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ECOLOGICAL PYRAMIDS

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            Graphic representation of trophic structure and function of an ecosystem, starting with producers at the base and successive trophic levels forming the apex is known as ecological pyramids .             Ecological pyramid may be of three types – pyramid of numbers , pyramid of biomass and pyramid of energy .             1. Pyramid of Numbers:- It represents the number of individual organisms at each trophic level. We may have upright or inverted pyramid of numbers depending upon the type of ecosystem and food chain.             As for example – Grassland and a pond ecosystem show an upright pyramid of numbers. The producers in grassland are grasses which are very large in numbers. So the producers form a broad base. The herbivores in the grassland are insects while tertiary carnivores are hawks and other birds which are gradually less and less in number and hence the apex of the pyramid becomes gradually narrower.             Pyramid of numbers may be inver
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FOOD CHAIN AND FOOD WEB

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                                                                             FOOD CHAIN             The transfer of food energy from the producers through a series of organisms (herbivores to carnivores and then to decomposers) with repeated eating and being eaten, is known as food chain.             The solar energy is trapped in the ecosystem by the green plants and produce energy rich carbohydrates. These green plants are known as primary producers. The green plants are eaten by plant eaters (herbivores) also called primary consumers. Herbivores are in turn eaten by meat eaters (carnivores) also called secondary consumers. Secondary consumers in turn may be still eaten by other carnivores which are known as tertiary consumers. After decay of both plants and animals simpler compounds are being released into the atmosphere due to the activity of decomposers which are re-utilized by green plants.             In nature, we generally distinguish two types of food chain – Gazing
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ECOSYSTEM - COMPONENTS OF AN ECOSYSTEM, BIOTIC AND ABIOTIC COMPONENTS

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            Ecosystem may be defined as a natural, functional, ecological unit comprising living organisms and their non living environment that interact to form stable, self supporting system.             COMPONENTS OF AN ECOSYSTEM             Components of an ecosystem can be classified into two major divisions – Biotic and Abiotic components.             1. Biotic Components:- All living organisms present in the environment are included within the biotic component. The biotic components can be sub divided into three major groups –             a) Producers – These includes all the autotrophic green plants which can make their own food with the help of sunlight. Besides these some organisms like Cyano-bacteria and some Chemo-systhetic bacteria can produce their own food, which are also included in producers.             b) Consumers – These includes all heterotrophic organisms which depend on plants and other organisms for food and nutrition. Based on the food they ea
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ENVIRONMENTAL STUDIES AS MULTIDISCIPLINARY SUBJECT

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            The science of environment studies is a multidisciplinary science because it depends on various disciplines like chemistry, physics, medical science, etc. It is the science of physical phenomena in the environment. It is inherently a multidisciplinary field that draws upon not only its core scientific areas, but also applies knowledge from other non-scientific studies such as economic, law and social science.             1. In the field of physical science it helps to understand the flux of material and energy interaction. It also helps to construct mathematical models of environment.             2. Environmental study is related with chemical science in the sense that it helps in understanding the molecular interactions in the system.             3. In the field of biological science it describes the effects within the plant and animal kingdom and their diversity.              4. In the field of atmospheric science , environmental studies deals with the exa
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ALTERNATION OF GENERATIONS IN PTERIDOPHYTES

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In the life cycle of Pteridophytes, two distinct individuals can be observed i.e., there is a typical heteromorphic alternation of sporophytic and gametophytic generations. These two generations alternate with each other in regular succession one after the other, i.e. from sporophyte to gametophyte and from gametophyte to sporophyte. The sporophytic or asexual generation is diploid (2n) , while the gametophytic or sexual generation is haploid (n) . The actual phenomenon responsible for bringing about alternation in generation is the “ Periodic Reduction of Chromosomes ” as a result of meiosis . Due to meiosis a reduction in the chromosome number takes place which leads to the formation of haploid individuals . The haploid individuals in turn by produce haploid gametes which proceed the process of fertilization to produce diploid individuals . 1. Gametophytic Generation:-  The haploid individual bears sex organs, antheridia and archegonia . Antheridia produce male gamete i.e
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HETEROSPORY AND SEED HABITAT IN PTERIDOPHYTES WITH RESPECT TO SELAGINELLA

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Heterospory is the condition that interprets the production of spores of two different sizes and two different development patterns. The two different sizes are smaller spores also known as microspores and the larger spores also known as megaspores . Hetrrospory can be observed in some of the pteridophytes such as Selaginella, Marsilea , etc. They have differential developmental patterns because the microspores germinate to produce male gametophytes or microgametophytes that bear male sex organs called antheridia , and the megaspores germinate to produce female gametophytes or megagametophytes that bear female sex organs called archegonia. The two kinds of spores are produced in two kinds of sporangia. The microspores are produced in microsporangia and the megaspores in megasporangia . The microspores are produced in large numbers and are comparatively smaller than megasporengia which are produced in lesser numbers and larger in size. Importance of Heterospory (a) Th
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MARSILEA - CLASSIFICATION, STRUCTURE OF SPOROPHYTE, REPRODUCTION, STRUCTURE OF GAMETOPHYTE AND FERTILIZATION

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A. CLASSIFICATION: Division – Pterophyta     Class – Leptosporangiopsida (Pteropsida)         Order – Marsileales             Family – Marsileaceae                 Genus – Marsilea The genus Marsilea comprises about 58 living species. The genus is worldwide in distribution and is very common in warmer parts of the world. The species of Marsilea are aquatic or amphibious plants – they grow either completely sub-merged in water, or partly or wholly out of water with their roots embedded in the muddy soil. In India, only 9 living species are found to occur. The common Indian species are – M. quadrifolia , M. aegyptica , M. coromandelica , M. brachypus , M. condenseta , etc. B. STRUCTURE OF THE SPOROPHYTE: 1. External structure:- The sporophyte, i.e., the plant body is well differentiated into – stem, leaves and roots. Stem – Stem consists of an elongated stolon-like rhizome with distinct nodes and internodes. Rhizome grows either on the surface of the soil or s
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