Ecosystem PDF

Ecosystem  DISCLAIMER The content provided in these notes are created and owned by the Authors and licensed to Sorting Hat Technologies Private Limited (Company) for the sole purpose of providing access to the agreed upon Learners of the Company’s Platform. The Co...

Ecosystem  DISCLAIMER The content provided in these notes are created and owned by the Authors and licensed to Sorting Hat Technologies Private Limited (Company) for the sole purpose of providing access to the agreed upon Learners of the Company’s Platform. The Company disclaims all rights and liabilities in relation to the content, images or any material of the notes. The Authors are the sole owners of the content and shall be solely responsible for, including without limitation, any claims, liabilities, damages, losses or suits that may arise with respect to the content in these notes.  Ecosystem INTRODUCTION y Ecology (Gr. Oikos-house; Logos-study) Definition involves the study of inter-relationships of Ecosystem: It is a organisms with one another and with their self-sustained and functional environment. unit of nature consisting of y In a given geographical area organisms biotic and abiotic factors, demonstrate interspecific and intraspecific where the living organisms relationships for survival. Biotic community (biotic factors) interact among lives in an environment which fulfills themselves and also with their its material and energy requirements physical environment (abiotic too. Hence, living organisms and their factors). physical environment are in an inseparable relationship. This relationship constitutes different ecosystems. y So ecosystem is the functional unit of nature. Previous Year’s Question ECOSYSTEM The maximum energy amongst y Sir Arthur Tansley coined the term ecosystems is contributed by ecosystem. (1) crops y Ecosystem is a self-sustained unit in which (2) forests living and non-living components interact (3) coal with each other. (4) fuel gas y Types of ecosystem Note: Crop fields, orchards, gardens and Gray Matter Alert!!! aquaria are some man-made ecosystems. Biogeocoenosis was the term used for ecosytem by Russian Ecosystem ecologist, Sukachev (1944). 1.  y Components of an ecosystem ECOSYSTEM: STRUCTURE AND FUNCTION y The interaction of biotic and abiotic components results in a physical structure characteristic of each type of ecosystem. y The two important structural features of an ecosystem are: ○ Species composition ○ Stratification y Species composition— All the plants, animals and microbial species present in the ecosystem. y Stratification— It refers to the vertical distribution of different species occupying different levels in the ecosystem. y Stratification in a forest ○ Trees above 40 feet occupy the top vertical layer of a forest. ○ Trees of 20-40 feet an height constitute dense canopy layer and understorey layer. ○ Shrubs occupy the second layer. ○ Herbs and grasses occupy the bottom layer. y Stratification in a deep pond or a lake Definition ○ Littoral zone is represented by shallow water having rotten strata which help in thriving Stratification: It refers to the rooted plants. vertical distribution of different ○ Limmetic zone occupies depth up to which species occupying different light penetrates in water and has planktons, Ecosystem levels in an ecosystem. nektons and neustons. 2.  ○ Profundal zone is represented by the area where sunglight cannot penetrate. This zone Gray Matter Alert!!! lacks photosynthetic organisms. The mud contains only anaeboric bacteria, fungi and Ecosystems in the tropics, such other micro-organisms. as tropical rain forests, have most of the species of plants and animals. Previous Year’s Question Ecosystem consists of (1) decomposers (2) producers (3) consumers Note: In shallow ponds, vertical stratification is (4) all of these very little. y Significance ○ Stratification increases the number of habitats which reduces interspecific competition. FUNCTIONS OF ECOSYSTEM y Ecosystem performs four major functions like productivity, decomposition, energy flow and nutrient cycling. Productivity y A constant input of solar energy is the basic requirement of any ecosystem to function and Definition sustain. y The biomass (organic matter) produced per unit Productivity: The rate of area over a time period by plants is expressed in production of biomass, is called terms of weight (g-2) or energy (kcal m-2). productivity. Ecosystem 3.  y The rate of biomass production is called primary productivity and is expressed in terms of g–2yr–1 or kcal m–2y–1. Primary productivity has two aspects y Gross Primary Productivity (GPP or PG) is the Definition rate of production of organic matter during photosynthesis. Primary Productivity: It is y It is measured in terms of assimilation number defined as the amount of I.e. amount of CO2 fixed by a gram of chlorophyll biomass or organic matter in an hour. produced per unit area over a y Net Primary Productivity (NPP) is the amount of time period by the plants during energy available in the producers after utilisation photosynthesis. of some energy for respiration, i.e., GPP–R = NPP (NPP is the amount of energy available in the producers for the consumption of herbivores). Factors affecting primary productivity ○ the plant species in a particular area Previous Year’s Question ○ availability of nutrients ○ photosynthetic capacity of plants, and Decomposers are ○ environmental factors. (1) Animalia and Monera y The annual net primary productivity of the whole (2) Protista and Monera biosphere is approximately 170 billion tons (dry (3) Fungi and Plantae weight) of organic matter. (4) Bacteria and fungi Ecosystem y Of this, the productivity of oceans is only 55 billion tons, while the rest is on land. 4.  Secondary productivity y It is defined as the rate of assimilation and Definition formation of new organic matter by consumers. Secondary Productivity: It is of two types: It is defined as the rate of ○ Gross secondary productivity is the amount assimilation and formation of food consumed minus egested material. It of new organic matter by varies for different consumers. consumers. ○ Net secondary productivity refers to rate of a resynthesized organic matter by the consumers. The average net productivity for all consumers is 10 per cent. So, it is low for herbivores and high for carnivores. Rack Your Brain Note: Two types of food chains get connected when a woodpecker Community productivity eats an earthworm. Justify. It is the rate of net synthesis of organic matter (biomass) by a community per unit time and area. It is calculated as net primary production minus heterotrophic consumption during a Definition specific period. Generally the entire growing season or year is considered. Decomposition: It is the process in which the complex Decomposition organic matter is broken down y Detritus is the raw material for decomposition. into simpler organic substances y Following are the steps in the process of and ultimately into inorganic decomposition: compounds. Fragmentation y It is the process of breaking of the detritus into smaller particles by detritivores. Definitions Leaching y It is the process in which water-soluble inorganic Detritus: The dead remains of substances run down into soil horizon and get the plants and animals and also precipitated as unavailable salts. the faecal matter, constitutes detritus. Catabolism Detritivores: Detritivores are y The enzymatic conversion of the detritus into those organisms which feed on simple organic compounds and then into the detritus and break it down inorganic compounds, is called catabolism. into smaller particles, e.g., Ecosystem y The enzymes are secreted by the decomposers earthworm. like bacteria and fungi. 5.  Humification Rack Your Brain y Humification during decomposition leads to Which process will primarily be the accumulation of dark coloured amorphous affected if all the bacteria and substances called humus. Ecosystem fungi get destroyed? 6.  Mineralisation y It is the process in which the humus is degraded Definition by certain microbes and the inorganic nutrients are released. Bioenergetics: The study of y Decomposition is largely an aerobic process, i.e., energy transfer from one trophic it requires oxygen. level to the next trophic level. y The factors affecting decomposition: ○ The chemical composition of detritus and the climatic factors. ○ Decomposition is slow, if detritus is rich in Gray Matter Alert!!! lignin and chitin. ○ Decomposition is faster if detritus is rich in Diclofenac has been banned in nitrogen and water-soluble substances (e.g., India since 2006. Diclofenac, was sugars). commonly used as a livestock ○ Temperature and soil moisture are the anti-inflammatory drug. It is one important climatic factors that regulate of the major contributing factors decomposition through their effects on the in declining populations of activities of soil microbes. vultures. Vultures are important ○ Warm and moist environment and aerobic members of food chains. conditions favour decomposition. ○ A dry environment, low temperature and anaerobic conditions inhibit decomposition. FOOD CHAIN Definition y It is a series of groups of organisms dependent on others for food. This relationship constitutes Food Chain: Food chain refers a chain hence, is called a food chain. to the transfer of energy (food) from the producer through a Types of food chain series of organisms. y In nature generally two types of food chain can be distinguished – grazing food chains and detritus food chains. Grazing food chain (GFC) Definition y It begins with the producers, that capture the solar energy and through photosynthesis feeds Ten per cent law: From one the energy into the food chain. trophic level to another trophic For example, level, about 90 per cent of the energy is lost Grass  → Goat  → Man and only 10 per cent of energy is (Producer ) (Consumer Primary ) (Secondary Consumer ) available to be transferred. Ecosystem 7.  y In a food chain there is unidirectional flow of Rack Your Brain energy from sun to producers and then to various consumers. Why there cannot be unlimited y Usually there are maximum four or five trophic number of trophic levels in a levels in a food chain. food chain? y Shorter food chains provide greater amount of energy to the top level consumers. Definition Note: In an aquatic ecosystem, GFC is the Trophic Level: Every step or level in major type of food chain for energy flow. Ecosystem a food chain is called a trophic level. 8.  Detritus Food Chain (DFC) y It begins with the dead organic matter and Previous Year’s Question decomposers (saprotrophs) e.g., bacteria and fungi. The driving force for an ecosystem y A larger fraction of energy flows through this is type of food chain than the grazing food chain in (1) Biomass terrestrial ecosystems. (2) Producers y The place or position occupied by an organism in (3) Carbohydrates in producers the food chain, is known as trophic level. (4) Solar energy y Producers occupy the first trophic level, the herbivores (primary consumers) occupy the second, and the carnivores (secondary consumers) are on the third. Definition y The amount of energy decreases at successive trophic levels; only 10 per cent of the energy is Standing Crop: The amount of transferred to each trophic level from the lower living matter (biomass) present trophic level. This is called as 10 per cent law of at every trophic level is known energy transfer. as standing crop. y So, the number of trophic levels in a grazing food chain is restricted to four or five. y At each trophic level, mass of living material at a particular time is called the standing crop. Gray Matter Alert!!! Note: Standing crop is measured as the mass of living organisms (biomass) or the number in Lindeman (1942) proposed 10 a unit area. per cent law. Characters Grazing Food Chain Detritus Food Chain Primary source of energy Solar radiations Detritus Detritivores (a mixed group in terms of trophic levels First trophic level All herbivores and may be herbivores, omnivores and primary carnivores) Size Long-sized chains Small-sized chains Mangrove fallen leaves in Predatory food chains on Examples brackish zone of South land and in water Florida Ecosystem 9.  Note: In nature, the food chains interact with Gray Matter Alert!!! each other forming a food web. The ten per cent law of transfer of ENERGY FLOW energy from one trophic level to the y Sun is the ultimate source of energy for all next can be attributed to Raymond ecosystems on the earth. Lindeman (1942). y Only about 50 per cent of the incident solar Lindeman did not call it a “law” and radiation is photosynthetically active radiation cited ecological efficiencies ranging (PAR). from 0.1 per cent to 37.5 per cent. y Plants capture only 2–10 per cent of the PAR and all organisms (herbivores, carnivores, omnivores and decomposers) are dependent for their food on producers, either directly or indirectly. Previous Year’s Question y The flow of energy from the sun to producers and then to consumers is unidirectional and it The 10 per cent law of energy keeping with the first law of thermodynamics. transfer law of food chain was y In an ecosystem, the energy transferred in the given by form of food and leads to degradation. The loss (1) Tansley (2) Stanley of a major part of food energy as heat during (3) Lindeman (4) Weisman Ecosystem 10.  metabolic activities and a very small fraction stored as biomass; and thus, it is keeping with Definition the second law of thermodynamics. Ecological Pyramids: The graphic ECOLOGICAL PYRAMIDS representation of the trophic y The food or energy relationship among organisms structure (organisms in various at different trophic levels can be expressed in trophic levels) of a food chain is terms of number, biomass or energy. called ecological pyramid. y The expression assumes the shape of a pyramid, where the base represents the producers or first trophic level, while the apex represents the tertiary or top level consumer. Previous Year’s Question y Each trophic level represents a functional level not any one species in particular. y Types of ecological pyramid usually studied: In an ecosystem, bacteria are ○ Pyramid of number considered as ○ Pyramid of biomass (1) micro consumers ○ Pyramid of energy (2) secondary consumers (3) macro consumers (4) primary consumers Gray Matter Alert!!! The term ecological pyramid was given by Charles Elton. The concept of pyramid of numbers was developed by him. Previous Year’s Question y In general, all the pyramids are upright. y Pyramid of energy is always upright (never The pyramid of energy is always inverted) because during the flow of energy from (1) inverted one trophic level to the next some energy is lost (2) upright as heat (at each step). (3) both of these (4) inverted in forest ecosystem Ecosystem 11.  Previous Year’s Question Exceptions y In a tree ecosystem, the pyramid of number Pyramid of energy is always is inverted (Number of insects and small birds (1) cup shaped feeding on the tree are more in number than one (2) upright tree). (3) inverted y Pyramid of biomass in a sea or ocean ecosystem (4) spindle shaped is inverted (biomass of a fish is far more than the phytoplanktons on which it feeds). y There are certain limitations of ecological pyramids, such as, y It does not take into account the same species belonging to two or more trophic levels. y It assumes a simple food chain, whereas in nature it does not exist; y Saprophytes/decomposers are not given any place in ecological pyramids. ECOLOGICAL EFFICIENCIES y The percentage ratios between energy flow at different trophic levels of a food chain. Ecosystem 12.  Types of Ecological Efficiency y Trophic level energy intake efficiency (Lindeman’s Rack Your Brain efficiency) ratio between the amount of energy assimilated at two successive trophic levels. Why is pyramid of biomass in a y It varies from 1-5 per cent for producers. sea generally inverted? y It is 10-20 per cent for higher trophic levels. y Trophic assimilation efficiency is percentage ratio between net production and energy assimilated Previous Year’s Question at trophic level. y It varies from 10-50 per cent. Energy transfer from one trophic y Photosynthetic efficiency is percentage ratio level to other in a food chain is between gross primary productivity and incident (1) 20% (2) 1% solar radiation. (3) 10% (4) 2% y It varies from 1-5 per cent. y Net production efficiency is the percentage ratio between net primary productivity and gross primary productivity. y It is about 50 per cent. ECOLOGICAL SUCCESSION y It is a community-controlled phenomenon in which the structure and composition of communities change in an orderly and sequential Gray Matter Alert!!! manner, leading ultimately to the establishment of a climax community. The term ecological succession y There is a gradual and fairly predictable change was given by Ragnar Hault in in the species composition of a given area during 1885. succession. Ecosystem 13.  y During succession, pioneer species colonise an area and their populations become more Definition numerous. y In these successive seral stages, there is a Pioneer Species: The species change in the diversity of species, increase in the which invade a bare area and number of species and organisms and also in the initiate the ecological succession, total biomass. are called pioneer species. y The individual transitional communities are called seral stages or seral communities. y Succession is of two types. Rack Your Brain SUCCESSION OF PLANTS y Based on the nature of the habitat, succession of Why does standing state vary on plants can be grouped into two categories: seasonal basis in any ecosystem? ○ Hydrarch succession ○ Xerarch succession Hydrarch Succession y It starts in life-less water bodies or wet areas Definition and progresses from aquatic to mesic conditions. y In primary hydrarch succession, pioneers are Sere: The entire sequence of phytoplanktons. communities, that successively y Later on following changes occur successively change in a given area resulting like rooted submerged plants grow → rooted in a climax community, is called floating angiosperms plants develop → free a sere. floating plants arise → reed swamp stage → marsh meadow stage → scrub stage → climax community. Previous Year’s Question Which of the following is correct about food chain? (1) Zooplanktons → Phytoplanktons → Fishes (2) Phytoplanktons → Fishes → Zooplanktons (3) Phytoplanktons → Zooplanktons → Fishes (4) None of these Ecosystem 14.  Xerarch Succession y It starts in dry or xeric conditions (bare rocks) and progresses from xeric to mesic conditions. Gray Matter Alert!!! y Pioneer species is lichens as these are able to secrete acids to dissolve rocks. Thus, help in Reed-swamp stage is also known weathering of rocks and soil formation. as amphibious stage. y Later on bryophytes colonise the area. Gradually, some other lower plants, small plants and finally trees grow. Ecosystem 15.  y The stages in xerarch succession are as follows: Previous Year’s Question The boundary or transition between two or more communities is called (1) ecotone (2) thermocline (3) biome (4) ecotype y Similiarities and dissimilarities between hydrarch and xerarch are shown in the table below: S.No. Hydrarch Succession Xerarch Succession It takes place in water bodies or It takes place in dry or xeric 1. wet areas. conditions (bare rocks). Succession progresses from hydric Succession progresses from 2. to mesic conditions. xeric to mesic conditions. Pioneer species is lichens as 3. Pioneer species is phytoplanktons. these are able to secrete acids to dissolve rocks. 4. Climax community is forest. Climax community is forest. Ecosystem 16. y In secondary succession, the type of pioneer species depends on the following factors: Definition ○ Condition of the soil ○ Availability of water Autogenic succession: Once, ○ Environmental conditions ecological succession starts ○ Seeds or other propagules. the vegetation modifies its own environment The two general facts about succession and eventually keeps replacing y Primary succession is a very slow process that may itself by new ecological take thousands of years for the establishment of communities. climax community. y All succession, hydrarch or xerarch, lead to the establishment of similar mesic communities. S.No. Primary Succession Secondary Succession Takes place in a region where life existed in Takes place in a place where the past but got destroyed completely. For 1. no life existed before. example, forest fires, earthquakes usually destroy the life of an area. 2. Extremely slow process. Comparatively fast process. Suitable substratum and soil Suitable substratum and soil is already 3. needs to be formed. present. Note: Succession and evolution are parallel Rack Your Brain processes. Why is secondary succession NUTRIENT CYCLING (Biogeochemical Cycles) faster than primary succession? y The nutrients are never lost from an ecosystem, but are recycled through living organisms, rocks, soil, air and water. y The amount of nutrients such as carbon, nitrogen, Definition phosphorus, calcium, etc., present in the soil at any given time is referred as standing state. Standing State: The amount y Each bio-geochemical cycle is comprised of two of nutrients such as nitrogen, types of pools: phosphorus, calcium, etc., ○ Reservoir pool: It is the large, slow-moving present in the soil at any given and generally non-biological. time is called standing state. ○ Exchange or cyclic pool: It is small, fast moving Ecosystem component which is exchanging rapidly 17.  between organisms and their immediate environment. Rack Your Brain y On the basis of movement of nutrients, bio- geochemical cycles are of 2 types: Give the term for biomass at a ○ Perfect cycles: In these cycles e.g., gaseous particular time for a trophic level. cycles, nutrients remain in circulation more or less uniformly. In these cycles nutrients self-adjust rather quickly because of large reservoir. ○ Imperfect cycles: These cycles get more easily disrupted by local disturbances as the bulk of material remains in the relatively inactive and immobile reservoir on the earth’s crust e.g., sedimentary cycles of phosphorus, sulphur, calcium, potassium, etc. Definition y On the basis of nutrient reservoir cycles are of two types: gaseous cycles and sedimentry cycles. Biogeochemical Cycle or y Gaseous cycles Nutrient Cycle: The continuous ○ The reservoir for gaseous cycles exists in exchange of nutrients or the atmosphere, e.g., carbon cycle, nitrogen elements among organisms and cycle, etc. between organisms and their y Sedimentary cycles physical environment is called ○ The reservoir for sedimentary cycles exists biogeochemical cycle. in the earth’s crust, e.g., phosphorus cycle, sulphur cycle, etc. ○ Environmental factors like temperatures, soil nature and moisture can regulate the rate of release of nutrients. ○ The function of the reservoir is to meet the deficit which occurs due to imbalances in the rate of influx and efflux. CARBON CYCLE Previous Year’s Question y Carbon cycle occurs in atmosphere, oceans and living and dead organisms. Which one of the following is a y About 49 per cent of dry weight of an organism is sedimentary cycle? constituted by carbon. (1) Carbon cycle y Carbon dioxide in the atmosphere and fossil fuel (2) Oxygen cycle represent the reservoir of carbon. (3) Hydrogen cycle y About 71 per cent of the global carbon is found (4) Phosphorus cycle Ecosystem dissolved in the ocean and this oceanic reservoir 18.  regulates the amount of carbon dioxide in the Rack Your Brain atmosphere. y About 4 × 1013 kg of carbon is fixed in the biosphere Why are nutrient cycles also through photosynthesis annually. called biogeochemical cycles? Ecosystem 19.  y A considerable amount of this is returned to the atmosphere as carbon dioxide through the Previous Year’s Question respiratory activities of producers and consumers and decomposition by decomposers. A bamboo plant is growing in a y Additional sources which add carbon dioxide forest. What will be its trophic to the atmosphere are burning of fossil fuels, level? fuel, wood and organic matter, forest fires and (1) T1 volcanic activity. (2) T2 y Some amount of fixed carbon is lost as sediments (3) T3 (limestone, dolomite, etc.) (4) T4 Note: Decomposers contribute substantially to CO2 pool by their activities. PHOSPHORUS CYCLE y The natural reservoir of phosphorus is a rock in the form of phosphates. Ecosystem 20. y Minute quantities of phosphates get dissolved in the soil solution during weathering of rocks. Definition y Phosphates enter the plants through their roots and then the food chain. Ecosystem Services: The y The organic wastes and dead organisms are products of ecosystem decomposed by phosphate-solubilising bacteria, processes are termed as which release phosphorus back into the soil. ecosystem services. y The atmospheric input of phosphorus through rainfall or gaseous exchange of phosphorus between organisms and environment is negligible. ECOSYSTEM SERVICES y Robert Constanza et al. have tried to put price tags on nature’s life-support services. Ecosystem 21.  y Researchers have estimated them to be 33 trillion US dollar a year which is nearly twice the GNP. Rack Your Brain y While our global gross national product (GNP) is only 18 trillion US dollars. Interaction of biotic and abiotic y The following services are provided by forests: factors in a pond forms a _______. ○ Purify air ○ Mitigate droughts and floods ○ Help in cycling of nutrients ○ Provide habitat to a number of wildlife ○ Act as store house of carbon ○ Influence the hydrological cycle ○ Maintain biodiversity Previous Year’s Question Approximate cost of various ecosystem services Inverted pyramid of biomass can y Out of total cost of various ecosystem services be traced in one of the following the soil formation accounts for about 50 per cent. ecosystems. y Contribution to other services, e.g., recreation (1) Rain forest and nutrient cycling are less than 10 per cent (2) Desert each. (3) Ocean y The cost of climate regulation and habitat for (4) Tundra wildlife are about 6 per cent each. Note: Ecotone The word ecotone was coined by Alfred Russel Wallace in 1859. It is formed by the combination of ecology and tone, in Greek tonos or tension means a place where ecologies are in tension. It is a transition area between two biological communities where the communities meet and integrate. The area of meeting can be a narrow stretch or a wide well-demarcated area. For example, change in the colour of foliage or height of the plants, etc. If different animal species are able to survive in both the biomes, then ecotone is considered to be species rich. Examples of ecotone are reed beds (common form of lakeside of ecotones), salt marshes, riparian zones, etc. Ecosystem 22. Summary Ecosystem 23.  Solved Exercise Q1 An ecosystem is (1) Different communities of plants, animals and microbes together with their physicochemical environment. (2) Different communities of plants and microbes along with their physicochemical environment. (3) A localised assemblage of several plants and animals. (4) An assemblage of plants, animals and their surroundings. A1 (1) An ecosystem is a self-sustained unit where all the biotic components interact with each other as well as with their physicochemical environment. Q2 The importance of ecosystem lies in (1) Cycling of materials (2) Flow of energy (3) Both (1) and (2) (4) Its biomass A2 (3) In an ecosystem, the decomposers help in nutrient cycling by making the simple inorganic components available to the plants after the decomposition of dead complex organic matter. The producers convert solar energy to chemical energy which is transferred to the primary consumers and then to the next trophic levels in the form of food. Q3 Which ones occurs at the same trophic level (1) Crow and Cow (2) Snake and Earthworm (3) Tiger and Wild Boar (4) Deer and Bee Ecosystem 24. A3 (4) Deer feeds on plants and honey bee sucks nectar from the flowers so both belong to the second trophic level. Q4 Biotic components of an ecosystem include (1) Producers, consumers and decomposers (2) Producers and consumers (3) Producers only (4) Consumers only A4 (1) Biotic components mean all the living components of any system and in an ecosystem. These are all plants, animals, detritivores and microbes. Q5 Energy stored at the consumer level is (1) Gross primary productivity (2) Net primary productivity (3) Net productivity (4) Secondary productivity A5 (4) Secondary productivity means the formation of new organic matter by consumers. Q6 Pyramid of numbers in a pond ecosystem is (1) Irregular (2) Inverted (3) Upright (4) Spindle shaped A6 (3) In a pond, producers are aquatic plants (phytoplanktons, free-floating and Ecosystem 25.  rooted plants) and generally the consumers are zooplanktons, small aquatic creatures, frogs, big freshwater fish. The number of producers is always more than the number of primary consumers and likewise, the number of organisms at successive levels is always less than the previous level. So, the Pyramid of numbers in a pond ecosystem is always upright. Q7 The correct sequence of the food chain is (1) grass → snake → insect → deer (2) grass → wolf → deer → buffalo (3) grass → insect → bird → snake (4) bacteria → grass → rabbit → wolf A7 (3) In a terrestrial food chain, the first level is occupied by the producers and the second, third and fourth trophic levels by the herbivores, secondary and tertiary consumers respectively. So, grass → insect → bird → snake is the correct sequence given here. Q8 Lithosphere is a reservoir of (1) Carbon (2) Phosphorous (3) Nitrogen (4) Oxygen A8 (1) The natural reservoir of phosphorus is rock which contains phosphorus in the form of phosphates. Q9 Sere means (1) The sequence of communities. (2) The entire sequence of communities that successively change in a given area. (3) The entire sequence of communities. (4) The whole communities that successively do not change in a given area. Ecosystem 26. A9 (2) During ecological succession, there is always a sequential change in the communities. So, the entire sequence of communities that successively change in a given area is called sere(s). Q10 Food chain in which microorganisms breakdown the complex organic matter is (1) Parasitic food chain (2) Detritus food chain (3) Consumer food chain (4) Predator food chain A10 (2) The detritus food chain begins with dead organic matter which is decomposed mainly by fungi and bacteria. Ecosystem 27. Ecosystem 28.