2.81 describe the geotropic responses of roots and stems

Okay so i've included a little about what auxins are which I have put in red but if you don't need that just skip past the red...

Auxins are the plant hormones which control growth at the tips of roots and shoots of plants - incase you were wondering, they move to the tips of the shoots and roots in a solution (they are dissolved in water). They work by diffusing backwards to stimulate the cell elongation process which occurs in the cells just behind the tip of the shoot/root. They are involved in the growth of plants in response to light (phototropism) and gravity (geotropism). NOTE: in shoots, extra auxins promote growth but in roots extra auxins slows down growth.

Negative geotropism - when a shoot is growing sideways, gravity will produce an uneven distribution of auxins (more of the bottom than on the top). This means that the underside of the shoot will grow much faster than the side with light (as it has auxins which stimulate growth). This bends the shoot upwards.

Postive geotropism - likewise to a stem, a root growing sidewise will have more auxins on its lower side as gravity will produce an unequal distribution of auxins. However, in roots, extra auxins will slow down growth. This means that the cells on the top side of the root will elongate faster, meaning the root will bend downward.