Cell membrane function and difference-digieduco

on
  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 th...
0

Types of Germination-digieduco

on
There are three types of germination, e.g. (i) Hypogeal (ii) Epigeal and (iii)Viviparous types.


I. Hypogeous or Hypogeal germination-In this type of germination the cotyledon(s) remain in the same place where the seed was placed first-neither they are moved upward nor are they transformed into first pair of leaves of the seedling. The radicle is the first to come out piercin g the seed coat near the micropyle, it gradually grows and always bends down to the earth ; the plumule in the meantime grows upwards.

Among dicotyledonous exalbuminous seeds, gram (Cicer arietinum), pea (Pisum sativum), mango (Mangifera indica) etc. and among dicotyledonous albuminous seeds water lily (Nymphaea esculenta) are the examples of hypogeous germination, Monocotyledonous exalbuminous seeds like Pothos, Amorphophallus, etc. and monocot albuminous seeds like maize (Zea mays), rice ( Oryza sativa) etc. are the typical examples of this type of germination. .

II. Epigeous or Epigeal germination-Here the radicle comes out first, bends down to the earth to form tap root as usual, the consequent growth and deveIopment of plumule to form shoot system is delayed a bit. The hypocotyl grows faster and forms a loop which straightens up, as a result the cotyledons are carried upwards.

Examples epigeous germination :

Dicotyledonous exalbuminous seeds : bean (Dolichos lablab), tamarind (Tamarindus indica), gourd (Cucurbita maxima) etc. Dicotyledonous albuminous seeds : castor (Ricinus communis), Basella sp., etc.

Monocotyledonous exalbuminous seed-Alisma plantago.

Monocotyledonous albuminous seeds-onion (Allium cepa), hoghla (Typha elegans) etc.
Types of Germination-digieduco

III. Vivipary or Viviparous germination -Several genera of mangrove plants i.e. halophytes show this phenomenon. Here the embryo of seed undergoes development (i.e. germination) without any resting period with the fruit still attached to and nourished by the parent plant. In species of Ceriops, Rhizophora of the family
Rhizophoraceae , the embryo grows out not only from seed but emerges out from the fruit, so that the hypocotyl and the radicle grow and project out to a considerable length from die fruit-finally the seedling breaks, falls vertically on the salty mud and gets embedded in it, and thrusts the radicle in the muddy saline soil. The cotyledons serve as sucking organs. In Aegiceras sp. (Myrcinaceae) the embryo comes out of the seed, but remains within the fruit, it is green and has a large plumule. 

Comments

Post a Comment