NCERT grounding
NCERT Class 11 Biology, Morphology of Flowering Plants, section 5.7, states that the ovules after fertilisation develop into seeds, and that a seed is made up of a seed coat and an embryo. The embryo, in turn, is made up of a radicle, an embryonal axis and one cotyledon (as in wheat and maize) or two cotyledons (as in gram and pea). Section 5.7.1 details the dicot seed and section 5.7.2 the monocot seed, the two structures illustrated in Figures 5.14 and 5.15.
"A seed is made up of a seed coat and an embryo. The embryo is made up of a radicle, an embryonal axis and one (as in wheat, maize) or two cotyledons (as in gram and pea)."
NCERT Class 11 Biology · Section 5.7
Anatomy of a seed
A seed is the structure into which a fertilised ovule matures. It packages a dormant embryo together with a food reserve inside a protective coat, allowing the new plant to survive unfavourable conditions and to be dispersed away from the parent. Whatever the species, every seed is built from two fundamental components named by NCERT — the seed coat and the embryo — to which a stored-food tissue, the endosperm, may or may not be added.
The outermost covering is the seed coat. It has two layers: the outer testa and the inner tegmen. On the coat lies the hilum, a scar marking where the developing seed was attached to the fruit (it is the point of former attachment to the funicle of the ovule). Just above the hilum is a small pore, the micropyle, through which water is first imbibed and through which the radicle usually emerges at germination.
Within the coat lies the embryo — the young, undeveloped plant. It comprises an embryonal axis bearing one or two cotyledons (seed leaves), and at the two ends of the axis are the radicle (the embryonic root) and the plumule (the embryonic shoot). The number of cotyledons — one versus two — is the single morphological character that splits angiosperm seeds into monocotyledonous and dicotyledonous types, and from it most other differences follow.
Three structural tiers of a seed. Read from outside inward — coat, then stored food (if present), then embryo. Every labelling question reduces to placing a term in one of these tiers.
Seed coat
Testa — outer, protective layer.
Tegmen — inner, thinner layer.
Hilum — attachment scar; micropyle — pore above it.
Stored food
Endosperm — formed by double fertilisation.
Persists in endospermic seeds (castor, maize).
Consumed by cotyledons in non-endospermic seeds (gram, bean, pea).
Embryo
Embryonal axis with cotyledon(s).
Radicle — future root.
Plumule — future shoot.
The dicot seed
In a dicotyledonous seed such as gram, bean or pea, the seed coat (testa + tegmen) encloses an embryo with two cotyledons. The cotyledons are often fleshy and packed with reserve food. Between and below them runs the embryonal axis, carrying the radicle at one end and the plumule at the other. The hilum and the micropyle are visible on the seed coat, the micropyle sitting just above the hilum.
NCERT draws a sharp internal distinction within dicot seeds based on where the food is stored. In seeds such as castor, the endosperm — formed as a result of double fertilisation — persists as a food-storing tissue in the mature seed; these are endospermic (albuminous) seeds. In plants such as bean, gram and pea, the endosperm is not present in the mature seed because it has been completely used up during development, and the food is instead stored in the swollen cotyledons; such seeds are non-endospermous (exalbuminous). Castor is therefore the standard NEET example of a dicot that is endospermic, which is why it is so heavily tested.
Figure 1. A dicotyledonous bean seed in section. The seed coat (testa + tegmen) encloses two fleshy cotyledons and an embryonal axis bearing the plumule and radicle; the hilum scar and micropyle pore lie on the coat. (After NCERT Fig. 5.14.)
The monocot seed
Monocot seeds are best studied through the cereal grain of maize. Strictly, the maize grain is a one-seeded fruit (a caryopsis), so its seed coat is membranous and generally fused with the fruit wall. Inside, the bulk of the structure is the endosperm, a large food-storing tissue. The outer covering of the endosperm, adjacent to the embryo, is a proteinous layer called the aleurone layer, which on germination secretes enzymes that mobilise the starchy reserves.
The embryo of maize is small and lies in a groove at one end of the endosperm. It consists of one large, shield-shaped cotyledon — the scutellum — pressed against the endosperm, plus a short axis carrying a plumule and a radicle. Crucially, these two are enclosed in protective sheaths: the plumule is sheathed by the coleoptile and the radicle by the coleorhiza. These sheaths and the scutellum are the diagnostic monocot structures with no counterpart in a dicot seed.
Figure 2. Longitudinal section of a maize grain. The membranous seed coat is fused with the fruit wall; a bulky endosperm is bounded by the proteinous aleurone layer; the embryo bears the shield-shaped scutellum, with the plumule sheathed by the coleoptile and the radicle by the coleorhiza. (After NCERT Fig. 5.15.)
Endospermic vs non-endospermic seeds
A common error is to equate "endospermic" with "monocot" and "non-endospermic" with "dicot." The true basis is whether the endosperm — formed by double fertilisation — is still present in the mature seed. If it persists and stores the food, the seed is endospermic; if it is fully consumed during embryo development and the food shifts to the cotyledons, the seed is non-endospermic.
Endospermic dicot
Castor — a dicot whose mature seed retains endosperm.
Non-endospermic monocot
Orchids — monocots whose seeds lack endosperm.
Those two examples are exactly why the equation breaks. NCERT states that castor is an endospermic dicot, and that while monocot seeds are generally endospermic, some such as orchids are non-endospermic. The reliable rule is to classify by cotyledon number (one vs two) for the monocot/dicot identity, and separately by endosperm presence for the endospermic/non-endospermic identity.
Dicot vs monocot — full comparison
With both seeds dissected, the side-by-side anchors the diagnostic features. The cotyledon count is the primary divide; the scutellum, coleoptile and coleorhiza are monocot-only; the persistent endosperm and the fusion of seed coat with fruit wall typify the cereal grain.
Dicotyledonous seed
2
cotyledons
- Two cotyledons, often fleshy and food-laden
- Seed coat distinct (testa + tegmen), free from fruit wall
- Commonly non-endospermic (bean, gram, pea); castor is endospermic
- No scutellum, coleoptile or coleorhiza
- Examples: gram, bean, pea, castor
Monocotyledonous seed
1
cotyledon (scutellum)
- One shield-shaped cotyledon — the scutellum
- Seed coat membranous, fused with fruit wall
- Generally endospermic with proteinous aleurone layer; orchids non-endospermic
- Plumule and radicle sheathed by coleoptile and coleorhiza
- Examples: maize, wheat and other cereals
| Factor | Dicot seed | Monocot seed |
|---|---|---|
| Cotyledon number | Two | One (scutellum) |
| Seed coat | Distinct testa + tegmen; free | Membranous; fused with fruit wall |
| Food reserve | Cotyledons (non-endospermic) or endosperm (castor) | Bulky endosperm (generally) |
| Aleurone layer | Absent | Present (proteinous) |
| Plumule sheath | None | Coleoptile |
| Radicle sheath | None | Coleorhiza |
Worked examples
In a maize grain, the protective sheath enclosing the plumule and the protective sheath enclosing the radicle are, respectively:
The plumule (shoot) of a monocot embryo is enclosed by the coleoptile, and the radicle (root) is enclosed by the coleorhiza. The order matters — coleoptile is the shoot sheath (think "optile/upward"), coleorhiza the root sheath (think "rhiza = root").
Name one dicotyledonous seed that is endospermic and one monocotyledonous seed that is non-endospermic.
The endospermic dicot is castor, in which the endosperm formed by double fertilisation persists as the food store. The non-endospermic monocot is the orchid, whose seeds lack endosperm. These two examples disprove the assumption that "dicot = non-endospermic, monocot = endospermic."
Identify the shield-shaped single cotyledon of the maize seed and state its function.
It is the scutellum — the one large, shield-shaped cotyledon pressed against the endosperm. It absorbs the food stored in the endosperm and transfers it to the growing embryo during germination.