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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What is ovule and its structure-digieduco

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The ovule may be characterized as a juvenile seed or an unripened integumented megasporangium.

It may also be designated simply as “the egg containing organ within ovary.” After fertilization the ovule develops into seed. In angiosperms, ovules are protected by megasporophyll which forms a closed structure (ovary), that is why seeds remain enclosed. In gymnosperms, ovules are not protected but exposed on megasporophyll i.e. carpel resulting into the formation of naked seeds.


What is ovule and its structure-digieduco

STRUCTURE OF AN OVULE

(1) The stalk with which the ovule remains attached to the placenta is called funicle
or funiculus
(2) The point of attachment of the funicle to the body of the ovule is called hilum.
(3) The basal part of the ovule from where the integument or integuments arise is
known as chalaza.

(4) The extension of the funicle beyond the hilum alongside the body of the ovule is known a raphe. A raphe may be ventral or dorsal in an ovule, and may extend up to the base i.e. chalaza of the ovule.
(5) The main body of the ovule consists of a central mass of tissue-the nucellus Winch Is surrounded by one or two envelopes called integuments ; the integuments enclose the nucellus except at the apex, where a small opening is left called micopyle.
(6) Near the micropylar end, a sac-like structure known as embryo sac (female gametophyte), lies embedded into the nucellus. Within the embryo sac towards the micropyle there are three naked cells. The middle one is the largest and is known as oosphere or ovum i.e. egg cell ; two lateral ones are the synergids. Oosphere and the synergids constitute what is known as egg-apparatus. At the centre of the embryo sac lies a composite nucleus, formed by the union of two polar (one nucleus from each pole of the embryo sac) nuclei-this is known as secondary or definitive nucleus. Towards the chalazal end of the embryo sac there are three walled-cells known as antipodal cells. 

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