3 Water and Life Lecture Slides Notes

Importance of Water in Biology

• Water is essential for life, contributing significantly to various biological processes.

Unique Properties of Water

Polarity and Hydrogen Bonds

• Water molecules are polar due to uneven distribution of electrons; the electrons spend more time near the oxygen than the hydrogen.

• This polarity enables water to form hydrogen bonds.

Emergent Properties of Water

• Water's properties that support life include:

  • Cohesive behavior: High surface tension and support for organisms.

  • Ability to moderate temperature: Water can absorb/release heat with minimal temperature change.

  • Expansion upon freezing: Ice is less dense than liquid water, allowing it to float.

  • Versatility as a solvent: Water dissolves a wide range of substances.

Cohesion and Adhesion

• Cohesion: Hydrogen bonds hold water molecules together, creating high surface tension.

• Adhesion: Water's attraction to other substances aids in water transport in plants.

  

Temperature Regulation

• Water absorbs heat, stabilizing temperature changes in organisms and environments.

• Specific Heat: Water's high specific heat is due to hydrogen bonding, enabling it to resist temperature changes.

• Kinetic energy: the energy of motion.

• Thermal energy: the kinetic energy associated with random motion of atoms or molecules.

• Heat: thermal energy transfer from one body of matter to another.

• Calorie (cal): the amount of heat required to raise the temperature of 1 g of water by 1 degree C, or the amount of heat released when 1 g of water cools by 1 degree C.

• kilocalories (k cal); 1 k cal= 1,000 cal. (the “calories’ on food packages).

• joule (J): another unit of energy; 1 J= 0.239 cal, or 1 cal= 4.184 J.

Water’s High Specific Heat

• Heat is absorbed when hydrogen bonds break

• Heat is released when hydrogen bonds form

• The high specific heat of water minimizes temperature fluctuations to within limits that permit life. This property is crucial for maintaining stable climates and supporting the metabolic processes of organisms.

• Serves to moderate air temperature in coastal areas.

Evaporative Cooling

• Evaporation cools water's surface, which is crucial for temperature regulation in organisms.

• Heat of vaporization: the heat a liquid must absorb for 1 g to be converted to gas.

• Evaporative cooling: helps stabilize temperatures in organisms and bodies of water.

Ice Density and Environmental Impact

• Ice's crystalline structure makes it less dense, preventing oceans from freezing.

• Global warming poses risks to ecosystems dependent on ice.

Water as a Solvent

Aqueous Solutions

• Solutions contain a solute dissolved in a solvent (usually water).

• Solution: a liquid that is a completely homogeneous mixture of substances.

• Solvent: dissolving agent of a solution.

• Solute: substance that is dissolved.

• Aqueous solution: one in which water is the solvent.

• Hydrogen shell: a sphere of water molecules that surround and interact with an ion or polar molecule, facilitating its solubility in water.

• Water's polarity allows it to dissolve ionic and polar substances effectively.

Hydrophilic and Hydrophobic Substances

• Hydrophilic substance: one that has an affinity for water.

• Hydrophobic substance: one that does not have an affinity for water.

• Oil - hydrophobic (non-polar bonds)

Acidic and Basic Conditions

pH Scale

• pH measures acidity/basicity; biological fluids typically range from 6 to 8.

• Acids: Increase hydrogen ion concentration.

• Bases: Decrease hydrogen ion concentration.

Buffers

• Buffers resist changes in pH, vital for maintaining stable conditions in living organisms.

Environmental Concerns

• Ocean acidification from increased CO2 levels affects marine life, particularly organisms requiring calcium carbonate for structure.