Class 12 – Biology – Biodiversity and Conservation – Important Questions

1.Biodiversity can be defined as the occurrence of different types of genes, gene pools, species, habitats and ecosystem in a given region.

(i) The term biodiversity was given by a sociobiologist Edward Wilson to describe the combined diversity at all the levels of biological organisation.

(ii) There are more than 20,000 species of ants, 3,00,000 species of beetles, 28,000 species of fishes and nearly 20,000 species of orchids.

(iii) Biodiversity can be divided into following three levels:

(a) Genetic diversity is the diversity at the genetic level.

  • It enables a population to adapt to its environment.
  • India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango.

Example, Genetic variation in the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges might be in terms of the potency and concentration of the active chemical (reserpine) that the plant produces.

(b) Species diversity is diversity at the species level. For example, the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.

(c) Ecological diversity is the diversity at ecosystem level. For example, India with its deserts, rainforests, mangroves, coral reefs, wetlands, estuaries and alpine meadows has a greater ecosystem diversity.

2. Global species diversity means total species present on the earth.

  • According to IUCN (2004) the total number of plant and animal species is slightly more than 1.5 million.
  • For many taxonomic groups, species inventories are more complete in temperate than in tropical countries.
  • A more conservative and scientifically sound estimate by Robert May, places the global species diversity at about 7 million.
  • More than 70% of all the species recorded are animals, while plants comprise no more than 22% of the total.
  •  Among animals, insects are most species rich-taxonomic group, making about 70% of the total. It means, out of every 10 animals, 7 are insects on the earth.

3. Biodiversity in India

  • Although India has only 2.4% of the world’s land area, its share of the global species diversity is 8.1%. This makes India one of the 12 megadiversity countries of the world.
  • About 45,000 species of plants and twice as many of animals have been recorded from India.

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  • According to May’s global estimates, only 22% of the total species have been recorded so far. If this proportion.is applied to India’s diversity figures, there may be probably more than 1,00,000 plant species and more than 3,00,000 animal species yet to be discovered and described.

4. Patterns of biodiversity indicate that the biodiversity is not uniform throughout the world because it is affected by:

(i) Latitudinal gradients demonstrates the decrease in species diversity as we move away from the equator towards the poles.

  • Tropics (latitudinal range of 23.5 °N to 23.5 °S) harbour more species than temperate or polar areas.
  • Example, Colombia located near the equator has around 1,400 species of birds, while New York at 41 °N has 105 species and greenland at 71 °N has only 56 species.
  • Studies indicate that the tropical areas have more biodiversity.

For example,

  • India with much of its land area in the tropical latitudes, has more than 1,200 species of birds.
  • A tropical forest in equator has up to 10 times as many species of vascular plants as a forest of equal area in a temperate region like the midwest of USA.
  • Tropical Amazonian rainforest in South America has the greatest biodiversity on earth. It homes 40,000 species of plants, 3,000 of fishes, 1,300 of birds, 427 of mammals, 427 of amphibians, 378 of reptiles and of more than 1,25,000 invertebrates.
  • Scientists estimate that in these rainforests, there might be at least 2 million insect species waiting to be discovered and named.

(d) Reasons for Greater Biodiversity in Tropics

  • Speciation is generally a function of time. The temperate regions were subjected to frequent glaciation in the past, but the tropics have remained undisturbed and hence, had evolved more species diversity.
  • Tropical environments, unlike temperates are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity.
  • More solar energy is available in tropics, which contributes to higher productivity, this in turn might contribute indirectly to greater diversity.

(ii) Species-Area Relationships

  • Alexander Von Humboldt, a German naturalist and geographer observed that within a region, species richness increased with increasing explored area, but up to a limit.
  • In fact, the relation between species richness and area for a wide variety of taxa (like angiosperm plants, birds, bats and freshwater fishes) turn out to be rectangular hyperbola.

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NOTE On log scale the relationship becomes linear

  • On a logarithmic scale, the relationship is a straight line as given in the following equation

logS = log C + Z logA where, S = Species richness, A=Area

C = Y-intercept, Z = Slope of the line (regression coefficient)

  • The value of Z lies in the range of 0.1-0.2 regardless of taxonomic group or the region.
  • If we analyse the species-area relationship among very large areas like the entire continents, the slope of the line will be much steeper, i.e. Z values in the range of 0.6-1.2. For example, for fruit eating birds and mammals in the tropical forests of different continents, the slope is found to be 1.15.

5.  Importance of Species Diversity to the Ecosystem

(i) According to ecologists, communities with more species tend to be more stable than those with less species.

(ii) Attributes of a stable community are

  • It should not show too much variation in productivity from year to year.
  • It must be either resistant or resilient to occasional disturbances (natural or man made).
  • It must be resistant to invasions by alien species.

(iii) David Tilman’s longterm experiments on ecosystem found that plots with more species showed less year-to-year variation in total biomass. He also showed that increased diversity contributed to higher productivity.

(iv) It is not clear how species richness contributes to the well-being of an ecosystem. But, it is enough to realise that rich biodiversity is not only essential for ecosystem health but imperative for the survival of the human race on this planet.

(v) Paul Ehrlich through his rivet popper hypothesis tried to explain the importance of biodiversity for the survival of species.

  • The hypothesis assumes the ecosystem to be an airplane and the species to be the rivets joining all parts together.
  • If every passenger pops a rivet to take home (resulting in species extinction), it may not affect the flight safety initially (proper ecosystem functioning) but with time as more and more rivets are removed, the plane becomes dangerously weak.
  • Loss of rivet on the wings (key species that drives major ecosystem functions) is a more serious threat to flight safety than loss of a few rivets on the seats or windows of the plane.

6. Loss of biodiversity is caused by the over population, urbanisation and industrialisation.

(i) The colonisation of tropical Pacific Islands by humans have led to the extinction of more than 2,000 species of native birds.

(ii) The IUCN Red list (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years.

(iii) Some latest examples of recent extinctions are dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller’s sea cow (Russia) and three sub-species (Bali, Javan and Caspian) of tiger.

(iv) The last twenty years alone have witnessed the disappearance of 27 species.

(v) Presently, 12% of bird species, 23% of all mammal species, 32% of all amphibian species and 31% of all gymnosperm species in the world face the threat of extinction.

(vi) Careful analysis of records shows that amphibians appear to be more vulnerable to extinction.

(vii) The grim scenario of extinctions is the fact that more than 15,500 species world wide are facing the threat of extinction.

Results of Loss of Biodiversity in a Region

  • Decline in plant production.
  • Lowered resistance to environmental perturbations, such as drought.
  • Increased variability in certain ecosystem processes such as plant productivity, water use, pest and disease cycles.

Causes of Biodiversity Losses

These are mainly four as given below. They are also named as The Evil Quartet.

(i) Habitat Loss and Fragmentation

(a) The main cause of extinction of species is the destruction of their habitat

(b) Examples,

  • Tropical rainforests once covering more than 14% of the land surface, now cover only 6% of land area.
  • Amazon rainforest (called lungs of the planet) is being cut and cleared for the cultivation of soybeans and for conversion to grasslands for raising beef cattle.

(c) When large habitats are broken up into small fragments due to various human activities, mammals and birds requiring large territories and certain animals with migratory habits are badly affected, leading to their population decline.

(d) The degradation of many habitats by pollution also threatens the survival of many species, many have extincted in last 500 years.

(ii) Over-exploitation of natural resources by humans results in degradation and extinction of the resources. For example, Steller’s sea cow, passenger pigeon and many marine fishes have extincted in last 500 years.

(iii) Alien (exotic) Species Invasions

When alien (exotic) species are introduced unintentionally or deliberately, some become invasive and cause harmful impact resulting in extinction of the indigenous species. Examples,

  • Nile perch a large predator fish when introduced in Lake Victoria (East Africa) caused the extinction of an ecologically unique species of cichlid fish in the lake.
  • Invasive weed species like Parthenium (carrot grass), Lantana and Eichhornia (water hyacinth) caused environmental damage and pose threat to native species.
  • The recent example is of the African cat fish (Clarias gariepinus) introduced for aquaculture purpose, is posing a threat to the indigenous cat fishes of Indian rivers.

(iv) Co-extinctions When a species become extinct, the plant and animal species associated with it in an obligatory manner, also become extinct. For example, if the host species becomes extinct, all those parasites exclusively found on it will also become extinct. In plant pollinator mutualism, extinction of one results in the extinction of the other.

Previous Years Examination Questions  

1 Mark Questions  

1.Identify A and B in the figure given below representing proportionate number of major vertebrate taxa.  [Delhi 2014]
important-questions-for-class-12-biology-cbse-biodiversity-q1
Ans.  In the above mentioned figure, among the major vertebrate taxa

A represent mammals

B represents ambhibians                                                             (1)

2.Write the level of biodiversity  represented by a mangrove. Give another example falling in the same level.       [Delhi 2014C]

Ans.The mangroves represents biodiversity at ecological level. Other examples of ecological diversity are deserts, rainforests, coral reefs, etc.

3.Name the type of biodiversity represented by the followings

  • 1,000 varieties of mangoes in India.
  • Variations in terms of potency and concentration of reserpine in Rauwolfia vomitoria growing in different regions of Himalayas.    [All India 2013]

Ans.  (i) Genetic diversity

(ii) Genetic diversity

4. Why is tropical environment able to support greater species diversity?  [Delhi 2011C]

Ans. Tropical latitudes have remained  undisturbed for millions of years and had a long evolutionary time for species diversification. Thus, it supports greater species diversity.

5. Eichhornia crassipes is an alien  hydrophyte introduced in India. Mention the problem posed by this plant.[All India 2010C]

Ans. Water hyacinth (Eichhornia) introduced in  India is threatening the existing aquatic life in ponds and lakes, etc., as it clogs the stagnant water bodies very fast, thus, the native species are endangered.

6.  The Amazon rainforest is referred to as the lungs of planet. Mention any one human activity which causes loss of biodiversity in this region.  [All India 2010C]

Ans. Human activity causing loss of biodiversity are:

(i) Many plants are cut in Amazon rainforest

(ii) Forests are converted   to grasslands for  raising beef cattle.

7. Name the unlabelled areas A and B of the pie chart representing biodiversity of vertebrates showing the proportionate number of species of major taxa.  [Foreign 2009]
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Ans.  A- Fishes

B   Amphibians
8.Name the unlabelled areas A and B of the pie chart representing the global biodiversity of invertebrates showing their proportionate number of species of major taxa.  [Delhi 2009]
important-questions-for-class-12-biology-cbse-biodiversity-q8

Ans. A- Insects

B  Molluscs
9.Name the unlabelled areas A and B of the pie chart representing the biodiversity of plants showing their proportionate number of species of major taxa. [All India 2009]
important-questions-for-class-12-biology-cbse-biodiversity-q9

Ans. A- Fungi

B   Angiosperms
10.About 200 species of cichlid fish became extinct when a particular fish was introduced in Lake Victoria of Africa. Name the invasive fish.  [Foreign 2008]  

Ans. Nile perch is the invasive fish introduced in Lake Victoria.

2 Marks Questions  

11.List four causes of biodiversity loss.  [Delhi 2014C]

Ans.  (i) Habitat loss and fragmentation (ii) Over-exploitation (iii) Alien species invasions

12.What is meant by alien species invasion? Name one plant and one animal alien species that are a threat to our Indian native species. [All India 2013]

Ans. Intentional or chance introduction of exotic species into new islands or countries by man is called alien species invasion.  For example,  Nile perch introduced into Lake Victoria in East Africa caused loss of more than 200 species of cichlid fish. Plant alien species-Lantana camara and animal alien species – Clarius gariepinus are a threat to our Indian native species.

13. Justify with the help of an example where a deliberate attempt by humans has led to the extinction of a particular species.                       [Delhi 2011]

Ans. Over-exploitation of natural resources or over hunting of animals has led to extinction of particular species,

e.g. Steller’s sea cow and passenger pigeon.

14. The given graph shows species-area relationship. Write the equation of the Curve A and Explain. [All India 2011]
important-questions-for-class-12-biology-cbse-biodiversity-q14

Ans. The equation for the curve A is

S  – CAZ

where, S-Species richness,

A- Area C-Y-interecept,

Z- Slope of line

(regression coefficient)

(i) Alexander Von Humboldt observed that within a region, species richness increased with increasing explored area, but only up to a limit.

(ii) The relation between species richness and area for a wide variety of taxa like angiosperms, birds, fishes, etc., turns out to be a rectangular hyperbola.

15.With the help of an example, explain how alien species invasion causes biodiversity loss?  [Delhi 2011]

or

Alien species are a threat to native species. Justify taking examples of an animal and a plant alien species.  [All India 2010]

or

Sometimes alien species affect the indigenous organisms leading to their extinction. Substantiate this statement with the help of any two examples.  [Delhi 2010 C]

Ans. Alien species become invasive, compete with the native species and cause extinction of indigenous species.

(i) Introduction of Nile perch into Lake Victoria lead to extinction of more than 200 species of cichlid fish in that lake.

(ii) Carrot grass (Parthenium and Lantana) introduced in our country have become invasive and cause environmental damage. They pose a threat to the native species of plants in our forests.

16.Giving two reasons explain why  there is more species biodiversity in tropical latitudes than in temperate ones.                     [All India 2010]

Ans. Biodiversity is more in tropical latitudes than in temperate ones. The reasons are:

(i) Speciation is a function of time. The  temperate regions were subjected to frequent glaciation in the past, while the tropics have remained undisturbed and so had longer time to evolve more species diversity.

(ii) More solar radiation is available in tropical region. This leads directly to more productivity and indirectly to greater species diversity.

(iii) The environment of tropics is less seasonal and relatively more constant and predictable, which encourages niche specialisation and species diversity.

17.In the biosphere, immense  biological diversity exists at all levels of biological organisation. Explain any two levels of  biodiversity.         [All India 2010]

Ans. Levels of biodiversity in biosphere

(i) Genetic diversity It refers to the  diversity of genes within a species.

For example, there are more than 50,000 genetically different strains of rice in India.

(ii) Species diversity It refers to the number of different species within a given region. For example, Western Ghats have a greater amphibian species diversity than Eastern Ghats.

18.List the features that make a stable biological community.  [All India 2010]

Ans. Features of stable biological community

(i) It should not show much variation in productivity from year-to-year.

(ii) It should be resistant or resilient to occasional disturbances both natural and man-made.

(iii) It must be resistant to invasions of alien species.

19.Write any two hypothesis put forth by ecologists explaining the existence of greater biodiversity in tropical regions than in temperate regions. [Foreign 2010]

Ans. Hypothesis put forth by ecologists explaining the existence of greater biodiversity in tropical regions, than in temperates are:

(i) Speciation is a function of time, the temperate regions were subjected to frequent glaciation in the past, while the tropics have remained undisturbed and hence, had longer time to evolve more species diversity.                       (1)

(ii) The tropical environments are less seasonal and relatively more constant  and predictable than temperate regions, niche specialisation has been promoted/favoured by such constant environments and hence, there is greater species diversity.

20.Name the sociobiologist who popularised the term biodiversity. Identify the levels of biodiversity in India represented by

  • Diversity among amphibian in Eastern and Western Ghats.
  • 50,000 strains of rice in India.
  • Presence of deserts,  mangroves and coral reefs of India.                       [All India 2009]

Ans.  Edward Wilson, a sociobiologist popularised the term biodiversity. (1/2)

(i) Species diversity Western Ghats have a  greater amphibian species diversity than the Eastern Ghats.

(ii) Genetic diversity India has more than 50,000 genetically different strains of rice.

(iii) Ecological diversity Presence of deserts, mangroves and coral reefs in India in greater than in Scandinavian country like  Norway.

21.Observe the global biodiversity distribution of major plant taxa in the diagram and answer the questions that follow.
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  • Which group of plants are the most endangered?
  • Why are mosses/fems so few? Give reason.
  • How do fungi that are heterotrophs sustain themselves as a large population?
  • Which group of plants is most  advanced and which one is most primitive?         [Delhi 2009C]  

Ans. (i) Ferns and allies.

(ii) They grow in humid and shady places  and need water for fertilisation. Due to the high temperature and dry condition, few of them survived.

(iii) Fungi has saprotrophic mode of nutrition,  they depend only on organic matter for their survival and hence, survive in any environment.

(iv) Angiosperms are most advanced and  algae are most primitive.

3 Marks Questions  

22. The following graph shows the species-area relationship. Answer the following questions as directed.
important-questions-for-class-12-biology-cbse-biodiversity-q22
(i) Name the naturalist who studied the kind of relationship shown in the graph. Write the observations made by him.

(ii) Write the situations as discovered by the ecologists when the value of Z (slope of the line) lies between

  • 1 and 0.2
  • 6 and 1.2

What does Z stand for?

(iii) When would the slope of the line ‘b’ become steeper? [All India 2014]  

Ans.  (i)  Alexander Von Humboldt studied the  relationship shown in above graph. He observed that the species richness in an area increased with an increase in exploring area, up to a certain limit only.

(ii) (a) Ecologists have observed that when the value of Z lies between 0.1 – 0.2 when the species are considered for a small or average area.

(b) When the value of Z lies between  0.6-1.2, the area considered is very large. Z represents the slope of the line, i.e. regression coefficient.

(iii) The slope of the line ‘b’ will become steeper when very large areas such as continents are considered for species area relationship.

23. Explain giving three reasons, why  tropics show greatest levels of species diversity? [All India 2014]

or

List the reasons that account for the greater biological diversity in tropics.     [Foreign 2012]

Ans. Levels of biodiversity in biosphere

(i) Genetic diversity It refers to the  diversity of genes within a species.

For example, there are more than 50,000 genetically different strains of rice in India.

(ii) Species diversity It refers to the number of different species within a given region. For example, Western Ghats have a greater amphibian species diversity than Eastern Ghats.

24. Alien species are highly invasive and are a threat to indigenous species. Substantiate this statement with any three examples.  [All India 2012]

Ans.  Alien species become invasive, compete with the native species and cause extinction of indigenous species.

(i) Introduction of Nile perch into Lake Victoria lead to extinction of more than 200 species of cichlid fish in that lake.

(ii) Carrot grass (Parthenium and Lantana) introduced in our country have become invasive and cause environmental damage. They pose a threat to the native species of plants in our forests.

(iii) Introduction of African cat fish Clarius  gariepinus for aquaculture posses a threat to indigenous cat fishes in Indian rivers.

25. Explain by giving example, how co-extinction is one of the causes of loss of biodiversity? List the three causes also (without description).  [Foreign 2011]

Ans.  Co-extinction is one of the cause of loss of biodiversity as when a species become extinct, the plant and animal species associated with it in an obligatory manner, also become extinct.

For example,

(i) In plant pollinator mutualism, extinction of one results in the extinction of other.                               ‘

(ii) If a host fish become extinct, the unique , parasites depending on it would also  become extinct.

The other causes of loss of biodiversity are:

  • Habitat loss fragmentation
  • Over-exploitation
  • Invasion of alien species.

26. Explain rivet popper hypothesis. Name the ecologist who proposed it.  [Foreign 2011]

Ans. Rivet popper hypothesis

(1) The hypothesis was proposed by Paul Ehrlich.

(ii) In an airplane (ecosystem), all parts are joined together using thousands of rivets (species).

(iii) If every passenger travelling in it, starts popping a rivet to take home (causing a species to become extinct), it may not affect the flight safety (proper functioning of ecosystem) initially, but as more and more rivets are removed, the plane becomes dangerously weak after some time.

(iv) Further, which rivet is removed may also be critical loss of rivets on the wings.  (Key species that drive major ecosystem function) is obviously a more serious threat to flight safety than loss of a few rivets on the seats or windows inside the plane.

27. Why are

  • alien species invasion and
  • loss of habitat and fragmentation  considered to be the major cause of loss of biodiversity? Explain with the help of one example each.  [Foreign 2009]

Ans. (i) The alien species become invasive and cause extinction or decline of indigenous species.

For Example, the Nile perch introduced into Lake Victoria in East Africa led to the extinction of more than 200 species of cichlid fish in the lake.

(ii) Loss of habitat and fragmentation drive animals and plants to extinction.

For example, as the Amazon forest is cut and cleared for cultivating soybeans or for conversion to grasslands for raising beef cattle, many species are affected and leads to decline in their population.