Edexcel IGCSE Biology Standard-form Numbers

Practise Edexcel IGCSE Biology standard-form numbers by converting biological quantities into powers of ten for cells, nitrogen and nerve impulses.

Exam points

Calculate red blood cell totals and express the result in standard form.
Add or convert large biological quantities such as nitrogen masses using powers of ten.
Calculate nerve impulse time and write the answer in standard form seconds.

[Maximum number: 3]

Neurones transmit nerve impulses.
The diagram shows a neurone.

Figure for Question 1B Standard-form numbers question 1 — 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

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1B Standard-form numbers question 1