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KS4 Biology
B5a / Side 1
The Human Breathing system
Breathing is caused by muscular movements where oxygen is taken into our bodies
and carbon dioxide is removed. Oxygen and carbon dioxide diffuses into and out of
the blood at the respiratory surfaces in the lungs, this is known as gaseous
exchange.
Note: Chemical reactions in all living cells in which food is broken down to release
energy using oxygen in the process is known as respiration, do not confuse this with
breathing!
The structure of the respiratory system
Air enters and leaves the body via the nose and mouth. It travels along a series of
tubes to get to the lungs. The lungs are situated in the thorax (chest cavity). They
are protected by the ribs and sternum (breastbone).
Using your textbook, label the structures in the diagram.
Sha Tin College
Science Department - June 17
KS4 Biology
B5a / Side 2
(1) Complete the missing parts of the table:
Name of structure
Features and function
Warms, moistens and filters inhaled air
Made of spongy tissue and is able to inflate and deflate
Intercostal muscles
Flap of cartilage prevents food from entering trachea
during swallowing.
Protects lungs and heart
Trachea
Secrets a fluid that prevents friction between lungs and
ribs during breathing
Lies in front of trachea, contains vocal cords
Bronchus
Bronchioles
Air sacs covered with blood capillaries, site of gas
exchange.
Muscle that separates the thorax and abdomen
(2) Why is the left lung smaller than that the right?
(3) Why are the trachea and bronchi made of cartilage rings? Suggest a reason why
the cartilage rings are C shaped in the trachea.
(4) The lungs are surrounded by an air tight pleural cavity, explain the function of
the pleural cavity.
(5) Write down the order at which air passes through the lungs, starting at the nose
and ending at the alveoli.
Sha Tin College
Science Department - June 17
KS4 Biology
B5a / Side 3
Looking at the lungs
Your teacher will show you a pair of lungs from
mammal.
(1) Describe the texture and the colour of the
lungs.
(2) How is the trachea kept open yet able to
bend?
(3) How does the texture and colour of the lungs vary when they are inflated?
(4) Do you have to squeeze the lungs to push the air out?
(5) What do the lungs look like across a cut edge? Draw a diagram of the cross
section below.
(6) What forces air in and out of your lungs as you breathe?
Sha Tin College
Science Department - June 17
KS4 Biology
B5b / Side 1
Gas exchange
Inhaled air contains more oxygen and les carbon dioxide than exhaled air. Oxygen in
inhaled air diffuses from the lungs into the blood stream while carbon dioxide
diffuses out of the bloodstream into the lungs to be exhaled. This opposite
movement of the lungs is known as gas exchange and it happens across the alveoli.
The alveoli are very well adapted (have special features) to make them more
efficient at gas exchange.
Cluster of alveoli
Section through alveolus to show gas exchange
Using the diagrams above answer the following questions.
(1) Describe what is happening at each of the labelled stages A-F
A
B
C
D
E
F
(2) What difference is there between the blood at A and F? Give an explanation for
this difference.
Sha Tin College
Science Department - June 17
KS4 Biology
B5b / Side 2
(3) Define the term diffusion
(4) Explain why oxygen diffuses out of the alveoli into the bloodstream
(5) Explain why carbon dioxide diffuses out of the bloodstream into the alveoli (use
the idea of concentration gradients).
(6) Alveoli show a number of features or adaptations that make them more efficient
for the process of gas exchange. For the features listed in the table below,
explain how they help gas exchange.
Feature
The alveoli are permeable to gases
Explanation
There are millions of alveoli
The alveoli are well supplied with
blood
The walls of the alveoli and the
surrounding capillaries are very thin
(one cell thick)
The alveoli are moist
(7) The alveoli in one lung would cover half a tennis court if they were all spread out.
Emphysema is a disease where the walls of the alveoli break down. Explain why
people with this disease suffer from breathlessness all the time.
Sha Tin College
Science Department - June 17
KS4 Biology
B5b / Side 3
The mechanism of breathing (ventilation)
Breathing in and out is known as inhalation and exhalation. Changes in the volume and
pressure of the thorax cause air to enter and leave the lungs. These changes are
brought about by two sets of muscle:


The diaphragm which is a domed shape sheet of muscle separating the thorax and
abdomen
Two sets of intercostal muscles (internal and external) which connect and move
the ribs
(1) Complete the following table to describe the changes that occur during
ventilation, use the diagrams above to help you.
Changes in:
Inhaling (in)
Exhaling (out)
Diaphragm
Intercostal muscles
Rib cage
Volume in thorax
Pressure in thorax
Movement of air
Lungs
Sha Tin College
Science Department - June 17
KS4 Biology
B5b / Side 4
(2)
The diagram above represents a model of the human thorax.
a) What parts of the human thorax do the labels A to F represents?
b) What happens to the rubber balloons when the sheet is pushed upwards?
What part of breathing does this represent?
c) What happens to the balloons when the rubber sheeting is pulled down?
What part of breathing does this represent?
d) In what way is this model an inaccurate demonstration of how we breathe in and
out?
Sha Tin College
Science Department - June 17
KS4 Biology
B5c / Side 1
How are our air passages kept clean?
The air passages of the respiratory system (trachea, bronchi and bronchioles) are all
lined with specialised epithelial tissue. Mucus secreting cells called goblet cells are
found here along with cilia small hair like projections from the cells. The slimy mucus
and the waving motion of the cilia are like an air conditioning system for the lungs.
(1) What is mucus and what job does it do for the respiratory system?
(2) Where in the respiratory system would you find mucus being secreted?
(3) Describe how mucus is removed from the respiratory system.
(4) Cystic fibrosis is an inherited disease. One symptom of the disease is the over
production of mucus by the epithelial tissue lining the respiratory tract. Explain
one way in which the large amounts of mucus will affect the breathing of cystic
fibrosis sufferers.
(5) Tar is a complex mixture of chemicals found in cigarette smoke that paralyses
cilia and stimulates goblet cells. What effects would this have on your breathing
and subsequently your health?
Breathing
Health
Sha Tin College
Science Department - June 17
KS4 Biology
B5d / Side 1
Smoking and the respiratory system
Smoking is the largest single preventable cause of death, killing more people than all
other avoidable dangers added together including fires, drugs, alcohol and road
accidents.
Statistic in Hong Kong
 Smoking kills 5,700 people per year.
 Smoking is estimated to kill 16 people in Hong Kong everyday. Of which lung
cancer claims the lives of nearly 8 victims a day.
 Smoking accounts for 90% of lung cancer deaths in men and more than 30% of all
cancer deaths.
 A study carried out in Hong Kong in 1999 found that at the age of 14, 12% of
boys and 10% of girls are daily smokers.
 80% of teenage smokers who smoke regularly will continue to do so in adult life.
Tobacco smoke is estimated to contain over four thousand chemicals, many of which
are highly toxic and carcinogenic (cancer causing agents).
The three main diseases closely linked with smoking are:
 Coronary heart disease
 Lung cancer
 Chronic bronchitis
Smoke machine
Your teacher will set up the following apparatus
Sha Tin College
Science Department - June 17
KS4 Biology
B5d / Side 2
(1) Label the diagram 1-3
(2) What difference did you notice in the colour of the cotton wool from A? What
substance found in cigarette smoke do you think caused this change?
(3) What does the colour of the indicator tell you about cigarette smoke? What
component of cigarette smoke caused this change?
(4) Explain the purpose of the set up with the unlit cigarette.
Nicotine, tar and carbon monoxide are the components of cigarette smoke that do
the most harm.
Find out the effects of these substances from textbooks or search the Internet
website of the Hong Kong council on smoking and health at www.info.gov.hk/hkcosh/
Complete the following table on the effects of cigarette smoke on they body.
Component of cigarette smoke
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Effects on health
Science Department - June 17
KS4 Biology
B5d / Side 3
Air pollution and the respiratory system
Air pollution as well as smoking can cause serious health problems. Research has
shown a strong connection between air pollution and diseases such as emphysema and
lung cancer. If a person’s lungs are perpetually irritated by air pollutants it will
cause inflammation of the bronchial airways leading to chronic bronchitis. These air
pollutants can also aggravate asthma, a condition where the muscles of the
bronchioles contract narrowing the airways that lead to the alveoli. Air pollution has
been linked to emphysema and lung cancer.
Hong Kong is a densely populated city and suffers from major pollution problems.
The air quality here is deteriorating fast. A major contributor to air pollution are
the congested roads. Vehicle emissions especially from diesel vehicles leads to the
problem of smog which decreases the visibility across many areas of Hong Kong.
Search on the following website: http://www.epd.gov.hk/epd/eindex.html (click
on Air icon on top, then the API & Air quality) for the answers to the questions
that follow below.
(1)
What are Hong Kong’s two main air pollution issues?
The local air pollution index is reported everyday as part of the weather forecast.
(2)
What does the air pollution index (API) tell us?
(3)
What type of air pollutants are indicated by the API that is present in the
air?
Sha Tin College
Science Department - June 17
KS4 Biology
B5d / Side 4
(4)
What is today’s API at Shatin?
(5)
Why would it be useful to know about the API? Which groups of people would
need to know about the API in particular?
(6)
What advice is given to people when the API is at very high or severe levels?
(7)
State the main sources and the health effects of the following air pollutants:
Sulphur dioxide
Nitrogen dioxide
Carbon monoxide
Sha Tin College
Science Department - June 17
KS4 Biology
B5e / Side 1
The composition of inhaled and exhaled air
Your teacher will set up the following apparatus:
1. Exhaled air is collected by breathing out into the tube fitted under the gas
cylinder until all the water has been displaced.
2. A burning candle is placed into two gas jars, one containing exhaled air and the
other atmospheric air.
3. Time how long it takes for the candle to burn in the exhaled air and normal
atmospheric air.
Sha Tin College
Science Department - June 17
KS4 Biology
B5e / Side 2
4. Complete the table below.
Time taken for combustion (sec)
Exhaled air
Atmospheric air
5. What is your explanation for the observation?
6. Find out the actual percentages of gases found in inhaled and exhaled air and the
reason for their differences. Complete the table below.
Gas
Oxygen
Inhaled air (%)
Exhaled air (%)
Reason for difference
Carbon dioxide
Nitrogen & inert
gases
7. Apart from the differences in the composition of gases what offer difference
would be present in exhaled air compared to inhaled air?
Sha Tin College
Science Department - June 17
KS4 Biology
B5e / Side 3
Extra questions
(1) Put these statements in the right order to describe how a human inhales.
a)
A The air pressure inside is lower than the air pressure outside.
B The ribs moves up and out and the diaphragm moves down.
C Air rushes in to equalize the two pressures.
D This increases the volume of the chest cavity, decreasing the air pressure
inside.
E The muscles between the ribs and in the diaphragm contract.
b) Use similar statements to describe how a human exhales.
2. Explain carefully why smokers often cough and why they often get infections of
the breathing system.
3. Bronchitis is an infection that affects the bronchial tubes, which lead to the
lungs.
What general pattern is shown by this information?
Sha Tin College
Science Department - June 17
KS4 Biology
B5e / Side 4
The diagram show the effects of cigarette smoke on small hairs called cilia in the
bronchial tubes.
a) What effect does cigarette smoke have on the movement of mucus?
b) Suggest why smokers tend to cough more than non-smokers do.
c) Smokers are sometimes short of breath. Suggest how smoking affects lungs to
cause this.
4. The diagrams below show microscopic sections of A healthy and B diseased lung
tissue from adult humans.
a) Give two structural differences between the healthy and the diseased lung, which
can be seen on the diagrams.
b) Suggest for each difference you have described why it would make the diseased
lung work less well.
Sha Tin College
Science Department - June 17