Class 12 Biology - CBSE
Organisms and Populations
Organisms and Populations is a foundational ecology chapter in Class 12 CBSE Biology that explores how living beings interact with each other and their physical surroundings. You will study key environmental factors like temperature and water, physiological adaptations, and population attributes such as birth rate, death rate, and age pyramids. The chapter dives deep into population growth models (exponential and logistic) and various interspecific interactions like mutualism, competition, and parasitism. It is a high-scoring chapter that frequently appears in board exams through direct definition questions, curve-based numerical problems on population growth, and case-based application questions.
Start Learning FreeKey Concepts
Adaptation
Any morphological, physiological, or behavioural attribute of an organism that enables it to survive and reproduce in its habitat.
Population Attributes
Characteristics of a population rather than an individual, including birth rate (natality), death rate (mortality), sex ratio, and age distribution.
Population Growth Models
Mathematical models showing how population size changes over time, categorized into exponential growth (resource-abundant) and logistic growth (resource-limited with carrying capacity).
Interspecific Interactions
Biological interactions between different species that can be beneficial (+), detrimental (-), or neutral (0), such as mutualism, competition, predation, and parasitism.
Homeostasis
The process by which organisms maintain a constant internal environment despite varying external environmental conditions.
Important Formulas
Board Exam Info
In the CBSE Class 12 Biology exam, this chapter typically carries around 3 to 5 marks as part of the Ecology unit. Questions often include differentiating between population growth models, explaining specific population interactions with examples (like brood parasitism or mutualism), or interpreting age pyramids.
Frequently Asked Questions
Exponential growth occurs when resources are unlimited, resulting in a J-shaped curve (dN/dt = rN). Logistic growth occurs when resources become limiting due to carrying capacity (K), resulting in a sigmoid or S-shaped curve.
Exponential growth occurs when resources are unlimited, resulting in a J-shaped curve (dN/dt = rN). Logistic growth occurs when resources become limiting due to carrying capacity (K), resulting in a sigmoid or S-shaped curve.
How do regulators differ from conformers?
Regulators maintain homeostasis through physiological and behavioural means (e.g., birds and mammals maintain constant body temperature). Conformers cannot maintain a constant internal environment, so their body temperature or osmotic concentration changes with the ambient surroundings.
What is carrying capacity?
Carrying capacity (represented as K) is the maximum number of individuals of a population that a given environment can sustainably support with its available resources.
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