Biology 1020 Lecture 2 Water as a vehicle for life
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Properties of water that support life (on Earth)
- - Versatility
- - Expansion upon freezing
- - Cohesive Behaviour
- - Moderation of temperature
Attraction between H atom in a polar covalent bond and another electronegative atom (like a oxygen atom).
Liquid that is a homogeneous mixture of substances
Solutes dissolved in water (the solvent).
- Each ion of an aqueous solution is surrounded by a hydration shell.
- - Cations (+ve ions) oxygen closet
- - Anions (+ve ions) hydrogen closet
Water as a solvent
- Can dissolve many types of solutes
- - ionic molecules
- - compounds made of non-polar molecules
- - Large polar molecules (ex. proteins) if they have ionic and polar regions
- Has an affinity for water
- (relatively polar bonds)
- Does not have an affinity for water
- (relatively nonpolar bonds)
H-bonding in ice is more ordered that in liquid water
Ice is less dense and has a larger volume
Freezing Point Depression
- Presence of solutes decreases the freezing point of a solvent.
- - Freezing point of seawater lower than freshwater (-1.8 c)
- - Solutes disrupts H bonding
- - High concentration of solutes in some organisms in colder climate can prevent body fluids from freezing.
- - Sticking together
- - Water molecules form hydrogen bonds with other polar molecules and each other
Cohesion of Water
- - Water moves by capillary action - "wicks"
- - Cohesion (with each other) and adhesion (other surfaces) important in water transport in plants
Cohesion of Water: Surface Tension
- - How hard it is to break the surface of a liquid
- - High in water in part due to its cohesive behaviour
Temperature moderation by water
- - Water has a high specific heat. (H bonding)
- - Amount of heat to change temperature
- 1g, raised by 1 degree celsius
amount of KE due to molecular motion
intensity of heat
- - Large quantity of heat must be absorbed to make liquid -> Gas
- - Remaining surface cools as liquid evaporates -> evaporative cooling
- * helps stabilize temp. in organisms and bodies of water.
Temperature moderation by water
- - Ocean absorbs heat from warmer air
- - Releases stored heat to cooler air
- - Only slight change in water temperature
- (Temp. more moderate near oceans than prairies).
Equilibruim of Water
- - H atom in a H-bond between two water molecules can shift from one to the other.
- - H2O molecules dissociate at the same rate at which they are being reformed.
Equilibruim of Water #2
- H atom leaves its e- behind
- -> transformed as a proton (H+ ion)
ion (hydronuim ion) molecules that lost H+
donates a proton to a solution, increases H+ concentration of a solution.
accepts a proton from the solution, decreases H+ concentration of a solution
pH and biological systems
Most biological fluids - pH 6-8
- Changes in pH can drastically affect the chemistry of a cell
Minimize changesin concentration of H+ and OH- in a solution.
Acid-base pair that reversibly combines with H+
pH buffering in biological systems
- CO2 + H2O --> H2CO3 or HCO3- + H+
- H2CO3 <---> HCO3- + H+
- Acid Base
Acidification of Biological Systems
- - Air pollutants mix with water in atmosphere: decrease pH
- - Can fall at some distance from the source
- - Lakes and streams, soil chemistry
Ocean water quality:
and a decrease in the ability of corals to form calcified reefs.
- Algae dies, (with higher pH).
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