Unit 1 AP Bio

Properties of H₂O

1. Polarity makes it the universal solvent

2. Hydrogen bonding

3. Less dense as solid

4. High specific heat

5. High heat of vaporization

Polarity

• Polarity comes from the covalent bond between O and H’s within a single H₂O molecule

• A single H₂O molecule has “unequal charges”

  • H = positive

  • O = negative

Polarity contributes to H bonds forming between

different water molecules

Universal solvent

Polarity makes H₂O the US —> it dissolves many substances

Polar substances are

Hydrophilic

Hydrophilic

• charged (+ end & - end)

• attracted to H₂O

• dissolved by H₂O

• examples: sugar, salts

Nonpolar substances are

Hydrophobic

Hydrophobic

• uncharged

• repelled by H₂O

• not dissolved by H₂O

• examples: lipids

Hydrogen bonding

H bonds are attractions between polar molecules

H bonding between H₂O molecules is

cohesion

• creates surface tension (water is sticky)

H bonding between H₂O & other substances is

adhesion

• meniscus in cylinder

• up a tree

• raindrops on glass

H₂O is less dense as a

solid (most are more dense when solid)

• H bonds form a crystal

• Ice floats —> lakes don’t freeze solid so living things can survive below ice

Water’s specific heat is

high

• H₂O resists changes in temp

  • takes a lot of heat to raise temp & cooling to lower temp

• H₂O moderates temps on Earth

Water requires ___ energy/heat to turn water from solid to gas

high

Atoms & molecules from environment are used by living things to build

biomolecules (biomolecules)

4 biomolecules are essential to all living things

1. carbohydrates

2. lipids

3. proteins

4. nucleic acids

Elements found in ALL biomolecules

• carbon

• hydrogen

• oxygen

others:

• Phosphorus - needed to build nucleic acids & phospholipids

• Sulfur - needed to build proteins

• Nitrogen - needed to build proteins & nucleic acids

Phosphorus need to build

nucleic acids & phospholipids