5.4 Tropisms Flashcards

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1
Q

A tropism is growth in response to what?

A

A stimulus

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2
Q

What is the difference between a positive and negative tropism?

A

Positive - growth toward

Negative - growth away

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3
Q

A phototropism is growth in response to what?

A

Direction of light

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4
Q

Geotropism is growth in response to direction of what?

A

Gravity

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5
Q

Which hormone controls direction of plant growth in response to stimuli?

A

Auxin

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6
Q

(Phototropisms) due to movement of auxins across shoot or roots if exposed to what?

A

Light stronger on one side than the other

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7
Q

(Phototropisms) will plants in low light grow faster or slower?

A

Faster in search of light

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8
Q

(Phototropisms) if plants are exposed to light on one side what happens?

A

Auxins move to the dark side causing shoots to bend toward the light

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9
Q

(Phototropisms) are roots positively or negatively phototropic? Why?

A

Negatively they grow away from the light

To reach nutrients in the soil

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10
Q

(Unilateral light) where plants are partially shaded the shoots do what?

A

Grow toward the light then straight toward it

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11
Q

(Unilateral light) why does the shoot do this in unilateral light?

A

Due to the effect of auxin movement

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12
Q

(Unilateral light) the side of a shoot exposed to light had less auxin than what?

A

The side not illuminated

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13
Q

(Unilateral light) light causes auxin to do what?

A

Move laterally across the shoot so there is greater auxin concentration on the unluminated side

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14
Q

(Unilateral light) the higher auxin concentration on the unluminated side stimulates what?

A

Cell elongation and growth in that side causing growth toward the light

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15
Q

(Unilateral light) once the shoot grows toward the light transport of auxin stops and the shoot does what?

A

Grows straight toward the light

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16
Q

(Investigating phototropisms) seeds can be grown in different what conditions?

A

Light

We can observe and record patterns of growth and even use time lapse photos

17
Q

(Investigating phototropisms) how can we investigate which wavelengths of light trigger a phototropic response?

A

Using unilateral light with different colour filters

18
Q

(Investigating phototropisms) what did Darwin do in his classic experiments?

A

Covered tips with foil
Removed tips
Placed auxin impregnated agar on one side of decapitated coleoptiles

19
Q

(Dark) if a plant is in the dark what has it’s imperative?

A

To grow rapidly to reach the light to photosynthesise

20
Q

(Dark) which hormone is responsible for extreme elongation of internodes when plant is grown in the dark?

A

Gibberellin

21
Q

(Dark) once a plant is exposed to light the slowing of upward growth is needed so resources can be used on what?

A

Photosynthesis in leaves

Strengthening of stems

22
Q

(Dark) farmers sometimes use this to force plant growth what is etiolation?

A

Rapid upward growth taking place in a plant grown in the dark

23
Q

(Dark) etiolated plants are thin and pale, why?

A

The plant is deprived of light and little chlorophyll develops in the leaves

24
Q

(Geotropisms) in normal conditions gravity always acts in which direction?

A

Down

25
Q

(Geotropisms) are shoots negatively or positively geotropic?

A

Negatively they grow away from the gravitational pull

26
Q

(Geotropisms) roots are positively geotropic as they grow where?

A

Toward the gravitational pull

27
Q

(Geotropisms) what can be used for investigating geotropisms?

A

A clinostat (rotating drum)

28
Q

(Geotropisms) plants can be grown in a slowly rotating clinostat so the gravitational stimulus is applied where?

A

Evenly to all sides of the plant so the roots and shoots grow straight

29
Q

(Geotropisms) seeds can be placed in Petri dishes and stuck where?

A

To the walls of a lab

30
Q

(Geotropisms) what happens to the dishes as the seedling grows?

A

Rotates at 90 degree intervals

31
Q

(Darwin) if unilateral light is shone on a shoot what happens to it and why?

A

Bends toward the light as it is positively phototropic

32
Q

(Darwin) of the shoot tip is removed what happens and what does this suggest?

A

No response

Suggesting the tip detects stimuli or produces messenger

33
Q

(Darwin) if a lightproof cover is placed over the shoot what happens and what does this suggest?

A

No response

Suggesting light must be detected by the tip

34
Q

(Darwin) if a thin impermeable barrier or mica is placed on the side exposed to light what happens?

A

Movement of chemical down shaded side

Plant bends toward light

35
Q

(Darwin) if a thin impermeable barrier of mica is placed in the shaded side what happens?

A

No response

Chemical can’t move down shaded side

36
Q

(Darwin) if a tip is removed and gelatine block inserted and the tip replaced what happens?

A

Chemical moves down shaded side and bends toward light as Galatia allows chemicals to pass through