Auxin bends shoots towards light
The shady side grows longer.
The leaning plant
A plant on a windowsill leans towards the window. The light is on one side, but the bending happens in the shoot.
On which side of the shoot do you think the cells grow longer?
What this lesson covers
The idea
Auxin, synthesised at the shoot tip, helps cells grow longer; with light from one side it diffuses to the shady side, whose cells grow longer, so the shoot bends towards light.
The leaning plant
A plant on a windowsill leans towards the window. The light is on one side, but the bending happens in the shoot.
On which side of the shoot do you think the cells grow longer?
- The side away from the light
- The side facing the light
- Both sides grow longer by the same amount
Follow the auxin
Press Next step. Light comes from the right.
Why it bends
The side with longer cells gets longer, so the shoot curves over to the other side, towards the light.
Auxin, synthesised at the shoot tip, helps cells grow longer. With light from one side it diffuses to the shady side, whose cells grow longer, so the shoot bends towards light.
Notes
Auxin, made at the shoot tip, helps cells grow longer. With light from one side it diffuses to the shady side, whose cells grow longer, so the shoot bends towards light.
Check yourself
Where is auxin synthesised?
When light comes from one side, to which side does auxin diffuse?
What does auxin do to the cells on the shady side?
Why does a shoot appear to bend towards light?
- At the shoot tip — correct. Yes!
- In the roots. The book says auxin is synthesised at the shoot tip.
- On the side facing the light. Auxin is made at the shoot tip, then moves to the shady side.
- The side facing the light. Auxin diffuses towards the shady side.
- The shady side, away from the light — correct. Yes!
- It stays at the tip. The book says auxin diffuses towards the shady side of the shoot.
- It makes them divide more quickly. Cytokinins promote cell division. Auxin helps cells grow longer.
- It makes them swell and shrink with water. That is how cells of a sensitive plant change shape. Auxin helps cells grow longer.
- It helps them grow longer — correct. Yes!
- Cells on the side away from the light grow longer — correct. Yes!
- Cells on the side facing the light grow longer. The longer cells are on the shady side, the side away from light.
- The light pulls the shoot towards itself. The bending is caused by auxin making cells on the shady side grow longer.