Page 1 : CHAPTER 13, , , , , , 12083CH13, , , , ORGANISMS AND POPULATIONS, , 13.1 Organismand Its, Environment, , 13.2 Populations, , , , Our living¢world isfascinatingly diverse and amazingly, complex.” We,Gan try to understand its complexity by, investigating processes at various levels of biological, organisation—macromolecules, cells, tissues, organs,, individual organisms, population, communities,, ecosystems and biomes. At any level of biological, organisation we can ask two types of questions - for, example, when we hear the bulbul singing early morning, in the garden, we may ask — ‘How does the bird sing?’, Or, ‘Why does the bird sing ?’ The ‘how-type’ questions, seek the mechanism behind the process while the ‘whytype’ questions seek the significance of the process. For, the first question in our example, the answer might be in, terms of the operation of the voice box and the vibrating, bone in the bird, whereas for the second question the, answer may lie in the bird’s need to communicate with its, mate during breeding season. When you observe nature, around you with a scientific frame of mind you will, certainly come up with many interesting questions of both, types - Why are night-blooming flowers generally white?, How does the bee know which flower has nectar? Why, does cactus have so many thorns? How does the chick, spures recognise her own mother?, and so on., , 2020-21

Page 2 : Ww, , 4, , BIOLOGY, , You have already learnt in previous classes that Ecology is a subject, which studies the interactions among organisms and between the, , organism and its physical (abiotic) environment., , Ecology is basically concerned with four levels of biological, organisation — organisms, populations, communities and biomes. In this, , chapter we explore ecology at organismic and population levels., , 13.1 OrGanism anp Its ENVIRONMENT, , Ecology at the organismic level is essentially physiological ecology which, tries to understand how different organisms are adapted to their, environments in terms of not only survival but also reproduction. You, may have learnt in earlier classes how the rotation of our planet around, the Sun and the tilt of its axis cause annual variations in the intensity, , and duration of temperature, resulting in distinct seasons., , These, , variations together with annual variation in precipitation (remember, precipitation includes both rain and snow) account for the formation of, major biomes such as desert, rain forest and tundra (Figure 13.1)., , , , , , , , , , , , , , , , , , 30, , 254, oS, xc 20 Tropical forest, o, £, E 154 Temperate forest, £, o, a 107, 5, 2 54, 7 Coniferous forest, 3 4, & oO, a, g 87, g, S -~104 Arctic and Alpine tundra, , 15 T T 7 7 7 + T T, 50 100 150 200 250 300 350 400 450, Mean annual precipitation (cm), , , , Figure, , 13.1 Biome distribution with respect to annual temperature and precipitation, , Regional and local variations within each biome lead to the formation of a, wide variety of habitats. Major biomes of India are shown in Figure 13.2., On planet Earth, life exists not just in a few favourable habitats but even, in extreme and harsh habitats — scorching Rajasthan desert, rain-soaked, Meghalaya forests, deep ocean trenches, torrential streams, permafrost, (snow laden) polar regions, high mountain tops, thermal springs, and, stinking compost pits, to name a few. Even our intestine is a unique, , habitat for hundreds of species of microbes., , 2020-21

Page 3 : ORGANISMS AND POPULATIONS, , , , @, , Figure 13.2 Major biomes of India : (a) Tropical ram forest? ‘(b) Deciduous forest;, (c) Desert; (d) Sea coast ( Y, , What are the key elements that lead to somuch variation in the, physical and chemical conditions of-.different habitats? The most, important ones are temperature, water, light‘and soil. We must remember, that the physico-chemical (abiotic) components alone do not characterise, the habitat of an organism completely; the habitat includes biotic, components also — pathogens, parasites, predators and competitors — of, the organism with which they interact constantly. We assume that over a, period of time, the organism had through natural selection, evolved, adaptations to optimise its survival and reproduction in its habitat., , Each organism has an invariably defined range of conditions that it, can tolerate, diversity in the resources it utilises and a distinct functional, role in the ecological system, all these together comprise its niche., , arse Se es, , Temperature: Temperature is the most important ecologically relevant, environmental factor. You are aware that the average temperature on, land varies seasonally, decreases progressively from the equator towards, the poles and from plains to the mountain tops. It ranges from subzero Sees, levels in polar areas and high altitudes to >50°C in tropical deserts in, summer. There are, however, unique habitats such as thermal springs, , and deep-sea hydrothermal vents where average temperatures exceed, 100°C. Itis general knowledge that mango trees do not and cannot grow, , 2020-21