What you need to know
- 7.9–7.16Original mixed practice. cardiac outputThe volume of blood pumped by one ventricle per minute: cardiac output = stroke volume × heart rate. and minute ventilationThe volume of air breathed in per minute: tidal volume × breathing rate. use invented numbers.
No mark allocations. Positive-feedback detail beyond the direction of the response is not required.
By the end, you should be able to…
- Use antagonisticDescribes a pair of muscles that work in opposite directions: when one contracts, the other relaxes. muscles and band lengths correctly.
- Calculate cardiac output and minute ventilation.
- Classify a feedback example by direction.
Build your understanding
Structures before numbers
tendonTough, inelastic connective tissue that attaches a muscle to a bone. versus ligamentStrong connective tissue that joins bone to bone at a joint., flexorA muscle that bends a joint when it contracts. versus extensorA muscle that straightens a joint when it contracts., A band constant, slow versus fast fibres, sinoatrial nodeThe pacemaker: a patch of tissue in the right atrium wall that sends out a wave of excitation across the atria. then atrioventricular nodeTissue between the atria that delays the impulse briefly, so the atria finish emptying, then passes it to the bundle of His. then Purkyne fibresConducting fibres in the ventricle walls that spread the impulse upwards from the apex, so the ventricles contract from the bottom up.. If those sentences are secure, the calculations are short multiplications.
Illustrative arithmetic
cardiac outputThe volume of blood pumped by one ventricle per minute: cardiac output = stroke volume × heart rate. = heart rateThe number of heartbeats per minute. × stroke volumeThe volume of blood pumped out of one ventricle in one heartbeat.. minute ventilationThe volume of air breathed in per minute: tidal volume × breathing rate. = tidal volumeThe volume of air breathed in or out in one breath. × breathing rateThe number of breaths taken per minute.. An example pair: 80 beats/min × 90 cm³ = 7200 cm³/min. And 0.6 dm³ × 20 /min = 12 dm³/min. Invented.
Make your reasoning visible
Purkyne
Use the specification spelling if you name the fibres.
Direction decides feedback
Opposes the change: negative. Amplifies it: positive.
Avoid this misconception
The claim: The I band is myosin and it stays the same length.
The correction: The A band is the myosin length and stays the same. The I band is actin that does not overlap myosin, and it shortens.
Check your understanding
Try each question before opening the suggested answer.
Check your understanding (continued)
Practice question
Retrieval and explanation · suggested answer
Name the extensor at the elbow and the structure that joins it to bone.
Show suggested answer
Triceps. A tendon joins it to bone.
Practice question
Retrieval and explanation · suggested answer
State one structural and one physiological difference of slow twitch fibres compared with fast twitch fibres.
Show suggested answer
More mitochondria or myoglobin or capillaries; they fatigue more slowly and rely on aerobic respiration.
Practice question
Retrieval and explanation · suggested answer
Give the conduction order from SAN to ventricular muscle.
Show suggested answer
SAN, atrial muscle, AVN delay, bundle of His, Purkyne fibres, ventricular muscle from the apex.
Practice question
Retrieval and explanation · suggested answer
Heart rate 90 per minute, stroke volume 80 cm³. Calculate cardiac output.
Show suggested answer
7200 cm³ per minute, or 7.2 dm³ per minute.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
A graph of a blood variable shows larger and larger swings after each “correction”, and the corrections are in the same direction as the original change. Classify the feedback. What would narrow limits look like instead?
Show a hint
Look at direction and at whether the band widens.
Explore the reasoning
This is positive feedback, or failed negative feedback behaving as amplification: each response pushes further and the range widens. Narrow limits would show small reversals around a set point, with the response opposite to the disturbance. No disease name is justified from the sketch alone.
Recall this lesson
Lesson recall questions
Question 1 of 5: How does the inelastic nature of a tendon help movement?
Muscles, tendons, ligaments, skeleton
Practice question
Retrieval and explanation · suggested answer
How does the inelastic nature of a tendon help movement?
Lesson: 7B 1: Tissues of the Skeletal System
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
The recording aids a clinician
7B · Exam PracticeNHLBI describes an electrocardiogram as a recording of how fast the heart is beating and whether the rhythm is steady, including the timing of electrical impulses. Use that…Specification 7.12(iii)Read & use the scienceClose article
Why this matters
NHLBI describes an electrocardiogram as a recording of how fast the heart is beating and whether the rhythm is steady, including the timing of electrical impulses. Use that as the meaning of 7.12(iii). Do not treat a practice calculation of cardiac output as a reading from that test. 7.9–7.16: movement and control. The ECG is the electrical record, not the cardiac-output formula. An injury, symptom or whole-body performance result is not a direct image of a sarcomere or cardiac conduction pathway.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.12(iii) How ECGs aid diagnosis of abnormal heart rhythms.
Use the science
Cardiac output uses volume per beat. What does an ECG add that the formula does not contain?
Explore a possible response
The electrical pattern and whether the rhythm is regular. The formula needs heart rate and stroke volume. An ECG does not, by itself, give stroke volume.
Explore the source
- NHLBI: heart testsUS National Heart, Lung, and Blood Institute
An ECG records rhythm, it does not finish the medicine
7B · Cardiac Muscle and Control of the HeartbeatThe NHS describes an electrocardiogram as a test that records the electrical activity of the heart, including rate and rhythm, and that can be used when an abnormal…Specification 7.12(iii)Read & use the scienceClose article
Why this matters
The NHS describes an electrocardiogram as a test that records the electrical activity of the heart, including rate and rhythm, and that can be used when an abnormal rhythm is suspected. That matches 7.12(iii). It is not an invitation to interpret a real trace, and it does not replace the SAN–AVN order you still have to write. 7.12: myogenic conduction through SAN, AVN, bundle of His and Purkyne fibres; an ECG can help identify an abnormal rhythm.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.12(iii) How ECGs aid diagnosis of abnormal heart rhythms.
Use the science
Why is a faster heart rate on an ECG not automatically a damaged AVN?
Explore a possible response
Rate can change because the SAN is speeding up under nervous or hormonal control, which is normal in activity. An AVN problem is about delay or block between atria and ventricles. Speed alone does not locate the fault.