PAPER 3 JUNE 2019

• describe how ultrafiltration occurs at the glomerulus

  high hydrostatic pressure, so this causes small molecules such as water and urea to be forced out of the glomerulus and through the small gaps in the capillary endothelium, and through capillary basement membrane.
• describe the role of saprobionts in the nitrogen cycle

  they use enzymes to hydrolyse proteins in dead matter useful components such as amino acids.
• Eutrophication can cause water to become cloudy. You are given samples of water from three different rivers. Describe how you would obtain a quantitative measurement of their cloudiness.

  use a colorimeter, measure the absorbance, to standardize the method make sure to zero the colorimeter beforehand.
• what is valve And chamber B?

  valve A is left atrioventricular valve and chamber b is left ventricle.
• Give two safety precautions that should be followed when dissecting a heart

  wear gloves and cut away from self and others
• Caffeine affects the autonomic nervous system. Suggest how caffeine could account for the results of Group I in Figure 3 at 60 minutes.

  more impulses are sent through the sympathetic nervous system to the SAN which increases heart rate as shown in figure 3.
• Before taking the drink, the mean heart rate of Group J was 68 beats per minute. Fifteen minutes after taking the drink, the mean volume of blood leaving the hearts of Group J was 4700 cm3 per minute. Calculate the mean volume of blood leaving the heart at each beat fifteen minutes after taking the drink


  64 bpm = 1 minute, 4700 cm3 = 1 minute so 4700/64=73.4cm3
• The increase seen in Group I could be due to the combination of caffeine and sugar. Suggest one drink to be given to an additional group that should be investigated to find out if this is true. Give a reason for your answer.

  the additional drink should be made up of sugar but no caffeine, the reason behind it to only see the effect of the sugar alone.
• The control regions of Group T and Group C were the same length. Name the type of gene mutation that is most likely to have occurred at nucleotide position 16 519

  substitution
• A student concluded from Figure 4 and Figure 5 that training has a positive effect on VO2max and CS activity. Evaluate the student’s conclusion

  (VO2 max and CS activity) increased for both groups 2. No statistical test, so do not know if differences are significant, Only 8 weeks training, might not be true for all types of exercises.
• The mitochondrial DNA (mtDNA) control region is an area of mtDNA that is non-coding. This region stimulates the synthesis of both mtDNA and mitochondrial messenger RNA. Use this information to suggest two reasons why the mutation at nucleotide position 16 519 could lead to the differences seen in Figure 5

  less mitochondrial replication and less transcription of genes for mtDNA
• ‘Having thymine at nucleotide position 16 519 in Group T causes an increase in ability to exercise for longer.’ Evaluate this conclusion. Use all the data in this question.

  In figure 5 the CS activity increased which means the KREBS cycle occurs more often, so more respiration, in figure 4 vo2 max increases which means more oxygen available for aerobic respiration. there is no correlation between CS activity and vo2 max
• Marine biologists used a choice chamber to investigate the effects of flashing and constant light on the behaviour of COTS.State a null hypothesis the marine biologists tested in this investigation.

  the type of light does not have an effect on the movement of COTS.
• The natural habitat of COTS is coral reefs of tropical oceans. Suggest two factors that should be kept constant in the choice chambers so that COTS display normal behaviour.

  temperature and pH.