Chemistry of Water and Its Importance

Importance of Water

• Water is vital for all life, comprising 60-80% of most organisms.
• Functions in transporting materials (e.g., blood, sap), regulating temperature, and producing cell products (saliva, tears, sweat, stomach acids).
• Provides support and structure in organisms (e.g., jellyfish) and facilitates movement (e.g., hydraulic systems in worms and starfish).

Chemistry of Water

• Water (H2O) forms by two hydrogen atoms bonded to a single oxygen atom through covalent bonds, sharing electrons.
• The water molecule has a V shape with a bond angle of 104.5 degrees.
• Oxygen's larger size results in unequal electron sharing, creating slight electrical charges: negative at the oxygen end and positive at the hydrogen end.

Polar Nature of Water

• A polar molecule with distinct electrical charges allows it to dissolve many substances, earning it the title of "universal solvent."
• Hydrogen bonds form between the negative pole of one water molecule and the positive pole of another, creating unique properties for water.

Unique Properties of Water

• High boiling point of 100°C (212°F).
• Ice is less dense than liquid water, allowing it to float.
• Cohesion: attraction among water molecules keeps them together, forming puddles instead of droplets.
• Adhesion: water molecules stick to polar surfaces, influencing capillary action essential for plant water uptake.

Solvent Properties

• Water's hydrogen bonds enable it to dissolve ions and other polar substances easily, facilitating biological functions.
• Water organizes nonpolar molecules, influencing their shapes and behaviors in solutions (e.g., hydrophilic vs. hydrophobic).

Density and Temperature Relations

• Density is defined as mass per unit volume; water deviates from normal density behavior below 4°C, becoming less dense as it freezes.
• This decrease in density prevents bodies of water from freezing solid from the bottom up, critical for aquatic life survival.
• In winter, denser water remains beneath ice, allowing ecosystems to thrive.

Temperature & Solvent Dynamics

• Warm water can hold more dissolved solids than colder water, increasing solubility (e.g., hot water dissolves more salt).
• Oxygen depletion in warmer water occurs as oxygen molecules escape, necessitating diffusion from deeper areas to replace them.

Carbohydrate Synthesis in Plants

• Main process: Photosynthesis, involving light-dependent reactions and the Calvin cycle to convert light energy into glucose.
• Light-Dependent Reactions: Occur in chloroplast thylakoid membranes; water (H2O) is split, producing oxygen, ATP, and NADPH.
• Calvin Cycle: Takes place in chloroplast stroma, where carbon dioxide (CO2) is converted into glucose using stored energy.

Carbohydrate Metabolism in Animals

• Comprises glycolysis, the Krebs cycle, and the electron transport chain for energy production from carbohydrates, primarily glucose.
• Glycolysis: Converts glucose to pyruvate in the cytoplasm, generating ATP and NADH without oxygen.
• Krebs Cycle: Takes place in mitochondria, breaking down acetyl-CoA to produce ATP, NADH, FADH₂, and CO2 when oxygen is available.
• Electron Transport Chain: Located in the inner mitochondrial membrane, it produces significant ATP through oxidative phosphorylation using electrons from NADH and FADH₂.