Chapter 2 Water Acids Bases

Principles of Biology: Cells & Genetics BI 211 Water, Acids, and Bases (Chapter 2)

Importance of Water in Life

• Life Under the Ocean

  • Estimated 50-80% of all life on Earth is found below the ocean surface.

  • Oceans contain 99% of the planet's living space.

  • Comprises 97% of all Earth’s water.

Origin and Characteristics of Water

• Life Began in Water

  • Life originated over 4 billion years ago in water.

  • Evolved for approximately 3 billion years before colonizing land.

  • Water covers ¾ of Earth's surface.

• States of Water

  • Water exists as solid, liquid, and gas, the only common substance to do so.

  • Solid form (ice) is less dense than liquid water, allowing it to float.

• Role of Water in Life

  • Essential for biological functions; imagine life without water.

Unique Properties of Water

• Structure and Behavior of Water Molecules

  • Water's V-shaped structure is due to the arrangement of electrons.

  • The shape influences its interactions and properties.

  • Each water molecule is polar due to the electronegative oxygen atom attracting electrons.

Emergent Properties of Water

• High Specific Heat

  • Water's specific heat is high due to hydrogen bonding.

  • It resists temperature changes, impacting organisms and bodies of water.

• High Heat of Vaporization

  • Hydrogen bonds resist water changing to gas, which is essential for processes like evaporative cooling (e.g., sweating).

Cohesion and Adhesion

• Cohesion

  • Water molecules attract each other due to hydrogen bonds.

• Adhesion

  • Water can also stick to other surfaces, aiding in transport against gravity in plants.

  • Contributes to surface tension, allowing organisms like water striders to walk on water.

Water as a Universal Solvent

• Dissolution Process

  • Water dissolves solutes, e.g., sugar in water forms an aqueous solution.

  • It dissolves ionic compounds due to water's polarity creating hydration shells around ions.

  • Even large molecules like sugars and proteins can dissolve in water.

• Chemical Reactions

  • Most biochemical reactions occur in solutions where solutes are dissolved in water.

Hydrophilic and Hydrophobic Substances

• Hydrophilic Substances

  • Molecules with charged or polar portions that are attracted to water (e.g., proteins, sugars).

• Hydrophobic Substances

  • Molecules without charged portions that repel water (e.g., lipids).

Concentration and Molarity

• Calculating Molecular Mass

  • Determining the number of molecules in biochemical reactions using molecular mass.

  • Example: Sucrose (C12H22O11) has a total molecular weight of 342 daltons.

• Moles as Units

  • 1 mole contains 6.02 x 10^23 particles (Avogadro’s number).

  • Conversion of daltons to grams for molarity calculations (e.g., 342 grams of sucrose gives 1 mole).

Preparing Solutions

• Creating Solutions

  • To make a 1 M solution of sucrose, dissolve 342 grams in water until a total volume of 1 L.

• Molarity

  • Molarity is a unit of concentration for solutes in aqueous solutions.

Acids and Bases

• Ionization of Water

  • A hydrogen atom may shift from one water molecule to another, forming hydronium (H3O+) and hydroxide (OH-) ions.

  • At neutral pH, water has a concentration of H+ and OH- ions at 10^-7 M.

• Characteristics of Acids and Bases

  • Acids donate H+ ions to increase H+ concentration.

  • Bases reduce H+ concentration either directly or indirectly (e.g., NaOH increases OH-).

pH Scale and Biological Relevance

• Understanding pH

  • pH is the negative logarithm of hydrogen ion concentration, indicating acidity or basicity.

  • pH 7 is neutral; biological systems typically range from pH 6 to 8.

  • The scale is logarithmic; a decrease in pH represents an increase in acidity.

Biological Buffer Systems

• Role of Buffers

  • Buffers stabilize pH by accepting or donating H+ ions as needed.

  • Examples include:

    • Hemoglobin’s role in oxygen transport.

    • Carbonic acid and bicarbonate system in blood, balancing pH.