Even though each pollen grain has 2 male gemetes, why at least 20 pollen are required to fertilise, 20 ovules in carpel?

What is the function of the two male gamets produced by each pollen grain in angiosperms?

A plane is in level flight at constant speed and each of its two wings has an area of 20m^(2). If the speed of the air is 180 km/h over the lower wing and 216 km/h over the upper wing surface, determine the plane's mass. (Take air density to be 1 kg m ^(-3) and g= 10m//s ^(2)).

How many mitotic divisions are required to produce a mature male gametophyte from a single pollen grain …………..