REPRODUCTION

 REPRODUCTION

Reproduction is the biological process which produces new individual organisms.It guarantees that the species will continue to exist.Living things,progenitors ,are able to multiply and generate new living things called young or descendants.

Two types:

ASEXUAL REPRODUCTION

One progenitor produces a new,genetically identical living thing.Is common in unicellular organisms.It is only found in some invertebrates,which also have sexual reproduction.

Two types:

Fragmentation:A new organisms grows from a fragment of the progenitor.Each fragment develops into a fully grown adult individual.

Budding:Grows from the body of the progenitor and develops into a new individual.In the case of coral,the bud remains attached to the progenitor and a colony is formed.

SEXUAL REPRODUCTION

Is the most commun form of reproduction. in animals.Each individual has reproductive organs called gonads which produce reproductive cells called gametes.The descendant receive characteristics from both parents,and are similar to them but no identical.

Almost all animals have separate sexes:male and female.Each sex produces only one type of gamete ,sperm or ova.Males and females can be distinguished by physical differences like size,shape or colour.This is called sexual dimorphism.

Testicles:Male gonads.

Sperm.Male gamete produced in the testicles.It is small and motile with a flagellum.

Ovaries:Female gonads.

Ovum:Female gamete produced in the ovaries.It is larger than sperm,but not motile.It contains nutritive substances that the embryo can use.

Hermaphrodites.Each individual has male and female gonads.When mating,one individual acts as the male and the other as the female.Earthworms and snails are hermaphrodites.

Alternation of generations.Some animals,like jellyfish,alternate between asexual and sexual reproduction.