[14.2] plant growth factors

Question 1

what is tropism?

Answer 1

• directional growth responses to specific stimuli
• eg. geo, photo, hydro

Question 2

what type of tropism and in what direction do shoots and roots show?

Answer 2

• shoots = negative geotropism
• roots = positive geotropism

Question 3

what is IAA?

Answer 3

a molecule which either stimulates or inhibits cell elongation depending on where it is affecting

Question 4

what conditions are needed for phototropism?

Answer 4

• tip present and able to detect light (IAA produced in tip)
• substance causing response needs to be able to move down shoot from tip

Question 5

describe phototropism

Answer 5

1. phototropin in tip of shoot detects direction of light stimulus
2. IAA is synthesised by cells in tip and moves down stem
3. IAA transporter proteins are moved into plasma membrane at shady sides of cells of shoot
4. IAA moves through these transporter proteins and accumulates in cells on shaded side
5. in shoots, IAA stimulates cell elongation, so cells on shaded side elongate faster, causing shoot to grow towards light

Question 6

describe geotropism

Answer 6

1. amyloplasts settle due to gravity
2. amyloplasts cause IAA transporter proteins to be inserted into plasma membrane of root cells
3. IAA transporter proteins move IAA, produced in root tip, in direction of pull of gravity
4. IAA accumulates in cells on underside of root
5. IAA inhibits elongation of these root cells
6. cells at top suprface of root elongate more, causing root to grow downwards