Biosphere: Life on the Earth | ISC Class 11 Geography Notes

This note covers the nature of the biosphere and the concept of ecosystems, the three levels of biodiversity, the reasons for valuing and conserving biodiversity, the roles biodiversity plays in sustaining mankind, India as a mega diversity nation with its unique ecosystems and endemic species, and the in-situ and ex-situ strategies for conservation.

What is the biosphere and how do its components interact?

The biosphere is the zone of the earth where life exists. It is the meeting place of the three great realms of the earth: the lithosphere (the solid crust of rock and soil), the hydrosphere (all the water of the earth) and the atmosphere (the envelope of gases).

Life draws on all three: plants root themselves in the soil of the lithosphere, take water from the hydrosphere and carbon dioxide from the atmosphere, and animals depend on plants and on one another.

Definition: The biosphere is the part of the earth, together with its atmosphere, hydrosphere and lithosphere, in which living organisms exist and interact with one another and with their surroundings.

The living part of the biosphere is not a loose collection of species. It is organised into ecosystems. An ecosystem is a community of living organisms together with the non-living parts of their environment, working as a unit.

The living members are the biotic components and the non-living members are the abiotic components.

The interaction between the components of the biosphere is what keeps life going. The basic cause of the variety of vegetation, and hence of biodiversity, is the input of solar energy and water.

Areas rich in these inputs are the areas with a wide spectrum of biodiversity. The weathering mantle of rock, which varies with climate, is the basis for the diversity of vegetation.

1. Solar energy falls on the earth and is captured by green plants, which are the producers of the ecosystem.
2. Producers use water from the hydrosphere and carbon dioxide from the atmosphere to make organic matter, storing energy in their tissues.
3. Herbivores eat the producers and pass the stored energy along; carnivores eat the herbivores.
4. Decomposers break down dead organic material and return nutrients to the soil of the lithosphere.
5. Water and nutrients are cycled through the ecosystem, atmospheric gases are fixed, and the climate is helped to be regulated.

Nothing in an ecosystem evolves and sustains without reason. Every organism, besides extracting its own needs, also contributes something useful to other organisms. Species capture and store energy, produce and decompose organic materials, help to cycle water and nutrients throughout the ecosystem, fix atmospheric gases and help regulate the climate.

What is biodiversity and what are its three levels?

Biodiversity is a combination of two words, Bio (life) and diversity (variety). In simple terms, biodiversity is the number and variety of organisms found within a specified geographic region.

It refers to the varieties of plants, animals and micro-organisms, the genes they contain and the ecosystems they form.

It relates to the variability among living organisms on the earth, including the variability within and between the species and that within and between the ecosystems.

Biodiversity as we have today is the result of 2.5 to 3.5 billion years of evolution. Before the advent of humans, the earth supported more biodiversity than in any other period.

Since the emergence of humans, however, biodiversity has begun a rapid decline, with one species after another bearing the brunt of extinction due to overuse.

The number of species globally varies from 2 million to 100 million, with 10 million being the best estimate.

New species are regularly discovered, most of which are yet to be classified; an estimate states that about 40 per cent of fresh water fishes from South America are not classified yet.

Biodiversity is not found evenly on the earth. It is consistently richer in the tropics. As one approaches the polar regions, one finds larger and larger populations of fewer and fewer species. Tropical forests are very rich in biodiversity.

Biodiversity can be discussed at three levels:

Genes are the basic building blocks of various life forms. Genetic biodiversity refers to the variation of genes within species. Groups of individual organisms having certain similarities in their physical characteristics are called species. This genetic diversity is essential for a healthy breeding of populations of species.

Species diversity relates to the number of species in a defined area. Areas rich in species diversity are called hotspots of diversity.

Ecosystem diversity is constituted by the broad differences between ecosystem types and the diversity of habitats and ecological processes within each.

The boundaries of communities (associations of species) and ecosystems are not very rigidly defined, so the demarcation of ecosystem boundaries is difficult and complex.

Draw rolling grassy hills with patches of forest (sholas) lying in the folds and valleys of the hills, under an overcast sky, to show two different habitats within one landscape as an example of ecosystem diversity.

Why should biodiversity be valued and conserved?

Biodiversity has contributed in many ways to the development of human culture and, in turn, human communities have played a major role in shaping the diversity of nature at the genetic, species and ecological levels. The reasons for valuing and conserving it are several.

Ecological reasons. The more diverse an ecosystem, the better are the chances for the species to survive through adversities and attacks, and consequently the more productive it is.

The loss of species would decrease the ability of the system to maintain itself. Just like a species with a high genetic diversity, an ecosystem with high biodiversity may have a greater chance of adapting to environmental change.

In other words, the more the variety of species in an ecosystem, the more stable the ecosystem is likely to be.

Economic reasons. For all humans, biodiversity is an important resource in their day-to-day life. One important part of biodiversity is crop diversity, also called agro-biodiversity. Biodiversity is seen as a reservoir of resources to be drawn upon for the manufacture of food, pharmaceutical and cosmetic products.

Scientific reasons. Each species can give us some clue as to how life evolved and will continue to evolve. Biodiversity also helps in understanding how life functions and the role of each species in sustaining ecosystems, of which we are also a species.

Ethical and moral reasons. It is our ethical responsibility to consider that each and every species along with us has an intrinsic right to exist. Hence it is morally wrong to voluntarily cause the extinction of any species.

The level of biodiversity is a good indicator of the state of our relationships with other living species. In fact, the concept of biodiversity is an integral part of many human cultures.

Aesthetic reasons. The variety of life, from the flowering trees of the Western Ghats to the red panda of the eastern Himalaya, gives pleasure and wonder.

Forests, wetlands and wildlife draw visitors to national parks and sanctuaries, and the variety of nature has inspired art, poetry and festivals in many cultures.

Note: The reasons for conserving biodiversity are often grouped as ecological, economic, scientific, ethical and moral, and aesthetic. A good answer names the group and then gives one concrete point for each.

What roles does biodiversity play in sustaining mankind?

Biodiversity plays ecological, economic and scientific roles.

The ecological role

Species of many kinds perform some function or the other in an ecosystem. Species capture and store energy, produce and decompose organic materials, help to cycle water and nutrients throughout the ecosystem, fix atmospheric gases and help regulate the climate.

Plants and micro-organisms also control pollution: plants take in carbon dioxide and trap dust, and wetland plants and bacteria break down wastes in water. These functions are important for ecosystem function and human survival.

A more diverse ecosystem is more likely to survive adversity and is more productive.

The economic role

Biodiversity is an important resource in day-to-day life. Some of the important economic commodities that biodiversity supplies to humankind are food crops, livestock, forests, fish and medicinal resources.

The concept of biological resources as a reservoir to be drawn upon is itself responsible for the deterioration of biodiversity, and it is also the origin of new conflicts dealing with rules of division and appropriation of natural resources.

The scientific role

Each species can give us some clue as to how life evolved and will continue to evolve.

Biodiversity also helps in understanding how life functions and the role of each species in sustaining ecosystems, of which we are also a species.

This fact must be drawn upon by every one of us so that we live and let other species also live their lives.

What causes the loss of biodiversity?

Since the last few decades, growth in human population has increased the rate of consumption of natural resources. It has accelerated the loss of species and habitation in different parts of the world.

The tropics cover about two-fifths of the earth's surface and are home to about two-fifths of the world's people, a share that is rising fast.

Over-exploitation of resources and deforestation have become rampant to fulfil the needs of a large population.

As tropical rain forests cover only about 6 per cent of the earth's land surface but contain about 50 per cent of its species, destruction of natural habitats has proved disastrous for the entire biosphere.

1. Population growth and over-exploitation. More people consume more natural resources, and over-exploitation of resources and deforestation have become rampant.
2. Destruction of habitat. Tropical rain forests hold 50 per cent of the species on the earth, so clearing them is disastrous for the whole biosphere.
3. Natural calamities. Earthquakes, floods, volcanic eruptions, forest fires and droughts cause damage to the flora and fauna of the earth, bringing change to the biodiversity of the affected regions.
4. Pollution. Pesticides and other pollutants such as hydrocarbons and toxic heavy metals destroy the weak and sensitive species.
5. Exotic species. Species which are not the natural inhabitants of the local habitat but are introduced into the system are called exotic species; a natural biotic community may suffer extensive damage because of their introduction.
6. Hunting and poaching. Tigers, elephants, rhinoceros, crocodiles, minks and birds were hunted mercilessly by poachers for their horn, tusks and hides, rendering certain types of organisms endangered.

Definition: Exotic species are species which are not the natural inhabitants of the local habitat but are introduced into the system.

How are threatened species classified?

The International Union for Conservation of Nature and Natural Resources (IUCN) has classified the threatened species of plants and animals into three categories for the purpose of their conservation.

Note: Current IUCN categories. The three categories below are the ones used in the textbook. Since 1994 the IUCN Red List has used Critically Endangered, Endangered and Vulnerable as its three threatened categories; "rare" is an older category that is no longer used.

Draw two red pandas climbing or sitting on a tree trunk, and label the sketch as an example of an endangered species.

Why is India a mega diversity nation?

There are some countries situated in the tropical region which possess a large number of the world's species diversity. They are called mega diversity centres. There are 12 such countries: Mexico, Colombia, Ecuador, Peru, Brazil, Democratic Republic of Congo, Madagascar, China, India, Malaysia, Indonesia and Australia.

India's place among them rests on its varied climate and landscape, which give it a variety of unique ecosystems and endemic species. An endemic species is one found naturally in one region and nowhere else.

Draw a flowering plant with several large, elongated pale flowers among dark leaves, and label it as a highly rare endemic tree of the Southern Western Ghats.

On an outline map of India, shade and label the Sundarbans mangroves in the Ganga and Brahmaputra delta (West Bengal), the Himalayan mountain forests, the tropical evergreen forests of the Western Ghats and of the North-East, the desert of western Rajasthan and the thorn and scrub forests of the Deccan plateau. Then mark with a dot and label the Nilgiri Biosphere Reserve (Tamil Nadu, Kerala and Karnataka), the Nanda Devi Biosphere Reserve (Uttarakhand), the Gulf of Mannar Biosphere Reserve (Tamil Nadu), Jim Corbett National Park (Uttarakhand) and Desert National Park (Rajasthan).

In order to concentrate resources on those areas that are most vulnerable, conservation scientists have identified certain areas as biodiversity hotspots. The idea came from the ecologist Norman Myers in 1988, and Conservation International keeps the list.

Hotspots are defined according to their vegetation: a hotspot must have at least 1,500 species of vascular plants found nowhere else, and must have lost at least 70 per cent of its original vegetation.

Plants are important because these determine the primary productivity of an ecosystem. Most, but not all, of the hotspots rely on species-rich ecosystems for food, firewood, cropland and income from timber.

In Madagascar, for example, about 85 per cent of the plants and animals are found nowhere else in the world.

Other hotspots in wealthy countries are facing different types of pressures; the islands of Hawaii have many unique plants and animals that are threatened by introduced species and land development.

Draw a world outline with latitude lines at 30°, 60° and 90° N and S and longitude lines at 0°, 90° and 180°, and shade the hotspot regions.

Mark and label: Central American Highland Forests; Central American Lowland Forests; Western Ecuador and Colombian Choco; Tropical Andes; Atlantic Forest, Brazil; Upper Guinea Forests; Eastern Arc Mountains, Tanzania; Eastern Madagascar; Western Ghats, India; Eastern Himalaya; Sinharaja Forest, Sri Lanka; Indonesia;

Peninsular Malaysia; Philippines; Northern Borneo; Queensland; Melanesia (New Caledonia). Add a scale bar in kilometres.

What are the strategies for conserving biodiversity?

Biodiversity is important for human existence. All forms of life are so closely interlinked that disturbance in one gives rise to imbalance in the others. If species of plants and animals become endangered, they cause degradation in the environment, which may threaten human being's own existence.

Conservation strategies fall into two groups. In-situ conservation protects species in their natural habitat. Ex-situ conservation protects species outside their natural habitat.

In-situ strategies: protected areas

To protect, preserve and propagate the variety of species within natural boundaries, the Government of India passed the Wild Life (Protection) Act, 1972, under which national parks and sanctuaries are declared.

Biosphere reserves come from a separate scheme: UNESCO's Man and the Biosphere Programme (1971). India set up its first, the Nilgiri Biosphere Reserve, in 1986.

Ex-situ strategies

Ex-situ strategies keep species alive outside their natural habitat. Captive breeding is the breeding of threatened animals in controlled conditions, such as in a zoo, so that their numbers can be raised and individuals later released.

A zoo keeps live animals for breeding, study and public education. A botanical garden grows and displays a collection of living plants.

A gene bank stores seeds, or other genetic material, of many varieties under controlled conditions so that the genetic diversity of crops and wild plants is not lost.

India's national gene bank is at the National Bureau of Plant Genetic Resources in New Delhi, and one of its oldest botanical gardens is the Indian Botanic Garden at Howrah, founded in 1787.

International and community action

The Government of India, along with 155 other nations, signed the Convention on Biological Diversity at the Earth Summit held at Rio de Janeiro, Brazil in June 1992.

To put it into effect India passed the Biological Diversity Act, 2002, which set up the National Biodiversity Authority. The world conservation strategy has suggested the following steps for biodiversity conservation:

1. Efforts should be made to preserve the species that are endangered.
2. Prevention of extinction requires proper planning and management.
3. Varieties of food crops, forage plants, timber trees, livestock, animals and their wild relatives should be preserved.
4. Each country should identify habitats of wild relatives and ensure their protection.
5. Habitats where species feed, breed, rest and nurse their young should be safeguarded and protected.
6. International trade in wild plants and animals should be regulated.

There is an urgent need to educate people to adopt environment-friendly practices and reorient their activities in such a way that development is harmonious with other life forms and is sustainable.

There is an increasing consciousness of the fact that such conservation with sustainable use is possible only with the involvement and cooperation of local communities and individuals. For this, the development of institutional structures at local levels is necessary.

The critical problem is not merely the conservation of species nor the habitat but the continuation of the process of conservation.

How do the world's species and threatened species compare in numbers?

The figures below bring together the numbers that describe biodiversity and its loss. They show how unevenly species are spread, how large the estimate of global species is, and how the IUCN's three threatened categories differ in the size and range of their populations.

Draw two bars side by side, each standing for 100 per cent.

In the first, labelled "Earth's land surface", shade about 6 per cent as tropical rain forest. In the second, labelled "Earth's species", shade about 50 per cent as species living in tropical rain forests.

Add a key and the title, to show how a small area holds half of all species.

Case study: Madagascar, a hotspot of very high endemism

Madagascar is one of the 12 mega diversity centres, and it also shows how a hotspot is defined and why it matters. Hotspots are defined according to their vegetation, because plants determine the primary productivity of an ecosystem.

Most, but not all, of the hotspots rely on species-rich ecosystems for food, firewood, cropland and income from timber.

In Madagascar, about 85 per cent of the plants and animals are found nowhere else in the world.

This very high share of endemic species is what makes the island so important for conservation: a species lost there cannot be replaced from anywhere else.

The case shows why conservation agencies concentrate resources on those areas that are most vulnerable, and why the loss of habitat in a hotspot is a loss to the whole world and not only to the country concerned.

Case study: Hawaii, a hotspot under pressure from introduced species

The islands of Hawaii show a different kind of pressure on biodiversity. Hawaii has many unique plants and animals, but they are threatened by introduced species and by land development.

This is the same process that makes exotic species a cause of biodiversity loss: species which are not the natural inhabitants of the local habitat but are introduced into the system can cause extensive damage to a natural biotic community.

The two cases together bring out the point that hotspots in wealthy countries face different types of pressures from those in poorer tropical countries.

In Madagascar the pressure comes with poverty and dependence on species-rich ecosystems for food, firewood, cropland and income from timber; in Hawaii it comes from introduced species and land development. Conservation planning has to answer both.

Glossary

• Biosphere: the zone of the earth, with its atmosphere, hydrosphere and lithosphere, in which living organisms exist and interact.
• Ecosystem: a community of living organisms together with the non-living parts of their environment, working as a unit.
• Biodiversity: the number and variety of organisms found within a specified geographic region, including their genes and the ecosystems they form.
• Genetic diversity: the variation of genes within species, essential for healthy breeding of populations.
• Species diversity: the variety of species, measured through richness, abundance and types in a defined area.
• Ecosystem diversity: the broad differences between ecosystem types and the diversity of habitats and processes within each type.
• Hotspot: an area rich in endemic plant species that has lost most of its original vegetation, listed so that conservation resources go to the most vulnerable places.
• Exotic species: a species introduced into a habitat where it is not a natural inhabitant, which may damage the local community.
• Endangered species: a species in danger of extinction, listed by the IUCN in its Red List of threatened species.
• Vulnerable species: a species likely to be in danger of extinction in the near future if the threats to it continue.
• Rare species: a species with a very small world population, confined to limited areas or thinly scattered.
• Mega diversity centre: one of 12 tropical countries that together possess a large number of the world's species.
• Endemic species: a species found naturally in one region and nowhere else in the world.
• In-situ conservation: conservation of species within their natural habitat, as in biosphere reserves, national parks and sanctuaries.
• Ex-situ conservation: conservation of species outside their natural habitat, as in zoos, botanical gardens, captive breeding and gene banks.

Common errors and misconceptions

• Misconception: Biodiversity means only the number of animal species. Correct: It covers the varieties of plants, animals and micro-organisms, the genes they contain and the ecosystems they form.
• Misconception: Biodiversity is spread evenly over the earth. Correct: It is consistently richer in the tropics, and towards the polar regions there are larger populations of fewer species.
• Misconception: An endangered species and a vulnerable species are the same. Correct: An endangered species is already in danger of extinction; a vulnerable species is likely to be in danger in the near future if the threats continue.
• Misconception: A zoo is an in-situ method of conservation. Correct: A zoo keeps animals outside their natural habitat, so it is an ex-situ method.
• Misconception: Exotic species always enrich a habitat. Correct: Introduced species can cause extensive damage to a natural biotic community.
• Misconception: Hotspots are defined by the number of animals alone. Correct: Hotspots are defined according to their vegetation, because plants determine the primary productivity of an ecosystem.
• Misconception: Conservation is only the work of government. Correct: Conservation with sustainable use is possible only with the involvement and cooperation of local communities and individuals.

Exam-style questions with model answers

Q1. State what is meant by biodiversity and name its three levels. [2 marks]

1. Biodiversity is the number and variety of organisms found within a specified geographic region, covering the varieties of plants, animals and micro-organisms, the genes they contain and the ecosystems they form.
2. The three levels are genetic diversity, species diversity and ecosystem diversity.

Q2. Distinguish between an endangered species and a vulnerable species, as classified by the IUCN. [3 marks]

1. An endangered species is one which is in danger of extinction; the IUCN publishes information about such species world-wide as the Red List of threatened species.
2. A vulnerable species is one which is likely to be in danger of extinction in the near future if the factors threatening its extinction continue.
3. The survival of a vulnerable species is not assured because its population has reduced greatly, whereas an endangered species is already facing the danger of extinction.

Q3. Explain any three factors responsible for the loss of biodiversity. [3 marks]

1. Growth in human population has increased the consumption of natural resources, and over-exploitation of resources and deforestation have become rampant.
2. Destruction of natural habitat is disastrous because tropical rain forests, though covering only about 6 per cent of the earth's land surface, contain about 50 per cent of its species.
3. Pesticides and other pollutants such as hydrocarbons and toxic heavy metals destroy the weak and sensitive species, and introduced exotic species can damage a natural biotic community.

Q4. India is a mega diversity nation. Justify this statement with reference to its varied climate and landscape. [4 marks]

1. India is one of the 12 mega diversity centres of the world, the others including Mexico, Brazil, China, Malaysia, Indonesia and Australia.
2. Its varied climate and landscape give it a variety of unique ecosystems, such as the Sundarbans, the largest mangrove forest in the world.
3. It has vast mountain forests in the Himalayas and tropical evergreen forests in the Western Ghats and the North-East region.
4. It also has desert vegetation in Rajasthan and thorn and scrub forests on the plateaus, and it shelters endemic species such as Humboldtia decurrens, a highly rare endemic tree of the Southern Western Ghats.

Q5. Explain the ecological and economic roles of biodiversity. [4 marks]

1. Ecologically, species capture and store energy, produce and decompose organic materials, help to cycle water and nutrients, fix atmospheric gases and help regulate the climate.
2. The more diverse an ecosystem, the better the chances for species to survive adversities and attacks, and the more productive and stable the ecosystem is likely to be.
3. Economically, biodiversity is an important resource in day-to-day life, and crop diversity, also called agro-biodiversity, is one important part of it.
4. It supplies food crops, livestock, forests, fish and medicinal resources, and is a reservoir for the manufacture of food, pharmaceutical and cosmetic products.

Q6. Distinguish between in-situ and ex-situ strategies of conservation, giving two examples of each. [5 marks]

1. In-situ conservation protects species within their natural habitat, while ex-situ conservation protects species outside their natural habitat.
2. In-situ examples are biosphere reserves and national parks; wildlife sanctuaries are a third, established under the Wild Life (Protection) Act, 1972.
3. Ex-situ examples are zoos and botanical gardens; captive breeding and gene banks are further ex-situ methods.
4. In-situ conservation keeps the whole ecosystem and its processes intact, which is why protected areas are established within natural boundaries.
5. Ex-situ methods such as captive breeding and gene banks are useful for raising the numbers of threatened animals and for storing the genetic material of many varieties, but they remove the species from its habitat.

Q7. Why is it important to conserve biodiversity? Give ecological, ethical and aesthetic reasons. [5 marks]

1. All forms of life are so closely interlinked that disturbance in one gives rise to imbalance in the others; if species become endangered they cause degradation in the environment, which may threaten human being's own existence.
2. Ecologically, a more diverse ecosystem is more productive and more stable, and has a greater chance of adapting to environmental change.
3. Ethically, each and every species along with us has an intrinsic right to exist, so it is morally wrong to voluntarily cause the extinction of any species.
4. The level of biodiversity is a good indicator of the state of our relationships with other living species, and the concept of biodiversity is an integral part of many human cultures.
5. Aesthetically, the variety of life, from the grasslands and sholas of the Western Ghats to the red panda, gives pleasure and wonder, and human communities have in turn shaped the diversity of nature.

Key takeaways

• The biosphere is the living zone where the lithosphere, hydrosphere and atmosphere meet, and its components interact through ecosystems.
• Biodiversity is the number and variety of organisms in a region, and it exists at genetic, species and ecosystem levels.
• Biodiversity is richer in the tropics and poorer towards the poles, where there are larger populations of fewer species.
• Biodiversity is valued for ecological, economic, scientific, ethical, moral and aesthetic reasons.
• Population growth, habitat destruction, pollution, exotic species and poaching are the main causes of biodiversity loss.
• The textbook groups threatened species as endangered, vulnerable and rare; the current IUCN Red List uses critically endangered, endangered and vulnerable.
• India is one of 12 mega diversity centres, with the Sundarbans, Himalayan forests, Western Ghats, desert and plateau vegetation.
• In-situ conservation uses biosphere reserves, national parks and sanctuaries; ex-situ uses zoos, botanical gardens, captive breeding and gene banks.
• Conservation with sustainable use is possible only with the involvement and cooperation of local communities and individuals.

Test yourself

What is an ecosystem?

An ecosystem is a community of living organisms together with the non-living parts of their environment, working as a unit. Its living members are the biotic components and its non-living members the abiotic components.

What is genetic diversity?

Genetic diversity is the variation of genes within species. Human beings all belong to the Homo sapiens species yet differ in height, colour and physical appearance, and this diversity is essential for healthy breeding of populations.

What is an exotic species?

An exotic species is one which is not a natural inhabitant of the local habitat but is introduced into the system. Such introductions have caused extensive damage to natural biotic communities.

Name the three categories of threatened species given in the textbook.

They are endangered species, vulnerable species and rare species, from an older IUCN classification. Since 1994 the IUCN Red List has used critically endangered, endangered and vulnerable instead.

Which country hosted the Earth Summit at which the Convention on Biological Diversity was signed, and in which year?

The Earth Summit was held at Rio de Janeiro in Brazil in June 1992. The Government of India along with 155 other nations signed the Convention on Biological Diversity there.

What is a biodiversity hotspot and how is it defined?

A biodiversity hotspot is an area identified by conservation scientists to concentrate resources on the most vulnerable places. Hotspots are defined according to their vegetation, because plants determine the primary productivity of an ecosystem.

Give one example of an endemic species of India.

Humboldtia decurrens is a highly rare endemic tree of the Southern Western Ghats in India. Endemic species are found naturally in one region and nowhere else.

Which is the largest mangrove forest in the world?

The Sundarbans, in the delta of the Ganga and the Brahmaputra, is the largest mangrove forest in the world. It is one of the unique ecosystems that make India a mega diversity nation.