Edexcel IGCSE Biology Arithmetic Skills

Practise Edexcel IGCSE Biology arithmetic and numerical computation by calculating percentages, ratios, standard-form values and biological rates.

Exam points

Calculate percentages, percentage changes and scaled quantities from biological data.
Use standard form for cell counts, nitrogen masses or nerve impulse time calculations.
Work with ratios and unit conversions in contexts such as communication speed or stomatal density.

Covered syllabus points

1A Decimal-form numbers 1B Standard-form numbers 1C Ratios, fractions, percentages, powers and roots 1D Estimate simple calculations

[Maximum number: 3]

The diagram shows a fetus in the uterus of a woman.

Figure for Question 1 Arithmetic and numerical computation question 1 — Edexcel IGCSE Biology

The umbilical cord transports blood from the placenta to the fetus.
This blood contains molecules from the mother that are needed by the developing fetus.

Doctors recommend that pregnant women obtain more of some dietary components than women who are not pregnant.

The table shows the recommended percentage increase of some dietary components in the diet of a woman who is pregnant compared to a woman who is not pregnant.

Table for Question 1 Arithmetic and numerical computation question 1 — Edexcel IGCSE Biology

The actual mass of additional iron needed by the pregnant woman was 9.0 mg per day.

Calculate the actual total mass of iron needed by the pregnant woman.

9=50 % more

- $100 \%=9 \times 2=18$

- 18+9=27(1)

Allow one mark for 0.5 / 50\% / 1/2 / times 2

Allow 18 for two marks

Award full marks for correct numerical answer without working

exp

[Maximum number: 3]

Neurones transmit nerve impulses.
The diagram shows a neurone.

Figure for Question 1 Arithmetic and numerical computation question 2 — Edexcel IGCSE Biology

Some neurones do not have a myelin sheath.

A scientist investigates the impulse speed for neurones with different diameters. She does this for neurones with a myelin sheath and neurones without a myelin sheath.

The graph shows the scientist's results.

Impulse speed in m per s

The neurone is 90 cm long.

Calculate the time taken for an impulse to travel along this neurone.
Give your answer in standard form.
time $=\ldots$ .
s

$90 \mathrm{~cm}=0.9 \mathrm{~m}$

- $90 \div($ speed ) 440= 0.20s

$0.9 \div$ (speed) 4.4 $=0.20 \mathrm{~s}$

= seconds

- $2.0 \times 10^{-1}(3)$

award full marks for correct numerical answer without working regardless of speed used

allow 1 mark for 0.9 (m) or speed expressed as × $100 \mathrm{~cm} / \mathrm{s}$ ( 440 idea)

allow 1 mark for $90 \div$ speed or $0.9 \div$ speed

(if not 0.20455 etc)

allow 2 marks for marks for correct numerical answer without working but not in standard form

[Maximum number: 2]

Apples contain an enzyme called phenol oxidase.
When apple tissue is exposed to oxygen in the air, this enzyme turns the apple tissue brown.

A student uses this method to investigate the effect of pH on the time taken for apple tissue to turn brown.
- mash an apple to produce a pulp
- place 25 g of this pulp into a beaker
- mix a pH 7 buffer with the pulp to maintain the pH
- check the colour of the pulp every five minutes
- record the time when the pulp turns brown

The student repeats this method using pH buffers of 3, 5, 9, and 11.
The graph shows the student's results.

Figure for Question 1 Arithmetic and numerical computation question 3 — Edexcel IGCSE Biology

Calculate the percentage increase in time taken for the apple pulp to turn brown at pH 11 compared with the time taken at pH 7.
percentage increase = \%

1400 (\%)

One mark for 75-5

OR

OR

$\div 5$

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Covered syllabus points

1 Arithmetic and numerical computation question 1

1 Arithmetic and numerical computation question 2

1 Arithmetic and numerical computation question 3