The Molecule that Supports all Life

• Water is the only substance that can exist in the natural environment in all 3 states

• Water’s unique emergent properties make earth suitable for life

• Structure of water allows it to interact with other molecules (be available for any large molecules’ broken and empty bonds)

• Helps with the formation of different compounds/photosynthesis

• It is an electron donor

Polar Covalent Bonds in Water Molecules Result in Hydrogen Bonding

• Electrons (overall charge) are unevenly distributed (more attracted to the oxygen ion), making it a polar molecule with dipoles

• Its polarity allows it to interact and form hydrogen bonds with other substances

• Water molecules have a small charge that attracts it to others like itself

• COHESION: Attraction to others like itself

• ADHESION: Attraction to different substances than itself

4 Emergent Properties of Water That Contribute to Life

• Cohesive behavior

• Ability to moderate temperature

• Expansion upon freezing

• Versatility as a solvent

The Cohesion of Water Molecules

• Hydrogen bonds hold water molecules together, creating cohesion

• Cohesion & adhesion allows the water in plants to move against gravity

• Adhesion is in transpiration (as roots take up water to the leaves)

  • Capillary action = water going up a plant

  • Evaporation also pulls water upwards

• Spheres take the least amount of energy (why water forms globs in space)

  • Tendency towards chaos/disorder + maintain energy (why it is a sphere)

• Surface tension is the measure of how difficult it is to break the surface of a liquid

• Water has an unusually high surface tension due to hydrogen bonding and cohesiveness

Moderation of Temperature by Water

• water absorbs heat from warmer air and releases that heat into colder air (why regions beside lakes are cooler = because water is absorbing the heat)

• Water can hold onto heat for long periods of time & release/absorb a large amount of heat with only a slight change in its own temperature (changing its state)

• Temperature & Heat

  • Kinetic energy = energy in motion

  • A lot of energy is required to break water’s hydrogen bonds (cohesion) in large numbers

  • Thermal energy = kinetic energy’s association with the random motion of atoms and molecules

  • Heat = thermal energy being transferred from one body to another

    • Enzymes are picky with pH and temperature (water has a huge temperature range)

  • A calorie (cal) is the amount of energy required to raise 1g of water by 1 degree C

    • Also the amount of heat released when 1g of water cools

  • Joule is another unit of energy

^^Water’s High Specific Heat ^^

• The amount of heat that must be absorbed or lost for 1g of that substance to change by 1 degree C.

• Specific heat of water is 1 cal/(g x C)

• Rubbing alcohol has a lower high specific heat = evaporates quicker

• Water resists changing its temperature because of its high specific heat

  • Hydrogen bonding breaks = heat is absorbed

  • Hydrogen bonds form = heat is released

  • High specific heat limits water’s temperature fluctuations to which it can still sustain life

Evaporative Cooling

• Evaporation (vaporization) = transition from liquid to gas

• The heat of evaporation = the heat required for 1g of a liquid to be converted into a gas

• As the liquid evaporates, its remaining surface cools = evaporative cooling (the heat is released)

  • Helps stabilize temperatures in organisms and bodies of water

  • Ex. sweating (reduction of heat energy)

Floating of Ice on Liquid Water

• Ice floats in water because the hydrogen bonds are more “ordered”, making ice less dense than water

• Water is densest at 4 degrees (ex. bottom of the lake)

• If ice sank to the bottom of water bodies, the entire water body would freeze (ice formed at the top would keep sinking down)

• Global warming is affecting water bodies (heatsinks), making them unable to properly absorb heat

  • Objects around it are then heating up (ex. icebergs)

  • Creating challenges for animals that rely on ice

Water: The Solvent of Life

• Aqueous solution = water is the solvent

• Water is a versatile solvent due to its polarity

  • Ionic compounds can dissolve in water because its ions are surrounded by water molecules (ie. hydration shell/shield)

    • Ex. Glucose powder gets its molecules bent into rings when dissolved in water

• Water can dissolve non-ionic polar molecules + very large polar molecules if they have ionic/polar regions

Hydrophilic and Hydrophobic Substances

• Hydrophilic = affinity for water

• Hydrophobic = no affinity for water

  • Ex. oils because they have non-polar bonds

  • Oils and other non-polar molecules are the main substances for cell membranes

• Ex. Phospholipid Bilayer

  • Hydrophilic heads allow the cell to live in the water/in the body

  • The charge on the heads attract it together (cohesion)

  • Hydrophobic tails: water-soluble materials can not bypass the tails unless there is a carrier/receptor that brings it inside

  • If tails were on the outside, we would not survive (the cell would not be able to survive in water) and we would be oil-based organisms

  • If there is a slight charge, it is hydrophilic, if there is no charge, it is hydrophobic and non polar

Solute Concentrations in Aqueous Solutions

• Molecular mass = sum of all atoms’ masses in a molecule

  • of entities = avogadro’s number

• Molarity (M) = # of moles of solute/L of solution

• Ex. Vinegar in salad dressing = helps the hydrophobic vegetables to break down/have a change in pH

Acidic and Basic Conditions Affect Living Organisms

• A hydrogen atom in a hydrogen bond between 2 water molecules can shift between one and the other

• Molecule that lost the proton = OH-

• Molecule that gained a proton = H3O or H+

• All enzymes are proteins, but not all proteins are enzymes

• HCL is in stomach to lower pH (ex. of pepsin)

• Amylase needs a neutral place to work (mouth)

• Lower pH = more hydronium/hydrogen ions

• High pH = more OH ions

• When CO2 dissociates in water, it becomes carbonic acid or hydrogen carbonate

• Changes in concentrations of H and OH can drastically affect the chemistry of a cell and affect the organism

• Concentration of H and OH in pure water is the same

Acids and Bases

• Acid = increases the H concentration of a solution

• Bases = reduces the H concentration of a solution

• Strong acids and bases dissociate completely in water

• Weak acids and bases reversibly release and accept back H ions but can still shift the H and Oh away from neutrality

• Most bio fluids have a pH of 6-8

  • Inside intestine = 8 (water is absorbed, lining is thinner, and enzymes need s pH of 8)

==Buffers ==

• The internal pH of most living cells is close to 7

• Buffers are substances that limit changes in concentrations of H and OH in a solution

• Most buffer solutions contains a weak acid and its corresponding base, which combine reversibly with H ions

• Weak acid and weak base to maintain good pH