Breathing and blood: two systems doing one job

01 The path air takes

1. Nose (W) — warms, moistens and filters the air. Hairs and mucus trap dust.
2. Windpipe (X) — carries air down to the lungs.
3. Lungs (Y) — where the exchange happens.
4. Air sacs (Z) — tiny bags with very thin walls and a large surface, where gases cross into and out of the blood.

02 What actually gets exchanged

03 The blood's round trip

04 Why exercise changes both

05 How to say them

These are words most children have never said out loud, and a word you cannot say is a word you avoid using. Capitals mark the syllable you lean on. Tap the speaker to hear it.

• windpipemore than onewindpipes

  The tube carrying air from the nose and mouth down to the lungs.

• air sacs

  Tiny thin-walled bags in the lungs where oxygen enters the blood and carbon dioxide leaves it.

• oxygensayOK-si-juhn

  The gas the body needs, taken in from the air and carried by the blood.

• carbon dioxidesayKAR-buhn dy-OK-side

  The waste gas the body makes, carried by the blood to the lungs and breathed out.

• circulatory systemsaySUR-kyuh-luh-tree

  The heart, blood and blood vessels, which carry things round the body.

• blood vesselmore than oneblood vessels

  A tube carrying blood through the body.

• pulsemore than onepulses

  The beat you can feel where a blood vessel runs near the skin. It shows how fast the heart is beating.

06 What each level is tested on

The same topic, asked differently as it goes up. The percentage is the share of papers at that level in which it appears.

1. P3

   Naming the parts of the breathing system and what they do.

   Practise P3 Systems: Respiratory & Circulatory — 9 questions →
   52% of P3 papers

2. P4

   The path air takes, and the difference between breathed-in and breathed-out air.

   Practise P4 Systems: Respiratory & Circulatory — 10 questions →
   63% of P4 papers

3. P5

   The heart, blood vessels and the round trip, and the join between the two systems.

   Practise P5 Systems: Respiratory & Circulatory — 10 questions →
   63% of P5 papers

4. P6

   Exercise, pulse and breathing rate, and questions linking both systems in one answer.

   Practise P6 Systems: Respiratory & Circulatory — 9 questions →
   83% of P6 papers

07 Mistakes worth knowing about

Each of these is wrong. Decide why before you open it.

• ✕“Breathed-out air has no oxygen in it.”

  It has less, not none. That is why rescue breathing works at all.

• ✕“We breathe in oxygen and breathe out carbon dioxide.”

  Air is a mixture both ways. We breathe in air containing more oxygen and out air containing more carbon dioxide.

• ✕“The lungs pump the blood.”

  The heart pumps. The lungs are where the gases cross into and out of the blood.

• ✕“Blood goes round once and comes back.”

  It passes through the heart twice on a full circuit — once on the way to the lungs, once on the way to the body.

• ✕“The pulse rises because you are tired.”

  The muscles need more oxygen and are making more carbon dioxide, so the heart beats faster to move blood round more quickly.