How does auxin cause phototropism?
Reveal answer
Made in tip → moves to shaded side → cells elongate more → bends to light.
Key words: shaded side · elongate
3(j) CO-ORDINATION AND RESPONSE · RECALL
3.35 Auxin and phototropism in stems
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Where is auxin produced?
Reveal answer
In the shoot tip.
Key words: tip
What does auxin do to shoot cells?
Reveal answer
Stimulates cell elongation.
Key words: elongation
Why does a decapitated shoot not bend?
Reveal answer
No tip → no auxin → no uneven elongation.
Key words: auxin
What is meant by the term auxin?
Reveal answer
Plant growth regulator that influences cell elongation and other processes.
Key words: auxin
What is meant by the term differential growth?
Reveal answer
Different growth rates on opposite sides of an organ.
Key words: differential growth
What is meant by the term opaque?
Reveal answer
Not allowing light to pass through.
Key words: opaque
Classic phototropism treatments: for Intact tip + one-sided light, give the expected curvature and the inference.
Reveal answer
Expected curvature: Toward light. Inference: Normal detection and signalling.
Key words: Intact tip + one-sided light
Classic phototropism treatments: for Tip removed, give the expected curvature and the inference.
Reveal answer
Expected curvature: Little/no curvature. Inference: Tip is needed.
Key words: Tip removed
Classic phototropism treatments: for Opaque cap on tip, give the expected curvature and the inference.
Reveal answer
Expected curvature: Little/no curvature. Inference: Tip must detect light.
Key words: Opaque cap on tip
Classic phototropism treatments: for Transparent cap, give the expected curvature and the inference.
Reveal answer
Expected curvature: Curvature occurs. Inference: Covering alone is not the cause.
Key words: Transparent cap
Classic phototropism treatments: for Opaque sleeve below tip, give the expected curvature and the inference.
Reveal answer
Expected curvature: Curvature can occur. Inference: Light detection is mainly at tip.
Key words: Opaque sleeve below tip
True or false, and why? “Auxin makes the lit side grow faster in a shoot.”
Reveal answer
False. Greater auxin action on the shaded side promotes more elongation there.
True or false, and why? “Auxin moves toward light.”
Reveal answer
False. It is redistributed toward the shaded side under directional light.
True or false, and why? “Light simply destroys all auxin on one side.”
Reveal answer
False. Phototropism involves regulated transport and redistribution, not only destruction.