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 and position of ovule-digieduco

on
TYPES OR FORMS OF OVULES-
Mature ovules i.e. megasporangia in angiosperrns are mainly of five types. The principle of classification is based on the position of the micropyle, chalaza and hilum with regard to one another and also to the placenta.
Types and position of ovule-digieduco


1. Orthotropous or Atropous-In this type of ovule, the micropyle, chalaza and hilum are in one straight line so the ovule remains straight ; the hilum lies at the extreme base, the chalaza and the micropyle follow in succession. This type is noted in members of the families polygonaceae(polygonum) ,piperaceae,urticaceae.

2. Anatropous or Inverted-In this type the ovule is completely inverted, so much so, that the micropyle comes very close to hilum ; the chalaza is upwardly directed. This type is very common in dicotyledonous and monocotyledonous families like Labiatae, Boraginaceae, Euphorbiaceae (Ricinus sp.), Liliaceae, Amaryllidaceae etc.

3. Campylotropous-When the ovule is so curved that the micropyle comes nearer to
hilum. This type is met with in members of the families Cruciferae, Leguminosae, Caryophyllaceae etc.

4. Hemianatropous-When the curvature of the ovule is more pronounced and also affects the embryo sac, so that the embryo sac becomes bent like a horse shoe. This type is noted in families like Alismaceae, Butomaceae, Caryophyllaceae, Portulaccaceae etc.

5. Amphitropous-When the ovule is transverse i.e. nucellus and integuments lie more or less at right angles to the funiculus as seen in species of Lemna (Lemnaceae), Ranunculus (Ranunculaceae), Nothoscordum (Liliaceae) etc.

POSITION OF OVULES WITHIN THE OVARY CHAMBER-
Types and position of ovule-digieduco

1. Erect-When the ovule arises apparently from the base of the ovary directly as seen in Compositae, Polygonaceae etc.

2. Ascending-When the Ovule develops from the side of the ovary wall obliquely and is directed upwards e.g. some members of Ranunculaceae.

3. Pendulous-When the ovule hangs downwards from the top of the ovary e.g. in Some species of Euphorbiaceae, Annonaceae etc.

4. Suspended-The ovule hangs downwardly and obliquely from the upper corner side of the ovarian wall e.g. Ricinus communis (Euphorbiaceae).

5. Horizontal- The ovule arises horizontally from the side of the ovary wall e.g. podophyllum sp. (Berberidaceae).

Comments

Post a Comment