14.2- PLANT GROWTH FACTORS

Question 1

Do plants have a nervous system?

Answer 1

no

Question 2

How do plants respond to light?

Answer 2

shoots grow towards light as light needed for photosynthesis

Question 3

How do plants respond to gravity?

Answer 3

plants need to be firmly anchored in soil. Roots sensitive to gravity + grow in direction of its pull

Question 4

How do plants respond to water?

Answer 4

almost all plant roots grow towards water to absorb it for use in photosynthesis + other metabolic processes + for support

Question 5

What do plant responses to external stimuli involve?

Answer 5

plant growth factors

Question 6

How do plants exert their influence when they’re responding to an external stimuli?

Answer 6

exert their influence by affecting growth + they may be made by cells located throughout plant rather than in particular organs

Question 7

Unlike animal hormones, what do some plant growth factors affect?

Answer 7

tissues that release them rather than acting on distant target organ

Question 8

In what quantities are plant growth factors produced?

Answer 8

small quantities

Question 9

What is an example of a plant growth factor?

Answer 9

indoleacetic acid (IAA)

Question 10

What group of substances does IAA belong to?

Answer 10

auxins

Question 11

Among other things, what does IAA control?

Answer 11

plant cell elongation

Question 12

What is unilateral light?

Answer 12

light directed from one side

Question 13

What is produced at the tip of the shoot and taken where? #1 phototropism in flowering plants

Answer 13

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

Question 14

How is the IAA transported from shoot initially? #2 phototropism in flowering plants

Answer 14

IAA initially transported evenly throughout all regions as it begins to move down shoot

Question 15

How dies light affect the movement of IAA? #3 phototropism in flowering plants

Answer 15

light causes movement of IAA from light side to shaded side of shoot

Question 16

What happens to the concentration of IAA on the shaded side? #4phototropism in flowering plants

Answer 16

greater conc. of IAA builds up on shaded side of shoot than on light side

Question 17

What does IAA cause and what happens as there is a greater conc. of IAA on the shaded side? #5 phototropism in flowering plants

Answer 17

IAA causes elongation of shoot cells

cells on shaded side elongate more

Question 18

How does the shaded side elongate in comparison to the light side? #6 phototropism in flowering plants

Answer 18

shaded side of shoot elongates faster than light side, causing shoot tip to bend towards light

Question 19

What else does IAA control other than plant cell elongation?

Answer 19

controls bending of roots in response to light

Question 20

How does a high concentration of IAA in the roots affect it?

Answer 20

inhibits cell elongation in roots (opposite to in shoots)

Question 21

What is produced at the tip of the shoot and taken where? #1 gravitropism in flowering plants

Answer 21

cells in tip of shoot produce IAA, which is then transported along roots

Question 22

How is the IAA transported from shoot initially? #2 gravitropism in flowering plants

Answer 22

IAA initially transported to all sides of root

Question 23

How does gravity influence the movement of IAA? #3 gravitropism in flowering plants

Answer 23

gravity influences movement of IAA from upper side to lower side of root

Question 24

Where does a greater conc. of IAA build up in the roots? #4 gravitropism in flowering plants

Answer 24

greater conc. of IAA builds up on lower side of root than on upper side

Question 25

What does IAA do in the roots and as there is a greater conc. of IAA on the lower side what happens? #5 gravitropism in flowering plants

Answer 25

IAA inhibits elongation of root cells + there’s greater conc. of IAA on lower side, cells on this side elongate less than those on upper side

Question 26

What does the relatively greater elongation of cells on upper side compared to lower side cause? #6 gravitropism in flowering plants

Answer 26

causes root to bend downwards towards force of gravity

Question 27

How can IAA affect plant cell walls?

Answer 27

increasing plasticity (ability to stretch) of their cells walls

Question 28

When does the response of IAA causing increased plasticity of plant cells walls occur?

Answer 28

only occur on young cell walls where cells able to elongate. As cells mature they develop greater rigidity- so older parts of shoot/root will not be able to respond

Question 29

What is the proposed explanation of how IAA increases the plasticity of cells?

Answer 29

acid growth hypothesis

Question 30

What does IAA causing the increase of plasticity of cell walls involve?

Answer 30

active transport of hydrogen ions from cytoplasm into spaces in cell wall causing cell wall to become more plastic allowing cell to elongate by expansion

Question 31

What can the elongation of cells on one side only of stem or root lead to?

Answer 31

can lead to them bending