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

Dispersal by wind-digieduco

on
Dispersal by wind is one of the best carriers of seeds to distant places, so the morphological structures of such wind-borne seeds and fruits are expected to be in possession of such organs which can help them to float in air and can convey them to a distance, such contrivances in wind borne seeds are :

1. Light weight-Very small, dry seeds of orchids and grains (seeds and fruits) of grasses are easily carried by wind due to their light weight.
Dispersal by wind-digieduco

 2. Parachute mechanism-Some seeds and fruits are provided with appendages acting as parachute-these help them to float in air of these appendages the following are important :
Dispersal by wind-digieduco

 (a) Comma (tuft of hairy outgrowth of testa at one end of seeds, sometimes at both ends i.e. double)-In species of Alstonia, Holarrhena (Apocynaceae), Calotropis (Asclepiadaceae) etc. comma helps the seeds to be drifted along to a long distance.

(b) Pappus-It is the modification of calyx lobes in the form of hairs. The fruits of Vernonia sp. (Compositae), Dipsacaceae with tuft of pappus are seen being carried in air.

(c) Hairy outgrowth of testa as seen in seeds of Gossypium herbaceum (cotton, Malvaceae) all over their body.

(d) Persistent feathery styles-This is seen in fruits (achenes) of the species of Clematis, Naravelia, etc. of Ranunculaceae; by means of these structures fruits can float in air.

(e) Balloon-like inflated persistent calyx of Physalis sp, inflated ovaries of the legume of Colutea arborescens, inflated fruits (capsule) of Cardiospermum helicacabum help those plants to float in air for sometime.
Dispersal by wind-digieduco

3. Wings-Wing-like expansion of different types may develop in fruits and seeds which help them to float in air. The seeds of Moringa olifera (Moringaceae), Swietenia mahoganii (Meliaceae), Oroxylon sp. (Bignoniaceae) are winged (developed from testa). In Shorea robusta (Dipterocarpaceae) persistent sepals form wings. Hiptage benghalensis (Malpighiaceae) Dioscorea alata (Dioscoreaceae) and species of Fraxinus, Acer, etc. have fruit-wings developed from fruit pericarp.
Dispersal by wind-digieduco

4. Censer mechanism-This is a mechanism by which very small seeds are liberated from the fruits slowly through pores and dispersed to a distance after fruits are being shaken by wind. In Argemone mexicana, Papaver somniferum (Papaveraceae), Aristolochia gigas (Aristolochiaceae) etc. dispersal of seeds by this mechanism is noted. 

Comments

Post a Comment