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Biology · Unit 9

Heart and Circulation

The heart, blood and blood vessels

Circulation is a plumbing problem solved unusually well: one pump, two circuits, and a network fine enough to reach every cell in the body while staying under pressure.

The unit covers the heart's chambers and valves, the differences between arteries, veins and capillaries, what blood is actually made of, and why blood groups matter the moment you try to move blood between people.

This unit breaks down into 20 short steps and 120 questions, starting at difficulty 1 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps
20
Questions
120
Difficulty
1-3

What this unit covers

  • The Heart
  • Blood
  • Blood Vessels
  • Blood Groups
  • Circulation and Pressure

Where this fits

Best taken alongside Lungs and Breathing - the two systems meet at the alveoli and neither is complete without the other.

Where people slip

Arteries carry blood away from the heart and veins carry it back. That is the definition - it is not about oxygen, which is why the pulmonary artery carries deoxygenated blood without breaking the rule.

How the unit is structured

Heart and Circulation runs as 20 short steps that unlock in order. 15 are practice rounds and 5 are challenge rounds that pull together everything before them. Questions start at difficulty 1 and climb to 3 as you progress.

Step 1 · easierStep 20 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 120 in the unit altogether.

Blood

  • Fact or fibLevel 1

    1. Platelets help blood to clot.

    Answer: True

    True. Platelets clump together and help form a clot to seal a wound and stop bleeding.

  • Fill the blankLevel 1

    2. Red blood cells carry oxygen using a red pigment called ____.

    • haemoglobincorrect
    • insulin
    • keratin
    • chlorophyll

    Haemoglobin is the red pigment that binds to oxygen so red blood cells can transport it.

  • Match the pairsLevel 1

    3. Match each part of the blood to its main job.

    Answer: Red blood cells = Carry oxygen; White blood cells = Fight infection; Platelets = Help blood clot; Plasma = Carry dissolved nutrients

    Red cells carry oxygen, white cells fight infection, platelets help clotting, and plasma carries dissolved substances.

  • Multiple choiceLevel 1

    4. Which blood cells are responsible for carrying oxygen?

    • Red blood cellscorrect
    • White blood cells
    • Platelets
    • Nerve cells

    Red blood cells carry oxygen from the lungs to the rest of the body.

  • Choose all that applyLevel 2

    5. Which of these statements about red blood cells are true? (Choose all that apply.)

    • They carry oxygencorrect
    • They contain haemoglobincorrect
    • When mature they have no nucleuscorrect
    • They fight infection

    Red blood cells carry oxygen, are packed with haemoglobin, and lose their nucleus when mature; fighting infection is the job of white blood cells.

  • Guess the numberLevel 2

    6. How many oxygen molecules can a single haemoglobin molecule carry when fully saturated?

    Answer: 4 molecules

    Haemoglobin has four haem groups, each binding one oxygen molecule, so it carries four oxygen molecules in total.

Blood Groups

  • Multiple choiceLevel 1

    7. What are the four main ABO blood groups?

    • A, B, AB and O
    • A, B, C and D
    • 1, 2, 3 and 4
    • X, Y, Z and O

    The ABO system sorts blood into groups A, B, AB and O based on antigens on the red cells.

  • Fact or fibLevel 2

    8. The Rhesus (Rh) factor means blood can be positive or negative.

    Answer: True

    True. Having the Rhesus antigen makes blood Rh positive, and lacking it makes it Rh negative.

  • Fill the blankLevel 2

    9. Your ABO blood group is decided by the ____ found on your red blood cells.

    • antigenscorrect
    • platelets
    • valves
    • nuclei

    Antigens are marker molecules on the surface of red cells that define the blood group.

  • Type the answerLevel 2

    10. Which blood group is the universal recipient, able to receive blood from any ABO group?

    Answer: AB

    Group AB has no anti-A or anti-B antibodies in its plasma, so it can safely receive any ABO blood.

  • Match the pairsLevel 3

    11. Match each ABO blood group to the antibodies found in its plasma.

    Answer: Group A = Anti-B; Group B = Anti-A; Group O = Anti-A and anti-B; Group AB = No antibodies

    Each group makes antibodies against the antigens it lacks, so O has both and AB has none.

  • True or falseLevel 3

    12. Blood group AB has no ABO antibodies in its plasma.

    Answer: True

    True. Because AB carries both A and B antigens, its plasma makes neither anti-A nor anti-B antibodies.

Blood Vessels

  • Build the sentenceLevel 1

    13. Build the sentence that describes what veins do.

    Answer: Veins carry blood back to the heart

    Veins return blood from the body back towards the heart.

  • Multiple choiceLevel 1

    14. What is the main job of an artery?

    • Carry blood away from the heartcorrect
    • Carry blood back to the heart
    • Store spare blood
    • Make new blood cells

    Arteries carry blood away from the heart to the rest of the body.

  • Fill the blankLevel 2

    15. A capillary wall is only ____ cell thick, which makes exchange fast and easy.

    • onecorrect
    • two
    • five
    • ten

    Capillaries are just one cell thick so oxygen, food and waste can pass quickly between blood and tissues.

  • Odd one outLevel 2

    16. Which of these is NOT a risk factor for atherosclerosis and coronary heart disease?

    • Regular aerobic exercisecorrect
    • Smoking
    • High LDL cholesterol
    • High blood pressure

    Smoking, high LDL cholesterol and high blood pressure all raise the risk, whereas regular aerobic exercise helps protect against atherosclerosis.

  • Sort into groupsLevel 2

    17. Sort each feature into the type of blood vessel it belongs to.

    Answer: Thick muscular wall = Artery; Carries blood away from the heart = Artery; Has valves = Vein; Wide lumen = Vein

    Arteries have thick walls and carry blood away under high pressure; veins have wide lumens and valves to bring blood back.

  • Tap the pairsLevel 2

    18. Tap to match each blood vessel to a key feature.

    Answer: Artery = Carries blood away from the heart; Vein = Has valves to prevent backflow; Capillary = Only one cell thick; Aorta = Largest artery in the body

    Arteries carry blood away, veins have valves, capillaries are one cell thick, and the aorta is the largest artery.

Circulation and Pressure

  • Guess the numberLevel 1

    19. About how many times does a healthy adult's heart beat per minute while resting?

    Answer: 70 beats per minute

    A typical resting heart rate for an adult is around 60 to 100 beats per minute, often close to 70.

  • Build the sentenceLevel 2

    20. Build the sentence that explains how a fetus gets its oxygen.

    Answer: the fetus gets oxygen from the placenta

    A fetus does not breathe air; it takes in oxygen from the mother's blood across the placenta.

  • Fact or fibLevel 2

    21. Hypertension means blood pressure that stays abnormally high over a long period.

    Answer: True

    Hypertension is sustained high arterial blood pressure, which raises the risk of stroke, heart attack and kidney damage.

  • Fill the blankLevel 2

    22. The loop that carries blood between the heart and the lungs is called ____ circulation.

    • pulmonarycorrect
    • systemic
    • coronary
    • hepatic

    Pulmonary circulation moves blood to the lungs to pick up oxygen and drop off carbon dioxide.

  • Multiple choiceLevel 2

    23. In double circulation, how many times does blood pass through the heart in one full loop of the body?

    • Twicecorrect
    • Once
    • Three times
    • Four times

    Blood passes through the heart twice: once to reach the lungs and once to reach the body.

  • Sequence recallLevel 3

    24. Recall the path of blood through double circulation, starting after it enters the right side of the heart.

    Answer: Right atrium -> Right ventricle -> Lungs -> Left atrium -> Left ventricle -> Body

    Blood flows from the right atrium to the right ventricle, out to the lungs, back to the left atrium, into the left ventricle, and then out to the body.

The Heart

  • Fill the blankLevel 1

    25. The heart contains ____ that stop blood from flowing backwards.

    • valvescorrect
    • veins
    • arteries
    • nerves

    Heart valves open to let blood through and close to prevent it from flowing back the wrong way.

  • Multiple choiceLevel 1

    26. How many chambers does the human heart have?

    • Fourcorrect
    • Two
    • Three
    • Five

    The heart has four chambers: a left and right atrium on top and a left and right ventricle below.

  • Build the sentenceLevel 2

    27. Build the sentence that explains why the left ventricle has a thicker muscular wall.

    Answer: The left ventricle pumps blood at high pressure around the whole body

    The left ventricle has the thickest wall because it must generate a high pressure to pump blood all the way around the body in the systemic circulation.

  • Fact or fibLevel 2

    28. The 'lub-dub' sound of a heartbeat is made by the heart valves snapping shut.

    Answer: True

    The first sound comes from the atrioventricular valves closing and the second from the semilunar valves closing.

  • Choose all that applyLevel 3

    29. Which of these statements about heart valves are correct? (Choose all that apply.)

    • The atrioventricular valves stop blood flowing back into the atriacorrect
    • The semilunar valves stop blood flowing back from the arteries into the ventriclescorrect
    • A valve opens when the pressure behind it is higher than in frontcorrect
    • Valves actively squeeze to pump the blood along

    Valves are passive flaps opened by pressure; the atrioventricular and semilunar valves simply prevent backflow.

  • Match the pairsLevel 3

    30. Match each part of the conduction system to its job.

    Answer: Sinoatrial node = Sets the heartbeat rhythm; Atrioventricular node = Delays the impulse briefly; Bundle of His = Conducts down the septum; Purkinje fibres = Spread impulse through ventricle walls

    The SAN starts each beat, the AVN briefly delays it, the bundle of His carries it down the septum, and the Purkinje fibres spread it through the ventricle walls.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 17 different question formats, so you are recalling and applying rather than recognising the same layout every time.

  • Build the sentence
  • Choose all that apply
  • Fact or fib
  • Fill the blank
  • Guess the number
  • Listen and choose
  • Match the pairs
  • Multiple choice
  • Odd one out
  • Picture question
  • Put in order
  • Sequence recall
  • Sort into groups
  • Spell it
  • Tap the pairs
  • True or false
  • Type the answer

Practise Heart and Circulation

120 questions across 20 steps. Start with step one and crawl at your own pace.

Play this unit

Read about Heart and Circulation

Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.

More units in Biology

See all 18 units in Biology →