ch 12 chemical coordination in plants

Question 1

what are plants’ responses to stimuli?

Answer 1

growth movements

Question 2

define tropism.

Answer 2

tropism is a directional growth movement shown by a part of a plant in response to a unilateral stimulus, which is an external stimulus that comes from one direction.

Question 3

when a plant structure grows toward the stimulus, it shows ____ reponse.

Answer 3

positive tropic

Question 4

when a plant structure grows away from the stimulus, it shows a ____ response.

Answer 4

negative tropic

Question 5

name the tropism for light, gravity, and water.

Answer 5

phototropism, geotropism, hydrotropism

Question 6

define phototropism.

Answer 6

it is the growth movement of a part of a plant in response to unilateral light.

Question 7

what is the significance of positive phototropic response of the shoot?

Answer 7

• enables a stem to get to a position so that leave can receive as much sunlight as possible for photosynthesis
• bring flowers to an exposed position to increase the chance to pollination by insect or wind

Question 8

what is the significance of negative phototropic response of the root?

Answer 8

• helps the root to grow deep into the soil

Question 9

describe an experiment for studying phototropism.

Answer 9

for both set ups, put young seedlings into a light proof box with a small window in it. for set up A, use a stand to hold up the plant. for set up B, use a clinostat to hold up the plant.

Question 10

for the experiment studying phototropism, what is the purpose of putting the seedlings inside a box with a window on one side?

Answer 10

it ensures that the light reaching the seedlings is only from one direction.

Question 11

for the experiment studying phototropism, why do we use a stand with a height similar to that of the clinostat?

Answer 11

it ensures that the amount of light reaching the seedling is similar.

Question 12

for the experiment studying phototropism, suggest the reason for using a clinostat.

Answer 12

it is a control. this cancels out the effect of the unilateral light on the shoots and ensures that the shoots receive equal amount of light on all sides.

Question 13

for the experiment studying phototropism, what is the appearance of the shoots of the seedlings after two days?

Answer 13

pot A: the shoots grow towards the unilateral light.
pot B: the shoots grow vertically upwards.

Question 14

for the experiment studying phototropism, from the results of the experiment, what can you tell about the growth response of shoots?

Answer 14

the shoots in pot A are positively phototropic.

Question 15

define geotropism.

Answer 15

it is the growth movement of a part of a plant in response to gravity.

Question 16

what is the significance of negative geotropic response for shoots?

Answer 16

it helps the shoot to grow away from the soil so that it can obtain more light for photosynthesis.

Question 17

describe an experiment for studying geotropism.

Answer 17

seed X: with the radicle pointing downwards
seed Y: with the radicle placing horizontally
seed Z: with the radicle placing upwards
put both set ups in a light proof box
use a clinostat for the seeds fixed on cork disc B

Question 18

for the experiment studying geotropism, what is the use of the moist cotton wool?

Answer 18

to provide water for seed growth and helps to saturate the air inside the cork discs with water vapour.

Question 19

for the experiment studying geotropism, suggest the reason for using a clinostat for the seeds fixed on cork disc B.

Answer 19

it is a control. it cancels out the effect of gravity on the radicles.

Question 20

for the experiment studying geotropism, why is it necessary to place both set ups inside light proof boxes?

Answer 20

to eliminate the effect of light on the growth response of the radicles.

Question 21

for the experiment studying geotropism, what is the appearance of the radicles of the seeds after two days?

Answer 21

disc A: all radicles grow and bend vertically downwards
disc B: all radicles grow along their original directions

Question 22

for the experiment studying geotropism, from the results of the experiment, what can you tell about the growth response of roots?

Answer 22

the growth response of roots on cork disc A is positively geotropic.

Question 23

what is the importance of positive geotropic response on the roots?

Answer 23

1. to penetrate deeply into the soil for firm anchorage
2. allows roots to obtain sufficient amount of water and dissolved minerals

Question 24

where is the region responsible for growth of young shoots?

Answer 24

the region of elongation below the tip of the young shoot is responsible for growth in length.

Question 25

if the agar block in experiment D is replaced by a plastic plate, will the shoot grow?

Answer 25

if the agar block is replaced by a plastic plate, the shoot will not grow as plastic does not allow diffusion.

Question 26

where does the growth of the shoot occur?

Answer 26

the region of elongation, which lies below the shoot tip.

Question 27

the shoot tip controls the growth in the ____.

Answer 27

region of elongation

Question 28

the shoot tip produces ____, that diffuse down into the region of elongation.

Answer 28

auxins

Question 29

growth of the shoot is stimulated by an increase in ____, but inhibited by very high ____.

Answer 29

auxin concentration ; auxin concentration

Question 30

growth of the root is ____ at very low auxin concentrations, but is ____ by an increase in auxin concentration.

Answer 30

stimulated ; inhibited

Question 31

explain what happens if a black paper cap is used to cover the shoot tip and is shone with unilateral light. what does this suggest?

Answer 31

the young shoot grows vertically upwards. it suggests that the tip of the shoot, but not the region of elongation, is responsible for detecting the unilateral light and causing the uneven distribution of auxins in the region of elongation.

Question 32

explain why the young shoot grows towards unilateral light.

Answer 32

as increased auxin concentration promotes shoot growth, the shaded side contains more auxins than the illuminated side. the shaded side grows faster than the illuminated side.

Question 33

suggest experiments that study the effect of uneven distribution of auxins on shoot growth.

Answer 33

1. place the shoot tip on an agar block (diffusion). place the agar block on half of the shoot. 2. place a cover slip below the shoot tip on half of the shoot.

Question 34

what is the conclusion of the effect of uneven distribution of auxins on shoot growth?

Answer 34

the results show that the side with more auxins grows faster than the side with less auxins or no auxins. the growth curvature in a phototropic response is caused by an uneven distribution of auxins in the region of elongation, and that auxins are produced at the shoot tip.

Question 35

describe the mechanism of phototropism in shoots. (5 steps)

Answer 35

1. auxins are produced by the tip of the shoot 2. due to the unidirectional light, auxins diffuse from the illuminated side to the shaded side 3. when auxins diffused downwards into the region of elongation, the shaded side has a greater auxin concentration than the illuminated side 4. in the shoot, an increased auxin concentration stimulates growth 5. the shaded side grows faster than the illuminated side --> the shoot grows and bends towards the light

Question 36

auxins are produced at the ____ and ____.

Answer 36

root ; shoot tips

Question 37

when a seedling is placed horizontally, auxins diffuse to the lower side due to ____.

Answer 37

gravity

Question 38

an increased auxin concentration ____ the growth of the lower side of the root. as a result, the root ____.

Answer 38

slows down ; bends downwards

Question 39

an increased auxin concentration ____ the growth of lower side of the shoot. as a result, the shoot ____.

Answer 39

stimulates ; bends upwards

Question 40

when the seedling is placed horizontally, what happens to the shoot?

Answer 40

1. auxins are produced by the tip of the shoot 2. due to gravity, auxins diffuse and sink to the lower side of the shoot 3. the lower side of the shot has a greater auxin concentration 4. in the shoot, an increased auxin concentration stimulates growth 5. the lower side grows faster than the upper side of the shoot --> the shoot grows and bends upwards

Question 41

when the seedling is placed vertically, what happens to the shoot?

Answer 41

1. auxins are produced by the tip of the shoot 2. the auxins are evenly distributed --> the shoot grows vertically upwards

Question 42

when the seedling is placed horizontally, what happens to the root?

Answer 42

1. auxins are produced at the tip of the root 2. due to gravity, auxins diffuse and sink to the lower side of the root 3. the lower side of the root has a greater auxin concentration 4. in the root, an increased auxin concentration inhibits growth 5. the lower side grows slower than the upper side of the root --> the root grows and bends downward

Question 43

when the seedling is placed vertically, what happens to the root?

Answer 43

1. auxins are produced by the tip of the root 2. the auxins are evenly distributed --> the root grows vertically downwards