Auxin and Phototropism Flashcards
How are tropisms controlled
Plant growth factors (hormones)
What is an example of a plant growth factor
Indoleacetic acid (IAA)
What group does indoleacetic acid (IAA) belong to
Auxins
What are auxins responsible for
Controlling plant phototrophic and geotropic responses
How do auxins Control plant phototrophic and geotropic responses
by regulating cell elongation
What does IAA cause
Positive phototropism of stem (stem grows towards light), Negative phototropism of roots (roots grow away from light. Positive geotropism of roots (roots grow in direction of gravity), Negative geotropism (shoots grow in opposition of gravity)
How does IAA cause cell elongation
IAA causes an increase in the plasticity of plant cell walls so that they can stretch more easily when the cell elongates
What is the mechanism by which IAA increases cell wall plasticity
Acid growth hypothesis
What does IAA cause in the acid growth hypothesis
Protons to be actively pumped into spaces in the cell wall
What does the pumping of the protons into the plant cell wall cause
Causes proteins called expansins to be activated
What happens when proteins called expansins are activated
They cause the loosening of the cellulose in the cell wall and make the cell wall more plastic
Where is auxin IAA produced
In the tip of the shoot
Where is the auxin IAA transported
Distributed evenly throughout all regions of the shoot
What happens to the distribution of IAA if light shines on one side of the shoot
It causes the IAA to move away from the illuminated side of the shoot to the shaded side
What occurs as a result of the auxin IAA moving away from the illuminated side of the shoot
Cause cell elongation to occur more quickly on the shaded side of the stem. causes the shoot to bend towards the light (positive phototropism)
