Biology 9700/21 Oct Nov 2023 | Cambridge AS Level Past Papers With Mark Scheme

1. Active transport of potassium ions into red blood cells through sodium-potassium pumps, maintaining ionic gradients essential for cellular function.

2. Comparison of sodium ion transport via active processes and oxygen diffusion across membranes by passive means.

3. Role of the chloride shift in carbon dioxide transport as bicarbonate ions in red blood cells to maintain ionic balance and efficient gas exchange.

4. Protein synthesis pathways in epithelial cells, emphasizing the roles of rough endoplasmic reticulum and Golgi apparatus in extracellular protein secretion.

5. Hydrogen bonding in xylem vessel cohesion and adhesion, facilitating water transport and cooling via transpiration.

6. Insights into HIV infection rates and factors affecting transmission, along with the physiological consequences of related conditions like cardiac tamponade.

7. Structural analysis of alveolar surfactants, their synthesis, secretion, and the impact of cholesterol on surfactant release and function in lung epithelium.

8. DNA replication mechanisms, focusing on the roles of nucleotides, DNA polymerase, and the effects of modified nucleotides on chain elongation.