OCR AS Biology- Water

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  • Created on: 25-03-13 21:53
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Water
Catabolic: large to small molecules
Anabolic: small to large molecules
CONDENSATION
-Small molecules joined to make big ones
-Water molecule released
-Covalent bond formed
-Monomers join to make polymers
HydrogenBonding
-A weak interaction that can occur between molecules that contain a slightly
negatively charged atom and slightly positively charged hydrogen.
In a water molecule the nucleus of the oxygen has a stronger attractive force than the
hydrogen nucleus, so the electron cloud is likely to `pool' around the oxygen.
This causes water molecules to be attracted, as they form many hydrogen bonds.
Ice:Reduced temperature, less kinetic energy. Thus more hydrogen bonds form. Due to
the crystalline structure ice is less dense than liquid water and thus floats. As temperature
of liquid water is reduced, the water molecules have less kinetic energy and find it difficult
to move around. More hydrogen bonds form between the molecules, and are harder to
break than the previous bonds. Water becomes solid as hydrogen bonds formed hold the
structure in a semi-crystalline form, which is less dense than liquid water.
Liquid:Has many hydrogen bonds which are continuously being broken and being
formed. Molecules can move around freely but are still attracted to each other
Gas:Evaporation requires a lot of energy, due to the amount of hydrogen bonds that
must be broken. Heat energy is used as evaporating molecules `remove' heat from the
surface of the body of water. Most molecules similar to water are a gas at room

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H(2)S but due to the amount of hydrogen bonds H(2)O remains a
liquid.
WATER,HEATANDTEMPERATURE
If you heat water, the temperature of the water rises. Temperature relates to
the amount of kinetic energy that the water molecules have.
As heat energy is added to the water, a lot of the energy is used to break the
hydrogen bonds between the water molecules. Because so much heat energy is
used for this, there is less heat energy available to raise the temperature.…read more

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When liquid sweat lies on the surface of the skin, the water in the sweat
absorbs heat energy from the body as it evaporates. The heat needed to do
this is called latent heat of evaporation. It is our major cooling mechanism.
It also helps to cool plant leaves in hot climates, as water evaporates from the
surfaces of the mesophyll cells inside them.
Solvent properties
Water is an excellent solvent.…read more

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Solvent Metabolic processes rely 70/90% of the cytoplasm
on chemicals reacting in is water
a transport medium
together.
Liquid Movement of materials in an Blood (plasma)
organism require a liquid
solvent
Cohesion Water molecules may `stick' Xylem (transport up a plant)
to each other creating and small organisms moving
surface tension. on the surface
Freezing Frozen water is less dense Survival of aquatic organisms
due to a crystalline structure as helps thermal stability.
and thus floats, helping to
insulate water below.…read more

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Placing cells in a concentrated salt or sugar solution with a water potential lower than the
cell contents means there is a water potential gradient form inside to outside the cell.
Therefore water molecules move out via osmosis. This makes the cell shrink and in animals
the cell membrane `wrinkles up' or is crenated. In plant cells the cell surface membrane
will pull away from the cell wall, and this is when the cell is known as `plasmolysed.…read more

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