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A 1.1 Water

- What physical and chemical properties of water make it essential for life?
- What are the challenges and opportunities of water as a habitat?

A 1.1 Water

SL and HL Content 

A1 - 1.1—Water as the medium for life

Learning Objectives:

  • Students should appreciate that the first cells originated in water and that water remains the medium in which most processes of life occur.


A1 - 1.2—Hydrogen bonds as a consequence of the polar covalent bonds within water molecules

Learning Objectives:

  • Students should understand that polarity of covalent bonding within water molecules is due to unequal sharing of electrons and that hydrogen bonding due to this polarity occurs between water molecules.

  • Students should be able to represent two or more water molecules and hydrogen bonds between them with the notation shown below to indicate polarity.


A1 - 1.3—Cohesion of water molecules due to hydrogen bonding and consequences for organisms

Learning Objectives:

Include transport of water under tension in xylem and the use of water surfaces as habitats due to the effect known as surface tension.


A1.1.4—Adhesion of water to materials that are polar or charged and impacts for organisms

Include capillary action in soil and in plant cell walls.


A1.1.5—Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals

Emphasize that a wide variety of hydrophilic molecules dissolve in water and that most enzymes catalyse reactions in aqueous solution. Students should also understand that the functions of some molecules in cells depend on them being hydrophobic and insoluble.


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

Include buoyancy, viscosity, thermal conductivity and specific heat capacity. Contrast the physical

properties of water with those of air and illustrate the consequences using examples of animals that live in water and in air or on land, such as the black-throated loon (Gavia arctica) and the ringed seal (Pusa hispida).



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