Seed | Note 6 |standard 11| morphology of flowering plants | notes | NCERT| Biology

 

Standard 11 

Morphology of flowering plants

Morphology of flowering plants| Seed | Structure of Dicotyledonous seed | structure of monocotyledonous seed| NCERT short note| Best biology short note | standard 11

Note 6

Seed

The ovules after fertilisation, develop into seeds. 

A seed is made up of a seed coat and an embryo. 

The embryo is made up of 

• a radicle
• a plumule
• an embryonal axis 
• Cotyledon: one (as in wheat, maize) or two cotyledons (as in gram and pea).

Structure of a Dicotyledonous Seed

Seeds of dicotyledon plants - such as grams, pea, all pulses

The outermost covering of a seed is the seed coat. 

The seed coat has two layers, 

1. the outer testa and 
2. the inner tegmen. 

The hilum is a scar on the seed coat through which the developing seeds were attached to the fruit.

Above the hilum is a small pore called the micropyle. - important while germination 

Within the seed coat is the embryo,

- consists an embryonal axis and two cotyledons. 

The cotyledons are often fleshy and full of reserve food materials. - required for vitality of seed in adverse conditions

At the two ends of the embryonal axis are present the radicle and the plumule

Endospermic seeds: 

In some seeds the endosperm formed as a result of double fertilisation, 

Eendosperm is a food storing tissue

Such seeds are called endospermic seeds. 

Example: seeds of castor

Non-endospermous seeds: 

In some seeds, the endosperm is not present in mature seeds

It gets utilised during development of seed and embryo 

such seeds are called non-endospermous.

Example : bean, gram and pea 

Structure of Monocotyledonous Seed

Generally, monocotyledonous seeds are endospermic 

but some as in orchids are non-endospermic. 

In the seeds of cereals such as maize the seed coat is membranous and generally fused with the fruit wall. 

The endosperm is bulky and stores food. 

The outer covering of endosperm separates the embryo by a proteinous layer called aleurone layer. 

The embryo is small and situated in a groove at one end of the endosperm. 

It consists of 

• one large and shield shaped cotyledon known as scutellum
• and a short axis with a plumule and a radicle. 

The plumule and radicle are enclosed in sheaths.

Plumule is enclosed with coleoptile.

Radicle is enclosed with coleorhiza.