Seed Structure — Revision Notes

⚡ 30-Second Revision

Seed: — Fertilized ovule, contains embryo, food, seed coat.
Seed Coat (Testa): — Outermost protective layer. Has Hilum (attachment scar) & Micropyle (water/gas entry).
Embryo: — Baby plant. Consists of:

- Radicle: Embryonic root. - Plumule: Embryonic shoot. - Cotyledon(s): Seed leaves (1 in monocots, 2 in dicots).

Food Reserves:

- Endosperm: Separate nutritive tissue (e.g., Maize, Castor - endospermic). - Cotyledons: Store food directly (e.g., Pea, Bean - non-endospermic).

Monocot Seed Specifics (e.g., Maize):

- Single cotyledon (Scutellum). - Coleoptile: Sheath protecting plumule. - Coleorhiza: Sheath protecting radicle. - Aleurone layer: Proteinaceous layer separating endosperm from embryo.

2-Minute Revision

A seed is a reproductive unit formed from a fertilized ovule, comprising a protective seed coat, an embryo, and stored food. The seed coat (testa) shields the internal structures, featuring a hilum (attachment scar) and a micropyle (pore for water/gas entry).

The embryo is the miniature plant, consisting of an embryonal axis with a radicle (future root) and a plumule (future shoot), along with one or two cotyledons (seed leaves). Food reserves are crucial for initial growth.

In endospermic seeds (e.g., maize, castor), food is stored in the endosperm. In non-endospermic seeds (e.g., pea, bean), food is stored in the fleshy cotyledons. Monocot seeds (e.g., maize) have a single cotyledon called the scutellum, and specialized protective sheaths: coleoptile for the plumule and coleorhiza for the radicle.

They also possess an aleurone layer separating the endosperm from the embryo. Dicot seeds (e.g., pea) have two cotyledons and lack these specialized sheaths.

5-Minute Revision

Let's consolidate the crucial aspects of seed structure for NEET. A seed is essentially a dormant embryonic plant, packaged for survival and dispersal. It originates from a fertilized ovule and typically consists of three main parts: the seed coat, the embryo, and stored food.

1
Seed Coat: — This is the tough, outer protective layer, derived from the ovule's integuments. It prevents desiccation, mechanical damage, and pathogen entry. Key features on the seed coat include the hilum, a scar marking the point of attachment to the funicle, and the micropyle, a small pore vital for water and oxygen absorption during germination.

1
Embryo: — This is the 'baby plant'. It comprises an embryonal axis with a radicle (embryonic root, first to emerge) at one end and a plumule (embryonic shoot, future stem and leaves) at the other. Attached to this axis are the cotyledons, which are seed leaves. Their number distinguishes monocots (one cotyledon) from dicots (two cotyledons). The region above the cotyledonary attachment is the epicotyl, and below it is the hypocotyl.

1
Food Reserves: — These provide energy for the embryo's initial growth. Seeds are classified based on where this food is stored:

* Endospermic (Albuminous) Seeds: Have a persistent, well-developed endosperm (e.g., maize, wheat, castor). The cotyledons are thin and absorb nutrients from the endosperm. * Non-endospermic (Exalbuminous) Seeds: The endosperm is consumed during development, and food is stored directly in the large, fleshy cotyledons (e.g., pea, bean, groundnut).

Monocot vs. Dicot Seed Structure:

Dicot Seed (e.g., Bean): — Two large cotyledons (often food-storing), distinct seed coat, prominent hilum and micropyle, embryo with radicle and plumule. No specialized sheaths like coleoptile/coleorhiza.
Monocot Seed (e.g., Maize): — Single, shield-shaped cotyledon called the scutellum. Large, starchy endosperm as primary food storage, separated from the embryo by a protein-rich aleurone layer. The plumule is protected by the coleoptile, and the radicle by the coleorhiza. The seed coat is often fused with the fruit wall (pericarp).

Worked Example: Consider a maize grain. It's a monocot, so it has one cotyledon (scutellum). It's endospermic, meaning the large, starchy part is the endosperm. The embryo is small, located at one end, and protected by the coleoptile (for plumule) and coleorhiza (for radicle). The aleurone layer surrounds the endosperm. This contrasts sharply with a pea seed, which is a dicot, non-endospermic, with two large, food-filled cotyledons and no specialized sheaths.

Prelims Revision Notes

Seed Structure: NEET Quick Recall Notes

I. Definition & Components:

Seed: — Fertilized, mature ovule containing an embryo, stored food, and protective seed coat.
Main Parts: — Seed Coat, Embryo, Food Reserves.

II. Seed Coat (Testa):

Outermost protective layer, derived from integuments.
Functions: — Protection (mechanical, desiccation, pathogens), regulates germination.
Hilum: — Scar on seed coat, point of attachment of ovule to funicle.
Micropyle: — Small pore near hilum, allows entry of water and oxygen for germination.

III. Embryo:

Miniature plant, developed from zygote.
Embryonal Axis: — Central axis.

* Radicle: Embryonic root, develops into root system. First to emerge. * Plumule: Embryonic shoot, develops into stem and leaves. * Epicotyl: Part of embryonal axis above cotyledonary attachment (forms part of stem). * Hypocotyl: Part of embryonal axis below cotyledonary attachment (forms part of stem/root transition).

Cotyledon(s): — Seed leaves.

* Number: One (monocot) or two (dicot). * Function: Store food (non-endospermic) or absorb food from endosperm (endospermic).

IV. Food Reserves:

Endosperm: — Nutritive tissue formed from primary endosperm nucleus.

* Endospermic (Albuminous) Seeds: Endosperm persists and stores food. Examples: Castor (dicot), Maize, Wheat, Rice (monocots). * Non-endospermic (Exalbuminous) Seeds: Endosperm consumed during development; food stored in cotyledons. Examples: Pea, Bean, Gram, Groundnut (dicots).

V. Dicotyledonous Seed (e.g., Pea, Bean):

Cotyledons: — Two, large, fleshy, store food.
Endosperm: — Absent or very reduced (non-endospermic).
Seed Coat: — Distinct, with hilum and micropyle.
Embryo: — Radicle, plumule, epicotyl, hypocotyl.
Protective Sheaths: — Absent.

VI. Monocotyledonous Seed (e.g., Maize, Wheat):

Cotyledon: — One, called Scutellum (shield-shaped, absorbs food from endosperm).
Endosperm: — Large, prominent, stores food (endospermic).
Aleurone Layer: — Proteinaceous layer separating endosperm from embryo.
Seed Coat: — Often fused with fruit wall (pericarp) in cereals.
Embryo: — Small, located at one end of endosperm.

* Coleoptile: Protective sheath enclosing plumule. * Coleorhiza: Protective sheath enclosing radicle.

VII. Key Distinctions (Monocot vs. Dicot):

Cotyledons: — 1 vs. 2.
Endosperm: — Usually present vs. usually absent.
Sheaths: — Coleoptile/Coleorhiza present vs. absent.
Aleurone Layer: — Present vs. absent.
Seed Coat/Pericarp: — Fused vs. separate.

Vyyuha Quick Recall

Some Elephants Can Run Pretty Carefully

Seed Coat (Protection)
Embryo (Baby plant)
Cotyledons (Food storage/absorption)
Radicle (Root)
Plumule (Shoot)
Coleoptile (Protects plumule in monocots)
Coleorhiza (Protects radicle in monocots)