In this deck, we'll explore how plants control and coordinate their growth. Unlike animals, plants don't have a nervous system. Instead, they use chemical messengers called hormones to respond to their environment. We'll focus on how plants respond to light and gravity, and how we use these plant hormones in agriculture and gardening.

One of the most obvious plant responses is growing towards light. This is called phototropism. 'Photo' means light, and 'tropism' means turning or response. So, phototropism is a plant's growth response to light. This is controlled by a plant hormone called auxin.

Auxin is produced in the tips of shoots and roots. When light shines on a shoot from one side, auxin moves to the shaded side. This unequal distribution of auxin causes the cells on the shaded side to grow longer and faster than the cells on the light side. This difference in growth makes the shoot bend and grow towards the light source, which is known as positive phototropism.