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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
Hydrogen Bonding
Attraction between H atom in a polar covalent bond and another electronegative atom (like a oxygen atom).
Solution
Liquid that is a homogeneous mixture of substances
Aqueous Solution
Solutes dissolved in water (the solvent).
Hydration Shell
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
Hydrophilic Substance
Has an affinity for water
(relatively polar bonds)
Hydrophobic Substance
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.
Cohesion
- 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
Heat
amount of KE due to molecular motion
Temperature
intensity of heat
Evaporative Cooling
- 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)
=> H
3
O
+
ion (hydronuim ion) molecules that lost H
+
=> OH
-
Hydroxide
Acid
donates a proton to a solution, increases H
+
concentration of a solution.
Base
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
Buffers
Minimize changesin concentration of H+ and OH- in a solution.
Acid-base pair that reversibly combines with H+
pH buffering in biological systems
CO
2 +
H
2
O --> H2CO3 or HCO
3
-
+ 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:
Coral Bleaching
and a decrease in the ability of corals to form calcified reefs.
- Algae dies, (with higher pH).
Author
Birdnut
ID
235952
Card Set
Biology 1020 Lecture 2 Water as a vehicle for life
Description
Biology terms
Updated
9/28/2013, 7:07:32 AM
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