Why is it significant that pollen contains a multicellular male gametophyte instead of just male gametes?
the non-gamete cells of the male gametophyte provide protection from desiccation and uv radiation.
the non-gamete cells of the male gametophyte provide nutrition that supports the development of the embryo.
the non-gamete cells of the male gametophyte undergo meiosis.

The given options are false regarding the question, the correct answer should be -

multicellular male gametophyte has a non-gamete cell that controls growth and development to the pollen tube and the male gamete.

The importance of these nongenetic cells of the male gametophyte is to control the development and growth of pollen tube that is an essential structure for pollination and fertilization.

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.