Introduction
An ecosystem is the structural and functional unit of nature where living organisms interact with one another and with their physical environment. The term "ecosystem" was proposed by A.G. Tansley in 1935.
According to NCERT, an ecosystem is a functional unit of nature where living organisms interact among themselves and with the surrounding physical environment.
Examples:
- Pond ecosystem
- Forest ecosystem
- Grassland ecosystem
- Desert ecosystem
- Marine ecosystem
Components of Ecosystem
An ecosystem consists of two major components:
1. Abiotic Components
These are the non-living components of the environment.
Physical Factors
- Light
- Temperature
- Water
- Wind
- Humidity
Inorganic Substances
- Carbon dioxide
- Oxygen
- Nitrogen
- Phosphorus
- Calcium
Organic Substances
- Carbohydrates
- Proteins
- Lipids
- Humic substances
2. Biotic Components
These are the living components of an ecosystem.
A. Producers (Autotrophs)
They manufacture their own food through photosynthesis.
Examples:
- Green plants
- Phytoplankton
- Algae
B. Consumers (Heterotrophs)
They depend on producers directly or indirectly.
Primary Consumers (Herbivores)
- Rabbit
- Deer
- Grasshopper
Secondary Consumers
- Frog
- Small fish
Tertiary Consumers
- Snake
- Large fish
Top Consumers
- Hawk
- Tiger
- Lion
C. Decomposers
They break down dead organic matter into simpler substances.
Examples:
- Bacteria
- Fungi
Importance:
- Nutrient recycling
- Maintaining ecosystem balance
Functions of Ecosystem
The four basic functions of an ecosystem are:
1. Productivity
Rate of biomass production per unit area per unit time.
Primary Productivity
Produced by producers.
Gross Primary Productivity (GPP)
Total rate of photosynthesis.
Net Primary Productivity (NPP)
NPP = GPP – Respiration Losses
NPP represents the biomass available to consumers.
2. Decomposition
Breakdown of dead organic matter into simpler substances.
Steps of Decomposition
Fragmentation
Detritus is broken into smaller particles by detritivores.
Examples:
- Earthworms
- Termites
Leaching
Water-soluble nutrients move into the soil.
Catabolism
Microbial enzymes degrade organic matter.
Humification
Formation of dark-colored humus.
Mineralisation
Release of inorganic nutrients into the soil.
Factors Affecting Decomposition
Faster in:
- Warm temperature
- Moist conditions
- Oxygen-rich environment
Slower in:
- Low temperature
- Anaerobic conditions
3. Energy Flow
Energy enters the ecosystem through sunlight.
Key Points
- Sun is the ultimate source of energy.
- Energy flow is unidirectional.
- Follows the First and Second Laws of Thermodynamics.
- Energy is lost as heat at each trophic level.
Food Chain
A sequence of organisms through which energy flows.
Types of Food Chains
Grazing Food Chain (GFC)
Grass → Grasshopper → Frog → Snake → Hawk
Starts from living green plants.
Detritus Food Chain (DFC)
Dead organic matter → Earthworm → Bird
Starts from detritus.
Food Web
A network of interconnected food chains.
Advantages:
- Greater ecosystem stability
- Alternative pathways for energy flow
Trophic Levels
Each step in a food chain is called a trophic level.
Trophic Level 1
Producers
Trophic Level 2
Primary consumers
Trophic Level 3
Secondary consumers
Trophic Level 4
Tertiary consumers
Trophic Level 5
Top carnivores
Ecological Pyramids
Graphical representation of trophic levels.
Proposed by:
Charles Elton (1927)
Types of Ecological Pyramids
1. Pyramid of Number
Represents number of organisms.
Can be:
- Upright
- Inverted
Example:
Tree Ecosystem → Inverted
2. Pyramid of Biomass
Represents total biomass.
Upright
Grassland ecosystem
Inverted
Aquatic ecosystem
3. Pyramid of Energy
Represents energy at each trophic level.
Important:
- Always upright
- Cannot be inverted
Reason:
Energy decreases at each trophic level.
10 Percent Law
Proposed by:
Raymond Lindeman (1942)
Only 10% of energy is transferred from one trophic level to the next.
Example:
- Producers = 10,000 kcal
- Primary Consumers = 1,000 kcal
- Secondary Consumers = 100 kcal
- Tertiary Consumers = 10 kcal
This explains why food chains are generally short.
Ecological Succession
Orderly and predictable process of community change over time.
Types
Primary Succession
Starts on a barren area without soil.
Examples:
- Bare rock
- Newly formed volcanic island
Slow process.
Secondary Succession
Starts where a community existed earlier.
Examples:
- Burnt forest
- Abandoned agricultural field
Faster process.
Stages of Succession
- Nudation
- Invasion
- Competition
- Reaction
- Stabilization
Final stable community:
Climax Community
Succession in Plants
Hydrarch (Hydrosere)
Starts in water.
Sequence:
Phytoplankton → Submerged plants → Floating plants → Reed swamp → Marsh meadow → Scrub → Forest
Xerarch (Xerosere)
Starts in dry habitat.
Sequence:
Lichens → Mosses → Herbs → Shrubs → Trees → Forest
Ecosystem Services
Benefits provided by ecosystems to humans.
Examples:
- Oxygen production
- Pollination
- Climate regulation
- Soil formation
- Water purification
According to Robert Costanza (1997), global ecosystem services were valued at approximately 33 trillion dollars annually.
Important NCERT Facts for NEET
- A.G. Tansley proposed the term Ecosystem.
- Charles Elton proposed Ecological Pyramid.
- Raymond Lindeman proposed the 10% Law.
- Energy flow is always unidirectional.
- Pyramid of Energy is always upright.
- Detritus food chain begins with dead organic matter.
- NPP = GPP – Respiration.
- Decomposers play a crucial role in nutrient cycling.
NEET Quick Revision Table
| Topic | Important Fact |
|---|---|
| Ecosystem | Functional unit of nature |
| Producer | Autotroph |
| Consumer | Heterotroph |
| Decomposer | Bacteria and fungi |
| GPP | Total photosynthesis |
| NPP | GPP – Respiration |
| Food Web | Interconnected food chains |
| 10% Law | Lindeman |
| Energy Pyramid | Always upright |
| Succession | Predictable community change |
Conclusion
Ecosystem is one of the most important chapters for NEET Biology. Questions are frequently asked from ecological pyramids, energy flow, decomposition, succession, trophic levels, and ecosystem services. A clear understanding of NCERT concepts and diagrams is essential for scoring full marks from this chapter.
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