Properties of Water and Life

The Importance of Water

• Water is the biological medium on Earth, all living organisms need water.
• Cells are typically 70–95% water.
• The abundance of water is the main reason the Earth is habitable.

The Structure of Water

• Water is a polar molecule due to the uneven sharing of electrons between hydrogen and oxygen.
• The opposite ends of a water molecule have opposite charges.
• This polarity allows water molecules to form hydrogen bonds with each other.

Properties of Water

• Water's properties are responsible for creating an environment suitable for life.

Cohesion

• Hydrogen bonds hold water molecules together, this is cohesion.
• Cohesion helps water transport against gravity in plants.
• Adhesion is the attraction between different substances like water and plant cell walls.
• Surface Tension: This is the force needed to break the surface of a liquid and it’s related to cohesion.

Temperature Moderation

• Water has a high specific heat, meaning it absorbs or releases large amounts of heat with little change in its own temperature.
• The high specific heat of water minimizes temperature fluctuations to within limits that permit life.
• Heat is absorbed when hydrogen bonds break and released when they form.

Evaporative Cooling

• Evaporation is the transformation of a liquid to a gas.
• Heat of vaporization: the heat required to convert 1 g of a liquid into gas.
• As a liquid evaporates, its remaining surface cools, called evaporative cooling.

Insulation of Bodies of Water

• Ice floats because of its ordered hydrogen bonds, making it less dense.
• Water reaches its greatest density at 4°C.

Water as a Solvent

• A solution is a homogenous mixture of substances.
• Solvent: the dissolving agent.
• Solute: the substance that is dissolved.
• Aqueous solutions are those with water as the solvent.
• Water is a versatile solvent because of its polarity.
• Ionic compounds dissolve in water forming hydration shells around each ion.
• Hydrophilic substances have an affinity for water.
• Hydrophobic substances do not have an affinity for water.
• A colloid is a stable suspension of particles in a liquid.

Solute Concentration in Aqueous Solutions

• Most biochemical reactions occur in aqueous solutions.
• The concentration of solutes affects the rate of chemical reactions.

Acids, Bases, and pH

• The dissociation of water molecules produces hydrogen ions (H+) and hydroxide ions (OH–).
• The concentration of H+ and OH– affects the chemistry of cells.
• The pH scale measures the acidity or basicity of a solution.
• Acidic solutions have a pH less than 7, basic solutions have a pH greater than 7.
• Most biological fluids have a pH between 6 and 8.
• Buffers minimize changes in H+ and OH– concentrations in a solution.

Threats to Water Quality

• Acid precipitation: Rain, snow, or fog with a pH lower than 5.6.
• Acid precipitation is caused by pollutants mixing with water in the air.
• CO2 from fossil fuel combustion causes:
  • The “greenhouse” effect causing global warming.
  • Ocean acidification which affects coral reefs.

Explore the fundamental properties of water, including its biological importance, structure, and unique characteristics. This quiz covers cohesion, adhesion, and temperature moderation, highlighting how these properties support life on Earth. Understanding these concepts is crucial for appreciating the role of water in ecosystems and biology.