A-Level Edexcel Biology Decimal and Standard Form

Review A-Level Edexcel Biology decimal and standard form through cell sizes, DNA mass, biomass, gas volume and population calculations.

Exam points

express biological quantities such as DNA mass or cell counts in correct standard form
convert ordinary decimals into powers of ten while keeping the stated significant figures
compare magnitudes or rates using standard-form values from biological data

[Maximum number: 2]

There are many water-stressed countries in the world, mostly in the Middle East, North Africa and South Asia. Water-stressed countries have a shortage of fresh water needed for humans, animals and crops. Fresh water can be produced from sea water by desalination processes. The map shows the most water-stressed countries (shaded) in the world.

Figure for Question A.0.2—Decimal and standard form question 1 — Edexcel A-Level Biology AS

The estimate of the volume of water on Earth is $1.4 \times 10^{12} \mathrm{~km}^{3}$ . Fresh water makes up 2.5\% of this volume. 90\% of this fresh water is not available as it is frozen in ice caps and glaciers. Calculate the volume of available fresh water on Earth. Give your answer in standard form.

(volume of freshwater calculated as) $3.5 \times 10^{10}(1)$

- $3.5 \times 10^{9}\left(\mathrm{~km}^{3}\right)(1)$

ACCEPT $3.5 \cdot 10^{10}$ incorrect standard form e.g. $0.035 \times 10^{12}$

ACCEPT $3.50 \times 10^{9} / 3.5 \cdot 10^{9}$

Bald answer of $3.5 \times 10^{9}=2$ marks Bald answer of correct answer but in incorrect standard form = 1 mark correct answer for volume of freshwater in correct standard form $\left(3.5 \times 10^{10}\right)=1$ mark

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A.0.2—Decimal and standard form question 1