Water (page 20 - 21) Flashcards
WhaWhat percentage do water make up of a cells contents?
about 80%. It has loads of important functions, inside and outside cells.
Water is a reactant in loads of important chemical reactions including what?
hydrolysis reaction (see page 22).
Water is a solvent, what do this mean?
it means some substances dissolve in it.
most biological reactions take place in what solution, give examples?
Water, e.g. in the cytoplasm of eukaryotic and prokaryotic cells, - so water is pretty essential.
Water transports substances why?
the fact that it’s a liquid and a solvent means it can easily transport all sorts of materials, like glucose and oxygen, around plants and animals.
Why do water help with temperature control?
because it has a hight specific heat capacity and a high latent heat of evaporation.
Why is water a habitat?
the fact that it helps with temperature controk, is a solvent and becomes less dense when it freezes, (see page 21), means many organisms can survive and reproduce in it.
Examiners like asking you to relate structure to properties and function, so make sure you know the structure of water.
What is a molecule of water (H²O)?
it is one atam of oxygen (O) joined to two atoms of hydrogen (H²) by shared electrons.
With the water molecule, because the shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each hydrogen atom is left with what charge?
a slight positive charge.
regarding a water molecule what happens to the unshared negative electrons on the oxygen atom regarding its charge?
it is left with a slight negative charge.
This make water polar.
What do a polar molecule mean?
it has a partial negative (δ-) charge on one side and a partial positive (δ+) charge on the other
δ is the greek letter ‘delta’, so you read δ- as delta negative.
look at diagram 1 on page 20 for water molecule. - the slightly negatively-charged oxygen atoms attract the slightly positively-charged hydrogen atoms of other water molecules.
This attraction is called hydrogen bonding and it gives water some of its useful properties.
Hydrogen bonds give water a high or low specifit heat capacity/
gives a high specific heat capacity.
What is specific heat capacity?
it is the energy needed to raise the temperature of 1 gram of a substance by 1°C.
The Hydrogen bonds between water molecules can absorb a lot of energy, what do this mean?
water has a high specific heat capacity - it takes a lot of energy to heat it up.
this means water doesnt experience rapid temperature changes, which is one of the properties that makes it a good habitat - the temperature under water is likely to be more stable than it is on land.
Hydrogen Bonds give water a ‘High Latent Heat of Evaporation’, what do this mean?
1) it takes a lot of energy (heat) to break the hydrogen bonds between water molecules.
2) so water has a high latent heat of evaporation - a lot of energy is used up when water evaporates.
3) this is useful for living organisms because it means waters great for cooling things. this is why some mannals like us sweat when they’re too hot. when sweat evaporates, it cools the surface of the skin.
