water (biomols) Flashcards
what does polar mean
a polar molecule is one w an uneven charge distribution across it. so one part of the molecule is slightly negative + another part slightly positive
(polar does not mean the same as charged or ion)
why is water polar
water consists of 2 hydrogen atoms covalently bonded to 1 oxygen atom, they share electrons. the oxygen has a greater number of protons in its nucleus so it exerts a stronger attraction for the shared electrons, this means that the oxygen atoms becomes slightly negative and the 2 hydrogen atoms are slightly positive.
(theres a slight charge imbalance across the water molecule)
what does a polar nature mean for water
the water molecules attract eo and hydrogen bonds will form between water molecules
what is a hydrogen bond
a bond formed between a hydrogen atom + an electronegative atom
why is water is a liquid at room temp
water molecules constantly move around, as the molcules move around they continuously make and break hydrogen bonds, these hydrogen bonds between water molecules make it more difficult for the molecules to escape to form a gas. so water is a liquid at room temp, and it has a high bp
what are the advantages of water being liquid at room temp
- water is a habitat
- useful transport medium (xylem transports it)
- chemical reactions
- forms cytoplasm, tissue fluid, plasma
why is water a good solvent
since water is polar, anything that is an ion/charged/or polar can dissolve in it. (essential for life as all cellular reactions take place in solution). (this means various molecules and ions can dissolve in the blood plasma).
as water is polar, the slightly positive end of a water molecule is attracted to the negative ion, and the slightly negative end of a water molecule will be attracted to the positive ion - the ions will get surrounded by water mols = they’ll dissolve
(important as important ions can dissolve in water in blood to be transported around the body) (and in plants, water allows dissolved substances to be carried in xylem+phloem
what does solvent + solute make
a solution
why is water less dense when solid (ice)
its doe to water being polar. the water molecules in ice are held further apart bcos each water molecule forms 4 hydrogen bonds to other water molecules, making a spaced out lattice structure. the lattice is less dense than liquid water so the ice floats.
why is water being less dense as a solid (ice) useful for living organisms
floating sheets of ice are good for seals/polar bears to travel on.
as ice floats, only the top layer the sea freezes so fish are able to swim and survive under the ice.
the ice layer on top insulates the water below it which protects the water below from freezing - this allows animals to continue to live.
what is cohesion
its the force of attraction between molecules of the same type.
why is their cohesion between water molecules
this occurs between water molecules due to their polar nature (hydrogen bonds from). this helps water to flow as one mass which makes it useful for transporting substances, this is very useful in plants where water has to move from the roots to the leaves - where it evaporates from the leaves.
what allows adhesion between water molecules and cellulose xylem wall
hydrogen bonds
what is adhesion
its the force of attraction between different molecules, this is an additional force that also helps the water molecules to move upwards.
as well as cohesion being seen between water molecules, where else can it be seen
cohesion can be seem on the surface of water, this is surface tension. the water mols on the surface are hydrogen bonded to the water molecules underneath, and are more attracted to those than to the air molecules above. this means the surface of the water contracts, giving it the ability to resist force.
