Biology 9700/22 March 2020 | Cambridge AS Level Past Papers With Mark Scheme

1. Structural adaptations of phloem sieve tube elements for sap transport, including the role of sieve plates, cytoplasm, plasmodesmata, and cellulose walls in facilitating sap flow and reducing resistance.

2. Analysis of phosphatidate phosphatase (PAP) enzyme activity, focusing on magnesium ion dependency and substrate concentration effects, linked to enzyme type determination and metabolic roles in triglyceride and phospholipid synthesis.

3. Cardiac cycle events during ventricular diastole, including blood vessel dynamics, valve mechanisms, and blood pressure changes; impact of genetic mutations in sickle cell anemia on hemoglobin structure and oxygen transport efficiency.

4. Structural differences among trachea, bronchi, bronchioles, and alveoli in lung tissue; mitotic cell cycle phases and processes during interphase in respiratory stem cells.

5. Immune system disorders, contrasting mechanisms of myasthenia gravis and HIV/AIDS, with emphasis on the role of antiretroviral therapy (ART) in maintaining T-helper cell counts and analyzing trends in global ART treatment and HIV-related deaths.

6. Parenchyma cell support function through turgor pressure, tonoplast-mediated hydrogen ion transport maintaining acidic vacuole pH, and the adaptive advantage of acid hydrolases functioning exclusively in acidic environments.