UNIVERSITY OF SOUTH AFRICA
College of Agriculture and Environmental Sciences
⋄ ⋄ ⋄
Animal Physiology
Assignment 02 — Respiration, Gas Laws, and Oxygen Transport
⋄ ⋄ ⋄
ZOL2601
Module Code:
Animal Physiology
Module Name:
02
Assignment No:
01
Semester:
23 March 2026
Due Date:
Submitted in partial fulfilment of the requirements for ZOL2601 — UNISA 2026
,UNISA | ZOL2601 Animal Physiology: Respiration
Contents
Question 1: Factors Influencing Gas Dissolution in Water 3
Question 2: The Role of Skin in Respiration 5
Question 3: Oxygen Dissociation Curves in Mammals of Various Sizes 7
Question 4: Henry’s Law Calculations and Oxygen Consumption 9
Question 5: Airflow Through Bird Lungs and Structural Adaptations 12
Question 6: The E. Newton Harvey Principle 14
Reference List 16
Page 2 of 16
, UNISA | ZOL2601 Animal Physiology: Respiration
Question 1: Factors Influencing Gas Dissolution in Water
The amount of gas that can dissolve in water is not fixed. It shifts depending on specific phys-
ical and chemical conditions. Four main factors govern this, and each one has a clear, pre-
dictable direction of influence.
1.1 Temperature
Direction: Inverse. As water temperature increases, the amount of gas that can dissolve
in it decreases. This happens because higher temperatures give water molecules more kinetic
energy, which makes it harder for gas molecules to remain in solution. They escape back into
the gaseous phase more readily (Schmidt-Nielsen, 1997). This is why cold water holds more
dissolved oxygen than warm water, an important consideration for aquatic animal physiology,
particularly in warmer climates or during seasonal temperature fluctuations.
1.2 Pressure (Henry’s Law)
Direction: Direct. The higher the partial pressure of a gas above a liquid, the more of that
gas dissolves into it. This is the principle captured in Henry’s Law: the concentration of a
dissolved gas is directly proportional to its partial pressure at the surface of the liquid (Ran-
dall, Burggren & French, 2002). At higher altitudes, where atmospheric pressure and therefore
the partial pressure of oxygen is lower, less oxygen dissolves into water. This has direct conse-
quences for aquatic organisms living at altitude.
1.3 Salinity
Direction: Inverse. Saltwater holds less dissolved gas than freshwater at the same temper-
ature and pressure. The dissolved ions in saltwater compete with gas molecules for space and
interaction with water molecules, a phenomenon called the “salting-out” effect (Hill, Wyse &
Anderson, 2016). Marine organisms therefore generally live in water with lower dissolved oxy-
gen concentrations than their freshwater counterparts, all else being equal.
Page 3 of 16
College of Agriculture and Environmental Sciences
⋄ ⋄ ⋄
Animal Physiology
Assignment 02 — Respiration, Gas Laws, and Oxygen Transport
⋄ ⋄ ⋄
ZOL2601
Module Code:
Animal Physiology
Module Name:
02
Assignment No:
01
Semester:
23 March 2026
Due Date:
Submitted in partial fulfilment of the requirements for ZOL2601 — UNISA 2026
,UNISA | ZOL2601 Animal Physiology: Respiration
Contents
Question 1: Factors Influencing Gas Dissolution in Water 3
Question 2: The Role of Skin in Respiration 5
Question 3: Oxygen Dissociation Curves in Mammals of Various Sizes 7
Question 4: Henry’s Law Calculations and Oxygen Consumption 9
Question 5: Airflow Through Bird Lungs and Structural Adaptations 12
Question 6: The E. Newton Harvey Principle 14
Reference List 16
Page 2 of 16
, UNISA | ZOL2601 Animal Physiology: Respiration
Question 1: Factors Influencing Gas Dissolution in Water
The amount of gas that can dissolve in water is not fixed. It shifts depending on specific phys-
ical and chemical conditions. Four main factors govern this, and each one has a clear, pre-
dictable direction of influence.
1.1 Temperature
Direction: Inverse. As water temperature increases, the amount of gas that can dissolve
in it decreases. This happens because higher temperatures give water molecules more kinetic
energy, which makes it harder for gas molecules to remain in solution. They escape back into
the gaseous phase more readily (Schmidt-Nielsen, 1997). This is why cold water holds more
dissolved oxygen than warm water, an important consideration for aquatic animal physiology,
particularly in warmer climates or during seasonal temperature fluctuations.
1.2 Pressure (Henry’s Law)
Direction: Direct. The higher the partial pressure of a gas above a liquid, the more of that
gas dissolves into it. This is the principle captured in Henry’s Law: the concentration of a
dissolved gas is directly proportional to its partial pressure at the surface of the liquid (Ran-
dall, Burggren & French, 2002). At higher altitudes, where atmospheric pressure and therefore
the partial pressure of oxygen is lower, less oxygen dissolves into water. This has direct conse-
quences for aquatic organisms living at altitude.
1.3 Salinity
Direction: Inverse. Saltwater holds less dissolved gas than freshwater at the same temper-
ature and pressure. The dissolved ions in saltwater compete with gas molecules for space and
interaction with water molecules, a phenomenon called the “salting-out” effect (Hill, Wyse &
Anderson, 2016). Marine organisms therefore generally live in water with lower dissolved oxy-
gen concentrations than their freshwater counterparts, all else being equal.
Page 3 of 16
