Anita Akweshie-
what are plant hormones also known as
plant growth regulators
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what are auxins
a type of plant growth regulator that influence many aspects of growth including cell elongation
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what is the principle chemical in the group of auxins made by plants
Indole-3-acetic acid (IAA)
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what is Indole-3-acetic acid typically referred to as
auxin
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where is auxin synthesised
in the growing tips of roots and shoots (meristems)
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what are the three stages in which growth in meristems occurs
cell division by mitosis
cell elongation by absorption of water
cell differentiation
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what is involved in controlling growth by elongation
auxin
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controlling growth by elongation (1)
auxin molecules bind to a receptor protein on the cell surface membrane
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controlling growth by elongation (2)
auxin stimulates ATPase proton pumps to pump hydrogen ions from the cytoplasm into the cell wall across the CSM
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controlling growth by elongation (3)
this acidifies the cell wall by lowering the pH of the cell wall
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controlling growth by elongation (4)
this activates proteins known as expansins which loosen the bonds between cellulose microfibrils and potassium ion channels are opened
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controlling growth by elongation (5)
leads to an increase in potassium ion concentration in the cytoplasm which decreases the water potential of the cytoplasm
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controlling growth by elongation (6)
this causes the cell to absorb water by osmosis through aquaporins
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controlling growth by elongation (7)
this increases the internal pressure of the cell causing the cell wall to stretch and the cell elongates
