Structure Of Seeds - SS3 Biology Lesson Note

Seeds are the reproductive structures of flowering plants (angiosperms) and gymnosperms. They are responsible for the propagation and survival of plant species. The structure of a seed can vary among different plant species, but here is a generalized overview of the typical structure of a seed:

1.       Seed Coat: The outermost layer of a seed is called the seed coat or testa. It is a protective covering that surrounds and encases the internal structures of the seed. The seed coat helps to prevent desiccation, mechanical damage, and entry of pathogens. It can have various textures, colours, and patterns specific to different plant species.

2.       Embryo: The embryo is the young, developing plant contained within the seed. It consists of several important components:

a.       Embryonic Axis: The embryonic axis is the central part of the embryo and consists of the radicle, hypocotyl, and epicotyl. The radicle is the embryonic root, which will develop into the primary root upon germination. The hypocotyl is the region between the radicle and cotyledons, while the epicotyl is the region above the cotyledons, which develops into the shoot.

b.       Cotyledons: Cotyledons are seed leaves that provide nutrients to the developing embryo. In some plants, there is a single cotyledon (monocots), while in others, there are two cotyledons (dicots). Cotyledons may remain inside the seed until germination, or they may emerge and become photosynthetic structures.

3.       Endosperm: In some plant species, the seed may contain endosperm, a nutritive tissue that provides nourishment to the developing embryo. The endosperm is typically triploid, resulting from the fusion of the sperm cell and two polar nuclei during double fertilization. It can serve as a source of stored nutrients, such as starch, oils, proteins, and sugars.

4.       Plumule: The plumule is the embryonic shoot that develops into the leaves and stem of the plant. It is located above the cotyledons within the embryonic axis and will grow into the shoot system upon germination.

5.       Radicle: The radicle is the embryonic root that gives rise to the root system of the plant. It is the first structure to emerge from the seed upon germination and serves to anchor the seedling in the soil and absorb water and nutrients.

The structures within the seed, such as the embryo and endosperm, contain the genetic material and resources needed for the successful development and growth of a new plant. Seeds are adapted for dispersal, allowing them to be transported to new locations for germination, contributing to the survival and propagation of plant species.