2018 p1 (without q 7+9)

• What does the lens do when the eye changes from focusing on a distant object to focusing on a near object?

  The lens gets thicker to bend the light rays more
• Give a reason why people who are short-sighted cannot see distant objects clearly?

  Light is refracted too much
• State the type of lens that can be used to correct short-sightedness:

  Concave
• A student was given the hypothesis ‘People with brown eyes are more likely to be short-sighted than people with blue eyes.’

  Devise a plan to test this hypothesis:

  choose equal numbers of people with brown and blue eyes

  test their vision

  count the number of people in each group who are short-sighted
• Obesity increases the risk of a person developing cardiovascular disease. Losing weight can reduce the risk of this disease occurring. Explain why exercise can cause weight loss:

  exercise requires energy which is obtained from fat
• Potato chip A is transferred from the distilled water into a concentrated salt solution. Explain what will happen to the cells in potato chip A.

  Cells will lose water through osmosis and therefore will shrink. This is because there is more water content in the potato cells compared to the solution it is in (goes from a low solute solution to a high solute solution)
• The potatoes of a potato plant develop underground. Explain one difference in the sub-cellular structures in a cell in the potato and those in a cell in the leaf of the potato plant.

  There are no chloroplasts in the potato, therefore potato cells don't photosynthesise
• • Cells taken from parent plant.
  • Cells placed on agar growth medium.
  • Cells develop into tiny plantlets.
  • Plantlets grown in compost.
  • Some cells in each plantlet develop into root cells. Name the process occurring as these cells develop into root cells:

  Differentiation
• Describe the advantages of producing plants by differentiation:

  Quicker than sexual reproduction, reproduce are genetically identical, they have the desired characteristics
• An autoclave is used to prepare the agar growth medium in agar plates. Explain why the agar growth medium is autoclaved:

  It sterilises the agar growth medium destroying any unwanted pathogens
• Streptococcus bacteria can cause a sore throat or skin infection. An illness called scarlet fever can also develop during an infection with this bacterium. Give two precautions a doctor should take when treating a patient who is infected with Streptococcus:

  Wash hands after contact, wear gloves, wear a mask, sterilise equipment before and after
• Some bacteria are motile, meaning they can move themselves. Why is a Streptococcus bacterium not motile?

  It doesn't have flagella
• Most cases of scarlet fever occur in children. Adults have usually developed immunity to a toxin that the Streptococcus bacteria produce during infection. Explain how an adult develops immunity to the toxin:

  When an adult is exposed to a toxin, the body produces an immune response, including the production of lymphocytes/antibodies. Once the risk from the toxin is gone, memory lymphocytes remain to protect against the same infection if it were to occur again.
• Two scientists were awarded the Nobel prize for their research on stem cells. They showed that adult cells could be reprogrammed to become cells with the properties of embryonic stem cells. Describe the possible benefits of this research:


  There is potential to turn these cells into any cells you want, this can be used to treat conditions that are currently incurable and there is less chance of the patient rejecting their own cells
• Interphase is part of the cell cycle. Describe what happens during interphase:

  DNA is replicated and cell reactions occur resulting in cell growth
• Explain how a magnification of 400 × can be obtained using the lenses on a light microscope:


  Select the 40 x setting on the objective lens and this would combine with 10 x setting on the eye piece lens
• Potato cells contain the enzyme catalase. This enzyme catalyses the breakdown of hydrogen peroxide into oxygen and water. The potato discs all had the same mass. Explain why the student used potato discs with the same mass:

  Mass is a variable that will affect the results if changed. As they aren't changed the results can be compared to each reaction and will show the effect the concentration of hydrogen peroxide has.
• State and explain a conclusion based on these results (as hydrogen peroxide increases, so does rate):

  Increasing the concentration of hydrogen peroxide increases the rate of reaction as it provides more substrate therefore more active sites are occupied and forms more enzyme-substrate complexes. This causes a faster oxygen release.
• The student repeated the investigation with a 25% hydrogen peroxide solution and recorded a time of 75 seconds (the rate was slower than 20%) why is this not an anomalous result?

  Substrate is not the limiting factor (as all active sites are occupied)
• Myxopyronin inhibits bacterial RNA polymerase. Explain why the antibiotic myxopyronin can be used to treat bacterial infections in humans.

  The antibiotics will destroy the bacteria and also wont be harmful to the human. It also prevents the production of mRNA and proteins.
• Infections can be caused by viruses. Describe the lytic pathway of a virus and how this causes the spread of infection through a population:

  The virus will bind to the host cell and insert its genetic material into it. The virus uses the cell's machinery to produce viral proteins + nucleic acids which form new viral particles. These viruses then exit the host cell through the cell membrane and are released in bodily fluids which allows it to spread to another host.