RBSE Class 12 Biology Notes Chapter 13 Organisms and Populations

These comprehensive RBSE Class 12 Biology Notes Chapter 13 Organisms and Populations will give a brief overview of all the concepts.

RBSE Class 12 Biology Chapter 13 Notes Organisms and Populations

→ Ecology is a branch of biology and the study of the relationship of living organisms with the abiotic (physico-chemical factors) and biotic components (other species) of their environment. It encomposses four levels of biological organisation-organisms, populations, communities and biomes.

→ The most important physical factors of the environment to which the organisms are adapted in various ways are light, temperature, water and soil. Maintenance of a constant internal environment by the organisms is called homeostasis. Some organisms are capable of homeostasis to face the changing external environment, so these are called regulators. While some other organisms either partially regulate their internal environment or simply conform. Some organisms have evolved adaptations co avoid unfavourable conditions in space (migration) or in time (aestivation, hebernation and diapause).

→ Population ecology is an important area of ecology because natural selection is the way through which evolutionary changes take place at the population level. A population is a group of individuals of a given species sharing or competing for similar resources in a defined geographical area. Population have attributes as birth rates and death rates, sex ratio and age distribution.

→ Ecological effects of any factors on a population are generally reflected in its size (population density) which may be expressed in different ways (numbers, biomass, percent cover, etc.) depending on the species. Population grow through births and immigration and decline through death and emigration.

→ In nature populations of different species in a habitat do not live in isolation but interact in many ways.

→ Depending on the outcome, these interactions between two species are classified as competition (both species suffer), predation and parasitism (one benefits and the other suffers), commensalism (one benefits and the other is unaffected), amensalism (one is harmed, other unaffected) and mutualism (both species benefit). Predation is an important process by which trophic energy transfer is facilitated and some predators help in controlling their prey populations. In competition, it is presumed that the superior competitor eliminates the inferior one (the competitive exclusion principle), but many closely related species have evolved various mechanisms which facilitate their co-existence. Some of the most fascinating cases of mutualism in nature are seen in plant pollinator interactions.

→ Aestivation: An adaptation to avoid summer-related problems heat and dessication.

→ Biological Control ; Method adapted in agricultural pest control based on the ability of predator to regulate prey population.

→ Biosphere: The surface of earth with all life forms, i.e., union of all ecosystems. It is a highly ordered system.

→ Camouflaged: Cryptically-coloured to avoid being detected easily by the predator.

→ Diapause: A response, during unfavourable conditions many zooplankton species in lakes and ponds are known to enter a stage of suspended development.

→ Ectoparasites: Parasites that feed on the external surface of the host organism.

→ Endoparasite: Parasites that live inside the host body at different sites (liver, kidneys, lungs).

→ Eurythermal: Organisms can tolerate and thrive in a wide range of temperatures.

→ Hibernation: During winter is an example of escape in time.

→ Homeostasis: To maintain the constancy of its internal environment by the organism.

→ Niche: The ecological niche of an organism represents the physical space occupied by it, the resources it utilises and its functional role in the ecological system.

→ Phytophagous: Feeding on plant sap and other parts of the plants.

→ Casmophytes: Plants growing in rock crevices.

→ Demography: Scientific study of human population.

→ Halophytes: Plants growing in highly saline waters or soils.

→ Heliophytes: Plants growing in strong light intensities.

→ Humus: Fully decomposed and dark coloured organic matter.

→ Litter: Undecomposed organic matter. 

→ Osmoregulation: Regulation of osmotic concentration of body fluids.

→ Photoperiodism: Response to organisms to duration of light.

→ Sciophytes: Plants growing in lower light intensities.

→ Xerophytes: Plants found in Xeric (dry and hot) habitats.

→ Scavengers: Animals whose feeds on dead animals or leftover flesh.

→ Cannibals: Animals which can feed the animals of its own species.

→ Sexual Deceit: To get pollination done by a species of bee, e.g., in mediterranean ochid opherys.