Table 1 shows results from a public-health study of 240 newborn babies. The mothers were asked whether they had smoked cigarettes during the final three mon...
Question 1 Report
Table 1 shows results from a public-health study of 240 newborn babies. The mothers were asked whether they had smoked cigarettes during the final three months of pregnancy. A doctor uses the data when discussing ways to reduce low birth mass.
| Mother’s smoking status in final three months | Number of babies | Mean birth mass / kg |
|---|---|---|
| Did not smoke | 160 | 3.32 |
| Smoked 1 to 5 cigarettes each day | 48 | 3.05 |
| Smoked more than 5 cigarettes each day | 32 | 2.71 |
Fig. 1 is a simplified diagram showing the connection between a fetus and its mother. The blood of the fetus and the blood of the mother normally remain in separate blood vessels at the placenta.
(a) Use Table 1 to calculate the difference in mean birth mass between babies of non-smoking mothers and babies whose mothers smoked more than 5 cigarettes each day. Give your answer in kg. [2]
(b) Describe the relationship between the number of cigarettes smoked and mean birth mass. [2]
(c) Name two substances, other than oxygen, that pass from the mother’s blood to the fetus through the placenta. [2]
(d) Explain how carbon monoxide in cigarette smoke can reduce the oxygen supply to fetal cells. [3]
(e) Explain why the blood of the mother and fetus should not mix directly at the placenta. [3]
Answer Details
(a) \[3.32\text{ kg} - 2.71\text{ kg}=0.61\text{ kg}\] The difference in mean birth mass is 0.61 kg. [2]
(b) As the number of cigarettes smoked increases, mean birth mass decreases. The data show an association, but this study alone does not prove that smoking is the only cause. [2]
(c) Two substances that can pass from mother to fetus are glucose and amino acids. Fatty acids, water and antibodies are also acceptable. [2]
(d) Carbon monoxide enters the mother’s blood and binds to haemoglobin in red blood cells. This leaves less haemoglobin available to carry oxygen to the placenta and fetal cells, reducing the fetal oxygen supply. [3]
(e) Maternal and fetal blood may have different blood groups. Direct mixing could cause an immune reaction, including agglutination. Keeping the blood supplies separate avoids this, while useful substances and wastes can still diffuse across the placenta. [3]
Download The App On Google Playstore
Everything you need to excel in your exams
