AQA Tags Archives: Inorganic Ions

Inorganic ions

Biological molecules (AQA AS Biology) PART 8 of 8 TOPICS



TOPICS: Carbohydrates  Lipids  Proteins  Many proteins are enzymes  Nucleic acids  ATP  Water  Inorganic Ions

Inorganic ions:

Inorganic ions can either occur in high concentrations or low concentrations in the cytoplasm and body fluids.

H+ ions regulate how acidic a solution is where the more protons there are the more acidic a solution is.

Iron ions in haemoglobin bind to oxygen so that oxygen can be released to respiring cells (more on this in a later module in AS, check it out).

Sodium ions are used for the transfer of glucose to the cells by co transport:

  • Sodium ions are pumped out of the cell into the blood by the sodium-potassium pump powered by Pi. (Potassium ions come in from the blood also but have no relevance to co transport)
  • This causes the concentration of sodium ions in the cell to drop so the sodium ions from the lumen comes into the cell down its concentration gradient along with glucose going up its concentration gradient by facilitated diffusion through the coupled transport protein. This is called a symport.

NB: Sodium-potassium pump is on the opposite side to the coupled transport protein of the cell when glucose is transported which is described above. When it comes to amino acids the sodium-potassium pump is on the same side to the coupled transport protein of the cell. Sodium ions are actively transported into the ileum from the epithelial cells instead of into the blood. Then the sodium ions diffuse back in along with amino acids into the epithelial cells.

Phosphate ions are used to make nucleotides, ATP and making bones strong by reacting with calcium to make calcium phosphate [Ca3(PO4)2]

] That is all that you need to know about inorganic ions [


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TOPICS: Carbohydrates  Lipids  Proteins  Many proteins are enzymes  Nucleic acids  ATP  Water  Inorganic Ions


Monosaccharides are the monomers from which larger carbohydrates are made. These include glucose, fructose and galactose. Only the structure of glucose needs to be known for the whole of a level which is illustrated as follows on either side. Notice the OH group and the hydrogen are on opposite sides on carbon number 1 (there is no particular way of counting the carbons however exam questions will refer to this particular carbon as carbon 1. Number 4 is always the carbon opposite carbon number 4).

Two monosaccharides form a disaccharide in any combination where glucose is always one of the reactants –

Glucose + Glucose = Maltose

Glucose + Fructose = Sucrose

Glucose + Galactose = Lactose


Polysaccharides are made by the condensation reactions of many monosaccharides. Glycogen and starch are made from many alpha glucose molecules and cellulose is formed from many beta glucose molecules. As part of AQA, you need to know the characteristics of these three polysaccharides:

Starch:  Is insoluble so it does not draw water in by osmosis. Starch will not diffuse easily out and is stored in a tight place because it is compact due to the coils it has. It can easily be hydrolysed into alpha glucose molecules which can used in respiration. Starch is found in plants.

Glycogen: Is shorter and is more branched than starch. It is more readily hydrolysed than starch.

Cellulose: Is made up of many straight unbranched chains of beta glucose molecules that run parallel to one another. Hydrogen bonds link these chains together which gives cellulose its strength which we are familiar with when talking about cell walls.

Knowing the tests for the sugars and for starch has to be known for the exam:

Reducing sugars (includes glucose, fructose, galactose, maltose and lactose):

  • Add Benedict’s reagent and heat


  • Blue to brick red precipitate

Non-reducing sugar (sucrose):

  • Add HCl (hydrochloric acid) and boil
  • Add NaOH (sodium hydroxide) to neutralise
  • Add Benedict’s reagent


  • Blue to brick red precipitate


  • Add Iodine Potassium solution


  • Blue-black colourisation


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