section 2: biological molecules - topic 1: water Flashcards
what are the 5 functions of water?
- it’s a reactant in lots of important chemical reactions, including hydrolysis reactions.
2.it’s a solvent, meaning some substances dissolve in it - most biological reactions take place in solution. - it transports substances - since it’s liquid and a solvent, it can easily transport all sorts of materials, like glucose & oxygen, around plants and animals.
- it helps with high temperature control because it has a high specific heat capacity and a high latent heat of evaporation.
- it’s a habitat - the fact it helps with temp. control, is a solvent, and becomes less dense when it freezes means many organisms can survive & reproduce in it.
what constitutes the structure of water?
the polarity and hydrogen bonding.
describe the polarity of water.
a molecule of water is 1 atom of oxygen joined to 2 atoms of hydrogen by shared electrons.
because the shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each hydrogen atom is left with a slight positive charge.
the unshared negative electrons on the oxygen atom give it a slight negative charge.
this makes water a polar molecule - it has a partial negative charge on one side & a partial positive charge on the other.
describe the hydrogen bonding in water.
the slightly negatively-charged oxygen atoms attract the slightly positively-charged hydrogen atoms of other water molecules.
^ this attraction is called hydrogen bonding & it gives water some of its useful properties.
what are the 5 properties of water?
- high specific heat capacity
- high latent heat of evaporation
- very cohesive
- lower density when solid
- good solvent
description of the high specific heat capacity.
hydrogen bonds give water a high specific heat capacity - this is the energy needed to raise the temperature of 1g of a substance by 1 degree celsius.
the hydrogen bonds between water molecules can absorb a lot of energy, so water has a high specific heat capacity as it takes a lot of energy to heat it up.
this means water doesn’t experience rapid temperature changes, which is one of the properties that makes it a good habitat - the temp. under water is likely to be more stable than it is on land.
description of the high latent heat of evaporation.
it takes a lot of energy (heat) to break the hydrogen bonds between water molecules - so water has a high latent heat of evaporation as a lot of energy is used up when water evaporates.
this is useful for living organisms because it means water is great at cooling things.
^ this is why some mammals sweat when they’re too hot - when sweat evaporates, it cools the surface of the skin.
description of the cohesion.
cohesion is the attraction between molecules of the same type.
water molecules are very cohesive because they’re polar.
this helps water to flow, making it great for transporting substances.
it also helps water to be transported up plant stems in the transpiration stream.
description of the lower density when solid.
water molecules are held further apart in ice than they are in liquid water because each water molecule forms 4 hydrogen bonds to other water molecules, making a lattice shape.
^ this makes ice less dense than liquid water - why ice floats.
this is useful for living organisms because, in cold temps, ice forms an insulating layer on top of water - the water below doesn’t freeze.
so organisms that live in water, like fish, don’t freeze and can still move around.
description of it being a good solvent.
a lot of important substances in biological reactions are ionic (i.e. salt).
^ this means they’re made from 1 positively-charged atom & 1 negatively-charged atom (i.e. salt is made from a positive sodium ion & a negative chloride ion).
because water is polar, the slightly positive end of a water molecule will be attracted to the negative ion & vice versa.
this means the ions will get totally surrounded by water molecules.
