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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Anther or microsporangia in angiosperm-digieduco

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Anthers or Microsporangia: Anthers in angiosperm are composed of two anther sacs or lobes separated by a tissue called connective-each lobe or sac consists of two microsporangia separated by a septum. So in an anther there are altogether four microsporangia. Hence a fully developed anther shows quadrilocular structure. In majority of the cases anthers appear bilocular in structure due to absorption of septa separating the two sporangia of anther sac or lobe. Unilocular or one-celled anther, as seen in Malvaceae, arises either due to (a) abortion of one anther lobe and the dissolution of the septum between the two sporangia, or (b) due to the destruction of partition wall (connective) of the two lobes as well as of the septa between the sporangia of each lobe.


Anthers may be introrse (when grooved anther-face, particularly the line of dehiscence, is directed towards the gynoecium or centre of the flower) or extrorse (when grooved anther-face is directed towards petals).
Anther or microsporangia in angiosperm-digieduco

A. ATTACHMENT OF ANTHER TO THE FILAMENT

There are four modes of attachment as follows : .

(a) Innate or Basifixed-When the filament is firmly attached to the base of the anther e.g. species of Carex (Cyperaceae), Solanum (Solanaceae), members of Cruciferae etc.

(b) Adnate-When the filament or its continuation, the connective, is attached to the back of anther throughout the whole length, e.g, Nymphaea sp. (Nymphaeaceae), Magnolia sp. (Magnoliaceae) etc.

(C) Dorsifixed-When the filament lS firmly attached to the back of the anther, e. g Passiflora sp. (Passifloraceae) , sesbania sp  (papilionaceae) etc.

(d) versatile-When filament is attached at a point near the middle of the back of the connective in such a way that the anther can swing free in air, e.g. in some members of Liliaceae, Amarylhdaceae, all members of Gramineae etc.
Anther or microsporangia in angiosperm-digieduco
Dehiscence of anthers

B. DEHISCENCE OF ANTHERS

Anther lobes i.e. microsporangia of angiosperms dehisce or burst in order to enable the pollen grains to come out.

The dehiscence may be :

(1) Transverse-It is seen in one-called anther of Malvaceae,Lemna sp. (Lemnaceae) etc. due to horizontal placing of anther lobe the dehiscence appears to b transversely slit like the lid of a box.

(2)Apical or Porous-In Solanum sp. the dehisccnce of anther lobes takes place through apical pores.

(3) Valvular-When dehiscence or bursting of anther lobes is effected by means of trap door-like, fiappy valves as in Berberis sp. (Berberidaceae), Litsea sp., Cinnamomum zeylanicum (Lauraceae) etc.

(4) Longitudinal- This is very common here the anther lobe splits lengthwise from base to apex along the line of suture, e.g vitis vinifera(Vltaceae), Datura sp. (Solanaceae) ,
Anther or microsporangia in angiosperm-digieduco

C. FORMS OF ANTHER LOBES- Anther lobes may be:

(1) linear--the anther lobes are long and narrow, as in Acalypha sp. (Euphorbiaceae).
(2) Round or Oval as in Mercurialis annua (Euphorbiaceae).
(3) Appendiculate-where the anther lobes are provided with appendages of different
kinds e.g. flattened leafy in Erica cinerea (Ericaceae), pointed in Vaccinium sp. (Vacciniaceae), Justicea sp. (Acanthaceae) etc.
(4) Reniform i.e. kidney-shaped as in members of Malvaceae.
(5) Sagittate i.e. arrow-shaped e.g. in Lochnera (Vinca) sp. (Apocynaceae).
(6) Sinuous-Lobes convoluted forming ‘S’-shaped structure, e.g. in members of Cucurbitaceae.
(7) Filamentous-When the lobes are thread-like, e.g. Zostera sp. (Potamogetonaceae).





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