Cell membrane function and difference-digieduco

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  Functions of cell membrane : (a) The proteins and enzymes present in the cell membrane helps in the transport of certain substances like sugar, sodium and other ions etc. across the cell membrane. (b) Cell membrane protects the internal structures of the cell and different organelles of the cytoplasm. (c) It maintains the shape of the cell. (d) It acts as a selective permeable membrane because it allows to pass certain substances while others are not, hence it helps in the transport of selective materials from and to the cells. (e) The membranes on the cytoplasmic organelles and nucleus most probably formed from the plasma membrane. (f) Other important functions of cell membrane of the cells are endocytosis and exocytosis . Endocytosis is the process by which materials are transported into the cells by the formation of vesicles. It includes two processes-phagocytosis (cell eating) and pinocytosis (cell drinking). The reverse process of endocytosis is exocytosis. During this p
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Germination of different kinds of Seeds and Grains-digieduco

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Germination of different kinds of Seeds and Grains : 

I. HYPOGEAL TYPES

A. Dicotyledonous exalbuminous seeds-
Germination of different kinds of Seeds and Grains-digieduco

1.PEA (Pisum sativum, Papilionaceae)--Radicle is the first to come out, it gradually grows and always bends down to the soil forming the root system. Usually it forms the main root with secondary branches. In the meantime the plumule grows upwards due to the elongation of epicotyl and forms the shoot. The cotyledons remain under the soil, the function of which is the storing of food to be utilised at the time of germination.


2. GRAM (Cicer arietinum, Papilionaceae)-Like pea, cotyledons remain in the same place where the seed was placed first-the storing food of cotyledons is utilised at the time of germination.
Germination of different kinds of Seeds and Grains-digieduco

3. MANGO (Mangifera indica, Anacardiaceae)-The seed is provided with seed coat find hard endocarp-endocarp and seed coat rupture due to swelling as a result of the Intake of water. The radicle first comes out and fdrms the tap root system : next the epicotyl grows and comes out and as a resuit the plumule is taken out of the soil through a slit of the shoot system. The cotyledons remain as it is within the endocarp which remain on or Within the soil, thus the germination is hypogeal.


B. Monocotyledonous albuminous seeds

4. MAIZE OR INDIAN CORN (Zea mays, Gramineae)--Here the single cotyledon 0r scutellum neither comes outof the seed during germination nor forms a green structure but, remains all along attached to the vast endosperm functioning as sucker. At first the radicle is to come out piercing the fruit wall and coleorhiza and immediately after it, several other roots (generally 3) develop from a region above the radicle-those roots are called seminal roots. Radicle and seminal roots may persist forever but adventitious mots develop very soon from the base of the plumule above the mesocotyl. In the meantime Coleoptile and mesocotyl elongate, and the plumule breaks through the coleoptile and develops into shoot.


 5. RICE GRAIN (Oryza sativa, Gramineae)--Like maize but radicle and seminal roots do not persist, instead adventitious roots develop from the base of the plumule and form the fibrous root system. First coleorhiza pierces the base of the grain and then radicle comes out to the soil piercing the coleorhiza.
Germination of different kinds of Seeds and Grains-digieduco

6. PALM TYPE-This type of germination is the characteristic of Palmae e. g coconut (Cocos nucifera), fan palm (Borassus flabellifer), date palm (Phoenix sylvestris) etc.

In this type of germination the cotyledon at first begins to grow. The basal part of cotyledon emerges out of the seed by forcing open the soft tissue above the embryo, and grows to a long semi-hollow tubular structure which penetrate the soil ; the axis of the embryo is slender and small, carried off along with this long tubular structure known cotyledonary sheath and is encased by it near the tip. The upper part of the cotyledon also grows into a spongy mass lying attached to the endosperm functioning as sucking and digestive organs ; later the radicle pierces the radicle sheath and grows to form primary root system in the soil. Next the plumule bursts out from one side of the sheath and form aerial leaves. The radicle does not persist to form tap root but in its place numerous adventitious roots come out from the base of the shoot.

II. EPIGEAL TYPES
A. Dicotyledonous exalbuminous seeds

1.TAMARIND (Tamarindus indica, Caesalpinaceae)--The hard testa bursts and radicle comes out first, bends down to the soil and forms root system. Now the hypocotyl grows faster and pulls out the two fleshy cotyledons above the soil. The plumule then grows out into the aerial shoot. The cotyledons remain attached to the elongated vertical hypocotyl for pretty long time, then become greenish, shrivel up gradually and finally fall off after the utilization of food matter.
Germination of different kinds of Seeds and Grains-digieduco

2. GOURD (Cucurbita maxima, Cucurbitaceae)-Like tamarind the radicle grows out first and fixes the seed to the soil by the root system developing from the radicle. The hypocotyl grows rapidly,forms a loop which straightens up and pulls out the seed. Finally the seed coat gets detached and the cotyledons are exposed and become leaf-like green bodies ; then they are turned into a pair of seedling leaves. Now the plumule which lies hidden between the two cotyledons is exposed and forms the aerial shoot.

B. Dicotyledonous albuminous seed-

3. CASTOR (Ricinus communis, Euph orbiaceae)--Here the testa is hard and SheII-Iike which bursts near the caruncle and the radiclc grows out through it. The two leafy cotyledons
together with endosperm are pushed upwards and come out of the soil by the rapid growth of the hypocotyl. Next the testa cracks and falls off and the cotyledons  open up to form green leafy structures after the endosperm is consumed by the cotyledons. The plumule gradually develops into a leafy shoot.Finally the cotytedonary leaves Wither and fall off.

C. Monocotyledonous albuminous seed
Germination of different kinds of Seeds and Grains-digieduco

4. ONION (Allium cepa, Liliaceae)-This is an albuminous seed as the endosperm is stored within the seed ; embryo is curved and embedded within the endosperm.

The radicle comes out through the sharp end of the seed and goes into the soil. The cotyledon elongates, as a result the base of the curved cotyledon grows out of the seed forming a loop-it turns green and forms the first leaf-like structure ; further growth pushes out the seed from the soil. The coiled end of the cotyledon still remains within the seed and absorbs food material from the endosperm. Further growth of the cotyledon results in the straightening of the green leafy cotyledon bearing the seed at the apex. The plumule, which is not visible and remains covered by the base of the cotyledon in the form of sheath now pierces the sheath, and comes out in the form of a cylindrical foliage leaf. In the meantime adventitious roots develop from the base of the bulb which is actually formed from the base of the plumule sheath.

D. Monocotyledonous exalbuminous seeds
Germination of different kinds of Seeds and Grains-digieduco

5. In Alismaceae, e.g. species of Alisma, Sagittaria, etc. the seeds are exalbuminous, the food for the nourishment of the embryo is stored either in the single cotyledon or in the large hypocotyl. Here the radicle comes out first, after breaking through the seed coat, it does not grow to form the main root. The hypocotyl after emerging from the seed grows upwards with the single cotyledon being carried at its tip ; circle of fibrous roots spring from the base of the hypocotyl.

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