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

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NCERT Solutions PDF Class 12 PDF

This chapter delves into the critical concepts of Biodiversity and Conservation for Class 12 Biology students. It explores the fundamental components of biodiversity, including genetic, species, and ecosystem diversity. The solutions explain the methods ecologists use to estimate global species richness and present hypotheses for the exceptionally high species diversity found in tropical regions. It further discusses the significance of the species-area relationship and its regression slope. Crucially, the chapter outlines the major threats leading to species loss, such as habitat destruction, over-exploitation, alien species invasions, and co-extinction. These detailed NCERT Solutions are designed to provide clear explanations and step-by-step guidance, aiding students in understanding complex ecological principles and preparing thoroughly for their board examinations.

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BoardCBSE
ClassClass 12
SubjectBiology
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 15

Chapter summary

Chapter 15 of the CBSE Class 12 Biology syllabus focuses on Biodiversity and Conservation. The NCERT Solutions provided cover the essential aspects, including the three levels of biodiversity (genetic, species, ecosystem), methods for estimating global species numbers, and reasons for higher biodiversity in tropics. It also explains the species-area relationship and details the primary causes of species extinction: habitat loss, over-exploitation, invasive species, and co-extinction. These solutions offer a clear breakdown of each topic, facilitating student comprehension and revision.

Learning outcomes

  • Understand the three main components of biodiversity.
  • Learn how ecologists estimate global species richness.
  • Explain the hypotheses behind tropical species richness.
  • Analyze the significance of the species-area relationship.
  • Identify and describe the major causes of species loss.

Topics covered

Paper topics

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

Important topics

  • Components of Biodiversity
  • Hypotheses for Tropical Richness
  • Major Causes of Species Loss
  • Species-Area Relationship
  • Alien Species Invasions

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Questions and Solutions

Question 1

What are the three important components of biodiversity?
Solution: Biodiversity refers to the variety of life forms found in a particular habitat or on 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:
  1. Genetic diversity: This refers to the variety of genes within a single species. It includes the different alleles and genotypes present in the population, which contribute to variations in traits and adaptability.
  2. Species diversity: This represents the variety of different species within a given area or ecosystem. It is often measured in terms of species richness (number of species) and species evenness (relative abundance of species).
  3. Ecosystem diversity: This component describes the variety of different habitats, biological communities, and ecological processes within a region or across the globe. Examples include deserts, forests, grasslands, wetlands, and marine ecosystems.

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 comparative analysis allows them to estimate the total species richness across the entire planet. Current estimates suggest there are approximately seven million species on Earth.

Question 3

Give three hypotheses for explaining why tropics show greatest levels of species richness.
Solution: The exceptionally high species richness observed in tropical regions compared to temperate or polar areas is explained by several hypotheses:
  1. Higher Productivity: Tropical latitudes receive more direct solar energy throughout the year. This abundant energy supports higher rates of photosynthesis and primary productivity, which in turn can sustain a larger number of species and larger populations.
  2. Environmental Stability: Tropical regions generally experience less seasonal variation and have a more stable, constant climate compared to temperate zones. This consistent environment reduces the likelihood of species extinction due to extreme conditions and allows for greater niche specialization, where species evolve to utilize specific resources or habitats, thus increasing overall diversity.
  3. Evolutionary Time and Lack of Glaciation: Unlike temperate regions that were repeatedly subjected to severe glaciations during the ice ages, tropical areas remained relatively undisturbed. This longer period of stable conditions allowed more time for speciation to occur and for existing species to evolve and diversify without catastrophic interruptions.

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 found in a given area increases as the area 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 relatively consistent across different taxonomic groups and regions. However, when analyzing larger areas, the slope of the regression line typically becomes much steeper, indicating that species richness increases more rapidly as the area expands. This steeper slope signifies a stronger relationship between area size and the number of species present.

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 a geographical region include:
  1. Habitat Loss and Fragmentation: This is considered the most significant cause. Human activities such as deforestation for agriculture and urbanization, mining, and dam construction destroy or degrade natural habitats. When large habitats are broken into smaller, isolated patches (fragmentation), it restricts the movement of species, reduces gene flow, and makes populations more vulnerable to extinction.
  2. Over-exploitation: The excessive use of biological resources by humans, such as over-hunting, over-fishing, and unsustainable harvesting of plants, can deplete populations to the point of extinction. Historically, species like the passenger pigeon and the tiger have been driven to endangerment or extinction due to over-exploitation.
  3. Alien Species Invasions: When non-native (exotic or alien) species are introduced, either accidentally or intentionally, into a new ecosystem, they can outcompete, prey upon, or introduce diseases to native species. This can lead to the decline or extinction of indigenous species. A classic example is the introduction of the Nile perch into Lake Victoria, which caused the extinction of over 200 native cichlid fish species.
  4. Co-extinction: Biodiversity is interconnected. In many cases, a species depends obligatorily on another species for its survival. If the dependent species goes extinct, the species relying on it will also likely go extinct. For instance, if a specific host plant species becomes extinct, any insect species that exclusively feeds on that plant will also face extinction. Similarly, the extinction of a host animal can lead to the extinction of its specific parasites.

Common mistakes

  • Confusing the different levels of biodiversity.
  • Not clearly articulating the hypotheses for tropical richness.
  • Failing to explain the implications of the regression slope in species-area relationships.
  • Underestimating the impact of human activities on biodiversity loss.

Revision tips

  • Focus on understanding the definitions of genetic, species, and ecosystem diversity.
  • Memorize the four major causes of species loss and their examples.
  • Review the hypotheses explaining tropical biodiversity for potential essay questions.
  • Practice explaining the species-area relationship and the meaning of the regression slope.

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 primarily by:

Q3. Which hypothesis suggests that constant environmental conditions in the tropics promote niche specialization?

Q4. A steeper slope of regression in a species-area relationship typically indicates:

Q5. The introduction of the Nile perch into Lake Victoria led to:

Frequently asked questions

What are the three main components of biodiversity as per NCERT Class 12 Biology?

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 communities).

How do scientists estimate the total number of species on Earth?

Ecologists estimate the total number of species by statistically comparing the species richness of well-studied groups (like insects) in temperate and tropical regions and then extrapolating these ratios to other groups and the entire planet.

Why is species richness generally higher in the tropics?

Several hypotheses explain this: tropics receive more solar energy leading to higher productivity, they have less seasonal variation promoting niche specialization, and they were less affected by past glaciations compared to temperate regions.

What is the significance of the regression slope (z) in the species-area relationship?

The slope of regression (z) quantifies how species richness increases with area. While its value is relatively constant for smaller areas across different groups, it can be steeper in larger areas, indicating a more rapid increase in species richness with increasing area.

What are the four major causes of species extinction discussed in this chapter?

The four major causes are habitat loss and fragmentation, over-exploitation of resources, invasion by alien species, and co-extinction, where the extinction of one species leads to the extinction of another dependent species.

How can these NCERT Solutions help in exam preparation?

These solutions provide clear, rewritten explanations for each question, breaking down complex topics like biodiversity components, tropical richness hypotheses, and causes of species loss into understandable steps, aiding effective revision and concept clarity for exams.

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