Module 2; Biological molecules Flashcards
Structure of water
One atom of oxygen joined to two hydrogens by a covalent bond.
H’s shared electrons are pulled to the oxygen atom, causing each H to be slightly positive.
Oxygen is left slightly negative.
This makes water a polar molecule, a dipole.
What are the features of hydrogen bonding between water molecules?
The slightly negative charge on the oxygen atom is attracted to and forms a hydrogen bond with the slightly positive charge of a hydrogen on another water molecule.
We use the delta sign to show slightly negative and slightly positive.
What are the 5 main properties of water?
1- High specific heat capacity
2- Cohesive and adhesive
3- Hight latent heat of vaporisation
4- Lower density when solid
5- Good solvent
What is meant by a high specific heat capacity of water and what is the benefit of this?
SHC is the energy needed to raise the temperature of a gram of a substance by 1 degree.
H bonds between water molecules can absorb a lot of energy.
Water has a high SHC.
Important bc large fluctuations in temp are not good for aquatic organisms.
What is meant by High latent heat of vaporization and why is it important?
Lots of energy is needed to break the bonds between water molecules to change water from a liquid to a gas. This makes water an excellent coolant.
Roles of water as a coolant.
Sweat evaporates, carries heat away.
Plants transpiration, water evaporates from leaves and carries heat away.
Temperature buffer for chemical reactions in prokaryotes and eukaryotes.
Proper function of enzymes- active in a narrow temp range.
What is cohesion in water?
Cohesion is the attraction between water due to hydrogen bonding.
What are the roles of water being cohesive?
Transport
Transpiration
Blood
Phloem
Surface tension (provides habitat)
Why is surface tension formed?
Water molecules are more attracted to each other than the air.
How do hydrogen bonds behave in water related to cohesion?
They are relatively weak so break and reform constantly, however they occur in such large numbers that water remains cohesive.
What is adhesion?
The attraction between a water molecule and another polar molecule.
What are the roles of cohesion and adhesion together?
The combination of the two is capillary action, this is what allows water to move through the xylem tubes.
Why does water have a lower density when solid?
As water changes state from liquid to solid, each water molecule forms four hydrogen bonds to other water molecules, creating a hexagonal lattice structure. This makes ice less dense than liquid water and is why ice floats.
Why is water being less dense when solid than liquid important?
Ice forms a protective barrier which reduces the rate of heat loss and makes the environment more stable for aquatic organisms.
How does water dissolve substances?
Water is polar and therefore the slightly positive end of water will be attracted to negative ions and vice versa. Water molecules surround each ion and dissolve the substance.
