Basic Chemistry 2 : The Chemical Foundation of Life (Chapter 2)

Hydrophilic

Meaning: Water - Loving

Polarity : Polar or charged

Dissolves in water? Yes

Examples : Salt, sugar, amino acids

Biological role : Move in blood/cytoplasm

Hydrophobic

Meaning : Water - Fearing

Polarity : Nonpolar

Dissolves in water? No

Examples : Fats, oils, cholesterol

Biological role : Form membranes

Phospholipid

Cohesion

Water molecules stick to each other because of hydrogen bonds

Ex. Water droplets forming beads on a leaf

Adhesion

Water molecules stick to other surfaces

Ex. Water climbing up plant stems (capillary action)

Surface Tension

The surface of water resists being broken due to cohesive hydrogen bonds

Ex. A water strider insect walking on water

Temperature stability / specific heat

Water absorbs and releases heat slowly because hydrogen bonds take energy to break

Ex. Oceans and lakes maintain stable temperatures

Universal solvent

Water dissolves many substances because its polarity allows it to surround ions and polar molecules

Ex. Salt (NaCl) dissolving in water

Properties of water

Acid

A substance that releases hydrogen ions (H⁺) when dissolved in water

Base

A substance that removes hydrogen ions (H⁺) or releases hydroxide ions (OH⁻)

Buffer

A substance that resists changes in pH by accepting or donating H⁺ ions

Acid

Ex. Hydrochloric acid (HCl) in the stomach

Biological Importance: Helps digestion; maintains low pH for enzyme activity

Base

Ex. Sodium hydroxide (NaOH), ammonia (NH₃)

Biological Importance: Neutralizes acids; maintains pH balance

Buffer

Ex. Bicarbonate buffer in blood

Biological Importance: Keeps blood pH stable (~7.4)

pH Scale

Ranges from 0 to 14:

0–6: Acidic (more H⁺ ions)

7: Neutral (pure water)

8–14: Basic (more OH⁻ ions)

Enzyme Function

Enzymes work best at specific pH levels. Even small changes can denature them

Cellular Processes

pH affects chemical reactions, nutrient transport, and energy production

Homeostasis

Organisms use buffers to maintain stable internal pH — essential for survival

Environmental Balance

Aquatic life depends on stable pH; acid rain or pollution can disrupt ecosystems

Hydroxyl (Alcohol)

Structure : -OH

Charge? No

Polar? Yes

Common in : Sugars, alcohols

Carboxly

Structure : -COOH

Charge? Yes (acidic)

Polar? Yes

Common in : Amino acids, fatty acids

Amino

Structure : –NH₂ / –NH₃⁺

Charge? Yes (basic)

Polar? Yes

Common in : Amino acids, proteins

Phosphate

Structure : –PO₄²⁻

Charge? Yes (negative)

Polar? Yes

Common in : ATP, DNA, RNA

Methyl

Structure : –CH₃

Charge? No

Polar? No

Common in : Lipids, gene regulation

Carbon

Property	Description	Example
4 valence electrons	Forms 4 bonds	CH₄ (methane)
Bonds with many elements	Creates diverse molecules	C–H, C–O, C–N
Forms chains and rings	Builds complex structures	Glucose, fatty acids
Backbone of life	Found in all biomolecules	DNA, proteins
Recycled in nature	Moves through carbon cycle	CO₂ ↔ organic carbon