbohydrates and carbon dioxide.

Answer to Problem 3STP

Correct answer :

The correct answer is option C. Photosynthesis and respiration

Explanation of Solution

Explanation/justification for the correct answer:

Option C. Photosynthesis and respiration- During photosynthesis green plants and algae use carbon dioxide from the atmosphere to form carbohydrates and release oxygen back into air. So here the CO₂ moves from abiotic part of ecosystem (atmosphere) to biotic system (green plants and algae). The carbohydrates are used as a source of energy by other organisms in the food web. They respire and release CO₂ back to the air. Hence, this is the correct option.

Explanation for incorrect answer:

Option A. Dissolved CO₂- Carbon moves from abiotic part of the ecosystem to biotic part when the producers convert CO₂into food. A very small part of CO₂ gets dissolved in oceans and water and is available to living organisms. The release of this carbon back to the atmosphere is a very slow process. Hence, this is not a correct option.

Option B. Fuel combustion- Carbon is trapped in fossil fuels for millions of years before they are released by burning of fuels. Hence, this is an incorrect option.

Option D. Volcanic activity- Carbon moves from abiotic part of the ecosystem to biotic part when the producers convert CO₂into food. Carbon is also released through volcanic activities but it is a slow process. Here carbon moves from abiotic to biotic part of ecosystem. Hence, this option is incorrect.