5.4 Tropisms

Question 1

A tropism is growth in response to what?

Answer 1

A stimulus

Question 2

What is the difference between a positive and negative tropism?

Answer 2

Positive - growth toward

Negative - growth away

Question 3

A phototropism is growth in response to what?

Answer 3

Direction of light

Question 4

Geotropism is growth in response to direction of what?

Answer 4

Gravity

Question 5

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

Answer 5

Auxin

Question 6

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

Answer 6

Light stronger on one side than the other

Question 7

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

Answer 7

Faster in search of light

Question 8

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

Answer 8

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

Question 9

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

Answer 9

Negatively they grow away from the light

To reach nutrients in the soil

Question 10

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

Answer 10

Grow toward the light then straight toward it

Question 11

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

Answer 11

Due to the effect of auxin movement

Question 12

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

Answer 12

The side not illuminated

Question 13

(Unilateral light) light causes auxin to do what?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

Grows straight toward the light

Question 16

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

Answer 16

Light

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

Question 17

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

Answer 17

Using unilateral light with different colour filters

Question 18

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

Answer 18

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

Question 19

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

Answer 19

To grow rapidly to reach the light to photosynthesise

Question 20

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

Answer 20

Gibberellin

Question 21

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

Answer 21

Photosynthesis in leaves

Strengthening of stems

Question 22

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

Answer 22

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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

Down

Question 25

(Geotropisms) are shoots negatively or positively geotropic?

Answer 25

Negatively they grow away from the gravitational pull

Question 26

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

Answer 26

Toward the gravitational pull

Question 27

(Geotropisms) what can be used for investigating geotropisms?

Answer 27

A clinostat (rotating drum)

Question 28

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

Answer 28

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

Question 29

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

Answer 29

To the walls of a lab

Question 30

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

Answer 30

Rotates at 90 degree intervals

Question 31

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

Answer 31

Bends toward the light as it is positively phototropic

Question 32

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

Answer 32

No response

Suggesting the tip detects stimuli or produces messenger

Question 33

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

Answer 33

No response

Suggesting light must be detected by the tip

Question 34

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

Answer 34

Movement of chemical down shaded side

Plant bends toward light

Question 35

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

Answer 35

No response

Chemical can’t move down shaded side

Question 36

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

Answer 36

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