3.3.2 Gas exchange exam questions

Question 1

Explain the role of the diaphragm in breathing out. (3 marks)

Answer 1

Diaphragm moves up/becomes dome-shaped.
Reduces thoracic volume/increases pressure.
Air forced out due to pressure gradient.

Question 2

Name the structure through which gases enter and leave the body of an insect. (1 mark)

Answer 2

Spiracles.

Question 3

Explain how oxygen moves into an insect’s gas exchange system when it is at rest. (3 marks)

Answer 3

Oxygen is used in respiration.
Creates a concentration gradient.
Oxygen diffuses in down this gradient.

Question 4

Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange. (3 marks)

Answer 4

Thin walls of tracheoles for short diffusion distance.
Highly branched system increases surface area.
Air-filled tubes allow rapid diffusion.

Question 5

Explain how the counter-current mechanism in fish gills ensures maximum oxygen transfer. (3 marks)

Answer 5

Blood and water flow in opposite directions.
Maintains concentration gradient across the gill.
Ensures maximum diffusion of oxygen into the blood.

Question 6

Describe and explain two features of fish gills that make them efficient for gas exchange. (2 marks)

Answer 6

Large surface area due to many filaments and lamellae.
Thin epithelium reduces diffusion distance.

Question 7

Describe the pathway taken by an oxygen molecule from an alveolus to the blood. (2 marks)

Answer 7

Oxygen diffuses across alveolar epithelium.
Passes through capillary endothelium into the blood.

Question 8

Describe the mechanism of breathing in and out. (5 marks)

Answer 8

Inspiration:
External intercostal muscles contract; ribs move up/out.
Diaphragm contracts, increasing thoracic volume.
Air drawn in due to pressure decrease in thorax.

Expiration:
Internal intercostal muscles contract.
Thoracic volume decreases; pressure increases.
Air forced out.

Question 9

Forced Expiratory Volume (FEV1) is a measure of lung function. Explain how a low FEV1 value could cause difficulty walking upstairs for someone with emphysema. (3 marks)

Answer 9

Less oxygen reaches muscles due to decreased gas exchange.
Reduced elasticity leads to trapped air, less efficient breathing.
Reduced FEV1 limits aerobic respiration.

Question 10

Describe how oxygen in the air reaches capillaries surrounding the alveoli. (4 marks)

Answer 10

Air enters trachea, then bronchi, and bronchioles.
Reaches alveoli where oxygen diffuses into capillaries.
Thin alveolar walls and extensive capillaries ensure diffusion.

Question 11

Explain why the death of alveolar epithelium cells reduces gas exchange. (3 marks)

Answer 11

Reduces surface area for diffusion.
Increases diffusion distance.
Thickened tissue reduces gas permeability.

Question 12

Explain the advantage for larger animals of having a specialized system for gas exchange. (2 marks)

Answer 12

Larger animals have a smaller surface area-to-volume ratio.
Specialized system ensures efficient oxygen delivery over long diffusion pathways.

Question 13

How does the structure of a damselfly larva’s gills adapt it to hunting prey? (2 marks)

Answer 13

Large surface area allows efficient oxygen uptake.
Supports active lifestyle requiring high metabolic rate.

Question 14

Explain how gas exchange occurs in single-celled organisms and why this method cannot be used by large, multicellular organisms. (3 marks)

Answer 14

Gas exchange occurs by diffusion across the cell membrane.
Single-celled organisms have a large surface area-to-volume ratio.
Multicellular organisms have longer diffusion pathways and higher demands for oxygen.

Question 15

Explain why plants grown in dry soil grow slowly. (2 marks)

Answer 15

Stomata close to reduce water loss, limiting carbon dioxide uptake.
Reduced photosynthesis limits glucose production for growth.

Question 16

Suggest and explain two xerophytic adaptations of plants to reduce water loss. (2 marks)

Answer 16

Thick waxy cuticle reduces water evaporation.
Sunken stomata trap water vapor, reducing diffusion gradient for water loss.

Question 17

Describe how stomata contribute to gas exchange in plants. (3 marks)

Answer 17

Stomata open to allow carbon dioxide in for photosynthesis.
Oxygen diffuses out as a by-product of photosynthesis.
Guard cells regulate opening to balance gas exchange and water loss.

Question 18

Explain how a tubifex worm survives in oxygen-poor water. (2 marks)

Answer 18

Hemoglobin in tubifex worms has a high affinity for oxygen.
Allows efficient oxygen uptake even at low partial pressures.

Question 19

Describe and explain why tubifex worms cannot survive in seawater. (2 marks)

Answer 19

Water potential in seawater is lower than in the worm.
Water leaves the worm by osmosis, causing dehydration.

Question 20

Describe two features of efficient gas exchange surfaces and explain their importance. (2 marks)

Answer 20

Large surface area: Increases the area available for diffusion, enabling more gases to exchange at a faster rate.
Thin exchange surface: Reduces diffusion distance, so gases can move quickly between cells and their environment.

Question 21

Explain how the counter-current mechanism in fish gills maximizes oxygen uptake. (3 marks)

Answer 21

Blood and water flow in opposite directions across the gill lamellae.
Maintains a concentration gradient along the entire length of the lamella.
Oxygen continues to diffuse from water (high concentration) into blood (low concentration).

Question 22

Describe how xerophytic plants reduce water loss while maintaining gas exchange. (4 marks)

Answer 22

Sunken stomata: Trap moist air, reducing the water potential gradient for evaporation.
Thick waxy cuticle: Reduces water loss through transpiration.
Rolled leaves: Protect stomata and trap humid air.
Fewer stomata: Limits the points where water can evaporate.

Question 23

Describe how oxygen in the air reaches capillaries surrounding the alveoli in the human lungs. (4 marks)

Answer 23

Air enters through the trachea, bronchi, and bronchioles.
Reaches the alveoli, where gas exchange occurs.
Oxygen diffuses across the thin alveolar epithelium and capillary endothelium.
Enters the blood and binds to hemoglobin in red blood cells.

Question 24

Explain why single-celled organisms do not need a specialized gas exchange system. (2 marks)

Answer 24

They have a large surface area-to-volume ratio.
Diffusion alone is sufficient as all parts of the cell are close to the external environment.

Question 25

Explain how spiracles and tracheoles in insects are adapted to minimize water loss while allowing gas exchange. (3 marks)

Answer 25

Spiracles can open and close to control water loss.
Tracheoles have thin walls to reduce diffusion distance for gases.
Air sacs store air for use during activity, reducing reliance on open spiracles.

Question 26

Why do larger organisms need a specialized gas exchange system? (2 marks)

Answer 26

They have a smaller surface area-to-volume ratio.
Diffusion is too slow over longer distances to meet metabolic demands.

Question 27

Forced expiratory volume (FEV1) is reduced in people with emphysema. Explain why this happens. (3 marks)

Answer 27

Alveolar walls break down, reducing surface area for gas exchange.
Loss of elasticity in alveoli prevents efficient exhalation.
Trapped air decreases the efficiency of ventilation.

Question 28

How does the structure of gills in fish ensure efficient gas exchange? (4 marks)

Answer 28

Large surface area: Many filaments and lamellae.
Short diffusion distance: Thin epithelium of lamellae.
Counter-current flow: Maintains a concentration gradient along the gill.
Ventilation system: Continuously supplies water over the gills.

Question 29

Explain why the presence of hemoglobin with a high oxygen affinity helps organisms like Tubifex worms survive in low-oxygen environments. (2 marks)

Answer 29

Hemoglobin can bind to oxygen even at low partial pressures.
Maximizes oxygen uptake for respiration in oxygen-poor water.

Question 30

Describe the adaptations of alveoli in the human lungs for efficient gas exchange. (3 marks)

Answer 30

Large surface area provided by millions of alveoli.
Thin walls (one cell thick) for a short diffusion pathway.
Surrounded by capillaries to maintain a steep concentration gradient.

Question 31

Compare and contrast gas exchange in fish and insects. (6 marks)

Answer 31

Both systems have adaptations to maintain a concentration gradient (e.g., ventilation in fish, body movements in insects).
Both rely on diffusion of oxygen into tissues.
Large surface area (lamellae in fish gills, extensive tracheal system in insects).
Differences:
Fish use gills and a counter-current mechanism, while insects use a tracheal system.
Fish rely on water as the medium for oxygen, while insects rely on air.
In fish, oxygen is transported in blood; in insects, oxygen is directly delivered to tissues through tracheoles.

Question 32

Describe the role of guard cells in regulating gas exchange in plants. (3 marks)

Answer 32

Guard cells control the opening and closing of stomata.
When turgid, guard cells open the stomata to allow gas exchange.
When flaccid, guard cells close the stomata to reduce water loss.

Question 33

Explain how changes in thoracic pressure result in inhalation. (3 marks)

Answer 33

Diaphragm contracts and moves downward.
External intercostal muscles contract, lifting the ribcage.
Thoracic volume increases, causing pressure to decrease below atmospheric pressure, and air is drawn into the lungs.

Question 34

Why do plants close their stomata at night? (2 marks)

Answer 34

Photosynthesis does not occur at night, so carbon dioxide is not needed.
Closing stomata prevents unnecessary water loss.

Question 35

Why is a large surface area important for gas exchange? (2 marks)

Answer 35

Increases the area available for diffusion.
Enables more oxygen and carbon dioxide to exchange quickly.

Question 36

Explain why a steep concentration gradient is essential for gas exchange. (3 marks)

Answer 36

Ensures gases diffuse quickly across the exchange surface.
Oxygen moves into tissues (higher to lower concentration).
Carbon dioxide moves out of tissues, maintaining efficient gas exchange.

Question 37

Describe how abdominal pumping in insects aids gas exchange during activity. (3 marks)

Answer 37

Abdominal muscles contract, reducing the volume of the tracheal tubes.
This increases air pressure inside, pushing air out.
Relaxation allows air to flow back in, maintaining a concentration gradient for oxygen.

Question 38

How do the tracheoles in insects ensure efficient oxygen delivery to cells? (2 marks)

Answer 38

Tracheoles have thin walls, shortening the diffusion pathway.
Their branching ensures oxygen reaches all cells directly.

Question 39

Why is it important for water to flow continuously over fish gills? (2 marks)

Answer 39

Maintains a concentration gradient for oxygen to diffuse into the blood.
Prevents stagnation, ensuring fresh, oxygenated water is always available.

Question 40

Explain why fish gills are less efficient in air than in water. (3 marks)

Answer 40

Gills rely on water to support their structure; in air, they collapse, reducing surface area.
Air has a lower density, making counter-current flow less effective.
Evaporation in air can dry out the gill surface, hindering gas exchange.

Question 41

Explain the difference between inspiration and expiration in terms of muscle activity and pressure changes. (4 marks)

Answer 41

Inspiration:
Diaphragm contracts and flattens; external intercostal muscles contract, lifting the ribcage.
Thoracic volume increases, causing pressure to decrease below atmospheric pressure, and air is drawn in.
Expiration:
Diaphragm relaxes and returns to a dome shape; internal intercostal muscles contract during forced expiration.
Thoracic volume decreases, increasing pressure, forcing air out.

Question 42

How does smoking damage the lungs and reduce gas exchange efficiency? (4 marks)

Answer 42

Tar damages alveoli, reducing their surface area.
Irritation causes inflammation, narrowing the airways.
Mucus production increases, obstructing airflow.
Cilia are damaged, reducing their ability to clear mucus.

Question 43

Describe how the spongy mesophyll layer in leaves contributes to gas exchange. (3 marks)

Answer 43

Contains air spaces that allow gases to diffuse freely within the leaf.
Provides a large surface area for gas exchange.
Facilitates movement of oxygen and carbon dioxide between stomata and photosynthetic cells.

Question 44

Explain how xerophytes are adapted to reduce water loss while maintaining gas exchange. (5 marks)

Answer 44

Thick waxy cuticle reduces evaporation.
Sunken stomata trap humid air, reducing water potential gradient.
Rolled leaves protect stomata from dry air.
Hairs on leaves trap moisture, lowering water loss.
Fewer stomata reduce the points of water evaporation.

Question 45

Why can single-celled organisms rely on diffusion alone for gas exchange? (2 marks)

Answer 45

They have a large surface area-to-volume ratio.
Short diffusion distance ensures efficient gas exchange.

Question 46

Compare and contrast the gas exchange mechanisms of humans and plants. (6 marks)
Similarities:

Answer 46

Similarities:
Both have large surface areas for gas exchange (alveoli in humans, mesophyll in plants).
Both rely on diffusion.
Both maintain a concentration gradient (ventilation in humans; stomatal opening in plants).

Differences:
Humans actively ventilate lungs, while plants rely on passive diffusion.
Gas exchange in humans occurs continuously; in plants, it’s dependent on light availability.
Humans use hemoglobin for oxygen transport, while plants transport gases directly.

Question 47

A student investigates how temperature affects the rate of oxygen uptake in an insect. Design an experiment to test this, including control variables. (6 marks)

Answer 47

Method:
Place an insect in a sealed respirometer.
Use soda lime to absorb CO₂.
Measure the movement of a liquid marker as oxygen is consumed.
Repeat at different temperatures (e.g., 10°C, 20°C, 30°C).
Control variables:

Use the same species and size of insect.
Keep the volume of the respirometer constant.
Ensure constant light and humidity.
Analysis:

Calculate the rate of oxygen uptake at each temperature.
Compare results to identify trends.

Question 48

Explain the role of the counter-current mechanism in fish gills and how it differs from concurrent flow. (4 marks)
Counter-current:

Answer 48

Counter-current:
Blood and water flow in opposite directions.
Maintains a concentration gradient along the entire length of the gill lamella.

Concurrent flow (inefficient):
Blood and water flow in the same direction.
Gradient is lost halfway, limiting oxygen diffusion.

Question 49

What is emphysema, and how does it affect gas exchange? (3 marks)

Answer 49

Emphysema is a lung disease caused by the destruction of alveolar walls.
It reduces the surface area available for gas exchange.
Leads to reduced oxygen uptake and carbon dioxide removal.

Question 50

Define Forced Expiratory Volume (FEV1) and explain what it measures. (2 marks)

Answer 50

FEV1 is the volume of air a person can forcefully exhale in one second.
It measures lung function and airway obstruction.

Question 51

Describe the role of alveoli in gas exchange and how they are affected by lung diseases like emphysema. (3 marks)

Answer 51

Alveoli provide a large surface area for gas exchange.
Thin walls allow rapid diffusion of oxygen and carbon dioxide.
In emphysema, alveolar walls break down, reducing surface area and diffusion efficiency.

Question 52

What is fibrosis, and how does it impact lung function? (2 marks)

Answer 52

Fibrosis involves thickening and scarring of lung tissue.
It reduces lung elasticity and increases diffusion distance, impairing gas exchange.

Question 53

Smoking can cause chronic obstructive pulmonary disease (COPD). Explain two ways smoking damages the lungs. (4 marks)

Answer 53

Tar in cigarette smoke damages cilia, reducing their ability to remove mucus.
Smoking causes inflammation and excess mucus production, narrowing airways.

Question 54

Explain how the loss of elasticity in lung tissue can lead to difficulty in exhalation. (2 marks)

Answer 54

Loss of elasticity prevents alveoli from recoiling after inhalation.
Air becomes trapped in the lungs, reducing the efficiency of exhalation.

Question 55

Describe how tuberculosis (TB) reduces lung capacity and affects gas exchange. (4 marks)

Answer 55

TB forms scar tissue in the lungs, reducing elasticity.
Damages alveolar walls, decreasing surface area for gas exchange.
Increases diffusion distance, slowing oxygen uptake.
Reduces lung volume, lowering the amount of air that can be inhaled.

Question 56

Explain why people with asthma often have a reduced Forced Vital Capacity (FVC). (3 marks)

Answer 56

During an asthma attack, bronchioles constrict.
Excess mucus further narrows airways.
Reduces the volume of air that can be forcefully exhaled.

Question 57

A graph shows the FEV1 of smokers and non-smokers over 10 years. Explain the trend you would expect to see in the FEV1 of smokers compared to non-smokers. (3 marks)

Answer 57

FEV1 in smokers would decrease faster than in non-smokers.
Smoking damages lung tissue and reduces elasticity, leading to airway obstruction.
Non-smokers would show a slower decline due to natural ageing.

Question 58

The graph below shows the oxygen dissociation curves for a healthy person and a person with emphysema. Explain how emphysema affects oxygen transport in the blood. (4 marks)
Answer:

Answer 58

Emphysema reduces oxygen uptake due to decreased alveolar surface area.
Blood has a lower oxygen saturation as less oxygen diffuses into the capillaries.
Curve for emphysema shifts downward, showing reduced hemoglobin saturation.
Reduced oxygen availability limits aerobic respiration.

Question 59

A scientist investigates how particulate matter in polluted air affects lung capacity. Design an experiment to measure its impact on FEV1. Include control variables. (6 marks)

Answer 59

Method:
Recruit two groups: people exposed to high particulate levels and those in low particulate areas.
Measure FEV1 using a spirometer.
Repeat measurements over 6 months to track changes.
Control Variables:
Ensure groups are matched for age, gender, and smoking status.
Use the same spirometer and protocol for all participants.
Analysis:
Compare mean FEV1 between the two groups.

Question 60

An experiment measures oxygen uptake in people with different lung diseases. Suggest how the setup might differ for patients with asthma versus emphysema. (4 marks)

Answer 60

Use a spirometer to measure FEV1 for asthma patients to assess airway obstruction.
For emphysema patients, measure both FEV1 and residual volume to evaluate trapped air.
Monitor oxygen saturation using a pulse oximeter for both groups.

Question 61

A patient with cystic fibrosis has thick mucus in their airways. Explain how this reduces their ability to exercise. (4 marks)

Answer 61

Thick mucus blocks airways, reducing airflow to alveoli.
Less oxygen reaches the blood, limiting aerobic respiration.
Increased breathing effort leads to fatigue.
Reduced gas exchange lowers energy availability for exercise.

Question 62

A law bans smoking in cars carrying children. Evaluate this policy using evidence about smoking and lung health. (5 marks)

Answer 62

Positive effects:
Reduces children’s exposure to secondhand smoke, which contains harmful particulates.
Protects developing lungs from damage caused by tar and nicotine.
Limitations:
May not address exposure to smoke at home.
Enforcing the law may be challenging.
Conclusion: The policy is effective in protecting children’s health but needs to be part of broader anti-smoking measures.

Question 63

Compare and contrast the effects of asthma and fibrosis on lung function. (6 marks)

Answer 63

Similarities:
Both reduce airflow into and out of the lungs.
Both reduce the efficiency of gas exchange.

Differences:
Asthma involves airway constriction and excess mucus; fibrosis involves thickened lung tissue.
Asthma is reversible with treatment; fibrosis causes permanent damage.
Asthma primarily affects airflow (FEV1); fibrosis affects diffusion (reducing vital capacity).