ENVIRONMENTAL SCIENCE (GRADE-9) CHAPTER: HOW ECOSYSTEM WORKS

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1 ENVIRONMENTAL SCIENCE (GRADE-9) CHAPTER: HOW ECOSYSTEM WORKS 1. What is EVS? Environmental science is an academic field that integrates physical, biological and information sciences [including ecology, biology, physics, chemistry, zoology (animal biology), mineralogy (study of minerals), oceanology (study of oceans), limnology (study of lakes and other inland waters), soil science, atmospheric science] to the study of the environment, and the solution of environmental problems. 2. What is ECOLOGY? "Environmental science" and "ecology" are often used interchangeably, but technically, ecology refers only to the study of organisms and their interactions with each other and their environment. Ecology could be considered a subset of environmental science, which also could involve purely chemical or public health issues. 3. What is an ECOSYSTEM? An ecosystem is a community of living organisms in conjunction with the non-living components of their environment (things like air, water and mineral soil), interacting as a system. These biotic and abiotic components are regarded as linked together through nutrient cycles and energy flows. 1

2 4. What are the BIOTIC COMPONENTS OF AN ECOSYSTEM? A biotic factor is any living component that affects the population of another organism, or the environment. This includes animals that consume the organism, and the living food that the organism consumes. Each biotic factor needs energy to do work and food for proper growth. All species are influenced by biotic factors in one way or another. Biotic components usually include: Producers OR autotrophs: e.g. plants, they convert the energy [from photosynthesis (the transfer of sunlight, water, and carbon dioxide into energy)] into food. Consumers OR heterotrophs: e.g. animals, they depend upon producers and other consumers for food. o Primary consumer OR Herbivore: Organisms that eat plants are called primary consumers. E.g.: rabbit, cattle o Secondary consumer OR Carnivore: Organisms that eat herbivores are called secondary consumers. E.g.: mice, foxes o Tertiary consumer OR Carnivore: Carnivores that eat other carnivores are called tertiary consumers. E.g.: wolf, snake o Quaternary consumer OR Apex Carnivore: Apex carnivores are organisms that have no predators. E.g.: lions, eagle Scavengers: Scavengers feeds on dead animal and plant material present in its habitats. E.g.: vultures Decomposers OR detritivores: e.g. fungi and bacteria, they break down chemicals from producers and consumers (usually dead) into simpler form which can be reused. The biotic factors result in the formation of a food chain. 5. What is a FOOD CHAIN? A food chain is the sequence of who eats whom in a biological community (an ecosystem) to obtain nutrition. A food chain starts with the primary energy source, usually the sun or boiling-hot deep sea vents. The next link in the chain is an organism that make its own food from the primary energy source. E.g.: photosynthetic plants that make their own food from sunlight (using a process called photosynthesis) and chemosynthetic bacteria that make their food energy from chemicals in hydrothermal vents. These are called autotrophs or primary producers. Next come organisms that eat the autotrophs; these organisms are called herbivores or primary consumers. E.g.: a rabbit that eats grass. The next link in the chain is animals that eat herbivores - these are called secondary consumers. E.g.: a snake that eat rabbits. In turn, these animals are eaten by larger predators also known as tertiary consumers. E.g.: an owl that eats snakes. The tertiary consumers are eaten by quaternary consumers. E.g.: a hawk that eats owls. Sun Plants Rabbit Snake Eagle Decomposers 2

3 Each food chain ends with a top predator, and animal with no natural enemies (like an alligator, hawk, or polar bear). The arrows in a food chain show the flow of energy, from the sun or hydrothermal vent to a top predator. As the energy flows from organism to organism, energy is lost at each step. 6. Give some examples of FOOD CHAINS. Food Chains on Land Dead plants - centipede - robin Nuts - squirrels hawk Decayed plants - worms - birds - eagle Plants - mule deer - mountain lion Fruits - bats - eagles Rice - rat owl Fruits - monkeys - monkey-eating eagle Sun - berries bear Grass - antelope - tiger - vulture Sun - grass - ant - echidna dingo Grass - cow - man Sage brush - elk wolf Grass - deer - eagle Shark grass - earthworm - chicken - snake Grass - earthworms - bird - snake Sun - bamboo pandas Grass - grasshopper - frog - snake - eagle Sun - eucalyptus leaves koalas Grass - rabbit - snake - owl - hawk Sun - grass - mice lion Grass - snail - bird - fox Sun - grass - zebra lion Leaves - ants - anteaters Weeds - elephants vulture Leaves - caterpillar - birds - snake Weeds - zebra - lion coyote Leaves - giraffes - lion Food Chains in Water Algae - mosquito larva - dragonfly larva - fish - raccoon Phytoplankton - zoo plankton - anchovy - tuna humans Crayfish - catfish - humans Phytoplankton - zoo plankton - fish - seal - great white shark Mayflies - trout - humans Plankton - snail - mackerel shark Phytoplankton - copepod - fish - squid - seal - orca Plankton - snail - tuna dolphin Phytoplankton - copepod - bluefish - swordfish - Plankton - threadfin shad - bass humans human Phytoplankton - copepod - blue head wrasse - Turtles - alligators humans striper All plants and animals are part of a food chain. These examples of food chains are only a small part of the food chains; but, they are included to show the variety of plants and animals involved in any particular food chain. 7. What are TROPHIC LEVELS? The trophic level of an organism is the position it occupies in a food chain. Trophic levels can be represented by numbers, starting at level 1 with plants. Further trophic levels are numbered subsequently according to how far the organism is along the food chain. Level 1: Plants and algae make their own food and are called primary producers. Level 2: Herbivores eat plants and are called primary consumers. Level 3: Carnivores that eat herbivores are called secondary consumers. Level 4: Carnivores that eat other carnivores are called tertiary consumers. Level 5: Apex carnivores that have no predators are at the top of the food chain. 3

4 8. What is a FOOD WEB? A food web (or food cycle) is the natural interconnection of food chains of what-eats-what in an ecological community. Another name for food web is a consumer-resource system. 9. Write about the ENERGY IN AN ECOSYSTEM? An ecosystem depends upon a supply of energy. All living things need energy for growth, movement and other essential activities. The energy needed by living things comes from the sun. Every ecosystem depends on green plants to trap the energy in sunlight and change it into chemical energy. The process by which green plants convert the sun's energy is called photosynthesis. Green plants also take minerals, such as nitrates and phosphates, into their bodies through their roots. These minerals are needed for the healthy growth of the plants. The core functions of the ecosystems are: 4

5 Production: the conversion of solar energy into chemical energy or potential energy by the process of photosynthesis. Consumption: it is the transfer of chemical energy produced by the plants to other organisms through the process of eating and being eaten. Decomposition: it is the breaking down of organic matter to recycle the material and release nutrients and energy in form if heat. The functional aspect of ecosystem are: Energy Flow Cycle of Nutrients 10. How does ENERGY and NUTRIENTS flow in an ecosystem? Energy Flow: Ecosystems maintain themselves by cycling energy and nutrients obtained from external sources. At the first trophic level, primary producers (plants, algae, and some bacteria) use solar energy to produce organic plant material through photosynthesis. Herbivores animals that feed solely on plants make up the second trophic level. Predators that eat herbivores comprise the third trophic level; if larger predators are present, they represent still higher trophic levels. Organisms that feed at several trophic levels (for example, grizzly bears that eat berries and salmon) are classified at the highest of the trophic levels at which they feed. Decomposers, which include bacteria, fungi, moulds, worms, and insects, break down wastes and dead organisms and return nutrients to the soil. On average about 10 percent of net energy production at one trophic level is passed on to the next level. The low rate of energy transfer between trophic levels makes decomposers generally more important than producers in terms of energy flow. Decomposers process large amounts of organic material and return nutrients to the ecosystem in inorganic form, which are then taken up again by primary producers. Energy is not recycled during decomposition, but rather is released, mostly as heat (this is what makes compost piles and fresh garden mulch warm). Thus, the ENERGY FLOW IN AN ECOSYSTEM IS UNIDIRECTIONAL. Energy Lost in an Ecosystem Cycle of Nutrients: Not all organisms produce their own food. Organisms that need to consume other organisms to obtain their energy are called consumers or heterotrophs. Animals, humans, fungi and bacteria are all consumers. They obtain their nutrients and energy by eating other organisms. 5

6 The materials like water, carbon (as carbon dioxide) and nitrogen (as minerals) are taken up by the plants from soil, air and water bodies, etc., and made into food. This food is then passed on to the animals like herbivores and carnivores in a food chain. After the death and decay of plants and animals, the materials like water, carbon and nitrogen present in their bodies are returned to soil, air and water, from where they were taken originally. These materials can then be reused for the growth of new plants. In this way, the same materials are used again and again, the materials are not lost from the environment. So, the FLOW OF NUTRIENTS like water, carbon and nitrogen, etc., IN THE ECOSYSTEM IS CYCLIC. 11. What is a FOOD PYRAMID? The study of trophic relationships indicate that starting from the producers, one finds a regular decrease in the properties or characters (such as number, energy and biomass) of the organism occupying a trophic level in a food chain. When represented graphically these relationships give a shape of a pyramid. These pyramids are known as Ecological Pyramids and are of three types: Pyramid of Number: The population of each organism in a food chain can be shown in a sort of bar chart called a pyramid of numbers. The more organisms there are, the wider the bar. The producer in the food chain always goes at the bottom of the pyramid of numbers. Pyramid of biomass: An ecological pyramid is a graphical representation designed to show the biomass or bio productivity at each trophic level in a given ecosystem. Biomass is the amount of living or organic matter present in an organism. Biomass pyramids show how much biomass is present in the organisms at each trophic level, while productivity pyramids show the production or turnover in biomass. Pyramid of Energy: An energy pyramid is a graphical model of energy flow in a community. The various levels represent different groups of organisms that might compose a food chain. 6

7 12. What is BIOACCUMULATION? Bioaccumulation is the gradual build up over time of a chemical in a living organism. This occurs either because the chemical is taken up faster than it can be used, or because the chemical cannot be broken down for use by the organism (that is, the chemical cannot be metabolized). Toxins enter a food chain through several means: they can be ingested, absorbed through skin or inhaled, and plants take in toxins directly from soil. To bio-accumulate, a substance needs to be fat-soluble, long-lived, biologically active and mobile -- able to be taken up by organisms. When herbivores eat contaminated plants, the toxins accumulate in their fatty tissues. If a carnivore eats several toxin-laden herbivores, the toxins become even more concentrated in its body. This process of bio-magnification continues up the food chain. 13. What are the different NUTRIENT CYCLES present in an ecosystem? (A) WATER CYCLE: The water cycle, describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly constant over time but the partitioning of the water into the major reservoirs of ice, fresh water, saline water and atmospheric water is variable depending on a wide range of climatic variables. The water moves from one reservoir to another, such as from river to ocean, or from the ocean to the atmosphere, by the physical processes of evaporation, condensation, precipitation, infiltration, runoff, and subsurface flow. In doing so, the water goes through distinct phases: liquid, solid (ice), and gas (vapor). The water cycle involves the exchange of energy, which leads to temperature changes. For instance, when water evaporates, it takes up energy from its surroundings and cools the environment. When it condenses, it releases energy and warms the environment. These heat exchanges influence climate. The evaporative phase of the cycle purifies water which then replenishes the land with freshwater. The flow of liquid water and ice transports minerals across the globe. It is also involved in reshaping the geological features of the Earth, through processes including erosion and sedimentation. The water cycle is also essential for the maintenance of most life and ecosystems on the planet. 7

8 (B) CARBON CYCLE: Human activities like heating homes and cars burning fuels (combustion) give off carbon into the atmosphere. During respiration, animals also introduce carbon into the atmosphere in the form of carbon dioxide. The Carbon dioxide in the atmosphere is absorbed by green plants (producers) to make food in photosynthesis. When animals feed on green plants, they pass on carbon compounds unto other animals in the upper levels of their food chains. Animals give off carbon dioxide into the atmosphere during respiration. Carbon dioxide is also given off when plants and animals die. This occurs when decomposers (bacteria and fungi) break down dead plants and animals (decomposition) and release the carbon compounds stored in them. Very often, energy trapped in the dead materials becomes fossil fuels which is used as combustion again at a later time. (C) NITROGEN CYCLE: Nitrogen is introduced into the soil by precipitation (rain, lightning). Nitrates don t only come from Nitrogen in the air. They can also be obtained by the conversion of ammonia, commonly used 8

9 in fertilizers by nitrifying bacteria in the soil. Some root nodules can also convert nitrogen in the soil into nitrates. Plants build up proteins using nitrates absorbed from the soil. When animals like cows, eat these plants, they, in turn, use it to build animal protein. When these animals (cows) poop, pee or die, the urea, excreta or carcass are broken down by decomposers and the nitrogen is re-introduced into the soil in the form of ammonia. Nitrates in the soil can also be broken down by denitrifying bacteria (in specific conditions) and sent into the air as nitrogen. This process can help make the soil infertile because it will lack the nitrates needed for plant use. Once nitrogen gets back into the air, the cycle continues. 14. What is meant by SUCCESSION IN AN ECOSYSTEM? Ecological succession is the gradual process by which ecosystems change and develop over time. Nothing remains the same and habitats are constantly changing. There are two main types of succession, primary and secondary. Primary succession is the series of community changes which occur on an entirely new habitat which has never been colonized before. For example, a newly quarried rock face or sand dunes. Secondary succession is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat. For example, after felling trees in a woodland, land clearance or a fire. 15. What are the TWO MAIN CAUSES of ECOLOGICAL SUCCESSION? Allogenic Succession: In ecology, allogenic succession is succession driven by the abiotic components of an ecosystem. An allogenic succession can be brought about in a number of ways which can include: o Volcanic eruptions o Meteor or comet strike o Flooding o Drought o Earthquakes o Non-anthropogenic climate change Autogenic Succession: In ecology, autogenic succession is succession driven by the biotic components of an ecosystem. The plants themselves (biotic components) cause succession to occur. o Light captured by leaves 9

10 o Production of detritus o Water and nutrient uptake o Nitrogen Fixation 16. What is MAN S IMPACT ON CARBON AND NITRGEN CYCLE? The two main human impacts on the carbon cycle are: BURNING OF FOSSIL FUELS: Under natural conditions the release of carbon from fossil fuels occurs slowly, as they are sub ducted into the mantle, and CO2 is released through volcanic activity. However, humans are heavily reliant on fossil fuels, and extract it from the lithosphere in great quantities. Burning coal, oil, natural gas, and other fossil fuels for industrial activity and power generation for example, removes the carbon from the fossil fuels and emits it as CO2 into the atmosphere. LAND USE AND LAND COVER CHANGE (E.G. DEFORESTATION): Large amounts of carbon are stored in living plants. Therefore, land use changes, especially the clearance of forests (which are very densely inhabited by plants, and therefore contain a large amount of carbon), can influence the carbon cycle in two ways. Firstly, the removal of vegetation eliminates plants which would otherwise be capturing carbon from the atmosphere through photosynthesis. Secondly, as dense forests are replaced by crops/pasture land/built environments, there is usually a net decrease in the carbon store, as smaller plants (and worse still, concrete) store far less carbon than large trees. Deforestation also allows much more soil to be eroded, and carbon stored in the soil is rapidly taken into rivers. Man s impact on nitrogen cycle: The major human activities that today influence the global N cycle are fossil fuel combustion, the production and use of chemical fertilizer, and the growing of N-fixing crops. These activities are reported to have doubled the magnitude of N fixation over continents. The major environmental issues associated with this enhancement are global climate change, stratospheric ozone depletion, regional smog, visibility degradation, acid rain, water-use impairment, and eutrophication ***************************************