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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Protoplasm and its properties-digieduco

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The protoplasm is the living substance ; Without protoplasm no life can exist. According to Huxley protoplasm is the “physical basis of life".

A. PHYSICAL PROPERTIES-

The protoplasm is a jelly-like, elastic, viscous, semi-transparent, colloidal and colourless homogeneous fluid. Specific gravity of protoplasm is a little higher than that of water. Protoplasm is mainly jelly-like, i.e. it remains in a gel phase. A gel is a gmup of suspended particles in a semi-solid condition. These gel molecules are held together by different chemical bonds of Varying strength. These bonds of the molecules are changed during the metabolic cycle of the cell. This change of bonds is called sol, i.e., solation.

Structure of the protoplasm may be either-

(a) Reticulate or net-like, or (b) consists of fine fibrils, or (c) granular, or (d) of minute droplets of varying size and shape that remain suspended in another continuous liquid substance as an emulsion. Under the microscope, protoplasm looks granular in structure. Protoplasm exhibits irritability under the innuence of external stimuli like heat shocks, chemicals etc.

B. CHEMICAL PROPERTIES-

Chemically protoplasm is a complex substance. Its formula is still unknown. It is composed of about 85-90% of water and 10-15% of other materials. Of these other materials, about 90% constitute organic matter while the rest are inorganic. Water may exist “free" i.e. as water of solution or “bound”, usually to ionised groups of proteins. Free water is the main solvent of the cell and serves as a medium for a variety of metabolic reactions. Both free and bound water are intimately associated to maintain the colloidal state of protoplasm. The reactions of protoplasm are either neutral or slightly alkaline-sometimes also acidic .Of the organic substances the following are important:

(a) Carbohydrates-composed of carbon (C), hydrogen (H) and oxygen (O). The ratio of hydrogen and oxygen is 2:1, i.e. like water (H2O). The main carbohydrates of the protoplasm are the hexose and pentose sugars. Insoluble polysaccharides are also found to be present in the protoplasm. The percentage of carbohydrates varies from 1 to 1.5.

(b) Proteins-mainly composed of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) ; sometimes sulphur (S) and phosphorus (P) are also present. Albumins, globulins, histories, protamines, nucleoproteins etc. are the main types of proteins found in the protoplasm. The percentage of protein varies from 7 to 10.

(c) Fatty substances-Lipids are the main type of fatty substances, percentage of which varies from I to 2. These are composed of carbon, hydrogen and oxygen. Protoplasm often contains phospholipids-a complex derivative of fats containing nitrogen and phosphorus. The ratio of hydrogen and oxygen is not 2: 1, i.e. not like water.

Inorganic substances-Various types of inorganic salts in the form of chlorides, phosphates, sulphates and carbonates of magnesium (Mg), calcium (Ca), sodium (Na), potassium (K) and iron (Fe) occur within the protoplasm.

Besides, other elements e.g. boron (B), manganese (Mn), zinc (Zn), molybdenum (Mo) etc. may be present in traces. The percentage of these inorganic substances varies from I to 1.5.

Tests for protoplasm-
(1) protoplasm+heat to burning =>smell of ammonia.
(2) protoplasm+ alcohol=> protoplasm coagulates.
(3) protoplasm+iodine solution=> brownish colouration.
(4) protoplasm+ dilute KOH=> protoplasm dissolves.
(5) protoplasm+ Millions reagent=> brick red colouration.
(6) Protoplasm + sulphuric acid and cane sugar=> rose red colouration.

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