Biology 9700/02 Oct Nov 2001 | Cambridge AS Level Past Papers With Mark Scheme

1. Plant stem structures: xylem (A) for water transport, lignified walls for support; companion cell (C) supports phloem transport of photosynthetic products.

2. Alveoli in smokers vs. non-smokers: reduced elasticity (X fibers), enlarged air spaces impair gas exchange; smoking-linked lung cancer evidenced by higher incidence rates and experimental induction in animal models.

3. Polypeptide and polysaccharide distinctions: amino acids form peptides via peptide bonds, while saccharides form polysaccharides with glycosidic linkages; collagen′s tensile strength from cross-linking and helical structure, cellulose from hydrogen bonds and microfibril arrangements.

4. Protein synthesis: mRNA translation to polypeptides on ribosomes; amino acid alterations by base sequence mutations affect protein functionality.

5. Phagocytes: engulf bacteria via endocytosis; lysosomal enzymes degrade pathogens; electron microscopy reveals cellular ultrastructure not visible under light microscopy.

6. Disease transmission: bacterial origin of cholera and TB, vector-based malaria transmission, and sexually transmitted HIV; sickle cell prevalence in malaria-endemic areas due to heterozygote advantage reducing infection severity.