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& myCBSEguide.com, , A Complete guide for CBSE students, , CBSE Class 12 Biology, Revision Notes, CHAPTER-13, ORGANISMS AND POPULATIONS, , Ecology is the branch of biology that deals with the interactions among organisms and, between the organism and its physical (abiotic) environment . Study of ecology is important, to strike a balance between development and maintenance of natural environmental and, biotic communities, use and conservation of resources, solve local , regional and global, environmental problems., , e Itis basically concerned with four levels of biological organisation — organisms,, populations, communities and biomes., , e Ecological hierarchy or ecological level of organization connected with ecological, grouping of organisms., , Individual (Organism), , Population, , Biotic community, , Ecosystem, , Landscape, , Biosphere, , e Organism and its Environment, , e The sum total of all biotic and abiotic factors, substances and conditions that, surround and potentially influence organisms without becoming their constituent, part is called environment., , At organism level, physiological ecology tries to understand how different organisms, are adapted to their environment in terms of survival and reproduction. The, variation in the intensity and duration of temperature along with annual variations in, precipitation results in formation of major biomes like desert, rain forest and tundra., , Material downloaded from myCBSEguide.com. 1/10
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& myCBSEguide.com, A Complete guide for CBSE students, , , , , , ‘e300 ae 300 400 ane, , , , , , ican anenal precipitating im), , , , e Regional and local variations within each biome lead to the formation of different, kinds of habitats like tropical rain forest, deciduous forest, desert, sea coast etc., , e The habitat includes biotic components like pathogens, parasites, predators and, competitors of the organism with which they interact constantly., , Major Abiotic Factors, , a) Temperature- is the most important ecological factor to determine the bio-mass of a, place. Average temperature on land varies seasonally and decreases progressively, from the equator towards the poles and from plains to mountain tops. Temperature, affects the kinetics of enzymes and basal metabolism along with physiological, functions of the organisms., , e The organisms that can tolerate wide range of temperature are called, eurythermal ,for example cat , dogs , tigers etc., , e The organism which have the ability to tolerate only a narrow range of, temperature are called stenothermal ,for example Penguin, fishes,crocodile.etc., , b) Water- life on earth is unsustainable without water. Productivity and distribution, of plants is heavily dependent on water. For aquatic organisms the quality (chemical, composition, pH) of water becomes important. The salt concentration (measured as, salinity in parts per thousand), is less than 5 in inland waters, 30-35 in the sea and >, 100 in some hypersaline lagoons, , e The organisms that can tolerate wide range of salinities are called euryhaline ,for, example salmon , hierring etc., , e The organism which have the ability to tolerate only a narrow range of salinities are, called stenohaline, for example goldfish ( freshwater ) and haddock ( marine, , Material downloaded from myCBSEguide.com. 2/10
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Internal level —>, , , , , , myCBSEguide.com, A Complete guide for CBSE students, , water )etc., , c) Light- plants produce food through photosynthesis in presence of sunlight. Some, plants are adapted to low light conditions because they are overshadowed by tall, canopied trees. Flowering in some plants occurs only in presence of critical day light, called Photoperiodism. The availability of light and land is closely linked that of, temperature as the sun is the source of both. UV component of sunlight is harmful to, plants and animals., , d) Soil- Types of soil depends upon climate, weathering process, whether soil is, transported or sedimentary and how soil development occurred. Soil composition,, grain size and aggregation determine the percolation and water holding capacity of, the soils along with pH, mineral, composition and topography determine the, vegetation in any area., , Responses to Abiotic Factor : In the course of evolution, many species have evolved, constant internal environment to permits all biochemical reactions and physiological, functions to work with maximum efficiency to have over all fitness of species., Organisms try to maintain the constancy of its internal environment, (homeostasis)inspite of varying external environment. There are various ways to, establish hemostasis, External level, , Regulate- all birds and animals are capable of maintaining homeostasis by, physiological means which ensures constant body temperature, constant osmotic, concentration etc. Thermoregulation and osmoregulation is the source of success of, mammals in all the environmental conditions. In summer, when outside temperature, is more than our body temperature, we sweat oftenly, resulting evaporative cooling,, , Material downloaded from myCBSEguide.com. 3/10
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myCBSEguide.com, A Complete guide for CBSE students, , which brings down the body temperature. In winter we start to shiver, a kind of, exercise which produces heat and raises the body temperature., , Conform- most of animals and plants, their body temperature change with ambient, temperature. In aquatic animals osmotic concentration of the body fluid change with, that of the ambient water osmotic concentration. These animals are called conformer., Conformer are not able to bear the energetic expenses to maintain the constant body, temperature., , Heat loss or heat gain is a function of surface area. Since small animals have a larger, surface area relative to their volume, they tend to lose body heat very fast when it is, cold outside; then they have to expend much energy to generate body heat through, metabolism. This is the main reason why very small animals are rarely found in polar, regions., , Migrate- the organism move away for time being from the stressful unfavorable, habitat to more suitable habitat and return back when stressful period is over. Many, birds undertake long-distance to migrate to more hospitable areas. Siberia birds, migrate to Keolado National park, Bharatpur, India., , Suspend- in microorganisms like bacteria, fungi and lower plants a thick walled, spores is formed which help them to survive unfavorable conditions. These spores, germinate on return of suitable conditions. In higher plants, seeds and some other, vegetative reproductive structures serves the means to tide over periods of stress and, help them in dispersal also. The metabolic activities are reduced to minimum during, this dormant period., , a)Hibernation - the condition or period of an animal or plant spending the winter in a, dormant state e.g bear, , b)Aestivation - the condition or period of an animal or plant spending the summer to, avoid heat and dessication in a dormant state e.g snails ., , c)Diapause - a stage of suspended development in zooplankton species in lakes and, ponds., , Adaptation is the attribute of organism morphological, physiological and behavioral changes, that enables the organism to survive and reproduce in its habitat., , Material downloaded from myCBSEguide.com. 4/10
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myCBSEguide.com, A Complete guide for CBSE students, , Kangaroo rat in North American deserts fulfill the water requirement by internal, oxidation of fat in absence of water.It also has the ability to concentrate its urine so, that minimal volume of water is used to remove excretory products., , Thick cuticle in many plants also prevents loss of water. CAM plants open their, stomata during night to reduce the loss of water during photosynthesis., , Mammals from colder climates have shorter ears and limbs to minimize heat loss., This is called Allen’s Rule., , In polar seas aquatic mammals like seals have a thick layer of fat called blubber,, , below their skin that acts as an insulator and reduces loss of body heat., , Altitude sickness is observed at higher altitude that includes symptoms like nausea,, fatigue, heart palpitations due to less oxygen and atmospheric pressure. The person, gradually get acclimatized and stop experiencing altitude sickness. This is type of, physiological adaptation., , A number of marine invertebrate and fish live in temperature always less than zero, and some lives in greatdepth in ocean where pressure is very high by array of, biochemical adaptations., , Some organisms like desert lizard lack the physiological ability that mammals have, but deal with high temperature of their habitat by behavioral means. They bask in the, sun and absorb heat and when their body temperature drops below the comfort zone,, but moves in shade when the ambient temperature starts increasing., , Populations : Individuals of any species live in groups in well-defined geographical area,, , share or compete for similar resources, potentially interbreed and constitute a population., , Population Attributes : A population has certain attributes that an individual organism, does not such as an individual may have births and deaths, but a population has birth rates, , and death rates., , The birth and death rates are referred as per capita births or deaths respectively,, which is increase and decrease with respect to members of the population., , Sex ratio is another attributes of population. An individual may be male or female but, population has sex ratio., , A population at given time composed of different individual of different ages. If the, , Material downloaded from myCBSEguide.com. 5/10
