Inorganic ionsAQA A-Level Biology: Subtopic test

1. 1
   Blood plasma contains sodium ions at a concentration of about 140 mmol dm⁻³, whereas free iron ions are present at less than 0.02 mmol dm⁻³. Most of the iron in blood is found inside red blood cells, as part of haemoglobin.

   (a)

   Which ion is a component of haemoglobin and binds to oxygen so that it can be transported in the blood?

   [1 mark]

   • AMagnesium ion, Mg²⁺
   • BIron(II) ion, Fe²⁺
   • CSodium ion, Na⁺
   • DCalcium ion, Ca²⁺

   (b)

   Which conclusion about inorganic ions is supported by the information about plasma?

   [1 mark]

   • AAll ions occur at similar concentrations in body fluids
   • BIron ions have no role because their concentration is low
   • CSodium ions are found only inside red blood cells
   • DIons occur at different concentrations in body fluids and each type has a specific role

   (c)

   A person's diet is deficient in iron. Explain why this reduces the amount of oxygen their blood can carry.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   During a 400 m sprint, a runner's muscle cells respire anaerobically and produce lactic acid. The pH of the muscle cell cytoplasm falls from 7.1 to 6.6 by the end of the race.

   (a)

   What happens to the concentration of hydrogen ions in the muscle cell when its pH falls from 7.1 to 6.6?

   [1 mark]

   • AIt increases
   • BIt decreases
   • CIt stays the same
   • DIt falls to zero

   (b)

   Which statement about the muscle cell cytoplasm at pH 6.6 compared with pH 7.1 is correct?

   [1 mark]

   • AIt is more alkaline
   • BIt is neutral
   • CIt is more acidic
   • DIt is unaffected by hydrogen ions

   (c)

   Explain why the pH of the muscle cell cytoplasm falls during the sprint.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A grower finds that tomato plants given a nutrient solution that lacks phosphate ions grow slowly, make few new cells and have small roots. Radioactively labelled phosphate ions (³²P) are then supplied to a healthy group of plants to find out where phosphorus is used.

   (a)

   Explain why a lack of phosphate ions reduces the growth of the plants.

   [3 marks]

   (b)

   Name two molecules in the plant cells that would contain the radioactive label, and explain why each would contain it.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Epithelial cells lining the ileum absorb glucose and amino acids from the gut lumen, even when the concentration of these molecules inside the cell is higher than in the lumen. A student making revision notes lists sodium ions, iron ions, phosphate ions and hydrogen ions as examples of inorganic ions that each have a particular role in a mammal.

   (a)

   Explain the role of sodium ions in the absorption of glucose and amino acids by the epithelial cells of the ileum.

   [6 marks]

   (b)

   Describe the roles of iron ions, phosphate ions and hydrogen ions in a mammal.

   [6 marks]

   Total for question 4: 12 marks

End of questions