Understanding Water: The Key Component of Life

Importance of Water in Biology

• Water is a vital molecular component of life.
• The first cell formed in water; it remains the main medium for life processes.

Structure and Polarity of Water

• Composition: Water consists of one oxygen and two hydrogen atoms.
• Polarity:
  • Water molecules are polar due to their asymmetrical structure and polar covalent bonds.
  • Unequal charge distribution: Partially negative (oxygen) and partially positive (hydrogen) sides.
  • Electrons are attracted closer to oxygen due to its higher electronegativity.
  • Polarity is visualized by the ability to draw a line separating charges on a molecule.

Hydrogen Bonds in Water

• Opposite charges attract: Water molecules form hydrogen bonds.
• Hydrogen bonds are weak but significant for life.

Properties of Water

1. Cohesion

• Water molecules attract and stick to each other.
• Role in Biology:
  • Essential for water movement in plants (xylem function).
  • Transpiration creates tension, pulling water from roots to leaves.
  • Enables organisms like water striders to "walk" on water due to surface tension.

2. Adhesion

• Water molecules stick to other surfaces.
• Examples:
  • Soil: Water moves through soil via capillary action.
  • Plant xylem walls: Polar attraction helps water movement against gravity.

3. Solvent Properties

• Water dissolves particles due to polarity and hydrogen bonding.
• Hydrophilic Substances: Attracted to water's polar charges, e.g., salt.
• Hydrophobic Substances: Nonpolar and do not dissolve in water, e.g., phospholipids in cell membranes.

Physical Properties of Water

1. Specific Heat

• Water has a high specific heat, requiring more energy to change temperature.
• Maintains stable temperatures for biochemical reactions.

2. Thermal Conductivity

• Water efficiently conducts heat.
• Example: Fennec foxes use blood vessels in ears to dissipate heat.

3. Buoyancy

• Water's density influences whether substances float or sink.
• Algae use trapped oxygen and gas vacuoles for buoyancy.

4. Viscosity

• Describes the flow of substances.
• Water has low viscosity, but it increases with added solutes like in blood plasma.

Comparative Study: Black-throated Loon and Ringed Seal

• Both organisms interact with land and water but are affected differently by water's properties.
• Ringed Seal:
  • Spends more time in water, affected by viscosity, buoyancy, and heat conductivity.
  • Adaptations include thick fur for temperature regulation.
• Black-throated Loon:
  • Experiences less thermal loss and energy use in air compared to the seal in water.

Exam Preparation

• Understand the physical properties of water and their biological significance.
• Be able to compare examples like the loon and the seal in terms of adaptations to their environments.