Plant Responses Part 2: Plant Hormones

8SCIENCE: Mon. Feb. 21

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