Plant Hormones

Question 1

What is IAA?

Answer 1

Indoleacetic acid; type of auxin

Question 2

Describe how IAA works in plant shoots

Answer 2

Phototropism
~ when light shines on one side of shoot, IAA is transported to shaded side
~ high concentration of IAA causes increase in cell elongation, so shoot bends towards light

Question 3

Describe how IAA works in plant roots

Answer 3

Geotropism
~ in roots, high concentration of IAA causes lower rate of cell elongation
~ IAA transported to lower side of roots, resulting in its high concentration, inhibiting cell elongation
~ lower side grows more slowly so than upper side, causing root to bend downward

Question 4

How does IAA generally control growth?

Answer 4

Alters transcription of genes in the plant —> altering the expression of genes which code for proteins involved in cell growth
- produced in growing parts of cell and moved to other tissues via diffusion or active transport

Question 5

How do plants control flowering at different night lengths?

Answer 5

When nights reach certain length, genes controlling flowering are turned on/off; those turned on are expressed so protein they code for is produced + vice versa

Question 6

Describe two forms of phytochrome

Answer 6

Pr —> inactive form, absorbs red light (660nm wavelength)
Pfr —> active form, absorbs far red light (730nm)

Question 7

Describe reaction between two types of phytochrome

Answer 7

• when Pr absorbs red light, converted into Pfr
• when Pfr absorbs far red light, converts back to Pr
• in absence of red light, unstable Pfr converts slowly back into Pr

Question 8

Describe how levels of phytochromes change during day and night

Answer 8

🌞 Day —> levels of Pfr rises, as sunlight contains more 660nm wavelengths so conversion of Pr to Pfr is more rapid than Pfr to Pr
🌚 Night —> levels of Pr rise, red light not available so Pfr slowly converted back to Pr