Importance of Water in Biology

Importance of Water

• Essential for life, covering 70% of Earth's surface and making up 95% of living organisms' matter.
• Plants absorb approximately 500 grams of water for every gram of organic matter produced, highlighting water's vital role in cellular processes.
• Water constitutes 80 to 95% of mass in growing plant tissues; common vegetables like carrots and lettuce contain up to 95% water.

Molecular Structure of Water

• Composed of an oxygen atom covalently bonded to two hydrogen atoms, forming a 105° bond angle.
• Oxygen's higher electronegativity gives it a partial negative charge, while hydrogen carries a partial positive charge, resulting in a neutral molecule overall.
• Breaking hydrogen bonds to increase the air-water interface requires energy, contributing to water's surface tension.

Cohesion and Surface Tension

• High surface tension influences the shape of the water surface and creates pressure within the liquid.
• Surface tension supports water transport through plants, facilitating movement in vascular systems.
• Cohesive forces grant water high tensile strength; it can withstand tensions over –30 MPa, significantly higher than most liquids.

Cavitation Phenomenon

• The formation of gas bubbles in water under tension can lead to cavitation, collapsing the liquid tension and hindering water transport in plants.

Water as a Universal Solvent

• Water dissolves a greater variety of substances than other solvents due to its small size and polar nature, making it effective for ionic and polar compounds.
• Hydration shells form around ions and molecules, increasing solubility by neutralizing electrical attractions and facilitating dissolution.
• Water's high dielectric constant enables it to be an excellent solvent for charged ions/molecules while poorly dissolving non-polar substances.

Specific Heat Capacity

• Water has the highest specific heat capacity among common liquids, requiring significant energy to raise its temperature.
• High specific heat and thermal conductivity allow water to effectively stabilize temperature in living tissues and environments.
• Water dissipates heat quickly, preventing localized overheating and maintaining cellular temperature stability.

Heat of Vaporization

• Water requires about 44 kJ/mol to evaporate, contributing to its cooling effect.
• Evaporation cools surfaces by releasing energy from high-energy molecules, essential for temperature regulation in plants through transpiration.

Heat of Fusion

• High heat of fusion (335 J/g) for water illustrates the energy needed to convert ice to liquid water, protecting citrus crops from frost during freezing.

Viscosity and Flow Dynamics

• Water's viscosity is higher than many liquids due to hydrogen bonding, with a reference value of 1.0 centipoise at 20°C.
• Viscosity decreases with increasing temperature, affecting liquid transport in plants.

Volume and Density

• Water achieves maximum density near 4°C; ice is less dense, causing it to float and insulate aquatic life underneath.
• This unique property prevents large bodies of water from freezing solid, essential for sustaining aquatic organisms.

Transparency of Water

• Water's transparency allows visible light penetration, crucial for photosynthesis and supporting life forms like phytoplankton.

Water as a Buffer

• Water ionizes into H+ and OH- ions, acting as a reservoir to maintain pH stability in biological systems.
• It protects organisms from extreme pH changes, maintaining the narrow pH range essential for cellular function.

This quiz explores the critical role of water in sustaining life and its unique molecular structure. It covers topics such as water's significance in plant growth, its cohesion, and surface tension. Understand how water's properties influence biological processes and the environment.