Why do gametes in their final step contain single chromosomes? how will this create another organism?

In order for the zygote, the fertilized egg cell to have a diploid number of chromosomes (2N) the gametes must have half of that number (N).
Chromosome pairs are divided into single chromosomes in gametes in order to be fused with another gamete with single chromosomes as well.
This way, the zygote gets one set of chromosomes from its father's side and one set of chromosomes from the mother's side. The zygote uses this information gained from both of the parents to develop into an embryo and later into an adult organism.

It depends on the surface of the levels. the rougher the surface, the greater is the frictional force. for rougher surfaces, you would need to exert greater force to move the object. the concept is that, you must overcome the frictional force in order to bring the object into motion. this is the reason why we add lubricants to the joints so they could easily move. this answer was on