Plants have neither a nervous system nor muscles, even then they respond to stimuli. For example, the leaves of chhui-mui (touch-me-not) plant when touched begin to fold up and droop.

(a) How is the information communicated in "touch-me-not" plants ?

(b) What enables the plant cells to bring out the observable response ?

(c) Differentiate the movement mentioned above from the movement of tendrils in a pea plant.

(a) What are chromosomes ?

(b) Explain in brief how stability of DNA content of a species is ensured in sexually reproducing organisms ?

Consider the following electric circuit :

Calculate the values of the following :

(a) The total resistance of the circuit

(b) The total current drawn from the source

(c) Potential difference across the parallel combination of 10 Ω and 15 Ω resistors

(a) Write the relationship between resistivity and resistance of a cylindrical conductor of length l and area of cross-section A. Hence derive the SI unit of resistivity.

(b) Why are alloys used in electrical heating devices?