Water

Biology 189: Fundamentals for Life Sciences

Introduction to Water

• Water is fundamental to life.

• Approximately 75% of Earth's surface and 70% of the human body is water.

• Life on Earth evolved from water; thus, water chemistry is critical to understanding biology.

Learning Objectives

• Understand the significance of water for living organisms on Earth.

• Describe emergent properties of water:

  • Cohesion/Adhesion

  • Ability to absorb heat

  • Excellent solvent capacity

  • Ice formation and flotation

• Define key terms: solutes, solvents, solutions, and molarity.

• Differentiate between hydrophobic and hydrophilic molecules.

Properties of Water

States of Water

• Exists in three states:

  • Solid (ice/glaciers)

  • Liquid (oceans)

  • Gas (water vapor)

Polarity of Water

• Water is a polar molecule, leading to many hydrogen bonds with itself:

  • Cohesion: Water molecules adhere to each other, creating surface tension and forming droplets.

  • Adhesion: Water molecules adhere to other surfaces, leading to the phenomenon of wetting.

Emergent Properties of Water

1. Cohesion:

   • Causes water to form droplets and creates surface tension.

   • Allows certain objects to rest on the surface without sinking.

2. Adhesion:

   • Affects how water interacts with different surfaces, facilitating processes like capillary action.

3. Heat Absorption:

   • High specific heat allows water to absorb significant heat without significant temperature changes.

   • High heat of vaporization results in effective evaporative cooling, critical for homeostasis.

4. Universal Solvent:

   • Water interacts effectively with hydrophilic substances due to its polarity.

   • Can break ionic bonds in compounds (e.g., KCl dissociating into K+ and Cl- in water).

5. Ice Formation:

   • Ice is less dense than liquid water, allowing it to float.

   • Insulates water below, which is vital for aquatic life during freezing temperatures.

Definitions and Vocabulary

• Solute: The substance dissolved in a solution.

• Solvent: The dissolving agent; in biological contexts, this usually refers to water.

• Solution: A homogeneous mixture of solute and solvent.

• Aqueous Solution: Water is the solvent.

• Molarity: A way to measure concentration in the lab (moles of solute per liter of solution).

Hydrophobic and Hydrophilic Molecules

• Hydrophobic: Molecules that do not interact well with water; tend to be nonpolar.

• Hydrophilic: Molecules that readily interact with water; tend to be polar.

• Example: Vitamin C is hydrophilic, while Vitamin A is hydrophobic, soluble in fat.

Importance of Ice and Water’s Density

• Ice's lower density allows it to float, creating an insulating layer on water bodies.

• This property is essential for maintaining ecosystems in winter conditions, enabling organisms to survive beneath the ice.

Summary of Properties of Water

1. Heat Storage: Stabilizes temperatures due to high bonding energy.

2. Ice Formation: Ice crystals are organized and spread apart, resulting in lower density.

3. High Heat of Vaporization: Requires significant energy for evaporation.

4. Cohesion: Water molecules cling together through hydrogen bonds.

5. Polarity: Attracts ions and polar compounds effectively.

Vocabulary Overview

• Cohesion

• Adhesion

• Solute

• Solution

• Aqueous solution

• Specific heat

• Heat of vaporization

• Evaporative cooling

• Hydrophilic

• Hydrophobic

• Molarity

• Ionization

• Acid

• Base

• Solvent