Describe the structure of a xylem vessel.

It is a column of dead cells stacked end to end with their end walls broken down, forming a continuous hollow tube.

What is lignin and why is it useful in xylem?

It is a tough substance in the vessel walls that strengthens and waterproofs them, holding the tube open and supporting the plant.

Why is it an advantage that xylem cells are dead and empty?

There is nothing inside to obstruct the water, so it can flow freely up the tube.

What are sieve plates?

They are the perforated end walls between phloem cells, which let the sugar solution pass from one cell into the next.

OCR GCSE Biology A J247

Cell Level Systems

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Scaling Up

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Scaling Up

Xylem and phloem

3 things to know
Paper 3

Overview

What xylem and phloem transport and in which direction, the structure of a xylem vessel, lignin and why dead empty xylem cells help, sieve plates, living sieve tube cells and their companion cells, why transport in phloem needs energy, and how movement in phloem differs from movement in xylem.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What do xylem and phloem each transport and from where, why does phloem transport need energy, and how do their directions of movement differ?

Key term

What does xylem transport, and in which direction?

Key term

What does phloem transport, and where does it come from?

Questions from this subtopic

Each one with the model answer underneath.

1
What does xylem transport, and in which direction?
Model answer
Water and dissolved mineral ions, upwards from the roots to the leaves.
2
What does phloem transport, and where does it come from?
Model answer
Dissolved sugars, from the leaves where they are made to the rest of the plant.
3
Describe the structure of a xylem vessel.
Model answer
It is a column of dead cells stacked end to end with their end walls broken down, forming a continuous hollow tube.
4
What is lignin and why is it useful in xylem?
Model answer
It is a tough substance in the vessel walls that strengthens and waterproofs them, holding the tube open and supporting the plant.
5
Why is it an advantage that xylem cells are dead and empty?
Model answer
There is nothing inside to obstruct the water, so it can flow freely up the tube.
6
What are sieve plates?
Model answer
They are the perforated end walls between phloem cells, which let the sugar solution pass from one cell into the next.

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