Ch 13Organisms and Populations — Class 12 Biology, concept-first.

Ecology is the study of the interactions among organisms, and between organisms and their physical (abiotic) surroundings. The word was first used by Reiter, but it was E.

A habitat is the specific place or area in which a particular species lives. Factors such as sunlight, average rainfall, annual temperature, the type of soil present, and other abiotic (topographic) f…

The term ecological niche was first used by J. Grinnell (1917) to denote the functional role played by an organism in its environment.

Every habitat type is regulated by a number of abiotic, or physico-chemical, factors -- these are the non-living components of the environment, as opposed to the biotic (living) components such as the…

Temperature is the single most ecologically relevant environmental factor. Average land temperature ranges from sub-zero levels at the poles and at high altitudes, up to around 50 degrees C in tropica…

Water availability is a critical factor for organisms, unsurprisingly since life on Earth originated in water.

The nature and properties of soil depend on the local climate and on the weathering processes that have acted on the parent rock.

Light is the energy source plants use for photosynthesis, and photosynthesis is, ultimately, the only source of energy for the entire ecosystem, since it can occur only in the presence of sunlight.

Adaptation is any attribute of an organism -- morphological, physiological, or behavioural -- that enables it to survive and reproduce successfully in its habitat.

When regulation is not possible and stressful conditions cannot simply be tolerated, an organism has two further options.

Some species cope with environmental variation primarily through behaviour rather than through internal physiological change.

In nature we rarely, if ever, find isolated single individuals of a species. Organisms live in groups occupying a well-defined geographical area, sharing or competing for similar resources, and potent…

Besides size and density, a population has several further characteristic attributes: natality, mortality, immigration, emigration, its age structure (often shown as an age pyramid), the shape of its…

The density of a population in a given habitat, over a given period, fluctuates because of four basic processes.

No natural habitat exists that contains only a single species of plant or animal. Every species needs, at a bare minimum, some other species -- most commonly as a source of food.

Mutualism is an obligatory and interdependent interaction that benefits both of the participating species.

Competition is the type of interaction in which both species involved are, in some sense, at a loss. It can occur between completely unrelated species that happen to compete for the same resource -- f…

Parasitism has evolved independently across a very wide range of taxonomic groups, from plants right up to the higher vertebrates.

Predation is the interaction in which one organism, the predator, kills and consumes another, the prey.

Commensalism is the interaction in which one species benefits while the other is neither harmed nor benefited.

Sample papers and previous-year board questions for this subject.