Explain why an organism with a homozygous dominant genotype has the same phenotype as an organism with a heterozygous genotype

In phenotype (visible physical characteristics), only dominant/recessive will show. If an organism is homozygous dominant (e.g. AA), then the dominant allele will result in a dominant phenotype. If an organism if heterozygous dominant (e.g. Aa), then even though it has a recessive gene, the dominant allele will overpower the recessive one, resulting in only the dominant trait showing in the phenotype.

Cells of an organism tell each other when predators are near.

We can plant more trees and plants.