Help with a Biology AS-Level Question!

Hey guys! I have been stuck on this question for a while and tried looking in my text books and even searching it up on the internet, but there isn't much I have been able to use! Would anyone mind trying it?

a.) Describe why Hydrogen, Iron, Phosphate and Sodium are important ions in organisms. (7 marks)

My teacher said I should write about a paragraph but I don't see how I can! Any help would be much appreciated!

Thanks!

So, hydrogen ions are what determines blood, ECF and cytosol pH (as well as bicarbonate ions). It is the concentration of hydrogen ions in solution that determines its pH, and the pH is important because any small change in pH can damage important proteins, such as enzymes in the cell or transport proteins in the blood. Iron is a pretty easy one; iron ions form complex ions in the haem groups in haemoglobin, which bind to oxygen ligands, allowing us to carry oxygen in our blood. I assume phosphate is important because DNA and ATP contain phosphate groups, and they are both vital molecules in organisms (I don't know if you've done about ATP yet though if you're AS, but it might impress your teacher if you write about it!). And finally sodium is the main determinant of blood osmolarity, i.e. how concentrated bodily fluids are with charged molecules. I can't remember if you do osmosis at AS, but basically, charged ions decrease the water potential of a solution, and thus this solution will draw water into it if there is a solution of a higher water potential on the other side of a semi permeable membrane. Sodium is therefore the most important ion in controlling body fluid levels, because if more sodium is reabsorbed in the kidneys (which is controlled by a hormone called aldosterone) then this will reabsorb more water too back into the blood, and therefore sodium is involved in controlling blood pressure (in fact the kidneys are the main way that blood pressure is controlled). Finally, sodium is the main ion that causes depolarisation in neurones, allowing an action potential to form.

I hope that helps, I can't remember what you're expected to know at AS, so maybe pick out anything you recognise in what I've written, there should be enough to make a small paragraph!