The male gametophytes of flowering plants are also referred to as sporophytes, embryo sacs, endosperm, pollen grains, megaspores

pollen grains

Explanation:

Pollen grains are structures in the seed plants (spermatophytes) which contain vegetative cells  but also reproductive cells - microgametophytes. Microgametophytes produce 2 male gametes or sperm cells. Vegetative cells produce pollen tube which is involved in the transfer of sperm cells to the ovule (female structure that forms female gametes). Pollen grains are different in shape, size and color, but all of them are enveloped with hard coat that has protective role.

Pollen grains

Explanation:

Pollen grains are make gametophytes

-I took the course :)

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".