Our Environment (Class 10 Science)

Cheatsheet Content

1. Ecosystem: What are its Components? (NCERT Page 254) Definition: An ecosystem consists of all the organisms in an area together with the non-living physical components of the environment, interacting as a unit. Components: Biotic Components: Living organisms. Producers: Organisms that produce food (e.g., green plants, some bacteria). They convert solar energy into chemical energy. Consumers: Organisms that depend on producers for food. Herbivores (Primary Consumers): Eat plants (e.g., deer, rabbit). Carnivores (Secondary/Tertiary Consumers): Eat other animals. Secondary eat herbivores (e.g., snake, frog); Tertiary eat secondary consumers (e.g., eagle, tiger). Omnivores: Eat both plants and animals (e.g., humans, bear). Decomposers: Organisms that break down dead organic matter (e.g., bacteria, fungi). They recycle nutrients back into the environment. Abiotic Components: Non-living factors (e.g., temperature, rainfall, sunlight, soil, minerals, air, water). Types of Ecosystems: Natural: Forests, ponds, lakes, oceans, deserts. Artificial (Man-made): Crop fields, aquariums, gardens. 2. Food Chains and Food Webs (NCERT Page 255-256) Food Chain: A sequence of organisms through which energy is transferred from one trophic level to the next by eating and being eaten. Example: Grass $\rightarrow$ Deer $\rightarrow$ Tiger Each step is called a trophic level . Trophic Levels: First Trophic Level: Producers (e.g., Green plants) Second Trophic Level: Primary Consumers (Herbivores) Third Trophic Level: Secondary Consumers (Small carnivores) Fourth Trophic Level: Tertiary Consumers (Large carnivores) Energy Flow: Energy flows unidirectionally from producers to consumers. 10% Law: Only about 10% of the energy from one trophic level is transferred to the next trophic level; the remaining 90% is lost as heat to the environment or used for metabolic processes. Due to this loss, food chains usually consist of only 3-4 steps. Food Web: Interconnected food chains operating in an ecosystem. It shows multiple feeding relationships among different organisms. 3. How Do Our Activities Affect the Environment? (NCERT Page 257-259) Ozone Layer Depletion: Ozone ($O_3$): A molecule formed from three atoms of oxygen. Stratospheric Ozone: Acts as a protective shield, absorbing harmful ultraviolet (UV) radiation from the sun. UV Radiation Effects: Causes skin cancer, cataracts, damage to immune system, and harms plant life. Depletion Causes: Primarily by Chlorofluorocarbons (CFCs), used in refrigerators, fire extinguishers, and aerosols. Montreal Protocol (1987): An international treaty to phase out CFC production. Managing the Garbage We Produce: Biodegradable Substances: Substances that are broken down by biological processes (e.g., bacteria, fungi) (e.g., vegetable peels, paper, wood). Non-biodegradable Substances: Substances that are not broken down by biological processes and persist for a long time (e.g., plastics, glass, DDT, heavy metals). These cause pollution. Methods of Waste Disposal: Landfills: Waste buried in low-lying areas. Composting: Biodegradable waste converted into manure. Recycling: Non-biodegradable waste (plastic, paper, metal) collected, processed, and reused. Incineration: Burning waste at high temperatures to reduce volume. Biogas Plants: Use organic matter to produce biogas and manure. Sewage Treatment Plants: Treat wastewater before discharge. 4. Important Questions & Answers (PYQ & NCERT based) Q1: What are the components of an ecosystem? (NCERT Page 254) A: An ecosystem has two main components: Biotic Components: All living organisms, including producers (plants), consumers (animals), and decomposers (bacteria, fungi). Abiotic Components: All non-living physical and chemical factors like temperature, light, water, soil, air, and minerals. Q2: Distinguish between food chain and food web. (NCERT Page 255-256) A: Feature Food Chain Food Web Definition A single, linear sequence of organisms showing who eats whom. A network of interconnected food chains in an ecosystem. Complexity Simple, straightforward. Complex, multiple feeding pathways. Stability Less stable; removal of one organism can severely disrupt it. More stable; provides alternative food sources. Energy Flow Shows a single path of energy flow. Shows multiple paths of energy flow. Q3: Explain the 10% law of energy transfer in a food chain. (NCERT Page 256) A: The 10% law states that during the transfer of energy from one trophic level to the next, only about 10% of the energy is transferred to the higher trophic level. The remaining 90% of the energy is lost as heat to the environment or used by the organism for its life processes (respiration, digestion, growth). This limited energy transfer explains why food chains usually have only 3-4 trophic levels. Q4: What is the role of decomposers in an ecosystem? (NCERT Page 254) A: Decomposers (bacteria and fungi) play a crucial role in an ecosystem by breaking down dead organic matter (dead plants, animals, and waste products). This process: Recycles nutrients back into the soil, making them available for producers. Cleans up the environment by removing dead organisms. Helps maintain the balance of nutrients in the ecosystem. Q5: Why is the depletion of the ozone layer a cause for concern? (NCERT Page 257) A: The depletion of the ozone layer is a serious concern because: The ozone layer in the stratosphere absorbs harmful ultraviolet (UV) radiation from the sun. Its depletion allows more UV radiation to reach Earth's surface. Increased UV radiation can cause skin cancer, cataracts, and suppress the immune system in humans. It can also damage crops, reduce plankton populations (affecting aquatic food webs), and harm other life forms. Q6: Suggest some methods to dispose of waste properly. (NCERT Page 258-259) A: Effective waste disposal methods include: Segregation: Separating biodegradable and non-biodegradable waste at the source. Composting: Converting biodegradable waste into useful manure. Recycling: Processing non-biodegradable materials like plastic, paper, and glass into new products. Landfilling: Burying waste in designated areas (though this has environmental limitations). Incineration: Burning waste at high temperatures to reduce its volume (requires careful management of emissions). Biogas Plants: Using organic waste to produce biogas (fuel) and bio-manure. Reduce, Reuse, Recycle (3Rs): A fundamental principle for waste management. Q7: Why are pesticides like DDT considered harmful for the environment? (NCERT Page 257) A: Pesticides like DDT are harmful because: They are non-biodegradable , meaning they cannot be broken down by natural processes and persist in the environment for a long time. They undergo biomagnification (or biological magnification), where their concentration increases at successive trophic levels in a food chain, reaching highest levels in top consumers. This high concentration can cause severe health problems, hormonal imbalances, and even death in higher organisms, including humans.