Control & Coordination in Plants (Cambridge (CIE) A Level Biology): Flashcards
Exam code: 9700
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What triggers the Venus flytrap to close?
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Cards in this collection (19)
What triggers the Venus flytrap to close?
The bending of the sensory (trigger) hairs on the lobes of the modified leaves.
How does the Venus flytrap avoid closing on false alarms?
A trigger hair must be stimulated twice (or two hairs touched) within about 20–30 seconds before the trap closes.
What happens when a trigger hair is bent?
It produces a receptor potential.
If a second stimulus follows quickly, an action potential is generated and spreads rapidly across the leaf.
Explain how the closure of the trap is achieved.
The action potential causes a rapid change in turgor pressure and cell volume in the cells of the lobes.
This makes the leaf snap from convex to concave, closing the trap in a fraction of a second.
The Venus flytrap closes when its sensory are stimulated.
The Venus flytrap closes when its sensory hairs are stimulated.
True or False?
A single touch of one trigger hair is enough to close the Venus flytrap.
False.
Usually two stimuli within about 20–30 seconds are needed, which prevents the trap closing on false alarms.
Define auxin.
Auxin (e.g. IAA) is a plant hormone that promotes cell elongation in growing regions.
Explain how auxin causes cell elongation.
Auxin stimulates proton (H^+^) pumps in the cell surface membrane to pump H^+^ into the cell wall.
The wall becomes acidic, activating expansins that loosen bonds between cellulose microfibrils.
The wall becomes more flexible, so the cell takes up water by osmosis and elongates.
What does auxin stimulate in the cell surface membrane?
Proton (H^+^) pumps, which use ATP to actively pump hydrogen ions into the cell wall.
Why does acidifying the cell wall allow elongation?
The low pH activates expansins, which loosen the links between cellulose microfibrils, making the wall more plastic/extensible so it can stretch.
Auxin stimulates proton pumps that the cell wall, allowing it to loosen.
Auxin stimulates proton pumps that acidify the cell wall, allowing it to loosen.
True or False?
Auxin makes the cell wall more rigid to support growth.
False.
Auxin loosens the cell wall (making it more flexible), which allows the cell to elongate.
Define gibberellin.
Gibberellin is a plant hormone that promotes seed germination (and stem elongation).
Describe the role of gibberellin in the germination of barley.
On hydration, the embryo produces gibberellin.
Gibberellin diffuses to the aleurone layer and switches on the genes for amylase.
Amylase hydrolyses starch in the endosperm into maltose/glucose, providing the embryo with substrates for growth.
Which enzyme's production does gibberellin stimulate in barley seeds?
Amylase.
Where in the barley seed is amylase produced?
In the aleurone layer, which surrounds the endosperm.
Why does the germinating barley seed need amylase?
To hydrolyse the stored starch in the endosperm into maltose/glucose, providing energy and substrates for the growing embryo.
In germinating barley, gibberellin stimulates the aleurone layer to produce .
In germinating barley, gibberellin stimulates the aleurone layer to produce amylase.
True or False?
Gibberellin breaks down starch directly in the barley endosperm.
False.
Gibberellin stimulates the production of amylase, and it is amylase that breaks down the starch.
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