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A1.1.6—Physical properties of water for aquatic animals

Compared with air, water is denser, more viscous, more thermally conductive and more temperature-stable, shaping aquatic organisms’ support, movement and insulation.

Syllabus
First assessment 2025
Objective
A1.1.6
Level
SL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceNovember 2025
Most common paper—
Typical marks1

Common command terms

  • Identify
  • Describe
  • Distinguish

Scoring notes

Common mistake
Confusing thermal conductivity with specific heat capacity.

Recent exam appearances

November 2025Paper1A SL · TZ11[ 1 ]A1.1.6—Physical properties of water for aquatic animals
November 2021Paper1 SL · TZ07[ 1 ]A1.1.6—Physical properties of water for aquatic animals

Coverage 2021–2025 · Updated 14 Jul 2026

Water changes the costs of temperature control and movement

Property of water compared with air Opportunity Constraint
higher specific heat capacity habitat and water-rich body temperatures change slowly much energy is exchanged before water temperature changes
higher thermal conductivity heat moves readily through the surrounding water a warm animal loses heat faster than in air
much greater density and buoyancy displaced water supports body mass upthrust must be overcome during a dive
greater viscosity feet and flippers can push against the fluid drag raises the cost of movement

Specific heat capacity describes the energy needed to change temperature; thermal conductivity describes how readily heat passes through a material. Water can therefore provide a stable habitat while still removing heat quickly from a warm animal.

Predict the adaptation from the constraint: insulation limits heat transfer, streamlining reduces drag, broad propulsive surfaces push water backward, and increased mass or reduced trapped air helps an animal dive.

A loon and a seal meet the same habitat in different ways

Aquatic challenge Black-throated loon Ringed seal
reduce heat loss trapped air in feathers limits conduction and convection thick blubber insulates beneath the skin
produce thrust with low drag streamlined body; rear webbed feet push water backward streamlined body; flippers provide propulsion
manage buoyancy while diving solid bones and compressed air reduce upthrust blubber adds buoyancy, so swimming force is needed to descend
A black-throated loon and ringed seal with labels for webbed feet, flippers, trapped air and blubber.

An adaptation is explained by linking a structural feature to the relevant property of water and then to its consequence for heat balance, propulsion or diving—not by listing the feature alone.

Recover the chain from molecule to biological consequence

Unequal electron sharing + bent geometry → a polar molecule → hydrogen bonding and attraction to charged or polar matter. Begin every explanation from the interaction that produces the property.

Interaction or physical property Biological opportunity Constraint or boundary
water–water attraction xylem continuity; surface tension cohesion does not create transpiration pull
water–surface attraction capillary movement and wet cell walls adhesion is not the main force resisting xylem tension
attraction to ions and polar solutes reactions, diffusion and transport non-polar O₂ and N₂ remain poorly soluble
heat capacity, conductivity, buoyancy and viscosity stable habitat, support and propulsion heat loss, diving cost and drag require adaptations

Make a comparison, not two isolated descriptions

[ 2 ]

Distinguish between the physical properties of water and air.

Concept essentials

  • Water is denser and more buoyant than air.
  • Higher viscosity increases resistance to movement.
  • Higher thermal conductivity increases heat loss from animals.
  • High specific heat capacity stabilises aquatic temperatures.
  • Aquatic adaptations match distinct physical challenges.