5.4 Tropisms Flashcards
A tropism is growth in response to what?
A stimulus
What is the difference between a positive and negative tropism?
Positive - growth toward
Negative - growth away
A phototropism is growth in response to what?
Direction of light
Geotropism is growth in response to direction of what?
Gravity
Which hormone controls direction of plant growth in response to stimuli?
Auxin
(Phototropisms) due to movement of auxins across shoot or roots if exposed to what?
Light stronger on one side than the other
(Phototropisms) will plants in low light grow faster or slower?
Faster in search of light
(Phototropisms) if plants are exposed to light on one side what happens?
Auxins move to the dark side causing shoots to bend toward the light
(Phototropisms) are roots positively or negatively phototropic? Why?
Negatively they grow away from the light
To reach nutrients in the soil
(Unilateral light) where plants are partially shaded the shoots do what?
Grow toward the light then straight toward it
(Unilateral light) why does the shoot do this in unilateral light?
Due to the effect of auxin movement
(Unilateral light) the side of a shoot exposed to light had less auxin than what?
The side not illuminated
(Unilateral light) light causes auxin to do what?
Move laterally across the shoot so there is greater auxin concentration on the unluminated side
(Unilateral light) the higher auxin concentration on the unluminated side stimulates what?
Cell elongation and growth in that side causing growth toward the light
(Unilateral light) once the shoot grows toward the light transport of auxin stops and the shoot does what?
Grows straight toward the light
(Investigating phototropisms) seeds can be grown in different what conditions?
Light
We can observe and record patterns of growth and even use time lapse photos
(Investigating phototropisms) how can we investigate which wavelengths of light trigger a phototropic response?
Using unilateral light with different colour filters
(Investigating phototropisms) what did Darwin do in his classic experiments?
Covered tips with foil
Removed tips
Placed auxin impregnated agar on one side of decapitated coleoptiles
(Dark) if a plant is in the dark what has it’s imperative?
To grow rapidly to reach the light to photosynthesise
(Dark) which hormone is responsible for extreme elongation of internodes when plant is grown in the dark?
Gibberellin
(Dark) once a plant is exposed to light the slowing of upward growth is needed so resources can be used on what?
Photosynthesis in leaves
Strengthening of stems
(Dark) farmers sometimes use this to force plant growth what is etiolation?
Rapid upward growth taking place in a plant grown in the dark
(Dark) etiolated plants are thin and pale, why?
The plant is deprived of light and little chlorophyll develops in the leaves
(Geotropisms) in normal conditions gravity always acts in which direction?
Down
(Geotropisms) are shoots negatively or positively geotropic?
Negatively they grow away from the gravitational pull
(Geotropisms) roots are positively geotropic as they grow where?
Toward the gravitational pull
(Geotropisms) what can be used for investigating geotropisms?
A clinostat (rotating drum)
(Geotropisms) plants can be grown in a slowly rotating clinostat so the gravitational stimulus is applied where?
Evenly to all sides of the plant so the roots and shoots grow straight
(Geotropisms) seeds can be placed in Petri dishes and stuck where?
To the walls of a lab
(Geotropisms) what happens to the dishes as the seedling grows?
Rotates at 90 degree intervals
(Darwin) if unilateral light is shone on a shoot what happens to it and why?
Bends toward the light as it is positively phototropic
(Darwin) of the shoot tip is removed what happens and what does this suggest?
No response
Suggesting the tip detects stimuli or produces messenger
(Darwin) if a lightproof cover is placed over the shoot what happens and what does this suggest?
No response
Suggesting light must be detected by the tip
(Darwin) if a thin impermeable barrier or mica is placed on the side exposed to light what happens?
Movement of chemical down shaded side
Plant bends toward light
(Darwin) if a thin impermeable barrier of mica is placed in the shaded side what happens?
No response
Chemical can’t move down shaded side
(Darwin) if a tip is removed and gelatine block inserted and the tip replaced what happens?
Chemical moves down shaded side and bends toward light as Galatia allows chemicals to pass through
