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4.3Unit 1: Breathing and respiration

Breathing — Cambridge Checkpoint Biology 0893 Revision Notes & Topical Questions

5 min read 8 parts Lesson 3 of 4 2 quizzes

📚 Cambridge Checkpoint Biology 0893 Hub / Topical Revision
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Lesson summary

4.3 Breathing — CHECKPOINT BIOLOGY 0893 notes: Explain how the diaphragm, ribs and intercostal muscles change the volume and pressure of the chest to move air in and out, and measure the volume of air breathed out.Breathing = the movement of air into and out of the lungs.Respirat…

  • Respiration
  • Limitation
  • The intercostal muscles between the ribs contract (get shorter), and this pulls the ribs upwards and outwards
  • The muscles of the diaphragm contract, and this pulls the diaphragm downwards
  • These two movements make more space inside the chest cavity, so the volume increases
  • When the volume increases, the pressure inside the chest cavity and lungs decreases

Section 1 of 8Breathing and respiration

Breathing
Breathing the movement of air into and out of the lungs.
Respiration
Respiration the chemical reaction in cells that releases energy from glucose.
Breathing is not the same as respiration.

Section 2 of 8Breathing in

1
The intercostal muscles between the ribs contract (get shorter), and this pulls the ribs upwards and outwards.
2
The muscles of the diaphragm contract, and this pulls the diaphragm downwards.
3
These two movements make more space inside the chest cavity, so the volume increases.
4
When the volume increases, the pressure inside the chest cavity and lungs decreases.
5
Air moves down the trachea into the lungs to fill the extra space.

Section 3 of 8Breathing out

1
The intercostal muscles relax, which lets the ribs drop down into their natural position.
2
The muscles of the diaphragm relax, which lets the diaphragm return to its normal domed shape.
3
These two movements make less space inside the chest cavity, so the volume decreases.
4
When the volume decreases, the pressure increases.
5
Air is squeezed out of the lungs.

Section 4 of 8A model of breathing

The model uses a syringe, a balloon and a bottle or tube with a hole.
  • The balloon represents the lungs.
  • The tube represents the trachea.
  • The plunger or rubber sheet represents the diaphragm.
  • The bottle or syringe barrel represents the rib cage.
Pulling the plunger out makes the volume bigger and the pressure lower, so air enters and the balloon inflates.
Pushing the plunger in reverses this.
Limitation
  • Limitation the model does not show the ribs, intercostal muscles or the airway branches, and the real lungs are not hollow bags.

Section 5 of 8Measuring the volume of air breathed out

  • Method:
1
Mark a volume scale on a plastic bottle using a measuring cylinder.
2
Fill the bottle to the top with water and put the lid on.
3
Half fill a large bowl with water, turn the bottle upside down in it and carefully remove the lid so that the water stays in the bottle.
4
Slide clean bendy tubing into the top of the bottle under the water.
5
Take a deep breath in and breathe out as much air as possible through the tubing.
6
Read the volume of air from the water pushed out of the bottle.
7
Repeat two more times and calculate the mean.
Safety
  • Safety the bottle and tubing must be clean, the water must be safe to drink, and spilt water on the floor must be avoided.
The volume of air breathed out can be related to body size.

Section 6 of 8Breathing and exercise

Breathing and exercise
During exercise, breathing rate and depth increase.
This supplies more oxygen and removes more carbon dioxide.

Section 7 of 8Key terms

TermMeaning
BreathingThe movement of air into and out of the lungs.
DiaphragmA sheet of muscle below the lungs that contracts and flattens to help breathing in.
Intercostal musclesThe muscles between the ribs that move the rib cage.
Rib cageThe ribs that protect the lungs and move during breathing.
ContractTo get shorter.
RelaxTo return to normal size.

Section 8 of 8Exam technique

1
Saying air is sucked in by the lungs — the muscles change the volume and the pressure difference pushes the air in.
2
Saying the diaphragm moves up when breathing in — it contracts and moves down.
3
Saying breathing and respiration mean the same thing — breathing moves air, respiration releases energy in cells.
4
Saying the volume decreases when breathing in — the volume increases.
5
Forgetting that the intercostal muscles move the ribs up and out when breathing in.

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