Gas Exchange (Edexcel IGCSE Science (Double Award): Biology): Flashcards
Exam code: 4SD0
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Define thorax.
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Define thorax.
The chest cavity in humans, which contains the respiratory system.
Name the structures found in the thorax.
Ribs
Intercostal muscles
Diaphragm
Trachea
Lungs, containing the bronchi, bronchioles and alveoli
Pleural membranes
Give the order air passes through on the way to the alveoli.
Trachea ➔ bronchus ➔ bronchiole ➔ alveolus
What is the function of the ribs?
A bone structure that protects the internal organs, such as the lungs.
What is the function of the intercostal muscles?
They lie between the ribs and control their movement, causing inhalation and exhalation.
What is the function of the diaphragm?
A sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation.
What is the function of the trachea?
The windpipe, which connects the mouth and nose to the lungs.
What are the bronchi?
The large tubes branching off the trachea that connect to the bronchioles.
Human lungs contain two — one bronchus each.
What are the bronchioles?
The smaller tubes that connect the bronchi to the alveoli.
What are the alveoli?
Tiny, balloon-like air sacs at the ends of the bronchioles.
They are the specialised gas exchange surfaces, where oxygen diffuses into the blood and carbon dioxide diffuses out.
What are the pleural membranes?
Thin layers of tissue that surround the lungs and line the inside of the thorax.
Name four adaptations of the human respiratory system.
A large surface area, provided by many alveoli
Alveolus and capillary walls that are one cell thick
Good ventilation with air
A good blood supply
The last three all help maintain a high concentration gradient.
The windpipe that connects the mouth and nose to the lungs is the ＿＿＿＿＿＿＿＿.
The windpipe that connects the mouth and nose to the lungs is the trachea.
Gas exchange takes place in the ＿＿＿＿＿＿＿＿ at the ends of the bronchioles.
Gas exchange takes place in the alveoli at the ends of the bronchioles.
True or False?
Air passes through the bronchioles before the bronchi.
False.
Air passes through the trachea, then the bronchi, and only then the bronchioles.
True or False?
A good blood supply maintains a high concentration gradient.
True.
It carries blood with a high concentration of oxygen away from the alveoli, keeping the gradient steep for diffusion.
Why are there two sets of intercostal muscles?
Because muscles can only pull on bones, never push.
The external and internal intercostal muscles therefore work antagonistically.
What do the external intercostal muscles do?
They contract to pull the rib cage up during inhalation.
What do the internal intercostal muscles do?
They contract to pull the rib cage down during forced exhalation.
Where is the diaphragm and what is it?
A thin sheet of muscle that separates the chest cavity from the abdomen.
Describe what happens during inhalation.
The diaphragm contracts and flattens.
The external intercostal muscles contract, pulling the ribs up and out.
The volume of the thorax increases, so the air pressure inside the lungs decreases relative to outside.
Air is drawn in.
Describe what happens during normal exhalation.
The diaphragm relaxes and moves upwards into its domed shape.
The external intercostal muscles relax, so the ribs drop down and inwards.
The volume of the thorax decreases, so the air pressure inside the lungs increases relative to outside.
Air is forced out.
What is forced exhalation?
When the internal intercostal muscles also contract to pull the ribs down and in, decreasing the thorax volume further and forcing air out more quickly.
When is forced exhalation needed, and why?
During strenuous activity, when there is a greater need to remove the increased carbon dioxide produced.
It allows a greater volume of gases to be exchanged.
What happens to the pressure in the lungs as their volume increases?
The pressure decreases relative to outside the body, so air is drawn in.
During inhalation the diaphragm contracts and ＿＿＿＿＿＿＿＿.
During inhalation the diaphragm contracts and flattens.
During normal exhalation the diaphragm relaxes and returns to its ＿＿＿＿＿＿＿＿ shape.
During normal exhalation the diaphragm relaxes and returns to its domed shape.
True or False?
The internal intercostal muscles are used during normal exhalation.
False.
Normal exhalation only needs the external intercostal muscles to relax. The internal ones contract during forced exhalation.
True or False?
Inspiration and inhalation mean the same thing.
True.
Inhalation / inspiration both mean breathing in, and exhalation / expiration both mean breathing out.
Name five adaptations of the alveoli for gas exchange.
Many rounded alveolar sacs, giving a very large surface area to volume ratio
Thin, single layers of cells in the alveoli and capillaries
Ventilation, maintaining a steep concentration gradient
A good blood supply
A layer of moisture on the alveolar surface
Why do the many rounded alveolar sacs help gas exchange?
They give a very large surface area to volume ratio, so more gas can diffuse at the same time.
Why are the walls of the alveoli and capillaries so thin?
They are single layers of cells, which minimises the diffusion distance for the gases.
How does ventilation maintain a steep concentration gradient?
It keeps oxygen levels high and carbon dioxide levels low in the alveolar air space.
How does a good blood supply maintain the concentration gradient?
It ensures a constant supply of blood that is high in carbon dioxide and low in oxygen, keeping the gradient steep in both directions.
Why is the layer of moisture on the alveoli important?
The gases can dissolve in it, which helps them diffuse.
In which direction does each gas diffuse at an alveolus?
Oxygen diffuses from the alveolar air into the blood
Carbon dioxide diffuses from the blood into the alveolar air
The walls of the alveoli and their capillaries are only ＿＿＿＿＿＿＿＿ cell thick.
The walls of the alveoli and their capillaries are only one cell thick.
A layer of ＿＿＿＿＿＿＿＿ on the alveolar surface lets the gases dissolve.
A layer of moisture on the alveolar surface lets the gases dissolve.
True or False?
Blood arriving at the alveoli is high in oxygen.
False.
Blood arriving at the alveoli is low in oxygen and high in carbon dioxide — which is what maintains the concentration gradients for diffusion.
True or False?
Gas exchange at the alveoli happens by diffusion.
True.
Every alveolar adaptation exists to make diffusion between the air in the lungs and the blood in the capillaries as fast as possible.
Why does a large surface area speed up gas exchange?
More particles can diffuse across the surface at the same time, so the overall rate of exchange is higher.
How does nicotine affect the circulatory system?
It narrows blood vessels and increases heart rate, raising blood pressure.
High blood pressure can cause blood clots in the arteries, leading to a heart attack or stroke.
How does carbon monoxide reduce oxygen transport?
It binds irreversibly to haemoglobin, reducing the oxygen-carrying capacity of the blood.
Why does carbon monoxide strain the breathing system?
Breathing frequency and depth must increase to supply the same amount of oxygen, because less can be carried by the blood.
How does carbon monoxide increase the risk of heart disease?
The circulatory system must pump blood faster, which raises blood pressure and increases the risk of coronary heart disease and stroke.
Why is tar in cigarettes dangerous?
Tar is a carcinogen, linked to an increased chance of cancerous cells developing in the lungs.
It also contributes to COPD.
Define carcinogen.
A substance, such as the tar in cigarettes, that increases the chance of cancerous cells developing.
Which two conditions occurring together make up COPD?
Chronic bronchitis
Emphysema
How does tar cause chronic bronchitis?
It stimulates goblet cells and mucus glands to enlarge and produce more mucus.
Mucus builds up, blocking the smallest bronchioles and leading to infections.
Why can smokers not clear the mucus from their airways?
The build-up of mucus damages the cilia, so they cannot beat to move mucus up and out of the lungs.
A smoker's cough is the attempt to move it instead.
How does emphysema develop?
Repeated infections and inflammation damage the walls of the alveoli, so many of them break down and burst.
This reduces the surface area available for gas exchange.
What are the symptoms of emphysema?
Patients become breathless and wheezy, and may need a constant supply of oxygen to stay alive.
Why do smokers get lung infections more often?
Because of the build-up of mucus in the lungs, which the damaged cilia cannot remove.
Carbon monoxide binds irreversibly to ＿＿＿＿＿＿＿＿, reducing the oxygen-carrying capacity of the blood.
Carbon monoxide binds irreversibly to haemoglobin, reducing the oxygen-carrying capacity of the blood.
Tar damages the ＿＿＿＿＿＿＿＿ lining the airways, so mucus can no longer be swept out of the lungs.
Tar damages the cilia lining the airways, so mucus can no longer be swept out of the lungs.
True or False?
Emphysema increases the surface area available for gas exchange.
False.
The alveoli burst, which reduces the surface area for gas exchange.
True or False?
Smoking is a risk factor for coronary heart disease.
True.
Both nicotine and carbon monoxide raise blood pressure, increasing the risk of coronary heart disease and stroke.
Outline the method for investigating exercise and breathing rate.
Each participant sits quietly for 1 minute and counts their breaths.
Each then performs the same exercise, such as running on the spot for 1 minute.
Immediately after exercise, count the breaths taken in 1 minute again.
Calculate the change in breathing rate, then repeat and find mean values.
What counts as one breath when measuring breathing rate?
One inhale plus one exhale.
How is the change in breathing rate calculated?
breathing rate after exercise − breathing rate at rest
What effect does exercise have on breathing?
It increases both the frequency and the depth of breathing.
Why is an increased breathing rate useful during exercise?
It allows more oxygen to be taken in and carbon dioxide to be removed more quickly.
Which variables should be kept the same in this investigation?
Type and duration of exercise
Environment, including temperature
Rest period before measuring
Time of day
Method of counting breaths
Why is varying exercise intensity a limitation?
Participants may work harder or less hard depending on motivation or ability.
Using a controlled exercise, such as step-ups at a set pace or cycling at a fixed power output, improves consistency.
Why is breathing rate difficult to measure accurately?
It changes quickly after exercise, and timing or counting errors reduce reliability.
An improvement is to start counting immediately and measure a short fixed period, such as 15 seconds, then multiply up.
Which external conditions can affect breathing rate?
Temperature, air quality and stress levels.
Running the investigation indoors in similar conditions for everyone reduces their effect.
Why is it hard to control variables between participants?
Their fitness, lifestyle and any health conditions all differ and cannot easily be matched.
Exercise increases both the frequency and the ＿＿＿＿＿＿＿＿ of breathing.
Exercise increases both the frequency and the depth of breathing.
Repeating the measurement with several participants allows a ＿＿＿＿＿＿＿＿ to be calculated.
Repeating the measurement with several participants allows a mean to be calculated.
True or False?
Breathing rate should be measured immediately after exercise ends.
True.
Breathing rate falls quickly once exercise stops, so any delay would underestimate the effect.
True or False?
A single participant is enough for a reliable conclusion.
False.
Several participants are needed so that a mean can be calculated and individual differences do not distort the result.
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