Plant Responses Part 2: Plant
Hormones
Review: What are plant responses?
• Called tropisms
– When a plant responds to an outside stimulus
• What are some examples of plant stimuli?
– Sunlight, water, carbon dioxide, temperature
• What are some types of tropisms or responses?
– Gravitropism
– Phototropism
– Thigmotropism
Plants have hormones like other living things
• Plant hormones are chemical substances that
affect GROWTH
• Two types to learn:
– Auxin
– Ethylene
Plant Hormones: Auxin
• Auxin causes plant stems and leaves to show positive
phototropism
– Plants will Grow TOWARDS the sun/light
• When light shines on a plant on one side, auxin
works on the shaded side to curve it towards the
light
Plant Hormones: Ethylene
• Organic compound made of carbon and hydrogen
• Causes different plant responses but mainly used to
RIPEN fruit
• Fruits are picked when they are still green (e.g.
bananas, oranges) and during transportation to the
store are exposed to ethylene gas