What traumatic event does Zitkala-Sa describe at the school?

The forcible cutting of her long hair

Why was the cutting of her hair so humiliating to Zitkala-Sa?

Among her people, shingled hair was worn by cowards and mourners

Differentiate between gross primary productivity (GPP) and net primary productivity (NPP).

GPP is the total rate of production of organic matter by producers, while NPP is the GPP minus the energy lost in respiration (NPP = GPP - R), available to consumers.

State the ten per cent law of energy transfer.

Only about 10 per cent of the energy stored at one trophic level is passed on to the next higher trophic level, the rest being lost mainly as heat.

Why is the pyramid of energy always upright?

Because energy is lost as heat at each trophic level (following the ten per cent law), so energy available always decreases at successive higher trophic levels.

Give an example of an inverted pyramid of biomass.

In a pond or sea ecosystem, the biomass of phytoplankton (producers) is less than that of the consumers, giving an inverted pyramid of biomass.

Differentiate between primary and secondary succession.

Primary succession begins on a bare area with no previous life (e.g., bare rock), whereas secondary succession occurs where a community has been removed but soil is present.

What is a climax community?

A climax community is the final, stable community in ecological succession that is in equilibrium with the environment.

Differentiate between a grazing food chain and a detritus food chain.

A grazing food chain starts with green plants (producers) and goes to herbivores, while a detritus food chain begins with dead organic matter (detritus) consumed by decomposers.

What are the two main reservoirs of the carbon cycle?

The atmosphere (as CO2) and the oceans, along with fossil fuels and living and dead biomass, serve as the major carbon reservoirs.

What is meant by ecosystem services? Give examples.

Ecosystem services are the products and processes supplied by natural ecosystems, such as pollination, climate regulation, purification of air and water, nutrient cycling and pest control.

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Q: What are the steps in the process of decomposition?

Fragmentation, leaching, catabolism, humification and mineralisation.

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Chapter 12: Ecosystem — Class 12 Biology

Biology · 13 chapters

Summary, key terms, important questions and a practice quiz with AI diagnosis for each.

Chapter 12: Ecosystem

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Net primary productivity (NPP) is equal to:

Summary

This chapter examines the structure and function of ecosystems, the functional units of nature where living organisms interact with the physical environment. The structural components include biotic (producers, consumers, decomposers) and abiotic (climate, inorganic and organic substances) factors, while functional aspects include productivity, decomposition, energy flow and nutrient cycling. Productivity is divided into primary productivity (gross and net, GPP and NPP) and secondary productivity. Decomposition breaks down detritus through fragmentation, leaching, catabolism, humification and mineralisation, carried out by decomposers (saprotrophs). Energy flow follows the food chain (grazing and detritus) and food web, obeying the unidirectional flow of energy and the ten per cent law as energy passes through trophic levels. Ecological pyramids of number, biomass and energy depict trophic structure; the pyramid of energy is always upright, while pyramids of number and biomass can be inverted. Ecological succession, the gradual and predictable change in species composition over time, is described for both primary and secondary succession, leading toward a stable climax community, with hydrarch and xerarch examples. Biogeochemical cycles (nutrient cycling) of carbon and phosphorus are explained, distinguishing gaseous and sedimentary cycles. The chapter also covers ecosystem services such as pollination, climate regulation, nutrient cycling and water purification provided by nature.

Ecosystem structure and functionProductivity and decompositionEnergy flow and food chainsEcological pyramidsEcological successionNutrient cycling and ecosystem services

Key terms

Productivity

The rate of biomass production in an ecosystem, divided into primary and secondary productivity.

Decomposition

The breakdown of complex organic matter (detritus) into inorganic substances by decomposers.

Trophic level

A specific level in a food chain occupied by organisms based on their source of nutrition.

Ten per cent law

The principle that only about 10 per cent of energy is transferred from one trophic level to the next.

Ecological succession

The gradual and predictable change in the species composition of a community over time toward a climax stage.

Biogeochemical cycle

The cyclic movement of nutrients between the biotic and abiotic components of the biosphere.

Important questions

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The rate of biomass production in an ecosystem, divided into primary and secondary productivity.

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Practice quiz · Ecosystem

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Ecosystem

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