Gas Exchange in Humans (Cambridge (CIE) IGCSE Biology)
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Which process takes place at the alveoli?
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Which process takes place at the alveoli?
The process that takes place in the alveoli is gas exchange.
True or False?
Alveoli are surrounded by several layers of cells.
False.
Alveoli are surrounded by a single layer of cells to minimise diffusion distance.
What are the features of alveoli that make them an efficient exchange surface?
Alveoli are an efficient gas exchange surface because they have a:
large total surface area
short diffusion distance
steep concentration gradient, maintained by a good blood supply and good ventilation
How is a steep concentration gradient for both oxygen and carbon dioxide maintained in the alveoli?
A steep concentration gradient for both oxygen and carbon dioxide is maintained in the alveoli as follows:
good ventilation supplies oxygen to, and removes carbon dioxide from, the alveoli
A good blood supply means that the blood immediately next to each alveolus is always low in oxygen and high in carbon dioxide
Why is a large surface area important for gas exchange within the lungs?
A large surface area is important for gas exchange within the lungs because it allows for faster diffusion of oxygen and carbon dioxide across the alveoli walls.
What are the structures labelled A-D?
The structures are:
A = trachea
B = diaphragm
C = bronchiole
D = intercostal muscle
What is the function of the trachea?
The trachea, or windpipe, connects the nose and mouth to the lungs.
Describe the alveoli.
Alveoli are tiny air sacs surrounded by a network of capillaries, serving as the site of gas exchange between the air and the blood.
What is the role of the bronchi?
The bronchi (singular bronchus) branch off the trachea and carry air into the right and left lungs. They contain mucus to trap dust and pathogens.
True or False?
The diaphragm is located next to the larynx.
False.
The diaphragm is a sheet of connective tissue located beneath the lungs, while the larynx is the voice box, located at the top of the trachea.
What structures are shown in the image?
The structures shown in the image are:
alveoli
capillaries
the end of a bronchiole
What is inspired air?
Inspired air is air drawn into the body from the environment.
True or False?
Expired air is air breathed out from the body.
True.
Expired air is air breathed out from the body. Also known as exhaled air.
What is the role of limewater in an investigation into the composition of inspired and expired air?
Limewater will turn from colourless to milky/cloudy white in the presence of carbon dioxide, indicating whether CO2 is present in inspired or expired air.
What results would be expected in tube A and tube B in an investigation into inspired and expired air?
The following results would be expected in tubes A and B:
Limewater in tube A would remain clear as inspired air is drawn through its left-hand tube
Limewater in tube B would change to a cloudy white colour because expired air is breathed out into it via tube labelled 'breathe out'
How does the oxygen content of inspired and expired air differ?
Inspired air contains a higher oxygen concentration than expired air.
How does the carbon dioxide content of inspired and expired air differ?
Inspired air contains a lower carbon dioxide concentration than expired air.
True or False?
The water vapour concentration of inspired and expired air is the same.
False.
Inspired air contains a lower concentration of water vapour than expired air.
True or False?
Exercise causes breathing rate to increase.
True.
Exercise causes the rate (and depth) of breathing to increase to provide more oxygen for respiration.
How can a student's breathing rate at rest be calculated?
Breathing rate is measured in breaths per minute. To calculate a student's breathing rate at rest, either:
Count breaths over a minute
Count breaths for 30 seconds and multiply by 2
Count breaths for 15 seconds and multiple by 4
Repeat several times to obtain an average.
When investigating the effect of exercise on breathing rate, what is the purpose of repeating the investigation for each student several times?
When investigating the effect of exercise on breathing rate, repeating the investigation for each student allows several measurements to be taken. This allows any anomalies to be identified and left out when calculating a mean.
When investigating the effect of exercise on breathing rate, which variables should be kept constant?
Variables that should be kept the same when investigating the effect of exercise on breathing rate include:
the age and general fitness level of the students
students have all eaten similar meals at the same time prior to exercise
the type of exercise
the temperature of the room
When investigating the effect of exercise on breathing rate, how can consistency of exercise intensity be ensured for each repeat?
To replicate exercise intensity consistently, students should be given an exercise type where intensity can be measured, such as running at a set speed on a treadmill or cycling with a specific power output on a watt bike.
When investigating the effect of exercise on breathing rate, how can the effects of fatigue on results be limited?
When investigating the effect of exercise on breathing rate the effects of fatigue on results can be limited by ensuring that students take a period of rest in between each repeat.
True or False?
When investigating the effects of physical activity on the rate and depth of breathing, the breathing rate is the independent variable.
False.
When investigating the effects of physical activity on the rate and depth of breathing, the breathing rate is the dependent variable.
The independent variable in this instance is the exercise intensity.
Which sets of muscles are indicated by labels A and B? (Extended Tier Only)
The labels indicate:
A = external intercostal muscles
B = internal intercostal muscles
What is the function of cartilage in the trachea? (Extended Tier Only)
The function of the cartilage is to support the airways and keep them open during breathing.
Define the term ventilation. (Extended Tier Only)
Ventilation is the movement of air into and out of the lungs during breathing.
What is the role of the external intercostal muscles during ventilation? (Extended Tier Only)
The function of the external intercostal muscles is to pull the ribcage up. This occurs when the external intercostal muscles contract during inhalation.
True or False?
The diaphragm relaxes during inspiration. (Extended Tier Only)
False.
The diaphragm contracts during inspiration, pulling downwards to increase the volume of the thorax.
True or False?
During inspiration the volume of the chest cavity decreases. (Extended Tier Only)
False.
During inspiration the volume of the chest cavity increases.
What happens to the diaphragm during expiration? (Extended Tier Only)
During expiration the diaphragm relaxes and moves upwards into its domed shape, decreasing the volume of the chest cavity.
What happens to the pressure inside the chest cavity during expiration? (Extended Tier Only)
During expiration the pressure inside the chest cavity increases due to the decreased volume of the chest cavity. This causes air to be forced out of the lungs.
What is the role of the internal intercostal muscles in ventilation? (Extended Tier Only)
The function of the internal intercostal muscles is to pull the ribcage down. This occurs when the internal intercostal muscles contract during forced expiration.
Why is there a higher percentage of carbon dioxide in expired air compared to inspired air? (Extended Tier Only)
Carbon dioxide is produced within the body during aerobic respiration. This is breathed out as a waste gas so is present at a higher percentage in exhaled air compared to inhaled air.
Why is there a higher percentage of oxygen in inspired air compared to expired air? (Extended Tier Only)
There is a higher percentage of oxygen in inhaled air compared to exhaled air because oxygen is used within the body for aerobic respiration and so there is less oxygen in exhaled air.
Why is there a difference in water vapour concentration between inspired and expired air? (Extended Tier Only)
There is a higher concentration of water vapour in expired air than inspired air because it is produced as a product of respiration and excreted via the lungs.
True or False?
The increased blood carbon dioxide concentration that occurs during exercise is detected by the muscles. (Extended Tier Only)
False.
The increased blood carbon dioxide concentration that occurs during exercise is detected by the brain.
Why do rate and depth of breathing increase during exercise? (Extended Tier Only)
Rate and depth of breathing increase during exercise in response to an increase in blood carbon dioxide concentration. The increased breathing increases the removal of carbon dioxide from the blood.
In addition to this, increased breathing increases the supply of oxygen to respiring cells.
What causes an increase in carbon dioxide concentration in the blood during exercise? (Extended Tier Only)
An increase in carbon dioxide concentration in the blood during exercise is caused by increased aerobic respiration in the muscle cells which releases carbon dioxide as a waste product.
What is the role of goblet cells in the airways? (Extended Tier Only)
The role of goblet cells is to produce mucus in the airways.
True or False?
Mucus helps to trap pathogens and and particles in the airways. (Extended Tier Only)
True.
Mucus traps any pathogens and particles that enter the airways, reducing the risk of infection in the lungs.
What is the role of ciliated cells in the trachea? (Extended Tier Only)
The role of ciliated cells in the trachea is to beat the cilia on their surface and so push mucus out of the airways towards the nose and throat.
True or False?
Cilia are hairs within the nose and trachea. (Extended Tier Only)
False.
Cilia are hair-like projections found on the surface of ciliated cells which line the inside surface of the trachea.