Sexual Reproduction in Plants: From Flower to Seed
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Sexual Reproduction in Plants
Understanding the Process
Sexual reproduction is typical of plants with seeds. The reproductive organs are inside the flower, where gametes are produced. After pollination, fertilization and the formation of embryos and seeds take place. Pollination is the transfer of pollen grains from the anther of the stamen to the stigma of the pistil.
Flower Structure
A flower is the reproductive unit of a plant. It consists of the following parts:
- Calyx: Green sepals which protect the developing flower.
- Corolla: Brightly colored petals.
- Stamen: The male reproductive organ of the flower. It consists of a stalk (filament) and sacs (anthers), where pollen is stored.
- Pistil: The female reproductive organ of the flower. It consists of one or more carpels with an ovary, a style, and a stigma.
Fertilization and Seed Formation
Fertilization in plants occurs when the male and female gametes unite in the ovary. At this point, the embryos and seeds start developing.
- The pollen grains land on the pistil. Then pollen tubes develop until they reach the ovary.
- Inside the ovary, the male and female gametes fuse to form the zygote. The zygote grows into an embryo.
- The ripened ovule becomes a seed. The seed contains the endosperm.
- The ripened ovary becomes the fruit. It is responsible for protecting and dispersing the seed.
- Seed germination: The embryo can contain one or two leaves with food reserves, called cotyledons.
Phases of Floral Reproduction
- Formation of Gametes:
- In the stamens, pollen grains are formed. From each grain, male gametes are formed.
- Inside the carpels are the ovules. Within each ovule, a female gamete is formed.
- Pollination: Transfer of pollen from the anther of a stamen to the stigma of a carpel.
- Pollen Germination: Each grain emits a pollen tube, inside which are the sperm nuclei.
- Fertilization: A sperm nucleus unites with the egg cell, forming the zygote.
- Embryo Formation: From the zygote, by successive divisions.