Pollination and fertilization are two distinct processes that occur in the reproduction of flowering plants (angiosperms). They have different roles and occur at different stages of plant reproduction.
Pollination:
Pollination is the first step in the process of plant reproduction.
It involves the transfer of pollen from the male reproductive part of a flower (anther) to the female reproductive part (stigma) of the same or a different flower.
Pollination can occur through various agents, including wind, water, animals (insects, birds, bats), or even self-pollination (when pollen from the same flower reaches the stigma).
The primary purpose of pollination is to bring the male and female reproductive structures into proximity so that fertilization can potentially occur.
Pollen grains contain the male gametes (sperm cells), and their transfer to the stigma is necessary for the next step, which is fertilization.
Fertilization:
Fertilization is the second step in plant reproduction and occurs after successful pollination.
Fertilization involves the fusion of the male and female gametes (sperm and egg cells) to form a zygote, which develops into an embryo.
After pollen lands on the stigma, it germinates and forms a pollen tube that grows down into the flower’s style, ultimately reaching the ovule (female gametophyte) located in the ovary.
Inside the ovule, one of the sperm cells from the pollen tube fuses with the egg cell, resulting in the formation of a diploid zygote.
The zygote then undergoes cell divisions and develops into an embryo, which is the first stage of the new plant’s growth.
Meanwhile, another sperm cell from the pollen tube fuses with two polar nuclei in the ovule to form a triploid endosperm, which provides nutrients to the developing embryo.
In summary, pollination is the transfer of pollen to the female reproductive structure, while fertilization is the fusion of gametes to form a zygote, initiating the development of a new plant embryo. Pollination sets the stage for fertilization, as it brings the necessary male gametes (sperm) to the vicinity of the female gametes (egg cells) within the ovule.