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biology > ch 12 chemical coordination in plants > Flashcards

ch 12 chemical coordination in plants Flashcards

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1
Q

what are plants’ responses to stimuli?

A

growth movements

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2
Q

define tropism.

A

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.

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3
Q

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

A

positive tropic

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4
Q

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

A

negative tropic

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5
Q

name the tropism for light, gravity, and water.

A

phototropism, geotropism, hydrotropism

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6
Q

define phototropism.

A

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

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7
Q

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

A
  • 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
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8
Q

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

A
  • helps the root to grow deep into the soil
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9
Q

describe an experiment for studying phototropism.

A

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.

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10
Q

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

A

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

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11
Q

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

A

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

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12
Q

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

A

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.

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13
Q

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

A

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

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14
Q

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

A

the shoots in pot A are positively phototropic.

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15
Q

define geotropism.

A

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

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16
Q

what is the significance of negative geotropic response for shoots?

A

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

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17
Q

describe an experiment for studying geotropism.

A

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

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18
Q

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

A

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

19
Q

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

A

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

20
Q

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

A

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

21
Q

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

A

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

22
Q

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

A

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

23
Q

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

A
  1. to penetrate deeply into the soil for firm anchorage
  2. allows roots to obtain sufficient amount of water and dissolved minerals
24
Q

where is the region responsible for growth of young shoots?

A

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

25
Q

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

A

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

26
Q

where does the growth of the shoot occur?

A

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

27
Q

the shoot tip controls the growth in the ____.

A

region of elongation

28
Q

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

A

auxins

29
Q

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

A

auxin concentration ; auxin concentration

30
Q

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

A

stimulated ; inhibited

31
Q

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?

A

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.

32
Q

explain why the young shoot grows towards unilateral light.

A

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.

33
Q

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

A
  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.
34
Q

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

A

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.

35
Q

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

A
  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
36
Q

auxins are produced at the ____ and ____.

A

root ; shoot tips

37
Q

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

A

gravity

38
Q

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

A

slows down ; bends downwards

39
Q

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

A

stimulates ; bends upwards

40
Q

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

A
  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
41
Q

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

A
  1. auxins are produced by the tip of the shoot
  2. the auxins are evenly distributed –> the shoot grows vertically upwards
42
Q

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

A
  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
43
Q

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

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

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