Biology Chapter 3: Water and Life Quiz

Water Molecules and Polarity

• Water molecules consist of an oxygen atom (O) in the center and two hydrogen atoms (H) on either side, forming a bent shape.
• Water is a polar molecule due to the unequal sharing of electrons, with oxygen being more electronegative, resulting in partial negative (δ-) and partial positive (δ+) charges.

Hydrogen Bonding

• Hydrogen bonds form between the slightly positive hydrogen of one water molecule and the slightly negative oxygen of another, allowing water molecules to hold together.
• One water molecule can form up to four hydrogen bonds, contributing to water's unique properties.

Cohesion vs. Adhesion

• Cohesion refers to the attraction among water molecules due to hydrogen bonding, while adhesion is the attraction between water and other substances.
• The beading of water on a waxed car hood demonstrates adhesion, as water molecules cling to each other to form droplets.

Surface Tension

• Water's high surface tension enables insects like water striders to walk on water due to the ordered arrangement of molecules at the surface.

Caloric Properties

• A calorie is the amount of heat required to raise 1g of water by 1ºC and vice versa, equivalent to 4.184 Joules.
• Water has a high specific heat (1 cal/g °C), meaning it can absorb significant amounts of heat with minimal temperature changes.

Temperature Regulation

• Water's high specific heat aids in moderating environmental temperatures, preventing drastic temperature fluctuations in coastal areas and supporting life.

Evaporation and Heat of Vaporization

• Evaporation is the process where liquid turns into gas, helping organisms regulate temperatures (e.g., cooling through sweat).
• The heat of vaporization is the energy necessary for liquid water to become gas, influencing the severity of steam burns.

Ice Properties

• Ice floats because it is less dense than liquid water, a result of its hydrogen bonding structure.
• This floating behavior insulates bodies of water, preventing them from freezing solid and allowing life to thrive beneath the surface.

Solutions and Solubility

• Water is known as a solvent, capable of dissolving various solutes due to its polarity.
• Hydrophilic substances attract water and are soluble, while hydrophobic substances repel water and do not dissolve (e.g., oil).

Molarity and Ion Concentration

• Molarity is the concentration of solute in a solution, expressed as moles of solute per liter of solution.
• Water dissociates into hydronium (H3O+) and hydroxide ions (OH-), with a neutral pH of 7 indicating equal concentrations of both ions (10^-7 M).

pH Scale and Buffers

• The pH scale reflects the concentration of hydrogen ions, with each unit change representing a tenfold change in acidity or basicity.
• Buffers maintain stable pH in solutions by absorbing or releasing H+ ions, essential for biological systems.

Carbon Dioxide and Blood pH Regulation

• Carbonic acid forms from the reaction of CO2 and water, dissociating to help regulate blood pH through equilibrium with bicarbonate and hydrogen ions.

Acid Precipitation and CO2 Effects

• Human activities, particularly the burning of fossil fuels, contribute to acid precipitation, altering the pH and temperature of water bodies.
• Increased CO2 levels lead to ocean acidification, harming marine life due to decreased carbonate concentrations essential for shell formation.