Aerobic respiration: glycolysis and the Krebs cycleEdexcel A-Level Biology A: Mind map

Exam questions on Aerobic respiration: glycolysis and the Krebs cycle

1. A student is calculating the energy yield of the first stage of respiration in a yeast cell. This stage takes place in the cytoplasm. It begins with the phosphorylation of a hexose sugar and ends with the formation of pyruvate.
   Explain why the conversion of pyruvate to lactate allows glycolysis to continue when no oxygen is available.2 marks
2. A biochemist incubates isolated, intact mitochondria in a solution containing pyruvate, coenzyme A, NAD, FAD and ADP, with plenty of oxygen. She collects the gas released and analyses the compounds that accumulate during the reactions that take place in the mitochondrial matrix.
   Calculate the total number of molecules of reduced NAD and of carbon dioxide produced in the link reaction and Krebs cycle from one molecule of glucose. Show your working.2 marks
3. Glycolysis takes place in the cytoplasm of a cell, whereas the link reaction and the Krebs cycle take place in the mitochondria. A mitochondrion has a double membrane, and its inner membrane is folded into cristae that enclose a fluid matrix. A student claims that it makes no difference where in the cell these stages happen.
   Explain why the link reaction and the Krebs cycle take place in the mitochondria and not in the cytoplasm.3 marks