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UNIT VI REPRODUCTION
Chapter 1 : Sexual Reproduction in Flowering Plants
Chapter 2 : Human Reproduction
Chapter 3: Reproductive Health
UNIT VII GENETICS AND EVOLUTION
Chapter 4 : Principles of Inheritance and Variation
Chapter 5: Molecular Basis of Inheritance
UNIT VIII BIOLOGY IN HUMAN WELFARE
Chapter 7 : Human Health and Disease
Chapter 8: Microbes in Human Welfare
UNIT IX BIOTECHNOLOGY
Chapter 9 : Biotechnology : Principles and Processes
Chapter 10 : Biotechnology and its Applications
UNIT X ECOLOGY
Biodiversity occurs not only in the species level, but also in the macromolecular levels.
Biodiversity as described by Edward Wilson is the combined diversity at all levels of biological organisation.
The most important forms of biodiversity are:
Genetic diversity (diversity at the genetic level)
Species diversity (diversity at the species level)
Ecological diversity (diversity at the ecosystem level)
There are close to 1.5 million plants and animals that have to be discovered and described. More species have been discovered in temperate regions as compared to tropics.
According to an estimate made by Robert May, global species biodiversity is about 7 million.
Of the total species discovered so far, 70% are animals and 22% are plants. Of the animals, 70% are insects.
India has 2.4% of the world’s land and 8.1% of the total species diversity. According to May’s estimate, 78% of the biodiversity is still to be discovered.
Applying this to India’s biodiversity figures, there still is a scope for discovery of over 1 lakh species of plants and 3 lakh species of animals.
Patterns of Biodiversity
Latitudinal gradients − The plants and animals are not distributed evenly worldwide. The diversity of living forms decreases as we go from the equator towards the poles. A huge amount of plants and animals are concentrated in the tropical region because of the following reasons.
Tropical environment is less seasonal and almost constant and predictable as compared to temperate environment.
Tropics receive the major part of the solar energy, which contributes to great productivity.
Speciation is dependent upon time. Tropical areas have remained undisturbed for millions of years unlike temperate regions, which have experienced frequent glaciations in the past.
Species-Area relationships − Alexander von Humboldt observed that biodiversity increases with increase in explored area. This relationship can be given by,
log S = log C + Z log A
Where,
S = Species richness
A = Area
Z = Slope of the line (regression co-efficient)
C = Y-intercept
Value of Z is found to lie in the range of 0.1 to 0.2 for comparatively smaller areas such as countries while for very large areas such as entire continents, the slope of the line is much steeper with Z value lying from 0.6 to 1.2.
Importance of biodiversity & Loss of Biodiversity
What is the importance of biodiversity on the Earth?
There is no exact answer to this question, but experiments conducted by many ecologists have demonstrated that a system with greater biodiversity is more stable and has greater productivity.
In the long run, biodiversity is related with overall health of our ecosystem and survival of human race on the earth.
Characteristics of a stable community:
It should not show much variation in productivity from year to year.
It must be either resistant or resilient to occasional disturbances.
It must be resistant to invasion by alien species.
Loss of Biodiversity
Due to human activities, the natural wealth is getting lost rapidly.
The last 20 years have seen the loss of 27 species.
Some of the causes of this loss are:
Habitat loss and fragmentation − This is the major cause for loss of biodiversity. Habitat destruction is caused by human activities such as deforestation and increasing pollution, leading to the loss of many plants and animals.
Over-exploitation − Humans due to their greed and increased exploitation of natural resources have contributed to the endangerment of commercially important species of plants and animals. Example − Species such as Steller’s sea cow and passenger pigeon have been extinct due to over exploitation by humans.
Alien-species invasion − The unintentional or deliberate introduction of alien species causes the declination of the indigenous species. Example − Nile perch introduced in Lake Victoria led to the extinction of more than 200 species of cichlid fish in the lake.
Co-extinction − When a plant or animal becomes extinct, another plant or animal which is dependent on it in an obligatory way also becomes extinct. Example − In case of plant-pollinator mutualism, the extinction of one partner will eventually lead to the extinction of other also.
Biodiversity Conservation
Biodiversity conservation is necessary because of the following reasons:
Many commercially important products are obtained by nature such as food, fibre, wood, and countless industrial products.
Certain activities and products cannot be accomplished without the help of nature such as production of oxygen and pollination.
Intangible benefits such as aesthetic pleasure are derived from nature.
Conserving the species we share our planet with and passing the rich legacy of biodiversity to our future generations is our ethical duty.
Biodiversity can be conserved by:
In-situ conservation - In order to conserve biodiversity better, some of the world’s biodiversity hotspots (with high degree of biodiversity and endemism) have been identified and are protected. In India, biosphere reserves, wildlife sanctuaries, and national parks are built for this purpose.
Ex-situ conservation - The threatened species of plants and animals are taken out of their habitats and are kept in special settings as in zoological parks, botanical gardens, and wildlife parks.
Nowadays, the gametes of endangered species can be preserved viable by methods such as cryopreservation and can be fertilized in-vitro followed by propagation through tissue culture methods. Similarly, seeds can be preserved in seed banks.
NCERT Solutions
Genetic diversity, species diversity, ecological diversity, different types of species, patterns of diversity, loss of biodiversity, biodiversity conservation, and other topics are covered in Biodiversity and Conservation. Ex situ and in situ biodiversity conservation are both possible. In situ conservation protects endangered species in their natural habitat, thereby protecting the entire ecosystem. Ex situ conservation methods include protecting threatened species in zoos and botanical gardens, in vitro fertilisation, tissue culture propagation, and gamete cryopreservation. Biodiversity - Concept, patterns, and importance; biodiversity loss; biodiversity conservation; hotspots, endangered organisms, extinction, Red Data Book, Sacred Groves, biosphere reserves, national parks, wildlife, sanctuaries, and Ramsar sites are among the topics covered in Chapter Biodiversity and Conservation.
1. Name the three important components of biodiversity.
Solution:
The variety of living forms found in different ecosystems is referred to as biodiversity which includes variability in life forms from all possible sources such as air, water and land.
The three significant components of biodiversity are as follows:
• Species diversity
• Genetic diversity
• Ecosystem diversity
2. How do ecologists estimate the total number of species present in the world?
Solution:
Living entities exhibit a vast diversity on Earth. Researchers estimate it to be close to seven millions. Ecologists can estimate the total number of species on Earth through a statistical comparison between a species richness of a well-studied group of insects of tropical and temperate regions. Later these ratios are extrapolated with groups of other plants and animals to estimate the net species richness found on Earth.
3. Give three hypotheses for explaining why tropics show greatest levels of species richness.
Solution:
Three hypotheses used by scientists to explain species richness in the tropics are as follows:
• As tropical latitudes receive more solar energy compared to temperature regions, it results in high species diversity and high productivity
• Tropical regions have less seasonal variations and more or less constant environment promoting specialization and hence high species richness
• In the ice age, temperate regions faced glaciations whereas tropical regions were unchanged leading to an increase in the species diversity in that region.
4. What is the significance of the slope of regression in a species – area relationship?
Solution:
The slope is very helpful in finding the species-area relationship. An analysis of the species-area relationship in smaller regions reveals that the values of slopes of regression is the same irrespective of the taxonomic assemblage or the region. But, when the same analysis is carried out in large areas, the slope of regression was found to be much steeper.
5. What are the major causes of species losses in a geographical region?
Solution:
Biodiversity is referred to the variety of living forms found in different ecosystems including variability observed in life forms from different sources such as air, water and land. However, biodiversity all around the globe is fast declining. Following are the major causes:
• Habitat loss and fragmentation – uncontrolled and unsustainable human activities such as slash, deforestation, mining, burn agriculture and urbanization causes habitats of different entities to be destructed or altered. This leads to the breakup of habitat into smaller pieces affecting the migrationmof animals and also a decline in the genetic exchange between populations resulting in a decline in the species.
• Co-extinction – One species is connected to the other in a native habitat in an intricate network. Hence, extinction of one species causes the extinction of the other wherein they are associated with each other in an obligatory connection. For instance, the extinction of host would cause the extinction of parasites.
• Over-exploitation – Humans have caused species to get extinct or endangered due to over-exploitation and over-hunting of different plants and animals. (extinction of passenger pigeons and tigers)
• Alien species invasions – Intentional introduction of non-native species into a particular habitat causes extinction of indigenous species. Example – Nile perch caused the extinction of more than two hundred species of native fish of Lake Victoria in Kenya when they were introduced in the lake.
6. How is biodiversity important for ecosystem functioning?
Solution:
Biodiversity refers to the variety of life on earth at all the levels. It is important for the following:
• An ecosystem is more stable when it has a high species diversity when compared to a low species diversity ecosystem
• Higher biodiversity causes the ecosystem to more stable in productivity, hence more resistant to any disturbance such as floods or alien species invasions
• The ecological balance in an ecosystem rich in biodiversity remains unchanged
• As different tropic levels are connected through food chains, illness of one organism at any tropic level would disrupt the whole food chain. For instance, if plants are destroyed in a food chain, then it would create an imbalance in the world of herbivores due to scarcity of food. Eventually, if all deers die, the tigers will also die soon. Thus, if an ecosystem is rich in species, each tropic level will have other food alternatives which would increase the life expectancy rate of entities. Therefore, biodiversity has a significant role in preserving the ecological health and balance of an ecosystem.
7. What are sacred groves? What is their role in conservation?
Solution:
Sacred groves are referred to the tracts of forests that are restored in the places of worship. These are found to be in Western Ghats of Karnataka, Rajasthan, Maharashtra, Madhya Pradesh, and Meghalaya. These groves help in safeguarding threatened, rare and endemic species of animals and plants present in a region. The act of deforestation is sternly banned in tribal regions. Thus, the sacred groves are a rich region.
8. Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?
Solution:
Ecosystem has two types of components, the abiotic and the biotic components. While the abiotic components are air, light, water, temperature, soil etc, biotic components are constituted by the animals, plant, humans. The role of plants is crucial in controlling soil erosion and floods. Plant roots secure and bind the soil particles together, thus inhibiting the top layer of the soil to get eroded by running water or wind. Plant roots cause the soil to be porous enabling ground water infiltration and averting floods. This is how,
plants are able to prevent erosion of soil and other natural calamities such as droughts and floods. Also, they are critical in enhancing biodiversity and increasing the fertility of soil.
9. The species diversity of plants (22 per cent) is much less than that of animals (72 per cent). What could be the explanations to how animals achieved greater diversification?
Solution:
There is a huge difference in the percentage of species diversity of plants (22%) and the species diversity of animals (72%). It is due to the following reasons:
• Adaptation of animals to changing environments for survival. For instance – animals and insects have grown to develop a complex nervous system for coordinated and controlled body movements. Also, insects have grown to be versatile and developed a potential to survive in different habitats in comparison to other life forms as they possess repeated body segments with external cuticles and paired appendages
• Plants are immobile while animals can move around. Hence, animals have achieved more diversity as they have moved and adapted to different habitats.
10. Can you think of a situation where we deliberately want to make a species extinct? How would you justify it?
Solution:
Yes, there has been such a situation where different types of parasites and disease-causing micro-organisms would want to be eradicated from the planet. Scientists are working extensively to fight and wipe them out completely as these microbes are harmful to human existence and have been successful in eliminating small pox from the Earth through the successful use of vaccination which shows how humans deliberately want to makes these species extinct. Some other programmes aiming at eradication are for Hepatitis B, polio vaccinations etc to eliminate those microbes that cause diseases.
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