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3.3.2 Gas exchange

AQA A-level Biology 3.3.2 practice on Gas exchange, with free MCQs, clues and worked explanations drawn from the Organisms exchange substances with their environment section of specification 7402.

Specification route
3.3.2
Question bank
22 questions
Course stage
AS / Year 12

Sample questions

QUESTION 1 · 3.3.2 · LEVEL 3

What structural and functional compromise must be balanced by both terrestrial insects and xerophytic plants?

  • The opposing needs for efficient gas exchange and the limitation of water loss.
  • The need for rapid heat loss versus the retention of carbon dioxide.
  • The need to absorb maximum sunlight versus the limitation of oxygen loss.
  • The need for active transport of gases versus the limitation of ATP usage.
Show clue

Opening pores to let gases in also lets a vital liquid evaporate out.

Show answer and explanation

Answer: The opposing needs for efficient gas exchange and the limitation of water loss.

Structural and functional compromises exist between the opposing needs for efficient gas exchange and the limitation of water loss shown by terrestrial insects and xerophytic plants. A misconception is that plants 'want' to lose water; it is an unavoidable consequence of opening stomata for $CO_{2}$.

QUESTION 2 · 3.3.2 · LEVEL 1

Which structure provides the primary surface for gas exchange in fish?

  • The gills
  • The tracheal system
  • The body surface
  • The alveoli
Show clue

These structures are highly adapted to extract dissolved oxygen from water.

Show answer and explanation

Answer: The gills

Adaptations of gas exchange surfaces are shown by gas exchange... across the gills of fish.

QUESTION 3 · 3.3.2 · LEVEL 1

What is the correct sequence of structures that air passes through during inspiration in the human respiratory system?

  • Trachea, bronchi, bronchioles, alveoli
  • Trachea, bronchioles, bronchi, alveoli
  • Bronchi, trachea, bronchioles, alveoli
  • Alveoli, bronchioles, bronchi, trachea
Show clue

Air travels from the largest singular tube down into increasingly smaller branching tubes.

Show answer and explanation

Answer: Trachea, bronchi, bronchioles, alveoli

The gross structure of the human gas exchange system is limited to the alveoli, bronchioles, bronchi, trachea and lungs. A frequent misconception is confusing the order of bronchi and bronchioles; bronchi are the larger branches.

QUESTION 4 · 3.3.2 · LEVEL 3

During human inspiration, how is a decrease in pressure brought about in the thoracic cavity?

  • The diaphragm contracts (flattens) and the external intercostal muscles contract.
  • The diaphragm relaxes (domes upwards) and the internal intercostal muscles contract.
  • Both the external and internal intercostal muscles contract simultaneously to expand the ribs.
  • The diaphragm actively pumps air into the lungs via muscular spasms.
Show clue

To decrease pressure, the volume of the chest cavity must increase.

Show answer and explanation

Answer: The diaphragm contracts (flattens) and the external intercostal muscles contract.

The mechanism of breathing includes the role of the diaphragm and the antagonistic interaction between the external and internal intercostal muscles in bringing about pressure changes in the thoracic cavity. A common misconception is that the diaphragm relaxes during inspiration; relaxation actually causes expiration by decreasing volume.

QUESTION 5 · 3.3.2 · LEVEL 2

Why is the alveolar epithelium an essential feature for efficient gas exchange?

  • It is extremely thin (one cell thick), providing a very short diffusion pathway for gases.
  • It is composed of thick, multi-layered muscle cells that actively pump oxygen into the blood.
  • It contains large carrier proteins that actively transport oxygen against its concentration gradient.
  • It is lined with ciliated cells that mechanically push oxygen molecules into the capillaries.
Show clue

Gas exchange relies entirely on simple diffusion.

Show answer and explanation

Answer: It is extremely thin (one cell thick), providing a very short diffusion pathway for gases.

The essential features of the alveolar epithelium act as a surface over which gas exchange takes place. Students often hold the misconception that lungs actively transport or pump oxygen into the blood; it occurs strictly via passive diffusion across a thin surface.

QUESTION 6 · 3.3.2 · LEVEL 2

Insects do not possess a circulatory system for transporting respiratory gases. How is oxygen delivered directly to their respiring tissues?

  • Through a highly branched tracheal system that terminates in thin-walled tracheoles.
  • Through a specialized fluid called haemolymph that mimics red blood cells.
  • By simple diffusion across their chitinous outer exoskeleton.
  • By active transport pumps located along their ventral nerve cord.
Show clue

Insects have a network of tubes piping air directly to cells.

Show answer and explanation

Answer: Through a highly branched tracheal system that terminates in thin-walled tracheoles.

Adaptations of gas exchange surfaces, shown by gas exchange... in the tracheal system of an insect. A common misconception is that insect 'blood' (haemolymph) carries oxygen; it does not.

QUESTION 7 · 3.3.2 · LEVEL 2

In dicotyledonous plants, which structural feature represents the primary adaptation for efficient gas exchange in the leaves?

  • The presence of many stomata and a spongy mesophyll layer with large air spaces.
  • A thick, waxy cuticle covering the upper epidermis to trap oxygen.
  • A highly developed phloem network that transports dissolved $CO_{2}$.
  • Xylem vessels that actively pump oxygen into the leaf cells.
Show clue

Gas exchange in leaves requires a short diffusion pathway and a large internal surface area.

Show answer and explanation

Answer: The presence of many stomata and a spongy mesophyll layer with large air spaces.

Adaptations of gas exchange surfaces are shown by gas exchange... by the leaves of dicotyledonous plants. The spongy mesophyll provides a large surface area, and stomata allow gases to diffuse directly into the leaf interior.

QUESTION 8 · 3.3.2 · LEVEL 3

Which of the following is an adaptation found in xerophytic plants to limit water loss while maintaining gas exchange?

  • Sunken stomata in pits to trap moist air and reduce the water potential gradient.
  • A vastly increased number of stomata on the upper epidermis.
  • The complete removal of the waxy cuticle to allow rapid diffusion.
  • Active transport of water vapour back into the leaf cells.
Show clue

Xerophytes live in dry conditions and must minimize transpiration.

Show answer and explanation

Answer: Sunken stomata in pits to trap moist air and reduce the water potential gradient.

Structural and functional compromises between the opposing needs for efficient gas exchange and the limitation of water loss are shown by... xerophytic plants. Sunken stomata trap water vapour, reducing the gradient for evaporation.

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