Primary 4 · Science · Systems: Respiratory & Circulatory
Systems: Respiratory & Circulatory questions for Primary 4 Science
10 questions to work through online, 2 of them written out the way the paper asks. Answer and you get the working straight away, then a score at the end. No sign-up, and you can retake it as often as you like.
- Gas exchange
- Comparing inhaled and exhaled air
- How the two systems work together
- Why the lungs have many air sacs
- Recovery after exercise
- What blood carries
- Why breathing through the nose is better
- Naming the waste gas
- Naming the organ
- Reasoning about the systems
| Gas | In breathed-in air (%) | In breathed-out air (%) |
|---|---|---|
| oxygen | 21 | 16 |
| carbon dioxide | 0.04 | 4 |
| nitrogen | 78 | 78 |
| Time | Heartbeats per minute |
|---|---|
| resting | 76 |
| just after running | 148 |
| 2 minutes later | 112 |
| 5 minutes later | 80 |
Answers and explanations for all 10 questions
Every answer with the reasoning behind it. Worth reading after you have tried the set — or on its own, if you are a parent marking it.
At the part labelled S in the diagram above, what passes from the air into the blood?
Answer: oxygen
S is where the blood meets the air. Oxygen passes from the air into the blood, and carbon dioxide passes out of the blood into the air.
Based on the table above, which statement is correct?
Answer: Breathed-out air still contains a good deal of oxygen.
Oxygen falls from 21% to 16%, so only about a quarter of it is used. That is why mouth-to-mouth resuscitation works at all.
Which two of these describe how the breathing and circulatory systems work together?
Answer: A and B only
The lungs load the blood with oxygen and the heart pushes that blood out to the body. Neither system is any use without the other.
Why are the lungs made of millions of tiny air sacs rather than two hollow bags?
Answer: to give a very large surface for oxygen to pass into the blood
Millions of tiny sacs have a far greater total surface than two smooth bags would, so oxygen can pass into the blood quickly enough to keep up with the body.
Based on the table above, which statement is correct?
Answer: The heart rate returned close to resting within five minutes.
The readings fall 148, 112, 80 over five minutes, ending close to the resting rate of 76. Once the muscles stop demanding extra oxygen, the heart slows again.
Which two of these does blood carry away from the body's cells?
Answer: A and B only
Blood works in both directions: it delivers oxygen and digested food to the cells, and carries carbon dioxide and other waste away.
Why is it better to breathe in through the part labelled P in the diagram rather than through the mouth?
Answer: The nose warms the air and traps dust before it reaches the lungs.
Hairs and moisture in the nose trap dust and warm the air, so what reaches the lungs is cleaner and closer to body temperature.
The blood brings a waste gas back to the lungs so that it can be breathed out. Which gas is it?
Answer: carbon dioxide
The waste gas carried back to the lungs and breathed out is carbon dioxide.
This organ is a muscle that squeezes about seventy times a minute all your life, pushing blood around the body. What is it?
Answer: heart
The muscle that pumps blood around the body is the heart.
Why does a person feel out of breath after climbing many flights of stairs?
Answer: Their leg muscles used oxygen faster than the lungs could supply it.
Working muscles use oxygen faster than usual. Breathing hard afterwards is the body catching up on the oxygen it fell behind on.