question_answer 47)

  Select the odd one out (a) The movement of water across a semi permeable membrane is affected by the amount of substances dissolved in it. (b) Membranes are made of organic molecules like proteins and lipids (c) Molecules soluble in organic solvents can easily pass through the membrane. (d) Plasma membranes contain chitin sugar in plants.

Answer:

  (d) Each cell is bounded by an extremely delicate, thin elastic living membrane, called the plasma membrane. The plasma membrane is made up of two layers of lipid (fat) molecules with protein molecules which is sand witched between lipid layer. The structure of plasma membrane can be observed under an electron microscope only. It is a selectively permeable membrane which allows the flow of only some substances into the cell and out of the cell. Viruses do not have any membranes. Functions 1. It gives a definite shape to the cell. 2. It provides protection to the in contents of the cell. 3. It regulates entry and exit of substances in to and out of the cell. 4. It can internalize solid and liquid materials by in folding or extending around them. This is the process of active intake of materials, 5. In animal cells, it is involved in adhesion, recognition and in the formation of vesicles, cilia, flagella, microvilli etc.