IB DP Biology Diversity of organisms Study Notes

A3.1.1— Variation between organisms as a defining feature of life

Levels of Organization

Organisms  –> populations (species) –> Communities –> ecosystem –> Biome –> Biosphere
Fig :  Ecological hierarchy

(i) Organism : An organism is a living unit in nature which performs all the life processes in its body.
(ii) Population : This is a group of individuals of a species growing in a given area at a particular time.
(iii) Species : Species is formed by all the populations of same kind of organisms.
(iv) Community : Collection of populations of different species that live in a particular area is called community.
(v) Ecosystem : It is the sum total of interacting biotic & abiotic factors that are capable of independent existence.
(vi) Biome : Biome represents large sized ecosystem delimited by specific climate having flora and fauna.
(vii) Biosphere : Any part of earth, where living beings live is called biosphere. The latter involves atmosphere, hydrosphere and lithosphere.

Genetics term was given by W.Bateson. (1905) (Father of Modern Genetics).
Genetics = Branch of biology which deals with the study of heredity and variation

Heredity – Transmission of genetic characters from generation to generation.
Variation – Individuals of same species have some difference, these are called variation.

INHERITANCE : HEREDITY AND VARIATIONS
Heredity : It is the transmission of genetic characters from parents to the offsprings. It deals with the phenomenon of ‘‘like begets like’’ e.g., human babies are like human beings in overall characteristics.
Variations are common in sexually reproducing organisms. Variations are of following two types :

Somatogenic : These are acquired variations and are non-inheritable in nature. The ability of an organism to alter its phenotype in response to environment is called phenotypic plasticity.
Blastogenic Variations : These are germinal variations and are hereditary in nature. They are again of two types:

Continuous variations : These are the fluctuating variations and can not give rise to new species. These are further of two types

Substantive : Variation in size, shape and color of organism.
Meristic : Variation in number of parts e.g. number of grains in an ear of wheat

Discontinuous Variations : Also known as mutations, sports or saltations. These variation are responsible for formation of new species and organism thus formed is called mutant.
Types of discontinuous variations

Substantive variations : These influence shape, colour, size etc., e.g., hairless cat, short legged ancon sheep.
Meristic variation : These affect number of parts e.g. polydactyly in humans.
Variations are significance in evolution as they make the organism better suited to modifying environmental conditions, produce new trait in organism and provide raw material for evolution.

A3.1.2—Species as groups of organisms with shared traits