A-Level Edexcel Biology SI Unit Prefixes

Review A-Level Edexcel Biology SI unit prefixes through graticule measurements, micrometre conversions, nanometre ratios and cell-structure sizes.

Exam points

convert graticule measurements from metres to micrometres for pores or pith cells
compare ribosome and lysosome diameters by converting nm and µm before forming a ratio

[Maximum number: 2]

Fibres from the stems of hemp plants are widely used in industry for their great tensile strength.

The relationship between tensile strength and fibre diameter was investigated.
The photograph shows a cross section of a part of a hemp fibre and an eyepiece graticule. The fibre bundle is made up of pith cells, some of which are shown here.

Figure for Question A.0.P—SI unit prefixes question 1 — Edexcel A-Level Biology AS

Each of the smallest units on the graticule is $3 \times 10^{-6} \mathrm{~m}$ .

Calculate the width of the pith cell labeled A in micrometres ( $\mu \mathrm{m}$ ).

Answer $\mu \mathrm{m}$

An answer that includes the following steps:

- reading of diameter using scale (1)

- width calculated (1)

Example of calculation: 19 units
So actual width is $19 \times 3$ $=57(\mu \mathrm{~m})$
correct answer with no
working gains both
marks
Accept diameters from
15 to 20 units

(2)

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A.0.P—SI unit prefixes question 1