What is the main cause of variations among organisms during sexual reproduction?

What happens when the following situations are initiated:
$(a)$ $A$ $Planaria$ is cut into three different pieces.
$(b)$ $A$ leaf of the $Bryophyllum$ with notches falls on the soil.
$(c)$ Testosterone is released in the male reproductive system.

The correct sequence of organs in the male reproductive system for the transport of sperms is:

Explain what happens when:
$(a)$ Testosterone is released in males.
$(b)$ Pollen grain falls on the stigma of the flower.
$(c)$ Egg fuses with sperm cell.
$(d)$ Planaria is cut into many pieces.
$(e)$ Buds are formed on the notches of the Bryophyllum leaf.

Where is $DNA$ found in a cell?

What are the functions of the testes in a young male?