CBSE Class 12 Biology Chapter 15: Biodiversity and Conservation NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 12 PDF

This chapter delves into the critical concepts of Biodiversity and Conservation for CBSE Class 12 Biology students. It explores the multifaceted nature of biodiversity, breaking it down into genetic, species, and ecosystem diversity. The solutions explain the ecological estimations of global species richness, particularly focusing on why tropical regions exhibit higher biodiversity than temperate zones. It further elaborates on the significance of the species-area relationship and the regression slope. A significant portion is dedicated to identifying and explaining the major causes of species loss, including habitat destruction, over-exploitation, invasive alien species, and co-extinction. These solutions provide clear, step-by-step explanations to help students grasp complex ecological principles and prepare effectively for their examinations.

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Board	CBSE
Class	Class 12
Subject	Biology
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 15: Biodiversity and Conservation

Chapter summary

Chapter 15 of the CBSE Class 12 Biology syllabus focuses on Biodiversity and Conservation. The NCERT Solutions cover the fundamental components of biodiversity (genetic, species, ecosystem), methods for estimating global species numbers, and hypotheses explaining tropical species richness. It also addresses the species-area relationship and critically examines the primary drivers of species loss: habitat loss, over-exploitation, alien species invasion, and co-extinction. These solutions aim to provide a clear understanding of ecological diversity and the urgent need for its conservation.

Learning outcomes

Understand the three main components of biodiversity.
Learn how ecologists estimate global species richness.
Explain the reasons for higher species richness in tropical regions.
Interpret the significance of the regression slope in species-area relationships.
Identify and describe the major causes of species loss.
Recognize the interconnectedness of species and the concept of co-extinction.

Topics covered

Paper topics

Components of Biodiversity
Genetic Diversity
Species Diversity
Ecosystem Diversity
Estimation of Species Richness
Tropical Biodiversity
Species-Area Relationship
Regression Slope (z)
Causes of Species Loss
Habitat Loss and Fragmentation
Over-exploitation
Alien Species Invasion
Co-extinction

Important topics

Components of Biodiversity
Hypotheses for Tropical Species Richness
Species-Area Relationship
Major Causes of Species Loss
Habitat Loss and Fragmentation
Alien Species Invasion

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Questions and Solutions

Question 1

Name the three important components of biodiversity.

Solution: Biodiversity refers to the variety of life forms found within a given ecosystem, biome, or the entire Earth. It encompasses the variability among living organisms from all sources, including terrestrial, marine, and other aquatic ecosystems, as well as the ecological complexes of which they are part. The three fundamental components of biodiversity are:

Genetic diversity: This refers to the total number of genetic characteristics, in the genetic makeup of a species. It represents the variation of genes within a single species.
Species diversity: This is the variety of different species present in a particular region or ecosystem. It is often measured by the number of species (species richness) and their relative abundance (species evenness).
Ecosystem diversity: This refers to the variety of different habitats, biological communities, and ecological processes within a given area or across the Earth. Examples include deserts, rainforests, grasslands, and wetlands.

Question 2

How do ecologists estimate the total number of species present in the world?

Solution: Estimating the total number of species on Earth is a complex task due to the vastness and unexplored nature of many ecosystems. Ecologists employ a method based on statistical extrapolation. They begin by studying the species richness of a well-documented group of organisms, such as insects, in both temperate and tropical regions. By analyzing the ratio of species richness in these well-studied groups and regions, they can then extrapolate these findings to other groups of plants and animals. This statistical comparison allows them to estimate the total species richness across the entire planet. Current estimates suggest there are about seven million species on Earth.

Question 3

Give three hypotheses for explaining why tropics show greatest levels of species richness.

Solution: The significantly higher species richness observed in tropical regions compared to temperate or polar regions is explained by several ecological and evolutionary hypotheses. Three prominent hypotheses are:

The Productivity Hypothesis: Tropical latitudes receive more direct solar energy throughout the year. This higher energy input supports greater primary productivity, leading to more resources available for a larger number of species and thus higher biodiversity.
The Environmental Stability Hypothesis: Tropical regions generally experience less seasonal variation and more constant environmental conditions compared to temperate zones. This stable climate promotes niche specialization, allowing species to adapt to specific conditions and coexist, leading to higher species diversity.
The Evolutionary Time Hypothesis: Temperate regions have historically been subjected to severe glaciations during ice ages, which caused mass extinctions and reset ecological processes. In contrast, tropical regions remained relatively undisturbed and warmer, providing a longer, continuous period for species to evolve, diversify, and accumulate over evolutionary time.

Question 4

What is the significance of the slope of regression in a species – area relationship?

Solution: The species-area relationship describes how the number of species in a given area increases as the area itself increases. The slope of the regression line, often denoted by the letter 'z', is a crucial parameter in this relationship. It quantifies the rate at which species richness increases with area. For smaller geographical areas, the value of 'z' tends to be similar across different taxonomic groups and regions, typically ranging between 0.1 and 0.2. However, when analyzing species-area relationships across much larger areas, such as entire continents, the slope of the regression becomes significantly steeper, often ranging between 0.6 and 1.2. This steeper slope indicates a more rapid increase in species richness as the area expands at larger scales.

Question 5

What are the major causes of species losses in a geographical region?

Solution: The rapid decline in biodiversity worldwide is attributed to several major anthropogenic and natural causes. The primary drivers of species loss in any geographical region include:

Habitat Loss and Fragmentation: This is considered the most significant cause. Human activities such as deforestation for agriculture and urbanization, slash-and-burn cultivation, mining, and dam construction destroy or alter natural habitats. Fragmentation breaks large, continuous habitats into smaller, isolated patches, which can hinder species movement, reduce gene flow, and make populations more vulnerable to extinction.
Over-exploitation: This occurs when humans harvest organisms at a rate faster than their ability to reproduce and replenish their populations. Over-hunting, over-fishing, and excessive collection of plants for medicinal or commercial purposes have led to the endangerment and extinction of many species, such as the passenger pigeon and the tiger.
Alien Species Invasions: When non-native (exotic) species are accidentally or intentionally introduced into a new habitat, they can outcompete, prey upon, or introduce diseases to native species, leading to their decline or extinction. A classic example is the introduction of the Nile perch into Lake Victoria, which caused the extinction of over 200 endemic cichlid fish species.
Co-extinction: Biodiversity is interconnected. When a species becomes extinct, any species that depend on it obligately for survival also face extinction. For instance, if a specific host insect goes extinct, any specialized parasite that lived only on that insect will also become extinct.

Common mistakes

Confusing the different levels of biodiversity.
Underestimating the impact of human activities on species loss.
Not clearly articulating the hypotheses for tropical biodiversity.
Misinterpreting the species-area relationship and regression slope.

Revision tips

Create flashcards for the three components of biodiversity and the four major causes of species loss.
Draw diagrams to illustrate habitat loss and fragmentation.
Summarize the hypotheses for tropical species richness in your own words.
Review the examples provided for each cause of species loss to solidify understanding.

Practice MCQs

Q1. Which of the following is NOT considered a primary component of biodiversity?

Q2. Ecologists estimate the total number of species on Earth by:

Q3. Which hypothesis suggests that stable, non-seasonal environments in the tropics promote niche specialization and thus higher species richness?

Q4. According to the species-area relationship, what is generally observed about the slope of regression (z) in larger areas?

Q5. Which of the following is an example of a cause for species loss due to alien species invasion?

Frequently asked questions

What are the three main components of biodiversity discussed in Chapter 15?

The three main components of biodiversity are genetic diversity (variations within a species), species diversity (variety of species in an area), and ecosystem diversity (variety of habitats and ecological processes).

Why is species richness generally higher in the tropics?

Several hypotheses explain this, including higher solar energy input leading to greater productivity, stable and less seasonal environments promoting specialization, and the fact that tropical regions were less affected by past glaciations, allowing more time for diversification.

What does the slope of regression (z) signify in a species-area relationship?

The slope of regression (z) quantifies the rate at which species richness increases with an increase in area. It is found to be steeper in larger areas compared to smaller ones.

What are the four major causes of species loss mentioned in the NCERT solutions?

The four major causes are habitat loss and fragmentation, over-exploitation, alien species invasions, and co-extinction.

Can you give an example of co-extinction?

Yes, if a specific parasite species can only survive on a particular host species, the extinction of the host species will inevitably lead to the extinction of its associated parasite.

How do these NCERT solutions help in preparing for exams?

These solutions provide clear, detailed, and accurate answers to all questions from the NCERT textbook, helping students understand complex ecological concepts and revise effectively for their board examinations.

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