1. Aim: How do plants respond to changes in the environment?

2. Plant Hormones: Plant hormones are responsible for controlling many plant functions including: seed germination, growth, flowering, & leaf production.

3. Plant Hormones: Auxin Auxin is a hormone produced in the stem of a plant that allows for plant growth (primary – length).

4. What does this experiment tell us about the effects of auxin?

5. How does auxin work? Auxin builds up on the shaded side of the plant & Stimulates growth beneath the tip. The cells on the shaded side are exposed to more auxin they grow more than the side exposed to the light.

6. What are tropisms? Tropisms are growth responses that cause parts of a plant to grow slowly toward or away from a stimulus. 1)Thigmotropism – a change in plant growth due to touch. 2)Phototropism – the growth of a plant toward or away from light.

7. What are tropisms? 3)Gravitropism – a plant’s response to gravity. Roots grow downward and stems grow upward in response to gravity.

8. Other Plant Hormones: Cytokinins – encourages branching of plants. Gibberellins – stimulate growth of stems & fruit development

9. Other Plant Hormones: Abscisic Acid – induces dormancy (stops growing) in plants & seeds. Also causes the closing of the stomates. Ethylene – promotes leaf drop.

10. How do plants respond to changes in day length & seasons? Photoperiodism – plants use the relative lengths of day and night to detect the time of year and respond to these changes. Short-Day Plants Flower in the winter Long-Day Plants Flower in the Summer