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Biological Molecules
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Date : 25/07/2023
Author Information
Uploaded by : Chloe Laura
Uploaded on : 25/07/2023
Subject : Biology
2.2Biological Molecules.
(a) how hydrogen bonding occurs between water molecules, and relate this, and other
proper8es of water, to the roles of water for living organisms
The proper8es of water:
- solvent,
- transport medium,
- coolant,
- habitat
AND roles illustrated using examples of prokaryotes and eukaryotes.
Water has unique chemical properAes due to its ability to form HYDROGEN BONDS with other molecules and other molecules of water.
Water is able to form HYDROGEN BONDS because it is a POLAR molecule.
POLAR = when there is a separa:on of posi:ve and nega:ve charge
in a molecule, due to an UNEVEN SHARING OF THE ELECTRONS IN A
COVALENT BOND.
(covalent bonds are a type of strong bond that joins atoms together. Covalent bonds are made by two atoms sharing electrons).
The polarity is caused by an uneven sharing of electrons in the covalent bond of the water molecule. This means the electrons (which are negaAvely charged) are closer to the oxygen than the hydrogen. This makes the oxygen more negaAve and the hydrogens more posiAve.
When electrons are unevenly shared in a covalent bond we refer to it as a
dipole.
A hydrogen bond is a weak bond that is caused by opposite aOrac:on between posi:ve and nega:ve areas of the water.
The presence of Hydrogen Bonds create a large network of bonds connecAng many water molecules to each other, it takes more energy than we would expect to break all these Hydrogen Bonds.
The hydrogen bonds give water unique properAes:
- water is a great solvent.
o This means ionic and polar substances can dissolve in water easily, by forming hydrogen bonds with the water.
o For example, nutrients and oxygen dissolve easily in water, thus making water a good habitat, and transport medium for oxygen and glucose in the body.
o Water is also able to carry metabolites and chemical reactants, allowing reacAons to happen easily in water.
- Water has a high specific heat capacity.
o This is how much energy is needed to increase the temperature (of water) by
1 degrees Celsius.
o This means water also has high melAng and boiling points, and can cool other
substances very easily.
o Therefore it takes a lot of thermal energy to overcome the hydrogen bonds.
o This makes water very stable and a constant temperature, which is important
part of making water a good habitat.
o This also lets water regulate body temperature by cooling the body when it
gets too hot, by absorbing the thermal energy.
- Water has a high latent heat of vaporisaAon.
o How much energy is needed to turn 1gram of liquid into gas.
o Again, due to the energy needed to overcome the hydrogen bonds.
o This lets water “take” heat with it when it evaporates to provide a cooling
affect. For example, when humans sweat the sweat evaporates it removes
some heat.
- Water has a high surface tension.
o This means some insects like pond-skaters can stand on water.
o The hydrogen bond network is strong enough to hold the pond skater.
- Water is less dense as a solid o This is why ice floats.
o The hydrogen bonds push each individual water molecule further away when water freezes. This means the water molecules are more spread out, thus solid water has a lower density.
o This means that water freezes at the top first, maintaining the aquaAc environment underneath and insulaAng it to prevent further freezing and maintaining the habitat.
SOLID LIQUID
Cohesion and adhesion.
Cohesion = the ability of water molecules to be aXracted to other water molecules due to the presence of hydrogen bonds forming between the molecules. This allows water to “sAck” together.
- This helps create surface tension.
Adhesion = the ability of water molecules to be aXracted to other molecules.
This resource was uploaded by: Chloe Laura