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Organisms and Populations

CBSE · Class 12 · Biology

Quick revision notes for Organisms and Populations — CBSE Class 12 Biology. Key concepts, formulas, and definitions for last-minute revision.

50 questions100 flashcards5 concepts

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Key Topics to Revise

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1. Population Attributes and Density

  • A population is a group of individuals of the same species living in a defined geographical area, sharing or competing for similar resources, and potentially interbreeding.
  • Population attributes do not belong to an individual organism; they belong to the group as a whole.
  • An individual may have births and deaths, but a population has birth rates and death rates.
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2. Population Growth

  • Population density changes because of four basic processes: natality, mortality, immigration, and emigration.
  • Natality and immigration increase density; mortality and emigration decrease density.
  • Under normal conditions, births and deaths are the most important factors affecting density.
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3. Life History Variation

  • Populations evolve to maximise reproductive fitness, also called Darwinian fitness.
  • Organisms evolve different reproductive strategies under different selection pressures.
  • Some organisms breed only once in their lifetime, such as Pacific salmon fish and bamboo.
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4. Population Interactions

  • Species in nature do not live in isolation; they interact to form biological communities.
  • Interspecific interactions may be beneficial, harmful, or neutral to one or both species.
  • The main interaction types are mutualism, competition, predation, parasitism, commensalism, and amensalism.

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Full Notes

Key Concepts

Ecology studies living organisms in relationA population is a groupA population has birth ratePopulation density is the sizeBirth rate is the number

Frequently Asked Questions

What are the important topics in Organisms and Populations for CBSE Class 12 Biology?
Organisms and Populations covers several key topics that are frequently asked in CBSE Class 12 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
How to score full marks in Organisms and Populations — CBSE Class 12 Biology?
Understand the core concepts first, then work through the 50 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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