The pollen grain of a flowering plant has a fluid cytoplasm material inside that contains one or more vegetative cells and one generative cell. A vegetative cell is a nonreproductive cell. A generative cell is a reproductive cell.
The grain, known as the microgametophyte, is essentially a cell with more cells inside. The cytoplasm keeps the inside cells from drying out or dying.
The vegetative cell, or tube cell, produces an elongated pollen tube for delivering sperm cells to the female gamete. The generative cell contains two male sperm nuclei and divides to form the two sperm cells needed for fertilization.
The cells and surrounding cytoplasm are encased within an outer shell consisting of two cell walls. The inner wall is called the intine and is partly made of cellulose. The complex outer layer is called the exine. It is made largely of sporopollenin and is one of nature’s most sophisticated polymers.
The exine is waterproof and resists deterioration, helping ensure the cells within have a good chance of survival. Its surface often contains folds or spikes to add protection, somewhat like an extra layer of armor.
The textured surface also aids the process of pollination by making it more likely that the grains attach themselves to the legs of visiting insects or get captured by the wind.