- The subcomponents of biological molecules and their sequences determine the properties of that molecule
Properties of Water
- Water: 2 hydrogen and 1 oxygen bonded together with (Polar) COVALENT bonds bcuz oxygen is more electronegative, so electrons pulled closer to it
- Water is POLAR- overall charge is unevenly distributed (+ & -), allows molecules to form HB
- The hydrogen bonds between water molecules result in cohesion, adhesion, and high surface tension, self-regulation, expansion upon freezing, versatility as a solvent
- Cohesion: water molecules attached to each other (bcuz of HB)
- Makes water “sticky”
- Ex: water molecules evaporate from leaf by pulling on neighboring water which then draw up molecules behind them
- Adhesion: water molecules attached to OTHER things
- Positively charged part attract negatively charged ends of other polar compounds and vice versa
- Cohesion + Adhesion allows for capillary action: transport of water up roots & against gravity
- Water pulls each other up and can adhere to narrow tubing during transpiration
- Surface tensions: “Tendency of molecules to be pulled from the surface to the interior of a liquid”
- Water has high surface tension bcuz of increased HB forces at surface that resist being stretched/broken → allows organisms to walk on water
Self-regulation
- Water has high specific heat because lots of energy is absorbed when bonds break and released when hydrogen bonds form
- So body of water can absorb lots of heat and resist chemical change; needs lots of energy to freeze
- Cool air when it is warm and release heat in the winter
- Stabilizes ocean temperature, climate, and organisms (bcuz they are mostly made up of water)
- When water changes physical state, energy is absorbed but water temp remains constant → absorbed energy just changes HB
Evaporative Cooling
- As water evaporates, cools the surface of the earth & organisms bcuz molecules with more heat energy evaporate quicker
- Hydrogen bonds need to break for water to vaporize
Expansion Upon Freezing
- Water is less dense/expands as a solid bcuz weak HB stabilize/crystalize, keeping molecules too far apart (also slow) to break them
- So ice floats and insulates water, reducing heat loss from water below → warmer water that is less likely to freeze
- If sank then all water would freeze over → no aquatic life
Versatility as a Solvent
- Solvent: dissolving agent Solute: substance dissolved
- Water versatile solvent because polar molecules are attracted to other polar molecules and form HB (adhesive)
- (+) and (-) attraction
- Ionic compounds are soluble because poles of polar water molecules interact with them and separate into ions
- Water helps cell transport substances throughout the body (ex. nutrients, antibiotics)
- Hydrophilic: affinity for water, polar Hydrophobic: repel water, nonpolar
Acids and Bases
- Water molecule can transfer H+ to another water forming OH (hydroxide) and hydronium ion
- Water is an acid and base
- Hydrogen Ion: Single proton, highly reactive/energy/unstable
- Acids and bases cause imbalance in H and OH
- Acids: decrease pH, ione in water to increase H+, less hydronium ion. 0-6
- Bases: increase pH decreases H+, more OH; 8-14
- Bases break into OH which can combine with H+ to create water (accept H+)
- Buffer solutions: maintain a ~constant pH when either acids or bases are added
- Resist shifts in pH by donating H⁺ to a solution when bases are added, and accepting H⁺ when acids are added
- pH Scale: measures the concentration of H+ → Formula: pH = -Log[h+]
- Change of one pH number represents a tenfold change in hydrogen concentration
- Ex: pH of 3 is ten times more acidic as pH of 4
- Change of one pH number represents a tenfold change in hydrogen concentration
Water Potential
- “Measure of potential energy of water & eagerness to go from high potential to low”
- Water potential = pressure potential + solute potential
- High water potential = more water molecules (higher concentration) & will move somewhere else
- More solutes = increases osmolarity and decreases water potential