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CBSEScience (English Medium) Class 12
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Syllabus

Overview of Biodiversity and Its Conservation

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Topics

CBSE: Class 12

Key Points: Patterns of Biodiversity (Latitudinal Gradient)

  • Species diversity is highest in the tropics and gradually decreases from the equator towards the poles.
  • Tropical regions (23.5°N–23.5°S) harbour far more species than temperate and polar regions, as seen in birds, plants and other organisms.
  • The Amazon rainforest shows the greatest biodiversity on Earth, with thousands of plant, animal and insect species.
  • Higher tropical diversity is due to long uninterrupted evolutionary time, stable and less seasonal climate, and greater solar energy leading to high productivity.
CBSE: Class 12

Key Points: Patterns of Biodiversity (Species–Area Relationship)

  • Species richness increases with an increase in the explored area, but only up to a certain limit.
  • The relationship between species richness and area follows a rectangular hyperbola and becomes a straight line on a logarithmic scale.
  • The relationship is expressed by the equation: log S = log C + Z log A, where Z represents the slope of the line.
  • For small regions, Z usually ranges from 0.1–0.2, but for very large areas like continents, steeper slopes (0.6–1.2) indicate a much faster increase in species richness with area.
 
CBSE: Class 12

Key Points: The importance of Species Diversity to the Ecosystem

  • Communities with higher species diversity are generally more stable, showing less year-to-year variation in productivity and better resistance to disturbances and invasions.
  • Experimental studies (e.g., David Tilman’s work) show that increased species diversity leads to higher productivity and stability in ecosystems.
  • Loss of species can weaken ecosystem functioning, even if the effects are not immediately visible.
  • The rivet popper hypothesis explains that continuous loss of species can critically damage ecosystems, especially when key species are lost.
CBSE: Class 12

Key Points: Need for Biodiversity Conservation

  • Biodiversity provides direct economic benefits such as food, fuel, fibre, industrial products and medicines (narrowly utilitarian value).
  • A large proportion of modern and traditional medicines are derived from plants, with many more potential resources yet to be discovered.
  • Biodiversity supports vital ecosystem services like oxygen production, pollination, climate regulation and nutrient cycling (broadly utilitarian value).
  • Nature offers important aesthetic, cultural and recreational benefits that improve human well-being.
  • Ethically, every species has intrinsic value, and humans have a moral responsibility to protect biodiversity for future generations.
CBSE: Class 12

Key Points: Methods of Biodiversity Conservation

Aspect In situ Conservation Ex situ Conservation
Meaning Conservation of species in their natural habitats Conservation of species outside their natural habitats
Level protected Protects whole ecosystems and communities Protects individual species
When used When species can survive in natural conditions When species are endangered or near extinction
Main methods Biosphere reserves, national parks, sanctuaries Zoos, botanical gardens, seed banks
Indian examples Western Ghats, Himalayas, sacred groves Zoological parks, botanical gardens
Advanced techniques Habitat protection, hotspot conservation Cryopreservation, tissue culture
Importance Maintains natural evolution and interactions Prevents immediate extinction
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