Our Environment — Class 10 Science

An ecosystem includes all living organisms (biotic) and their physical environment (abiotic) within a defined area. Biotic components: Producers (plants, algae) create food via photosynthesis. Consumers: Primary (herbivores eating plants), Secondary (carnivores eating herbivores), Tertiary (apex predators). Decomposers (bacteria, fungi) break down dead matter, returning nutrients to soil. Abiotic components: Sunlight (energy source), Temperature (affects metabolism and distribution), Water (essential for life), Soil (supports plants, provides minerals), Atmospheric gases (O₂ for respiration, CO₂ for photosynthesis). Energy flows one direction: Sunlight → Producers → Consumers → Decomposers. Matter cycles repeatedly through ecosystem. Ecosystem types: Forest (high biodiversity), Grassland (grass dominance), Desert (low water), Aquatic (freshwater/marine). Stable ecosystems resist environmental changes due to biodiversity and complex food webs.

Food chain: Linear sequence showing energy transfer through organisms. Example: Plant → Grasshopper → Frog → Snake → Eagle. Each organism eats the one before it, receiving chemical energy stored in food. Producer (autotroph): Plants create energy via photosynthesis (6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂). Consumers: Heterotrophs eat organic matter. Herbivores eat plants (1° consumer). Carnivores eat herbivores (2° consumer) or other carnivores (3° consumer). Omnivores eat both. Decomposers: Break down dead organisms and waste, return minerals to soil. Food web: Multiple interconnected food chains showing realistic diet complexity. Example: Frog eats grasshoppers AND flies; Eagle eats frogs AND snakes. Webs show:organisms have multiple food sources (stable if one source fails), predators have multiple prey options, nutrient recycling pathways, competition for food. Trophic level: Position in food chain. Level 1 = Producers (plants). Level 2 = Primary consumers (eat plants). Level 3 = Secondary consumers (eat herbivores). Level 4 = Tertiary consumers (eat carnivores). Most ecosystems have 4-5 trophic levels (energy limits higher levels). Energy decreases dramatically at each level (~10% rule).

Energy flow (10% Law): Only ~10% of energy transfers to next trophic level; ~90% lost as heat via respiration, movement, digestion. Example: If grass captures 100,000 kcal from sun → Grasshoppers receive ~10,000 kcal → Frogs ~1,000 kcal → Eagles ~100 kcal. This explains why: (1) Ecosystems support more plants than herbivores, (2) More herbivores than carnivores, (3) Predators are larger/stronger (compensates for fewer numbers), (4) Food chains rarely exceed 4-5 levels (insufficient energy). Pyramid of numbers: Bars show organism count at each level. Producer level (base) = most numerous. Predator level (top) = few individuals. Example: Millions of grass → Thousands of grasshoppers → Hundreds of frogs → Few eagles. Inverted pyramid possible: Few large trees support many small insects. Pyramid of biomass: Bars show total organism mass at each level. Usually pyramid shape (base largest). Biomass = mass of all organisms at level. Measured in grams/square meter/year. Most energy-efficient representation. Pyramid of energy: Bars show energy content at each level. Always pyramid shape (never inverted) because energy always decreases. Most accurate representation of energy flow. These pyramids explain ecosystem stability, carrying capacity (maximum organisms environment supports), and why top predators are rare and endangered.

Nutrient cycles recycle matter through ecosystems indefinitely. Unlike energy (flows one direction), matter cycles: Abiotic reserves (atmosphere, soil, water) → Biotic community → Back to abiotic. Carbon cycle: CO₂ in atmosphere. (1) Photosynthesis: Plants absorb CO₂, convert to glucose (6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂). Carbon stored in plant biomass. (2) Respiration: Plants/animals release CO₂ back (C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy). (3) Decomposition: Dead organisms broken down, CO₂ released. (4) Fossil fuels: Millions of years of dead organisms form coal/oil/gas. Burning releases ancient CO₂ → Greenhouse effect → Climate warming. Nitrogen cycle: Atmosphere = 78% N₂ (but unusable by most organisms). (1) Nitrogen fixation: Lightning OR bacteria convert N₂ to NO₃⁻ in soil (accessible to plants). (2) Assimilation: Plants absorb NO₃⁻, make proteins. Animals eat plants. (3) Decomposition: Dead organisms broken down. (4) Denitrification: Bacteria convert NO₃⁻ back to N₂, released to atmosphere. Water cycle: (1) Evaporation: Sun heats water → H₂O vapor. (2) Transpiration: Plants release water vapor (combined = evapotranspiration). (3) Condensation: Vapor cools → liquid droplets. (4) Precipitation: Rain/snow falls. (5) Collection: Water in oceans/lakes/groundwater. Cycle repeats. These cycles maintain ecosystem nutrient balance and organism survival.

Biodiversity: Variety of different species, genes, and ecosystems in an area. Genetic diversity: Different genes within species (increases survival flexibility). Species diversity: Different species types (ecosystems with many species are more stable). Ecological diversity: Different ecosystems in region. Importance of biodiversity: (1) Stability - diverse ecosystems resist environmental changes better than monocultures. (2) Productivity - more species = better use of resources. (3) Human benefits - foods, medicines, textiles, pollination, pest control. (4) Ecosystem services - oxygen production, water purification, climate regulation. Loss of biodiversity: Endangered species (very few remaining), Extinct species (no individuals alive). Causes: Habitat destruction (forests cut, wetlands drained), Poaching/hunting, Pollution (chemicals, plastics), Climate change, Competition from invasive species. Conservation strategies: (1) Protected areas: National parks, wildlife sanctuaries preserve habitat. (2) Breeding programs: Captive breeding increases population numbers. (3) Legal protection: Laws against poaching, trade bans on endangered species. (4) Habitat restoration: Replanting forests, cleaning polluted water. (5) Sustainable practices: Controlled logging, sustainable agriculture reduce resource depletion. (6) Education: Awareness programs promote conservation value. India's biodiversity: High due to varied geography (Himalayas, plains, coasts, deserts). Examples: Tiger, Asian elephant, Indian rhinoceros (all endangered). Project Tiger: Conservation program protecting remaining tigers. Biodiversity hotspots: Areas with exceptional species diversity + high threat level. Example: Western Ghats (India) - many endemic species (found nowhere else).

Environmental issues result from human activities exceeding ecosystem capacity. Pollution: Contamination of air, water, soil. Air pollution: Smoke, CO₂ (greenhouse gas), NOₓ (nitrogen oxides), SO₂ (sulfur dioxide) from vehicles, factories. Effects: Respiratory diseases, acid rain (SO₂ + NO₂ dissolves in water), ozone depletion (CFCs destroy stratospheric O₃ protecting from UV). Water pollution: Industrial waste, pesticides, sewage, plastic. Effects: Reduced aquatic biodiversity, unsafe drinking water, eutrophication (excess nutrients → algal bloom → dead zone). Solid waste: Plastics, electronics. Effects: Landfill overflow, ocean accumulation, toxic chemical leaching. Deforestation: Removing forests for agriculture, logging. Effects: Habitat loss, increased CO₂ (fewer trees absorbing), soil erosion, floods, climate change. Climate change: Rising CO₂/greenhouse gases trap heat → warmer atmosphere → melting ice caps, rising sea levels, extreme weather. Sustainable development: Meeting current needs without harming future generations' ability to meet theirs. Strategies: (1) Renewable energy (solar, wind, hydro replace coal/oil). (2) Resource conservation: Reduce consumption, reuse products, recycle materials (3Rs). (3) Sustainable agriculture: Organic farming, crop rotation, reduced pesticide use. (4) Protected areas: Preserve ecosystems. (5) Policies: Government regulations limiting pollution, carbon taxes. (6) Individual actions: Using public transport, reducing waste, supporting eco-products. Circular economy: Products designed to be recycled/reused rather than discarded. Zero-waste lifestyle minimizes environmental impact. Global cooperation essential: Climate change, pollution cross borders; requires international treaties (Paris Agreement) and unified action.