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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Gynoecium or pistil in angiosperm-digieduco

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Gynoecium or Pistil :-Gynoecium or pistil in angiosperm portion.


A. SIMPLE AND COMPOUND GYNOECIUM-A gynoecium is said to be simple When it consists of one carpel only i.e. monocarpellary, this is seen in members of the family Leguminosae-but in case of compound gynoecium, it consists of two or more carpels- this compound type is also known as polycarpellary gynoecium.
Gynoecium or pistil in angiosperm-digieduco

Compound gynoecium may be :
(a) Apocarpous i.e. when carpels are completely free from one another as seen in families Magnoliaceae, Ranunculaceae, Alismaceae etc., and (b) Syncarpous i.e. when two or more carpels of a compound gynoecium are united with each other as seen in families like Cruciferae, Malvaceae, Apocynaceae, Liliaceae etc.

B. COHESION OF CARPELS-Carpels may be united throughout their length (e.g, Solanaceae, Boraginaceae, Acanthaceae etc.), or ovaries and styles are united but stigmas are free (e.g. in Malvaceae), or ovaries are united but styles and stigmas are free (e.g. Dianthus-Caryophyllaceae, Linum usitatissimum-Linaceae), or ovaries are free but upper part of styles and stigmas are united as seen in members of Asclepiadaceae and Apocynaceae.

C. CARPEL AND ITS PARTS-Carpel is the leafy member of gynoecium i.e. pistil. It is the female reproductive organ of flowering plants. A carpel is a megasporophyll which in angiosperms becomes folded (along the midrib, i.e. the dorsal suture and the margins meet-the ventral suture) and modified into following parts-

(a) Basal swollen portion is the ovary containing one or more ovules i.e. megasporangia.

(b) Short or long stalk-Iike protrusion of the ovary is the style. Usually the style is apical i.e. it arises from the top of the ovary ; sometimes style arises from near the base or from the side of the ovary-former is called basillar and the latter is called lateral, e.g Mangifera indica (mango). In plants belonging to the family Labiatae (Leonurus, Leucas, etc.), the ovary is four-lobed with an apical depressionhere the style appears to arise from the innermost base of the ovary and is called gynobasic.

(c) The receptive end (for pollen grains) of the style, which is usually knob-like in
appearance is the stigma. The stigma may be papillose, hairy or lobed-the lobed stigma is often described as bifid, trifid etc. In Crocus sativus (Family lridaceae), the stigmas have funnel shaped form. In Begonia sp. the stigma is profusly branched. Striate i.e. star-like
radiating stigmas is found in Papaver sp.



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