WJEC Biology for A2 Level: Revision Workbook

Ceri’s answers a) Buffer maintains a constant pH. ✗ Ice-cold slows down enzymes. ✓ b) Mitochondria cannot produce carbon dioxide or lactate. ✗ Mitochondria release carbon dioxide when incubated with pyruvate, because pyruvate is hydrolysed during Link, and Krebs cycle. ✓ The supernatant is made from cell cytoplasm which is where glycolysis occurs, so lactate is produced by anaerobic respiration. ✓ c) The results would be the same as for the mitochondria ✓ as all the reactions that produce carbon dioxide occur there. ✗ Ceri achieves 4/9 marks MARKER NOTE Ceri has confused isotonic buffer with pH buffer, and whilst the reason for having the buffer ice-cold could have been more reasoned the idea is there. MARKER NOTE This is purely descriptive, there is no explanation. MARKER NOTE Ceri mentions the reactions but could have included where they take place, i.e. mitochondrial matrix. MARKER NOTE Ceri needs to be clearer as to why, i.e. that reactions in link and Krebs cycle that produce carbon dioxide occur in the mitochondrial matrix. MARKER NOTE Ceri did not explain why carbon dioxide and lactate are not produced when the supernatant is incubated with pyruvate, i.e. because the link and Krebs cycle do not occur in the cytoplasm. EXAM T I P It is important that you refer to stages in respiration and state exactly where they occur. 3.1 Importance of ATP and 3.3 Respiration | 23 Unit 3 Energy, Homeostasis and the Environment Copyright: Sample material