Hello students welcome to the IIT PAL series of biology. I am Rikisha Bhaumik PGT biology at Hindi, Vidyalaya sector 2 Rkpuram before beginning our session. Today, if I ask you a question, what is the most unique thing about our planet earth you most probably would say that the presence of life is what makes earth unique. Next, if I ask you what is the most amazing thing about life on earth? After seeing these photographs, you would surely say that the diversity in living organisms is the most amazing thing about life on earth. In our life, whenever we go anywhere on roadside or in a garden, we see so many diverse types of plants, trees, herbs, shrubs, climbers, creepers. Even among ourselves, if we see each other, we all differ from each other, except obviously the identical twins. So, the enormous diversity in living organism is the most amazing thing about life on earth. In today’s session we will be exploring more about biodiversity and its importance and its conservation in our chapter: biodiversity and conservation class 12th. So, this is the part 1 session, 1 of biodiversity and conservation. This chapter will give you insights on questions such as. Why are there so many species? Did such great diversity exist throughout earth’s history? How did this diversification come about these questions? If you recall, we did the sessions on evolution and we have discussed these questions there are so many species if you recall that evolution or the process of speciation and natural selection gives us an insight on the great diversity which has come about the process of speciation, led to the formation of many species. And today, whatever biodiversity has accumulated is due to a protracted process which took millions of years. How - and why is this diversity important to the biosphere? Would it function any differently if the diversity were much less? These last two questions. We will deliberate upon these sessions on biodiversity and conservation, so you will get an estimate or a precise idea from general to specific about what is biodiversity, how it got accumulated. What is its importance, and why should we conserve it and if we need to conserve it, what should we do to conserve it with this? The last question which arises because we humans are always thinking about our self, how this biodiversity is important for us. How will it benefit us, so we will also investigate this aspect of how humans can benefit from the diversity of life. As I have told you that biodiversity refers to the variety or variations variety variations, variability refers to the tendency to show variations of living organisms present on earth. This may also be referred to as biological diversity, biological diversity, the living organisms comprises biological and the differences. The variety variations variability among these living organisms can be referred to as biological diversity, and these two terms, biological and diversity. They got compressed to form this one term biodiversity and all this happened in 1980s. This term biodiversity was coined by Walter g Rosen, but it was popularized by a famous socio biologist named Edward Wilson. Let us have a summary of what I told you biodiversity is the variety and variability of several types of lives found on the earth and the variation within species. The term biodiversity was coined by Walter g Rosen, but it was popularized by a famous socio biologist, Edward Wilson, in nineteen eighties. So, the term biodiversity or this subject has gained importance lately in nineteen eighties, can you guess why is it so? You are correct. This is because the impact of human activities or the anthropogenic activities on the environment has become quite apparent, and that is why there is so much focus on biodiversity these days. Now the next thing, which amazes us that we have discovered and described many species; anyone would be awestruck to notice that there are more than 20,000 species of ants. More than 3 lakh species of beetles, more than 28,000 species of fishes, more than 20,000 species of orchids, more than 2 lakh hundred 81 one species of vascular plants and more than nine thousand nine hundred ninety species of birds - and these are the estimates of only those species which have been recorded and described there are so many species yet to be discovered. You will be again astonished to know that 80 percent of the species are yet to be explored and described. Indeed, this diversity is amazing and the it is a constant effort of humans to know more about these species next, coming to the levels of biodiversity, Biodiversity is a composite term and includes in its domain major three types of diversity. This biodiversity is ranges from the molecular level to the biome level, but the three major levels of biodiversity can be identified as number one. Genetic diversity, number two species, diversity, and number three is ecological diversity, so biodiversity is a composite or it comprises of all these three types of diversity. All these three types of diversity, genetic species, and ecological biodiversity - are interdependent and intertwined with each other to comprise the biodiversity of this earth. Now, let us try to understand each of these diversity in detail, starting with the first one, which is the genetic diversity as the name suggests, is the diversity in the genes or the variation in the gene or the genetic composition of an organism can be referred to as genetic diversity. So, what is a gene? A gene can be referred to as a functional segment of DNA. DNA is the heredity substance. It the full form of DNA is deoxyribonucleic acid and what is DNA. DNA is again made up of polynucleotide chains, polynucleotides chains and the double helical model of DNA, which we draw is like this. These two strands are the polynucleotide strands. These polynucleotides again are comprised of the nitrogenous bases. These bases are complementary to each other. There is complementary base pairing between the two polynucleotide strands in DNA. There are four types of nitrogenous bases: adenine, guanine, cytosine, and thymine. So, the alteration in the sequence of these bases, alteration in the sequence of these bases is what causes variation and this kind of variation is known as genetic variation. So, genetic diversity arises because of certain changes or alteration in the sequence of these nitrogenous bases. Now what is the importance of this genetic diversity? More is the genetic diversity. It has been seen that more is the chance of that population population words, it can be said that if a population of a species comprises of several types of genes, they will be in a better position to cope up with the changing environmental situations. So, genetic diversity is a particularly important level which is helping in maintaining the ecological diversity and the species diversity for examples. If we take the example of a medicinal plant, ravelfy or vomitoria, many different varieties of this medicinal plant can be seen in the Himalayas, but the difference in these varieties is based on the potency and concentration of its active chemical or alkaloid named recipient. The level and the concentration, the toxic, the toxicity, or potency of this compound varies in several types of raw vomitoria. Similarly, if we take some common examples like that of rice and mangoes, we find that there are so many distinct typesf rice available in the market. Whenever there is the season of mangoes, we find that there are so many distinct types of mangoes based on its shape size and the content or the quality of the food or the taste of mango. They have been named differently because they represent different varieties. So, this is what is genetic diversity? Genetic diversity is seen within a species when the when there are diverse types of genes within the population of a species, it is referred to as genetic diversity next coming to the species diversity. Now, what is species diversity again before discussing about species diversity? We should be able to define what do we mean by a species diversity? Species is a group of morphologically, similar organisms, and the most important thing in this is that they should be able to interbreed and perpetuate their population, should be able to interbreed. They should be able to reproduce and should be able to increase its population. So, when we talk about species diversity, we are connoting towards the diversity of species level within a particular region. Now, if we talk about animals, we know that animals can be divided into invertebrates and vertebrates again, these vertebrates can have further five subgroups. These are Pisces amphibia, Reptilia, Aves and mammals. So, by species diversity I mean to say that within each subgroup there are so many diverse types of species. If we take, for example, Pisces there are so many diverse types of fishes among amphibians. There are so many distinct species of amphibia. Likewise in reptiles, apes, and mammals, we know of so many distinct types of species representing that group. So, what is species diversity? Now, for example, if I take amphibia and compare two regions like western guard and eastern guards of India, we see that there are a greater number of species of amphibia in western ghat as compared to eastern guard. So, we can say that western guard shows more species diversity than eastern guard, so this is what is: species diversity, the diversity at species level within a particular region? Now, moving on to ecological diversity, we are moving from lower towards the broader type of diversity. First, we discuss genetic, then species and now moving on to ecological diversity, so ecological diversity will cover the entire diversity of a region of a country or even the globe. So, it is the variation in the ecosystem found in a region or the variation in ecosystems. Over the whole planet, for example, if we are considering two different countries, for example, one is India which is subtropical and the other Scandinavian countries like Norway, Scotland, and Iceland. We find that there are a greater number of biomes in India. We can see deserts forest hills, mangroves. Coral reefs, wetlands, estuaries, etc., so it has greater ecosystem biodiversity as compared to these Scandinavian countries. So, this was all about the levels of biodiversity. Next, moving on to the number of species on earth, can you estimate the total number of species on earth? No, it is disappointing to realize that we have not been able to discover and describe about 80 percent of this species on earth, but the all these species which we have described and discovered have been recorded, and this record is kept by international union for conservation of nature. IUCN, so, according to the IUCN statistics of 2004, there are slightly more than 1.5 million animal and plant species on earth. But as I told you that we still do not have accurate data as many species are yet to be discovered and described, and many estimates of how many total numbers of species are there on earth are only educated guesses and these educated guesses vary widely from 3 million to 100 million. So, in this scenario, we follow a more logical, a precise and scientific estimate given by a scientist Robert may. According to his estimate, there are seven to eight million of total species on earth. The next thing which interests us is that tropics are more biodiverse than temperate areas. When we reveal the species inventory, we saw that tropics show more biodiversity as compared to the temperate areas. The species inventories, therefore are more complete in the temperate as compared to the tropical countries because of the large number of biodiversity present in the tropics, it has not been possible to complete the inventory of the tropical areas, but more so we have a complete inventory of The temperate areas and the most exhaustively studded taxonomic group - is that of insects and keeping the that as a standard biologist, make a statistical comparison of the temperate tropical species, richness of insects and extrapolate or extend this estimate to other groups of animals to come up with the gross estimate of all the animals, since it is not possible to physically count each and every organism each and every species, so biologists prefer to use this extrapolation method to estimate the number of species present in respective groups next coming to the global biodiversity. The species inventory have revealed certain interesting aspects about the global biodiversity global biodiversity when we are referring to the earth as entire, so 70 percent of the recorded species are that of animals and only 22 percent of the plants, and these plant includes fungi algae, thallophytes, bryophytes Teredo hides gymnosperms angiosperms every group is included in this, so only twenty two percent of the plants have been recorded till now, and seventy percent of the species among animals also insects are the most species rich and it is about seventy percent of the total. So, it can be said that of ten animals, seven are insect out of ten animals, seven will be insects, then fungal species in the world are more than the combined total of species of fishes, amphibians, reptiles, and mammals. Again, a greater number of fungal species have been recorded. So, we can understand this with the help of these pie. Charts this pie chart show you about the total number of invertebrates which have been described and recorded. We have been successful in describing a greater number of insects. 70 percent of this graph shows insects followed by other animal groups, mollusks, and crustaceans. Similarly, among vertebrates’ fishes have been recorded more followed by birds, reptiles, amphibians, and mammals among plants. Fungi and angiosperms are the most recorded species followed by algae, mosses, lichens, ferns, and allies. So, this was about plants and animals, but what about the prokaryotes? So, what about prokaryotes? What about the estimate of prokaryotes? Surprisingly, we still do not have estimates for prokaryotes, and why is it so? The reasons being number one conventional taxonomic method is not suitable for identifying microbial species by conventional taxonomic methods. Again, we mean doing field studies going and exploring the diverse types of organisms and recording them, which is not possible in case of microbial species, because they are very nude and cannot be observed by naked eyes. Secondly, many of these species are not at all culturable under laboratory conditions, they cannot be cultured, they have genomes, and the study of these genomes have explored a new branch of biology which is known as meta genomics. Thirdly, if we apply the biochemical or molecular criteria, it will give their estimates in millions because it will show so many variations genetic variations and they can mutate at a faster rate. So, it is difficult to give a proper estimate for prokaryotes next. Moving on from global biodiversity, let us investigate the biodiversity of India. Fortunately, India is among the 17 mega diverse countries of the world with only 2.4 percent of the world’s land area. It shares 8.1 percent of the global species - diversity, which is indeed impressive. So, there are about forty-five thousand species of plants and ninety thousand species of animals in India, which has been recorded and described. But if we go by maize estimate, this diversity may go up to 1 lakh species of plants and 3 lakh species of animals. In this map of India, you can see the Himalayas losing green cover, so it is especially important for us to preserve this biodiversity. Our country is rich in biodiversity. More biodiversity means a greater number of resources available for us, and if we are losing it, we are losing a vast number of resources. Next, I would like to quote one of these statements given by albert Einstein regarding biodiversity. If the bee disappeared off the surface of the globe, then man would only have four years of life left, no more bees, no more pollination, no more plants, no more animals. So, no more man. To certain extent, the statement is quite apt, but if we replace bees with pollinators and pollinators are no more there, if these pollinators become extinct, they are doing such a big ecosystem service. For us they are doing pollination, helping in fertilization, and growing of new plants. If there are no more pollinators, there will be no more pollination, no more plants, no more animals and the survival of human will be in danger. With this, let us move on to our next topic. That is how much of the species are we losing now. You know that this era is dominated by humans and humans are exerting extreme influence over the environment. We are witnessing rapid loss of species today this has been estimated to be between thousand and one thousand times higher than the natural extinction rates. It is not so that the extinction has not been there. It is a natural process. There have been many ah episodes of extinction. There has been five extinction episodes in the nature, but their pace was not as fast as it is today. If this loss continues at this pace, we could lose all our natural wealth in just less than two centuries. So again, I would reiterate here that the biodiversity which we see is an accumulation of an exceptionally protracted process which took millions of years and losing it just in two centuries, will be very disheartening, and this may be regarded as a sixth extinction crisis. And this sixth extinction crisis is being guided by the anthropogenic activities. So, the question which strikes our mind is that would we ever be able to complete the inventory of the biological wealth of our country or of the world? To answer this question, we would investigate certain facts that we need a lot of time to complete the inventory. Apart from time. We need skilled workforce in form of taxonomist, who can do this thing properly, but given other fact that we are losing the species at an extremely high rate, this becomes quite hopeless. We can be disappointed or hopeless to realize that it is difficult for us to complete the inventory of the biological wealth of our country. So, nature’s biological library is burning even before we catalog the titles of all the books to stock there. It is a matter of dismay that there are so many species present on earth. Human who is so inquisitive and curious by nature, wants to discover and explore about all the organism without being acknowledged. These species are getting extinct and this is the major much anxiety for all of us now. Moving on to the patterns of biodiversity, is there any pattern of biodiversity or is it random? No, it is not random. There is a pattern of biodiversity. If we look on the earth, we see that as we move away from the equator biodiversity decreases. This is known as latitudinal gradient, latitudinal gradient, the latitudes, which are the imaginary lines, have been formed on earth so that we can locate a place properly on it. When we move away from the equator, we see that a greater number of species are present on those countries which are closer to equator as compared to those which are away from the equator. For example, Columbia, which is located near the equator, has about fourteen hundred species of birds. If you move a little away from the equator in New York, which is at forty-one degrees, knot has one hundred five species and if you move further above towards green land, which is at 71 degrees north, it has only 56 species of birds. So, we are seeing a trend, a gradual decline in the number of species of birds from those countries which are closely located to equators towards those which are away from it. So, there is a latitudinal gradient which is seen in the pattern of biodiversity. Some areas are extremely rich in biodiversity. The most biodiverse region of our earth is the amazon forest located near the tropics in south America. The Amazonian rain forest are called the lungs of earth because of the huge biodiversity and plants at harbor. It is home to more than forty thousand species of plants, the three thousand species of fishes: thirteen hundreds of birds, four, twenty-seven of mammals, four, twenty-seven of amphibians, three, seventy-eight of reptiles and of more than one like twenty-five thousand species of invertebrates. This biodiversity in the Amazonian rainforest is extremely rich. Scientists estimate that at least 2 million insect species are waiting to be discovered and named itself in the Amazonian Forest. Now we also learned that tropics harbor more biodiversity as compared to the temperate regions. What is the reason behind this number? One temperate region was subject to frequent glaciation, whereas tropics have remained undisturbed for millions of years and thus have a long evolutionary time for species diversification that that is when we again look back at the evolutionary at the evolutionary sense. We see that the temperate regions were more under the frequent glaciation period and the tropics were undisturbed, and so they got more time for the evolution of species. So, the process of speciation initiated earlier as compared to the temperate regions in the tropical regions, and that is why we see that a greater number of biodiversity or a greater number of species has accumulated in the tropics. Secondly, the tropical environments are less seasonal. They are more constant and predictable. So, since there is less fluctuation in the seasons, they are more constant and their environment is more so predictable and such constant environment promote niche specialization. Now, the term which comes here is niche specialization. What do you mean by niche specialization, knee specialization or ecological niche is the summary of the conditions and resources available for a species to increase its population? So, it is a summary of the conditions and resources available for a species to increase its population, and knee specialization means if an organism has been provided with ample resources and conditions to acquire it in the form of a habitat as well as it has a certain role and function to perform in that habitat that is known as an ecological niche, so such niche specialization was possible in tropics because of constant and predictable seasons and the environmental conditions. Thirdly, there is more solar energy in the tropics being closer to the equator. The sun’s rays fall directly on it and more solar energy contributes to higher productivity and which, in turn leads to greater diversity. Productivity, again is the rate of biomass production. If there will be more sunlight, there will be more primary productivity among the plants. There will be more photosynthesis and if there will be more photosynthesis, more amount of biomass will be available for the next trophic level. So, these are the reasons why the tropics are more biodiverse as compared to the temperate region number one tropical regions. They got more time as they were not subjected to glaciation, and so the process of speciation or evolution started much earlier as compared to the temperate areas. Second, the tropics are less seasonal, they show less fluctuation in season. They are more constant and predictable, and that is why they allowed niche specialization and therefore there is a greater number of species in tropics. Thirdly, the solar energy, which falls directly on these areas, has contributed to more productivity, more primary productivity, leading to more biomass production and more efficiency. Next, we will move on to an important topic, which is species area relationship, species area relationship. The species area relationship was given by a German naturalist and geographer alexander Vaughn Humboldt, and he said that, as the area increases, the species richness also increases up to a certain extent. For this he plotted a graph like this on x axis we take area and on y axis we take species richness. So, it is a relationship of species richness with area. If we take a straight-line log scale and we plot a curve, we get a curve like this, which is known as rectangular hyperbola rectangular hyperbola. The curve which is obtained is a rectangular hyperbola. That is, as the area increases, the species richness is also increasing, but up to a certain extent, then it stops. This can be represented with the help of an equation, which is s is equal to c as to the power z taking log on both sides. We can write it as log s is equal to log c, plus z, log, a where s represents species. Richness c is the y intercept. Z is the slope or regression coefficient and a is the area, so this kind of graph is obtained when we plot a graph between the area and species richness, many ecologists. They have found that the value of z is 0.1 to 0.2, irrespective of the taxonomic groups. Irrespective of the region, but for a large area like a big continent, it has been found to be 0.6 to 1.2. So, what is z is the slope and the steepness of the slope represents the species richness steeper. The slope more will be the species richness, so let us again see, with the help of this slide, alexander Juan Humboldt, a German naturalist and geographer observed that within a region, species richness increased with increasing explored area, but only up to a limit. This is the figure which has been given in your NCR day. Book area is represented on the x axis species richness on the y axis, with reference to the log scale. If we plot a curve, we will get a rectangular hyperbola and the equation is s? Is equal to c as to the power z which, on applying log becomes log? S is equal to log c, plus z, log, a using this equation, the ecologist they can determine the slope or the species richness. By determining the slope, they can find out. The species richness of a particular area, the value of z, lies in between 0.1 to 0.2, except exceptionally large areas where it can be much steeper and have values of 0.6 to 1.2. So next, moving on to an especially important topic is importance of species diversity. We are talking so much about species. There are so many diverse types of species. We have realized that these species emerged on the earth by the process by a gradual process of evolution. But what is the importance of these species? Are they important for us? Does the number of a species in a community real ma really matter to the functioning of the ecosystem? Many ecologists believe that communities with more species tend to be more stable than those with less species. Although there is no precise answer to these questions like what is the importance of species, what will happen if few species are removed from ecosystem? Will it matter for the well-being of the ecosystem? Although these have not been answered, such name questions have not been answered precisely or accurately, but we can have a perspective on these many ecologists. They have believed - and there have been certain experiments to prove that more is the biodiversity of a region. More will be, the better will be the health of an ecosystem. So, what exactly is the stability for a biological community? We are talking about stability, that if there is more biodiversity, it will be more stable. What is referred by the stability of a community number one? It should not show too much variation in productivity from year to year for being stable. The first criteria are that it shows it should show a constant productivity from year to year again coming back to productivity, productivity is the rate of biomass production. At each level, there are two type of productivity, primary productivity which is related to the production of biomass in plants and secondary productivity is related to the next trophic level. Next, it must be either resistant or resilient to occasional disturbances. There may be occasional disturbances. These may be because of natural disturbances or manufactured disturbances, but the community should show resistance or resilience toward these occasional disturbances. Thirdly, it also must be resistant to invasion of alien species if certain alien or species from a different ecosystem are brought into a particular ecosystem. It should be able to compete with it and it should be able to flourish. So, these are the features of a stable community and ecologists believe that these three features are shown by a stable community, and these features are again enhanced. If there is a greater number of biodiversity, so we have studied about biodiversity, that there are three levels of biodiversity, genetic species, and ecological biodiversity. Obviously, if there is more biodiversity, it means that there are chances of a greater number of species and genetic diversity in it, which will finally contribute in making a community more stable, and this has also been proved by David Tillman’s experiment. David Tillman did long term ecosystem experiment using outdoor plants. Through some, these throw some light on how these attributes are linked to species richness in a community. He found that plots with more species showed less year-to-year variation in total biomass, so he did experiments and he observed that the year-to-year variation in the total biomass production was less in such communities, which had more species diversity. He also showed that in his experiments, increased diversity contributed to higher productivity. So, if there is a greater number of biomass production, it will lead to more productivity. So again, after understanding these experiments, let us again come back to the importance of biodiversity. Rich biodiversity is not only essential for the health of an ecosystem because it is contributing to its stability, but it is also imperative for the very survival of humans on this planet. We are also a part of the nature we humans are also a part of this ecosystem and if there is a disturbance or deterrence in the ecosystem, it will eventually come back to us. So, the biodiversity of the species, diversity is also imperative or important. We cannot do without it. The survival of humans is governed by these by the biodiversity. Now we have started understanding this earlier. We did not understand its importance, but now we have started understanding by looking at the impact of biodiversity loss on the nature and environment, biodiversity and its conservation has acquired international concern the world over and every year there are international conventions which occur to discuss how to conserve this biodiversity at a time when we are losing species at an alarming rate, one might ask: does it really matter to us if a few species become extinct again? This question keeps on coming to minds of some people that does it really matter to us. If a few species become extinct, would western guard ecosystem be less functional if one of its tree frog species is lost forever to understand this, we can refer to the rivet proper hypothesis. A revert, proper hypothesis will not directly answer this question, but it will again help in developing a perspective towards this question river pop a hypothesis was given by Paul Ellick a Stanford ecologist and he used an analogy to describe how species affect the stability of an ecosystem. He compared the ecosystem with an airplane and said that in an airplane all the parts of the airplane, the wings, the sea, the body, the engine they are joined together using thousands of rivets, which means the details which fixes them together. Similarly, in an ecosystem, the function of the ecosystem, which comprises of nutrient cycling, decomposition productivity, energy flow, these all are governed or maintained, with the help of the species, and removal of rivets might not affect flight safety initially, but as more and more rivets are removed, the Plane becomes dangerously weak over a period of time and the similar applies to our ecosystem also if the species are being removed initially, it might not show any it might not show any effect on the health of the ecosystem, but gradually, if more and more species are Disappearing, it will start showing its effect on the ecosystem. The ecosystem will become weak, its sustenance will come in danger again. One more thing is that which rivet is removed may also be critical. For example, if the rivet on wing is removed, it will hamper the flight safe, the flight safety to a larger extent as compared to the rivets of the seats or the window panes. Similarly, in an ecosystem, there are certain species which are known as keystone species. If they are removed from an ecosystem, they will cause a much deterrence or a much disadvantage to the health of an ecosystem, because many other species their survival is dependent on these keystone species. So, this is giving us a perspective on how ecosystem is being damaged by the removal or the loss of this species. Lesser number of species, which might not be especially important for that ecosystem may not cause initially any effect on it, but gradually, when a greater number of species are being lost from that ecosystem, it will start showing its impact. Similarly, in even in the initial stages, if a keystone species removed from an ecosystem, the effect might be much faster and much detrimental. So, a keystone species is a plant or animal that plays a unique and crucial role in the way an ecosystem functions. Survival of many other species depend on these keystone species, for example, corals in a coral reef system. In coral reef system corals are the main keystone species and they provide breeding habitats and shelter food to many other organisms which are living in this marine habitat. So, if these corals are removed, this ecosystem will end all together. Now, let us summarize what we have studied till now in this part, 1 of biodiversity and conservation chapter of class 12. Today we have learnt about the concept of biodiversity. Biodiversity refers to the variety variations variability of living organisms present on earth. Biodiversity is a compressed term which has been formed by adding or joining up two terms. Biological diversity - and this term was coined by Walter g Rosen. The contribution of Edward Wilson, who did a lot to aware people about the biodiversity and its importance, cannot be undermined. We have discussed about the levels of biodiversity. We have discussed that there are three important levels of biodiversity: genetic biodiversity, species, biodiversity, and ecological biodiversity, and all these three diversities are intertwined with each other. They are interlinked and interdependent and is forming the composite biodiversity of earth. Then we made a total estimated. Total estimate of this species identified and unidentified IUCN has recorded more than 1.5 million species of plants and animals. These are under the category of identified, but the unidentified species are much more in number and we follow Robert mays logical, precise, and scientific estimate of about seven to eight million total species on this earth. Then we have discussed about the global biodiversity in which we saw that a greater number of animals have been recorded as compared to the plants among animals. Also, insects are again more in number and among plants. We have seen that fungi and angiosperms they have been described and recorded. We still do not have any estimate about the prokaryotes, because ah they are not culturable and if we apply the biochemical or molecular techniques, their number will be in millions. Then we have investigated the Indian biodiversity that India is fortunate to have a rich biodiversity, and that is why it is among the 17 mega diverse countries of the world. We have also learnt about the pattern of biodiversity. We have seen the latitudinal gradient. We have also seen the species area relationship given by alexander van Humboldt, who gave a curve which shows that, with increasing area, there will be increase in species richness, but up to a certain extent. He has also given a mathematical equation by following that equation. We can find out the slope which will give us the measure of species richness. We have also learnt or tried to generate a perspective on importance of species diversity with the help of river proper hypothesis. Now let us evaluate what we have learnt till now number one question: how is the presently occurring species extinction different from the earlier mass extinction? Yes, you are right that the present species extinction is occurring at a fast rate as compared to the earlier and natural mass extinction. Today, the rate is one thousand to ten thousand times more as compared to the earlier mass extinction, and this is also known as the sixth extinction crisis, which is guided by anthropogenic activities. Why are conventional methods not suitable for the assessment of biodiversity of bacteria? These bacteria being very minute, they have certain characteristics which make them unsuitable to be cultured under laboratory conditions, so these cannot be studied, and if we apply the biochemical methods again, we will tend to calculate its number in millions. This has also given rise to a new branch of biology, which is known as meta genomics where the researchers are trying to find out about the genomes of bacteria. Is it true that more solar energy available in the tropics? Yes, it is true that more solar energy is available in the tropics, and this is evident when we see that, as we move away from the tropics, the length of the day decreases and the length of night or the duration of the night increases. This shows that more solar energy duration of solar exposure is more in the tropics as compared to the temperate and the polar regions. Next, how do scientists extrapolate the total number of species on earth? I told you earlier that the total number of species on earth cannot be estimated because it is a vast number and it is physically impossible for us to verify each species. So, the species which have been exhaustively studied like that of insects, their ratio in the temperate and tropical regions are determined, and then this is extrapolated to other groups. Other taxonomic groups. What do you understand by a keystone species? A keystone species is a species which is especially important for the functioning of an ecosystem, and the survival of other species depend on it on the keystone species with this I am giving you certain questions to reflect over number. One primary productivity varies from ecosystem to ecosystem. Explain find out what is a tree line? Can you give any one example, based on your day-to-day observation showing how loss of one species may lead to extinction of another, and do you think that more biodiversity enhances the chances of a community to remain stable or resilient under changing environmental situations? How, with these questions, I am leaving you for the next session so that we can continue with it and discuss these questions till then good, bye and have a nice day. Thank you.