Class 12 Biology - WEST-BENGAL
Ecosystem
The chapter 'Ecosystem' in Class 12 Biology explores the structural and functional units of nature where living organisms interact with each other and their physical environment. Students will learn about ecosystem structure, biotic components, energy flow through trophic levels, ecological pyramids, and nutrient cycling such as carbon and phosphorus cycles. It also covers crucial concepts like ecological succession and ecosystem services. This chapter is vital for the West Bengal Board (WBBSE) examinations as it frequently features descriptive questions, numerical problems based on ecological efficiency, and diagrammatic representations of biogeochemical cycles, making it a high-scoring section.
Start Learning FreeKey Concepts
Trophic Levels
The specific feeding position of organisms in a food chain, starting from producers at the base to top carnivores at the apex.
10 Percent Law
Proposed by Lindeman, it states that only about 10 percent of energy is transferred from one trophic level to the next, while the rest is lost as heat.
Ecological Pyramids
Graphical representations of the trophic structure and function of an ecosystem, which can be pyramids of number, biomass, or energy.
Ecological Succession
The predictable and gradual change in the species composition of a given area over time, leading to a climax community.
Nutrient Cycling
The movement of nutrient elements through the various components of an ecosystem, also known as biogeochemical cycles.
Important Formulas
Board Exam Info
In the West Bengal (WBBSE) Class 12 Biology examination, the 'Ecosystem' chapter typically carries around 5 to 7 marks. Questions commonly include short answer type questions (2-3 marks) on ecological pyramids or the 10% law, long answer descriptive questions (5 marks) detailing nutrient cycles or ecological succession, and multiple-choice questions (MCQs).
Frequently Asked Questions
Can a pyramid of energy be inverted?
No, the pyramid of energy is always upright because energy is lost as heat at each trophic level according to the 10 percent law.
What is the difference between GPP and NPP?
Gross Primary Productivity (GPP) is the total rate of biomass production during photosynthesis, whereas Net Primary Productivity (NPP) is the available biomass left for consumption after subtracting plant respiration losses.
What is the difference between primary and secondary succession?
Primary succession starts in areas where no living organisms ever existed (like bare rock), while secondary succession begins in areas that have lost all previous life (like a burnt forest) but still retain soil.
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