A-level Biology Essay Question

Hello, I wrote an answer to this essay question and I was wondering if anyone could read through it and maybe give me a score out of 25 like an examiner would?
Inorganic ions include those of sodium, phosphorus and hydrogen. Write an essay to describe how these and other inorganic ions are used in living organisms. (25 marks)
Phosphate ions are important as they form phospholipids which are necessary in cell membranes. The phosphate group on a phospholipid is polar and hydrophilic, in a phospholipid bilayer the hydrophilic heads face outwards allowing it to form hydrogen bonds with water and act as a partially permeable membrane. The phospholipid bilayer is used in living organisms to allow lipid soluble molecules to enter and leave the cell as well as restricting water soluble molecules from entering and leaving the cell. Without the phosphate ion that is used to make up the phospholipid molecule, there would be no cell membranes and therefore there would be no barrier between the internal and external cell environment.
Phosphate ions are also used in the formation of ATP. ATP is made up of adenine, ribose and three phosphate groups. The bonds between the phosphate groups are unstable and have a low activation energy. When ATP is hydrolysed into ADP and Pi, the broken bond from the inorganic phosphate releases a large amount of energy. This is used in living organisms as the energy released can be used in processes such as active transport so that molecules such as sodium can be actively transported or to provide energy for muscle contraction. The phosphate ion is important as it contains energy for these processes in its bonds and without the ion we would not be able to use ATP as an immediate energy source.
Sodium ions are important as they are involved in the cotransport of glucose and amino acids across the epithelial cells. Sodium is actively transported out of epithelial cells by the sodium-potassium pump and into the blood. This creates a concentration gradient where there is a high concentration of sodium ions in the lumen of the intestine and a low concentration inside the epithelial cells. In living organisms, sodium ions are used as a co-transport molecule since sodium ions diffuse down the concentration gradient into the epithelial cells whilst also carrying glucose or amino acid molecules into the cell. This co-transport ensures that glucose and amino acid molecules are completely absorbed to be used as an energy source or to build and repair tissues. Without sodium ions, glucose and amino acids would not be absorbed into the epithelium to be used by the organism.
Hydrogen ions are used in the light dependent stage of photosynthesis in plants. In the thylakoid space, the photolysis of water takes place which releases two hydrogen ions. A proton pump actively transports hydrogen ions from the stroma into the thylakoid space to create a concentration gradient. Since there is a high concentration of H+ ions in the thylakoid space and a low concentration in the stroma, the hydrogen ions diffuse down the concentration gradient through an ATP synthase channel. This causes the structure of the ATP synthase enzyme to change which catalyses the formation of ATP from ADP and Pi. ATP and NADPH are used to act as an energy source to form sugars in the Calvin cycle. This shows that hydrogen ions are important as they catalyse the formation of ATP which provides energy for the plant to use.
Nitrate ions are absorbed from the soil by plant roots using active transport. The nitrate ions are then reduced to ammonium ions to be used to make amino acids. These amino acids are used by the plant to make proteins. Nitrate ions are important as they are also used to synthesise DNA and chlorophyll. Proteins are used to make enzymes and for growth, DNA is required for cell division and to reproduce, chlorophyll is used for photosynthesis. Without nitrate ions, plants would not be able to grow, reproduce or carry out photosynthesis making it an essential inorganic ion.

My Own Assessment: 19 out of 25
Benefits:Your answer reflects a good understanding of biological principles that include phosphate and sodium and hydrogen ion and nitrate functions. Your explanations are good and comprehensive in phospholipid structure, membrane function, ATP structure, processes of hydrolysis, functioning of the sodium-glucose cotransport system, and photosynthesis' chemiosmosis. You do a good job of relating each ion structure to its biological role.
Functions of phosphate in phospholipids and ATP are especially well delineated.
Improvement:To move up a mark group, mention more ions, like calcium, magnesium, chloride, or potassium, as you would commonly anticipate a higher range for a question of this score.
A few of these statements need to be corrected. For example, describing ATP synthase as a channel is inaccurate; it is actually an enzyme. Hydrogen ions' function in ATP synthesis is to supply energy rather than to catalyze the reaction itself.
Make your essay flow by having improved part-to-part transitions. While material on phosphate is thorough, it would be desirable to have a more balanced coverage of other ions as well. It is also important to include sodium's part in conducting nerve impulses.
My Own Comments: You have shown good biological understanding with good facts. To make it better, aim to cover more ions with a little less information on each, and make it balanced throughout the specification.
A short introduction and conclusion would also make it easier to set your answer out.
The marks will typically divide into understanding/knowledge (15-16 marks) and essay writing (9-10 marks).
Ciao,
Sandro