- An ecosystem is a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment .
- Ecosystem varies greatly in size from a small pond to a large forest or a sea .
- Many ecologists regard the entire biosphere as a global ecosystem , as a composite of all local ecosystems on Earth.
Types of Ecosystem
- Natural Ecosystems – Occur naturally without human interference.
- Terrestrial: Found on land.
- Forest: Dense vegetation, high biodiversity.
- Grassland: Dominated by grasses, moderate rainfall.
- Desert: Low rainfall, sparse vegetation, extreme temperature.
- Tundra: Cold climate, permafrost, mosses and lichens.
- Aquatic: Found in water.
- Freshwater: Rivers, lakes, ponds – low salt content.
- Marine: Oceans, seas – high salt content, largest ecosystem.
- Terrestrial: Found on land.
- Artificial Ecosystems – Man-made and maintained by human activities.
- Crop fields, gardens, aquariums.
Ecosystem: Structure and Function
- Structure of Ecosystem
- The ecosystem consists of biotic (living) and abiotic (non-living) components.
- Biotic Components:
- Producers: Autotrophs (e.g., green plants) that convert solar energy into food.
- Consumers:
- Primary consumers: Herbivores (e.g., deer)
- Secondary/Tertiary consumers: Carnivores (e.g., lion)
- Decomposers: Break down dead organisms (e.g., fungi, bacteria).
- Abiotic Components:
- Non-living factors like light, temperature, water, soil, nutrients, etc.
- Function of Ecosystem
- Main functions:
a) Energy Flow
b) Nutrient Cycling
c) Decomposition
d) Productivity - Ecosystems ensure energy transfer and maintain ecological balance.
- Self-sustaining System:
- Energy enters via sunlight, flows through biotic components, and exits as heat.
- Nutrients are recycled within the system (unlike energy).
- Main functions:
Basic Components of Ecosystem:
1. Productivity
- Definition: Productivity refers to the rate of biomass production in an ecosystem over time. It is a key functional aspect of ecosystems.
- Types of Productivity: a) Gross Primary Productivity (GPP)
- Total amount of energy captured by producers (plants) during photosynthesis.
- Includes energy used in respiration. b) Net Primary Productivity (NPP)
- Energy left after respiration, available to herbivores and decomposers.
- Formula: NPP = GPP – R (Respiration loss)
- NPP represents energy stored as biomass. c) Secondary Productivity
- Rate at which consumers (herbivores, carnivores) form new biomass by feeding on producers or other consumers.
- It depends on the efficiency of energy transfer at consumer levels. d) Net Ecosystem Productivity (NEP)
- Net energy or biomass accumulation in an ecosystem after accounting for all losses.
- Formula: NEP = GPP – (Respiration by producers + decomposers + consumers)
- Productivity varies with:
- Light intensity, temperature, water availability, nutrients, and type of vegetation.
- Tropical forests show high NPP; deserts and oceans have low NPP.
- Comparison Table of Productivity Types:
| Type | Occurs In | Formula / Definition | Availability to |
|---|---|---|---|
| GPP | Producers | Total energy fixed during photosynthesis | Not directly available |
| NPP | Producers | GPP – Respiration | Available to consumers |
| Secondary Productivity | Consumers | Biomass formed from eating producers/consumers | Consumer biomass |
| NEP | Whole ecosystem | GPP – All respiration losses | Indicates carbon balance |
2. Decomposition
- Definition: Decomposition is the breakdown of complex organic matter (dead plants, animals, feces) into simpler inorganic substances by decomposers.
- It is essential for nutrient recycling and soil fertility.
- Steps of Decomposition:
- Fragmentation
- Detritivores (earthworms, termites) break down dead material into smaller particles.
- Increases surface area for microbial action.
- Leaching
- Water-soluble nutrients (like salts) are removed from detritus and absorbed into the soil.
- Catabolism
- Microorganisms (bacteria and fungi) break down fragmented material into simpler molecules using enzymes.
- Humification
- Formation of humus, a dark-colored, stable substance rich in nutrients and resistant to microbial action.
- Mineralisation
- Microbes further decompose humus and release inorganic nutrients (e.g., nitrates, phosphates) into the soil.
- Types of Decomposers:
- Microfauna: Bacteria, fungi
- Macrofauna: Earthworms, millipedes
- Decomposition Rate Depends On:
- Litter quality (e.g., cellulose-rich matter decomposes faster than lignin-rich)
- Environmental factors like temperature and moisture
- Factors Affecting Decomposition:
| Factor | Effect on Decomposition |
|---|---|
| Temperature | High temperature speeds up microbial activity |
| Moisture | Moderate moisture enhances decomposition |
| Oxygen | Aerobic conditions promote faster breakdown |
| Chemical Nature | Lignin and chitin slow decomposition; soft tissues decompose faster |
| Microorganism Type | Efficient microbes speed up decomposition |
3. Energy Flow
- Definition: Energy flow is the unidirectional movement of energy through the trophic levels in an ecosystem.
- Unlike nutrients, energy is not recycled; it flows and is lost as heat.
- Trophic Levels:
- Each step in the food chain where energy is transferred.
- Levels:
- Producers – Green plants, algae (autotrophs)
- Primary Consumers – Herbivores (e.g., deer, grasshopper)
- Secondary Consumers – Carnivores (e.g., frog, small birds)
- Tertiary Consumers – Top predators (e.g., lion, hawk)
- Food Chains:
a) Grazing Food Chain (GFC)- Starts with green plants (e.g., grass → grasshopper → frog → snake).
- Begins with dead organic matter (e.g., leaf litter → earthworm → bird).
- Food Web:
- Interconnected food chains in an ecosystem.
- Ensures stability and resilience.
- Ten Percent Law (Lindeman’s Law):
- Only 10% of energy is transferred from one trophic level to the next.
- 90% is lost as heat or used in metabolism.
- Energy Flow Diagram:
Sunlight
↓
Producers (1000 J)
↓ 10%
Herbivores (100 J)
↓ 10%
Carnivores (10 J)
↓ 10%
Top Carnivores (1 J)- Importance of Energy Flow:
- Supports all life processes.
- Determines trophic structure and ecosystem dynamics.
Summary:
- Productivity measures how much energy is made and stored.
- Decomposition recycles nutrients through specific steps.
- Energy flow is a one-way stream from sun to producers to consumers, with major losses at each level.
- Together, these components maintain balance, stability, and sustainability in ecosystems.
Frequently Asked Topics in Ecosystem (NEET)
- Types of Productivity (GPP, NPP, etc.)
- Definitions, formulae, comparison
- Direct MCQs and match-the-column type questions
- Ten Percent Law of Energy Transfer
- Application-based questions
- Energy flow pyramid logic
- Decomposition Process
- Steps (Fragmentation, Leaching, Catabolism, etc.)
- Order of steps is often asked
- Factors affecting decomposition
- Ecological Pyramids
- Types: Pyramid of Number, Biomass, Energy
- Shape and exceptions (e.g., inverted biomass in aquatic systems)
- MCQs on which pyramid is always upright (Answer: energy)
- Food Chain vs. Food Web
- Features, stability of food web
- Detritus vs. Grazing food chain
- Trophic Levels
- Questions based on levels in a food chain
- Identification of producer/consumer levels
- Standing Crop vs. Standing State
- Basic definitions asked in one-liners
- Carbon Cycle & Nutrient Cycling
- Diagram and key steps in biogeochemical cycles
- NCERT-based factual questions
Important Topics for NEET 2025
Based on trends and NCERT focus, prioritize the following:
| Topic | Why It’s Important |
|---|---|
| Productivity (GPP, NPP, etc.) | Frequently asked in match-the-pair, formula-based questions |
| Energy Flow & Ten Percent Law | Easy marks; graphical/logical questions |
| Decomposition Steps | NCERT lines often directly quoted in MCQs |
| Ecological Pyramids | Conceptual + diagram-based; energy pyramid always upright |
| Food Chain vs. Food Web | Often tested in assertion-reason or “choose the correct” type |
| Nutrient Cycling (Carbon Cycle) | Common in questions with diagrams |
| Ecosystem Functions | General but essential for indirect questions |
Tips for NEET 2025 (for Ecosystem):
- Focus on NCERT line-by-line, especially diagrams and flowcharts.
- Be thorough with definitions, examples, and sequences (esp. decomposition steps).
- Solve previous 10 years’ NEET questions from this chapter — patterns repeat.
- Practice MCQs on formula-based productivity and pyramid logic.