A1.1.6 Physical properties of water and the consequences for animals in aquatic habitats Notes

Four Key Physical Properties

1. Water and air have very different physical properties.
2. These differences profoundly affect how animals move, maintain body temperature, and expend energy in aquatic versus terrestrial or aerial environments.

Buoyancy

1. In water:
   1. Water is dense, providing significant buoyant force.
   2. Organisms with similar density to water experience strong upward support.
   3. Less energy needed to stay afloat and counteract gravity.
2. In air:
   1. Air is far less dense than water.
   2. Provides negligible buoyant force.
   3. Organisms must actively generate lift (e.g., flying) or support their weight on land.

Viscosity

1. In water:
   1. Water has viscosity about 50 times greater than air.
   2. Aquatic organisms experience high drag forces while moving.
   3. Must overcome significant resistance to swim.
2. In air:
   1. Air has low viscosity, creating minimal resistance.
   2. Allows relatively frictionless movement.

Thermal Conductivity

1. In water:
   1. Water has high thermal conductivity: conducts heat away from the body efficiently.
   2. Warm-blooded animals lose heat rapidly in water.
2. In air:
   1. Air has low thermal conductivity: poor conductor of heat.
   2. Animals retain body heat more easily.

Specific Heat Capacity

1. In water:
   1. Water resists temperature changes, acting as a thermal buffer.
   2. Aquatic environments experience stable temperatures with minimal fluctuations.
2. In air:
   1. Air temperature changes rapidly with environmental conditions.
   2. Terrestrial and aerial environments experience greater temperature variability.

Comparing Physical Properties of Water and Air

Example Organisms and Their Adaptations

These physical properties create different challenges for organisms living in water versus air. Two species illustrate these contrasts:

Aquatic Organism: Ringed Seal (Pusa hispida)

1. Habitat: Arctic marine environments, icy waters.
2. Adaptations to water's properties:
   1. Buoyancy: Floats easily, conserving energy while resting.
   2. Viscosity: Streamlined body reduces drag; powerful flippers propel through viscous water.
   3. Thermal conductivity: Thick blubber layer insulates against rapid heat loss; counter-current heat exchange in flippers minimizes heat loss.
   4. Specific heat capacity: Benefits from stable water temperatures in Arctic seas.

Aerial Organism: Black-Throated Loon (Gavia arctica)

1. Habitat: Lakes and rivers; migrates over open water and land.
2. Adaptations to air and water:
   1. Buoyancy: Must generate lift actively when flying in air; floats easily when swimming.
   2. Viscosity: Low air viscosity allows efficient flight, but takeoff requires overcoming air resistance; webbed feet aid swimming.
   3. Thermal conductivity: Feathers trap air for insulation in both air and water; waterproof coating prevents heat loss when diving.
   4. Specific heat capacity: Adapts to variable air temperatures during flight; benefits from stable water temperatures when diving.