Lecture+Slide+Deck

Learning Objectives of Water and Buffers

  • Four Properties of Water: Explain the four properties that arise from water's ability to form hydrogen bonds.

  • Terminology: Distinguish between hydrophobic and hydrophilic substances; define solute, solvent, and solution.

  • Acids and Bases: Define acid, base, and pH.

  • Buffers: Explain the functioning of buffers.

Properties of Water

  • Biological Importance: Water is the biological medium essential for life on Earth. It constitutes 70-95% of most cells, making its prevalence a key factor in the Earth’s habitability.

Major Fluid Compartments of the Body

  • Total Body Water: 40L, comprising 60% of body weight.

  • Extracellular Fluid: 15L (20% of body weight).

  • Intracellular Fluid: 25L (40% of body weight).

  • Interstitial Fluid: 12L (80% of ECF).

  • Plasma Volume: 3L (20% of ECF).

Polarity and Hydrogen Bonds

  • Polarity: Water is a polar molecule with opposite charges on either end, which facilitates hydrogen bonding between molecules.

  • Hydrogen Bonds: Allows for the formation of transient attachments that contribute to water's unique properties.

Emergent Properties of Water

  1. Cohesive Behavior: Hydrogen bonds hold water molecules together, essential for water transport in plants.

  2. Temperature Moderation: Water moderates temperatures, absorbing heat from warmer air and releasing it slowly.

  3. Expansion Upon Freezing: Ice is less dense than liquid water, allowing it to float.

  4. Solvent Versatility: Water's polarity allows it to dissolve various substances.

Cohesion and Adhesion

  • Cohesion: Facilitates movement against gravity in plants, creating water columns.

  • Adhesion: Attraction between water and different substances, e.g., water with plant cell walls.

  • Surface Tension: High due to cohesive forces, allowing organisms like water striders to walk on water.

Temperature Regulation

  • Specific Heat: Water has a specific heat of 1 cal/g/ºC, helping it resist temperature changes through heating and cooling.

  • Heat of Vaporization: High energy is required for water to evaporate, promoting evaporative cooling.

  • Density of Ice: Ice's lattice structure allows it to float, maintaining aquatic life beneath.

Water as a Solvent

  • Solution Composition: A solution consists of a solvent (water) and solutes (compounds dissolved in it).

  • Ionic and Polar Molecules: Water forms hydration shells around ions, facilitating the dissolution process.

Hydrophilic vs. Hydrophobic

  • Hydrophilic: Attracts water (e.g., polar molecules).

  • Hydrophobic: Repels water (e.g., oils), which contain nonpolar bonds.

Chemical Reactions in Water

  • Most biochemical reactions occur in aqueous solutions. Concentration of solutes impacts reaction rates significantly.

Acids and Bases

  • pH Definition: pH is the negative logarithm of hydrogen ion concentration. Neutral water has a pH of 7 (equal concentrations of H+ and OH–).

  • Acids: Substances that contribute H+ ions, leading to pH values less than 7.

  • Bases: Substances that contribute OH–, resulting in pH values greater than 7.

Buffer Systems

  • Function: Buffers maintain pH close to 7 by minimizing changes in H+ and OH– concentrations.

  • Buffer Composition: Typically consist of a weak acid and its conjugate base, allowing for reversible reactions to absorb excess H+ or OH– ions.

Bicarbonate Buffer System in Blood

  • The bicarbonate (H2CO3) and bicarbonate ion (HCO3–) pair operate to maintain blood pH around 7.4. Exhalation of CO2 helps stabilize blood pH by adjusting H2CO3 levels as necessary.

Practical Applications

  • Understanding the properties of water and its interactions with biological systems is crucial for various fields in biology, chemistry, and environmental science.