Biology 9700/21 Oct Nov 2013 | Cambridge AS Level Past Papers With Mark Scheme

1. Identification and function of mitotic structures in Drosophila melanogaster cells, including homologous chromosomes and centromeres.
2. Biological roles of ions like phosphate, magnesium, and iron in cellular processes, and mechanisms of nitrogen fixation by nitrogenase enzymes.
3. Comparative ion transport in root cells, highlighting membrane protein functions and active transport against concentration gradients.
4. Lung diseases (TB and COPD), alveolar adaptations for gas exchange, and macrophage-mediated immune responses in respiratory tissues.
5. Cholesterol synthesis and transport in liver cells, roles of lipoproteins, and vesicle-mediated secretion processes.
6. Genetic coding errors in sickle cell anemia, impacts of single nucleotide changes on amino acid sequences and protein functionality.
7. Role of keystone species like sea otters in ecosystem stability, trophic interactions, and energy transfer efficiency in marine food webs.