MODULE 02
Respiration and Gas Exchange
This is one of the characteristics of living things . We will study this in both
plants and humans.
Gas exchange structures and how they facilitate gas exchange in
humans
Respiration as a chemical process with and without oxygen
You will be able to:-
*Higlighted pages are from MacKean
**Italic pages are from the IGCSE book
NOTE although Mackean is on the booklist it is here simply to supplement the
information in the IGCSE textbook. Mackean contains more detail and may be
useful to supplement or give additional information on a particular topic.
This is a new section in your notes covering part of chapter 9 page 112,
Respiration
• Define respiration as the chemical reactions that break down nutrient molecules in living cells to release energy
 Chapter 3 Page 19. Page 112 chapter 9 Make a note of the definition of
RESPIRATION as the chemical process which releases energy from food..
• State the uses of energy in the body of humans: muscle contraction, protein synthesis, cell division, active transport,
growth, the passage of nerve impulses and the maintenance of a constant body temperature
 You need to know the reasons why organisms need energy. There is a list
on page 112.
Aerobic respiration
• Define aerobic respiration as the release of a relatively large amount of energy in cells by the breakdown of food
substances in the presence of oxygen
 Page 113. There is a definition here which needs to be learned. Note that
aerobic respiration releases a large amount of energy
 Familiarise yourself with the experiment to demonstrate respiration in peas
– you might be able to try this yourself.
• State the word equation for aerobic respiration
 Make a note of the word equations for aerobic respiration and be able to
describe the process page 113.
• State the equation for aerobic respiration using symbols (C6H12O6 + 6O2 → 6CO2 + 6H2O)
 You also need the equation in symbols if you are doing the higher tier..
Anaerobic respiration
• Define anaerobic respiration as the release of a relatively small amount of energy by the breakdown of food
substances in the absence of oxygen
 Page 115 make a note of the definition of anaerobic respiration here. This
needs to be learned. Note there is a different equation for plants and
animals.
 Remember the key difference is that anaerobic respiration occurs in the
ABSENCE of oxygen
• State the word equation for anaerobic respiration in muscles during hard exercise (glucose → lactic acid) and the
microorganism yeast (glucose → alcohol + carbon dioxide)
 You also need to learn the word equation for anaerobic respiration Page 115
• Compare aerobic respiration and anaerobic respiration in terms of relative amounts of energy released
 Anaerobic respiration releases a much smaller amount of energy than
aerobic respiration. Make sure you make notes on this process and learn
them.
 Look at the comparison table of aerobic and anaerobic respiration. Copy
out this table into your notes and learn these differences.
 Page 115 &123 remember that during anaerobic respiration animals
produce lactic acid and plants produce ethanol (alcohol). NOTE that in
animals NO carbon dioxide is produced during anaerobic respiration.
• State the balanced equation for anaerobic respiration in muscles (C6H12O6 → 2C3H6O3) and the
microorganism yeast (C6H12O6 → 2C2H5OH + 2CO2), using symbols
 If you are doing the higher tier you need to learn the equation in symbols for
anaerobic respiration.
• Describe the role of anaerobic respiration in yeast during brewing and bread-making
 Page 115 The anaerobic respiration of yeast is used in both brewing and
bread making. You need to know what happens during brewing and bread
making. Make notes on this
• Describe the effect of lactic acid in muscles during exercise (include oxygen debt in outline only)
 Page 123 You should be able to explain what happens when lactic acid
builds up in muscles and what the term ‘oxygen debt’ means. This explains
why you should ‘cool down’ after exercise. So you shouldn’t suddenly stop
exercising, but do some gentle stretching exercises or walking .
Gas exchange
• List the features of gas exchange surfaces in animals
 Page 116/117 write down the features of a gas exchange surface
• Identify on diagrams and name the larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries
 Page 117 Make a large labelled diagram in your notes of the gas exchange
system in humans ( you might find a better diagram on the internet than
in your text). For each of the following briefly describe the structure (24 sentences should be enough) and function of each of the following RIBS,
INTERCOSTAL MUSCLES, DIAPHRAGM, TRACHEA, BRONCHI,
BRONCHIOLES, ALEOLI and PLEURAL MEMBRANES
• Explain the role of mucus and cilia in protecting the gas exchange system from pathogens and particles
 Make sure you understand the function of the lining of the trachea in
terms of removing particles from inhaled air. Fig 9.2 Pg 118
• Describe the role of the ribs, the internal and external intercostal muscles and the diaphragm in producing
volume and pressure changes leading to the ventilation of the lungs
 Pg 119-121 Fig 13.6 & 13.7 make sure you understand the sequence of
events leading to air being drawn into the lungs. Try and put these in
bullet points pay particular attention to the volume and pressure changes
in the thorax.
 Explain precisely what happens in the alveoli and what the adaptaions are
which make the alveoli effective in absorbing gases. Page 119
 Look at the diagrams on page 121 and explain what is happening here. fig
13.9. LEARN THE SEQUENCE OF EVENTS. This comes up frequently in
exams
• State the differences in composition between inspired and expired air
• Use lime water as a test for carbon dioxide to investigate the differences in composition between inspired and
expired air
 Draw the table comparing inhaled and exhaled air. Page 122. Look at the
activity 9.5 which uses indicators to detect the presence of carbon
dioxide. Make sure you know what these two indicators are and the
changes which take place to indicate the presence of carbon dioxide.
 Page 123remember that plants also respire and need to take in oxygen.
They respire all the time, but also photosynthesise in the light. This
produces oxygen as a waste product, some of which is used in respiration.
At night they can’t photosynthesis so have to take in more oxygen and
give out carbon dioxide. During the day this carbon dioxide is used in
photosynthesis.
• Investigate and describe the effects of physical activity on rate and depth of breathing
• Explain the link between physical activity and rate and depth of breathing in terms of changes in the rate at
which tissues respire and therefore of carbon dioxide concentration and pH in tissues and in the blood
 You can try to see what the effect of exercise is on your breathing rate.
Observe your breathing rate at rest and then do some vigorous exercise
and see how your breathing changes. Try to explain this..
•
Describe the effects of tobacco smoke and its major toxic components (tar, nicotine, carbon monoxide, smoke
particles) on the gas exchange system.

Make notes on the effect of smoking on the gas exchange system from
page 162. You should concentrate on the effects of the different
components of cigarette smoke ie carcinogens & irritants, nicotine and
carbon monoxide