1. 1
   A doctor is explaining to a patient why, after eating a carbohydrate-rich meal, their blood glucose concentration rises and then falls back to normal within about two hours. The doctor explains that some of the absorbed glucose is used immediately in respiration, whilst the rest is converted into a storage carbohydrate in the liver and muscles.

   (a)

   What is the storage carbohydrate that excess glucose is converted into in the liver and muscles?

   [1 mark]

   • AStarch
   • BGlycogen
   • CCellulose
   • DGlucagon

   (b)

   Which of the following best describes metabolism?

   [1 mark]

   • AThe sum of all the reactions in a cell or the body
   • BOnly the reactions that release energy in a cell
   • COnly the reaction of respiration in a cell
   • DOnly the reactions that take place in the liver

   (c)

   Explain why it is important for the patient's body to convert excess glucose into glycogen rather than leaving it in the blood.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A gardener is growing tomato plants in a greenhouse. She notices that plants supplied with a nitrate-rich fertiliser grow bigger leaves and develop stronger cell walls than plants grown without fertiliser. She wants to understand how the plants use the glucose produced in photosynthesis, together with the fertiliser, to build these structures.

   (a)

   Which ions are combined with substances made from glucose to form amino acids in the tomato plant?

   [1 mark]

   • ASulfate ions
   • BPhosphate ions
   • CChloride ions
   • DNitrate ions

   (b)

   Which molecule, produced from glucose, combines with glycerol to form lipid (fat and oil) molecules in the plant?

   [1 mark]

   • ACellulose
   • BAmino acids
   • CFatty acids
   • DStarch

   (c)

   Describe how glucose produced in photosynthesis is used to strengthen the cell walls of the tomato plant.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A patient on a high-protein diet has more amino acids in their blood than their body needs for building new proteins. Their doctor explains that the liver breaks down the excess amino acids and that the resulting waste product is removed from the body by the kidneys.

   (a)

   Describe what happens to the excess amino acids in the patient's liver.

   [3 marks]

   (b)

   Explain why it is important that excess amino acids are converted into urea rather than being excreted as ammonia directly, and describe how urea is then removed from the patient's body.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   During a marathon, a runner's muscles carry out many different metabolic reactions at the same time to keep the body functioning: producing energy, building and repairing tissue, and removing waste products. Sports scientists monitoring the runner want to understand how these different reactions are linked together as part of the runner's overall metabolism.

   (a)

   Using your knowledge of metabolism, explain the range of reactions taking place in the runner's muscles and body during and immediately after the marathon, including respiration and the production and removal of waste substances.

   [6 marks]

   (b)

   Metabolism is described as 'the sum of all the reactions in a cell or the body'. Using examples from the runner's body, evaluate how different metabolic reactions work together to build new molecules, store energy and remove waste, in addition to respiration.

   [6 marks]

   Total for question 4: 12 marks

End of questions