(i) Biodiversity refers to variety and variability of life on Earth. It is also known as biological diversity. It is the combination of two words Bio and diversity. Bio means life and diversity means variety. It includes microorganism, plants, animals and ecosystem such as coral reefs, forests, deserts etc. The term biodiversity is popularised by the sociobiologist Edward Wilson. It is not distributed evenly on Earth. It is richer in tropical regions. It is very important for maintaining balance of the ecosystem. Greater biodiversity in ecosystems leads to greater stability.

(ii) The different levels of biodiversity are:

*Genetic diversity: It refers to the variation of genes within species. It is essential for a healthy breeding of population of species. For example, India has more than 50,000 genetically different strains of rice and 1000 varieties of mango.

*Species diversity: It refers to the variety of species. For example, the Western Ghats have greater amphibian species diversity than the Eastern Ghats.

*Ecosystem diversity: It refers to the variety of habitats, natural communities and ecological processes in the biosphere. For example, deserts, wetlands, forest, grasslands etc.

(iii) Hotspots are the areas rich in species diversity. It is a biogeographic region with significant levels of biodiversity that is threatened with humans. It is important ecosystem in the world and habitat of endemic species. Initially 25 biodiversity hotspots were identified but subsequently nine more have been added to the list. Total numbers of biodiversity hotspots in the world are 34. India hosts 4 biodiversity hotspots: the Western Ghats, the Himalayas, the Indo-Burma region and the Sundaland.

(iv) Animals are important to humans in many ways:

*Animals are part of the food chain and keep ecosystems in balance.

*Animals have made human life much easier by providing us with food, medicine, clothing etc.

*Animals help to bring out the nutrients from the cycle while others help in decomposition, carbon, and nitrogen cycle.

*Animals like horses, ox, buffalo etc are used for transportation.

*Animals provide milk which is the essential in human lives.

*Fishing, rearing of hens and pigs in farms provide employment for the humans.

(v) Exotic species are species of plants and animals that are not the natural inhabitants of the local habitat, but are introduced into the system. It is also known as alien species, invasive species and non-indigenous species. Examples of exotic species are brown rat, house sparrow, carrot grass, Lantana and water hyacinth. It causes damage to the environment, human economy and human health. Some of the exotic species leads to extinction of indigenous species. It can change the food web in an ecosystem by destroying or replacing native food sources.