What do the letters in a chemical formula represent?

How does a gymnosperm prevent itself from pollinating the same tree

Suppose you are provided with an actively dividing culture of e. coli bacteria to which radioactive thymine has been added. what would happen if a cell replicates once in the presence of this radioactive base?

How do the sperm cells get from the stigma to the ovules? a. they slide down the petals to the bottom of the flower. b. they travel through pollen tubes. c. they travel along filaments. d. insects carry the sperm cells from the stigma to the ovules.