CAIE IGCSE Biology 16.4.10 Pathogens & Toxins Crossing the Placenta

Practise explaining how some pathogens and toxins cross the placenta and harm fetal growth or development.

Exam points

state that the placenta is not a complete barrier to all pathogens and toxins
identify nicotine, alcohol, some drugs and viruses as substances that may cross
link exposure to miscarriage, premature birth, low birth mass or impaired development

[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

Table 2.1 shows a range of substances and their diameters.

Table 2.1

State the names of all the toxins and pathogens listed in Table 2.1 that could pass through the placenta and enter the umbilical cord.

Use the data in Fig. 2.1 to make your choice.

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16.4.10—Some pathogens and toxins can pass question 1