2020 Paper

• Describe how mRNA is formed by transcription in eukaryotes

  • MUST refer to RNA nucleotides / polymerase when describing transcription
• Describe how a polypeptide is formed by translation of mRNA - missed mark points:

  • Start codon on mRNA! associates with a ribosome
  • tRNA anticodons bind to COMPLEMENTARY mRNA codons
  • The use of ATP in the formation of peptide bonds was rarely seen
  • tRNA released (after amino acid joined to polypeptide);
  • The ribosome moves along the mRNA to form the polypeptide
• Describe gene mutation and describe how it has a positive effect and no effect on an individual [4 marks]

  • Few students demonstrated the understanding that any mutation would result in a new allele being formed
  • Gene mutation must expand to the idea of increased survival chances or reproductive success
• Describe gene mutation and describe how it has a positive effect and no effect on an individual [4 marks]

  • No effect on individual - missed marking points:
  • 3. Genetic code is degenerate so amino acid sequence may not change
  • OR Mutation is in an intron so amino acid sequence may not change
  • 4. Does change amino acid but no effect on tertiary structure
  • 5. New allele is recessive so does not influence phenotype;
• Describe the role of micelles in the absorption of fats into cells lining the ileum [3 marks]

  1. Micelles include bile salts and fatty acids
  2. Make the fatty acids (more) soluble in water
  3. Bring/release/carry fatty acids to cell/lining (of the ileum)
  4. Maintain higher concentration of fatty acids to cell/lining (of the ileum)
  5. Fatty acids absorbed by diffusion;
• Explain why death of alveolar epithelium cells reduces gas exchange in human lungs

  1. Reduced surface area
  2. Increased distance for diffusion
  3. Reduced RATE of gas exchange / slower gas exchange

  Examiners Report = at A-Level, students should be able to discuss changes in the RATE! of diffusion
• • Thrown by 'allergic reaction' rather than primary and secondary immune response (AO1)
  • Answers oftened lacked detail of formation of memory cells SO larger and faster production of antibodies at repeated exposure
• Figure 5 (shows percentage of cells going through DNA replication)

  • SHOWS DNA Replication started EARLIER!
  • NOT more cells undergoing DNA Replication
  • THEREFORE leads to a tumour - which is abnormal mass of cells
• 2020 Q9.4 A Jounralist saw figure 10 and suggested future increases in atmospheric CO2 concentration could result in less transpiration. Evaluate his suggestion [4 marks]

  • MP1 = MUST DESCRIBE THE CORRELATION, not just state negative correlation ie Increasing carbon dioxide (concentration) shows decreased stomatal DENSITY;
  • MP2 = FEWER stomata means less transpiration
• 2020 paper - increasing concentration of carbon dioxide, reduced stomata density

  • No idea how long stomata are open for
  • Other factors affect transpiration (accept named factors)
  • No idea the size of stomata
  • No idea if leaf size has changed
  • No idea if this is true for all species of plant
  • SAME Volume of carbon dioxide can be absorbed for photosynthesis with smaller number of stomata