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

Plant Hormones:

Plant hormones are responsible for controlling manyplant functions including: seed germination, growth, flowering, & leaf production.

Plant Hormones: Auxin

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

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

How does auxin work?

Auxin builds up on the shaded side of the plant &Stimulates growth beneath the tip. The cells on theshaded side are exposed to more auxin they grow morethan the side exposed to the light.

What are tropisms?

Tropisms are growth responses that cause parts ofa plant to grow slowly toward or away from a stimulus.

1)Thigmotropism – a change in plant growth due totouch.

2)Phototropism – the growth of a plant toward or away from light.

What are tropisms?

3)Gravitropism – a plant’s response to gravity.Roots grow downward and stems grow upward inresponse to gravity.

Other Plant Hormones:Cytokinins – encourages branching of plants.

Gibberellins – stimulate growth of stems & fruit development

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

Ethylene – promotes leaf drop.

How do plants respond to changes in day length & seasons?

Photoperiodism – plants use the relative lengths of dayand night to detect the time of year and respond tothese changes.

Short-Day Plants Flower in the winter

Long-Day PlantsFlower in the Summer