2 Exam Questions

Question 1

Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake. [2]

Answer 1

Larger organisms have a smaller surface area:volume ratio and therefore a larger diffusion pathway
Creates a shorter diffusion pathway for oxygen

Question 2

Mammals such as a mouse and a horse are able to maintain a constant body temperature.
Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse. [3]

Answer 2

Mice are smaller so have a larger surface area to volume ratio
This means they have a larger amount of heat loss
The higher rate of metabolism is to release heat

Question 3

Describe the relationship between size and surface area to volume ratio of organisms. [1]

Answer 3

As size increases, the ratio decreases

Question 4

Explain why oxygen uptake is a measure of metabolic rate in organisms. [1]

Answer 4

Oxygen is used in respiration which is a metabolic process which provides ATP

Question 5

Tidal volume is the volume of air inhaled and exhaled during a single breath when a person is resting.
Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and alveoli. [3]

Answer 5

Less carbon dioxide is exhaled
Reduces concentration gradient between blood and alveoli
Less movement of carbon dioxide out of blood

Question 6

Explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system. [2]

Answer 6

Blood and water flow in opposite directions
Concentration gradient is maintained along length of lamella for diffusion

Question 7

Describe and explain the mechanism that causes lungs to fill with air. [3]

Answer 7

Diaphragm and external intercostal muscles both contract
Causes volume increase and pressure decrease
Air moves down the pressure gradient from the atmosphere into the lungs

Question 8

Describe the pathway taken by an oxygen molecule from an alveolus to the blood. [2]

Answer 8

Across alveolar epithelium
Then epithelium of capillary

Question 9

Explain how one feature of an alveolus allows efficient gas exchange to occur. [2]

Answer 9

The alveolar epithelium is one cell thick
Creating a short diffusion pathway

Question 10

Describe the gross structure of the human gas exchange system and how we breathe in and out. [6]

Answer 10

Structure: trachea, bronchi, bronchioles, alveoli
Breathing in - diaphragm and external intercostal muscles both contract
Causing volume increase and pressure decrease in thoracic cavity so air moves down pressure gradient from atmosphere into lungs
Breathing out - Diaphragm relaxes and internal intercostals muscles contract
Causing volume decrease and pressure increase in thoracic cavity meaning air moves down pressure gradient from lungs to atmosphere

Question 11

Explain three ways in which an insects tracheal system is adapted for efficient gas exchange. [3]

Answer 11

Tracheoles have thin walls so short diffusion distance to cells
Large number of tracheoles so large surface area for gas exchange
Body can move air so maintains concentration gradient for gas exchange