UNIVERSITY OF SOUTH AFRICA
College of Agriculture and Environmental Sciences — Department of Life Sciences
⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄⋄
ZOL2601: Animal Physiology
Assignment 2 — Semester 1, 2026
⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄⋄
Gas Solubility · Skin Respiration · Oxygen Dissocia-
tion · Henry’s Law · Bird Lungs · Harvey Principle
ZOL2601
Module Code:
Animal Physiology
Module Name:
Assignment 2 (Semester 1)
Assignment:
23 March 2026
Due Date:
Department of Life and Consumer Sciences
Department:
University of South Africa (UNISA)
Institution:
Submitted in partial fulfilment of the requirements for ZOL2601 — UNISA 2026
,UNISA | ZOL2601 Animal Physiology Assignment 2 — Semester 1, 2026
Contents
1 Question 1 — Factors Influencing Gas Solubility in Water 4
Question 1: Gas Solubility Factors 4
1.1 1.1 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 1.2 Partial Pressure of the Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 1.3 Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 1.4 Nature and Molecular Properties of the Gas . . . . . . . . . . . . . . . . . . . 5
2 Question 2 — The Role of Skin in Respiration 6
Question 2: Skin Respiration 6
2.1 Requirements for Effective Cutaneous Respiration . . . . . . . . . . . . . . . . . . 6
2.2 Cutaneous Respiration Across Animal Groups . . . . . . . . . . . . . . . . . . . . 6
2.3 Limitations of Cutaneous Respiration . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Question 3 — Oxygen Dissociation Curves: Mammals of Various Sizes 8
Question 3: Oxygen Dissociation Curves 8
3.1 Labelled Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Explanation of the Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2.1 Small mammals: high O2 affinity, left-shifted curve . . . . . . . . . . . . . 8
3.2.2 Large mammals: lower O2 affinity, right-shifted curve . . . . . . . . . . . . 9
3.2.3 The biochemical mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4 Question 4 — Henry’s Law Calculations 10
Question 4: Henry’s Law Calculations 10
4.1 4.1 Quantity of Oxygen in 200 L of Fresh Water at Two Altitudes . . . . . . . . . 10
4.1.1 Henry’s Law Statement and Formula . . . . . . . . . . . . . . . . . . . . . 10
4.1.2 Scenario A: 100 metres above sea level (PO2 = 157 mmHg) . . . . . . . . 11
4.1.3 Scenario B: 2,500 metres above sea level (PO2 = 117 mmHg) . . . . . . . 11
4.2 4.2 Time for Rainbow Trout to Consume All Oxygen . . . . . . . . . . . . . . . . 11
4.2.1 Step 1: Calculate the fish’s total O2 consumption rate . . . . . . . . . . . 12
4.2.2 Step 2: Time to consume all O2 at each altitude . . . . . . . . . . . . . . 12
Page 2 of 20
,UNISA | ZOL2601 Animal Physiology Assignment 2 — Semester 1, 2026
5 Question 5 — Airflow Through Bird Lungs 14
Question 5: Bird Lung Airflow 14
5.1 Overview: Why Bird Lungs Are Exceptional . . . . . . . . . . . . . . . . . . . . . 14
5.2 Structural Differences from Mammalian Lungs . . . . . . . . . . . . . . . . . . . . 14
5.3 The Air Sac System and Two-Cycle Breathing . . . . . . . . . . . . . . . . . . . . 14
5.4 The Cross-Current Gas Exchange Advantage . . . . . . . . . . . . . . . . . . . . 15
5.5 Benefits of Bird Respiratory Adaptations . . . . . . . . . . . . . . . . . . . . . . . 15
6 Question 6 — The E. Newton Harvey Principle 17
Question 6: E. Newton Harvey Principle 17
6.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.2 Core Principle: Annotated Line Diagram . . . . . . . . . . . . . . . . . . . . . . . 17
6.3 Explanation of the Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.4 Biological Relevance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Reference List 20
Page 3 of 20
, UNISA | ZOL2601 Animal Physiology Assignment 2 — Semester 1, 2026
Question 1 — Factors Influencing Gas Solubility in Water
The ability of a gas to dissolve in water isn’t fixed; it shifts in response to physical and chemi-
cal conditions of the surrounding environment. Four main factors govern how much gas, specif-
ically oxygen and carbon dioxide, can dissolve in water at any given moment (Schmidt-Nielsen,
1997:3).
1.1 Temperature
Direction of influence: Inverse relationship — as temperature increases, gas solubility
decreases.
Water molecules move faster at higher temperatures, and this increased kinetic energy makes
it harder for gas molecules to remain dissolved. They’re essentially bumped out of solution.
This is why warm tropical surface waters hold significantly less dissolved oxygen than cold po-
lar waters, even at the same atmospheric pressure. A trout in a sun-warmed river during sum-
mer is living in a fundamentally more oxygen-deficient environment than the same species in a
cold mountain stream, even if the partial pressure of oxygen above both is identical (Randall,
Burggren & French, 2002:11).
1.2 Partial Pressure of the Gas
Direction of influence: Direct relationship — as partial pressure increases, gas solubility
increases.
This is the principle formalised in Henry’s Law: the amount of a gas that dissolves in a liq-
uid is directly proportional to the partial pressure of that gas above the liquid. At sea level,
atmospheric pressure is higher, meaning oxygen has a higher partial pressure and more of it
dissolves into water. At altitude, atmospheric pressure drops, partial pressure of oxygen falls,
and less oxygen goes into solution (Schmidt-Nielsen, 1997:5). This relationship is central to
Question 4.
1.3 Salinity
Direction of influence: Inverse relationship — as salinity increases, gas solubility de-
creases.
Page 4 of 20
College of Agriculture and Environmental Sciences — Department of Life Sciences
⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄⋄
ZOL2601: Animal Physiology
Assignment 2 — Semester 1, 2026
⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄⋄
Gas Solubility · Skin Respiration · Oxygen Dissocia-
tion · Henry’s Law · Bird Lungs · Harvey Principle
ZOL2601
Module Code:
Animal Physiology
Module Name:
Assignment 2 (Semester 1)
Assignment:
23 March 2026
Due Date:
Department of Life and Consumer Sciences
Department:
University of South Africa (UNISA)
Institution:
Submitted in partial fulfilment of the requirements for ZOL2601 — UNISA 2026
,UNISA | ZOL2601 Animal Physiology Assignment 2 — Semester 1, 2026
Contents
1 Question 1 — Factors Influencing Gas Solubility in Water 4
Question 1: Gas Solubility Factors 4
1.1 1.1 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 1.2 Partial Pressure of the Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 1.3 Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 1.4 Nature and Molecular Properties of the Gas . . . . . . . . . . . . . . . . . . . 5
2 Question 2 — The Role of Skin in Respiration 6
Question 2: Skin Respiration 6
2.1 Requirements for Effective Cutaneous Respiration . . . . . . . . . . . . . . . . . . 6
2.2 Cutaneous Respiration Across Animal Groups . . . . . . . . . . . . . . . . . . . . 6
2.3 Limitations of Cutaneous Respiration . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Question 3 — Oxygen Dissociation Curves: Mammals of Various Sizes 8
Question 3: Oxygen Dissociation Curves 8
3.1 Labelled Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Explanation of the Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2.1 Small mammals: high O2 affinity, left-shifted curve . . . . . . . . . . . . . 8
3.2.2 Large mammals: lower O2 affinity, right-shifted curve . . . . . . . . . . . . 9
3.2.3 The biochemical mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4 Question 4 — Henry’s Law Calculations 10
Question 4: Henry’s Law Calculations 10
4.1 4.1 Quantity of Oxygen in 200 L of Fresh Water at Two Altitudes . . . . . . . . . 10
4.1.1 Henry’s Law Statement and Formula . . . . . . . . . . . . . . . . . . . . . 10
4.1.2 Scenario A: 100 metres above sea level (PO2 = 157 mmHg) . . . . . . . . 11
4.1.3 Scenario B: 2,500 metres above sea level (PO2 = 117 mmHg) . . . . . . . 11
4.2 4.2 Time for Rainbow Trout to Consume All Oxygen . . . . . . . . . . . . . . . . 11
4.2.1 Step 1: Calculate the fish’s total O2 consumption rate . . . . . . . . . . . 12
4.2.2 Step 2: Time to consume all O2 at each altitude . . . . . . . . . . . . . . 12
Page 2 of 20
,UNISA | ZOL2601 Animal Physiology Assignment 2 — Semester 1, 2026
5 Question 5 — Airflow Through Bird Lungs 14
Question 5: Bird Lung Airflow 14
5.1 Overview: Why Bird Lungs Are Exceptional . . . . . . . . . . . . . . . . . . . . . 14
5.2 Structural Differences from Mammalian Lungs . . . . . . . . . . . . . . . . . . . . 14
5.3 The Air Sac System and Two-Cycle Breathing . . . . . . . . . . . . . . . . . . . . 14
5.4 The Cross-Current Gas Exchange Advantage . . . . . . . . . . . . . . . . . . . . 15
5.5 Benefits of Bird Respiratory Adaptations . . . . . . . . . . . . . . . . . . . . . . . 15
6 Question 6 — The E. Newton Harvey Principle 17
Question 6: E. Newton Harvey Principle 17
6.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.2 Core Principle: Annotated Line Diagram . . . . . . . . . . . . . . . . . . . . . . . 17
6.3 Explanation of the Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.4 Biological Relevance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Reference List 20
Page 3 of 20
, UNISA | ZOL2601 Animal Physiology Assignment 2 — Semester 1, 2026
Question 1 — Factors Influencing Gas Solubility in Water
The ability of a gas to dissolve in water isn’t fixed; it shifts in response to physical and chemi-
cal conditions of the surrounding environment. Four main factors govern how much gas, specif-
ically oxygen and carbon dioxide, can dissolve in water at any given moment (Schmidt-Nielsen,
1997:3).
1.1 Temperature
Direction of influence: Inverse relationship — as temperature increases, gas solubility
decreases.
Water molecules move faster at higher temperatures, and this increased kinetic energy makes
it harder for gas molecules to remain dissolved. They’re essentially bumped out of solution.
This is why warm tropical surface waters hold significantly less dissolved oxygen than cold po-
lar waters, even at the same atmospheric pressure. A trout in a sun-warmed river during sum-
mer is living in a fundamentally more oxygen-deficient environment than the same species in a
cold mountain stream, even if the partial pressure of oxygen above both is identical (Randall,
Burggren & French, 2002:11).
1.2 Partial Pressure of the Gas
Direction of influence: Direct relationship — as partial pressure increases, gas solubility
increases.
This is the principle formalised in Henry’s Law: the amount of a gas that dissolves in a liq-
uid is directly proportional to the partial pressure of that gas above the liquid. At sea level,
atmospheric pressure is higher, meaning oxygen has a higher partial pressure and more of it
dissolves into water. At altitude, atmospheric pressure drops, partial pressure of oxygen falls,
and less oxygen goes into solution (Schmidt-Nielsen, 1997:5). This relationship is central to
Question 4.
1.3 Salinity
Direction of influence: Inverse relationship — as salinity increases, gas solubility de-
creases.
Page 4 of 20
