Ecology

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Ecology — Interactions Between Organisms and Their Environment

Key Definitions

• Ecosystem: community of living organisms + their physical environment, interacting as a unit
• Biome: large geographical region with characteristic climate and species
• Habitat: natural environment of an organism
• Ecological niche: role and function of a species in its ecosystem (Fundamental niche vs Realized niche)

Levels of Ecological Organisation Organism → Population → Community → Ecosystem → Biome → Biosphere

Population: group of individuals of same species in a given area

• Population growth models: $N_t = N_0 e^{rt}$ (exponential); $N_t = K/(1+[(K-N_0)/N_0]e^{-rt})$ (logistic)
• $r$ = intrinsic rate of increase; $K$ = carrying capacity

Community: assemblage of populations of different species living together

• Interspecific interactions: competition (-/-), predation (+/-), parasitism (+/-), mutualism (+/+), commensalism (+/0)

Food Chains and Energy Flow

Energy flow (10% law):

• Only ~10% of energy is transferred from one trophic level to the next
• Plants (producers) → Herbivores (primary consumers) → Carnivores (secondary consumers) → Top carnivores
• Energy decreases at each level → limits number of trophic levels

Trophic levels:

Level	Organism	Example
1st	Producers	Plants, algae
2nd	Primary consumers	Rabbit, deer
3rd	Secondary consumers	Snake, fox
4th	Tertiary consumers	Hawk, lion

⚡ NEET tip: In a food chain, the number of trophic levels is limited by energy loss (~90% lost at each step). Maximum 4–5 trophic levels usually.

Ecological Pyramids

• Pyramid of numbers: number of organisms at each level (can be inverted for parasites)
• Pyramid of biomass: dry weight of organisms at each level (can be inverted for ocean — small phytoplankton, large whales)
• Pyramid of energy: always upright — energy decreases at each level

---

🟡 Standard — Regular Study (2d–2mo)

For students who want genuine understanding.

Ecology — Detailed Study Guide

1. Biogeochemical Cycles

Water cycle (Hydrological cycle):

• Evaporation → condensation → precipitation → runoff → infiltration → transpiration
• Transpiration pull: cohesion-tension theory — water lost through stomata creates negative pressure pulling water up from roots
• Annual global transpiration: ~40% of total precipitation over land

Carbon cycle:

• CO₂ fixation: photosynthesis (plants) → carbon in organic compounds
• Decomposition: heterotrophic respiration → CO₂ back to atmosphere
• Combustion: burning fossil fuels → CO₂ to atmosphere
• Perturbation: anthropogenic CO₂ emissions → global warming

Nitrogen cycle:

1. Nitrogen fixation: N₂ → NH₃ (by Rhizobium in legume root nodules, or lightning)
2. Nitrification: NH₃ → NO₂⁻ (nitrite) → NO₃⁻ (nitrate) — by Nitrosomonas and Nitrobacter
3. Assimilation: plants absorb nitrate → incorporate into amino acids
4. Ammonification: dead organic matter → NH₃ (by decomposers)
5. Denitrification: NO₃⁻ → N₂ (by Pseudomonas in anaerobic conditions)

⚡ NEET Quick Recall: Legume crops (peas, beans, clover) fix ~100-500 kg N/hectare/year — farmers rotate crops to naturally fertilise soil.

Phosphorus cycle:

• No atmospheric pool — phosphate ($PO_4^{3-}$)Weathering of rocks → uptake by plants → food chain → decomposition → sedimentary rocks
• Limited by phosphate rock availability — major fertiliser component

2. Population Ecology — Growth Models

Exponential growth: $dN/dt = rN$ — occurs when resources are unlimited (invasive species, bacterial growth)

Logistic growth: $dN/dt = rN(1-N/K)$ — S-shaped curve; growth slows as N approaches K

• At N < K: population grows
• At N = K: zero growth (population at carrying capacity)
• Overshoot and dieback: when population exceeds K, resources depleted → population crashes

Population interactions (Lotka-Volterra equations):

• Competition: both species harmed (-/-) — Gause’s competitive exclusion principle: two species cannot occupy the same niche indefinitely
• Predator-prey: cyclical population oscillations — hare-lynx data (10-year cycle)

3. Ecosystem Structure

Abiotic factors: temperature, light, water, soil, wind, altitude Biotic factors: predation, competition, symbiosis, decomposition

Biomes of India:

Biome	Climate	Vegetation
Tropical rainforest	Hot, wet (200 cm rain)	Evergreen trees,多层林冠
Deciduous forest	Seasonal	Shed leaves in dry season
Desert	Arid	Xerophytic plants (succulents)
Himalayan	Cold, alpine	Conifers, rhododendrons
Mangrove	Coastal saline	Avicennia, Rhizophora

4. Ecological Succession

Primary succession: bare rock → lichen (pioneers) → moss → herbaceous → shrub → forest — takes 100s-1000s of years

Secondary succession: after disturbance (fire, agriculture) → faster — soil already present

Climax community: stable, self-perpetuating endpoint — but most ecosystems are in dynamic equilibrium (no true “climax” in changing climate)

Ecotone: transitional zone between two ecosystems (e.g., marsh between water and land) — often high biodiversity

5. Biodiversity and Conservation

Measures of diversity:

• Species richness: number of species
• Species evenness: relative abundance of each species
• Shannon diversity index: $H = -\sum p_i \ln(p_i)$

Biodiversity hotspots (India):

• Western Ghats — 6,000+ plant species, 139 endemic amphibians
• Eastern Himalaya — high endemism, glacial forests
• Sundarbans — mangrove ecosystem

Threats:

• Habitat loss (deforestation)
• Overexploitation
• Invasive species
• Climate change
• Pollution (eutrophication)

Conservation strategies:

• In situ: national parks, wildlife sanctuaries, biosphere reserves
• Ex situ: seed banks, botanical gardens, cryopreservation
• Legal: WPA (Wildlife Protection Act, 1972), CITES (treaty against illegal trade)

⚡ NEET tip: India has 18 biosphere reserves, 103 national parks, 553 wildlife sanctuaries.

---

🔴 Extended — Deep Study (3mo+)

Comprehensive theory for serious preparation.

Ecology — Deep Dive

1. Productivity of Ecosystems

Primary productivity: rate of biomass production by producers

• Gross primary productivity (GPP): total CO₂ fixed by photosynthesis
• Net primary productivity (NPP): GPP - respiration (R) = GPP - R
• NPP per year: terrestrial ≈ 56.4 Gt C/yr; marine ≈ 48.5 Gt C/yr

Secondary productivity: biomass produced by consumers per unit time — always less than NPP (low trophic efficiency ~10%)

Energy flow calculations:

• Energy at producer level: 10,000 kJ/m²/day
• At herbivore level: 10,000 × 0.1 = 1,000 kJ/m²/day
• At carnivore level: 1,000 × 0.1 = 100 kJ/m²/day
• At top carnivore: 100 × 0.1 = 10 kJ/m²/day

2. Ecological Efficiencies

Efficiency	Definition
Photosynthetic efficiency	% solar energy converted to chemical energy (~1-2%)
Trophic efficiency	% energy transferred between trophic levels (~10%)
Consumer efficiency	% producer biomass consumed (~1/3)
Assimilation efficiency	% ingested food assimilated (~50-90%)
Production efficiency	% assimilated energy used for growth (~10-40%)

3. Biogeographical Regions (Wallace’s Realms)

Six major realms: Palearctic, Nearctic, Neotropical, Afrotropical, Oriental, Australian

• Each evolved distinct fauna/flora due to continental isolation
• India is in Oriental realm — shares some Palearctic elements in Himalayas

Island biogeography theory (MacArthur & Wilson):

• Species richness on islands is balance between immigration rate and extinction rate
• Larger islands and islands closer to mainland have higher species richness
• Equilibrium point: when immigration = extinction

4. Climate Change and Ecology

Greenhouse effect:

• Natural: CO₂, CH₄, N₂O absorb infra-red radiation → warming
• Enhanced (anthropogenic): fossil fuel combustion, deforestation → increased greenhouse gases → global warming

• Ozone layer depletion:*

• CFCs break down ozone: $CFCl_3 + uv \rightarrow Cl^\bullet + CFCl_2^\bullet$; $Cl^\bullet + O_3 \rightarrow ClO^\bullet + O_2$; $ClO^\bullet + O \rightarrow Cl^\bullet + O_2$
• One chlorine atom destroys ~100,000 ozone molecules
• Montreal Protocol (1987): global treaty to phase out CFCs — success story

Eutrophication:

• Runoff of fertilisers → lakes → algal bloom → death of aquatic plants → decomposition → oxygen depletion → fish die
• Cultural eutrophication: accelerated by human activities

5. Human Population Ecology

• Demographic transition: as countries develop, birth rate and death rate both fall (Stage 2→3→4)
• India’s population: ~1.4 billion (2024); projected to surpass China
• Population momentum: even with replacement-level fertility, population continues to grow due to young age structure
• IPAT equation: Environmental Impact = Population × Affluence × Technology

6. Applied Ecology

Biological control of pests:

• Use of natural enemies to control pests (reduces pesticide use)
• Example: ladybird beetle controls aphid population; Bacillus thuringiensis (Bt) controls mosquito larvae

Biomagnification:

• Increase in concentration of persistent toxic substances at each trophic level
• Example: DDT in food chain: zooplankton (0.04 ppm) → small fish (0.5 ppm) → large fish (2 ppm) → fish-eating birds (25 ppm)
• Leads to eggshell thinning in birds (DDT interferes with calcium metabolism)

Carbon sequestration:

• Forests act as carbon sinks — photosynthesis draws down CO₂
• Tropical forests: ~50% of terrestrial NPP
• Deforestation releases stored carbon → net source

7. Previous Year NEET Questions on Ecology

• 2023 Qn: “Which of the following is a biogeochemical cycle?” → Nitrogen cycle (not nitrogen fixation alone)
• 2022 Qn: “In a food chain, energy transfer efficiency is approximately:” → 10% (10% law)
• 2021 Qn: “The role of decomposers in an ecosystem is:” → Break down dead organic matter, release nutrients back to soil

---

📊 NEET UG Exam Essentials

Detail	Value
Questions	200 (180 mandatory + 10 optional)
Time	3h 20min
Marks	720
Section	Physics (50), Chemistry (50), Biology (100)
Negative	−1 for wrong answer
Qualifying	50th percentile (general category)

🎯 High-Yield Topics for NEET UG

• Human Physiology — 18 marks
• Genetics & Evolution — 16 marks
• Ecology & Environment — 12 marks
• Organic Chemistry (Reactions) — 15 marks
• Electrodynamics (Physics) — 18 marks
• Chemical Equilibrium — 10 marks

📝 Previous Year Question Patterns

• Q: “A particle moves in a circle…” [2024 Physics — 2 marks]
• Q: “Identify the incorrect statement about DNA…” [2024 Biology — 4 marks]
• Q: “The major product ofFriedel-Crafts acylation is…” [2024 Chemistry — 3 marks]

💡 Pro Tips

• NCERT Biology is the single most important resource — 80%+ questions are from NCERT lines
• Focus on Human Physiology, Genetics, and Ecology — together they make ~40% of Biology
• In Physics, master Electrostatics + Current Electricity + Magnetism (combined ~20%)
• Organic Chemistry: learn named reactions with mechanisms — they repeat across years

🔗 Official Resources

• NTA Official
• NEET Syllabus PDF

---

Content adapted based on your selected roadmap duration. Switch tiers using the pill selector above.