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CAIE A Level Biology 9700 · Transport in plants

Transport in plants: explain question

Explain6 marksChallenge

A student prepared a transverse section of a leaf from a herbaceous dicotyledonous plant and observed the midrib region under a microscope. The following features were noted:

  • In the centre of the midrib, there is a large vascular bundle.
  • The xylem is located towards the upper (adaxial) side of the leaf.
  • The phloem is located towards the lower (abaxial) side of the leaf.
  • The xylem contains wide, thick-walled cells with no visible contents.
  • The phloem contains smaller cells with sieve plates and adjacent companion cells.

Explain how the distribution and the structural features of xylem and phloem in this leaf midrib are related to their respective functions in transport.

0 words · 6 marks

No account needed for your first marks. Your answer is used only to mark it.

How this question is marked

6 marks, so the mark scheme is looking for about 6 separate creditworthy points. Making the same point twice in different words earns it once.

Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.

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