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Dark treatment experimental control
A student investigated the effect of gravity on the growth of bean seedlings. The student set up apparatus A and apparatus B. Figure 6 shows both sets of apparatus.
The student left both sets of apparatus in a dark cupboard for 24 hours.
Give the reason why the student placed both sets of apparatus in the dark.
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Marking points
- 1 Explains that darkness prevents directional light/phototropism affecting root growth, leaving gravity as the relevant influence.
Full-mark answer
The dark prevents directional light causing phototropism, so any directional root growth can be attributed to gravity.
Why this answer loses marks
The plants need darkness to grow.
This does not connect darkness to preventing phototropism so gravity is the only directional stimulus.