Fusion of male gamete with female gamete to form zygote. In flowering plants, the male gamete is found in the pollen grains produced in the anthers and the female gamete is found in the ovules. Pollen must first move from the anther to the stigma through a process called pollination.
Pollen tube formation
When a pollen grain is placed on the stigma, it forms a pollen tube in the style of a flower. The nucleus of the pollen grain moves down the pollen tube as it grows towards the ovary and ovule.
The pollen tube reaches a small opening in the ovule, and then the tip of the pollen tube dissolves, allowing the pollen nucleus to enter the ovule, where the pollen nucleus fuses with the nucleus of the ovule cell. This fusion of two nuclei is fertilization. Fertilization creates a new cell called a zygote.
The single cell of the zygote divides and grows to become a plant embryo that has a stem and a root. What stem becomes the first chute of the plant, while what stem becomes the first root.
The remaining contents of the ovule develop into cotyledons, which serve as food storage for new plants. Seeds need their own food reserves for the first stage of growth because no food is produced by photosynthesis until the leaves develop. The seed is surrounded by a protective layer formed by the wall of the ovary. Finally, the egg turns into a seed and the ovary turns into a fruit.