2023 Paper 1 Question

• Give the three structural features found in ALL virus particles AND describe the function of one of these features.

  1. Genetic material, capsid and attachment protein
  2. Genetic material codes for viral protein
  3. Capsid protects the genetic material/RNA/DNA
  4. Attachment protein bind to receptors on cell
• Explain why viruses are described as acellular and non-living. [2 marks]

  1. Acellular no cell-surface membrane OR Not made of cells OR no organelles / no cytoplasm
  2. Non-living have no metabolism/metabolic reactions OR Cannot independently move/respire/replicate/excrete OR Have no nutrition
• Give one reason why antibiotics are not effective against viruses.[1 mark]

  • Do not have bacterial structures/enzymes OR
  • Do not have metabolic processes
  • OR Do not have a cell wall/murein
  • Do not have ribosomes
  • Viruses do not make protein / do not replicate (on itself!)
• Use Figure 1 to describe three ways the structure of chitin is similar to the structure of cellulose. [3 marks]

  1. Alternate monomers/glucoses are flipped/upside down/rotated by 180 degrees
  2. Joined by glycosidic bonds;
  3. Forms straight/linear/unbranched chains/molecules
  4. + Contains 1-4 linkages / bonds
  5. + Have beta glucose

  IGNORE both contain C, H, O (elements comparing)

  
• Explain the importance of one adaptation of the gas exchange surface in the tracheal system of an insect. [2 marks]

  1. TRACHEOLE (wall) thin/one cell thick
  2. So rapid diffusion into cells
  3. So short diffusion pathway/distance

  3. Tracheoles enter/supply tissues/muscle fibres;

  4. So diffusion direct into cells

  short diffusion pathway/distance

  so rapid diffusion into cells
• Gas exchange does not occur in the tracheae.

  Explain the importance of one adaptation of the gas exchange surface in the tracheal system of an insect. [2 marks]

  • 5. Tracheoles are highly branched / large number / many tracheoles
  • 6 So short diffusion distance/pathway
  • OR
  • So large surface area for rapid diffusion
• Lignin is a polymer found in the walls of xylem vessels in plants. Lignin keeps the xylem vessel open as a continuous tube.

  Explain the importance of the xylem being kept open as a continuous tube. [3 marks]

  1. Allows unbroken water column OR So no barrier to water movement = the idea of continuous flow / stream of water
  2. Cohesion from Hydrogen bonds / polar attraction between all water molecules
  3. Evaporation / transpiration causes tension in column
  4. Water moves from xylem into cells causes tension
  5. To pull up water creates tension in xylem
• Describe two functions of the Golgi apparatus in a eukaryotic cell.

  [2 marks]

  1. Modify/package/transport protein
  2. Make/transport glycoproteins;
  3. Modify/package/transport lipids
  4. Make/transport glycolipids;
  5. Forms/releases vesicles/lysosomes;
• In Africa today, most of the human population are resistant to malaria caused by P. vivax.

  Use your knowledge of natural selection to explain why this resistance is so common in Africa. [4 marks]

  1. Mutation produced ALLELE;
  2. Those with allele/resistance less likely to/do not get malaria/P viva
  3. Those with allele/resistance survive malaria/P vivax;
  4. So more likely to reproduce and pass on the allele;
  5. Over generations allele frequency increases;
• NATURAL SELECTION QUESTIONS

  4. Accept description of increasing frequency of allele

  • eg ‘higher proportion’, ‘more common’
  • but ‘ignore increase in number of allele’
• The toxins damage the cells lining the ileum, causing them to lose their microvilli.

  The damage to the cells reduces the absorption of the products of digestion and

  reduces the absorption of water, resulting in diarrhoea.

  1. Reduced surface area OR Fewer co transport/carrier/channel proteins;
  2. Decreases water potential in ileum/lumen OR
  3. Increases water potential in cells;
  4. So water moves out of cells/into ileum by osmosis OR
  5. so less/no water moves into cells/out of ileum by osmosis;
• Use Figure 4 to suggest how this passive immunity would work and which patients

  should be offered this anti-toxin antibody. [3 marks]

  • Anti-toxins/antibodies cause phagocytosis/ destruction/agglutination/neutralisation of toxin
  • Accept preventing toxin binding / damaging cells lining the ileum (AO2)
• Suggest why several bacterial species have been renamed in the recent years [1 mark]

  • DNA/mRNA/RNA BASE sequencing
  • Amino acid sequencing
  • Use of electron microscopes with greater resolution
  • Use of electron microscopes and improved staining/preparation;
• Using Figure 7, what can you conclude about how exposure to CO affects the loading and unloading of oxygen by haemoglobin?

  Explain your answer.

  • Maximum haemoglobin saturation is 50% for Carbon monoxide
  • 2. At low pO2 Hb has HIGHER affinity for oxygen
  • 3. What affinity means = Hb has more oxygen at low pO2 / unloads less oxygen at lower pO2

  
• The scientists suggest that the WHO recommendations for carbon monoxide

  concentrations resulting in 2.5% COHb should be reduced.

  Evaluate the scientists’ conclusion.

  • FACTORS THAT AFFECT HAEMOGLOBIN
  • Unknown effects of exercise on CO uptake
  • People vary in size/age/ethnicity OR different sex
  • Unknown effects on CO exposure for people with respiratory disease / SMOKERS
• Suggest why the fused cells allow continuous production of monoclonal antibodies.

  [2 marks]

  1. Cancer/fused cells divide/replicate rapidly/uncontrollably;
  2. B cells / plasma cells / memory cells produce monoclonal antibody

  
• Evaluate the ethics of the production process shown in Figure 12.

  [1 mark] = MUST HAVE THE IDEA OF FOR AND AGAINST

  • Harmful but not killed
  • Harmful but only used once
  • Harmful but stops human suffering
  • Harmful but produces (useful) medicine/drugs
  • Not harmed but injected (with a substance)
• The dengue virus causes damage to capillaries so that blood proteins move out of the capillaries into the tissue fluid.

  Explain how this would affect the return of tissue fluid into the capillaries.

  [2 marks]

  1. Increases water potential of blood/capillary OR Decreases water potential of tissue fluid;
  2. So) less WATER returns to blood/capillaries (by osmosis) (So) more WATER leaves blood/capillaries (by osmosis)
• Describe how quaternary protein is made from its monomers [5 marks]

  1. Amino acids joined by peptide bonds

  2. (By) condensation reaction(s);

  3. Secondary structure is formed by hydrogen

  bonding

  4. Tertiary structure formed by interactions

  between R groups

  5. Quaternary structure contains >1 polypeptide

  OR

  Quaternary structure formed by

  interactions/bonds between polypeptides
• Describe the structure of DNA and structure of a chromosome = chromosome [6 marks]

  • 6. DNA is associated with histones/proteins;
  • 7. During mitosis/when visible chromosome consists of two chromatids joined at a centromere;
• Mutation can result in an increase in genetic variation within a species.

  Describe and explain the other processes that result in increases in genetic variation within a species. [4 marks]

  1. Independent segregation of homologous Chromosomes/pairs;
  2. Crossing over between homologous chromosomes/pairs;
  3. Random fertilisation of gametes;
  4. Produces new combinations of ALLELES
  5. Accept as an additional mark point = Produces new combinations of maternal and paternal chromosomes