(i) Ecology is the branch of biology which studies the interaction of organisms with their physical environment and with each other. It is the study of ecosystems. The term ecology is derived from the Greek word ‘oikos’ meaning house, combined with the word ‘logy’ meaning the ‘study of’. We can study ecology at many different levels. For example, we may study organisms, populations, ecosystems and the biosphere in ecology. It is the study of interactions of biotic and abiotic factors.

(ii) Ecological system is a system consists of biotic and abiotic components. It includes all of the living things in a given area that interact with each other, as well as the non-living environments. The living and physical components are linked together through nutrient cycles and energy flows.

The major types of ecosystems in the world are:

*Terrestrial ecosystem: It is a type of ecosystem found only on biomes.

*Aquatic ecosystem: Communities of plants and animals living in water are known as aquatic ecosystems.

(iii) Food chain is the transfers of matter and energy in the form of form of food from one level to another. Each level of a food chain represents a different trophic level. Two types of food chain are: Grazing food chain and detritus food chain. Grazing food chain starts with plant as producers, herbivores are the intermediate level and ends with carnivores as consumers. Detritus food chain begins with dead organic matter. Example of grazing food chain is grass (producer) is eaten by goat (primary consumer) is eaten by man (secondary consumer). Grass is the first level, goat is the intermediate level and man is the last level.

(iv) Food web is a network of many different food chains. It is an important ecological concept. It represents feeding relationships within a community. Food webs are constructed to describe species interactions. Food web is also known as consumer resource system. For example, a mouse feeding on grain may be eaten by different secondary consumers (carnivores) and these carnivores may be eaten by other different tertiary consumers (top carnivores).

(v) A biome is a plant and animal community that covers a large geographical area. They can be found over a range of continents. They cover large areas. They comprise a variety of habitats. They are a way to divide the Earth’s surface. These divisions are based on the climate patterns, soil types, and the animals and plants that inhabit an area. There are five major biomes- forest, desert, grassland, altitudinal and aquatic biomes. Major biomes of India are tropical rain forest, deciduous forest, and desert.