Learn Reproduction in Organisms with Free Lessons & Tips

If organisms don't reproduce, new organisms will not be produced and because old organisms have to die (that's just how biology works, living cells. Thus the whole organism don't live forever), the entire species will disappear in one life-time of that organism.

Think it this way, along with the 4 billion years history of life evolution on earth there were many species which could not reproduce adequately. Because of that all of those species got eliminated. And that's why in today's world all organisms reproduce (effectively) because these are the survivor species, ancestors of today's organisms were the only one who figured out effective reproduction through the process of evolution. 

In plants, the units of vegetative propagation such as runner, rhizome, sucker, tuber, offset, bulb are all capable of giving rise to new offsprings.

Examples of vegetative propagation:

(i) Vegetative propagation by leaves, in Bryophyllum

(ii) Vegetative propagation by the stem (rhizome) in Ginger, Turmeric etc.

(c) Senescent phase. read less

(a) Juvenile phase:- It is the period of growth in an individual organism after its birth and before it reaches reproductive maturity

(b) Reproductive stage:- It is the period when a single organism reproduces sexually

(c) Senescent stage:- It is the period when an organism grows old and loses the ability to reproduce.

The type of fertilisation in which male and female gamete takes place outside the body of the female is called external fertilisation. It is commonly observed in aquatic animals like starfish, frog and fish. Disadvantages are most of the male and female gametes will go wasted, i.e. it will remain unfertilised. External surroundings may cause harm to the gametes, which is present outside.