14.2 Plant growth factors

Question 1

3 plant stimulus

Answer 1

1. light(phototropism)
2. gravity(gravitropism)
3. water(hydrotropism)

Question 2

plant growth factors

Answer 2

hormone like substances that exert their influence by affecting growth

made by cells located throughout plant

affect tissues that release them rather than acting on distant target organ

Question 3

IAA

Answer 3

indoleacetic acid
plant growth factor
increases plant cell elongation
inhibits plant root elongation

Question 4

Positive phototropism in plants

Answer 4

1. cells in tip of shoot produce IAA, which is transported down shoot

2.IAA initially transported evenly throughout all regions as moves down

3. light causes movement of IAA from light side to shaded side of shoot
4. a greater conc of IAA builds on shaded side of shoot
5. IAA causes shaded side cells to elongate faster than light side

6 shoot tip bends towards the light

Question 5

gravitropism in flowering plants

Answer 5

1. cells in tip of root produce IAA which is transported along root
2. IAA initially transported to all sides of root
3. gravity influences movement of IAA from upper side to lower side of root
4. greater conc of IAA builds up on lower side of root than upper
5. IAA ibhibits elongation of root cells so upper side elongates faster
6. root bends downwards to the force of gravity

Question 6

IAA acid growth hypothesis

Answer 6

increases plasticity of cell walls of young cells(adult too rigid)

caused by active transport of hydrogen ions from cytoplasm into spaces in cell wall