A Level Biology Practice Exam

What does an electrocardiogram (ECG) primarily measure?

1. Electrical activity of the skin

2. Changes in heart pressure

3. Tiny changes in the electrical conductivity of the skin

4. Blood flow in the arteries

The correct answer is: Tiny changes in the electrical conductivity of the skin

An electrocardiogram (ECG) primarily measures the electrical activity of the heart. It captures the electrical signals generated by the heart as it contracts and relaxes, providing insights into the heart’s rhythm and overall electrical function. The electrical impulses are recorded through electrodes placed on the skin, which is why the answer pertains to changes in electrical conductivity of the skin. While the heart does generate electrical activity that influences the conductivity of the skin, the primary focus of an ECG is to assess those specific signals originating from the heart itself, rather than its effects on skin conductivity. Other choices, such as measuring blood flow or changes in heart pressure, are not the central functions of an ECG; these parameters would be monitored through different methods, such as echocardiography or blood pressure measurement techniques.