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Structure of a Dicotyledonous Seed (Testa, Hilum, Micropyle)

Biology · Morphology of Flowering Plants · NEET

A dicotyledonous seed has a seed coat with two layers: the outer testa and inner tegmen. On the seed coat there is a scar called the hilum (where the seed was joined to the fruit) and above it a tiny pore called the micropyle. Inside is the embryo, which has two cotyledons (food store), and an embryonal axis carrying the radicle at one end and the plumule at the other. Memory hook: "Two Coats, Two Cotyledons" — Testa+Tegmen outside, two seed leaves inside.
Structure of a Dicotyledonous Seed (e.g. Bean)cotyledon(2, food)radicleTestaouter seed coatTegmeninner seed coatRadicleforms roothilum (scar)Micropylepore, water entry
A dicot seed (bean type): outer testa and inner tegmen form the seed coat; the hilum is a scar and the micropyle a pore above it; inside are two food-storing cotyledons and the embryonal axis with the radicle (future root) and plumule (future shoot).

Your doubts, answered

What is the difference between testa and tegmen?

The seed coat has two layers. Testa is the OUTER layer and is usually hard and thick. Tegmen is the INNER layer and is thin. Memory tip: Testa = Tough outside. NEET can ask which layer is outer, so remember testa is outermost.

What is the difference between hilum and micropyle?

Both are on the seed coat but they are different. Hilum is a SCAR (a mark) where the seed was attached to the fruit stalk. Micropyle is a small PORE (a tiny hole) located just ABOVE the hilum. Water enters the seed first through the micropyle during germination, so it is functional, while the hilum is only a scar.

Which part of a dicot seed becomes the root?

The RADICLE becomes the root when the seed germinates. The radicle is one end of the embryonal axis. The other end is the plumule, which becomes the shoot. NEET 2024 asked exactly this with a labelled figure, so learn radicle = future root, plumule = future shoot.

Is a gram (bean, pea) seed endospermic or non-endospermic?

Gram, bean and pea seeds are NON-ENDOSPERMOUS (also called ex-albuminous). Here the endosperm is used up during seed development, so it is not present in the mature seed, and food is stored in the two fleshy cotyledons instead. Castor is the opposite example — it is endospermic (albuminous).

How many cotyledons does a dicot seed have and what do they do?

A dicot seed has TWO cotyledons (that is why it is called di-cotyledonous). In non-endospermic dicot seeds like gram and pea, the cotyledons are fleshy and store reserve food for the growing embryo.

⚠️ The NEET trap
✗ Marking the micropyle as the part that develops into the root.
✓ The RADICLE develops into the root; the micropyle is only a tiny pore above the hilum through which water enters. NEET 2024 showed a labelled dicot seed and asked which part forms the root on germination — the answer was the radicle (label C).
🧠 Radicle = Root (both start with R). Micropyle = tiny pore for water, not a growing part.

Solved Morphology of Flowering Plants NEET PYQs

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Frequently asked

What are the main parts of a dicotyledonous seed?

Seed coat (outer testa + inner tegmen), hilum (scar), micropyle (pore), and the embryo. The embryo has two cotyledons and an embryonal axis bearing the radicle and plumule.

What is the function of the seed coat?

The seed coat, made of testa and tegmen, is a protective covering. It shields the delicate embryo inside from injury, drying and infection until the seed germinates.

Give an example of a dicot seed.

Gram, pea and bean are common non-endospermic dicot seeds. Castor is an endospermic (albuminous) dicot seed where endosperm stores the food.

Why is the micropyle important?

The micropyle is a small pore above the hilum. During germination, water is absorbed into the seed mainly through the micropyle, which triggers the embryo to grow.

Do dicot seeds have an endosperm?

Some do and some do not. Endospermic dicot seeds like castor keep the endosperm as food. Non-endospermic dicot seeds like bean, gram and pea use up the endosperm and store food in the cotyledons.

Related concepts:
Structure of a Monocot Seed: Scutellum, Coleoptile, ColeorhizaEndospermic (Albuminous) vs Non-Endospermic SeedsAleurone Layer, Scutellum, Epiblast and Perisperm ExplainedThe Fruit: Pericarp, True Fruit vs False FruitDrupe Fruit: Structure of Mango and Coconut (Edible Parts)
Practise Biology for NEET:
Biology MCQs (free, chapter-wise)Morphology of Flowering Plants PYQs