2019 Paper 3

• AO2 and AO3 using contexts - challenging in testing EVALUATION .

  Most students argued one side, rather than giving BALANCED

  ARGUMENTS.

  • Therefore in EVALUATE QUESTIONS, Do not forget to give BOTH SIDES of the argument!
• • Students also struggled to make links between their own knowledge and some of the contexts set.
  • Essay requires AO2 - about half the marks assess AO2
  • More successful essays demonstrate this - discussing the importance at A-Level standard
• Describe how ultrafiltration happens at a glomerulus.

  • Most students set the context of the blood arriving in the afferent arteriole and leaving via the efferent arteriole; a pity, as neither forms part of the glomerulus.
  • Many used this to justify an increase in pressure, but failed to state that the pressure was HIGH, and also failed to mention that it was BLOOD or HYDROSTATIC PRESSURE
• Describe ultrafiltration

  • Many made reference to small molecules that pass out - more able students included lists - water, glucose, ions, urea
  • Students mentioned the epithelium or endothelium but OMITTED to make reference to the GAPS
  • Correct answer = 3. (Through small) gaps/pores/fenestrations in (capillary) endothelium
• Majority of students failed to make the necessary link of understanding that the loop of Henle is in the medula of the kidney
• Explain why thicker the medulla, the more concentrated urine is

  • 2. The longer the loop of Henle means INCREASE in SODIUM ion concentration in medulla
  • OR (The longer the loop of Henle means) sodium ion gradient maintained for longer (in medulla)
  • OR More SODIUM ions are moved out into medulla
  • Many mentioned ions, not SODIUM IONS specifically
• Explain why increase in thickness of medulla increases concentration urine

  • 3. (Therefore) water potential gradient maintained for longer, so more water reabsorbed from loop and collecting duct
  • OR More water is reabsorbed from the loop of Henle / COLLECTING DUCT by osmosis;
  • MP3 - many failed to give mechanism of water movement - BY OSMOSIS!
• Describe the role of saprobionts in the nitrogen cycle. [2 marks]

  1. (They use enzymes to) decompose proteins/DNA/RNA/urea;
  2. Producing/releasing ammonia/ammonium compounds/ammonium ions;
• One environmental issue arising from the use of fertilisers is eutrophication. 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. [3 marks]

  • Use of a colorimeter
  • MEASURING THE absorbance / transmission of light
  • Standardisation of method - using same volume of water, zeroing colorimeter; same wavelength of light, shaking the sample
• Give two safety precautions that should be followed when dissecting a heart. [1 mark]

  • Use a sharp scalpel/scissors
  • Wash hands/wear gloves
  • Disinfect bench/equipment
  • Cover any cuts
  • Cut away from self/others/on a hard surface
  • Safe disposal
• 0 3 . 3 Explain how valve A in Figure 2 maintains a unidirectional flow of blood. [2 marks]

  1. Pressure in (left) atrium is higher than in ventricle/B causing valve to open
  2. (When) pressure ABOVE valve is higher than below valve it opens;
  3. Pressure in (left) ventricle/B is higher than in atrium causing valve to close
  4. OR (When) pressure in BELOW valve is higher than above valve it closes

  Tip: NOT in front / behind valve - this is in context of semi-lunar valve
• Caffeine affects the autonomic nervous system.

  Suggest how caffeine could account for the results of Group I in Figure 3 at 60 minutes. [2 marks]

  1. More impulses/action potentials along sympathetic nervous system pathway/branch
  2. To SAN increasing the heart rate seen in Figure 3
• 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. [2 marks] In group C =

  1. Less mitochondrial replication/production
  2. Less transcription of genes for mitochondrial proteins/CS
  3. Less translation of (mRNA into) mitochondrial proteins;

  
• Student concluded that substitution of thymine base into cytosine at 16519 nucleotide causes increase the ability to exercise for longer, EVALUATE THE CONCLUSION. [3 marks]

  • VO2 max/CS activity not the only measures of ability to exercise for longer

  I noticed a pattern in the markscheme =

  • 'Data...' is NOT the only measures of ability to exercise for longer

  Same as in 2023, Biodiversity Q Paper 3:

  • 'Species diversity and index of diversity' may not be the only measures of biodiversity
• Many failed to read the stem of the question and recognise this context; the scientists were not attempting to recreate or mimic the dynamic environment of the reef itself.

  • These are abiotic factors, usually pH, temperature and the salinity of the water
  • Amount / distribution of food
  • Oxygen / carbon dioxide concentration
  • Intensity / wavelength of flashing / constant light

  
• Suggest why scientists calculated a percentage change - Percentage change

  1. To allow comparison as tumours may differ in volume/size at the start of the investigation
• Suggest why scientists calculated Tumour volume

  2. As tumours may differ in length/width/shape OR

  As volume is best indication of the number of cells in tumour;
• To reduce the size of tumours, would it be better to use 30mg of Trexall per week, or 20 mg of Trexall per week? Explain your answer. [2 marks] - I picked out key points

  • There is a significantly greater reduction (in tumour size with 30 mg), as STANDARD DEVIATION (bars) do not overlap
  • There is too much/a lot of variation in effectiveness with 30 mg in contrast with 20 mg (ignore standard deviation too large unqualified)
  • No idea of extra COST of providing 30 mg per week
  • Increased risk of SIDE EFFECTS with higher doses;

  
• Apart from age and general health, give two important factors when choosing patients for this investigation. [1 mark]

  • Severity/duration of arthritis
  • Current/other medication
  • Type of arthritis
  • Weight/body mass
  • Ethnicity