1. GCSE Physical Education
Aerobic and Anaerobic Respiration
and the Respiratory System
Topic
Objectives (what you will learn)
Content (you should understand this)
Aerobic respiration
To be aware of the components that make up the respiratory system.
To consider what is meant by aerobic respiration.
To consider the process of gaseous exchange.
To look at and understand the action of breathing.
Aerobic respiration in the presence of oxygen, summarised as:
glucose + oxygen = energy + carbon dioxide + water
Anaerobic respiration
To consider what is meant by anaerobic respiration and the types of exercise that require it.
To consider what takes place during the recovery period.
To consider the function and role of the blood in this process.
Anaerobic respiration in the absence of oxygen, summarised as:
glucose = energy + lactic acid.
Oxygen debt as the result of muscles respiring anaerobically during vigorous exercise and producing a mild poison called lactic acid.
The recovery process from vigorous exercise.

2. The respiratory system

3. The respiratory system

4. The nasal passages and lungs
Air is drawn into the body via the nose or mouth. There are advantages to breathing through your nose:
the air is warmed so that it is closer to body temperature
tiny hairs and mucus in the nose filter the air, preventing larger dust and pollen particles reaching the alveoli
mucus moistens the air, making it easier for the alveoli to absorb.
Air then travels through the larynx, trachea (windpipe), bronchi (one bronchus to each lung) and bronchioles to the alveoli, where oxygen passes into the bloodstream.

5. Mechanisms of breathing – inspiration
When you breathe in:
Intercostal muscles pull ribs up and out
intercostal muscles between the ribs contract, pulling the chest walls up and out
the diaphragm muscle below the lungs contracts and flattens, increasing the size of the chest
the lungs increase in size, so the pressure inside them falls. This causes air to rush in through the nose or mouth.
Diaphragm contracts and moves down

6. Mechanisms of breathing – inspiration

7. Mechanisms of breathing – expiration
When you breathe out:
Ribs move in and down
Intercostal muscles between the ribs relax so that the chest walls move in and down.
The diaphragm muscle below the lungs relaxes and bulges up, reducing the size of the chest.
The lungs decrease in size, so the pressure inside increases and air is pushed up the trachea and out through the nose or mouth.
Diaphragm relaxes and bulges up

8. Mechanisms of breathing – expiration

9. Respiratory rate is how many breaths you take per minute.
You do not need to remember this
Measuring breathing
Tidal volume is the amount you breathe in and out in one normal breath.
Respiratory rate is how many breaths you take per minute.
Minute volume is the volume of air you breathe in one minute.
Vital capacity is the maximum volume of air you can breathe out after breathing in as much as you can.
Clarify and expand on the definitions with the students
Residual volume is the amount of air left in your lungs after you have breathed out as hard as you can.

10. You do not need to remember this
Measuring breathing

11. You do not need to remember this
Measuring breathing

12. Calculating minute volume
You do not need to remember this
Remember:
Minute volume is the volume of air you breathe in one minute.
You can calculate a person’s minute volume by multiplying the volume of air they breathe in one breath, by their respiratory (breathing) rate.
Question
If you breathe 14 times in one minute (respiratory rate) and you breathe 0.5 litres in each breath, what is your minute volume?
Get students to calculate the answer before revealing it.
Point out that at rest, the volume of air breathed in each breath will be the person’s tidal volume. During extreme exercise, it may be closer to their vital capacity.
Answer:
Minute volume = 14 × 0.5 litres
= 7.0 litres

13. Gas exchange at the alveoli
The alveoli are bunches of tiny air sacks inside the lungs.
Each individual sack is called an alveolus.
When you breathe in, they fill with air.
The alveoli are covered in tiny capillaries (blood vessels).
Gases can pass through the thin walls of each alveolus and capillary, and into the blood stream.
Gases can also pass from the blood stream, into the alveolus.

14. Gas exchange at the alveoli

15. Composition of inhaled and exhaled air
Gas
Amount in inhaled air
Amount in exhaled air
Oxygen
Carbon dioxide
Nitrogen
Water vapour
21%
Very small amount
79%
Small amount
17% 3%
79%
Large amount
What are the main differences between inhaled and exhaled air?
Ask the students to compare the relative amounts. Point out that:
The amount of oxygen inhaled is greater than the amount of oxygen exhaled. Consider the efficiency of respiration at the cells.
The amount of carbon dioxide is greater in exhaled air.
The amount of nitrogen is the same.
Mouth to mouth resuscitation works because there is still a lot oxygen left in exhaled air.
Why does mouth-to-mouth resuscitation work?

16. Breathing during exercise
During exercise the muscle cells use up more oxygen and produce increased amounts of carbon dioxide.
Your lungs and heart have to work harder to supply the extra oxygen and remove the carbon dioxide.
Your breathing rate increases and you breathe more deeply.
Heart rate also increases in order to transport the oxygenated blood to the muscles.
Image © 2006 Jupiterimages Corporation

17. Breathing during exercise
Muscle cell respiration increases – more oxygen is used up and levels of CO2 rise.
The brain detects increasing levels of CO2 – a signal is sent to the lungs to increase breathing.
Breathing rate and the volume of air in each breath increase. This means that more gaseous exchange takes place.
The brain also tells the heart to beat faster so that more blood is pumped to the lungs for gaseous exchange.
More oxygenated blood gets to the muscles and more CO2 is removed.

18. Breathing changes during exercise
You do not need to remember this
Breathing changes during exercise
Look at these statistics for a 16 year-old athlete:
During rest
During exercise
Respiratory rate
14 breaths/ minute
32 breaths/ minute
Volume per breath
0.4 litres
2.4 litres
Minute volume ?
Calculate the athlete’s minute volumes during rest and exercise.
Rest minute volume = 5.6 litres
Exercise minute volume = 76.8 litres

19. Respiration respiration energy glucose oxygen
Respiration is the process that takes place in living cells which releases energy from food molecules.
Glucose from food is used to fuel exercise.
Oxygen is required to ‘break down’ the glucose to produce energy. This energy is used to make muscles contract.
respiration
glucose
energy
oxygen
Waste products, including carbon dioxide, are produced as a result of the chemical reactions. These must be removed and excreted.

20. Aerobic respiration There are two different types of respiration.
When you exercise at a steady, comfortable rate, the cardiovascular system is able to supply the muscles with all the oxygen they need.
Under these conditions, aerobic respiration takes place.
carbon dioxide
glucose
+ oxygen
energy +
+ water
Aerobic exercise can be maintained for long periods without the performer getting breathless or suffering muscle cramps. Moderate activities like walking, jogging, cycling and swimming use aerobic respiration.

21. Aerobic respiration

22. Anaerobic respiration
When you exercise at a high intensity, the cardiovascular system cannot supply enough oxygen to the muscles.
Under these conditions, anaerobic respiration takes place.
glucose
energy
+ lactic acid
With no oxygen available, glucose is burned to produce energy and lactic acid.
Lactic acid is a mild poison. As it builds up, it causes muscle pain and eventually cramp.
Short, intense activities like sprinting, weightlifting, jumping and throwing use anaerobic respiration.

23. Oxygen debt
After anaerobic activity, oxygen is needed to neutralize the lactic acid. This is called an oxygen debt. It is repaid after exercise.
The oxygen reacts with the lactic acid to form CO2 and water.
Rapid and deep breathing is needed for a short period after high intensity exercise in order to repay the debt.
This also helps to remove the carbon dioxide which accumulates in the blood during intense exercise.
Image © 2006 Jupiterimages Corporation

24. Anaerobic exercise

25. The effects of exercise on lung structures
In the long-term, regular exercise strengthens the respiratory system.
The respiratory muscles (the diaphragm and intercostals) get stronger, so they can make the chest cavity larger.
This larger chest cavity means more air can be inspired, therefore increasing your vital capacity.
Relate these facts to improvements in performance. Emphasise that lungs are NOT muscles and therefore do not increase in size – they function more efficiently.
More capillaries form around the alveoli, so more gaseous exchange can take place.
Gas exchange can now take place more quickly meaning exercise can be maintained at a higher intensity for longer.

26. Exam-style questions
Describe the passage of oxygen from the nasal passages to the bloodstream.
David goes jogging once a week for 45 minutes.
David tries to increase his pace. He finds that he is forced to stop running and breathe hard for several minutes.
List two differences between the air that David inhales and the air that he exhales while jogging.
What two substances are used by David’s body cells to produce energy? What are the products of this reaction?
From the nasal passages, the oxygen in the air passes the larynx, down the trachea, into the bronchi. It then passes through the bronchioles and into the alveoli. Oxygen passes through the semi-permeable walls of the alveoli, into the capillaries which cover the alveoli walls.
a) There will be less oxygen, more carbon dioxide and more water vapour. b) Glucose and oxygen. The products are carbon dioxide and water. c) David had to stop because as exercise became more intense, his cardiovascular system could no longer supply his muscles with enough oxygen. Anaerobic respiration started, producing lactic acid. When the concentration of lactic acid in David’s muscles got too high, David was forced to stop and repay the oxygen debt. d) The body needs oxygen to neutralize lactic acid. Breathing hard after exercise also helps to get rid of any carbon dioxide that is left in the tissues.
c) Explain why David had to stop.
d) How did breathing hard help him to recover?

27. Can you remember all these keywords?
Larynx
Trachea
Bronchus / Bronchi
Bronchioles
Alveoli
Diaphragm
Intercostal muscles
Oxygen uptake
Respiratory rate
Aerobic respiration
Anaerobic respiration
Oxygen debt
Lactic acid