(i) Environmental Resistance: The sum total of inhibitory environmental factors, both biotic end abiotic such as drought, high temperature, shortage of food, shelter, predation, pathogens, diseases etc. which regulate population size and do not permit unlimited growth of population is called environment resistance. Because of environmental resistance, the populations are unable to reach full biotic potential.

(ii) Albinism: The individuals suffering from albinism are called albino. They lack melanin pigment in their skin, hair, iris of eye etc. Such persons are susceptible to bright sun rays and develop eye disorders and skin diseases. Albinism results from inheritance of autosomal gene mutation. Hence the individual lacks the enzyme tyrosinase which is essential for synthesis of melanin. The gene for albinism is a recessive gene (a) which can be expressed only in homozygous (aa) condition. A person with its dominant allele (A) will be normal. The condition is known to affect mammals, fish, birds, reptiles and amphibians. Albinism is a genetic disorder, while the most common term for an organism affected by albinism is ‘albino’. Most organisms with albinism appear white or very pale.

(iii) Plant Introduction : Plant introduction means introducing a plant having desirable characters (e.g., vigorous growth, high yield, disease resistance, etc) from a region or a country where it grows naturally to a region or country where it did not occur earlier.

The adaptation of an individual to a changed environment, or the adjustment of a species or a population to a changed environment over a number of generations is called acclimatization (or acclimation).

Plant introduction has played a significant role in the development of agriculture throughout . the world. Some of the most important commercial crops cultivated extensively in India today are introductions from other countries. For example, Gossypium hirsutum, Cinchona was first introduced into the Nilgris from Peru in 1860. Potato (Solanum tuberosum), chilli (Capsicum annuum), tobacco (Nicotiana tobaccum), guava (Psidium guajava), custard apple (Annona squamosa), cashewnut (Anacardium occidentale) and Papaya (‘Carica papaya) are some of the other examples of crops successfully introduced in India.

Plant introduction can be useful in three different ways :

(a) the introduced material can be used directly by increasing it enmass. 

(b) desirable strains can be selected from the introduced material. 

(c) the introduced material can be used as a parent for hybridisation with adapted local varieties.

(iv) Palaeontology : It is the study of past life based on the fossil record. The fossils are petrified (turned in to stone) remains or impressions of ancient organisms preserved by natural means in the sedimentary rocks or other media such as amber, asphalt, volcanic – ash, ice, peat bogs, sand and mud. Palaeontology furnishes the most direct and reliable evidence for evolution, as it deals with the actual organisms that lived in the past.