Class 12 Biology - CBSE
Ecosystem
The Ecosystem chapter in Class 12 CBSE Biology explores the complex interactions between biotic and abiotic components of nature. Students study the functional aspects of an ecosystem, which include productivity, decomposition, energy flow through trophic levels, and nutrient cycling. The chapter emphasizes ecological pyramids, ecological succession, and vital ecosystem services. For board exams, this is a high-scoring unit under the Ecology module, frequently featuring conceptual questions on energy transfer efficiency, differences between primary and secondary succession, and diagram-based questions on biogeochemical cycles.
Start Learning FreeKey Concepts
Productivity
The rate of biomass production, divided into Gross Primary Productivity (GPP) and Net Primary Productivity (NPP) after accounting for plant respiration.
Decomposition
The breakdown of complex organic matter into inorganic substances by decomposers, involving key steps like fragmentation, leaching, catabolism, humification, and mineralization.
Energy Flow
The unidirectional movement of energy through trophic levels, governed by the 10% law of energy transfer proposed by Lindeman.
Ecological Pyramids
Graphical representations of trophic structure parameters, which can be pyramids of number, biomass, or energy, with energy pyramids always being upright.
Ecological Succession
The predictable and progressive change in species composition in a given area over time, culminating in a stable climax community.
Important Formulas
Board Exam Info
In CBSE Class 12 Biology, the Ecosystem chapter is a part of the Ecology unit, which generally carries around 14 marks in total. Expect 1 to 3-mark direct questions, differentiation questions (e.g., GPP vs NPP, primary vs secondary succession), and diagram-based questions on ecological pyramids.
Frequently Asked Questions
Why is the pyramid of energy always upright while the pyramid of biomass can be inverted?
The pyramid of energy is always upright because energy is lost as heat at each trophic level during transfer, in accordance with the 10% law. In contrast, the pyramid of biomass can be inverted in aquatic ecosystems where the biomass of phytoplankton is much smaller than that of zooplankton at any given time.
What is the difference between primary and secondary succession?
Primary succession starts in areas where no living organisms ever existed (like bare rock or cooled lava) and is very slow. Secondary succession starts in areas that have lost all living organisms (like abandoned farmland or burned forests) and is much faster because the soil is already present.
What are the limitations of ecological pyramids?
Ecological pyramids do not take into account the same species belonging to two or more trophic levels, they assume a simple food chain rather than a complex food web, and saprophytes/detritivores are not given any place in ecological pyramids despite their vital role.
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