The number of chromosomes in parents and offspring of a particular species remains constant due to

Write true or false for the following statement: Menstruation lasts for about ten to fifteen days.

In which of the following living organisms does spore formation take place?

Leaves of $Bryophyllum$ fallen on the ground produce new plants. Why?

$(i)$ Some organisms have the capacity of reproducing by using a single parent. Such organisms have a simple body structure.
$(a)$ What is this method called?
$(b)$ Name any four types of this method.
$(c)$ Give two examples of organisms using this method for reproduction.
$(ii)$ Identify the method of reproduction used by $Spirogyra$ and $Rhizopus$.

At what age do boys typically reach puberty?