Problem Solving
National 5 Biology
• Your prelim will involve both Knowledge
and Understanding (KU) – the Biology
facts AND Problem Solving (PS) – the
Maths side of the course.
• Problem Solving Skills include graphs
(bar and line), averages, ratios,
percentage increases, percentage
decreases, pie charts, questions about a
passage, etc.
Problem Solving Questions
• The answer is usually in the data or
information provided, all you have to do
is find it
• Alternatively you may need to calculate
the answer from the data given e.g.
ratios and percentages
• You may have to draw a line graph, bar
chart or pie chart
• READ THE QUESTIONS CAREFULLY!
Working With Percentages
• Percent means per
hundred or for every
hundred
• To calculate a
percentage
Create a fraction and
multiply by 100
e.g. In a class of 24
pupils 14 are boys,
what is the % of girls
in the class?
ANSWER
• If 14 of the pupils are
boys, 10 of the pupils
are girls
• Express this as a
fraction
• Convert to a % by
multiplying by 100
• Percentage of girls in
the class is
10/
24 X 100 = ?
% Increase and Decrease
• You can be asked to
calculate a percentage
increase or decrease
Change
X 100
Original
e.g. a piece of carrot
of mass 10g is placed
in salt solution for 2
hours and then
reweighed. Its new
mass is 9.4g, calculate
the % decrease in
mass.
ANSWER
Change in mass =
0.6g
Original mass =10g
% decrease = 0.6 x
100
10
6%
=
Cont.
•
You may be asked to calculate a % of a
number e.g.
What is 40% of 200?
40 X 200 = 80
100
Ratios
A ratio compares two or more
quantities in a particular
order
Your answer must contain only
whole numbers e.g.
A class of 25 pupils contains
15 boys , calculate the
ratio of girls to boys in the
class.
ANSWER
Number of girls = 10
Number of boys =15
Ratio of girls to boys is
10:15
Both 10 and 15 can be divided
by 5
Ratio of girls to boys is 2:3
There is no number that can
divide both 2 and 3 without
giving a fraction so the
answer is left as 2:3
Averages
• You may be asked to
calculate an average
• What is average of
these numbers?
• 23, 45, 28,32
ANSWER
23+45+28+32 = 128
Divide by 4
Answer = 31
Control Experiments
• A control is an experiment where every
thing is kept the same except for one
factor
• This is usually the factor that is
thought to cause the effect we are
observing
• We can substitute a liquid with distilled
water
• Dead tissue or glass beads for living
tissue
• A control makes an experiment FAIR
Reliable Results
To make results reliable we can do several
things
1. Repeat the experiment several times
and calculate an average of the results
2. Get data from other students and
calculate an average of the results
Drawing Line Graphs
• You may be given a table of results and
be asked to use them to draw a line
graph
• Use the table headings to label the axes
• The factor that the experimenter
controlled is always put on the x-axis
• The factor that is measured in the
experiment is put on the y-axis
• Sometimes one of the axes is already
labelled for you
Plotting a Line Graph
• Choose a simple scale going up in multiples of
1, 2, 5, 10, 20, 50, 100 etc
• Make sure that the scale you have chosen
means that you will use more than half the
grid given
• Never choose an awkward scale like each
square going up in multiples of 3 or 7
• Plot each point using a sharp pencil and mark
with an X
• Join the points using a ruler
• Do not join to 0,0 unless it is in the table
Bar Charts
•
•
•
•
Chose a suitable scale as for line graphs
All the bars must be the same width
Do not waste time colouring in the bars
If you want to make them more visible ,
cross hatch them neatly
Pie Charts