(a) Why must a cell made 'competent' in biotechnology experiments ? How does calcium ion help in doing so ?
(b) State the role of 'biolistic gun' in biotechnology experiments.

why is making cells competent essential for biotechnology experiments? List any two ways by which this can be achieved.

(a) Why should a bacterium be made 'competent? (b) Explain the role of 'microinjection' and 'gene gun' in biotechnology .

Explain the following : (a) How does the middle ear help in hearing ? (b) Why does vitamin A deficiency produce night-blindness ? (c ) What is the role of lacrimal gland ? (d) How does the iris adjust the size of the pupil ?

State the working principle of potentiometer. With the help of the circuit diagram, explain how a potentiometer is used to compare the emf's of two primay cells. Obtain the required expression used for comparing the emfs. Write two possible causes for one sided deflection in a potentiometer experiment.