notes of structure and germination of seed

STUCTURE AND GERMINATION OF SEED

SEED :-  it is develop from a mature ovule after fertilization and is usually enclosed within the fruit.

                It is final product of sexual reproduction.

Seed dormancy is defined as a state in which seeds are prevented from germinating even under environmental conditions normally favorable for germination.

Basic structure of seed:-

·         Seed Coat:- it, is the outer protective covering of seed.

It is made up of two layer

o   Testa :- it is outer layer and it is thick, very hard and dry

o   Tegmen:- it is inner layer and it is thin

·         Hilum:- the structure where seed was attached to the ovary wall. it is concave side of the seed.

·         Micropyle:- the opening where pollen tube enters the ovule.

it serves two function:-

Ø  When soaked in water, the seeds absorb water mainly through it and make it available to the embryo for germination.

Ø  Diffusion of respiratory gases for the growing embryo takes place through it.

·         Embryo:-  it is fleshy and soft structure inside the seed coat.

Embryonal axis:- it is the short axis in which  seed leaves and cotyledons are attached. It formed 4 parts

1.       Radical:- it is the lower part of the axis that gives rise to the primary root.

2.       Plumule:- it is the part of the axis between the cotyledon which forms the shoot.

3.       Hypocotyl:- it is the part of the axis of the embryo between the cotyledons and the radical.

4.       Epicotyls:- it is the part lying above the cotyledon. It bears the plumule at its tip.

·         Endosperm:- it is food storing tissue in seed. Infact in coconut the water is nothing it is a endosperm .

TYPES OF SEED

MONOCOTYLEDONOUS SEED 1.       Only one cotyledon present in the embryo. 2.       Cotyledons is thin and small and lacks food materials. 3.       Endosperm is mostly present and stores food. 4.       Radicle is protected by coleorhiza and plumule by coleoptile. 5.       Example:- maize, rice, wheat

DICOTYLEDONOUS SEED 1.       Two lateral cotyledons are present in the embryo axis. 2.       Cotyledons are fleshy and store food. 3.       Endosperm is mostly absent and lacks food. 4.       Coleorhiza and coleoptiles are absent. 5.       Examples :- pea, bean, gram etc.

ALBUMINOUS OR ENDOSPERMIC  SEED 1.       In this seed food is stored in the endosperm 2.       Cotyledons are thin 3.       Example:- In dicoat seed castor, poppy, custard apple In monocoat seed maize, rice, wheat, palm and millets

EXALBUMINOUS OR NONENDOSPERMIC SEED 1.       In this seed food is stored in cotyledons 2.       Cotyledons are fleshy. 3.       Examples:- In dicoat Gram, pea, mango and mustard In monocot seed Vallinsneria, orchids and Amorphophallus.

QUESTION FOR PRACTISE

1.       differentiate between dicot and monocot seed

2.       differentiate between endospermic and non endospermic seed.

3.       Write the function of microplye.

Find out the monocoat and dicoat seed :- maize, rice, Vallinsneria, orchids , Amorphophallus wheat, palm ,millets

STRUCTURE OF BEAN SEED

·         It is dicotyledonous seed.

·         It is kidney shaped and reddish brown in colour.

·         Raphae:-  it is white line which is present on the convex side.

·         Micropyle:- it is a minute pore present at one end of raphae.

·         Hilum:- it is whitish scar present at other end of raphae.

·         Funiculus:- it is the structure where seed is attached to the fruit.

·         Testa:- it is hard and brownish and helps the seed from injury and infection.

·         Tegmen;- it is pale yellow in colour.

·         Radical:- it forms the root.

·         Plumule:- it forms the shoot.

STRUCTURE OF A MAIZE GRAIN

·         It is a monocotyledonous.

·         It is small, one seeded fruit.

·         It is caryopsis.

·         Caryopsis :-  in dry fruit where the seed coat is fused with the wall of the fruit.

·         It is yellowish in colour.

·         It has two unequal portion:-

·         Epithelium:- it is thin layer.

·         Endosperm:- it is the bigger portion which lies towards the broader side. The yellowish endosperm is the food storage tissue of the grain and rich in starch

·         Aleurone layer:- the outermost layer where protein is stored.

·         Embryo:- the endosperm towards the pointed end lies an opaque body called the embryo.

·         Scutellum:- the embryo consists of one large and shield shaped cotyledon. This is also called scutellum.

·         Plumule:- upper end of scutellum

·         Radical:- lower end of scutellum.

·         Coleoptile:- the sheath covering the plumule is known as coleoptile.

·         Coleorhizae:- the sheath covering the radical is known as coleorhizae.

Q . what are the reserve foods in seeds?

Ans. Seed contains starch, oil, proteins and carbohydrate.

Starch:- it found in wheat, rice, barley and oat seeds.

Oil:- it is found in castor, sunflower, groundnut

Protein :- pulses, pea

Carbohydrate:- potato

QUESTION FOR PRACTISE:-

1.       Write the difference between bean seed and a maize seed?

2.       Draw the diagram of bean seed and maize seed?

3.       Define the following:-

Aleurone layer, coleorhizae, coleoptile,

SEED GERMINATION

The process during which the food reserves present in a seed are broken down and the embryo starts to grow is called germination.

·         Nondormant seeds:- the seed which can germinate under favourable condition are called nondormant seeds.

·         Dormant seeds:- the seed which cannot germinate under favourable condition are called dormant seeds.

Q . write the condition under the dormant seeds?

Ans. After the development, the seed growth stops.

The seed now, begins the lose its water content.

The seed coat becomes impermeable to air and moisture.

At this stage, all the physiological activities are very slow and very little food is used.

Even respiration is very slow.

In this dry condition, the seed can remain alive and dormant for long periods.

The seed in this condition are called dormant, and this stage is called dormancy.

Q . define after ripening?

Ans. During the period of dormancy, the seeds undergo certain internal changes called after ripening.

PROCESS OF GERMINATATION

Imbibition of water

Rupture of seed coat

Absorption of water by embryo

Hydrolysis of carbohydrates, lipids and proteins

Transport of nutrients to embryo

 

Cell division and growth of embryo

 

Seedling formation

CONDITION NECESSARY FOR SEED GERMINATION

1.       MOISTURE

2.       TEMPERATURE

3.       OXYGEN

4.       LIGHT

·         MOISTURE :-  In the dormant seeds, the water content is only 10-15%.

Moisture softness the seed coat and the testa.

Seed swell up and embryo breaks through the softened seed coat and comes out easily.

Q . how you prove that water is necessary for seed germination?

Ans. (i) take two petridishes  and mark them as A and B. Spread cotton wool in both the petridishes. Moisten the cotton wool in petridishes A with water.

(ii) place equal no. Of garm seeds in both the petridishes. Keep both the petridishes in a room at normal temperature (25^.C to 30^.C).

(iii)we observe after two days that seeds in petridishes A will germinate whereas seed in petridish B will not germinate.

HYPOGEAL GERMINATATION 1.       The cotyledons remains underground 2.       In this germination epicotyl elongates 3.       Examples :- bean, gourd, castor, cotton and tarmarind.

EPIGEAL GERMINATION 1.       The cotyledons are pushed above the ground. 2.       In this germination hypocotyl elongates 3.       Examples :- gram, pea, maize, rice