Ernst Haeckel, a German biologist, coined the term 'oekologie' (ecology) in 1869. He defined it as the study of the relationship between organisms and their environment, establishing it as a distinct field of biological science that examines how living beings interact with both biotic and abiotic factors in their surroundings.

The tundra biome is characterized by extremely cold temperatures, low biotic diversity, and a very short growing season. The subsoil is often permanently frozen (permafrost), which limits root growth. Precipitation is generally low, and the harsh climate restricts vegetation to low-growing plants like mosses, lichens, and small shrubs, as the environment is too severe for most tree species.

Melanization refers to the darkening of soil horizons due to the accumulation and incorporation of organic matter (humus). This process is a key component of soil development, enhancing soil fertility and structure by darkening the topsoil layer.

Grasslands are known by different names globally: Steppes are found in Eurasia, Llanos are tropical grasslands in South America (Brazil/Venezuela), Savannas are typical of India and Africa, and Prairies are the temperate grasslands of North America and Canada.

The term 'Sal savannah' refers to specific ecological zones in Northern India dominated by the Sal tree (Shorea robusta) within an alluvial savannah landscape. These regions are characterized by specific soil types and vegetation patterns adapted to the local climate and alluvial deposits, distinguishing them from other types of savannah or forest classifications found in different geographical regions.

In phytosociology, an association is the basic unit of classification for plant communities. It refers to a stable plant community that exhibits a distinct and recurring floristic composition, occupies a uniform habitat, and maintains a characteristic physiognomy. Associations are used by ecologists to categorize vegetation types and understand the interactions between plant species and their environment within a specific ecosystem.

Statement 1 correctly identifies that ecological interactions involve mutual responses. Statement 2 accurately defines a feedback loop as a system where outputs influence future inputs. Statements 3 and 4 are reversed; negative feedback typically maintains homeostasis, while positive feedback amplifies changes, leading to instability or rapid shifts, making the provided answer key consistent with this interpretation.

Savannah ecosystems are characterized by distinct wet and dry seasons. The dry season, which often coincides with high temperatures (summer), acts as a physiological resting period for vegetation due to water scarcity, forcing plants to enter dormancy or shed leaves to conserve moisture.

Composting is a managed biological process where organic waste is broken down by a diverse community of microorganisms. Initially, aerobic bacteria dominate, generating heat. As oxygen is depleted in the center of the pile, anaerobic microorganisms continue the decomposition process. This succession of aerobic and anaerobic phases is essential for transforming raw organic matter into stable, nutrient-rich humus used as a soil conditioner.

Tropical moist deciduous forests are found in central and northern Burma. Tropical dry deciduous forests are characteristic of Central India. Tropical dry evergreen forests occur along the coasts of Andhra and Chennai. Sub-tropical pine forests are distributed in the belt from Kashmir to Assam and Burma. Matching these ecological distributions confirms option D as the correct classification.