2 - Plant Tropisms Flashcards
Name the tropism involved in: shoots growing towards light.
Positive phototropism
Name the tropism involved in: roots growing towards gravity
Positive geotropism
Name the tropism involved in: shoots growing away from gravity.
Negative geotropism
Name the tropisms involved in: roots growing away from light.
Negative phototropism
Name the tropism involved in: roots growing towards water
Positive hydrotropism
How do roots actually sense gravity? (starch-statolith hypothesis)
- gravity-sensitive organs contain starch filled plasmids called statoliths, which are specialised cells in their cytoplasm.
- statoliths fall to the lower side of the cell due to gravity.
- providing an internal stimulus, which is transmitted to growing region of organ
Name 2 biotic factors that could stimulate a response.
Competition, predation.
Name 2 abiotic factors that could stimulate a response.
Temperature, rainfall.
What are plant growth factors?
- made by cells throughout the plant
- affect growth
- also affect tissues that release them
What does IAA stand for?
Indoleacetic acid
What is IAA?
- plant growth factor
- belongs to a group of auxins
- controls plant cell elongation
Where is IAA produced?
Tips of roots & shoots
Where does IAA move to in order to act?
Growing region
Where does IAA move to in phototropism?
To shaded parts of roots & shoots
Where does IAA move to in gravitropism?
To underside of roots & shoots.
Outline phototropism in flowering plants.
- cells in tip of shoot produce IAA
- IAA transported down shoot, to be evenly distributed throughout
- light causes IAA to move to shaded area
- concentration of IAA builds in shaded area
- causes elongation of shoot cells on shaded side
- so shoot tip bend towards light
Outline gravitropism in flowering plants.
- cells in shoot tip produce IAA
- IAA transported down shoot to root to be evenly distributed throughout
- gravity causes IAA to move to underside of root
- greater concentration of IAA builds on underside of shoot
- IAA inhibits elongation of roots cells on underside
- so root bends downwards towards gravity
What were the conclusions of darwins experiments?
Growth stimulus is produced in the tip
Which is then transported to zone of cell elongation
Cells on shaded side elongate more
What were the conclusions of boysen-jensens experiments?
Materials which aren’t permeable to water sometimes stop curvature response
Materials permeable to water don’t interfere with curvature response
What were the conclusions of paals experiments?
Tip contains permeable substance that moves down side of the shoot, promoting curvature response.
What were the conclusions of went and briggs experiments?
The greater the concentration of auxin, the greater the curvature response.
Auxin effects cell elongation.
What are the effects of auxins?
Promote cell elongation
Inhibit growth of side shoots
Inhibit leaf abscission (leaf fall)
Prevents fruit drop
What are the effects of cytokinins?
Promote cell division
Prevents senescence (cell aging)
What are the effects of gibberellins?
Promote cell division
Promotes growth of stems (elongation)
What are the effects of abscisic acid?
Inhibits seed germination & growth
Cases stomatal closure when there is low water availability
What are the effects of ethene?
Inhibits growth & elongation
Promotes fruit ripening
