CBSE Class 12 Biology Revision Notes Chapter 13: Biodiversity and Conservation
Biodiversity includes variation within species, between species and across ecosystems. Its conservation protects ecological stability, biological resources and the natural systems that support human life.
Earth supports an enormous variety of plants, animals and microorganisms. This diversity has developed through millions of years of evolution, but human activities can destroy species and habitats within a much shorter period.
These CBSE Class 12 Biology Revision Notes Chapter 13 follow the current 2026–27 chapter sequence. They explain biodiversity levels, global patterns, species extinction and conservation methods through concise notes, examples and comparison tables.
Key Takeaways
- 7 million: Robert May’s conservative estimate of global species diversity.
- 8.1%: India’s share of global species diversity despite having only 2.4% of the world’s land area.
- 100–1,000 times: Current extinction rates compared with pre-human rates.
- 34: Number of biodiversity hotspots stated in the NCERT chapter.
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Biodiversity and Conservation Class 12 Notes Overview
The Biodiversity and Conservation Class 12 Notes explain how biological variety is distributed and why its rapid decline is a global concern.
The chapter also compares conservation within natural habitats with methods used outside those habitats.
| Chapter Area | Main Focus |
| Biodiversity | Genetic, species and ecological variation |
| Species diversity | Global and Indian species richness |
| Biodiversity patterns | Latitudinal gradients and species-area relationship |
| Ecosystem importance | Stability, productivity and resilience |
| Biodiversity loss | Extinction rates and the evil quartet |
| Conservation | In situ and ex situ methods |
Access Class 12 Biology Chapter 13 Biodiversity and Conservation Notes in 30 Minutes
Use this sequence for rapid revision:
- Learn the three levels of biodiversity.
- Revise global species estimates and India’s biodiversity.
- Understand the latitudinal gradient.
- Memorise the species-area relationship equation.
- Revise the link between species diversity and ecosystem stability.
- Understand the rivet popper hypothesis.
- Learn the consequences of biodiversity loss.
- Memorise the four causes in the evil quartet.
- Compare narrowly utilitarian, broadly utilitarian and ethical reasons.
- Finish with in situ and ex situ conservation methods.
What Is Biodiversity in Class 12 Biology?
Biodiversity refers to the combined diversity present at all levels of biological organisation.
The term was popularised by sociobiologist Edward Wilson.
Variation exists at several biological levels, ranging from molecules within cells to entire biomes. The three most important levels are:
- Genetic diversity
- Species diversity
- Ecological diversity
Types of Biodiversity in Class 12 Notes
The types of biodiversity describe variation within a species, among species and between ecosystems.
Genetic Diversity
Genetic diversity is the variation present within a single species.
Different populations of the same species may differ in:
- Genetic composition
- Physical traits
- Chemical production
- Environmental tolerance
- Disease resistance
The medicinal plant Rauwolfia vomitoria grows in different Himalayan regions. Its populations vary in the potency and concentration of reserpine.
India has:
- More than 50,000 genetically different strains of rice
- About 1,000 varieties of mango
Greater genetic diversity helps species adapt to changing environmental conditions.
Species Diversity
Species diversity refers to the variety of species within a region.
For example, the Western Ghats have greater amphibian species diversity than the Eastern Ghats.
Species diversity may be studied through:
- Species richness
- Relative abundance
- Distribution of different species
Ecological Diversity
Ecological diversity refers to the variety of ecosystems, habitats and ecological processes within a region.
India has several ecosystem types, including:
- Deserts
- Rainforests
- Mangroves
- Coral reefs
- Wetlands
- Estuaries
- Alpine meadows
This gives India greater ecological diversity than countries with fewer habitat types.
Genetic, Species and Ecological Diversity Compared
| Level | Meaning | Example |
| Genetic diversity | Variation within one species | Rice strains and mango varieties |
| Species diversity | Variety of species in a region | Amphibians in the Western Ghats |
| Ecological diversity | Variety of ecosystems | Deserts, forests and wetlands in India |
Global Species Diversity and Biodiversity Estimates
Scientists have recorded and named slightly more than 1.5 million plant and animal species, according to the IUCN figure cited in the chapter.
However, many species remain undiscovered, particularly in:
- Tropical forests
- Coral reefs
- Deep oceans
- Soil ecosystems
- Microbial habitats
Estimates of the total number of species vary widely.
Robert May provided a scientifically supported estimate of about 7 million species worldwide.
Distribution of Recorded Species
The recorded species show an uneven taxonomic distribution.
- More than 70% of recorded species are animals.
- Plants account for no more than 22%.
- More than 70% of animal species are insects.
- Fungi have more recorded species than fishes, amphibians, reptiles and mammals combined.
Prokaryotic diversity remains difficult to measure because:
- Many microbes cannot be cultured in laboratories.
- Conventional taxonomic methods may not identify them accurately.
- Molecular criteria may reveal millions of additional species.
Biodiversity in India Class 12 Notes
The section on biodiversity in India highlights the country’s exceptional biological richness.
India occupies only about 2.4% of the world’s land area but contains approximately 8.1% of global species diversity.
This makes India one of the world’s 12 mega-diversity countries, as described in the chapter.
Recorded Species in India
India has approximately:
- 45,000 recorded plant species
- Twice as many recorded animal species
If Robert May’s estimate is applied proportionately, India may contain:
- More than 1,00,000 undiscovered plant species
- More than 3,00,000 undiscovered animal species
Many species may become extinct before they are discovered, named or scientifically studied.
Patterns of Biodiversity Class 12 Notes
Species diversity is not distributed uniformly across Earth.
The two major patterns of biodiversity discussed in the chapter are:
- Latitudinal gradients
- Species-area relationships
Latitudinal Gradient in Biodiversity
The latitudinal gradient shows that species diversity generally decreases as we move from the equator towards the poles.
Tropical regions between 23.5° N and 23.5° S usually support more species than temperate and polar regions.
Examples of Latitudinal Diversity
| Region | Approximate Bird Diversity |
| Colombia near the equator | 1,400 species |
| India | More than 1,200 species |
| New York at 41° N | 105 species |
| Greenland at 71° N | 56 species |
A tropical forest in Ecuador may contain up to ten times more vascular plant species than an equal-sized temperate forest in the United States.
Biodiversity of the Amazon Rainforest
The Amazon rainforest supports exceptional species richness.
The chapter lists more than:
- 40,000 plant species
- 3,000 fish species
- 1,300 bird species
- 427 mammal species
- 427 amphibian species
- 378 reptile species
- 1,25,000 invertebrate species
Scientists estimate that at least two million insect species may still await discovery there.
Why Are Tropical Regions More Diverse?
Ecologists propose three main explanations for greater tropical biodiversity.
Longer Evolutionary Time
Temperate regions experienced repeated glaciations.
Tropical regions remained relatively undisturbed for millions of years, giving organisms more time to diversify.
Stable and Predictable Climate
Tropical climates are less seasonal and more constant.
Stable conditions promote niche specialisation and allow more species to coexist.
Greater Solar Energy
Tropical regions receive more solar energy.
Higher solar input may support greater productivity, which can indirectly support greater species richness.
Species-Area Relationship in Biodiversity
Alexander von Humboldt observed that species richness increases with the area explored, although only up to a limit.
The species-area relationship generally forms a rectangular hyperbola.
On a logarithmic scale, it becomes a straight line.
The equation is:
log S = log C + Z log A
Where:
S = Species richness
A = Area
Z = Slope of the regression line
C = Y-intercept
Value of Z
For most taxonomic groups and smaller geographical regions:
Z = 0.1 to 0.2
This range is similar for:
- Plants in Britain
- Birds in California
- Molluscs in New York
For very large areas such as continents:
Z = 0.6 to 1.2
For frugivorous birds and mammals in tropical forests across continents:
Z = 1.15
A steeper slope indicates that species richness increases more rapidly with area.
Species-Area Relationship Summary
| Area Studied | Typical Z Value |
| Small regions | 0.1–0.2 |
| Large areas and continents | 0.6–1.2 |
| Tropical frugivorous birds and mammals | 1.15 |
Importance of Biodiversity for Ecosystem Functioning
The importance of biodiversity extends beyond the number of species present.
Species-rich communities are generally expected to:
- Show greater stability
- Maintain more consistent productivity
- Resist environmental disturbances
- Recover more effectively after disturbance
- Resist invasion by alien species
David Tilman’s Experiments
David Tilman conducted long-term experiments using outdoor plots.
His findings showed that plots with more species:
- Had less year-to-year variation in biomass
- Showed greater productivity
These results suggest that species richness contributes to ecosystem stability and functioning.
Rivet Popper Hypothesis Class 12 Biology
Paul Ehrlich explained biodiversity loss through the rivet popper hypothesis.
An ecosystem is compared to an aeroplane, while species are compared to the rivets holding the aircraft together.
If passengers remove a few rivets:
- The aircraft may continue functioning initially.
- Continued removal gradually weakens the structure.
- Loss of critical rivets may cause rapid failure.
Similarly, an ecosystem may continue functioning after a few species disappear, but repeated extinction weakens ecological stability.
The loss of key species that perform major ecosystem functions may be especially damaging.
Loss of Biodiversity Class 12 Notes
The loss of biodiversity has accelerated because of human activities.
Species extinction is a natural process, but the current rate is far higher than background extinction rates.
Recorded Species Extinctions
The IUCN Red List data cited in the chapter records 784 species becoming extinct during the previous 500 years.
These include:
- 338 vertebrates
- 359 invertebrates
- 87 plants
Examples of extinct species include:
- Dodo
- Quagga
- Thylacine
- Steller’s sea cow
- Bali tiger
- Javan tiger
- Caspian tiger
Amphibians appear particularly vulnerable to extinction.
Species Facing Extinction
The textbook figures state that more than 15,500 species face the threat of extinction.
The threatened proportions include:
| Group | Threatened Species |
| Birds | 12% |
| Mammals | 23% |
| Amphibians | 32% |
| Gymnosperms | 31% |
Sixth Mass Extinction
Fossil records show that Earth has experienced five major mass extinction events.
The present biodiversity crisis is often called the sixth extinction.
Its main difference is the speed of species loss.
Current extinction rates are estimated to be:
100 to 1,000 times faster than pre-human extinction rates
Human activities are the main cause of this acceleration.
If the trend continues, nearly half of Earth’s species may disappear within the next century, according to the warning presented in the chapter.
Consequences of Biodiversity Loss
Biodiversity loss may lead to:
- Decline in plant production
- Lower resistance to drought
- Greater vulnerability to disturbances
- Increased variation in plant productivity
- Changes in water use
- Disturbed pest cycles
- Disturbed disease cycles
- Reduced ecosystem stability
Loss of species can also disrupt food webs, pollination and nutrient movement.
Causes of Biodiversity Loss: The Evil Quartet
The four major causes of biodiversity loss are collectively called the evil quartet.
They are:
- Habitat loss and fragmentation
- Overexploitation
- Alien species invasion
- Co-extinction
Habitat Loss and Fragmentation
Habitat loss and fragmentation are the most important causes of species extinction.
Habitat Loss
Tropical rainforests once covered more than 14% of Earth’s land surface.
The chapter states that they now cover no more than 6%.
Forests are cleared for:
- Agriculture
- Soya bean cultivation
- Cattle grazing
- Settlements
- Roads
- Industries
Pollution also degrades habitats and makes them unsuitable for sensitive species.
Habitat Fragmentation
Fragmentation divides a large habitat into smaller isolated sections.
It particularly affects:
- Large mammals
- Birds needing extensive territories
- Migratory animals
- Species with specialised habitats
Small isolated populations may lose genetic diversity and face greater extinction risk.
Overexploitation of Natural Resources
Overexploitation occurs when organisms are harvested faster than their populations can recover.
Examples include:
- Steller’s sea cow
- Passenger pigeon
- Commercially valuable marine fishes
Human dependence on natural resources becomes destructive when use exceeds ecological limits.
Alien Species Invasion
An alien species is introduced outside its natural geographical range.
Some alien species become invasive and harm native species.
Nile Perch in Lake Victoria
The introduction of Nile perch into Lake Victoria caused the extinction of more than 200 native cichlid fish species.
Invasive Plants in India
Major invasive weeds include:
- Carrot grass, or Parthenium
- Lantana
- Water hyacinth, or Eichhornia
These species spread rapidly and compete with native organisms.
African Catfish
The illegal introduction of Clarias gariepinus for aquaculture threatens native catfish species in Indian rivers.
Co-Extinction in Biodiversity
Co-extinction occurs when the extinction of one species causes another closely associated species to disappear.
Examples include:
- Parasites becoming extinct with their host
- Pollinators disappearing with specialised plants
- Plants becoming extinct after losing their only pollinator
Species involved in obligatory relationships are especially vulnerable to co-extinction.
Evil Quartet Summary
| Cause | Meaning | Example |
| Habitat loss | Destruction of natural habitat | Clearing the Amazon rainforest |
| Fragmentation | Division of habitat into smaller areas | Roads dividing forests |
| Overexploitation | Excessive harvesting | Passenger pigeon |
| Alien species invasion | Harm caused by introduced species | Nile perch |
| Co-extinction | Loss of associated species | Host and its parasite |
Biodiversity Conservation Class 12 Notes
Biodiversity conservation aims to protect genetic diversity, species and ecosystems.
Conservation is important because biodiversity provides economic, ecological and ethical value.
The reasons for conserving biodiversity fall into three categories:
- Narrowly utilitarian
- Broadly utilitarian
- Ethical
Narrowly Utilitarian Value of Biodiversity
The narrowly utilitarian value includes direct economic benefits obtained from nature.
Humans receive:
- Cereals
- Pulses
- Fruits
- Firewood
- Fibre
- Construction materials
- Tannins
- Lubricants
- Dyes
- Resins
- Perfumes
- Medicines
More than 25% of medicines sold worldwide are derived from plants, according to the chapter.
About 25,000 plant species contribute to traditional medicines used by indigenous communities.
Bioprospecting
Bioprospecting is the exploration of biological diversity for:
- Medicinal compounds
- Industrial products
- Useful genes
- Commercially valuable molecules
Countries with high biodiversity may benefit economically when biological resources are used responsibly and benefits are shared fairly.
Broadly Utilitarian Value of Biodiversity
The broadly utilitarian value refers to ecosystem services provided by biodiversity.
These services include:
- Oxygen production
- Pollination
- Water purification
- Climate regulation
- Flood control
- Soil protection
- Pest control
- Nutrient cycling
The chapter highlights the Amazon rainforest’s contribution to atmospheric oxygen through photosynthesis.
Pollinators such as bees, birds, bats and bumblebees support fruit and seed production.
Biodiversity also provides aesthetic benefits, such as:
- Enjoying forests
- Observing flowers
- Listening to birds
- Experiencing natural landscapes
Ethical Value of Biodiversity
The ethical value of biodiversity is based on the belief that every species has intrinsic worth.
Humans share Earth with millions of plants, animals and microorganisms.
Therefore, people have a moral responsibility to:
- Protect other species
- Prevent avoidable extinction
- Preserve biological resources
- Pass biodiversity to future generations
A species deserves protection even when it has no known economic value.
In Situ Conservation of Biodiversity
In situ conservation protects species within their natural habitats.
The entire ecosystem is protected so that its genetic, species and ecological diversity can continue functioning.
Examples include:
- Biosphere reserves
- National parks
- Wildlife sanctuaries
- Biodiversity hotspots
- Sacred groves
Biodiversity Hotspots Class 12 Notes
Biodiversity hotspots are regions with:
- Very high species richness
- High levels of endemism
- Rapid habitat loss
Endemic species occur naturally in a particular region and nowhere else.
The NCERT chapter states that 34 biodiversity hotspots had been identified worldwide.
Three hotspots covering important parts of India are:
- Western Ghats and Sri Lanka
- Indo-Burma
- Himalaya
Together, global hotspots cover less than 2% of Earth’s land area but support exceptionally high biodiversity.
Protecting them could reduce ongoing mass extinction substantially.
Biosphere Reserves, National Parks and Wildlife Sanctuaries
India protects biodiversity-rich regions through legally designated areas.
Biosphere Reserves
Biosphere reserves protect large ecosystems and support conservation, research and sustainable use.
National Parks
National parks provide strict protection to ecosystems, plants and animals.
Human activities are highly restricted.
Wildlife Sanctuaries
Wildlife sanctuaries protect animals and their habitats.
Some regulated human activities may be permitted.
The chapter records:
- 14 biosphere reserves
- 90 national parks
- 448 wildlife sanctuaries
These figures should be treated as textbook facts for chapter revision.
Sacred Groves and Biodiversity Conservation
Sacred groves are forest areas protected through religious and cultural traditions.
All trees and wildlife within these areas receive community protection.
Sacred groves occur in:
- Khasi Hills of Meghalaya
- Jaintia Hills of Meghalaya
- Aravalli Hills of Rajasthan
- Western Ghats of Karnataka
- Western Ghats of Maharashtra
- Sarguja
- Chanda
- Bastar
In Meghalaya, sacred groves serve as important refuges for rare and threatened plants.
Ex Situ Conservation of Biodiversity
Ex situ conservation protects threatened species outside their natural habitats.
It is used when a species faces a high risk of extinction in the wild and requires urgent care.
Methods include:
- Zoological parks
- Botanical gardens
- Wildlife safari parks
- Seed banks
- Tissue culture
- Cryopreservation
- In vitro fertilisation
Zoological and Botanical Conservation
Threatened species may be maintained in controlled settings where they receive:
- Food
- Veterinary care
- Protection from predators
- Breeding support
- Habitat management
Some animals extinct in the wild continue to survive in zoological parks.
Cryopreservation
Cryopreservation stores biological material at extremely low temperatures.
It can preserve:
- Gametes
- Embryos
- Seeds
- Tissues
The material can remain viable for long periods.
Tissue Culture and Seed Banks
Tissue culture allows rapid propagation of threatened plants.
Seed banks preserve seeds of different genetic strains for future use and restoration.
In Situ and Ex Situ Conservation Compared
| Feature | In Situ Conservation | Ex Situ Conservation |
| Location | Natural habitat | Outside natural habitat |
| Main focus | Whole ecosystem | Selected species or genetic material |
| Examples | National parks and sacred groves | Zoos and seed banks |
| Ecological interactions | Maintained | Limited or controlled |
| Best suited for | Protecting habitats and communities | Urgently threatened species |
International Biodiversity Conservation Efforts
Biodiversity does not follow political boundaries.
Its conservation requires cooperation between countries.
Earth Summit
The Convention on Biological Diversity was held at the Earth Summit in Rio de Janeiro in 1992.
It called on nations to:
- Conserve biodiversity
- Use biological resources sustainably
- Share benefits responsibly
World Summit on Sustainable Development
The World Summit on Sustainable Development was held in Johannesburg in 2002.
The chapter states that 190 countries pledged to reduce biodiversity loss at global, regional and local levels.
Biodiversity and Conservation Class 12 Quick Revision Tables
The following tables summarise the major concepts from the Class 12 Biology Chapter 13 Notes.
Levels of Biodiversity
| Level | Main Focus | Example |
| Genetic | Variation within a species | Rice strains |
| Species | Variety of species | Amphibians in Western Ghats |
| Ecological | Variety of ecosystems | Forests, mangroves and wetlands |
Biodiversity Pattern Terms
| Term | Key Point |
| Latitudinal gradient | Diversity decreases from equator to poles |
| Species-area relationship | Species richness rises with area |
| Z value | Slope of species-area regression |
| Endemism | Species restricted to one region |
| Hotspot | Rich, endemic and threatened region |
Major Biodiversity Figures
| Figure | Significance |
| More than 1.5 million | Recorded plant and animal species |
| About 7 million | Robert May’s global estimate |
| More than 70% | Recorded species that are animals |
| 2.4% | India’s share of world land area |
| 8.1% | India’s share of global species diversity |
| 45,000 | Recorded plant species in India |
| 100–1,000 times | Increase in present extinction rate |
Evil Quartet
| Cause | Key Effect |
| Habitat loss and fragmentation | Destroys and isolates populations |
| Overexploitation | Removes organisms faster than recovery |
| Alien species invasion | Harms native organisms |
| Co-extinction | Eliminates dependent species |
Conservation Methods
| Method | Examples |
| In situ conservation | Hotspots, parks and sacred groves |
| Ex situ conservation | Zoos, seed banks and tissue culture |
| Cryopreservation | Storage of gametes and seeds |
| In vitro fertilisation | Assisted reproduction |
| Community conservation | Protection of sacred groves |
Useful Links for Class 12 Biology
| Section | Useful Links |
| Syllabus | CBSE Class 12 Biology Syllabus |
| Revision Notes | CBSE Class 12 Biology Revision Notes |
| Biology Notes | CBSE Class 12 Biology Revision Notes Chapter 1 |
| NCERT Solutions | NCERT Solutions for Class 12 Biology |
| Sample Papers | CBSE Sample Papers for Class 12 Biology |
| Important Questions | Important Questions Class 12 Biology |
| NCERT Books | NCERT Books for Class 12 Biology |
| Class 12 Support | CBSE Class 12 Syllabus |
Q.1 What are the key elements that lead to so much variation in the physical and chemical conditions of different habitats?
Ans
The most important ones are temperature, water, light and soil.
Q.2 What happens when excessive discharge of fertilisers into water bodies takes place?
Ans
Eutrophication
Q.3 If natality is low, then what will happen to population density?
Ans
If natality is low, density will also be low.
Q.4 Name the term used when number of individuals of the population leave a particular habitat temporarily for the time under consideration.
Ans
Emigration
Q.5 Represent the age pyramids for human population.
Ans
Q.6 Define age pyramid.
Ans
Age pyramid is a graphical representation of the age distribution of a population. This also shows the relative proportion of females and males in a population.
Q.7 Explain Allen’s rule.
Ans
Allen’s rule states that endotherms from colder climates usually have shorter limbs (or appendages) than the equivalent animals from warmer climates. The theory behind Allen’s Rule is that endothermic animals with the same volume may have differing surface areas, which will aid or impede their temperature regulation. In cold climates, the greater the exposed surface area, the greater the loss of heat and therefore energy. Animals in cold climates need to conserve as much energy as possible. A low surface area to volume ratio helps to conserve heat.
Q.8 What type of interaction has been shown by the algae and fungi in Lichen?
Ans
Lichen is an example of obligate mutualism, where alga is the photosynthetic partner preparing food and fungus provides support and protection. Thus, both the partners are benefited from each other.
Q.9 Write the characteristic features of:
(a) Age distribution
(b) Population size
(c) Population density
Ans
(a) Age distribution:
- It is a percentage of individuals of a given age or age group.
- Age distribution graph plotted for a population is known as Age pyramid.
- Shape of pyramid reflects the dynamism of population.
(b) Population size:
- It depicts the number of individuals in a population of a single habitat.
- Change in size can be used to interpret the result of competition between individuals.
(c) Population density:
- It is a most appropriate measure to talk about a habitat.
- It depicts the number of individuals of a species per unit space available in that habitat.
Q.10 What is Darwinian fitness?
Ans
Populations evolve to maximise their reproductive fitness, called Darwinian fitness, in the habitat in which they live.
Q.11 With the help of suitable diagram describe the logistic population growth curve.
Ans
Logistic population growth: No population of any species in nature has its unlimited resources to permit exponential growth. This leads to competition between individuals for limited resources. In nature, a given habitat has enough resources to support a maximum number, beyond which no further growth is possible. This limit is called as nature’s carrying capacity (k) for that species in that habitat. A population growing in a habitat with limited resources, initially show a lag phase, followed by phases of acceleration and deceleration and finally an asymptote is achieved, when the population density reaches the carrying capacity. A plot of N in relation to time (t) results in a sigmoid curve.
This type of population growth is called Verhulst-Pearl Logistic Growth.
Where,
N= Population density at time t,
r= Intrinsic rate of natural increase,
K= Carrying capacity
Since, resources for growth for most animal populations are finite and become limiting sooner or later, the logistic growth model is considered a more realistic one.
Q.12 Define the following terms and give one example for each:
(a) Commensalism
(b) Parasitism
(c) Camouflage
(d) Mutualism
(e) Interspecific competiton
Ans
(a) Commensalism: An interaction in which one species gets the benefit and the other is neither harmed nor benefited, e.g., interaction between sea anemone that has stinging tentacles and the clown fish that lives among them. The fish gets protection from predators and the fish cause no harm or benefit to the sea anemone.
(b) Parasitism: In this relationship, one organism called parasite lives for food or shelter on or in the other organism called host, which is of some other species. In this interaction the parasite gets all the benefits, while the host is affected badly e.g., malarial parasite causes malarial fever to human being, who is their host.
(c) Camouflage: It is the ability of the animals to blend with the surroundings so that they are not easily recognisable by the enemies. e.g., stick insect.
(d) Mutualism: This interaction confers benefits on both the interacting species, e.g., Lichens is a good example which has the association of photosynthetic algae and fungi benefiting each other.
(e) Interspecific competition: Interaction between individuals of two species competing for the same resources, e.g., Monarch butterfly and Queen Monarch.
Q.13 List and explain any three important characteristics of a population.
Ans
Important characteristics of a population are:
1. Birth rates and Death rates – In a population, these rates refer to per capita births and deaths, respectively. The rates, hence, are expressed is the change in numbers (increase or decrease) with respect to the members of the population.
E.g., If in a pond there were 20 lotus plants last year and through reproduction 20 new plants are added, taking the current population to 28, the birth rate will be 8/20=0.4 offspring per lotus per year. Similarly, by subtracting the dead from total the death rate can be calculated.
2. Sex ratio – Sex ratio is the number of male and female in 100 individuals of a population.
3. Age distribution – A population at a given time is composed of individuals of different ages. If the age distribution is plotted for the population, the resulting structure is called an age pyramid. The shape of the pyramids reflects the growth status of the population – (a) whether it is growing, (b) stable and (c) declining.
Q.14 Write a short note on:
(a) Adaptations of desert animals
(b) Adaptations of plants to water scarcity
(c) Behavioural adaptations in animals
Ans
(a) Adaptations of desert animals:
Desert animals meet all their water requirements through their internal fat oxidation, in which water is a by product, e.g., Kangaroo rat in North American desert. They have the ability to excrete concentrated urine so that minimal volume of water is used to remove excretory products.
(b) Adaptations of plants to water scarcity:
Plants have a thick cuticle on their leaf surfaces to lessen the effect of high temperature.The stomata on their leaves are located in deep pits to minimise the water loss through transpiration. They also have a special photosynthetic pathway (CAM) that enables their stomata to remain closed during day time. In plants like Opuntia, the leaves are reduced to spines. The stem is modified into a flat green structure which performs the function of photosynthesis.
(c) Behavioural adaptations in animals:
Behavioural adaptations help the organisms to cope with variations in their environment, e.g., Desert lizard basks in the sun and absorb heat when their body temperature drops below the comfort zone, but moves into shade when the ambient temperature starts increasing. Some species are capable of burrowing into the soil to hide and escape from the above ground heat.
Q.15 Distinguish between the following:
(a) Hibernation and Aestivation
(b) Ectotherms and Endotherms
Ans
(a) Hibernation and Aestivation:
Hibernation is winter sleep to avoid the unfavourable and stressed conditions of cold climate.
Aestivation is summer sleep to avoid the unfavourable and stressed conditions of hot climate.
(b) Ectotherms and Endotherms:
Ectotherms are the cold-blooded animals whose body temperature keeps on changing with the change in climatic temperature, thus, they either hibernate or aestivate.
Endotherms are the warm blooded animals who can maintain their body temperature by physiological means (Homeostasis).
Q.16 List the attributes that populations, but not individuals possess.
Ans
(i) Birth rates
(ii) Death rates
(iii) Sex ratio
(iv) Age pyramid (population age distribution)
(v) Population dispersion
(vi) Population density
Q.17 What is ecology?
Ans
In ecology, we study the interactions among organisms and between the organism and its physical environment.
Q.18 How is diapause different from hibernation?
Ans
Diapause is the stage of suspended development under unfavorable conditions, e.g., many zooplankton species.
Hibernation is a state of inactivity and metabolic depression in animals, characterised by low body temperature, slow breathing and low metabolic rate.
Q.19 If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why or why not?
Ans
It is difficult for a marine fish to survive in a fresh water aquarium as the fish is adapted to live in saline water and won’t be able to cope up with the outside hypotonic environment due to the physiological problems.
Q.20 An orchid plant is growing on the branch of mango tree. How do you describe this interaction between an orchid and the mango tree?
Ans
The relationship of growing an orchid plant on the mango tree is an example of an epiphyte. In this interaction, one species is benefited, while the other is neither benefited nor harmed.
Q.21 What is the ecological principle behind the biological control method of managing with pest insects?
Ans
Biological control methods adopted in agricultural pest control are based on the ability of the predator to regulate prey population.
Q.22 Discuss about the importance of light to plants.
Ans
Importance of light in the life of plants is manifold, few are –
(i) In case of autotrophs, the basis of photosynthesis is sunlight.
(ii) Many plants meet their photoperiodic requirements for flowering.
(iii) Sunlight provides the direction for the growth of stem and roots, stems grow towards the sunlight while roots away from the sunlight.
Q.23 Give the reasons for believing evolutionary biologists that mammals are able to survive successfully in any environment.
Ans
It is because of their ability to maintain a constant body temperature in cold as well as the hot climate.
Q.24 Define phenotypic adaptation. Give one example.
Ans
Phenotypic adaptations are non-genetic, thus occur within the lifetime of an individual and decay when these circumstances no longer exist, e.g., acclimatisation, behavioural changes, etc.
Q.25 Most living organisms can not survive at temperatures exceeding 100o C. Why ?
Ans
In most living organisms, the metabolic reactions take place at optimal temperature (37o C in humans). At higher temperature, as the enzymes are denatured or destroyed, no metabolic activity takes place and thus; survival is not possible.
Q.26 Name important defence mechanisms in plants against herbivory.
Ans
(i) Thorns in Acacia, Cactus
(ii) Produce harmful chemicals
(iii) Spiny margins on leaves
(iv) Sharp silicated edges on the leaves
Q.27 How does the pseudo-copulation help in pollination? Explain with an example.
Ans
The Mediterranean orchid called Ophrys employes ‘sexually deceit’ to get pollination done by a species of bee. One petal of its flower bears an uncanny resemblance to the female bee in size, colour and markings. The male bee is attracted to what it perceives as a female and ’pseudocopulates’ with the flower. During that process, bee is dusted with pollens from the flower. When this same bee pseudocopulates with another flower, it transfer pollens to it and thus; pollinates the flower.
Q.28 Name the interaction shown by Sea anemone and Clown fish?
Ans
Commensalism
FAQs (Frequently Asked Questions)
Tropical regions have had more evolutionary time, experience relatively stable climates and receive more solar energy. These conditions support niche specialisation, productivity and species diversification.
A higher Z value produces a steeper slope. It indicates that species richness increases rapidly as the explored area becomes larger.
Fragmentation divides populations into small, isolated groups. It restricts migration, reduces breeding opportunities and increases the risk of genetic decline and local extinction.
Direct extinction occurs when a species disappears because of threats affecting it directly. Co-extinction occurs when another species disappears because it depends closely on the first species.
In situ conservation protects species within their natural ecosystem. It preserves ecological interactions, evolutionary processes, genetic diversity and the habitat supporting many organisms at once.