Our Environment — Class 10 Biological Science
"Everything is CONNECTED. The grass, the grasshopper, the frog, the snake, the eagle — and you. This is the web of life."
1. Ecosystem — The Functional Unit
An ecosystem consists of BIOTIC (living) and ABIOTIC (non-living) components interacting as a SYSTEM.
Abiotic: Sunlight. Temperature. Water. Soil. Air. Minerals. Biotic: Producers (plants — photosynthesise. 'Autotrophs — they bring energy INTO the ecosystem from the SUN.'). Consumers (animals — Primary/herbivores, Secondary/carnivores, Tertiary/top carnivores). Decomposers (bacteria, fungi — break down dead matter, return nutrients to soil. 'Without decomposers: the world would be buried in dead plants and animals.')
2. Food Chains and Food Webs
Food Chain — A Linear Sequence
Grass (Producer) → Grasshopper (Primary Consumer) → Frog (Secondary Consumer) → Snake (Tertiary Consumer) → Eagle (Quaternary Consumer).
Trophic Levels — The Energy Pyramid
At each step (trophic level), ENERGY is LOST. Only about 10% of energy transfers to the NEXT level. The rest (~90%) is lost as HEAT (metabolism, movement). 'This limits food chains to 4-5 levels. There's simply not enough energy at the TOP to support another level. This is why TOP PREDATORS are FEWER than herbivores.'
Food Webs — The Real Picture
'In reality, organisms eat MANY things. A snake eats frogs AND mice AND lizards. An eagle eats snakes AND rabbits AND fish. Food chains INTERCONNECT → FOOD WEB. The web is MORE STABLE than the chain — if one species declines, there are ALTERNATIVES.'
3. Biological Magnification
Harmful, NON-BIODEGRADABLE substances ACCUMULATE as they move UP the food chain. Pesticides (DDT). Heavy metals (mercury, lead). Concentration INCREASES at each trophic level. 'Highest concentration in TOP PREDATORS — including humans who eat fish. DDT in water: 0.003 ppb. In fish-eating birds: 25 ppm — a MAGNIFICATION of ~10 MILLION times!'
4. Ozone Layer (O₃)
Located in the STRATOSPHERE (15-35 km above Earth). Absorbs harmful ULTRAVIOLET (UV) radiation from the Sun. 'Without the ozone layer: skin cancer, cataracts, damage to crops and marine life.'
Ozone Depletion: CFCs (Chlorofluorocarbons — used in refrigerators, air conditioners, aerosol sprays) RISE to the stratosphere. UV breaks down CFCs → releases CHLORINE atoms. ONE chlorine atom destroys ~100,000 ozone molecules. 'The "ozone hole" over Antarctica was discovered in 1985 — a SHOCK to the world.'
Montreal Protocol (1987) : International treaty. PHASED OUT CFCs. 'One of the most SUCCESSFUL environmental treaties in history. The ozone layer is SLOWLY RECOVERING. Expected to return to pre-1980 levels by ~2066.'
5. Waste Management
| Type | Definition | Examples | Decomposition Time |
|---|---|---|---|
| Biodegradable | Broken down by MICROORGANISMS | Vegetable peels. Paper. Cotton. Wood. | Days to months |
| Non-biodegradable | NOT broken down. PERSIST. | Plastic. Glass. Metals. E-waste. | Hundreds to THOUSANDS of years |
The 3 R's
REDUCE (use less — refuse single-use plastic). REUSE (use again — cloth bags instead of plastic). RECYCLE (convert waste to new products — paper, glass, metal).
Plastic — A Special Problem
'Plastic is a MIRACLE material — cheap, durable, versatile. AND an environmental DISASTER. It does NOT biodegrade. It breaks into MICROPLASTICS — tiny particles that enter food chains. Microplastics have been found in human BLOOD, human PLACENTAS, and the deepest ocean trenches. There is NO "away" — everything we throw "away" goes SOMEWHERE.'
6. Common Mistakes
- 'Energy CYCLES in an ecosystem' — Energy FLOWS one way (Sun → producers → consumers → decomposers → HEAT lost). Nutrients CYCLE. Energy does NOT cycle.
- 'Ozone layer is in the troposphere' — It's in the STRATOSPHERE. Tropospheric ozone is a POLLUTANT.
- 'All waste eventually decomposes' — Non-biodegradable waste does NOT decompose. Plastic will outlast your grandchildren's grandchildren.
7. AP SSC Exam Focus
| Topic | Marks |
|---|---|
| Food chain and trophic levels | 3-4 |
| 10% energy rule | 2-3 |
| Biological magnification | 2-3 |
| Ozone depletion and CFCs | 2-3 |
| Biodegradable vs Non-biodegradable | 2-3 |
8. Ecosystem Components — In Detail
'An ecosystem is defined as the INTERACTION between living organisms (biotic) and their non-living environment (abiotic) in a particular area.'
Abiotic Components
Climatic factors: Sunlight (primary energy source), Temperature (affects metabolic rates), Rainfall (availability of water), Wind (pollination, seed dispersal), Humidity. Edaphic factors: Soil type (sandy, clay, loamy), Soil pH, Mineral content, Organic matter (humus). Physiographic factors: Altitude, Slope, Aspect (direction a slope faces).
Biotic Components — Trophic Classification
Producers (Autotrophs): GREEN PLANTS and PHOTOSYNTHETIC BACTERIA. Convert SUNLIGHT into chemical energy (glucose) through PHOTOSYNTHESIS. 'Every ecosystem depends on producers — they are the ENTRY POINT for energy. Without producers, there is NO energy, NO food, NO life.' Consumers (Heterotrophs):
- Primary Consumers (Herbivores): Eat producers directly. Example: cow (grass), rabbit (plants), grasshopper (leaves).
- Secondary Consumers (Carnivores): Eat herbivores. Example: frog (eats grasshopper), snake (eats frog).
- Tertiary Consumers (Top Carnivores): Eat secondary consumers. Example: eagle (eats snake), lion (eats zebra).
- Omnivores: Eat BOTH plants and animals. Example: humans, bears, crows. Decomposers (Saprotrophs): BACTERIA and FUNGI. Break down dead organic matter → release NUTRIENTS back to soil. 'Decomposers are the RECYCLERS of the ecosystem. Without them, nutrients would remain locked in dead bodies forever.'
9. Food Chains and Food Webs — In Detail
Grazing Food Chain
'Starts with LIVING plants. This is the most COMMON food chain in nature.' Grass → Grasshopper → Frog → Snake → Eagle
Detritus Food Chain
'Starts with DEAD organic matter (detritus). Important in forests and deep lakes.' Dead leaves → Earthworm → Bird → Snake OR Dead organisms → Bacteria/Fungi → Protozoans → Small fish → Large fish
'In MOST ecosystems, BOTH types of food chains exist. They INTERCONNECT.'
Food Web — A Network of Interconnected Food Chains
'In the REAL world, organisms rarely eat just ONE thing. A food web shows the MULTIPLE feeding relationships in an ecosystem. A food web is MORE STABLE than a single food chain. If one prey species declines, a predator can switch to ALTERNATIVE prey.'
Energy Flow and the 10% Law
'ENERGY flows ONE WAY through an ecosystem — it does NOT cycle. It enters as SUNLIGHT, passes through trophic levels as CHEMICAL ENERGY (in food), and is eventually LOST as HEAT.'
Lindemann's 10% Law: Only about 10% of the energy at one trophic level is transferred to the NEXT level. The remaining 90% is used for: Metabolism (cellular respiration), Movement, Growth, Reproduction, and is LOST as HEAT.
'This explains: (1) Food chains rarely have MORE than 4-5 trophic levels. (2) TOP CARNIVORES are FEWER IN NUMBER than herbivores. (3) The BIOMASS pyramid is always BROAD at the base (producers) and NARROW at the top (top carnivores).'
Worked Example — Energy Calculation
Suppose 10,000 J of sunlight hits a grassland ecosystem:
- Producers (grass) absorb ~1% (100 J) through photosynthesis.
- Primary consumer (grasshopper) gets ~10 J (10% of 100).
- Secondary consumer (frog) gets ~1 J (10% of 10).
- Tertiary consumer (snake) gets ~0.1 J (10% of 1).
- Quaternary consumer (eagle) gets ~0.01 J (10% of 0.1).
'This is why eagles need LARGE territories — the energy available at the top of the food chain is EXTREMELY limited.'
10. Biological Magnification — Detailed Study
'Biological magnification (also called BIOMAGNIFICATION) is the INCREASE in concentration of a toxic substance at each successive trophic level in a food chain.'
The DDT Story — A Classic Example
DDT (Dichloro-Diphenyl-Trichloroethane) was widely used as a PESTICIDE in agriculture after World War II. It was effective at killing insects. But DDT is NON-BIODEGRADABLE — it does not break down in the environment. It is FAT-SOLUBLE — it accumulates in the body fat of organisms.
Concentration in a Lake Ecosystem:
- Water: 0.000003 ppm (3 parts per trillion)
- Plankton: 0.04 ppm (13,000x concentration)
- Small fish: 0.5 ppm
- Large fish: 2 ppm
- Fish-eating birds (eagle, pelican): 25 ppm (8 MILLION times the water concentration!)
'DDT caused the EGGSHELLS of fish-eating birds to become THIN and BRITTLE. The eggs broke before hatching. Populations of bald eagles, peregrine falcons, and brown pelicans CRASHED. This led to the BANNING of DDT in many countries (USA in 1972, India in 1989 for agricultural use).'
AP Context — Pesticide Use in Agriculture
'Andhra Pradesh is one of India's largest consumers of pesticides. Cotton, chillies, and rice use HEAVY pesticide application. Pesticide residues have been found in Godavari and Krishna river systems, affecting aquatic life and potentially entering the food chain through fish.'
11. Ozone Depletion and CFCs — Detailed Mechanism
The Ozone Layer — Earth's Sunscreen
Ozone (O₃) is a molecule made of THREE oxygen atoms. It is formed in the STRATOSPHERE when UV radiation splits O₂ molecules → free oxygen atoms combine with O₂ → O₃.
How CFCs Destroy Ozone
Step 1: CFCs (Chlorofluorocarbons — compounds of carbon, chlorine, fluorine) are released from refrigerators, ACs, aerosol sprays, and industrial solvents. Step 2: CFCs are VERY STABLE — they do not break down in the lower atmosphere. They slowly RISE to the stratosphere (taking 5-10 years). Step 3: In the stratosphere, INTENSE UV RADIATION breaks down CFCs → releases CHLORINE atoms. Step 4: ONE chlorine atom reacts with an ozone molecule → destroys it → forms ClO and O₂. Step 5: The ClO molecule reacts with ANOTHER ozone molecule → releases the chlorine atom → it can destroy AGAIN. Step 6: A SINGLE CHLORINE ATOM can destroy ~100,000 OZONE MOLECULES through this catalytic cycle.
The Ozone Hole
'In 1985, British scientists discovered a THINNING of the ozone layer over ANTARCTICA — the 'ozone hole.' This was a shocking discovery. The hole was NOT a literal hole — it was a severe REDUCTION in ozone concentration (by up to 70% in spring).'
Ozone Depletion Effects
- Increased UV-B radiation reaching Earth's surface.
- Human health: SKIN CANCER (melanoma), CATARACTS (eye lens clouding), suppressed immune system.
- Agriculture: Reduced crop yields (UV damages plant DNA and photosynthesis).
- Marine life: Damages PHYTOPLANKTON — the base of the marine food chain.
The Montreal Protocol (1987) — A Success Story
International treaty to PHASE OUT OZONE-DEPLETING SUBSTANCES (CFCs, halons, carbon tetrachloride). 'The Montreal Protocol is the MOST SUCCESSFUL environmental treaty in history. It has been RATIFIED by all 198 UN member states. CFC production has been reduced by 99%. The ozone layer is SLOWLY HEALING. Full recovery of the Antarctic ozone hole is expected by ~2066.'
12. Waste Management — Detailed
Biodegradable vs Non-Biodegradable — Extended
| Feature | Biodegradable | Non-Biodegradable |
|---|---|---|
| Breakdown | By microorganisms (bacteria, fungi) | NOT broken down naturally |
| Time | Days to months | Hundreds to THOUSANDS of years |
| Examples | Paper, cotton, wood, vegetable peels, food waste | Plastic, glass, metal, polystyrene, e-waste |
| Effect on environment | Returns to natural cycles (compost, CO₂, water) | PERSISTS in environment. Causes pollution. |
E-Waste — A Growing Crisis
'E-waste (electronic waste) includes discarded computers, phones, TVs, batteries, and appliances. It contains: PRECIOUS METALS (gold, silver, copper — recoverable) AND TOXIC MATERIALS (lead, mercury, cadmium, arsenic — dangerous).'
India generates ~2 MILLION TONNES of e-waste annually — THIRD LARGEST in the world (after China and USA). Only about 20% is formally recycled. The rest is handled by INFORMAL SECTOR — often unsafely (burning wires to extract copper releases toxic fumes, acid baths for gold recovery poison water).
Solid Waste Management — Best Practices
Segregation: Separate waste into WET (biodegradable — kitchen waste) and DRY (non-biodegradable — plastic, metal, paper) at SOURCE. This is the MOST IMPORTANT step. Composting: Wet waste → decomposed in a compost pit or bin → produces RICH ORGANIC FERTILISER. Recycling: Dry waste → sorted → cleaned → processed into NEW products. Landfilling: Only NON-RECYCLABLE waste should go to landfill. Modern landfills have LINERS to prevent groundwater contamination and collect METHANE gas for energy. Waste-to-Energy: Burning non-recyclable waste in CONTROLLED conditions → produce ELECTRICITY. Controversial in India due to air pollution concerns.
13. AP Context — Environmental Issues
Godavari Pollution
The Godavari River — AP's LIFELINE — is increasingly POLLUTED. Sources: Industrial effluents from paper mills, sugar factories, and distilleries. Sewage from towns and cities along its banks. Agricultural runoff (pesticides, fertilisers). 'The Godavari Action Plan was launched to clean the river, but progress has been SLOW.'
Visakhapatnam Industrial Pollution
Vizag is a major INDUSTRIAL CENTRE — steel plant, petrochemicals, fertiliser plant, and a major PORT. Issues: Air pollution (PM 2.5, SO₂, NOₓ) from industries. Water pollution from industrial effluents in the Visakhapatnam coast. 'The 2020 gas leak at the LG Polymers plant in Vizag was a TRAGIC REMINDER of the risks of industrialisation without proper safety measures.'
Mangrove Conservation
Mangroves in the Godavari-Krishna delta (Coringa) are vital: Protect the coast from CYCLONES and TSUNAMIS. Provide NURSERY habitat for fish and shrimp. Support local LIVELIHOODS (fishing, honey collection). Store MORE carbon per hectare than tropical rainforests. Threats: Aquaculture expansion (shrimp farms), urbanisation, climate change-induced sea level rise.
14. Common Mistakes (Additional)
- 'Decomposers are at the top of the food chain' — Decomposers are NOT part of the linear food chain. They operate at ALL trophic levels, breaking down dead matter from every level.
- 'Ozone depletion causes global warming' — Ozone depletion and global warming are DIFFERENT issues. Ozone: caused by CFCs, affects UV radiation. Global warming: caused by greenhouse gases (CO₂, methane), affects Earth's temperature.
- 'All biodegradable waste is safe' — Biodegradable waste (like sewage) can be HARMFUL if it contains pathogens. It also produces METHANE (a powerful greenhouse gas) when it decomposes in landfills without oxygen.
15. Self-Test Questions
- Define an ECOSYSTEM. Name its TWO main components with examples.
- Differentiate between a FOOD CHAIN and a FOOD WEB.
- State and explain LINEDMANN'S 10% LAW with a numerical example.
- What is BIOLOGICAL MAGNIFICATION? Explain with the example of DDT.
- How do CFCs deplete the ozone layer? Write the steps.
- What is the MONTREAL PROTOCOL? Why is it considered a success?
- Differentiate between BIODEGRADABLE and NON-BIODEGRADABLE waste.
- What are MICROPLASTICS? Why are they a concern?
- Describe any TWO environmental issues facing Andhra Pradesh.
- Why is the role of DECOMPOSERS crucial in an ecosystem?
Answers to Selected Questions: Q3: Only 10% of energy transfers from one trophic level to the next. If grass has 100 J, the primary consumer gets 10 J, secondary gets 1 J, tertiary gets 0.1 J. The rest is lost as heat. Q5: CFCs rise to stratosphere → UV breaks CFCs → releases Cl → Cl destroys O₃ → each Cl atom can destroy 100,000 O₃ molecules.
