IB Biology SL Topic A1.1 (Water)

Four Properties of Water Useful for Life

1. Solvent Properties (Metabolism & Transport)

2. Cohesion/Surface Tension Properties (water sticks to itself allowing for habitat)

3. Thermal Properties

4. Adhesion (water sticks to other things allowing for things like capillary action)

Water Structure & Hydrogen Bonding

Relative Charges: Oxygen has a partial negative charge, Hydrogen atoms have a partial positive charge

Covalent Bonds: Polar covalent bonds hold the Oxygen and Hydrogen together within a single water molecule.

Hydrogen Bonds: Weak intermolecular attractions formed between the negative Oxygen of one water molecule and the positive Hydrogen of an adjacent water molecule (drawn as dashed lines).

Cohesion vs. Adhesion

Cohesion: water’s tendency to stick to itself

Adhesion: water’s tencency to stick to other things (polar)

Hydrogen Bonds and Boiling Point

The more hydrogen bonds a small molecule can form, the higher its boiling point.

Why: Hydrogen bonds are intermolecular forces that require significant thermal energy to break before molecules can separate into a gaseous state.

Polarity and Dissolution

Higher polarity or net charge makes a molecule more soluble in water ("like dissolves like").

Non-polar, uncharged molecules are poorly soluble or insoluble.

Hydrophilic Substances

Hydrophilic ("water-loving").

Glucose, sodium chloride (NaCl), amino acids (polar/charged types).

Hydrophobic Substances

Two Examples in Life: Triglycerides (fats/oils), cholesterol (or fatty acids).

Methane vs. Water

Both are small covalent molecules with low molecular mass.

Water is polar, methane is not.

Water forms hydrogen bonds while methane cannot.

Water’s boiling point high 100 methane boiling point low -160

Water specific heat is high (4.18) methane specific heat is Low 2.20

Consequences of Methane's Differences:

Methane exists as a gas at ambient Earth temperatures, whereas water is liquid.

Methane cannot act as a biosolvent or support life's metabolic transport systems.

Physical Properties of Water as a Habitat

• buoyancy - tendency to float

• viscosity - ability to float

• thermal conductivity - moving heat

• Specific heat capacity - amount of energy to raise water by 1 degree Celsius

Physical Properties: Water vs. Air for Organisms

Thermal Conductivity (Ability to transfer heat):

Water: High thermal conductivity. Aquatic organisms lose body heat to the environment much faster than terrestrial ones

Air: Low thermal conductivity (good insulator). Air allows organisms to retain body heat more efficiently.

Specific Heat Capacity (Heat needed to change temperature):

Water: Very high specific heat capacity. Aquatic environments provide thermally stable habitats that resist rapid temperature fluctuations.

Air: Low specific heat capacity. Terrestrial environments undergo rapid and extreme temperature fluctuations

Viscosity (Resistance to fluid flow):

Water: High viscosity compared to air. Moving through water requires streamline adaptations (e.g., seals/loons), but it offers physical support.

Air: Very low viscosity. Air provides minimal resistance to movement, making rapid locomotion and flight easier.

Buoyancy (Upward force exerted by a fluid):

Water: High buoyancy force Supports an organism's body mass, reducing the need for heavy skeleton structures.

Air: Negligible buoyancy. Terrestrial organisms require strong structural supports (e.g., rigid bones or stems) to counteract gravity.

Black Throated Loon

Buoyancy - float

Viscosity - streamlined body shape

Thermal Conductivity - hydrophobic feather

Specific Heat - respond to changing temp from air to water

Ringed Seal

Buoyancy - float

Viscosity - streamlined body shape

Blubber - to reduce heat loss in water

Specific Heat - easy to maintain body temp

4 carbon based macromolecules

1. proteins

2. carbohydrates (sugars)

3. lipids (such as fats)

4. nucleic acids

Carbon can make ___ bonds

Carbon can make four bonds, including four with itself allowing for a huge variety of molecules.

How does condensation form?

Water is taken out to allow bond, hydrolysis is the bonds breaking

Monomer

one molecule