The action mechanism of auxin

Which option correctly states the most common form of auxin?

• Integrated acetic acid (IAA)

• Inhibited-3-acetic acid (IAA)

• Indole-3-acetic acid (IAA)

Where is auxin produced?

• At the nodes

• Apex of the stem

• At the internodes

Which one of the followings is/are correct about IAA?

I- IAA activates proton pumps, which lowers the pH. This activates an enzyme to break bonds in the cell wall

II- IAA accumulate on the illuminated side the shoot.

III- IAA causes the illuminated side to elongate, that's why the shoot bends toward light.

• I and II

• I, II and III

• Only I

• II and III

Darwin investigated using oat coleoptiles. Which one of the followings is/are correct about Darwin's experiment on the action mechanism of IAA?

I- He found that there is no bending response to light when the coleoptile is removed.

II- When the tip is covered, there was no bending response

III- The tip was shone on the tip, but lower regions were covered, the coleoptile gave no bending response.

• I and II

• Only I

• I, II and III

• Only II

What happened when Boysen and Jensen inserted a thin flake of mica in the illuminated side?

What happened when a thin glass plate vertically inserted through the tip?