Why must a gamete have only one half the number of chromosomes found in body cells?

We are diploid organisms thus require two sets of chromosomes. In order to ensure the zygote is a diploid (has 2 sets of chromosomes) the gametes must be haploids (has 1 set of chromosomes) as two gametes join to make a zygote. 

Having half the set of chromosomes also ensures that the offspring receives half of its chromosomes from its father and half from its mother. This becomes very important as to ensure there is genetic diversity in the offspring, both the fathers and mothers genes are needed.  

We first assume that this gas is an ideal gas where it follows the ideal gas equation. the said equation is expressed as: pv = nrt. from this equation, we can predict the changes in the pressure, volume and temperature. if the volume and the temperature of this gas is doubled, then the pressure still stays the same.