Ch 2 · Heart · O Level Biology 5090
Topic 2 of 4 in Transport in Animals — O Level Biology 5090 — 57 lessons.
Introduction
The heart is a muscular pump that beats around 100 000 times a day. It appears in almost every 5090 session as a diagram to label, followed by questions on wall thickness, the cardiac cycle and coronary heart disease. Diagrams show the heart as if the person faces you, so its left side is on the right of the page.
Key ideas — Structures of the heart
🧑🏫 Teacher's explanation
Think of the heart as a sophisticated dual-pump system in a house. The right side is a small pump that only needs enough pressure to send water (blood) up a short pipe to the filter (lungs). The left side is a heavy-duty industrial pump designed to blast water through the entire plumbing system of a massive skyscraper (the whole body). Because the left side has to fight much higher resistance to reach your toes and brain, its walls must be much thicker.
📖 Definitions
🔍 Worked example — Easy
A student observes a cross-section of a mammalian heart. They notice the wall of the left ventricle is 3 times thicker than the wall of the right ventricle. Explain why this difference in thickness exists.
🔍 Worked example — Standard
Calculate the percentage increase in heart rate if a person's pulse rate increases from 70 bpm to 105 bpm during exercise.
🔍 Worked example — Exam-style
An individual has a blockage in their coronary arteries. Explain how this leads to a reduction in the efficiency of the heart and state one lifestyle factor that could reduce this risk.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
Key ideas — Why the walls differ in thickness
Both ventricles pump the same volume per beat; the difference is the pressure needed.
🧑🏫 Teacher's explanation
Think of the heart as a dual-pump system in a house. The atria are like small hand-pumps that move water just a few inches into a reservoir (the ventricles). Because the distance is short, you don't need much muscle. The ventricles, however, are like heavy-duty industrial pumps. The right ventricle only needs to push blood a short distance to the lungs, while the left ventricle has to blast blood through miles of vessels to reach your toes and brain.
📖 Definitions
🔍 Worked example — Easy
A student observes a diagram of a mammalian heart. They note that the wall of the left ventricle is 3.0 mm thick, while the wall of the right ventricle is 1.0 mm thick. Calculate the ratio of the thickness of the left ventricle to the right ventricle.
🔍 Worked example — Standard
Explain why the left ventricle has a thicker muscular wall than the right ventricle.
🔍 Worked example — Exam-style
An athlete's heart rate is 60 bpm at rest and 150 bpm during maximal exercise. Calculate the percentage increase in heart rate.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Identify the chamber that has the thickest muscular wall. [1] (b) Explain why this chamber requires a thicker wall than the other ventricle. [2] [3 marks]
Key ideas — How the heart works
Valves are passive: they open and close because of pressure differences.
🧑🏫 Teacher's explanation
Think of the heart as a dual-pump system in a house, where one pump handles the 'waste' (deoxygenated blood) and the other handles the 'clean' (oxygenated blood). To keep things efficient, the house has one-way doors (valves) that only open when the pressure from behind is high enough. If these doors fail, the water flows backward, ruining the whole system.
📖 Definitions
🔍 Worked example — Easy
Compare the thickness of the muscular walls of the left ventricle and the right ventricle.
🔍 Worked example — Standard
Explain why the semilunar valves close when the ventricles relax.
🔍 Worked example — Exam-style
A patient is diagnosed with coronary heart disease. Explain the physiological cause of this condition and how it affects the heart muscle.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
Key ideas — Monitoring heart activity and the effect of exercise
Heart activity can be monitored by an ECG (electrocardiogram), which records the electrical activity of the heart muscle; by pulse rate, counted at the wrist or neck; and by listening to the sounds of the valves closing with a stethoscope.
🧑🏫 Teacher's explanation
Think of your heart as a high-performance dual-action pump in a house. The right side handles the 'low-pressure' plumbing (sending blood to the lungs), while the left side handles the 'high-pressure' plumbing (sending blood to the whole body). Because the left side has to push blood much further, its muscular wall must be significantly thicker to generate that force.
📖 Definitions
🔍 Worked example — Standard
Explain why the muscular wall of the left ventricle is thicker than that of the right ventricle.
🔍 Worked example — Exam-style
A patient is diagnosed with coronary heart disease. Describe the physiological cause of this condition and state two lifestyle changes that could reduce the risk.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Calculate the percentage increase in heart rate from resting to immediately after exercise. [2] (b) Explain why the heart rate remains higher at 4 minutes than at 0 minutes. [2] [4 marks]
Key ideas — Coronary heart disease
Coronary heart disease (CHD) develops when fatty material builds up inside the coronary arteries, narrowing them until a blockage forms, often when a clot develops on the deposit. Muscle beyond the blockage is starved of oxygen and dies: a heart attack.
🧑🏫 Teacher's explanation
Think of your heart as a high-performance engine. To keep running, the engine doesn't just need fuel from the fuel tank; it also needs a dedicated lubrication system to keep its own internal parts moving. The coronary arteries are that lubrication system. They are the specialized pipes that deliver oxygen and nutrients directly to the heart muscle itself.
📖 Definitions
🔍 Worked example — Easy
A patient has a coronary artery with a diameter of 4.0 mm. Due to fatty deposits, the lumen (internal space) is reduced to 1.0 mm. Calculate the percentage reduction in the diameter of the lumen.
🔍 Worked example — Standard
Compare the role of diet and exercise in managing Coronary Heart Disease (CHD).
🔍 Worked example — Exam-style
Explain why a blockage in a coronary artery leads to a heart attack.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Describe how a diet high in saturated fats contributes to this condition. [2] (b) Suggest two lifestyle changes, other than diet, that could help reduce the risk of coronary heart disease. [2] [4 marks]
Worked example
Question. (a) Name the heart chamber with the thickest wall and explain why it is thicker than the chamber across the septum. [3] (b) Describe what happens to the valves when the ventricles contract. [2] (c) Explain why a blocked coronary artery can cause part of the heart muscle to stop working. [3]
🔍 Worked example — Easy
A student observes a diagram of a heart. They note that the wall of the left ventricle is significantly thicker than the wall of the right ventricle. Explain the biological reason for this difference in thickness. [2]
🔍 Worked example — Standard
Calculate the percentage increase in heart rate if a person's pulse rate increases from 72 bpm at rest to 115 bpm during exercise. [2]
🔍 Worked example — Exam-style
Explain how a blockage in a coronary artery leads to a heart attack (myocardial infarction). [3]
⚠️ Common errors
Common mistakes
Practice
Answers