Problem Solving

Standard Grade Biology

4th Year Supported Study

• 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 100Original 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.

ANSWERChange in mass = 0.6gOriginal 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.

ANSWERNumber of girls = 10Number of boys =15Ratio of girls to boys is 10:15 Both 10 and 15 can be divided

by 5 Ratio of girls to boys is 2:3There 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