Properties of Water and Its Importance

Extremophiles

• There are three types of extremophiles:

  • Bacteria

  • Eukaryotes

  • Archaea

• Extremophiles have adapted to live in extreme conditions due to the unusual properties of water, which include:

  • High salinity

  • Extreme temperatures

  • High pressure

Properties of Water

• Water’s unique properties allow it to play a critical role in the biology of extremophiles.

• Water molecules exhibit strong cohesive properties. This is due to:

  • High dipole moment

  • Separation of positive and negative charges

  • Uneven sharing of electrons, resulting in polar molecules

Cohesion and Adhesion

• Cohesion:

  • Defined as the attraction among like molecules, including water molecules.

  • This property is responsible for surface tension, which is the difficulty of breaking the surface of a liquid.

• Water also demonstrates Adhesion:

  • The attraction of unlike molecules.

  • The charged areas of water molecules can be attracted to oppositely charged areas of other substances.

• Capillary Action:

  • Result of the combined effects of cohesion and adhesion.

  • Example:

  • When a straw is placed in water, the water molecules are attracted to the inner walls of the straw (adhesion), leading to water molecules climbing upwards through capillary action due to cohesion, thereby creating a meniscus (curve).

Water as a Heat Regulator

• Water has a high specific heat capacity, which allows it to absorb and release heat slowly. This characteristic is important for:

  • Regulating temperatures in the environment

  • Maintaining homeostasis in organisms

• Specific Heat of water:

  • Specifically, it is $1 ext{ cal } ext{ g}^{-1} ext{ °C}^{-1}$ (calorie is the amount of heat required to raise 1 gram of water by 1 °C).

  • Kilocalorie:

  • The amount of heat required to raise 1 kg of water by 1 °C

  • $1 ext{ kcal} = 1000 ext{ cal}$.

• Water's high specific heat results from the hydrogen bonds that stabilize water molecules, requiring considerable energy to change their temperature.

• Large bodies of water can absorb heat and take longer to cool down.

Heat vs. Temperature

• Heat:

  • A measure of the total amount of kinetic energy of the molecules in a substance.

• Temperature:

  • A measure of the average speed of one molecule of a substance.

  • Example:

  • A pool may have a higher total heat energy than a hot cup of coffee, but the latter will have a higher temperature.

Evaporative Cooling

• Evaporative cooling is exemplified by sweating:

  • As sweat evaporates from the skin, it absorbs heat from the body, which results in a cooling effect.

• Each droplet of sweat requires a significant amount of heat to evaporate, due to water's strong hydrogen bonds.

• Heat of Vaporization:

  • Water has a high heat of vaporization, requiring approximately 580 calories of heat energy to convert 1 gram of liquid water into vapor.

Ice and Density

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

• This property is crucial for life to continue underwater during winter, as ice insulates the water beneath.

• In ice, hydrogen bonds are stable and constantly push away from each other, while in liquid water, they are constantly forming and breaking.

Universal Solvent

• Water is often referred to as the universal solvent because its polar nature allows it to dissolve many charged solutions and ionic compounds.

• Hydration Shell:

  • A layer of water molecules that surrounds an ion, protein, or other charged molecules when dissolved in water.

  • Example interaction:

  • The negative oxygen regions of polar water molecules are attracted to positive sodium ions (Na$^+$), while the positive hydrogen regions are attracted to negative chloride ions (Cl$^-$).

• Lysozyme, an enzyme protein, is surrounded by a hydration shell, helping it interact with bacteria.

Hydrophobic and Hydrophilic Interactions

• Hydrophobic Substances:

  • Water-fearing; typically nonpolar substances like oils and fats.

• Hydrophilic Substances:

  • Water-loving; polar and ionic substances such as ionic compounds, carbohydrates, and proteins.

• Rule of thumb: Like dissolves like.

• To dissolve a nonpolar compound, a nonpolar solvent is necessary.

Molarity and Solutions

• Molarity:

  • The number of moles of solute per liter of solution.

• Acidity and Alkalinity:

  • Water can dissociate into hydroxide (OH$^-$) and hydronium (H$_3$O$^+$) ions.

  • This dissociation requires two water molecules to occur.

  • In acids, the concentration of hydronium ions increases, while in bases it decreases.

  • pH scale:

  • Based on the negative logarithm of hydrogen ion concentration.

  • For example, pH of 1 indicates $1 imes 10^{-1}$ moles per liter, and pH of 2 indicates $1 imes 10^{-2}$ moles per liter, and so on.

Buffers

• Buffers are substances that maintain homeostasis by minimizing changes in concentrations of hydrogen and hydroxide ions in a solution.

• Example: Bicarbonate Buffer System:

  • Composed of an acid-base pair that donates or accepts hydrogen ions via reversible reactions to maintain pH balance.

• Components include:

  • Carbonic acid (H$2$CO$3$)

  • Bicarbonate ion (HCO$_3^-$)

  • This system helps to keep the internal pH of living organisms stable, particularly in humans, where the ideal pH is approximately 7.4.