Ecology and Environment

Why This Chapter Matters

Ecology carries 6-10 marks in NEET. Ecosystem components, food chains, energy flow (10% rule), biogeochemical cycles, biodiversity, and environmental issues are all tested.

Core Concepts

1. Organism and Environment

Abiotic factors: Temperature, light, water, soil (edaphic), wind, humidity

Biotic factors: Interactions between organisms

Adaptations:

Xerophytes: plants adapted to dry conditions (thick cuticle, sunken stomata, CAM photosynthesis — Opuntia)

Hydrophytes: aquatic plants (Hydrilla, Lotus)

Thermoregulation: endotherms regulate body temperature; ectotherms depend on environment

Population attributes:

Birth rate, death rate, sex ratio, age distribution

Population growth: J-shaped (exponential) or S-shaped (logistic) curves

Logistic growth: r = intrinsic rate of natural increase, K = carrying capacity

S-curve formula: dN/dt = rN(K-N)/K

2. Population Interactions

|---|---|---|---|

Gause's Competitive Exclusion Principle: Two species with similar niches cannot coexist indefinitely; one excludes the other.

3. Ecosystem

Components:

Abiotic: sunlight, water, soil, temperature

Biotic: producers (autotrophs), consumers (heterotrophs), decomposers

Trophic levels:

T1: Producers (grass, phytoplankton)

T2: Primary consumers (grasshopper, zooplankton)

T3: Secondary consumers (frog, small fish)

T4: Tertiary consumers (snake, large fish)

Energy flow:

Only ~10% of energy transferred to next trophic level (10% law, Lindeman 1942)

90% lost as heat, respiration, and waste

Maximum trophic levels in most ecosystems: 3-4

Standing crop: Amount of living biomass at each trophic level.

Pyramid of energy: always upright (energy always decreases up)

Pyramid of biomass: mostly upright; can be inverted in aquatic ecosystems (phytoplankton < zooplankton)

Pyramid of numbers: can be inverted (one tree supports many insects)

Productivity:

Gross Primary Productivity (GPP): total photosynthesis

Net Primary Productivity (NPP) = GPP − Respiration

Net Secondary Productivity (NSP) = growth of consumers

Decomposition:

Detritus → Fragmentation (physical) → Leaching (water dissolves nutrients) → Catabolism (enzyme breakdown) → Mineralisation → Humification → Humus

4. Biogeochemical Cycles

Carbon cycle: Photosynthesis (fixes CO₂), respiration (releases CO₂), decomposition, combustion.

Nitrogen cycle: N₂ fixation → nitrification → assimilation → ammonification → denitrification

Phosphorus cycle: No atmospheric phase. Rocks → soil → organisms → back to soil (weathering, mining, runoff).

Hydrological cycle: Evaporation → condensation → precipitation → runoff/infiltration.

5. Biodiversity

Three levels: Genetic, Species, Ecosystem diversity

Hotspots: Regions with high endemism and high biodiversity threat.

India's hotspots: Western Ghats + Sri Lanka, Indo-Burma, Himalayas, Sundaland (partly)

Global hotspots: 36 (originally 25) — cover 2.5% of Earth's land, hold 44% of plant species

Species diversity: Measured by species richness and relative abundance.

Threatened species categories (IUCN):

Extinct → Extinct in Wild → Critically Endangered → Endangered → Vulnerable → Near Threatened → Least Concern

Biodiversity loss causes (HIPPO):

H: Habitat loss and fragmentation (most important)

I: Invasive species

P: Pollution

P: Population growth (human)

O: Overexploitation (hunting, fishing)

Conservation:

In situ: within natural habitat — national parks, wildlife sanctuaries, biosphere reserves

Ex situ: outside habitat — zoos, botanical gardens, seed banks, cryopreservation

6. Environmental Issues

Air pollution: CO, CO₂, SO₂, NO₂, particulate matter.

Photochemical smog: formed from NOx + hydrocarbons + sunlight → ozone + PAN (peroxyacetyl nitrate).

Ozone depletion: CFCs release Cl atoms → destroy O₃.

Water pollution: BOD (Biochemical Oxygen Demand) — indicator of organic pollution. High BOD = polluted.

Eutrophication: excess nutrients → algal bloom → O₂ depletion → death of aquatic organisms.

Biomagnification: Persistent chemicals (DDT) increase in concentration up food chain.

Solid waste: Municipal solid waste, e-waste, nuclear waste.

PYQs (NEET)

NEET 2023: Which population growth model shows sigmoid (S-shaped) curve?

Logistic growth model. Shows S-shaped curve when population growth is limited by carrying capacity.

NEET 2022: The most important cause of biodiversity loss globally is:

Habitat loss and fragmentation — primarily due to deforestation and agricultural expansion.

NEET 2021: Pyramid of biomass is inverted in:

Aquatic ecosystems — phytoplankton (producers) have low biomass but high productivity; zooplankton consume much more and have higher total biomass at any given time.

NEET 2020: BOD is used to measure:

Organic pollution in water bodies. High BOD = high organic pollution = low dissolved O₂.

Revision Notes

INTERACTIONS (A/B):
Mutualism: +/+ | Commensalism: +/0 | Predation: +/- | Parasitism: +/- | Competition: -/- | Amensalism: 0/-

10% ENERGY LAW (Lindeman): only 10% of energy transferred to next trophic level
→ max 3-4 trophic levels practical

PYRAMIDS:
Energy: always upright
Biomass: mostly upright; inverted in aquatic
Numbers: can be inverted

PRODUCTIVITY:
GPP = total photosynthesis
NPP = GPP - Respiration

BIODIVERSITY HOTSPOTS (India):
Western Ghats + Sri Lanka | Indo-Burma | Himalayas | Sundaland

HIPPO (causes of biodiversity loss):
Habitat loss | Invasive species | Pollution | Population | Overexploitation

CONSERVATION:
In situ: national parks, sanctuaries, biosphere reserves
Ex situ: zoos, botanical gardens, seed banks, cryopreservation

BOD: high = polluted water | Eutrophication: excess nutrients → algal bloom → O₂ depletion