What was the purpose of applying the rooting medium? why was it applied to only one of each set and not to all of the plants?

by using rooting harmone  roots develop quickly at cutting and and it become  more robust than cuttings which don't receive rooting hormone. Cutting harmone is used mostly on ornamental plants in the landscape and to propagate succulents.

It cannot apply on whole plant since it will not mix with old one and a new catergory or plant will develop and it will distroy the originality of the actual plant

in 1972 the fluid—mosaic membrane model of membrane structure was proposed based on thermodynamic principals of organization of membrane lipids and proteins and available evidence of asymmetry and lateral mobility within the membrane matrix [s. j. singer and g. l. nicolson, science 175 (1972) 720–731].

the diploid number of chromosomes is sometimes represented by the symbol 2n. for the fruit fly, the diploid number is 8, which can be written as 2n = 8, where n represents twice the number of chromosomes in a sperm or egg cell.