DSE Biology | Human Transport Lesson-Prep Guide (Tutor Edition) | Cardiac Output, Vessel Area and Flow Speed

2026-11-01

Tutor lesson-prep guides · Secondary Biology

Students can label the four chambers but answer “because it is bigger” when asked why the left ventricle wall is thickest. This lesson links structure to pressure: thick means high pressure out.

Objectives — Students can: (1) calculate cardiac output from stroke volume and heart rate; (2) use total cross-sectional area to explain why capillary flow is slowest; (3) describe the three vessel types by structure and function and state where each side of the heart pumps.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Area of a circle	Area of radius 1 cm	about 3.14 cm2
Unit conversion	5250 cm3 in litres	5.25 L
Diffusion	Does distance slow diffusion?	Yes, so capillaries are thin and dense

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-8 min	Heart structure	Four chambers, valves, where each side pumps	Students draw the arrows
8-22 min	Cardiac output	Stroke volume times heart rate, unit conversion	Get 5.25 L per min
22-36 min	Vessels and speed	Total cross-section sets the speed	Get 0.03 cm per s
36-48 min	Blood components	Red cells, white cells, platelets, plasma	State each function
48-56 min	Answer format	Structure, function, consequence	Rewrite one answer
56-60 min	Exit check	Three questions marked on the spot	Independent work

03 Teaching script (read it out)

Scene 1: The cardiac cycle: what happens in 0.8 seconds

At 75 beats per minute one cycle lasts 0.8 s. Ventricular systole takes about 0.3 s, diastole about 0.5 s. Cardiac output equals stroke volume times heart rate: 70 x 75 = 5250 cm3 per minute, or 5.25 L per minute. Both factors rise in exercise, so output can increase several fold.

Ask the student: with the same stroke volume, what is the output at 150 beats per minute (10.5 L per minute).

Scene 2: Vessels: the larger the total area, the slower the flow

The aorta has a cross-section of 4.5 cm2 and a flow of 30 cm per second; all capillaries together measure 4500 cm2. By continuity, v2 = v1 x A1 / A2 = 30 x 4.5 / 4500 = 0.03 cm per second. Slow flow gives time for exchange, which is why the capillary wall is one cell thick.

Warn: a single capillary is narrow, but the total area is the largest, so flow is slowest. Keep the two ideas apart.

Scene 3: Double circulation: left to the body, right to the lungs

Systemic: left ventricle, aorta, body, vena cava, right atrium. Pulmonary: right ventricle, pulmonary artery, lungs, pulmonary vein, left atrium. The left ventricular wall is thickest because it drives blood around the body; the right side only reaches the lungs. The pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood.

Ask the student: which artery carries deoxygenated blood (the pulmonary artery).

04 Question types and worked steps

Type	Example	Steps	Answer
Calculation	Cardiac output	Stroke volume times rate, then litres	5.25 L per min
Calculation	Change in flow speed	v2 = v1 x A1 / A2	0.03 cm per s
Structure to function	Why the left wall is thickest	It must generate the highest pressure	Pumps the whole body
Comparison	Three vessel types	Wall, lumen, valves, speed	Artery fastest, capillary slowest

Sanity check (teach this): Cardiac output at rest is about 4 to 6 L per minute and flow always slows from aorta to capillaries. A capillary speed faster than the aorta means the single-vessel width was used instead of the total area.

05 Independent practice (3 questions)

Question	Answer	What to watch
Stroke volume 70 cm3 at 75 beats per minute	5.25 L per min	Convert to litres
Aorta at 30 cm per s feeding 4500 cm2 of capillaries	0.03 cm per s	Use total area
Oxygen state of pulmonary artery blood	Deoxygenated	The pulmonary artery is the exception

06 Common mistakes and what to say

Mistake	Student writes	Say this
Calling capillary flow the fastest	Answering “narrow means fast”	“Look at total area, not one vessel.”
Forgetting the unit change	Answering 5250 L per minute	“Divide cm3 by 1000 to get litres.”
Swapping the two sides	Answering right side to the body	“Right goes to the lungs, left goes everywhere.”
Pulmonary vein called deoxygenated	Answering deoxygenated	“The pulmonary vein returns from the lungs, so it is oxygenated.”

07 Homework (paper, section and question numbers)

DSE biology practice paper (human physiology) — Section A questions on heart and vessels
Secondary biology chapter index — All chapters

08 Exit check (last 5 minutes)

Question	Answer	Decision
Output at stroke volume 70 and rate 75	5.25 L per min	All three right: move to gas exchange
Why capillary flow is slowest	Largest total area	One wrong: reteach cross-section
Why the left ventricular wall is thickest	It pumps blood around the body	Two wrong: restart act one

09 Tutor FAQ

Must students memorise cardiac output?

Yes, about 5 L per minute at rest; the worked value here is 5.25.

Are valves one-way?

Yes, they prevent backflow; students should locate the atrioventricular and semilunar valves.

Why is the capillary wall thin?

To shorten the diffusion distance, which works together with slow flow.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.

Practice papers: Paper 1 (blood components and heart structure) · Paper 2 (the cardiac cycle and blood pressure) · Paper 3 (blood and health) · Paper 4 (cardiac output and gas transport)