Miscellaneous: UPSC Previous Year Questions (Science and Technology)

Explanation

The carbon cycle is a biogeochemical process where carbon atoms continuously move between the atmosphere, oceans, soil, and living organisms through processes like photosynthesis, respiration, decomposition, and combustion. Through photosynthesis, plants absorb atmospheric CO₂ to produce glucose, while animals release CO₂ through respiration, and when organisms die, decomposition returns their carbon to the soil and atmosphere, completing this vital planetary cycle.

Statement 1 is correct: Volcanic eruptions release CO₂ stored in Earth’s mantle into the atmosphere, contributing to the carbon cycle.

Statement 2 is correct: Respiration is the process by which organisms, including plants and animals, convert organic compounds into energy, producing CO₂ as a byproduct. This CO₂ is then released into the atmosphere.

Statement 3 is incorrect: Photosynthesis is the process by which green plants, algae, and some bacteria absorb CO₂ from the atmosphere and, using sunlight, convert it into glucose and oxygen. This process removes CO₂ from the atmosphere.

Statement 4 is correct: When organisms die, decomposers like bacteria and fungi break down their organic matter, resulting in the release of CO₂ back into the atmosphere through the process of decomposition.

Explanation

Ecological succession is the process of change in the species structure of an ecological community over time. Types of Succession:

Primary Succession occurs on newly formed or exposed land where no previous life existed (e.g., bare rock, lava flows). Pioneer species like lichens and mosses initiate the process, gradually leading to the development of soil and a stable ecosystem. Secondary Succession happens in areas where an ecosystem previously existed but was disturbed (e.g., after a forest fire or flood). Soil is already present, and recovery occurs more quickly than in primary succession.

Option (b) is correct: Lichens are among the first organisms to colonize bare rock or barren environments, breaking down minerals to create soil and paving the way for other plants and organisms. They are unique composite organisms resulting from a symbiotic association between a fungus and a photosynthetic partner, which can be either green algae or cyanobacteria. In this partnership, the fungal component, known as the mycobiont, provides structure and protection, while the photosynthetic partner, referred to as the photobiont, contributes nutrients through photosynthesis.