9.1.3 - Chemical control in plants Flashcards
Where does cell division occur in plants?
Meristem tissues - roots and shoots of plants
How to auxins (IAA) work in plant stems?
Cells in the shoot tip produce IAA.
The IAA diffuses back down to the zone of elongation.
IAA molecules bind to specific receptor sites o the cell membrane activating the pumping of H+ ions into cell wall spaces.
This lowers the pH to 5 which is optimum for the enzymes which break bonds between the cellulose myofibrils.
This means the cells can absorb more water by osmosis causing the cell walls to stretch which means the cells elongate and expand.
What are auxins involved in?
Apical dominance - suppressing the growth of lateral shoots so the main stem grows fastest.
Promoting root growth.
Response of plant shoots to light.
What do auxins do in shoots and roots?
Roots - they inhibit cell elongation
Shoots - promote cell elogation
Why do shoots grow towards light?
Auxins diffuse to the shaded side.
Greater concentration in the zone of elongation on the dark side.
Stimulates cells to grow and shoot grows towards light.
What do gibberellins do?
Growth regulators.
Promote growth of fruit.
Break dormancy of seeds.
Stimulate bolting.
Describe the structures present in a seed.
Endosperm (strores carbohydrates)
Aleurone layer
Seed coat
Embryo
What is the first stage in seed germination?
Seed absorbs water and swells - the embryo becomes activated
What happens in seed germination after the embryo becomes activated?
Embryo secretes gibberellin which diffuses to aleurone layer.
What does gibberellin do to the aleurone layer in seed germination?
Stimulates the aleurone layer to produce amylase which diffuses into endosperm and break down food stores.
What is the function of the endosperm in a seed?
Stores carbohydrates such as starch.
What are some roles of cytokinins?
Promote cell division in apical meristems (roots and shoots) and cambium.
Promote lateral bud development.
Work with ethene in the absicission (e.g natural removal of dying leaves)
