A1.1:  Water

Theme:  Unity and Diversity

Unity:
Water's consistent molecular structure and resulting properties (polarity, hydrogen bonding, solvency) unify all life by providing the essential medium for biochemistry.

Diversity:
The varying interactions of organisms with water, and the challenges or opportunities presented by water in different environments, have driven an incredible diversity of biological adaptations, structures, and functions.

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

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

Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• How do the various intermolecular forces of attraction affect biological systems?
• What biological processes only happen at or near surfaces?
• ​What are the implications of solubility differences between chemical substances for living organisms? (D2.3)

Key Terms to Know: * higher level only

Adhesion
Anion
Asteroid
Atom
Buoyancy
Capillary Action
Cation
Cohesion
Condensation
Covalent Bond
Electron
Enzyme

Extraplanetary*
Extraterrestrial*
Goldilocks Zone*
Hydrogen Bond
Hydrophilic
Hydrophobic
Insoluble
Ion
Ionic Bond
Neutron
Non-Polar Covalent Bond
Physical Property

Polar Covalent Bond
Proton
Soluble
Solvation
Specific Heat Capacity
Surface Tension
Thermal Conductivity
Viscosity
Water
Xylem

​

A1.1.1 - Water as medium of life.

• State that the first cells originated in water. 
• ​List reasons why water is a substance on which life depends​

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

• Describe the structure of an atom.
• Outline the formation of ionic and covalent bonds between atoms.
• Explain the sharing of electrons between atoms in a polar covalent bond.
• State the location of the polar covalent bond within a water molecule.
• Explain the partial charges of the oxygen and hydrogen atoms within a water molecule.
• Draw a water molecule, including notation to depict the partial charges of the atoms. 
• Outline the cause of the formation of hydrogen bonds between water molecules.
• Outline the consequences of the collective strength of hydrogen bonds between water molecules.​

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

• Define cohesion.
• Describe how water moves through the xylem of a vascular plant.
• Outline the cause of surface tension. 
• State a benefit to living things that results from surface tension.

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

• Define adhesion.
• Define polar.
• Define ion.
• Compare cation and anion.
• Explain why water is attracted to molecules that are polar or charged. 
• Outline the cause of capillary action.
• Describe capillary action in plant tissue.
• Outline the cause and effect of capillary action in soil.

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

• Identify solvent and solutes of a solution.
• Define solvation.
• Explain why water is able to dissolve charged and polar molecules.
• Outline the solvation of hydrophilic and hydrophobic substances.
• State an example of the function of a molecule depending on it being hydrophobic and insoluble. 
• State an example of the function of a molecule depending on it being hydrophilic and soluble. 
• Outline the role of water as a medium for metabolism.
• Describe the role of water as a medium for transport in vascular plants.
• Describe the role of water as a medium for transport in animal blood.

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

• Define physical property.
• List physical properties of water that are consequential for animals in aquatic habitats. 
• Outline the cause and effect of buoyancy. 
• Outline the cause and effect of viscosity. 
• Compare viscosity of air to water to blood. 
• Define thermal conductivity.
• Compare less conductive to more conductive materials. 
• Outline a consequence to life of the thermal conductivity of air and water.
• Define specific heat capacity.
• Describe why water has a high specific heat capacity.
• State two benefits to life of the high specific heat capacity of water. 
• Outline a benefit to life of water's high specific heat capacity.
• Compare the physical properties of water to those of air.
• Describe how the  black-throated loon (Gavia arctica) and/or the ringed seal (Pusa hispida) interact with the physical properties of water in their habitat.

AHL  A1.1.7— Extraplanetary origin of water on Earth and reasons for its retention.

• Explain  the hypothesis that asteroids are responsible for the origin of water on Earth.
• State two reasons why water was retained on early Earth.​

AHL  A1.1.8— Relationship between the search for extraterrestrial life and the presence of water.

• Explain why the presence of water is considered fundamental to the search for extraterrestrial life.
• Define “Goldilocks zone” in relation to the search for extraterrestrial life.