OxfordAQA International A Level Biology
OxfordAQA International A Level Biology 3.4.8 Control of Heart Rate Exam Questions
Free OxfordAQA International A Level Biology revision for 3.4.8 Control of Heart Rate: what you need to know, common mistakes and exam-style questions with answers. Covers myogenic heart muscle, the SAN, AVN, bundle of His and Purkinje tissue, and nervous control of heart rate.
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About OxfordAQA International A Level Biology 3.4.8 Control of Heart Rate
Control of heart rate in Unit 4 explains how the heart beats and how its rate changes. You need to describe myogenic stimulation and the spread of electrical activity from the sinoatrial node (SAN) across the atria to the atrioventricular node (AVN), and then down the bundle of His and the Purkinje tissue. You also need to explain how chemoreceptors and pressure receptors detect changes in the blood and send impulses to the medulla, which alters heart rate through the autonomic nervous system. It links to the cardiac cycle in Unit 2 and to Required practical 5 on heart or pulse rate.
What you need to know
- Myogenic stimulation Cardiac muscle is myogenic: it contracts without needing nervous stimulation. The SAN in the wall of the right atrium acts as the pacemaker.
- Spread of excitation A wave of electrical activity spreads from the SAN across both atria, causing them to contract. Non-conducting tissue stops it passing directly to the ventricles.
- AVN and Purkinje tissue The AVN delays the impulse so the atria finish contracting first. It passes along the bundle of His and the Purkinje tissue to the apex, so the ventricles contract from the bottom upwards.
- Receptors Chemoreceptors in the aorta and carotid arteries detect changes in carbon dioxide concentration (pH). Pressure receptors detect changes in blood pressure.
- Nervous control The cardiac centre in the medulla sends impulses along sympathetic neurones to speed up the SAN, or along parasympathetic neurones to slow it down. During exercise, increased carbon dioxide lowers blood pH, which increases heart rate.
Common mistakes in 3.4.8 Control of Heart Rate
- Saying the brain makes the heart beat. Heart muscle is myogenic; the nervous system only changes the rate.
- Forgetting the delay at the AVN. The delay allows the atria to empty before the ventricles contract.
- Saying chemoreceptors detect oxygen in this context. Focus on carbon dioxide concentration and the fall in blood pH.
- Mixing up sympathetic and parasympathetic effects. Sympathetic increases heart rate; parasympathetic decreases it.
Try three 3.4.8 Control of Heart Rate exam-style questions
1. Explain why there is a short delay at the AVN. (2 marks)
Show the mark scheme answer
Allows the atria to finish contracting and empty blood into the ventricles; before the ventricles contract.
2. Explain how heart rate increases during exercise. (4 marks)
Show the mark scheme answer
Respiration increases carbon dioxide concentration and lowers blood pH; detected by chemoreceptors in the aorta and carotid arteries; impulses to the cardiac centre in the medulla; more impulses along sympathetic neurones to the SAN, increasing heart rate.
3. Explain why the Purkinje tissue carries impulses to the apex of the ventricles. (2 marks)
Show the mark scheme answer
So the ventricles contract from the base (apex) upwards; pushing blood up into the arteries.
3.4.8 Control of Heart Rate FAQs
What does OxfordAQA International A Level Biology 3.4.8 Control of Heart Rate cover?
It covers myogenic heart muscle, the SAN, AVN, bundle of His and Purkinje tissue, and nervous control of heart rate.
Which unit is 3.4.8 Control of Heart Rate examined in?
It is part of Unit 4, Control, which is an International A2 paper. The Unit 5 synoptic paper can also draw on this content.
What should I learn for Required practical 5?
It investigates the effect of a variable, such as exercise or posture, on human heart rate or pulse rate. Plan to control other variables, take repeat readings and consider the ethics of working with human volunteers.
