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
