Ecology & Environment — NEET revision
The full NEET Ecology & Environment unit — the highest-weightage Biology area — in one place: concept notes on organisms and populations, ecosystems, biodiversity and conservation, differentiate tables, common doubts and quick-recall facts.
Key concepts
Unit 10 covers population attributes and interactions; ecosystem structure, productivity, decomposition and energy flow; ecological pyramids; and biodiversity patterns, importance, loss and conservation through hotspots, protected areas and sacred groves.
Population attributes
Population-level properties include density, birth rate, death rate, sex ratio and age distribution. These cannot be meaningfully assigned to a single individual.
- Birth rate + death rate change population size
- Age structure: pre-reproductive, reproductive, post-reproductive
Age pyramids
Age distributions may indicate expanding, stable or declining populations depending on the proportion in younger age classes.
- Expanding: broad young base
- Declining: fewer young individuals
Exponential growth
With unlimited resources, population increase can approximate exponential growth: dN/dt = rN, producing a J-shaped curve.
- dN/dt = rN
- J-shaped
Logistic growth & carrying capacity
When resources become limiting, growth slows near carrying capacity K: dN/dt = rN(1 − N/K), producing an S-shaped curve.
- K = carrying capacity
- S-shaped
Mutualism
Both species benefit. Examples include lichens, mycorrhiza and many plant-pollinator relationships.
- Mutualism: +/+
Competition
Both species are negatively affected when they use a limiting resource. Competition can occur within or between species.
- Competition: −/−
Predation
The predator benefits while prey is harmed. Predation transfers energy and can regulate prey populations.
- Predation: +/−
Parasitism
The parasite benefits while the host is harmed, usually without immediate killing because the host is the parasite's resource.
- Parasitism: +/−
Ecosystem components
An ecosystem includes abiotic factors and interacting producers, consumers and decomposers.
- Biotic + abiotic components
Productivity
Primary productivity is the rate at which producers form biomass. Gross primary productivity (GPP) includes all fixed energy; net primary productivity (NPP) is what remains after plant respiration.
- NPP = GPP − R
- NPP is available to consumers
Decomposition
Detritus is broken down through fragmentation, leaching, catabolism, humification and mineralisation. Warm, moist and oxygenated conditions usually speed decomposition.
- Fragmentation · leaching · catabolism · humification · mineralisation
Food chains & food webs
Energy passes through trophic levels in grazing and detritus food chains; interconnected chains form food webs.
- Producer → consumers → decomposers
Energy flow & 10% law
Energy flow is unidirectional. Roughly 10% of energy at one trophic level is transferred to the next in Lindeman's simplified rule.
- Sun → producers → consumers
- 10% law
Ecological pyramids
Pyramids show number, biomass or energy at successive trophic levels. The energy pyramid is always upright.
- Energy pyramid always upright
- Biomass can be inverted in aquatic systems
Biodiversity levels & patterns
Biodiversity includes genetic, species and ecosystem diversity. Species richness generally increases toward the tropics; species–area relationships show richness rising with area.
- Latitudinal gradient: tropics richer
- log S = log C + Z log A
Importance of biodiversity
Biodiversity supports ecosystem productivity, stability and services such as pollination, nutrient cycling, climate regulation and resources.
- Ecological + economic + ethical value
Loss of biodiversity
Major drivers include habitat loss/fragmentation, over-exploitation, alien species invasion and co-extinctions — the 'evil quartet'.
- Habitat loss is the major driver
- Evil quartet
In-situ conservation
In-situ conservation protects species in natural habitats through biosphere reserves, national parks, wildlife sanctuaries and sacred groves.
- Protect habitat + interacting community
Ex-situ conservation
Ex-situ conservation protects components outside natural habitats through zoos, botanical gardens, seed/gene banks and cryopreservation.
- Outside natural habitat
Hotspots, Red Data Book & extinction
Biodiversity hotspots combine exceptional endemism with severe habitat loss. Red lists/data books record conservation status; endangered species face high extinction risk.
- Hotspots prioritise conservation
- Extinction = irreversible species loss
Protected-area terms
Biosphere reserves are large landscapes with conservation and sustainable-use zones; national parks and sanctuaries are protected areas with differing rules; sacred groves are community-protected natural patches.
- Biosphere reserve · national park · sanctuary · sacred grove
Differentiate population and conservation concepts
Signs (+/−), growth curves and conservation location make these easy.
Species interactions
| Mutualism | + / + |
| Competition | − / − |
| Predation | + / − |
| Parasitism | + / − |
Population growth
| Exponential | Unlimited resources; J-shaped; dN/dt = rN |
| Logistic | Limited resources; S-shaped; carrying capacity K |
High-yield distinctions
These distinctions connect ecology to conservation.
GPP vs NPP ★
GPP
- Total primary production
- Before producer respiration
- Gross capture
NPP
- GPP − respiration
- Biomass available for consumers
- Net storage
In-situ vs ex-situ conservation ★
In situ
- Natural habitat
- Protects ecosystems/interactions
- Parks, sanctuaries, sacred groves
Ex situ
- Outside natural habitat
- Focused on selected species/material
- Zoos, gardens, gene banks
Predation vs parasitism
Predation
- Predator kills/consumes prey
- Interaction often brief
- Energy transfer
Parasitism
- Parasite lives on/in host
- Usually prolonged
- Host harmed but often not killed immediately
Pyramid of biomass vs energy ★
Biomass
- Can be upright or inverted
- Standing crop at a time
- Aquatic systems may invert
Energy
- Always upright
- Flow per area per time
- Energy lost at each transfer
Common NEET doubts
Can an individual organism have a birth rate?
No. Birth rate is a population attribute.
Does exponential growth continue indefinitely in nature?
Usually no. Resource limitation causes growth to deviate toward logistic behaviour.
Are predation and parasitism both +/− interactions?
Yes, but predators usually kill and consume prey, whereas parasites depend on a host over a longer period.
Is NPP larger than GPP?
No. NPP = GPP − respiration, so it is lower than or equal to GPP.
Can the energy pyramid be inverted?
No. Energy is lost at each trophic transfer, so the energy pyramid is always upright.
Does the 10% law mean exactly 10.0% always passes to the next level?
No. It is a simplified ecological rule of thumb used in NCERT/NEET, not an exact universal constant.
Is ex-situ conservation better than in-situ conservation in every case?
No. They are complementary. In-situ protects species with their habitats and interactions; ex-situ can rescue or maintain selected threatened populations/material.
Are hotspots simply places with many species?
They require high endemism plus severe habitat loss; species richness alone is not enough.
Are sacred groves formal zoos or gene banks?
No. They are natural patches protected by local communities, so they are in-situ conservation.
Quick recall
Q. Population growth equations for exponential and logistic growth?
dN/dt = rN; dN/dt = rN(1 − N/K).
Q. What does K represent?
Carrying capacity.
Q. Signs for mutualism, competition, predation and parasitism?
+/+, −/−, +/−, +/−.
Q. Define NPP.
NPP = GPP − producer respiration.
Q. Name the five major decomposition steps.
Fragmentation, leaching, catabolism, humification and mineralisation.
Q. State the 10% law.
About 10% of energy at one trophic level is transferred to the next.
Q. Which ecological pyramid is always upright?
The pyramid of energy.
Q. What is the species–area relationship?
Species richness increases with area; log S = log C + Z log A.
Q. Name the 'evil quartet'.
Habitat loss/fragmentation, over-exploitation, alien species invasion and co-extinctions.
Q. Give two in-situ conservation examples.
National parks, wildlife sanctuaries, biosphere reserves or sacred groves.
Q. Give two ex-situ conservation examples.
Zoos, botanical gardens, seed/gene banks or cryopreservation.
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