IGCSE Biology Paper-1: Specimen Questions with Answers 200 - 200 of 208

Question 200

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Question

MCQ▾

The diagram shows a germinated bean seed with a horizontal radicle. This is placed on a clinostat and is left for four days.

A Clinostat is a ClockWork

A Clinostat is a ClockWork

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Which diagram shows the appearance of the radicle after three days?

A Clinostat is a ClockWork

A Clinostat is a ClockWork

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Choices

Choice (4)
a.B
b.D
c.A
d.C

Answer

d.

Explanation

A clinostat is a clockwork or electric turntable, which rotates the seedlings slowly about four times an hour. Although gravity is pulling sideways on their roots, it will pull equally on all sides as they rotate. Place the jar and the clinostat in the same conditions of lighting or leave them in darkness for 2 days. The radicles in the clinostat will continue to grow horizontally but those in the jar will have changed their direction of growth, to grow vertically downwards.

Interpretation

The stationary radicles have responded to the stimulus of one-sided gravity by growing towards it. The radicles are positively gravitropic. The radicles in the clinostat are the controls. Rotation of the clinostat has allowed gravity to act on all sides equally and there is no one-sided stimulus, even though the radicles were horizontal.