Ch 11Organisms and Population — Class 12 Zoology, concept-first.

The word 'ecology' comes from the Greek oikos, meaning 'house', and logos, meaning 'study' -- so ecology is, quite literally, the study of the environmental 'house': every organism living in it, and e…

Every living organism has its own particular surrounding, or environment, with which it continuously interacts and to which it develops adaptations suited for survival.

A habitat can be thought of, informally, as an organism's 'address' — the actual physical place where it lives, forages, and carries out its life processes, as distinct from its niche, which is more l…

While habitat answers 'where does it live', ecological niche answers 'what does it do there' — the total functional role an organism plays in its community, combined with the sum of all the environmen…

Abiotic factors are the physical and chemical, non-living conditions of an environment that influence how organisms function and survive within it.

Temperature — the degree of hotness or coldness of an environment — is one of the most far-reaching abiotic factors, because nearly every biochemical process an organism runs, from metabolism to repro…

Light is an essential abiotic resource whose ecological effect depends on three separate properties: its quality (wavelength or colour), its intensity (the actual energy delivered, measured in units l…

Because life originated in the seas and roughly three-quarters of Earth's surface is covered by water, water availability and quality remain fundamental abiotic constraints on every organism.

Soil is a complex, life-supporting mixture of organic matter, mineral particles, gases, liquids and living organisms, occupying the zone known as the pedosphere.

Three further abiotic factors round out the environment's physical profile. Wind is simply the natural movement of air, driven mainly by differential heating between the equator and the poles together…

A biome is a large region of the Earth unified by broadly similar vegetation and climatic conditions, and biomes play a crucial role in sustaining life on the planet.

Aquatic biomes cover roughly seventy-one percent of the entire biosphere and are home to millions of aquatic organisms, including the vast diversity of fish species; the climate of coastal zones is it…

Terrestrial biomes are large communities of plants and animals occupying a distinct geographic region, distinguished primarily by their dominant vegetation type, which is itself mainly set by regional…

Every living organism must respond, in some way, to changes in its abiotic environment, and the chapter recognises four broad response strategies.

In biology, adaptation is the ongoing evolutionary process by which organisms come to fit their environment more closely, thereby improving their evolutionary fitness.

A population, in the ecological sense, is any group of organisms belonging to the same species that can interbreed among themselves, occupy a shared area, and together function as a component of the w…

Because a population behaves as a collective unit rather than a simple sum of individuals, it possesses attributes that an individual organism simply cannot have on its own.

Population density expresses the size of a population relative to a defined unit of space and time — in effect, how many individuals of a species are packed into their natural habitat.

Natality is the process by which populations gain new individuals through birth, hatching, germination or fission, and is essentially synonymous with birth rate; the two underlying biological contribu…

Populations show an inherent tendency to spread out or disperse in every direction until they encounter some barrier that stops further expansion, and this dispersal shows up as individuals moving int…

A population's age distribution is the proportion of its members falling into each of three broad age classes — pre-reproductive, reproductive, and post-reproductive — at a given point in time.

Populations do not grow in an arbitrary way over time; instead, they tend to follow one of two characteristic, recognisable growth patterns when population size is plotted against time.

The J-shaped growth form describes a population that increases rapidly and almost exponentially, driven by its full biotic potential, before stopping abruptly — not by gradually levelling off, but by…

The S-shaped, or sigmoid, growth form describes a population — small mammal populations are the chapter's example — that grows slowly to begin with, then accelerates into a faster growth phase, and fi…

Species differ in the overall life-history strategy they use to grow and reproduce, and ecologists broadly classify these strategies as r-selected or K-selected.

All animal populations carry an inherent tendency to keep increasing in number, but no population increases without limit.

Individuals belonging to different populations rarely live in isolation; they interact constantly with one another over food, shelter, mating opportunities and other necessities of life.

Amensalism is scored (--, 0): one species is actively harmed by the interaction while the other neither benefits nor loses anything from it.

Mutualism, scored (+, +), is the interspecific interaction in which both participating species come away better off.

Commensalism, scored (+, 0), is the interaction in which two or more species are associated in shared activities — most often centred on food, though the concept has been broadened in recent years to…

Competition, scored (--, --), describes individuals of the same species (intraspecific competition) or of different species (interspecific competition) vying for a resource that is in short supply — f…

Parasitism, scored (+, --), is a harmful interspecific interaction in which one partner, the parasite, benefits at the direct expense of the other, its host — drawing shelter, food and protection from…

Predation, scored (+, --), is the interaction in which one animal, the predator, kills another animal, its prey, and consumes it for food; like parasitism, predation shapes community dynamics, but the…

The Evaluation section closes the chapter with a mix of multiple-choice questions, short one- or two-line definitions, and longer descriptive questions that together sample every major topic covered a…

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