Topic- Growth factors in flowering plants + IAA Flashcards
What does the survival of plants depend on?
their ability to respond to changes in their environment
Give 3 examples of how plants respond to changes in their environment?
-Some plants produce poisonous substances to defend against herbivore damage
-Trees in forests grow very tall so they can reach a light source
-Some flowers can close up at night to reduce water loss in a dry environment
Do plants have a nervous system?
No
Responses that involve plants growing against gravity or towards light occur due to what?
Uneven growth
A seedling will 1.___ and grow 2.___ the light, this occurs because there is 3.____ growth on the shaded side than on the illuminated side
1.bend
2. towards
3. more
What is a tropism?
growth response towards a stimulus
What is phototropism?
a growth response to light
What is Gravitropism?
a growth response to gravity
What is meant by positive and negative tropisms?
Tropisms that cause the plant to grow towards or away from the stimulus
What are growth factors?
chemical substances that are released in response to a stimulus
How quick is the effect of growth factors
not as quick as that of an electrical nervous system but it still occurs at a substantial speed
How do growth factors move in flowering plants?
They move from the growing regions to other tissues, where they regulate the growth in response to a directional stimulus
What is IAA shortened for?
indoleacetic acid
What is IAA?
A specific growth factor
Are there other growth factors other than IAA?
Yes however their mechanism of action is still disputed
Where is IAA synthesised?
synthesised at the growing tips of roots and shoots- (ie in the meristem)
Where does IAA affect?
The elongating region
Where is the elongating region found?
just prior to the tip/area of cell division
Where does IAA bind to on the elongating region?
to the protein receptors on the cell membranes
How does IAA lower pH?
Releases hydrogen bonds
What are the growth stages in the meristem?
-Cell division by mitosis
-Cell elongation by absorption of water
-Cell differentiation
What is the effect of lower pH? How does this lead to elongation?
-some of the bonds found between the microfibrils in cellulose cell walls are broken
-causes the cell wall to loosen and allows the cells to be more easily stretched when the turgidity of the cells increases by an increase of water being stored in the vacuole
How is IAA involved in controlling growth?
By elongation
What is the 1st step of elongation?
IAA molecules bind to a receptor protein on the cell surface membrane
What is the 2nd step of elongation?
IAA stimulates ATPase proton pumps to pump hydrogen ions from the cytoplasm into the cell wall (across the cell surface membrane)
What is the 3rd step of elongation?
This acidifies the cell wall (lowers the pH of the cell wall)
What is the 4th step of elongation?
-activates proteins known as expansins, which loosen the bonds between cellulose microfibrils
-potassium ion channels are stimulated to open
What is the 5th step of elongation?
Open potassium ion channels- lead to an increase in potassium ion concentration in the cytoplasm, which decreases the water potential of the cytoplasm
What is the 6th step of elongation?
Decreased water potential in cytoplasm- causes the cell to absorb water by osmosis (water enters the cell through aquaporins) which is then stored in the vacuole
Where does phototropism affect?
shoots and the top of a stem
What is the 7th step of elongation?
Increased volume of water in the vacuole- increases the internal pressure of the cell, causing the cell wall to stretch (made possible by expansin proteins)
What does the concentration of IAA determine?
the rate of cell elongation within the region of elongation
How does IAA concentration impact uneven growth?
If it is not equal on either side of a root or shoot
What is positive phototropism?
When the shoots grow towards the light
In shoots 1.____ concentrations of IAA results in a greater rate of cell elongation
- higher
What have experiments shown about the movement of IAA?
IAA moves from the illuminated side of a shoot to the shaded side
The higher concentration of IAA on the 1.____ side of the shoot causes a faster rate of cell elongation
1.shaded
What does gravitropism affect?
Roots
What is poitive gravitropism?
When the roots grow towards gravity
What direction does IAA move?
Downwards
In roots, higher concentrations of IAA results in a 1._____ rate of cell elongation
1.Lower
Amylopasts are densely packed with starch and so they sink to the bottom of the cell, when a root is moved from the vertical plane to the horizontal plane ,what happens to these organelles?
They fall to the bottom of the cells
What are amyloplasts?
Heavy organelles (found in cells near the root tip)
How does a larger concentration of IAA cause the root to bend down?
-larger concentration of IAA at the lower side of the root inhibits cell elongation
- the lower side grows at a slower rate than the upper side of the root
Where is IAA actively transported to in the root tip?
Where the amyloplasts have sunk to
What are 4 features of plant responses?
-Growth
-Directional
-More growth on one side of the root/shoot causing it to bend
-Phototropism + gravitroism
What part of the shoot detects light?
Tip
