CAIE IGCSE Biology 2.2.3 Millimetres & Micrometres

Practise converting between millimetres and micrometres with 1 mm = 1000 μm, then carry the correct unit into specimen-size, radius or volume calculations.

Exam points

multiply millimetres by 1000 to convert to micrometres and retain the correct unit
divide micrometres by 1000 to convert to millimetres, including values written in standard form
complete the unit conversion before using magnification or comparing biological dimensions

[Maximum number: 1]

Pregnancy can occur after the fusion of a male gamete and a female gamete.

One of the functions of the placenta is to provide a barrier to toxins and pathogens.

A study was done on donated afterbirths. The afterbirth is a placenta with part of the umbilical cord attached.

The purpose of the study was to find the maximum size of particles that can pass through the placenta and enter the umbilical cord.

The researchers inserted beads with a diameter of $0.5 \mu \mathrm{~m}$ into blood vessels in the placenta. Three hours later they recorded the percentage of beads found in the blood in the placenta and in the umbilical cord.

They then repeated the tests using beads with diameters of $0.8 \mu \mathrm{~m}, 2.4 \mu \mathrm{~m}, 5.0 \mu \mathrm{~m}$ and $8.0 \mu \mathrm{~m}$ .

Their results are shown in Fig. 2.1.
percentage of beads found in the blood after 3 hours

Fig. 2.1

Key:
□ umbilical cord
□ placenta

Convert the diameter of the $5.0 \mu \mathrm{~m}$ beads into millimetres (mm).
. mm

$0.005(\mathrm{~mm})$ ;

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2.2.3—mm and micrometre conversions question 1