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QUESTIONS
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| 1. |
A biologist named Stephen Hales described how he carried out an
investigation in 1727.
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- I cut a branch (b) off an apple tree about 1 metre long, then sealed the
cut end (p) and tied a piece of wet bladder over it.
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- Then I cut off the other end of the branch at (i) and attached a glass
tube (z) to it.
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- After filling the glass tube with water, I placed the lower end in a bowl
of mercury (x).
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(Reproduced
from Vegetab[e staticks, Bales, S., by permission of the Royal Botanic
Gardens, Kew)
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- I left the apparatus outside on a warm afternoon.
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- By 3.00 p.m. the mercury .had risen over 30 cm.
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- When the mercury reached the cut end of the stem (i) air bubbles appeared
and the mercury slowly ran back into the bowl (x).
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| (a) |
Suggest a hypothesis that was being tested in this investigation.
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(1) |
| (b) |
(i) |
Through which tissue in the stem is most water
transported?
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(1) |
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(ii) |
Give one structural feature of this tissue which
enables it to transport water rapidly (as shown in Hales's demonstration).
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(1)
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| (c) |
Explain,
in terms of the cohesion-tension theory,
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(i)
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why
the level of mercury rose during the investigation;
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(2)
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(ii)
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why
the level of mercury fell towards the end of the investigation.
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(2) |