How is the cell cycle regulated?

Two groups of proteins, called cyclins and cyclin-dependent kinases (Cdks), are responsible for the progress of the cell through the various checkpoints. Cyclins regulate the cell cycle only when they are tightly bound to Cdks.

Explanation:

the generally accepted parts of modern cell theory include: all known living things are made up of one or more cells. all living cells arise from pre-existing cells by division. the cell is the fundamental unit of structure and function in all living organisms.

both male and female gametes are produced by meiosis of the germ cells. therefore, both male and female gametes are haploid. one male and one female gamete unite during the fertilization to form the diploid zygote. in seed bearing plants, pollen grain is the male gametophyte, which produces sperm cells.