a) Plants are sensitive to light, moisture and gravity:

■ their shoots grow towards light and against the force of gravity

■ their roots grow towards moisture and in the direction of the force of gravity.

b) Plants produce hormones to coordinate and control growth. Auxin controls phototropism and gravitropism (geotropism).

c) The responses of plant roots and shoots to light, gravity and moisture are the result of unequal distribution of hormones, causing unequal growth rates.

d) Plant growth hormones are used in agriculture and horticulture as weed killers and as rooting hormones.