1. Organisms and Environment
1.1 Ecology
Ecology is the study of interactions between organisms and their living (biotic) and non-living (abiotic) environment.
Levels of ecological organisation:
Organism → Population → Community → Ecosystem → Biome → Biosphere
1.2 Components of Environment
| Component | Examples |
|---|---|
| Biotic | Plants, animals, microorganisms |
| Abiotic | Temperature, water, light, soil, pH, minerals |
Example: In a pond, fish, algae and bacteria are biotic components, while water, temperature, sunlight and dissolved oxygen are abiotic components.
2. Population Interactions
Interactions between organisms of the same or different species are called biotic interactions.
Important interactions:
- Mutualism
- Competition
- Predation
- Parasitism
2.1 Mutualism (+/+)
In mutualism, both species benefit.
Examples:
- Lichen = Alga + Fungus
- Mycorrhiza = Fungus + Plant roots
- Flowering plants and pollinators
| Species A | Species B | Effect |
|---|---|---|
| + | + | Mutual benefit |
Example: In mycorrhiza, fungi help plant roots absorb water and minerals, while the plant provides food to the fungus.
2.2 Competition (-/-)
Competition occurs when organisms require the same limited resources.
Resources may include:
- Food
- Water
- Light
- Space
- Nutrients
- Mates
Types:
Intraspecific competition: Between individuals of the same species.
Interspecific competition: Between individuals of different species.
Example: Different plants growing closely together may compete for sunlight, water and minerals.
NEET Fact: Competition is often stronger when two species have similar resource requirements.
2.3 Predation (+/-)
In predation, one organism captures and consumes another organism.
- Predator: Organism that captures and eats another organism.
- Prey: Organism that is eaten.
Examples:
- Lion → Deer
- Snake → Rat
- Ladybird beetle → Aphid
Importance of predation:
- Controls prey population.
- Transfers energy through food chains.
- Can help maintain species diversity in communities.
2.4 Parasitism (+/-)
In parasitism, one organism obtains food and shelter from another organism and harms the host.
- Parasite: Benefits.
- Host: Suffers harm.
Examples:
- Cuscuta → Plant
- Tapeworm → Human
- Plasmodium → Human
Types:
- Ectoparasite: Lives on the external surface of the host.
- Endoparasite: Lives inside the host.
Example: Lice are ectoparasites, whereas tapeworms are endoparasites.
2.5 Summary of Population Interactions
| Interaction | Species 1 | Species 2 | Example |
|---|---|---|---|
| Mutualism | + | + | Lichen |
| Competition | – | – | Competition for resources |
| Predation | + | – | Lion–Deer |
| Parasitism | + | – | Tapeworm–Human |
3. Population Attributes
A population is a group of individuals of the same species living in a particular geographical area and interacting with one another.
Examples:
- All fish in a pond.
- All deer in a forest.
Important population attributes:
- Population density
- Natality
- Mortality
- Age structure
- Sex ratio
- Population growth
3.1 Population Density
The number of individuals of a population per unit area or volume is called population density.
Population density = Number of individuals / Area or volume
Population density may also be represented using:
- Biomass
- Percentage cover
- Relative density
3.2 Natality
Natality is the birth rate of a population during a particular period.
Higher natality → Population tends to increase.
3.3 Mortality
Mortality is the death rate of a population during a particular period.
Higher mortality → Population tends to decrease.
3.4 Immigration and Emigration
Immigration (I):
Movement of individuals into a population from another area.
Emigration (E):
Movement of individuals out of a population.
Population change can be represented as:
Population change = (Births + Immigration) − (Deaths + Emigration)
3.5 Population Growth
Population size changes continuously due to:
- Births
- Deaths
- Immigration
- Emigration
Two important growth patterns are:
- Exponential growth
- Logistic growth
3.6 Exponential Growth
When resources are unlimited or sufficiently abundant and environmental resistance is negligible, population may show exponential growth.
Equation:
dN/dt = rN
Where:
- N = Population size
- r = Intrinsic rate of natural increase
- t = Time
The graph is generally J-shaped.
Example: Bacteria may show rapid exponential growth under favourable laboratory conditions.
3.7 Logistic Growth
In natural ecosystems, resources are limited. Therefore, population growth eventually slows down.
Carrying capacity (K):
The maximum population size that an environment can support sustainably under given conditions.
Logistic growth:
- Initially slow.
- Becomes rapid.
- Slows near carrying capacity.
Equation:
dN/dt = rN (K − N)/K
The graph is S-shaped.
NEET Fact: Exponential growth assumes unlimited resources, whereas logistic growth considers limited resources and environmental resistance.
3.8 Age Structure
A population can be divided into age groups:
- Pre-reproductive
- Reproductive
- Post-reproductive
Age pyramids are generally:
| Population | Age Pyramid |
|---|---|
| Expanding | Broad base |
| Stable | Nearly bell-shaped |
| Declining | Narrow base |
Example: A population with a large number of young individuals may have a greater potential for future growth.
4. Ecosystem
4.1 Ecosystem: Definition
An ecosystem is a functional unit in which living organisms interact with one another and with their physical environment.
Basic structure:
Abiotic components + Biotic components = Ecosystem
4.2 Components of an Ecosystem
Abiotic Components
- Sunlight
- Temperature
- Water
- Air
- Soil
- Minerals
- pH
Biotic Components
1. Producers
- Mainly green plants and other autotrophs.
- Prepare organic food through photosynthesis.
2. Consumers
- Cannot prepare their own food.
- Depend directly or indirectly on producers.
Major categories:
- Primary consumers → Herbivores
- Secondary consumers
- Tertiary consumers
- Top consumers
3. Decomposers
- Break down dead organic matter.
- Mainly bacteria and fungi.
5. Productivity
Productivity refers to the rate of biomass production in an ecosystem.
5.1 Primary Productivity
The rate at which producers synthesise organic matter is called primary productivity.
Two important terms:
Gross Primary Productivity (GPP):
Total amount of organic matter produced by plants through photosynthesis.
Net Primary Productivity (NPP):
NPP = GPP − Respiration losses
NPP represents the biomass available to consumers.
5.2 Secondary Productivity
The rate of formation of new organic matter by consumers is called secondary productivity.
6. Decomposition
Decomposition is the breakdown of complex organic matter present in dead organisms into simpler substances.
Major steps:
Fragmentation → Leaching → Catabolism → Humification → Mineralisation
6.1 Fragmentation
Detritivores break dead organic matter into smaller pieces.
Example: Earthworms fragment dead leaves.
6.2 Leaching
Water-soluble substances are dissolved and carried deeper into the soil.
6.3 Catabolism
Decomposer organisms such as bacteria and fungi release enzymes that break complex organic compounds into simpler substances.
6.4 Humification
Formation of a dark-coloured, amorphous and relatively resistant substance called humus.
Humus:
- Is resistant to decomposition.
- Helps improve soil quality and nutrient retention.
6.5 Mineralisation
Conversion of organic nutrients into inorganic forms that can become available to plants.
NEET Fact: Decomposition is generally faster under warm and moist conditions than under cold or dry conditions.
7. Energy Flow in an Ecosystem
The ultimate source of energy for most ecosystems is the Sun.
General energy flow:
Sun → Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers
Important features:
- Energy flow is unidirectional.
- Energy is not recycled like nutrients.
- A significant amount of energy is lost as heat at each trophic level.
7.1 Trophic Levels
| Trophic Level | Organisms |
|---|---|
| First | Producers |
| Second | Primary consumers |
| Third | Secondary consumers |
| Fourth | Tertiary consumers |
Example:
Grass → Grasshopper → Frog → Snake
- Grass = Producer
- Grasshopper = Primary consumer
- Frog = Secondary consumer
- Snake = Tertiary consumer
7.2 10% Law
According to Lindeman’s 10% law, approximately 10% of the energy at one trophic level is transferred to the next trophic level.
Example:
10,000 J → 1,000 J → 100 J → 10 J
Thus, energy available generally decreases at higher trophic levels.
8. Ecological Pyramids
Ecological pyramids represent trophic levels in an ecosystem.
Three main types:
- Pyramid of Number
- Pyramid of Biomass
- Pyramid of Energy
8.1 Pyramid of Number
Represents the number of organisms present at each trophic level.
It may be:
- Upright
- Inverted
- Spindle-shaped
Example: In a tree ecosystem, one large tree may support numerous insects, so the pyramid can be inverted.
8.2 Pyramid of Biomass
Represents the total biomass present at each trophic level.
- Usually upright in terrestrial ecosystems.
- May be inverted in some aquatic ecosystems.
Example: In an aquatic ecosystem, phytoplankton may have a lower standing biomass than their consumers because of their rapid turnover.
8.3 Pyramid of Energy
Represents the amount of energy available at each trophic level.
It is always upright.
Reason:
- Energy is lost as heat during transfer between trophic levels.
NEET Fact: Pyramid of energy can never be inverted.
9. Biodiversity
9.1 Concept of Biodiversity
Biodiversity refers to the variety and variability of living organisms present in a particular region or on Earth.
Three major levels:
- Genetic diversity
- Species diversity
- Ecological diversity
9.2 Genetic Diversity
Variation in genes among individuals of the same species.
Example: Different varieties of rice.
9.3 Species Diversity
Variety of different species present in an area.
Example: Tropical forests may contain hundreds of plant and animal species.
9.4 Ecological Diversity
Variety of ecosystems within a geographical region.
Examples:
- Forests
- Grasslands
- Deserts
- Wetlands
- Marine ecosystems
10. Patterns of Biodiversity
10.1 Latitudinal Gradient
Species diversity generally:
Decreases from Equator → Poles
Tropical regions generally have greater species richness than temperate and polar regions.
10.2 Species-Area Relationship
Larger areas generally support more species.
The relationship is represented by:
S = CAᶻ
Where:
- S = Species richness
- A = Area
- C = Constant
- Z = Regression coefficient
The species-area relationship is associated with the observations of Alexander von Humboldt.
NEET Fact: Species richness generally increases with increasing area, but the increase is not unlimited.
11. Importance of Biodiversity
Biodiversity is essential for ecosystem functioning and human welfare.
Major benefits include:
- Food resources
- Medicines
- Fuel
- Fibre
- Timber
- Pollination
- Nutrient cycling
- Soil formation
- Climate regulation
- Ecosystem stability
- Cultural and aesthetic value
11.1 Ecosystem Services
Nature provides many services that directly or indirectly benefit humans.
Examples:
- Bees and other insects → Pollination
- Forests → Carbon storage and climate regulation
- Wetlands → Water purification and flood regulation
- Plants → Oxygen production
- Decomposers → Nutrient recycling
12. Biodiversity Loss
Major causes of biodiversity loss are commonly described as the Evil Quartet.
Evil Quartet
- Habitat loss and fragmentation
- Over-exploitation
- Alien species invasion
- Co-extinctions
12.1 Habitat Loss and Fragmentation
Destruction or division of natural habitats is one of the major causes of biodiversity loss.
Causes:
- Deforestation
- Urbanisation
- Agricultural expansion
- Roads
- Dams
- Industrial development
12.2 Over-exploitation
Excessive use of biological resources can reduce populations and may eventually cause extinction.
Examples:
- Excessive hunting
- Overfishing
- Excessive logging
12.3 Alien Species Invasion
An alien species introduced into a new ecosystem may multiply rapidly and threaten native species.
Examples:
- Water hyacinth (Eichhornia)
- Lantana
- Parthenium
12.4 Co-extinction
When the extinction of one species causes the extinction of another species that depends on it, the phenomenon is called co-extinction.
Example: A host-specific parasite may become extinct if its host disappears.
13. Biodiversity Conservation
The main objective of biodiversity conservation is to protect:
- Species
- Genetic diversity
- Ecosystems
Two major approaches:
- In situ conservation
- Ex situ conservation
13.1 In Situ Conservation
Species are conserved in their natural habitats.
Examples:
- Biosphere reserves
- National parks
- Wildlife sanctuaries
- Sacred groves
13.2 Ex Situ Conservation
Species or genetic material are conserved outside their natural habitats.
Examples:
- Zoos
- Botanical gardens
- Seed banks
- Gene banks
- Cryopreservation
| In Situ Conservation | Ex Situ Conservation |
|---|---|
| Natural habitat | Outside natural habitat |
| Protects organisms within ecosystems | Focuses on selected species/genetic material |
| National park | Zoo |
| Wildlife sanctuary | Botanical garden |
| Biosphere reserve | Seed bank |
14. Biodiversity Hotspots
A biodiversity hotspot is a region that has:
- High levels of endemic species.
- Significant loss of original habitat.
Hotspots receive high conservation priority.
Major hotspot regions associated with India include:
- Western Ghats–Sri Lanka
- Himalaya
- Indo-Burma
- Sundaland — includes the Nicobar Islands.
NEET Fact: Biodiversity hotspots are important areas for prioritising conservation efforts.
15. Endangered Species
Species facing a very high risk of extinction in the wild are classified as endangered.
Major threats:
- Habitat destruction
- Hunting
- Pollution
- Climate change
- Invasive species
- Over-exploitation
Examples: Tiger, Asian elephant and several other species require conservation efforts to maintain viable populations.
16. Extinction
Extinction occurs when no living individuals of a species remain.
Example: Dodo is an extinct bird.
16.1 Types/Concepts of Extinction
Background extinction:
Natural extinction occurring gradually over geological time.
Mass extinction:
A large number of species become extinct during a relatively short geological period.
Anthropogenic extinction:
Extinction caused or strongly accelerated by human activities.
17. Red Data Book
The Red Data Book contains information about threatened species and their conservation status.
It helps in:
- Identifying threatened species.
- Conservation planning.
- Monitoring the status of species.
NEET Point: The IUCN Red List is a major global source of information on the conservation status of species.
18. Biosphere Reserves
A Biosphere Reserve is a large protected area designed to conserve biodiversity while also promoting sustainable use of natural resources.
It is generally divided into three zones:
Core Zone
- Most strictly protected area.
- Human activities are highly restricted.
Buffer Zone
- Surrounds the core zone.
- Research, education and compatible activities may be permitted.
Transition Zone
- Outer zone.
- Human activities and sustainable development are integrated with conservation.
19. National Parks
A National Park is a legally protected area established for the conservation of wildlife, natural habitats and ecosystems.
Main objectives:
- Wildlife protection
- Habitat conservation
- Ecosystem preservation
Examples: Jim Corbett National Park, Kanha National Park.
20. Wildlife Sanctuaries
A Wildlife Sanctuary is a protected area where wild animals and their habitats are conserved.
Depending on applicable laws and management rules, certain regulated human activities may be permitted.
Main objectives:
- Wildlife protection
- Habitat conservation
- Protection of threatened species
21. Sacred Groves
Sacred groves are patches of natural vegetation protected by local communities because of religious, cultural or traditional beliefs.
Important features:
- Cutting trees may be traditionally prohibited or highly restricted.
- They help conserve local biodiversity.
- They may provide refuge to rare and endemic species.
Examples in India:
- Khasi and Jaintia Hills — Meghalaya
- Sacred groves of the Western Ghats
- Community-protected forest patches in parts of the Himalayas
NEET Fact: Sacred groves are an important traditional example of in situ conservation.
22. Important NEET Concept Points
- Ecology deals with interactions between organisms and their environment.
- Population consists of individuals of the same species living in a particular area.
- Natality increases population size, while mortality decreases it.
- Immigration generally increases population size, while emigration decreases it.
- Exponential growth produces a J-shaped curve.
- Logistic growth produces an S-shaped curve.
- Carrying capacity is represented by K.
- Producers occupy the first trophic level.
- Energy flow in an ecosystem is unidirectional.
- Energy is progressively lost as heat at successive trophic levels.
- According to the 10% law, approximately 10% of energy is transferred to the next trophic level.
- Pyramid of energy is always upright.
- Biodiversity exists at genetic, species and ecosystem levels.
- Species diversity generally decreases from the equator towards the poles.
- Habitat loss and fragmentation are major causes of biodiversity loss.
- The Evil Quartet includes habitat loss, over-exploitation, alien species invasion and co-extinction.
- In situ conservation protects species in their natural habitats.
- Ex situ conservation protects species or genetic material outside their natural habitats.
- Biosphere reserves, national parks, wildlife sanctuaries and sacred groves are examples of in situ conservation.
- Zoos, botanical gardens, seed banks and gene banks are examples of ex situ conservation.
- Sacred groves represent traditional community-based biodiversity conservation.