PAST PAPER 1 Exam Qs

• Give three environmental variables that should be controlled when growing the plants before treatment with the different sprays. [3 marks, 2017]

  1. Concentration of mineral ion/named mineral ion in soil;
  2. Soil pH (pH alone is insufficient)
  3. Temperature
  4. Light intensity/wavelength/duration
  5. Distance between seeds/plants
  6. Volume of water given
  7. CO2 concentration
  8. Humidity

  • REJECT AMOUNT for MP1, 4, 6, 7
  • Ignore Oxygen concentration
• The scientists incubated the flasks containing the leaf discs at 26 °C and gently shook the flasks.

  Suggest one reason why the scientists ensured the temperature remained constant [2017 Paper 1, 2 marks]

  1. Maintain temperature so that the rate of diffusion of ions out of cells remains constant OR
  2. Maintain temperature so no change in fluidity of phospholipids/kinetic energy of phospholipids
  3. Maintain temperature so no change in shape/structure/denaturation of membrane proteins;
• Suggest one reason why the leaf discs were shaken. [1 mark, RP4 2017 Paper 1]

  • 2. Shaking So all surfaces of the leaf discs are exposed (to water/so all submerged
  • OR To maintain diffusion/concentration gradient for ions out of leaf discs
• The adult damselfly uses a tracheal system for gas exchange. Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange. [3 marks]

  1. Tracheoles have thin walls so short diffusion distance to cells
  2. Highly branched/large number of tracheoles so short diffusion distance to cells
  3. Highly branched/large number of tracheoles so large surface area for gas exchange
  4. Tracheae provide tubes full of air so fast diffusion (into insect tissues
• The adult damselfly uses a tracheal system for gas exchange. Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange. [3 marks] (part two)

  1. Fluid in the end of the tracheoles that moves out into tissues during exercise so faster diffusion through the air to the gas exchange surface OR Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange)
  2. Body can be moved (by muscles) to move air so maintains diffusion/concentration gradient for oxygen/carbon dioxide;
• Students could use agar blocks containing indicator to determine the effect of surface area to volume ratio and concentration gradient on the diffusion of an acid or alkali.

  - State there variables the student controlled in order to obtain valid results [3 marks, 2023 AS Paper 1]

  1. Temperature
  2. Concentration of indicator
  3. pH/concentration of solution/acid
  4. pH/concentration of alkali in blocks
  5. Concentration/type of agar
  6. Ensure total surface area of the block is in contact with the solution/acid
• SPECIFICATION STATES:

  • The properties of an enzyme relate to the
  • tertiary structure of its active site
  • its ability to combine with complementary substrate(s) to form an enzyme-substrate complex.

  Explain why amylase produced in the human digestive system does not digest GOS.

  1. Active site only complementary to starch OR Active site not complementary to GOS;
  2. Due to tertiary structure;
• Name the type of blood vessel that controls blood flow to muscles and explain how these blood vessels change blood flow during exercise. [3 marks]

  • Arteriole
  • Circular / smooth muscle relaxes
  • Vasodilation increases blood flow (because more blood DURING exercise)
  • OR Widens/dilates (lumen of) blood vessel so increases blood flow;
• Scientists have produced a mutated rice variety in which there is no crossing over.

  Suggest and explain the similarities and differences in the causes of genetic variation within these rice populations.

  Similarities

  • Both populations have variation due to independent segregation/assortment of chromosomes/chromatids
  • Both populations have variation due to random fertilisation of gametes
  • Both populations have (further) mutations
  • Difference Crossing over causes variation in non-mutant only
• Describe how natural selection may have led to all mammals in a population producing CEL [4 marks]

  1. Mutation results in (a new) allele;
  2. Those with the (new) allele able to digest milk/triglycerides;
  3. Individuals with CEL/allele more likely to (survive and) reproduce;
  4. NAME THE TYPE OF SELECTION: Directional selection
  5. Increase in frequency of (this) allele in population
• The damselfly larva has gills to obtain oxygen from water.

  Some other of species have larvae do not actively hunt prey and do not have gills.

  Explain how the presence of gills adapts damselfy to its way of life. [2 marks]

  1. Damselfly larvae has higher metabolic/respiratory rate (BECAUSE it actively hunts prey)
  2. SO damselfly USES more oxygen per unit mass / per unit time (for aerobic respiration)

  MARKSCHEME NOTES:

  • NOT obtaining more oxygen, but the damselfly USES MORE oxygen
  • Idea of ‘more/high’ is needed for both mark points.
• Using information from Figure 5 and Table 4, what can you conclude about the adaptation of the gas exchange surfaces of these species of fish? (2019 AS)

  1. (Generally) lower the oxygen concentration, the higher ratio/(gill) surface area to body mass
  2. Supplies (enough) oxygen for RESPIRATION! ;

  • (Whole point of gas exchange surfaces is to have enough oxygen for aerobic respiration)
• Explain how the active site of an enzyme causes a high rate of reaction. [3 marks]

  1. Lowers activation energy
  2. Induced fit causes active site (of enzyme) to change shape;
  3. (So) enzyme-substrate complex causes bonds to form/break;
• Suggest why preventing the formation of spindle fibres (lines 2–3) stopped the cell cycle. [2 marks] (2019 AS P1)

  SPEC: The role of spindle fibres attached to centromeres in the separation of chromatids. + cancer treatments

  1. Chromosomes/centromeres cannot attach to spindle OR Chromosomes cannot line up on spindle
  2. (So, no) metaphase
  3. CHROMATIDS cannot separate on spindle
  4. (So, no) anaphase;

  • Tip: MENTION the phase (ie anaphase, metaphase) of mitosis when asked about cell cycle
  • CHROMATIDS (underlined in Markscheme) cannto separate in anaphase
• ATP is better than either glucose or fatty acids as an immediate energy source for cell metabolism. Explain why.

  • ATP energy released in single reaction
  • ATP energy released in small quantities / manageable quantities / less energy wasted / less heat produced;
• DO NOT FORGET ELEMENTS WHEN COMPARING BIOLOGICAL MOLECULES!

  • Both starch and cellulose contain carbon, hydrogen and oxygen
  • Both phospholipids and triglycerides contain carbon, oxygen, hydrogen but phospholipids contain phosphorous (P)