An ecosystem is the basic functional unit of ecology where living organisms interact with their non-living environment.

Structural Components

• Biotic Components: Includes producers (autotrophs), consumers (heterotrophs), and decomposers (saprotrophs).
• Abiotic Components: Includes inorganic substances (C, N, H2O), organic compounds (proteins, lipids), and climatic factors (temperature, light).

Ecosystem stability refers to the ability of an ecosystem to maintain a steady state (homeostasis) or return to it after a disturbance. This is maintained through complex species interactions and feedback loops that regulate energy and nutrient flow.

Energy flow in an ecosystem is unidirectional, moving from the sun to producers and then through various consumer levels.

Key Principles:

• Energy Flow Models: Models like the single-channel or Y-shaped model illustrate how energy is lost at each step.
• Ecological Efficiencies: This refers to the percentage of energy transferred from one trophic level to the next. Generally, only about 10% of the energy is transferred (Lindeman's 10% law).

Productivity is the rate at which organic matter is created in an ecosystem.

• Primary Productivity: The rate at which solar energy is captured by producers via photosynthesis. It is divided into Gross Primary Productivity (GPP) and Net Primary Productivity (NPP).
• Secondary Productivity: The rate of energy storage at consumer levels.
• Biomass: The total dry weight of all living organisms in a particular area at a given time.
• Standing Crop: The amount of living material (biomass) present in an ecosystem at any given time.

The feeding relationships in an ecosystem determine its trophic organization.

• Food Chain: A linear sequence of organisms where energy is transferred as one eats another. Examples include grazing food chains and detritus food chains.
• Food Web: A network of interconnected food chains, representing the complex feeding interactions in a real ecosystem.

Ecological pyramids are graphical representations of the relationship between different trophic levels.

Biogeochemical cycles involve the movement of nutrients between biotic and abiotic components.

• Carbon Cycle: Carbon is cycled through photosynthesis, respiration, decomposition, and combustion.
• Nitrogen Cycle: Involves nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.

8. Exam Focus: Tips and FAQs

Common Pitfalls

• Mistake: Confusing NPP and GPP. Correction: NPP = GPP - Respiration. NPP is the actual biomass available to consumers.
• Mistake: Forgetting the role of decomposers in cycles. Correction: Decomposers are essential for recycling nutrients back into the abiotic environment.

Frequently Asked Questions

Q: What is the difference between a Food Chain and a Food Web?
A: A food chain is a single linear path of energy, while a food web is a collection of all interacting paths in an ecosystem.

Q: What is "Standing Crop"?
A: It refers to the amount of living matter (biomass) present in an ecosystem at a specific moment.