Plant growth factors Flashcards
What is tropism?
the response of a plant to a stimuli, involving growth
What are tropisms controlled by?
growth factors
What does IAA stand for and what is it an example of?
indoleacetic acid, a growth factor which is a type of auxin
what does IAA do
control plants elongation
Where is IAA made?
in the roots and shoots, but it can diffuse to other cells
Why is it important that plants grow towards light?
as light is needed for the LDR for photosynthesis
Phototropism in flowering plants process
1) IAA produced in shoot
2) IAA transported evenly throughout all regions and transported down the shoot
3) light causes IAA to move from light side to shaded side of shoot
4) greater conc of IAA builds up on shaded side of soot than on light side
5) So there’s elongation of shoot cells and greater conc of IAA in shade side of shoot so cells on this side elongate more
6) shaded side of shoot elongates faster than light side causing shoot tip to bend towards light
disadvantage of high conc of IAA increasing cell elongation in roots
inhibits cell elongation in roots
Gravitropism in flowering plants process
1) cells in tip of root produce IAA ten transported along and sides of root
2) gravity influences movement of IAA from upper side to lower side of root
3) greater conc of IAA builds up on lower side of root than on upper side
4) as IAA inhibits elongation of root cells and there’s greater conc of IAA on lower side, cells on this side elongate less than those on upper side
5) greater elongation of cells on upper side than lower sides causes root to bend downwards towards force of gravity
Explain how the movement of IAA in the shoots helps a plant to survive
-moves away from light/to shaded area
-cells on shaded side elongate faster
-shoot bends towards the light
-maximises light intensity for photosynthesis -> more organic molecules made so more likely to survive
What would happen if the tip was cut off of a shoot and there was unilateral light?
-no IAA produced
-no uneven cell elongation
-so no response to light
Why does IAA affect cell elongation
-acid growth hypothesis
-increases plasticity of cell walls by H+ being actively transported from cytoplasm into spaces in cell wall
-changes H bonding within cellulose layers
-so becomes more plastic allowing cell to elongate by expansion
What can the elongation of cells on one side only of stem or root cause
-bending
