Free Biology NEET Video Lectures for Organisms And Population

00:00:31 [Music] [Applause] Hello students, welcome to the IIT PAL series of biology. I am Rkisha Bhik PGT Biology at Kindra Vidal Sector 2 AKU. 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

00:01:22 thing about life on earth. In our life, whenever we go anywhere on roadside or in a garden, we see so many different 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

00:02:02 and conservation class 12th. So this is the part one session one of biodiversity and conservation. Uh 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? Uh these questions if you recall we did the uh sessions on evolution and we have discussed these questions there. There are so many species. If you recall that evolution or the process of speciation and natural selection gives

00:02:46 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 long process which took millions of years. How and why is this diversity important to the biosphere? Would it function any differently if the diversity was much less? These last two questions we will deliberate upon these sessions on biodiversity and conservation. So you will get a rough idea or a precise idea from general to specific

00:03:29 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 ourself how this biodiversity is important for us how will it benefit us so we'll also look into these aspect of how humans can benefit from the diversity of life as I have told you that biodiversity biodiversity refers to the variety or variations. Variety

00:04:18 [Music] variations. Variability. 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 actually these two terms biological and diversity they got compressed to form this one term biodiversity and all this happened in

00:05:14 1980s. This term biodiversity was coined by Walter G. Rosen but it was popularized by a famous sociobiologist named Edward Wilson. Let us have a brief summary of what I told you. Biod diversity is the variety and variability of different 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 sociologist Edward Wilson in 1980s. So the term biodiversity or this subject has gained importance lately in

00:05:56 1980s. Can you guess why is it so? You are correct. This is because the uh the the impact of uh 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. Uh now the next thing which amazes us that we have discovered and described many species. Anyone would be aruck to notice that there are more than 20,000 species of ants, more than three lakh species of beetles, more than 28,000 species of fishes, more than 20,000 species of

00:06:44 orchids, more than 2 lak 81,621 species of vascular plants and more than 9,990 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% 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 and more about these species. Next coming to the levels of biodiversity. Biod diversity is actually

00:07:29 a composite term. Biod diversity is actually a composite term and includes in its domain major three types of diversity. This biod diversity is actually ranges from uh the molecular level to the biome level. But the three major levels of dio biod diversity can be identified as number one genetic diversity, number two species diversity and number three is ecological diversity. So biod diversity is a composite or it comprises of all these three types of diversity. All these three types of diversity genetic species

00:08:27 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. Genetic diversity as the name suggest 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.

00:09:18 DNA is the heridity substance. Uh it the full form of DNA is deoxy ribboucleic acid. And what is actually DNA? DNA is again made up of polyucleotide chains. Polyucleotide chains. And the double helical model of DNA which we draw is like this. These two strands are the polyucleotide strands. These polyucleotide again are comprised of the nitrogenous bases. These bases are complimentary to each other. There is complimentary base pairing uh between the two polyucleotide strands. In DNA we know that there are two there are four

00:10:07 types of nitrogenous bases. adinine, 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 basically. 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 particular

00:10:52 population to flourish. In other words, it can be said that if a population of a species comprises of different types of genes, they will be in a better position to cope up with the changing environmental situations. So, genetic diversity is a very important level which is helping in maintaining the ecological diversity and the species diversity. Uh for examples if we take the example of a medicinal plant Rulfia vomittoriia uh many different varieties of this particular medicinal plant can be seen

00:11:35 in the Himalayas. But the difference in these varieties is based on the potency and concentration of its active chemical or alkyoid named resuppine. uh the level and the concentration the toxic the toxicity or potency of this compound varies in different types of roalia vomitoriia. Similarly, if we take some common example like that of rice and mangoes, we find that there are so many different types of rice available in the market. Whenever there is the season of mangoes, we find that there are so many different type of mangoes on

00:12:12 the basis of its shape, size and uh the content or the quality of the food or the taste of mango. They have been named differently because they represent different varieties. So basically this is what is genetic diversity. Genetic diversity is seen within a species. when the when there are different 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

00:12:52 what do we mean by a species? 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 actually we are conoting towards the diversity of species level within a particular region. Now if we talk about animals we know that animals can be divided into

00:13:38 invertebrates and vertebbrates. Again these vertebbrates can have further five subgroups. These are pisces, amphibia, reptilia, aes and mammals. So by species diversity I mean to say that within each subgroup there are so many different type of species. If we uh take for example Pisces, there are so many different types of fishes. Among amphibians, there are so many different species of amphibia. Likewise, in reptiles, aes and mammals, we know of so many different type of species representing that particular group. So

00:14:31 what is basically species diversity? Now for example if I take amphibia and compare two regions like western guard and eastern garts of India we see that there are more number of species of amphibia in western guard 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. Uh we are moving from uh lower towards the broader type

00:15:16 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 more

00:15:51 number of biomes in India. We can see deserts, forest, hills, mangroves, coral reefs, wetlands, eststeries 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 actually estimate the total number of species on earth? No. It is disappointing to realize that we haven't been able to discover and describe about 80% of the species on earth. But the all these species which we have described

00:16:33 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 number of species are there on earth are actually only educated guesses and these educated guesses vary widely from 3 million to 100 million. So in

00:17:22 this scenario uh we follow a more logical a precise and scientific estimate given by a scientist Robert May. According to his estimate there are approximately 7 to 8 million of total species on earth. The next thing which interest us is that tropics are more biodiverse than temperate areas. uh when we reveal the species inventory we saw that tropics show more biod diversity as compared to the temporate areas. The species inventories therefore are more complete in the temperate as compared to the tropical countries.

00:18:04 Because of the large number of biod diversity present in the tropics, it has not been possible to uh complete the inventory of the tropical areas. But more so we have a complete inventory of the temperate areas. uh and the most exhaustively uh studied texonomic group is that of insects. And keeping the that as a standard, biologists make a statistical comparison of the temporary tropical species richness of insects and extrapolate or extend this estimate to other groups of animals to come up with a gross estimate

00:18:44 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% of the recorded species are that of animals and only 22% of the plants and these plant

00:19:27 includes fungi, algae, talopyes, bryophites, terodopites, gymnosperms, angioperms every uh group is included in this. So only 22% of the plants have been recorded till now and 70% of the species Among animals also insects are the most species rich and it is about 70% of the total. So it can be said that of 10 animals if seven are insect. Out of 10 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 more number

00:20:09 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 uh total number of invertebrates which have been described and recorded. We have been successful in describing more number of insects. 70% of this uh uh graph shows insects followed by other animal groups molllesk and crustaceians. Similarly among vertebbrates, fishes have been uh recorded more followed by birds, reptiles, amphibians and mammals. Among plants, fungi and angioperms are the

00:20:48 most recorded species followed by algae, mosses, lychans, ferns and allies. So this was about plants and animals. But what about the proariots? So what about proariots? Uh proariots. Uh what about the estimate of proariots? Uh surprisingly we still do not have estimates for procariots. And why is it so? The reasons being number one conventional taxonomic methods are not suitable for identifying microbial species. By conventional texonomic methods again we mean doing field studies going and exploring the

00:21:36 different types of organisms and recording them which is not possible in case of microbial species because they are very minute 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 metagenomics. Thirdly, uh if we apply the biochemical or molecular criteria, it will give their estimates in millions

00:22:13 because it will show so many variations, genetic variations and they have the ability to mutate at a faster rate. So it is very difficult to give a proper estimate for proariotss. Next moving on from global biod diversity let us look into the biodiversity of India. Fortunately India is among the 17 mega diverse countries of the world with only 2.4% of the world's land area. It shares 8.1% of the global species diversity which is indeed impressive. So there are about 45,000 species of plants and 90,000 species of

00:23:01 animals in India which has been recorded and described. But if we go by maze estimate this diversity may go up to one lakh species of plants and three lakh species of animals. In this map of India, you can see uh the Himalayas losing green cover. So uh it is very important for us to preserve this biod diversity. Our country is rich in biod diversity. More biod diversity means more amount of resources available for us. And if we are losing it, we are losing a vast amount of resources. Next, I would like to uh

00:23:50 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 and helping in fertilization

00:24:29 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 1,000 times higher than the natural extinction rates. It is

00:25:13 not so that the extinction has not been there. It is a natural process. There has been many uh episodes of extinction. There has actually been five extinction episode 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 actually an accumulation of a very long process which took millions of years and losing it just in two centuries will be very

00:25:55 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 look into certain facts that we need a lot of time to actually complete the inventory. Apart from time we need skilled manpower in form of taxonomist who can do this thing

00:26:36 properly. But given other fact that we are losing this species at an extremely high rate. This becomes quite hopeless. We can be disappointed or hopeless to realize that it is very difficult actually 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 stocked 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

00:27:14 and explore about all the organism without being acknowledged these species are getting extinct and this is the major grave concern for all of us. Now moving on to the patterns of biod diversity. Is there any pattern of biod diversity or is it random? No, it is not random. There is a pattern of biod diversity. If you look on the earth uh 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

00:27:55 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 more 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, Colombia, which is located near the equator, has about 1,400 species of birds. If you move a little uh away from the equator in New York, which is at 41° north, has 105 species. And if you move further above towards Greenland, which is at 71° north, it has

00:28:36 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 biod diversity. Uh some areas are extremely rich in biod diversity. The most biodiverse region of our earth is the Amazon forest located near the tropics in South America. The Amazonian rainforest are called the lungs of earth because of the huge biod diversity and

00:29:16 plants at harbor. It is home to more than 40,000 species of plants, 3,000 species of fishes, 1,300 of birds, 427 of mammals, 427 of amphibians, 378 of reptiles, and of more than one lakh 25,000 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

00:30:05 regions. What is the reason behind this? Number one, temperate regions were subject to frequent glaciation whereas tropics have remained relatively 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.

00:30:44 So the process of speciation initiated earlier as compared to the temperate regions in the tropical regions and that is why we see that more number of biodiversity or more number of species has accumulated in the tropics. Secondly the tropical environments are less seasonal. They are relatively more constant and predictable. Since there are 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

00:31:23 here is niche specialization. What do you mean by niche specialization? Niche specialization or ecological niche is actually 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 specialization means if an organism has been provided with ample resources and conditions to uh acquire it in the form of a habitat as well as it has a certain role and function to perform in that

00:32:29 particular 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

00:33:09 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 tropic 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 the the tropics are less seasonal.

00:33:46 They show less fluctuation in season. They are more constant and predictable and that is why they allowed niche specialization and therefore there is more 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 uh 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

00:34:39 naturalist and geographer Alexander one humbled 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 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

00:35:55 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 a 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

00:36:57 they have found that the value of zed is 0.1 to 0.2 irrespective of the taxonomic groups irrespective of the region but for a very large area like a big continent it has been found to be 0.6 to 1.2. So what is zed? Zed is the slope and the steepness of the slope represents the species richness. more steeper the slope more will be the species richness. So let us again see uh with the help of this slide. Alexander Juan Humboldt a German naturalist and geographer observed that within a region species richness increased with

00:37:41 increasing explored area but only up to a limit. This is the figure which has been given in your NCERT book. Area is represented on the x-axis, species richness on the y-axis. With reference to the log log scale, if we plot a curve, we will get a rectangular hyperola. And the equation is S is equal to C. A to the power Z, which on applying log becomes log S is equal to log C + 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

00:38:22 richness of a particular area. The value of zed generally lies um in between 0.1 to 0.2 except very large areas where it can be much steeper and have values of 0.6 to 1.2. So next moving on to a very important topic is importance of species diversity. We are talking so much about species. There are so many different 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 really important for

00:39:04 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 generally 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

00:39:41 precisely or accurately, but we can have a perspective on this. 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 uh more good 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 uh is referred by the stability of a community. Number one, it should not show too much variation in productivity

00:40:18 from year to year. For being stable, the first criteria is that it show 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 the animals. Next it must be either resistant or resilient to occasional disturbances. There may be occasional

00:40:54 disturbances. These may be because of natural disturbances or man-made 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 in a position to flourish. So these are the features of a stable community and ecologists believe that these three

00:41:29 features are shown by a stable community and these features are again enhanced if there is more 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 more 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 Tilman's experiment. David Tilman did long-term

00:42:06 ecosystem experiment using outdoor plants uh through some uh uh 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 actually 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

00:42:45 if there is more number of biomass production it will lead to more productivity. So again after uh understanding these experiments let us again come back to the importance of biod diversity. A rich biod diversity 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 the human race 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

00:43:27 the ecosystem, it will eventually come back to us. So the biod diversity or the species diversity is also imperative or important. We cannot do without it. The survival of the human race is governed by these by the biodiversity. Now we have started understanding this earlier. We didn't 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

00:44:06 every year there are international conventions which occur in order 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 uh can refer to

00:44:47 the rivet po proper hypothesis. Rivet po proper hypothesis will not directly answer this question but it will again help in developing a perspective towards this question. River popppe hypothesis was given by Paul Erile a Stanford ecologist and he used an analogy to describe how species affect the stability of an ecosystem. He compared the ecosystem with an aeroplane and said that in an aeroplane all the parts of the aeroplane the wings the seat the body the engine they are joined together using thousands

00:45:27 of rivets. rivet means the nuts and bolts 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

00:46:09 not show any uh it might not show any uh 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 rem rivet is removed may also be critical. For example, if the rivet on wing is removed, it will hamper the flight safe uh the flight safety to a larger extent as compared to the rivets of the seats or the window panes.

00:46:48 Similarly, in an ecosystem, there are certain species which are known as keystone species. If they are removed from an ecosystem, they will uh cause a much detrange 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 very important for that ecosystem may not cause initially any effect on it but gradually when more

00:47:34 and more 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 is 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 a coral reef system, corals are the main keystone species and

00:48:19 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 come to an end altogether. Now let us summarize what we have studied till now in this part one of biodiversity and conservation chapter of class 12. Today we have learned about the concept of biod diversity. Biodiversity refers to the variety, variations, variability of living organisms present on earth. Biod diversity is actually a

00:49:03 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 biod diversity, species biodiversity and ecological biodiversity. And all these three diversities are intertwined with

00:49:44 each other. They are interlin and interdependent and is forming the composite biodiversity of earth. Then we made a total estimated uh a 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 May's logical precise and scientific estimate of about 7 to 8 million total species on this earth. Then we have discussed about the

00:50:28 global biod diversity in which we saw that more 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 angioperms they have been properly described and recorded. We still do not have any estimate about the proariots because uh they are not culturable and if we apply the biochemical or molecular techniques their number will be in millions. Then we have looked into the Indian biodiversity that India is fortunate to

00:51:06 have a rich biodiversity and that is why it is among the 17 mega diverse countries of the world. We have also learned about the pattern of biod diversity. 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

00:51:41 will give us the measure of species richness. We have also learned or tried to generate a perspective on importance of species diversity with the help of river popper hypothesis. Now let's evaluate what we have learned 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 very fast rate as compared to the earlier and natural mass extinction. Today the rate is 1,000 to 10,000 times

00:52:23 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

00:53:04 of biology which is known as metagenomics where the researchers are trying to find out about the genomes of bacteria. Next, is it true that more solar energy available in the tropics? Yes, definitely 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

00:53:44 the temperate and the polar regions. Next, how do scientists extrapolate the total number of species on earth? uh I told you earlier that the total number of species on earth cannot be estimated because it is a huge number and it is physically impossible for us to verify each and every 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 uh groups other taxonomic groups. What do you understand by a

00:54:24 keystone species? A keystone species is a species which is very 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

00:54:58 biodiversity enhances the chances of a community to remain stable or resilient under changing environmental situations? How? With these questions, I'm leaving you for the next session so that we can continue with it and discuss these questions. Till then, goodbye and have a nice day. Thank you. [Music]