Organisms and Populations
Class 12 Biology · Biology · Chapter 11
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اردو (اختیاری)
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संस्कृतम् (केन्द्रिकम्)
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Physics
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हिंदी (ऐच्छिक)
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संस्कृत (ऐच्छिक)
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Physics
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اردو (کور)
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Chemistry
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Urdu Elective
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Computer Science
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Chemistry
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Fine Art · Painting
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हिंदुस्तानी संगीत (गायन / वादन)
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Informatics Practices
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Biotechnology
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सृजनात्मक लेखन और अनुवाद
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Economics
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History
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History
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History
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Geography
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Geography
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Geography
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Home Science
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Summary
This chapter introduces ecology at the levels of the organism and the population. It explains how organisms interact with their abiotic environment, with major factors being temperature, water, light and soil, and how these define habitats and biomes. Organisms respond to environmental stress by being regulators (maintaining homeostasis), conformers, by migration or by suspending activities through adaptations such as hibernation, aestivation, diapause and the formation of resistant stages. Adaptations, structural, physiological and behavioural, that fit organisms to their environment are described with examples like the kangaroo rat, desert plants, allen's rule and altitude sickness. At the population level, attributes such as population density, birth and death rates, sex ratio, age pyramids and dispersion are explained. Population growth is modelled by exponential growth (J-shaped curve, with intrinsic rate of natural increase r) and logistic growth (S-shaped curve constrained by carrying capacity K). The chapter then discusses population interactions, classifying them as mutualism, competition, predation, parasitism, commensalism and amensalism, with examples such as the predator-prey relationship, brood parasitism in the cuckoo, plant-pollinator mutualism in figs and wasps, and Gause's competitive exclusion principle.
Organism and its environmentAdaptations to abiotic factorsPopulation attributesPopulation growth modelsPopulation interactionsMutualism, predation, parasitism and competition
Key terms
Population
A group of individuals of the same species living in a defined geographical area and capable of interbreeding.
Carrying capacity (K)
The maximum population size that the resources of an environment can sustain.
Logistic growth
Population growth that follows an S-shaped (sigmoid) curve, limited by carrying capacity.
Mutualism
An interaction in which both interacting species benefit.
Commensalism
An interaction in which one species benefits and the other is neither harmed nor benefited.
Homeostasis
The maintenance of a constant internal environment by an organism despite varying external conditions.
Extra questions & answers
Try one from this chapter
The maximum population size an environment can sustain is its: