1. Cell structure and organisation
6 (a) Explain the part played by the cell membrane in the movement of substances into and out of a cell.  (2002 M/J)
Ans. Cell membrane is made up of protein and lipids. It is a partially permeable membrane. It allows the passage of substances in and out of the cells. It allows the water molecules to move in or out of the cells by osmosis. It also allows the movement of mineral ions, glucose, amino acids etc. by active transport where energy released in respiration is used.
(b) Describe a suitable method for preparing a cell for viewing under a microscope. 
Ans. Take a layer of epidermal cells from the inner surface of an onion leaf. Keep the layer of cells on a microscope slide. Put a drop of iodine solution. Keep a coverslip over the layer of cells at an angle to avoid the air bubbles. Use a filter paper to remove the excess iodine solution from the slide. Keep the prepared slide on the stage of the microscope and clip it.