Biology Chapter 3: Water and Life

Chapter 3: Water and Life

• Water is a polar molecule due to polar covalent bonds
• Opposite ends of the water molecule have opposite charges
• Polarity allows water molecules to form hydrogen bonds with each other
• Water's electron arrangement gives oxygen two partial negative charges
• Hydrogen bonds between water molecules give water unique properties
• Hydrogen bonds are responsible for water's high surface tension which allows some insects to walk on water
• Water has high specific heat; large amounts of heat are absorbed or released with only slight temperature fluctuations
• Water's specific heat stabilizes temperatures
• Evaporation is the transformation of a substance from liquid to gas
• Heat of vaporization is the heat a liquid needs to absorb for 1 gram to be converted to gas
• Evaporative cooling occurs when a liquid evaporates, its remaining surface cools
• Water's high specific heat and evaporative cooling help stabilize temperatures in organisms and bodies of water
• Ice floats in liquid water because hydrogen bonds in ice are more ordered and make ice less dense
• If ice sank, all bodies of water would eventually freeze solid, which makes life impossible on Earth
• A solution is a mixture that is homogeneous; a liquid dissolving agent is a solvent
• A solute is the substance that is dissolved in a solution
• Water is a versatile solvent due to its polarity
• Water is an effective solvent because it readily forms hydrogen bonds
• When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules; this is called a hydration shell
• Most biochemical reactions occur in water, and reactions depend on the concentration of solutes; these factors are important for the chemistry of a cell
• Molecular mass is the sum of the masses of all the atoms in a molecule. Numbers are usually measured in moles where one mole=6.02 x 10^23 molecules.
• Molarity is the number of moles of solute per liter of solution
• Water dissociation releases hydrogen ions (H+) and hydroxide ions (OH-)
• The hydrogen atom leaves its electron behind and is transferred as a proton; molecules with an extra proton are known as hydronium ions (H3O+). Molecules that lose a proton are known as hydroxide ions (OH-)
• The concentration of H+ and OH- is equal in pure water; adding acids and bases modifies the concentrations
• Biologists use the pH scale to describe how acidic or basic something is
• An acid increases the H+ concentration in a solution
• A base reduces the H+ concentration in a solution
• The pH of a solution is determined by the relative concentration of hydrogen ions
• Acidic solutions have pH values lower than 7
• Basic solutions have pH values greater than 7
• Most biological fluids have a pH value between 6 and 8
• Buffers are substances that minimize changes in the H+ and OH- concentration in solutions
• Most buffers consist of an acid-base pair that combines reversibly with hydrogen ions

The Threat of Acid Precipitation

• Acid precipitation refers to rain, snow, or fog below a pH of 5.6
• Acid precipitation is a result of pollutants mixing with the water in the air
• Acid precipitation damages life in lakes and streams
• It also affects soil chemistry, which then leads to the decline of forests.

Explore the essential properties of water in this quiz focusing on polar molecules, hydrogen bonds, and specific heat. Understand how these properties impact life and ecosystems, as well as phenomena like evaporation and temperature stabilization in organisms. Test your knowledge of the significance of water in biology.