CBSE Class 5 Science Seed Structure and Germination Notes Set 02

Seeds and new plants

Most fruits and vegetables contain seeds, and new plants grow from these seeds. A seed holds a tiny baby plant and the food it needs for its first days of growth.

Parts of a bean seed

1. Seed coat (testa): the tough outer covering that protects the baby plant inside. 2. Hilum: a scar on the curved side of the seed that shows where it was attached to the fruit. 3. Micropyle: a tiny pore near the hilum through which the seed takes in water. 4. Cotyledons: the two seed leaves that store food for the growing baby plant. 5. Embryo: the baby plant itself. It has two parts: the radicle, which grows into the root, and the plumule, which grows into the shoot.

Two types of seeds

Dicotyledonous seeds have two cotyledons, as in pea, bean, gram and mango. Monocotyledonous seeds have only one cotyledon, as in maize, rice, wheat and barley.

Germination

The growth of a seed into a young plant, or seedling, is called germination. A seed needs water, air and warmth to germinate. Light is not needed until the seedling has come out of the soil and starts making its own food.

Stages of germination of a bean seed

1. The seed takes in water, becomes soft and swells. 2. The seed coat breaks open and the radicle comes out and grows downward as the root. 3. The plumule grows upward as the shoot. 4. Small leaves open on the shoot and the plant starts making its own food. 5. The cotyledons shrink as their food is used and finally fall off.

Why seeds are sown with space

A seed grows into a plant that needs room for its roots and leaves. If seeds are sown too close together, the seedlings compete for water, light and nutrients, and many grow weak. A farmer therefore sows seeds at proper distances. Seeds are also sown at a suitable depth: too deep and the seedling cannot reach the surface, too shallow and the seed dries out or is eaten by birds.

Activity: what do seeds need?

Take four containers with bean seeds. In the first, give the seeds moist cotton and keep them in a warm place. In the second, drown the seeds in excess water, so they get no air. In the third, keep the seeds dry. In the fourth, keep moist seeds in a very cold place. After two days, only the first set sprouts. This shows that seeds need water, air and warmth to germinate.

Seed or fruit?

Seeds are formed inside fruits. When we eat a bean pod, a pea pod or a mango, we are opening a fruit that holds one or more seeds. The fruit protects the seeds while they develop and often helps to spread them. Seeds can stay alive but inactive for many months until they get enough water and warmth, which is why farmers can store seeds and sow them in the right season.

Worked examples

Example 1. Which part of the seed becomes the root? Answer: The radicle.

Example 2. Where does the seedling get food in its early days? Answer: From the cotyledons, which store food for the baby plant.

Example 3. Why should seeds be sown at some distance from one another? Answer: So that each seedling gets enough space, light, water and nutrients.

Quick Check Questions