What is a seed?
Before discussing seed germination, it's helpful to review the meanings of the terms fruit, seed, and grain. A fruit is an enlarged, ripened ovary with its wall forming the fruit wall, which encloses the seed. The fruit protects the seed and aids in its dispersal.
Examples include a mango and pea pod.
Seed
A seed is a mature ovule. It contains an embryo that can grow into a new plant. The seed coat protects the embryo from physical harm. Examples include bean seeds and peas.
Grain
In plants like maize and wheat, the grain is a fusion of the fruit wall and the seed coat, forming a single protective layer.
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Classification and Structure of Seeds
Types of Seeds
Seeds are broadly classified into two types: monocotyledonous and dicotyledonous.
Monocotyledonous seeds have one cotyledon (seed leaf), such as in maize and grasses.
Dicotyledonous seeds have two cotyledons, like in peas, grams, and beans.
Seed Size and Variety
Seeds come in various sizes:
Some are tiny and barely visible to the naked eye, like poppy and orchid seeds.
Some are large, such as in watermelons, pumpkins, or even mangoes (the stony part).
The largest seeds are from coconuts and double coconuts.
While the size, shape, and structure of seeds differ among plant species, most seeds share a similar basic structure.
Based on the presence of endosperm, seeds can be classified as follows:
(i) Albuminous (endospermic): In these seeds, the cotyledons are thin and membranous, and the endosperm remains present. Examples include:
Dicot albuminous seeds: poppy, custard apple.
Monocot albuminous seeds: cereals, millets, palm.
(ii) Exalbuminous (non-endospermic): In these seeds, the cotyledons store food, becoming thick and fleshy. Examples include:
Dicot exalbuminous seeds: gram, pea, mango, mustard.
Monocot exalbuminous seeds: Vallisneria, orchids, amorphophallus.
The Bean Seed
There are various kinds of beans, such as broad bean, lima bean, and French bean, but their seeds generally share the same structure. Most are kidney-shaped with both a convex and a concave side.
Structure of Bean Seed
A&B – External Structure, C – Testa Removed, D – Seed Cut Open to Show Various Parts
Seed Coat (Testa): The outermost, hard, brownish layer that protects the inner parts of the seed from damage and attacks by bacteria, fungi, and insects.
Tegmen: A thin inner layer next to the testa, providing additional protection.
Hilum: A distinct, white, oval scar on the concave side of the seed, indicating where the ovule was attached to the ovary wall.
Micropyle: A tiny pore near the hilum, marking the entry point of the pollen tube. It serves two functions:
Absorbs water for the embryo during germination.
Allows the diffusion of respiratory gases for the growing embryo.
Cotyledons: Two thick structures beneath the seed coat containing food for the embryo and providing protection. Separating them reveals the tiny embryo.
Embryo: Consists of:
Radicle: Later forms the root.
Plumule: Later forms the shoot, including a short stem with tiny leaves and a growing point.
(Note: Do not confuse "radicle" with "radical," a chemistry term, to avoid losing marks in exams.)
Maize Grain
Maize Grain: A fruit where the fruit wall and seed coat are fused into a protective layer, making it a grain.
Embryo Location: Indicated by a small, light-colored oval area on one side of the grain.
Endosperm: The major part of the grain, rich in starch, separated from the embryo by a thin epithelial layer. The outermost layer of the endosperm is rich in protein and called the aleurone layer.
Embryo: Contains a single cotyledon (scutellum), a radicle, and a plumule.
Radicle: Located towards the pointed end, enclosed in a protective sheath called the coleorhiza.
Plumule: Located towards the upper broader side, enclosed in a protective sheath called the coleoptile.
Monocotyledonous and Endospermic: Maize grain is a type of grain with one cotyledon and an endosperm. Examples include rice, wheat, and oats.
Major Differences between Bean Seed and Maize Grain
BEAN | MAIZE |
| One cotyledon (scutellum) Large endosperm present. Small embryo. Plumule leaves rolled. Plumule very small. Hilum and micropyle not visible. The seed wall and the fruit wall fused to form a single grain with no separate seed. |
Key features of a seed:
Formed from a fertilised ovule.
Has an embryo that grows into a new plant.
Contains stored food for early development.
Protected by a seed coat.
Capable of dormancy to survive harsh conditions.
Functions of a Seed
Reproduction – ensures continuity of plant life.
Food storage – provides nutrition for the embryo during germination.
Dispersal – seeds help plants spread to new areas.
Dormancy – allows seeds to survive unfavourable conditions.
Economic importance – seeds are the primary source of food for humans and animals (grains, pulses, nuts, etc.).
Structure of a Seed
Though seeds differ across species, the basic structure includes:
Seed Coat (Testa & Tegmen)
Outermost protective covering of the seed.
Testa is the outer coat; tegmen is the inner coat.
Protects the embryo from mechanical damage, pathogens, and water loss.
Embryo
The young plant inside the seed.
Consists of:
Radicle → develops into root.
Plumule → develops into shoot.
Cotyledons → seed leaves, storing or absorbing food.
Endosperm (in some seeds)
Nutritive tissue formed after fertilization.
Provides stored food (starch, proteins, oils) to embryo.
Hilum and Micropyle
Hilum: scar on seed coat marking attachment point to fruit.
Micropyle: small pore for water and gas entry during germination.
Importance of Seeds in Biology
Agricultural Importance
Basis of crop cultivation.
Provide grains, pulses, oilseeds, and nuts.
Ecological Importance
Seeds aid in plant dispersal by wind, water, or animals.
Maintain plant diversity.
Economic Importance
Source of food, oils, beverages, spices, and fodder.
Seeds like coffee, cocoa, and mustard have commercial value.
Survival Mechanism
Seeds ensure dormancy, helping plants survive harsh climates.
FAQ on Seed and Types of Seed
A seed is the mature reproductive structure of a flowering plant that contains an embryo capable of growing into a new plant. It also includes a protective outer covering called the seed coat and a stored food supply that nourishes the embryo during the early stages of germination. Seeds develop after fertilization inside the ovule and play a vital role in plant reproduction. They help plants spread to new locations and survive until environmental conditions become suitable for growth. Understanding seeds helps students learn about plant life cycles, reproduction, and the continuation of plant species.
Seeds are important because they ensure the reproduction and survival of plant species. They protect the developing embryo from harsh environmental conditions and provide stored nutrients that support early growth after germination. Seeds also help plants disperse to different locations through wind, water, animals, or human activities, reducing competition for resources. This ability increases the chances of successful growth in suitable environments. Studying the importance of seeds helps students understand how plants maintain their populations, adapt to changing conditions, and contribute to healthy ecosystems by producing future generations of vegetation.
A typical seed consists of three main parts: the embryo, the seed coat, and the food reserve. The embryo is the young developing plant that will grow into roots, stems, and leaves. The seed coat forms a protective outer layer that shields the embryo from physical damage and drying. The food reserve supplies nutrients required during germination until the young plant begins making its own food through photosynthesis. Understanding these parts helps students recognize how each component contributes to successful plant development. Together, they enable seeds to survive, germinate, and produce healthy new plants.
A seed grows into a new plant through a process called germination. When it receives enough water, oxygen, and the right temperature, the seed absorbs moisture and becomes active. The seed coat softens, allowing the embryo to begin growing. The root emerges first to absorb water and anchor the plant, followed by the shoot, which grows upward toward sunlight. As leaves develop, the young plant starts producing its own food through photosynthesis. Learning about germination helps students understand the early stages of plant growth and the conditions necessary for healthy plant development.