Water

Biology 189: Fundamentals for Life Sciences

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.

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.

Exists in three states:
- Solid (ice/glaciers)
- Liquid (oceans)
- Gas (water vapor)

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.

Cohesion:
- Causes water to form droplets and creates surface tension.
- Allows certain objects to rest on the surface without sinking.
Adhesion:
- Affects how water interacts with different surfaces, facilitating processes like capillary action.
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.
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).
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.

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: 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.

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.

Heat Storage: Stabilizes temperatures due to high bonding energy.
Ice Formation: Ice crystals are organized and spread apart, resulting in lower density.
High Heat of Vaporization: Requires significant energy for evaporation.
Cohesion: Water molecules cling together through hydrogen bonds.
Polarity: Attracts ions and polar compounds effectively.