Ncert Books Class 12 Biology Chapter 15 Free Download

Conserving biodiversity is essential for human survival and well-being. The key arguments, often asked in board exams, are:

• Narrowly Utilitarian: This argument focuses on the direct economic benefits derived from nature. Examples include food (cereals, pulses, fruits), firewood, fibre, industrial products (tannins, lubricants, dyes), and medicines. More than 25% of drugs are derived from plants.
• Broadly Utilitarian: This argument covers the wide range of ecosystem services that biodiversity provides. These include oxygen production by forests, pollination of crops by insects and birds, climate regulation, and aesthetic and cultural benefits like tourism.
• Ethical Argument: This focuses on the intrinsic value of every species. It suggests that all species have a right to exist, whether they are economically useful to humans or not. We have a moral duty to care for and pass on our biological legacy to future generations.

The 'Evil Quartet' is a term used to describe the four most significant causes of biodiversity loss. This is a very important question for the board exams. They are:

• Habitat Loss and Fragmentation: This is the primary driver of extinction. It occurs when large habitats are destroyed (e.g., deforestation for agriculture) or broken into smaller, isolated fragments, which cannot support large populations.
• Over-exploitation: When humans harvest species (e.g., Steller's sea cow, passenger pigeon) at a rate faster than they can replenish, it leads to their extinction.
• Alien Species Invasions: When non-native species are introduced into an ecosystem, they can outcompete native species for resources or introduce diseases, leading to the extinction of indigenous species. The introduction of the Nile perch into Lake Victoria is a classic example.
• Co-extinctions: When one species becomes extinct, plant and animal species associated with it in an obligatory way also face extinction. For example, the extinction of a host fish leads to the extinction of its unique parasites.

Biodiversity hotspots are regions with extremely high species richness and a high degree of endemism (species found nowhere else). Although these hotspots collectively cover less than 2% of the Earth's land area, they harbour an exceptionally large number of species. Therefore, by concentrating conservation efforts and providing strict protection to these hotspots, we can protect a vast number of species, especially the most vulnerable ones, in a very efficient way. It is estimated that protecting all hotspots could reduce the ongoing rate of mass extinctions by almost 30 percent. This makes it a crucial strategy for global conservation.

This is a key conceptual question. The primary difference lies in the location of conservation:

• In-situ (On-site) Conservation: This involves protecting and conserving species within their natural habitats. It is the most effective way to conserve the entire ecosystem and its biodiversity at all levels. Examples: National Parks (e.g., Jim Corbett National Park), Biosphere Reserves (e.g., Nilgiri Biosphere Reserve), and Sacred Groves.
• Ex-situ (Off-site) Conservation: This involves protecting threatened species outside their natural habitats in specially created facilities. This is often used when a species is critically endangered and its natural habitat is no longer safe. Examples: Zoological parks (zoos), botanical gardens, and cryopreservation (gamete and seed banks).

The species-area relationship, proposed by Alexander von Humboldt, describes a consistent pattern in ecology: within a region, species richness increases with the area explored, but only up to a certain limit. This relationship is represented by the equation S = CA^Z, where S is species richness, A is area, C is the Y-intercept, and Z is the slope of the line (regression coefficient).
This concept is critically important because the value of 'Z' (the slope) indicates how quickly species are lost as habitat area is reduced. A steeper slope means a faster loss of species with habitat destruction. Ecologists use this relationship to predict the number of species that might become extinct if a certain area of habitat, like a rainforest, is lost.

For the CBSE 2025-26 exam, you can expect MCQs and objective questions focusing on:

• Specific Data: The number of species of ants, beetles, fishes, or orchids. The total number of biodiversity hotspots in the world (34).
• Key Terms: Definitions of endemism, biodiversity hotspots, cryopreservation, and the full form of IUCN.
• Examples: Identifying examples of in-situ (e.g., sacred groves) vs. ex-situ conservation (e.g., seed banks). Identifying which of the 'Evil Quartet' is responsible for a given scenario (e.g., extinction of the dodo due to the passenger pigeon).
• Convention Dates: The year of The Earth Summit (Rio de Janeiro, 1992) and The World Summit on Sustainable Development (Johannesburg, 2002).

Sacred groves are tracts of forest set aside by local communities and dedicated to deities or ancestral spirits. All trees and wildlife within are given complete protection due to religious and cultural beliefs. This traditional practice is a powerful form of decentralised, community-led in-situ conservation.
Their contribution is significant because:

• They protect a large number of rare and threatened species that might otherwise be lost.
• They serve as a refuge for endemic species and a repository of medicinal plants.
• They represent the last remnants of native vegetation in many areas that have been otherwise cleared for agriculture or urbanisation, acting as biodiversity islands.