Water and pH in Biological Systems

Water Composition and Functions

• Water comprises 70-90% of living cells, existing as both free and bound water.
• Solids make up 10-30% of cells, while inorganic substances account for 1%, including Na, K, Ca, Mg, NH4, Cl-, SO4, PO4, and CO3.
• Trace elements such as Fe, I2, Cu, Mn, Co, and Zn are present in various organic combinations.

Importance of Water

• Acts as a universal solvent, facilitating the ionization of substances which accelerates chemical reactions.
• Exhibits hydrogen bonding capabilities, enabling the dissolution of organic biomolecules containing functional groups.
• Possesses high latent heat of evaporation, aiding in temperature regulation and heat conductivity.

Water as a Solvent

• Allows dissolved reactants to collide and form products, essential for metabolic processes.
• Aids in waste removal by dissolving waste products that are excreted in urine.
• Exhibits adhesion, enabling water to stick to unlike surfaces, enhancing interactions with polar compounds.

Thermal Properties of Water

• High specific heat allows water to absorb or release significant amounts of heat with minimal temperature fluctuations, stabilizing temperatures in cells and ecosystems.
• High heat of vaporization indicates that many hydrogen bonds must be broken for evaporation to occur, providing cooling effects.

Unique Characteristics of Water

• Lower density of ice results from hydrogen bonding, causing ice to float, which insulates aquatic environments.
• Water's polarity makes it an effective solvent for ionic and polar covalent molecules, facilitating nutrient transport in organisms like blood plasma, cytoplasm, and plant xylem.
• Supports hydration and dehydration reactions, crucial for various biochemical processes.

Hydrophilic and Hydrophobic Molecules

• Hydrophilic (water-loving) molecules readily dissolve in water, enabling biological functionality.
• Hydrophobic (water-fearing) molecules do not dissolve in water, often repelling it, which influences interactions in cellular structures and functions.