Cambridge International A Level Biology Revision Guide

Chapter P1: Practical skills for AS
a Name the tissues A, B, C and D. [4]
b i On one of the sheets of graph paper, draw the outline of the root. Use at least half the width of
the graph paper when making your drawing.
Now draw inside your outline a low-power plan of the xylem only. Be as accurate as you can in drawing
the correct proportions compared with the overall size of the root – you may find it useful to make some
measurements with a ruler. [4]
ii Now take the second sheet of graph paper and draw the outline of the stem. It does not have to be
exactly the same size as your drawing of the root.
Carefully make a low-power plan to show the vascular bundles only. Draw in outline the lignified
tissues sclerenchyma and xylem, and the tissue labelled C between them. [2]
iii Sclerenchyma and xylem are tissues which contain dead cells whose walls are thickened with a
mechanically strong substance called lignin. Lignin is used for strength and support. Count the
number of squares of graph paper covered by lignified tissue (xylem) in the root. Count the squares
that are more than half included in the drawing as whole squares, and do not count squares that are
less than half included. [1]
iv Count the number of squares covered by the whole root section (including the lignified tissue). [1]
v Calculate the percentage of squares occupied by lignified tissue in the root as follows:
c
number of squares occupied by lignified tissue
× 100
number of squares occupied by whole root
[1]
vi Repeat steps iii to v for the stem (remember lignified tissue in the stem is sclerenchyma plus xylem). [3]
vii Assuming the results you have obtained are typical of the whole stem, suggest an explanation
for the difference in percentage of lignified tissue in the root and the stem. [2]
If you try to imagine these structures in three dimensions, the lignified tissue in the root is a
central rod, but in the stem it is a circle of separate rods. Suggest the reasons for the different
distribution of lignified tissues in the root and the stem. [2]
[Total: 20]
5 A student decided to investigate the effect of temperature on the activity of enzymes in yeast. The student
measured the activity of the enzymes by counting the number of bubbles of carbon dioxide which were
released in three minutes.
The results of the student’s investigation are shown in the table.
265
Temperature / °C Enzyme activity / mean number of carbon dioxide bubbles released per minute
15 5
20 7
30 11
35 15
40 18
a i Plot a graph of the data shown in the table. [4]
ii From the graph, estimate the enzyme activity at 25 °C. [1]
iii Suggest how the student should make sure that the results of this investigation are as accurate
as possible and as reliable as possible. [3]
b In carrying out this investigation, the student made the hypothesis that ‘The activity of the enzymes in
yeast increases as temperature increases.’ State whether you think this hypothesis is supported by the
student’s results. Explain your answer. [2]
[Total: 10]
Cambridge International AS and A Level Biology 9700 Paper 31, Question 1c and d, June 2009