Ecosystem: Structure and Functions: British ecologist Arthur Tansley first defined the term Ecosystem. ECOSYSTEM :- The functional unit of nature, where living organisms interact among themselves and with the surrounding physical environment. Types of Ecosystems: - New Species Discovered in Different Ecosystems: Pinocchio: long nosed frog found in Indonesia Bald headed parrot in Amazon Yeti Crab (Kiwa hirsuta) near Easter islands. Structure of Ecosystems An Ecosystem has two components: Biotic components and Abiotic components Stratification: This is the Vertical Distribution of Different Species occupying Different Levels. The levels are called STRATA. Major Structure and Functions of an Ecosystem includes the following: 1. Energy flow and productivity 2. Nutrient cycling ( Biogeochemical cycles) 3. Ecological succession or ecosystem development 1. (A) ENERGY FLOW : The flow of energy from the producer to the top consumers is called as energy flow It is Unidirectional Sun -> Producers -> Consumers ► SUN- Main Source of energy ► 50% of incident light is PHOTOSYNTHETICALLY ACTIVE RADIATION (PAR) ► 2- 10 % of PAR is captured by plants. ► Only a small fraction of this (stored as organic compounds) is transferred to consumers; the rest is used up in respiration and other life-supporting activities of the plants. ► As energy is transferred as food, most part is lost as heat at each stage (10% LAW) TROPIC LEVEL INTERACTION : Trophic Levels (Trophe=Nourishment) I II III IV V Autotrophs Heterotrophs Heterotrophs Heterotrophs Heterotrophs Green Plants((Producers) Herbivore(Primary Consumers) Carnivores(Secondary Consumers) Carnivore(Teritary Consumers) Top Carnivores(Quarternary consumers) TROPIC LEVEL INTERACTION : 1.Food Chain 2.Food Web 3.Ecological Pyramids 1. FOOD CHAINS Transfer of energy / food from the producer through a series of organisms is known as FOOD CHAINS. Food chains represent energy flow through ecosystems. Different steps in a food chain are trophic levels Basic terms: Producers, Herbivores, Carnivores, Omnivores. A.GRAZING FOOD CHAIN (GFC) Primary source of energy - Solar radiations. First trophic level includes - All Herbivores. GFCs are Long-sized chains B.DETRITUS FOOD CHAIN (DFC) Primary source of energy is Detritus. First trophic level includes Detritivores. Detritus Food Chains are small-sized chains. SAPROPHYTES: These include decomposers (fungi, bacteria) which feed on detritus. 2.FOOD WEBS The Natural Interconnection of Several food chains forms a FOOD WEB. Provides alternate pathways for food availability. Unlike food chains, food webs are never straight. Help in ecosystem development and stability. TEN PERCENT LAW: Ø By Lindemann in 1942 Ø States that : during transfer of energy from one trophic level to another, only about 10% is stored at higher levels; remaining 90% is lost in respiration (heat) 1. (B) PRODUCTIVITY The rate of synthesis of organic matter (biomass) during a given period of time. It is measured as weight (g-2) or as energy (kcal m-2). It is used to compare productivity of different ecosystems. (i) Primary Productivity: It is the amount of biomass produced per unit area in a given time period by Plants during Photosynthesis. GPP – R = NPP *GPP-Gross Primary Productivity *NPP-Net Primary Productivity (ii )Secondary productivity It is the amount of biomass produced at any of the Consumer levels in a given period of time. (iii) DECOMPOSITION It is the process of breaking down of dead organic matter into smaller organic molecules and inorganic molecules by decomposers (bacteria, fungi) DETRITUS: Dead remains of plants and animals is called detritus. DETRITIVORES: Animals that feed on decaying organic matter (detritus). Examples: earthworms, termites, snails etc Mechanism of Decomposition: Fragmentation of Detritus: Detritivores feed on detritus ---breakdown --- increases the surface area of detritus particles for microbial action. Leaching: Soluble inorganic nutrients dissolve in water -– percolate through the soil --removed due to leaching action. Catabolism: Decomposers (bacteria, fungi) release enzymes --- decompose detritus --simpler inorganic compounds. Humification: Simplified detritus--- converted to HUMUS Humus is a Dark, Amorphous substance. Highly resistant to Microbial Action Undergoes Decomposition very Slowly. Reservoir of nutrients (due to colloidal nature) Mineralisation: Humus is degraded – releases inorganic substances ( CO2, H2O etc) and nutrients (Ca2+, Mg2+,K+ etc) Factors affecting rate of Decomposition: Chemical composition - decomposition rate will be slow when detritus is rich in lignin and chitin and rate increases when detritus is rich in nitrogen and water soluble substances like sugars. Climatic conditions – warm and moist environment favour decomposition and low temperature and anaerobiosis inhibit decomposition. 2. ECOLOGICAL PYRAMIDS Developed by Charles Elton in 1927. Pyramids are an expression of the relationship between organisms at different trophic levels in terms of their number, biomass or energy. Three types of pyramids: 1. Pyramid of Number 2. Pyramid of Biomass 3. Pyramid of energy Pyramid of Number: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of number called pyramid of number. Pyramid of Biomass: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of biomass called pyramid of biomass. It can be of two types: a) Upright (in case of grassland ecosystem) b) Inverted (in case of pond ecosystem) 3. Pyramid of energy: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of flow of energy called pyramid of energy. It is always upright. Limitations of Ecological Pyramids: It does NOT consider the same species belonging to two or more trophic levels. It is based on simple food chains, which hardly exist. Ecosystem Services Humankind benefits from a multitude of resources and processes that are supplied by natural ecosystems. Collectively, these benefits are known as ecosystem services. Some of the Factors of Ecosystem services include : Purify air and water Decomposition of waste materials Cycle nutrients Pollinate crops Maintain biodiversity Researchers have put an average price tag of US $33 trillion a year on these fundamental ecosystems services, which is largely taken for granted because they are free. QUESTIONS: 1. Multiple Choice Questions: a. Ecology deals with the study of ? (i) Living beings (ii) Living and non living components (iii) Reciprocal relationship between the living and non living components (iv) Environment b.Definition of ecosystem is? (i) The community of organisms together with the environment in which they live (ii) The abiotic component of a habitat (iii) The part of the earth and its atmosphere which inhibits living organisms (iv) A community of organisms interacting with one another c. In a food chain of grassland ecosystem the top consumers are? (i)Herbivores. (ii)Carnivores. (iii)Bacteria. (iii)Either carnivores or herbivores. d.Biotic potential is counteracted by ? (i) Competition with the other organisms (ii) Producer is the largest (iii) Limitation of food supply (iv) None of the above e.The source of energy in an ecosystem is (i) ATP (ii) Sunlight (iii) D.N.A (iv) R.N.A 2. Very short answer type questions: (A)List out the different types of ecosystems with the examples. (B) How organisms like Pseudomonas and thiobacillus are of great significance in the nitrogen cycle ? (C)Name the most crucial enzyme found in the root nodules for N2 Fixation ? Does it require a special pink coloured pigment for its functioning? Elaborate. (D) Carnivorous plants exhibit nutritional adaptation.Criting an example explain this fact. (E) A farmer adds/Supplies Na, Ca, Mg and Fe regularly to his field and yet he observes that the plants show deficiency of ca, mg, and fe . Give me a valid reason and suggest the way to help the farmer improve the growth of plants. 3. Short answer Type Questions: a. Write a short note on components of the ecosystem? b. Define ecological pyramids and describe with possible examples ,pyramids of number and biomass? c. Write a short note on Grazing food chain? d. Write a short note on Detritus Food Chain? e. Write a short note on Decomposition with suitable examples? f. Give an account of the factors affecting the rate of decomposition? g.Define primary productivity ? Give the range of primary productivity in different ecosystems of the world ? h.Give an account of energy flow in an ecosystem? i. Write down the salient features of nitrogen cycle? j. Write down the factors of ecosystem services? 4. Long Answer Type Questions: a. Mention and describe the important structural features of an ecosystem ? b. Describe the functions of the ecosystem? c. Explain in detail about the schematic representation of the nitrogen cycle operating in the biosphere? d. Enumerate the factors that the primary productivity? e. Describe the cycling of sulphur and phosphorous cycle? 5. Application-based question: a."The energy flow in the ecosystem follows the second law of thermodynamics". Explain b. What will happen to an ecosystem if ? All producers are removed All organisms of herbivore level are eliminated and All top carnivore population is removed c. A farmer harvests his crops and expresses his harvest in three different ways ? I have harvested 10 quintals of wheat I have harvested 10 quintals of wheat today in one acre of land I have harvested 10 quintals of wheat in one acre of land, 6 Months after sowing Do the above statements mean one and the same thing .If your answer is yes, give the reasons and if the answer is 'no' explain the meaning of each expression d. Give two examples of artificial or manmade ecosystems. List the salient features by which they differ from natural ecosystems? e.What will happen to an ecosystem if All the producers are removed . All organisms of herbivore level are eliminated and All top carnivore population is removed
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