Learning objectives
a) identify the larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries
and state their functions in human gaseous exchange
b) describe the process of breathing and the role of cilia, diaphragm, ribs and internal
and external intercostal muscles
c) explain how the structure of an alveolus is suited for its function of gaseous
exchange
d) state the major toxic components of tobacco smoke – nicotine, tar and carbon
monoxide, and describe their effects on health
e) define aerobic respiration in human cells as the release of energy by the
breakdown of glucose in the presence of oxygen and state the equation, in words
and symbols
f) define anaerobic respiration in human cells as the release of energy by the
breakdown of glucose in the absence of oxygen and state the word equation
g) explain why cells respire anaerobically during vigorous exercise resulting in an
oxygen debt that is removed by rapid, deep breathing after exercise
Learning objectives
a) identify the larynx, trachea, bronchi,
bronchioles, alveoli and associated capillaries
and state their functions in human gaseous
exchange
c) explain how the structure of an alveolus is suited
for its function of gaseous exchange
The Respiratory System
• The respiratory system comprises
various organs that facilitate
gaseous exchange.
• Gas exchange is the exchange of
gases between an organism and
the environment.
• In humans, the absorption of
atmospheric oxygen and the
removal of carbon dioxide from
the body occurs in the alveoli
(air sacs) in the lungs.
The Respiratory System
The Respiratory System
nostril
pharynx
larynx/
voice box
lungs
ribs
intercostal
muscles
trachea/
windpipe
Bronchus
(pl: bronchi)
bronchioles
alveoli
diaphragm
The Respiratory System
Route taken by air
Through nostrils
pharynx
larynx
trachea
bronchus
bronchioles
alveoli
bronchus
bronchioles
alveoli
Thinking question:
Why is there a need for such a complex
respiratory system in humans?
• In unicellular organisms, gaseous
exchange can take place by simple
diffusion.
• Large animals have a smaller
surface area-to-volume ratio
• Our external surfaces/ skin are often thickened for protection to
prevent water loss and hence not suitable for gas exchange
• We use special organs such as gills and lungs for gas exchange
• Such organs have large surface area to volume ratio and thin
coverings to enable efficient exchange of gases
The nose

Air enters through the nostrils

Walls of nostrils have nasal hairs and mucous
membranes that produce mucus
Functions :
❑
Hairs and mucus trap dust, foreign particles e.g.
bacteria
❑
Mucus warms and moistens air
❑
Sensory cells in mucous membrane detects
harmful chemicals
The Trachea
• Airway that lies in front of the oesophagus
• Supported by C-shaped rings of cartilage to ensure
that the trachea is always kept open
Trachea
Bronchi and bronchioles

The trachea branches into two tubes called the
bronchi (singular: bronchus)

Each bronchus branches repeatedly and ends in
numerous bronchioles

Each bronchiole ends in a
cluster of air sacs called
alveoli where gaseous
exchange takes place
Epithelium of Trachea and Bronchi
• Membrane next to the lumen is called the epithelium
• The epithelium consists of 2 types of cells
1. Gland cells
2. Ciliated cells
Epithelium of Trachea and Bronchi
cilia
mucus
Label your
diagram
gland cell
Epithelium of Trachea and Bronchi
Structure
Gland cells
Ciliated cells
Function
Secrete mucus that traps dust particles and
bacteria in the air passage
Have cilia which sweep the mucus containing
dust particles and bacteria up the bronchi
and trachea into the pharynx.
The mucus can be coughed out through the
pharynx or be swallowed into the oesophagus
What happens if food/water accidentally
enters the trachea?
Alveoli (air sacs)
• The alveoli are the sites of gas exchange
• Numerous alveoli are found in the lungs
• Each alveolus is surrounded by a
network of blood capillaries
Alveoli (air sacs)
Label the diagram with:
•
•
•
•
oxygen
carbon dioxide
oxygenated blood
deoxygenated blood
Gas exchange at the alveoli
• Gas exchange at the alveoli occurs by diffusion.
• Blood flowing to the lungs has a lower concentration of
oxygen
_______________
and a higher concentration of
_______________,
carbon dioxide than atmospheric air entering the lungs.
• A concentration gradient for oxygen
and carbon dioxide is set up between
the blood in the capillaries and air in
the alveolus.
Structure-function relationships
Lungs
• Numerous alveoli in lungs provide a large surface area to
volume ratio for more efficient gaseous exchange
Alveoli
• Thin walls (one-cell thick walls)
• Inner wall covered by layer of thin
film of moisture
• Surrounded by network of blood
capillaries
Alveoli (singular: alveolus)
1. Thin (one-cell thick) walls
• Provides a short diffusion distance for gases, ensuring more
efficient diffusion of gases in and out of alveoli
2. Thin film of moisture in inner walls of alveoli
• Allows gases to dissolve in it
3. Surrounded by network of blood capillaries
• Continuous flow of blood maintains concentration gradient of
gases
✓ Maintains ______ concentration of oxygen in alveoli than in blood
✓ Maintains ______ concentration of carbon dioxide in alveoli than in
blood
allowing more efficient diffusion of gases in and out of alveoli
Alveoli (singular: alveolus)
Video on gas exchange at alveoli
http://www.youtube.com/watch?v=XTMYSGXhJ4E
How is oxygen absorbed from the lungs into
blood and into cells of tissues?
higher concentration of oxygen than the
1. Alveolar air contains a ________
blood plasma
thin film of moisture in the inner wall of
2. Oxygen dissolves in the __________________
the alveolus and then ______________
into the blood capillaries.
diffuse
haemoglobin in red blood cells to
3. Oxygen combines with _________________
form ____________________.
oxyhaemoglobin
• This reaction is reversible.
+O2
- O2
Haemoglobin
Oxyhaemoglobin
How is oxygen absorbed from the lungs into
blood and into cells of tissues?
3. When the blood passes through oxygen-poor tissues,
the oxyhaemoglobin releases oxygen,
4. which will diffuse through the walls of the blood
capillaries into the cells of the tissues.
+O2
- O2
Haemoglobin
Oxyhaemoglobin
Checkpoint 1
1. What is the function of the incomplete rings of cartilage
around the trachea?
A. to filter dust and bacteria out of inhaled air
B. to force air out of the trachea
C. to prevent the collapse of the trachea
D. to protect the blood vessels supplying the lungs
(
A
)
Checkpoint 1
B
High O2
Low O2
Checkpoint 1
Any 2 of:
1.
Thin, one-cell thick walls, which provides a short diffusion distance, ensuring
more efficient diffusion of gases in and out of alveoli
2.
Thin film of moisture in inner walls of alveoli, which allows gases to dissolve in it
3.
Each alveolus is surrounded by network of blood capillaries. The continuous flow
of blood maintains concentration gradient of gases allowing more efficient
diffusion of gases in and out of alveoli
Checkpoint 1
Diffusion
Learning objectives
b) describe the process of breathing and the role of
cilia, diaphragm, ribs and internal and external
intercostal muscles
Breathing
• Breathing is part of the gas exchange process
• It refers to the muscular contractions and movements
of the ribs which result in air moving in and out of the
lungs.
• Breathing consists of two phases:
• Inspiration / Inhalation
= Taking in of air into lungs
• Expiration / Exhalation
= Giving out of air from lungs
Thoracic cavity (chest cavity)
• Space in the body that is protected by the rib cage and associated
skin and muscles
• 2 sets of intercostal muscles can be found between the ribs.
• Intercostal muscles and the diaphragm at the ribcage, enable the
change in volume of the thoracic cavity.
Intercostal muscles
• External intercostal muscles and internal intercostal
muscles are found between the ribs.
• They are antagonistic muscles
Diaphragm
• Found below thorax
• Made up of a dome-shaped sheet of diaphragm muscles
• When diaphragm muscle contracts – diaphragm flattens downwards
• When diaphragm muscle relaxes – diaphragm arches upwards
Diaphragm
Class Activity : Try this
How does breathing occur?
Does air move in first ?
Does your chest move first?
Can you control your breathing ?
Close your eyes and take a few deep breaths
and focus on these above questions
Class Activity : Try this
 Does air move in first?
No. The muscles contract first to bring the air in
 Does your chest move first?
The ribcage and diaphragm move at the same time,
before any air rushes into your nose and mouth
 Can you control your breathing?
Yes and no. There is a part of breathing that you
cannot control (your brain does it) and a part that you
can (like holding your breath for a while).
Inspiration vs. Expiration
Diaphragm
muscles relax
Diaphragm
muscles contract
Diaphragm arches
upwards
Diaphragm flattens
downwards
Inspiration vs. Expiration
Breathing in - Inspiration
• Diaphragm muscles contract, diaphragm flattens downwards
Side view
• External intercostal muscles contract
air enters lungs
• Internal intercostal muscles relax
• Ribs swing upwards and outwards
ribs raised
• Volume of thoracic cavity increases
• This decreases air pressure in the lungs
• Atmospheric pressure is now higher
than the pressure within the lungs
• This causes air from the atmosphere
to be forced into the lungs
diaphragm
flattens
lungs expand
Breathing out - Expiration
• Diaphragm muscles relax, diaphragm arches upwards and
becomes dome-shaped
Side view
• External intercostal muscles relax
air expelled from lungs
lungs volume
decrease
• Internal intercostal muscles contract
• Ribs swing downwards and inwards
ribs lowered
• Volume of thoracic cavity decreases
• This increases air pressure in the lungs
• Atmospheric pressure is now _______
than the pressure within the lungs
• This causes air to be forced out of the lungs
diaphragm
arches
upwards
“Volume of thoracic cavity increases, the air pressure in the
lungs decreases.”
“Volume of thoracic cavity decreases, the air pressure in the
lungs increases.”
What is the stimulus for breathing?
• Involuntary process controlled by the brain
• The stimulus for breathing is a high concentration of
carbon dioxide in the blood
Component
Inspired air
Expired air
Oxygen
About 21%
About 16.4%
Carbon dioxide
About 0.03%
About 4%
Nitrogen
About 78%
About 78%
Water vapour
Variable
Saturated
Temperature
Variable
About body temperature,
37O C
Dust particles
Usually present
Little or none
Checkpoint 2 – Question 1
Trachea
Bronchus
Bronchiole
Checkpoint 2 – Question 1
The muscles of structure D (diaphragm) relaxes, and the diaphragm
arches upwards and becomes dome-shaped.
Structure E (external intercostal muscles) relax, while the internal
intercostal muscles contract.
These causes the ribs to swing downwards and inwards, decreasing
the volume of the thoracic cavity.
Checkpoint 2 – Question 2
a) Calculate, in breaths per minute, the rate of normal breathing
between A and B.
3 breaths in 12 minutes
15 breaths/ minute
Checkpoint 2 – Question 2
b) State the volume of air remaining in the lungs after the
deep breath out.
1500 cm3
Checkpoint 2 – Question 2
c) Explain how the intercostal muscles are inhalation
involved in breathing from time B to time C.
During inhalation, external intercostal
muscle contract, internal intercostal
muscle relax, diaphragm muscles
contracts and diaphragm is flattened
downwards.
The rib cage swings outwards and
upwards and the volume of thoracic
cavity increases, causing a decrease in
the air pressure inside of lung.
Atmospheric air forced into lungs.
air enters lungs
ribs raised
diaphragm
flattens
lungs expand
Components of tobacco smoke
and the effects on heath
Learning objectives
d) state the major toxic components of tobacco
smoke – nicotine, tar and carbon monoxide,
and describe their effects on health
Chemical
Effects
Nicotine
• Increases chances of blood clot in blood vessels,
(Addictive drug)
therefore increase risk of coronary heart disease
• Causes release of hormone adrenaline
- increases heart rate and blood pressure
Carbon
monoxide
• Binds irreversibly with haemoglobin in red blood
cells to form carboxyhaemoglobin
- reduces ability of haemoglobin to bind to
oxygen, reduces efficiency of oxygen transport
• Increases risk of coronary heart disease
Tar
• Paralyses cilia in air passages, hence trapped dust
particles trapped in mucus cannot be removed.
• Contains cancer-causing (carcinogenic) chemicals
that cause uncontrolled cell division in the lungs
- increase risk of lung cancer
Other irritants
Like tar, other irritants found in tobacco smoke also:
• paralyse cilia lining the air passages
• increase risk of chronic bronchitis and emphysema
Diseases caused by tobacco smoke
1. Chronic bronchitis
2. Emphysema
3. Lung cancer
chronic obstructive pulmonary
disease (COPD)
Chronic Bronchitis
• Prolonged exposure to irritant particles in tobacco smoke leads to:
• Epithelium lining of air passages become inflamed (e.g Bronchi
inflammation)
• Excessive mucus secreted by epithelium
• Cilia on the epithelium paralysed
• Mucus and dust particles cannot be removed
• Air passage becomes blocked,
breathing becomes difficult
• Persistent and violent coughing to clear air passages
Emphysema
Persistent and violent coughing may lead to emphysema
• Partition walls between the alveoli break down because of the
force from the coughing.
• This results in ___________ surface area for gaseous exchange
• The lungs lose their elasticity and become inflated with air.
• Breathing becomes difficult,
wheezing and severe
breathlessness result.
Emphysema
Emphysema
Lung Cancer
• Carcinogens in tobacco smoke can
cause mutations in the DNA in lung cells
• Causes lung cancer, which is a result of
uncontrolled division of cells in the
lungs, producing lumps of tissues
(tumours) in lungs
Summary video: COPD
http://www.youtube.com/watch?v=2nBPqSiLg5E
Checkpoint 3
B
Nicotine
Tar, irritant particles
Carbon monoxide
A
Checkpoint 3
D
Test yourself!
https://www.bbc.co.uk/bitesize/guides/zsry39q/test
Learning objectives
e) define aerobic respiration in human cells as the release
of energy by the breakdown of glucose in the presence of
oxygen and state the equation, in words and symbols
f) define anaerobic respiration in human cells as the release
of energy by the breakdown of glucose in the absence of
oxygen and state the word equation
g) explain why cells respire anaerobically during vigorous
exercise resulting in an oxygen debt that is removed by
rapid, deep breathing after exercise
Respiration
Respiration is the oxidation of food substances
with the release of energy in living cells
Aerobic respiration
Anaerobic respiration
(requires oxygen)
(does not require oxygen)
Energy currency – ATP
• During respiration, ATP is produced
• ATP = Adenosine triphosphate
• A high-energy molecule that stores energy for cellular
processes
Respiration vs Breathing
2 different but related processes:
1. Respiration
Oxidation of food molecules within
living cells to release energy
(Aerobic & Anaerobic respiration)
2. Gaseous exchange (breathing)
Exchange of gases between the
body and the surroundings
Respiration
Respiration is the oxidation of food substances
with the release of energy in living cells
Aerobic respiration
Anaerobic respiration
(Requires oxygen)
(Does not require oxygen)
Aerobic respiration
Recall: What is this? What does it do?
Mitochondria: The site of aerobic respiration
Aerobic respiration
The breakdown of food substances (glucose) in the presence
of oxygen with the release of large amount of energy.
•
•
•
•
Occurs in the mitochondria
Glucose is oxidised,
producing carbon dioxide and water,
releasing a large amount of energy
o
some of the energy is released as heat
Aerobic respiration
The breakdown of food substances (glucose) in the presence
of oxygen with the release of large amount of energy.
Word equation
• glucose + oxygen → water + carbon dioxide
(A large amount of energy is released)
Chemical equation
• C6H12O6 + 6O2 → 6CO2 + 6H2O
Anaerobic respiration
The breakdown of food substances (glucose)
in the absence of oxygen
• Less efficient than aerobic respiration → less energy released
• In humans, anaerobic respiration can happen in muscle cells
during vigorous exercise
• Anaerobic respiration takes place in the cytoplasm of the
cell, not mitochondria
• In muscle cells, this process produces lactic acid and releases
a small amount of energy.
Anaerobic respiration
The breakdown of food substances (glucose)
in the absence of oxygen
Word equation:
glucose → lactic acid
(A small amount of energy is released)
Note: absence of carbon dioxide and water as products
Anaerobic respiration in yeast
• Anaerobic respiration could take place in many other
living organisms (e.g. yeast cells, bacteria).
• Lactic acid is not necessarily a product in some of
these cases.
E.g. Anaerobic respiration in yeast
glucose
ethanol + carbon dioxide
A small amount of energy is released
Aerobic and anaerobic respiration in
human muscles during exercise
Imagine doing a 2.4km run..
• There are more vigorous muscular contractions during
exercise.
• More _________
energy is required for more vigorous muscular
contractions.
aerobic respiration
• So, a higher rate of _________________
takes place in muscle cells.
• Glucose is oxidised at a higher rate to release energy at a
higher rate.
Imagine doing a 2.4km run..
Breathing rate increases:
• Oxygen is taken in at a higher rate
• So that aerobic respiration can take place at a higher rate, for more
efficient release of energy
• Carbon dioxide is also removed from body at a higher rate.
pant.. pant.. pant..
Imagine doing a 2.4km run..
Heart rate increases:
• So oxygen and glucose can be pumped to the muscles
at a higher rate
• This allows higher rate of aerobic respiration
to release energy faster
After long period of exercising…
Need more energy…
Not enough oxygen…
Anaerobic respiration in muscles
• During intense or long periods of vigorous exercise
e.g. 100m sprint, marathon
• Oxygen supplied to muscles is not enough to meet the oxygen
demand
• Amount of oxygen taken in is less than amount of oxygen required,
leading to an oxygen debt
▪ Oxygen debt is the amount of oxygen required to convert all the
lactic acid accumulated back to glucose.
• There is insufficient oxygen taken in for aerobic respiration to take
place fast enough to release the large amount of energy required.
(This is because there is a limit to our breathing rate and heart rate!)
Anaerobic respiration in muscles
• Anaerobic respiration takes place in the muscles, in
energy to release the extra
the absence of __________
energy required.
Lactic acid is produced and ____________________
small amount of energy
• ___________
is released in the process.
• Note: Maximum rate of aerobic respiration
is still taking place!
Anaerobic respiration in muscles
After a race…
1. Body needs to rest
2. Lactic acid is gradually removed from
muscles and transported to the liver
to be oxidised to glucose.
3. Breathing rate continues to be high for some time
•
•
Provides sufficient oxygen to muscle cells to repay oxygen debt
Provides oxygen to oxidise lactic acid into glucose in the liver
4. When all lactic acid has been converted, the oxygen debt is
repaid.
Checkpoint 4
Number of breaths per
second (rate of breathing)
Volume of air taken
in in each breath
during exercise
Checkpoint 4
• Volume of air taken in and given out in each breath is
larger during exercise than before exercise.
• More vigorous muscular contractions is needed during
exercise.
• More air is taken in during exercise to provide larger amount of
oxygen to muscle cells for aerobic respiration, for the release of
larger amount of energy for vigorous muscular contractions.
• More carbon dioxide is released in the process, so a larger
volume of carbon dioxide is brough to lungs to be released.
Checkpoint 4
• Rate of breathing is higher during exercise than before
exercise.
• This allow oxygen to be transported to muscle cells faster /
more efficiently.
• So aerobic respiration can take place more efficiently, and
release of large amount of energy for vigorous muscular
contractions faster.
• As carbon dioxide is released faster during exercise, the higher
rate of breathing allows carbon dioxide to be given out more
efficiently.
Checkpoint 4
Checkpoint 4
Lactic acid concentration is 0 arbitrary units in the muscles from 0 to 2 mins.
Aerobic respiration takes place in the first 2 minutes of the race, when there is
sufficient oxygen provided to the muscles. Lactic acid is not produced.
Lactic concentration in the muscles increases from 0 arbitrary units to 7.5
arbitrary units from 2 minutes after the start of rate to 6 minutes after the
start of race.
After 2 minutes, insufficient oxygen is taken in (oxygen taken in is lower than
oxygen demand) for aerobic respiration to take place to release energy.
As a result, anaerobic respiration also takes place, producing lactic acid.
From 6 minutes to 10 minutes, lactic concentration in the muscles
decreases from 7.5 arbitrary units to 4 units.
When the race ended after the first 6 minutes. Breathing rate remains high.
Lactic acid is brought to the liver, where it is oxidised to glucose.
Investigating respiration
Recall…
glucose +
oxygen →
energy
carbon dioxide +
water
is released
How can we show that respiration has taken place?
1. Carbon dioxide is produced
2. Energy is released
• In the form of heat
Investigating respiration
• Carbon dioxide production
• How to test for carbon dioxide?
Potassium hydroxide: Removes carbon dioxide
Limewater: White precipitate formed in limewater in presence of
carbon dioxide
Try it yourself!
• Potassium hydroxide in flask A removes carbon dioxide that enters.
• Air entering flask B should / should not contain carbon dioxide.
• White precipitate should / should not form in the limewater in flask B.
• Air entering flask C will/will not contain carbon dioxide.
• Hence, any carbon dioxide detected in flask D would be due to respiration by the snails.
Investigating respiration
Production of carbon dioxide
Using hydrogencarbonate indicator
• Carbon dioxide dissolves in water
to form a slightly acidic solution.
• What colour will the indicator in
each test tube turn?
orange / yellow
With insect: ____________
red
Control: ___________
• What is the use of the control?
• To show that any change in colour of
the indicator is due to the insect
Investigating respiration
Release of heat
Why use a vacuum flask?
What is the antiseptic for?
What is the purpose of the
cotton wool?
What is set-up B for?
What is the expected result?
Investigating respiration
• Why use a vacuum flask?
Prevent loss of heat to the surroundings
• What is the antiseptic for?
To kill microorganisms. When the
microorganisms respire, they release
heat. In addition, heat is also released
during decomposition of seed by
microorganisms.
• What is the purpose of the cotton wool?
Cotton wool is porous, allowing carbon
dioxide, oxygen and other gases to
diffuse in and out of the setup
Investigating respiration
• What is set-up B for?
Serve as a control to show that
change in temperature is due to
respiration of the live seeds.
• What is the expected result?
Temperature in A will increase but
temperature B will remain
constant.
Seeds in A are alive and some
energy released during respiration
is lost as heat. Dead seeds in B do
not respire; no heat is released.
Checkpoint 4:
Study the experiment testing respiration
and photosynthesis.
Answer the questions that follow.
Hydrogencarbonate solution
Results
Test tube
A
B
C
D
Content
Snail +
indicator
hydrilla
plant +
indicator
hydrilla
plant +
snail +
indicator
indicator
Initial colour of
hydrogencarbonate
solution
red
red
red
red
Final colour of
hydrogencarbonate
solution
yellow
purplish
red
light yellow
red
Purpose of rubber bung
To prevent carbon dioxide from the atmosphere
entering the test tube. Atmopheric carbon dioxide will
change the colour of the indicator from red to yellow.
To prevent loss of carbon dioxide from the set-up into
the atmosphere.
Conclusion
Test tube A:
Carbon dioxide given off during respiration dissolved in the
indicator and formed a weak acidic solution which turned the
indicator yellow.
Test tube B:
Rate of photosynthesis is higher than the rate of respiration.
Carbon dioxide was taken in by the plant resulting in a slightly
acidic to neutral solution turning the indicator yellowish red/
alkaline solution turning solution purplish red.
Conclusion
Test tube C:
Rate of respiration is higher than the rate of photosynthesis in
the hydrilla plant. Carbon dioxide was given out by both hydrilla
plant and snail resulting in a more acidic solution turning
indicator light yellow.
or
Test tube C:
Rate of photosynthesis is higher than respiration. CO2 given out
by both plant and snail is taken in by plant for photosynthesis,
less CO2→ less acidic, yellow.
Sources of experimental errors
▪
Rate of respiration / photosynthesis in the different
snails and hydrilla plants could be different, thus
affecting colour change of indicator.
▪
Light intensity reaching each container may not be
the same affecting the rate of photosynthesis for
container B and C thus affecting colour change.
Improving Accuracy
▪
Use different lamps with the same light intensity
for each container.
▪
Use parts of the same hydrilla plant in test tube B
and C; hydrilla plants should have same number of
leaves / of the same length.
▪
Use snails of the same size / age.
Extension
▪
Extension : Smoking and vaping
▪ Activity 3 in this SLS lesson:
https://vle.learning.moe.edu.sg/mrv/moelibrary/lesson/view/0c398f4b-712a-4f02-bb6b1dbde59dcfff/page/47227723
▪
Extension : Anaerobic respiration in yeast
▪
Extension : Let’s build a lung model
Extension: Let’s build your own lung model!
• Which part of the respiratory system does each part
of the model represent?
• Using the model, explain how you breathe.
• State two limitations of your model and how it does
not accurately represent the breathing mechanism.