The alveoli are the site of gas exchange in the lungs. 

Describe the pathway taken by a molecule of oxygen from an alveolus to the blood.

A large number of small alveoli allow for efficient gas exchange.

Explain why. 

Explain how one feature of a single alveolus allows efficient gas exchange to take place. 

Smoking can damage and eventually cause the death of alveolar epithelium cells.

When these cells die, they are replaced by non-specialised and thickened tissue.

Explain why damage to alveolar epithelium cells reduces gas exchange in the lungs.  

The diagram below shows the structure of the human gas exchange system. 

Name the parts labelled A, B, and C in the diagram above. 

An oxygen concentration gradient is maintained between the alveoli and the lung capillaries.

Describe how ventilation helps to maintain this concentration gradient. 

Other than ventilation, give one other way in which the concentration gradient between the alveoli and the capillaries is maintained. 

The composition of gases within inhaled and exhaled air are different.

Describe how these compositions are different and explain why. 

The diagram below shows a jumping worm. 

Name the process by which oxygen reaches the cells inside the body of the jumping worm.

Using the diagram above, explain how two features of the jumping worm allow for efficient gas exchange.

Jumping worms reproduce by laying eggs. Multiple eggs are encased within a spherical structure known as a cocoon.

A scientist calculated the surface area of several cocoons. The mean surface area of a cocoon was 24.62 mm².

The surface area of a sphere can be calculated using the equation below. 

Surface area = 4πr², where r is the radius of the sphere and π = 3.14.

Use this equation to calculate the mean diameter of a cocoon. Give your answer to 1 decimal place. 

Larger organisms, such as humans, need specialised systems that allow the uptake of oxygen.

Explain why. 

Many organisms, including insects, have evolved specialised exchange surfaces. 

Name the structure through which gases enter and leave an insect’s body. 

Name the small tubes that carry gases to and from an insect’s cells. 

Describe how the structure of the insect gas exchange system provides a large surface area.

Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.

When first hatched, the offspring of some species of fish are less than 3 mm in length.

Explain how oxygen can reach the cells of young fish without gills. 

Adult fish use gills for exchange of gases. 

Explain two ways in which the structure of gills allows for efficient gas exchange. 

The gas exchange system within fish uses a counter-current system. 

Describe and explain the advantage of this system in gas exchange across the gills. 

Proliferative gill disease (PGD) is caused by a myxozoan parasite that affects the gills of various fish species.

The disease results in the enlargement and inflammation of gill tissues.

Give two reasons why PGD reduces the efficiency of gas exchange in fish.  

The health of the lungs can be measured by calculating a quantity known as the FEV₁ : FVC ratio. 

FEV₁ is the maximum volume of air exhaled in one second. 

FVC is the maximum volume of air exhaled in one breath. 

The graph below shows the volume of air exhaled in one breath by two individuals, A and B. 

Use the graph above to calculate the FEV₁ : FVC ratio of individual A. 

Individual B has emphysema.

An individual with emphysema has a reduced tidal volume compared to that of a healthy person.

Tidal volume is the volume of air inhaled and exhaled in a single breath when the individual is resting.

Suggest and explain how emphysema affects the exchange of oxygen between the alveoli and the blood.

The intercostal muscles are involved in the process of inhalation.

Explain how. 

Describe how oxygen from the air reaches the capillaries surrounding the alveoli in the lungs. 

 The gas exchange system in mammals contains various tissues including cartilage and elastic tissue. 

Complete the table by placing a tick in the box if the feature is present and a cross if the feature is absent within each part of the gas exchange system. 

Describe the role of cartilage in the gas exchange system.

Describe the role of elastic fibres in the gas exchange system.

The diagram below shows a single-celled organism known as an amoeba.

Explain why a single-celled organism does not need a specialised surface for gas exchange. 

Mammals have lungs containing tissues that are adapted to enable efficient exchange of gases.

Explain how the squamous epithelium tissue improves the efficiency of gas exchange.

The human gas exchange system contains many specialised cells.

Describe the function of the following two specialised cells in the gas exchange system.

i) goblet cells

ii) ciliated cells 

Smaller organisms do not need specialised gas exchange systems whereas larger organisms do.

Explain why size of an organism determines whether it needs a gas exchange system.

Many mammals, including humans, have specialised gas exchange systems. 

Describe the structure of the human gas exchange system.

Explain how the human gas exchange system allows us to breathe in and out. 

The graph below shows the changes in the volume of air in an individual’s lungs. 

Explain how the graph shows that the individual is breathing. 

Describe how the shape of the diaphragm causes the volume of air in the lungs to increase. 

Some insects use a process known as abdominal pumping to force air in and out of the spiracles.

The table below shows the average rate of abdominal pumping for an insect at rest and an insect during flight. 

Calculate the percentage increase in the rate of abdominal pumping during flight compared to at rest. 

Explain the movement of oxygen into an insect’s cells when it is at rest. 

Insects open their spiracles less frequently in dry conditions.

Suggest an advantage of this behaviour. 

Fish use gills to obtain oxygen from surrounding water.

Explain how gills are adapted for efficient gas exchange.

The human gas exchange system is made up of many structures through which oxygen must pass through to reach the blood. 

List the main structures of the gas exchange system through which oxygen passes to reach the alveoli.

Start with the larynx. 

The smallest bronchioles closest to the alveoli are known as respiratory bronchioles.

Suggest and explain why bronchioles do not contain any goblet cells. 

The gas exchange system contains different types of tissues.

Name the two types of epithelial tissue found in the airways.