2023 Paper 2

• Describe and explain how improve performance of different types of muscle fibres during different types of exercise.

  1. Fast skeletal muscle fibres used during short-term/intense exercise
  2. Slow skeletal muscle fibres used during longer-term exercise;

  
• ATP is essential for muscle contraction (line 1).

  Describe the roles of ATP in muscle contraction. [2 marks]

  1. To break actinomyosin bridges
  2. To move/bend the myosin head/arm;
  3. So actin filaments are moved inwards
  4. For active transport of calcium ions into the sarcoplasmic/endoplasmic reticulum
• Genetic fingerprinting using STRs requires amplification of the STRs using the polymerase chain reaction (PCR).

  The short base sequences either side of a specific STR are known.

  Explain the importance of knowing these base sequences in PCR. [2 marks]

  1. For primers
  2. To produce a complementary base sequence
  3. Primers provide starting sequence for DNA/taq polymerase
  4. Primers stop (original) DNA strands re-joining;
• Suggest and explain how an alteration in the KRAS gene can cause a tumour to develop. [3 marks]

  1. Mutation in KRAS gene OR Change in base sequence (of KRAS gene);

  2. Change in (signalling) protein

  OR More (signalling) protein/K-Ras produced;

  3. Results in rapid/uncontrollable cell division;

  
• Give three reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem.

  [3 marks] (3 X AO1)

  1. Heat loss from respiration;
  2. Food not digested OR Not all eaten
  3. Excretion;
• Suggest two reasons for conserving rainforests.

  1. Conserve/protect species/plants/animals/organisms OR For biodiversity;
  2. Conserve/protect habitats/niches OR Provides/many habitats/niches;
  3. Reduces climate change;
  4. Source of medicines/drugs/wood;
  5. Reduces erosion/eutrophication;
  6. For tourism
• Decrease in blood pressure stimulates the release of ADH.

  Give the location of the receptors that detect a decrease in blood pressure and explain how the release of ADH will affect blood pressure.

  [3 marks]

  Location = Aorta OR Carotid artery/sinus

  Explanation =

  • ADH increases the reabsorption of water
  • Increases VOLUME of blood and PRESSURE increases
• Use Figure 3 and your knowledge of colour vision to explain how an orange colour is seen at 600 nm [3 marks]

  1. (Colour vision involves) cones;
  2. Each type of photoreceptor has a different pigment // Each type of photoreceptor absorbs particular/different (range of) wavelengths // Each type of photoreceptor stimulated by particular/different (range of) wavelength(s)
  3. More impulses along optic nerve from ‘red sensitive’ than ‘green sensitive' photoreceptors/cones

  
• The soil used in this investigation had the recommended concentration of fertiliser.

  Suggest two reasons why the soil contained the recommended concentration of fertiliser. [2 marks]

  • Affects (crop) production/growth/mass; / Limiting factor for NAMED nutrient / ion (nitrate ion)
  • So fertiliser is a controlled variable;
  • Concentration of fertiliser would affect water potential of soil;
  • Does not affect pH (of soil);
  • To provide usual farming conditions
• When the patients recorded the intensity of pain, suggest two reasons why it was important to use a statistically valid scale.

  [2 marks]

  1. (Sensation of) pain is subjective OR Pain sensitivity/threshold/tolerance varies;
  2. To ensure that differences (in pain detection) were (statistically) significant OR For (valid) comparison;