NCERT Solutions for Class 12 Biology Chapter 11 Organisms and Populations

Short Note:

• Organisms respond to environmental factors such as temperature, water, light and soil either by regulating (maintaining a constant internal environment, as in homeothermic animals), conforming (allowing their internal environment to change with external conditions, as in most plants and poikilothermic animals), migrating, or entering states of dormancy/suspended development (such as hibernation, aestivation, or diapause) to escape unfavourable conditions.

Short Note:

• Adaptations are morphological, physiological, or behavioural traits that enable an organism to survive and reproduce successfully in its particular habitat; examples include thick fur and small ears in polar animals to minimise heat loss (Allen's rule), and desert plants (like Opuntia) with reduced leaves (spines) and thick cuticles to reduce water loss.

Short Note:

• A population is a group of interbreeding individuals of the same species in a defined geographical area, characterised by attributes such as birth rate (natality), death rate (mortality), sex ratio, age distribution, and population density.

• Populations grow according to models such as the exponential growth model (unrestricted resources, J-shaped curve) and the more realistic logistic growth model (limited resources leading to an S-shaped curve that plateaus at the carrying capacity, K).

Short Note:

• Species interact in various ways, including mutualism (both species benefit, e.g. lichens), competition (both species are negatively affected, e.g. two species competing for the same resource), predation (one organism, the predator, kills and consumes another, the prey), parasitism (the parasite benefits at the host's expense), and commensalism (one species benefits while the other is unaffected, e.g. orchids growing on trees).