A machine keeps a donated liver and a donated kidney functioning separately. Blood plasma with a urea concentration of 4.0 mmol dm−34.0\,\mathrm{mmol\,dm^{-3}}4.0mmoldm−3 enters each organ. Assume any change in urea concentration is mainly due to urea production or removal.
Which prediction about the urea concentration in the plasma leaving each organ is correct?
Higher than 4.0 mmol dm−34.0\,\mathrm{mmol\,dm^{-3}}4.0mmoldm−3 leaving the liver, because it makes urea from excess amino acids; higher than 4.0 mmol dm−34.0\,\mathrm{mmol\,dm^{-3}}4.0mmoldm−3 leaving the kidney, because it also makes urea as it filters plasma
Lower than 4.0 mmol dm−34.0\,\mathrm{mmol\,dm^{-3}}4.0mmoldm−3 leaving the liver, because it converts urea into amino acids for making proteins; lower than 4.0 mmol dm−34.0\,\mathrm{mmol\,dm^{-3}}4.0mmoldm−3 leaving the kidney, because it removes urea into urine
Lower than 4.0 mmol dm−34.0\,\mathrm{mmol\,dm^{-3}}4.0mmoldm−3 leaving the liver, because it stores urea in the same way as it stores glycogen; higher than 4.0 mmol dm−34.0\,\mathrm{mmol\,dm^{-3}}4.0mmoldm−3 leaving the kidney, because it returns filtered urea to the blood
Higher than 4.0 mmol dm−34.0\,\mathrm{mmol\,dm^{-3}}4.0mmoldm−3 leaving the liver, because it makes urea from excess amino acids; lower than 4.0 mmol dm−34.0\,\mathrm{mmol\,dm^{-3}}4.0mmoldm−3 leaving the kidney, because it removes urea into urine
94 exam-style questions on Edexcel GCSE Biology 7.4 Blood glucose and the urinary system, covering 7.4.1 Insulin and blood glucose control, 7.4.2 Glucagon and blood glucose regulation, 7.4.3 Type 1 and type 2 diabetes, 7.4.4 Structure of the urinary system, 7.4.5 Structure and function of the nephron, 7.4.6 ADH and water regulation, 7.4.7 Treatments for kidney failure, and 7.4.8 Production of urea in the liver. Each one has a worked solution and a mark scheme showing where the marks go.