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 th...
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Androecium in angiosperm-digieduco

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Androecium : The androecium in angiosperm is the first essential and the third member of the floral whorl. Androecium is the male reproductive component of a flower and its individual members are the stamens which are the microsporophylls. Each stamen  has a stalk, called the filament and at its top a sac-like structure, called anther: Each anther has normally two lobes known as anther lobes.The anther lobes are connected by a tissue known as connective. Each anther lobe has two chambers called pollen sacs or microsporangia. Pollen sac contains pollen grains i.e. microspores.

Androecium in angiosperm-digieduco

The number of constituent stamens in an androecium varies from oneto many. In a floral whorl the stamens i.e. microsporephylls are inserted in one or more whorls, or stamens may be arranged spirally on an elongated thalamus as in Michelia champaca (Magnoliaceae).
Androecium in angiosperm-digieduco

Androecium is said to be diplostemonous when stamens occur in two whorls, those of outer one alternate with petals (antisepalous) and the inner whorl alternate with sepals (antipetalous). Examples-Cassia fistula (Caesalpinaceae), Lythrum sp. (Lythraceae) etc. Another condition is seen where there are two whorls of stamens of which the first whorl alternating with sepals (antipetalous) and the second whorl alternating with petals (antisepalous) This condition is described as obdiplostemonous. Example-Geranium sp. (Geraniaceae) and many species of the Family Rutaceae,oxalidaceae etc.
Androecium in angiosperm-digieduco

Isostemony is the term applied when stamens are in one whorl and the number of stamen equal to the number of sepals and petals.

Stamens in an androecium may vary in length In tetradynamous androecium, common in Cruciferae, the stamens are in two whorls; outer two are shorter and inner four longer as shown in formula A(2+4) or vice versa.

In didynamous androecium, 4 stamens are in one whorl-the posterior pair is shorter 1 an the anterior or vice versa as shown in formula A2+2. This is seen in families like
Labiatae, Acanthaceae, Scrophulariaceae etc. In a whorl, when stamens of different lengths occur, the androecium is termed heterodynamous e.g. Cassia sp. of Caesalpinaceae.

Stamens may vary in number as follows :
(i) Normally the number is equal to the number of Sepals and petals i.e. isostemonous.
(ii) Stamens may be monandrous , diandrous, triandrous, tetra-penta-hexa and polyandrous.


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