Biological Science - Our Environment (PDF)

/ Kuala Lumpur, Malaysia TERM: II NAME: _______________________ REF: 2024-25/ BIO/ T2/ STD 10/ HO11 CLASS: ___________________ SUBJECT: Biological Science DATE:...

/ Kuala Lumpur, Malaysia TERM: II NAME: _______________________ REF: 2024-25/ BIO/ T2/ STD 10/ HO11 CLASS: ___________________ SUBJECT: Biological Science DATE: TOPIC: Our Environment OUR ENVIRONMENT The environment includes our physical surroundings like air (or atmosphere), water bodies, soil (land and all the organisms such as plants, animals, human beings and micro- organisms like bacteria and fungi (called decomposers). The waste materials produced by the various activities of man and animals are poisonous and to some extent we can categorise wastes into two main groups. 1. Biodegradable Wastes: Substances that are broken down in nature in course of time by the microorganisms like fungi, bacteria, and other living organisms are called biodegradable wastes. Temperature and sunlight also play an important role in the decomposition of biodegradable substances. For Examples: Food waste, tea leaves, urine and faecal matter, sewage agricultural residue, paper, wood, cloth, cow-dung etc. 2. Non-Biodegradable Wastes: Substances that are not broken down by biological processes in nature are called non-biodegradable wastes. These substances may be in solid, liquid or gaseous form. These substances are inert and simply persist in the environment for a long time and may harm the various members of the ecosystem. For Example: DDT (Di-chloro-diphenyl trichloroethane), insecticides, pesticides, mercury, lead, arsenic, aluminium, plastics, polythene bags, glass, radioactive wastes. These non- biodegradable wastes are major pollutants of the environment. Ecosystem: An ecosystem is a self-contained unit of living things (plants, animals and decomposers), and their non-living environment (soil, air and water). An ecosystem needs only the input of sunlight for its functioning. Energy and matter are continuously exchanged between living and non-living components. An ecosystem can be both natural and man-made. Some examples of natural ecosystems are grass land, forest, sea, river, desert, mountain, pond, lake etc. Man-made artificial ecosystems are garden, crop fields, park, aquarium, etc. Page 1 of 10 Components of Ecosystem: There are two components of an ecosystem: 1. Biotic component: It includes three types of organisms: (a) Producers: All green plants, blue green algae can produce their food (Sugar and starch) from inorganic substance using light energy (Photosynthesis). Therefore, all green plants are called producers. They are also called autotrophs. Planktons are very minute or microscopic organisms freely floating on the surface of water in a pond, lake, river or ocean. Planktons are of two types: Phytoplanktons and Zooplanktons. The microscopic aquatic plants freely floating on the surface of water are called phytoplanktons. The microscopic aquatic animals freely floating on water are called zooplanktons. The freely floating protozoa are an example of zooplankton. (b) Consumers ( Heterotrophs): They are organisms which consume other organisms or their products as their food. All animals belong to this category. The consumers depend upon producers for their food directly or indirectly. They get their food by eating other organisms or their products. For example, man, goat, deer, fish, lion, cow, buffalo, etc., are common consumers. The consumers can be classified into the following types: (i) Herbivores: These are organisms (animals) which get their food by eating the producers (or plant) directly. Herbivores are also called primary consumers. Some common examples of herbivores are: deer, rabbit, rat, squirrel, goat, cattle, etc. (ii) Carnivores: Those animals which consume only flesh of other animals as food are called carnivores. Carnivores are usually of 2 types. Small and large carnivores. The small carnivores feed on herbivores (primary consumers) are called secondary consumers. Some common examples are snake, wild cat, jackal, frog, some birds, fishes, etc. The large carnivores which feed upon the small carnivores are called tertiary consumers. For example, birds of prey (hawk, eagle), tiger, lion, etc. iii) Omnivores: The organisms which feed on both plants and animals are called omnivores. For example Human beings, dog, crow, sparrow, bear, mynah, ant etc. (c) Decomposers: Fungi and bacteria which break down (decompose) complex organic compounds present in dead plants, animals and their products like faeces, urine etc., into simpler substances are called decomposers. The decomposers help in the replenishment of natural resources or recycling of nutrients back to soil. These are also known as micro- consumers or saprotrophs. Page 2 of 10 Importance of Decomposers Decomposers help in decomposing the dead bodies of plants and animals, and hence act as cleaning agent of the environment and create space for living, of newer generations of organisms. The decomposers help release minerals and other raw materials trapped in organic matter back to soil. These are picked up by plants. This also helps to maintain the fertility of soil. Decomposers help in recycling the materials in the biosphere so that, the process of life may go on and on like an unending chain. 2. Abiotic Components: These are non-living components of an ecosystem. These include the physical environment. Edaphic factors like soil texture, topography, water, and air. Inorganic substances like carbon dioxide, nitrogen, oxygen, water, phosphorus, sodium, potassium, and calcium. These are involved in the cycling of materials in the ecosystem. Organic compounds like proteins, carbohydrates, and lipids. These largely form the living body and link the abiotic and biotic components. Climatic factors: These are sunlight temperature, pressure humidity, moisture, rainfall, etc. these factors affect the distribution of the organisms. Functions of an Ecosystem 1. Ecosystem indicates available solar energy and the efficiency of an ecosystem to trap the same. 2. It gives information about the available essential minerals and their recycling periods. 3. It provides knowledge about the web of interactions and inter-relationship among the various populations as well as between the population and the abiotic environment. 4. It helps human beings to know about conservation of resources, protection from pollution and inputs required for maximizing productivity. 5. In the ecosystem, two processes of energy flow and biogeochemical cycles (nutrient movement) proceed side by side. The energy flow is unidirectional while the movement of nutrients is cyclic. Food Chain: The sequence of living organisms in a community, in which one organism consumes another organism to transfer food energy, is called a food chain. Page 3 of 10  For example, A food chain in grassland which has four steps: Grass (Producers) → Insect (Herbivores) → Frog (Carnivores) → Eagle (Secondary Carnivore) Significance of Food Chains 1. The study of food chains helps in understanding food relationships and interactions among the various organisms in an ecosystem. The food chains, transfer energy and materials between various living components of an ecosystem. 2. The food chains transfer energy and materials between various living components in an ecosystem or biosphere. 3. The food chains give dynamicity to an ecosystem or biosphere. 4. The movement of toxic substances like pesticides, weedicides, etc., through food chains, can prove very harmful. Food Web: The inter-connected food chains operating in an ecosystem which establish a network of relationship between various species are called a food web. In a food web, one organism may occupy a position in more than one food chain. An organism can obtain its food from different sources and in turn, may be eaten up by different types of organisms. Trophic Levels: The various steps in the food chain at which the transfer of food (or energy) takes place are called trophic levels. Page 4 of 10 There is a gradual decrease in the amount of energy transfer from one trophic level to the next trophic level in a food chain. Only 10% of energy is transferred to next trophic level while 90% of energy is used by present trophic level in its life processes. The various trophic levels are given below: The plant or the producers constitute the first trophic level. The herbivores or primary consumers form the second trophic level. Carnivores or secondary consumers make up the third trophic level. Large carnivores or the tertiary consumers which feed upon the small carnivores constitute the fourth trophic level. Flow of Energy Energy is used and conveyed from one trophic level to another in a food chain. This is called flow of energy. Green plants capture about 1% of the solar energy incident on the Earth through the biochemical process of photosynthesis. A part of this trapped energy is used by plants in performing their metabolic activities and some energy is released as heat into the atmosphere. The remaining energy is chemical energy stored in the plants as ‘carbohydrates’. When plants are eaten up by herbivores, the chemical energy stored in the plants is transferred to these animals. These animals (herbivores) utilize some of this energy for metabolic activities, some energy is “released as heat and the remaining energy is stored. The process of energy transferred is similarly repeated with carnivores and so on. Ten Percent Law: According to this law, only 10% of the energy entering the particular trophic level of organisms is available for transfer to the next higher trophic level. Environmental Problems: Changes in the environment affect us and our activities change the environment around us. This leads to the slow degradation of the environment that give rise to many environmental problems. For Example: Depletion of the Ozone Layer and waste disposal. Depletion of Ozone Layer: Ozone (O 3) layer is largely found in the stratosphere which is a part of our atmosphere from 12 km -50 km above sea level. This region is called ozonosphere. Ozone is deadly poisonous gas at the ground level. Ozone is formed as a result of the following photochemical reaction. Page 5 of 10 It is a protective blanket around earth which absorbs most of the harmful U.V. (Ultraviolet) radiation of the Sun, thus, protecting the living beings of the Earth from health hazards. The decline of Ozone layer thickness in Antarctica was first discovered in 1985 and was termed as OZONE HOLE. Cause of Ozone Hole: Excessive use of CFCs (Chloro Flouro Carbon) a synthetic, inert chemical. For example; Freon gas which is used as refrigerant gas and also in fire extinguishers causes Ozone depletion in the upper atmosphere. A single chlorine atom can destroy 1,00,000 Ozone molecules. Halons, Carbon tetrachloride and Methyl chloroform present in fire extinguishers and aerosol sprays also cause depletion of ozone layer. Nitrous oxide is another chemical that damages the ozone layer. [Note: The chlorine from the decay of CFCs is converted to a highly reactive gas by unusual clouds that only form in the stratosphere at extremely cold temperatures, which is why cold winters make for larger ozone holes. The return of sunlight to the polar latitudes in spring initiates the ozone-depleting reactions. But as spring progresses and temperatures rise, the clouds evaporate, the creation of highly reactive chlorine gas ceases, and the destruction of ozone stops. As the season continues, ozone from middle and lower latitudes flows into the polar stratosphere, filling the ozone hole back in for another year.] Chemical equation for ozone hole due to CFC is CFCl3+ UV Light ==> CFCl2+ Cl Cl + O3 ==> ClO + O 2 ClO + O ==> Cl + O 2 The free chlorine atom is then free to attack another ozone molecule Cl + O3 ==> ClO + O2 ClO + O ==> Cl + O2 This continues…. Effects of Ozone Layer Depletion Effects on Human and Animal Health: Increased penetration of solar UV-B leads to risks of eye diseases, skin cancer and infectious diseases. Effects on Terrestrial Plants: In forests and grasslands, increased radiation is likely to change species composition thus altering the bio-diversity in different ecosystems. Page 6 of 10 Effects on Aquatic Ecosystems: High levels of radiation exposure in tropics and subtropics may affect the distribution of phytoplanktons, which form the foundation of aquatic food webs. It can also cause damage to early development stages of fish, shrimp, crab, amphibians and other animals, the most severe effects being decreased reproductive capacity and impaired larval development. Also has effect on Bio-geo-chemical Cycles and air quality. Ozone Depletion Counter Measures 1. U.N.E.P. (United Nation Environment Programme) did an excellent job in forging an agreement to freeze CFC production at 1986 levels (KYOTO Protocol) by all countries. 2. Ozone friendly substitutes- HCFC (less ozone depleting potential and shorter life) 3. Recycling of CFCs and Halons 4.Afforestation Eutrophication Eutrophication is the process in which a water body becomes overly enriched with nutrients, leading to plentiful growth of simple plant life. The excessive growth (or bloom) of algae and plankton in a water body are indicators of this process. Eutrophication is considered to be a serious environmental problem since it often results in the deterioration of water quality and the depletion of dissolved oxygen in water bodies. Eutrophic waters can eventually become “dead zones” that are incapable of supporting life. The primary contributors to eutrophication include agriculture and industrial wastes. Excess fertilizers and sometimes phosphorus rich factory waste wash into water bodies. This leads to algal bloom. The excessive growth of algae in eutrophic waters is accompanied by the Page 7 of 10 generation of a large biomass of dead algae. These dead algae sink to the bottom of the water body where they are broken down by bacteria, which consume oxygen in the process. The hypoxic conditions at the lower levels of the water body lead to the suffocation and eventual death of larger life forms such as fish in those water bodies. Biological Magnification: The increase in concentration of harmful chemical substances like pesticides which are non-biodegradable in the body of living organisms at each trophic level of a food chain is called biological magnification. Example: Maximum concentration of such chemicals gets accumulated in human bodies. Managing the Garbage, we Produce: Industrialization and rise in demand of consumer goods have created a major problem in the form of wastes/garbage accumulation and its disposal especially in urban areas. The disposal of waste should be done in a scientific way. There are different methods of waste disposal. The method to be used depends on the nature of the waste. Some of the important modes of waste disposal are: 1. Recycling: The solid wastes are broken down into its constituent simpler materials. These materials are then used to make new items. Even non-bio degradable solid wastes like plastic, metal can be recycled. We should follow the 3 R’s, Reduce, Reuse, Recycle waste. Page 8 of 10 2. Incineration: Burning of waste on high temperature to form ash is called incineration. This process is carried out in an incinerator. Incineration is used to destroy household, chemical and biological wastes (Hospital wastes). 3. Landfills: Wastes are dumped in low lying areas and are compacted by rolling with bulldozers. A big landfill site can be used to dispose of waste for a considerable time. 4. Composting: Organic wastes are filled into a compost pit (2m × 1m × 1m). It is then covered with a thin layer of soil. After about three months the same garbage filled inside the pit changes into organic manure. 5. Sewage treatment: Sewage is disposed by treating the sewage water at the sewage treatment plant. This water is then released into water bodies like rivers, oceans etc. The organic matter present in sewage is ‘digested’ in the digesters of sewage treatment plant to produce ‘sewage gas’ (biogas) and ‘manure’. PRACTICE QUESTIONS 1. Explain how ozone being a deadly poison can still perform an essential function for our environment. 2. Give reason why a food chain cannot have more than four trophic levels. For 3 and 4 questions two statements are given- one labelled Assertion (A) and the other labeled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below: a) Both A and R are true, and R is correct explanation of the assertion. b) Both A and R are true, but R is not the correct explanation of the assertion. c) A is true, but R is false. d) A is false, but R is true. 3. Assertion: Food chain is responsible for the entry of harmful chemicals in our bodies. Reason: The length and complexity of food chains vary greatly. 4. Assertion: Greater number of individuals is present in lower trophic levels. Reason: The flow of energy is unidirectional. 5. Plastic cups were used to serve tea in trains in early days- these could be returned to the vendors, cleaned and reused. Later, kulhads were used instead of plastic cups. Now, paper cups are used for serving tea. What are the reasons for the shift from Plastic to kulhads and then finally to paper cups? 6. (a) What is ‘environmental pollution’? (b) Distinguish between biodegradable and non-biodegradable pollutants. (c) Choose the biodegradable pollutants from the list given below: Sewage, DDT, radioactive waste, agricultural waste. 7. How is the increase in demand for energy affecting our environment adversely? Page 9 of 10 8. How is ozone formed in the upper atmosphere? Why is the damage of ozone layer a cause of concern to us? State a cause of this damage. 9. Why are bacteria and fungi called decomposers? List any two advantages of having decomposers in our environment. 10. Construct an aquatic food chain showing four trophic levels. 11. Describe how decomposers facilitate recycling of matter in order to maintain balance in the ecosystem. 12. “Damage to the ozone layer is a cause for concern.” Justify this statement. Suggest any two steps to limit this damage. ‘ 13. Consider the following food chain which occurs in a forest: Grass -> Deer -> Lion If 10000 J of solar energy is available to the grass, how much energy would be available to the deer to transfer it to the lion? 14. What are the problems caused by the non-biodegradable wastes that we generate? 15. If all the waste we generate is biodegradable, will this have no impact on the environment? Page 10 of 10