water and inorganic ions

learn starred cards - others are just for y12 context/understanding

explain fully why water is a dipole:

water molecule is charged - O has a 𝛿- charge and the H atoms have a 𝛿+ charge

what are the key properties of water?

• is a metabolite

• is a solvent

• high specific heat capacity

• high latent heat of vaporisation

• strong cohesion

why is the e^- distribution on a H₂O molecule uneven?

• O is more electronegative than the H atoms

• so -vely charged e^- are more attracted to the O atom

explain H bonding between water molecules:

• e^- are more attracted to the O atom as it is more electronegative

• this means that O has a 𝛿- charge and the H atoms have a 𝛿+ charge

• the more electronegative 𝛿- O atom becomes attracted to the more electropositive 𝛿+ H atom of another polar molecule

what is the significance of the H bonds between water molecules?

• allows for strong cohesion → surface tension

• gives water high specific heat capacity - many H bonds can absorb a large amount of energy before being broken

what is cohesion?

the attraction of molecules for other molecules of the same kind

what is the significance of cohesion?

• supports columns of water in tube-like transport cells of plants

• produces surface tension where water meets air, supporting small organisms

what is adhesion?

the attraction of molecules for other molecules of a different kind

what is surface tension?

where a liquid’s SA is minimised and acts like a skin as a result of cohesion, allowing it to resist an external force (often occurs when water meets air)

give 3 factors in which surface tension is significant:

• capillary action

• insects walking on water

• formation of droplets

how is surface tension significant in capillary action?

can be seen through transpiration: surface tension (and adhesive forces between water and the xylem) allow the transpiration stream to travel up the xylem, against gravity

how is surface tension significant in insects walking on water?

surface tension creates a skin strong enough to support small organism e.g. pond skaters

how is surface tension significant in the formation of droplets?

surface water molecules pull inwards, minimising SA and forming droplets e.g. water beading

what does it mean for water to be a good metabolite?

is used/formed in many metabolic reactions, e.g. condensation and hydrolysis reactions

why is water a good solvent?

• ionic compounds and polar molecules can easily dissolve/disassociate in it

• this is because water is a polar molecule - +ve end attracts +ve ions and -ve end attracts -ve ions

why is it useful for water to be a good solvent?

• so metabolic reactions can occur faster in solution

• so allowing transport of substances

what does it mean for water to have a relatively high specific heat capacity?

it requires a lot of energy to raise the temperature of 1g of water by 1^oC

why is it significant that water has a relatively high specific heat capacity?

• buffers changes in temperature (as most organisms consist primarily of water)

• takes a lot of heat/energy to change temperature

what does it mean for water to have a relatively large latent heat of vaporisation?

it requires a lot of energy to evaporate 1g of water (high bpt)

why is it significant for water to have a high specific latent heat of vaporisation?

provides a cooling effect (w/ little loss of water) through evaporation

what is the role of Fe²⁺ ions in a cell?

haemoglobin binds with/associates with/transports/loads oxygen

what is the role of Na⁺ ions in cells?

• co-transport of glucose/AAs (into cells)

• Na⁺ moved out by active transport/Na-K pump

• creates a Na⁺ conc/diffusion gradient

• affects osmosis/water potential

what is the role of PO₄^3- ions in cells?

• affects osmosis/water potential

• joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/nucleotides

• used in/to produce ATP

• phosphorylates other compounds making them more reactive

• hydrophilic/water soluble part of phospholipid bilayer

compare and contrast the processes by which water and inorganic ions enter cells (3)