• Quick retrieval from earlier learning (Follow blood through the heart and lungs). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Following blood from the lungs to the body: where does blood go straight after the lungs? (left ventricle / left atrium / pulmonary vein / aorta) → pulmonary veinPrompt: This side of the heart carries oxygenated blood.
2. Humans have a double circulatory system. What does that mean? (we have two hearts / only half the blood reaches the lungs / blood passes through the heart twice on each full trip round the body / blood flows both ways in each vessel) → blood passes through the heart twice on each full trip round the bodyPrompt: One loop goes to the lungs, one to the body.
3. Why is the wall of the left ventricle thicker than the right? (It pumps blood all round the body, so it needs more force / It pumps blood to the lungs only / It is older / It holds more blood) → It pumps blood all round the body, so it needs more forcePrompt: Compare how far blood goes from each ventricle.

• Ask everyone to find their pulse, then jump for 30 seconds and find it again.
• Share the objective: Heart rate, stroke volume and cardiac output. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: A person's stroke volume is 90 cm³ and their heart rate is 72 beats per minute. What is their cardiac output, in cm³ per minute?
• Step 1: 90 × 72 = 6480
• Step 2: So the answer is: 6480 cm³/min
• Answer: 6480 cm³/min
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. A person's stroke volume is 80 cm³ and their heart rate is 150 beats per minute. What is their cardiac output, in cm³ per minute? → 12000 cm³/minPrompt: cardiac output = stroke volume × heart rate
2. During exercise an athlete's cardiac output is 15 dm³ per minute and their stroke volume is 100 cm³. What is their heart rate, in beats per minute? (1 dm³ = 1000 cm³) → 150 bpmPrompt: Convert the cardiac output to cm³ first.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. After exercise, a student counts 18 pulse beats in 15 seconds. What is the heart rate in beats per minute? → 72 bpmPrompt: How many lots of this time fit into 60 seconds?
2. During exercise an athlete's cardiac output is 4.2 dm³ per minute and their stroke volume is 60 cm³. What is their heart rate, in beats per minute? (1 dm³ = 1000 cm³) → 70 bpmPrompt: Convert the cardiac output to cm³ first.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-9.