2019 Paper 1

• Suggest and explain one way the leaf growth of xerophytic plants would be different from the leaf growth of sunflowers in Figure 9. [2 marks]

  1. Low/slow growth
  2. Due to smaller number/area of stomata for gas exchange

  3. Growth may continue at lower water potentials

  4. Due to adaptations in enzymes involved in photosynthesis/metabolic reactions

  
• Food frequency questionnaire ass how often they have eaten many types of food over past year. ADVANTAGE =

  • Over longer period so more representative (data)
  • Diet over 24 hr may not be representative
  • Diet may vary during the year/from day to day
• Alternate method to calculate fibre eaten is nurse to ask each question detailed questions about what they have eaten in last 24 hours.

  Suggest one disadvantage of using FFQ compared with alternative method.

  • Recall of 24 hr diet likely to be more ACCURATE
  • Relies on long term memory so may not be accurate
  • Person may be more honest when being interviewed;
  • Estimation from Food frequency questionaire may be less accurate than details of last 24hrs

  For accurate accept ONLY VALID / CLOSE TO TRUE VALUE
• Use the data in Table 3 and your knowledge of the immune response to suggest why HIV controllers do not develop symptoms of AIDS. [3 marks] (These marking points are knowledge)

  • So more/continued activation of B cells/cytotoxic T cells/phagocytes
  • With B cells - more/continued production of plasma cells/antibodies
  • OR (With cytotoxic T cells more/continued) ability to kill virus infected cells
  • 5. More able to destroy other microbes/pathogens OR More able to destroy mutated/cancer cells;
• Use Figure 5 to explain how human mass at birth is affected by stabilising selection. [3 marks]

  • .Extreme mass babies least likely to survive to reproduce and so less likely to PASS on their ALLELES for extreme mass at birth
  • Most likely to be transferred to a special care unit are those under 2800 g / over 4200g (This is using the data in the question).
  • Extreme mass at birth decreases in frequency (in the population) OR
  • ALLELES for extreme mass at birth decrease in FREQUENCY (in the population)

  
• No large lipid droplets are visible with the optical microscope in the samples from suspension A. Explain why. [2 marks]

  1. Emulsification
  2. Cannot be seen DUE TO RESOLUTION of optical microscope - LONG WAVELENGTH of light
• 1. Trend of decreasing percentage heart cells undergoing mitosis from before birth to 21 days - MUST APPRECIATE START AND END POINTS FOR THIS INVESTIGATION
  2. Explanation - DNA replication happens before mitosis (3.2.2 spec)
  3. OR Heart growth slowing UNTIL (fully) developed
  4. These cells lost the ABILITY TO divide

  
• Mammals such as a mouse and a horse are able to maintain a constant body temperature. Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse.

  Mouse

  1. Smaller so larger surface area to volume ratio
  2. More/faster heat loss per gram/in relation to body size
  3. Faster rate of respiration/metabolism releases heat

  MP1 and MP2 must be COMPARATIVE