JAMB - Biology (2000 - No. 33)

Gibberellins are plant growth regulators that cause cell elongation. Gibberellins stimulate cell elongation by altering the rheological properties of the cell wall; as a consequence, the water potential of the cell is lowered allowing for water uptake and therefore an increase in cell volume.

Cytokinins are the plant hormones that promote rapid cell division.

Auxin is the plant hormone that controls tropic responses in plants.Auxin causes cells on the shaded side of a plant to grow longer, which makes the plant bend toward the light(Phototropism). Auxin has the opposite effect in roots, where the shaded side grows less, causing the root to bend away from the light(Geotropism).