water + ions Flashcards
why is water vital to living organism
it is a metabolite in lots of important metabolic reactions - including condensation and hydrolysis reactions
it is a solvent - some substances dissolve in it, most metabolic reactions occur in solution eg in cytoplasm of cells
water helps with temperature control - high latent heat of evaporation and high specific heat capacity
water molecules are very cohesive - which helps water transport in plants as well as transport in other organisms
structure of water molecules
a molecule of water is one atom of oxygen joined to two 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 slightly positive charge
the unshared negative electrons on the oxygen atom give it a slight negative charge
this makes water a polar molecule - partial negative charge on one side and a partial positive charge on the other
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 provides water will useful properties
metabolite
many metabolic reactions involve a condensation or hydrolysis reaction
a hydrolysis reaction requires a molecule of water to break a bond
a condensation reaction releases a molecule of water as a new bond is formed
for example, amino acids are joined together to make polypeptides (proteins) by condensation reactions
energy from ATP is released through a hydrolysis reaction
high latent heat of vaporisation
it takes a lot of energy to break down the hydrogen bonds between water molecules
so water has a high latent heat of vaporisation - a lot of energy is used up when water evaporates
this is useful for living organisms because it means they can use water loss through evaporation to cool down
buffer changes in temperature
the hydrogen bonds between water molecules can absorb a lot of energy
so water has a high specific heat capacity - it takes a lot of energy to heat it up
this is useful for living organisms as it means that water doesn’t experience rapid temperature changed - underwater habitats - the temperature underwater is more stable than on land - helping organisms to maintain a constant internal body temperature
good solvent
a lot of important substances in metabolic reactions are ionic - this means that they are made from one positively charged atom or molecule and one negatively charged atom or molecule
because water is polar, the positive end of a water molecule will be attracted to the negative ion, and the negative end of the water molecule will be attracted to the positive ion
this means the ions will get totally surrounded by water molecules - they’ll dissolve
strong cohesion between water molecules
cohesion is the attraction between molecules of the same type
water molecules are very cohesive because they’re polar
strong cohesion helps water to flow, making it great for transporting substances for example, it’s how water travels in columns up the xylem in plants
strong cohesion also means that water has a high surface tension when it comes into contact with air - this is the reason that pond skaters can form a habitat on the water’s surface
what is an ion
an ion is an atom that has an electric charge
what is a cation
an ion with a positive charge
what is a anion
an ion with a negative charge
what is an inorganic ion
an ion that doesn’t contain carbon
where are inorganic ions found
in solution, in the cytoplasms of cells and in the body fluids of organisms
iron ions and haemoglobin
haemoglobin is a large protein that carried oxygen around the body, in the red blood cells
it’s made up of four different polypeptide chains, each with an iron ion (Fe2+) in the centre
it’s the Fe2+ that actually binds the oxygen in haemoglobin - making it a key component
when oxygen is bound, the Fe2+ ion temporarily becomes an Fe3+ ion, until oxygen is released
hydrogen ions and pH
pH is calculated based on the concentration of hydrogen ions in the environment. The more H+ present, the lower the pH
sodium ions help transport glucose and amino acids across membranes
glucose and amino acids need help crossing cell membranes
a molecule of glucose or an amino acid can be transported into a cell alongside sodium ions (Na+)
This is known as co-transport
