Unit 3 past paper question

• Benedict’s test for reducing sugars

  -Pipette the solution being tested into the test tube followed by Benedict’s solution

  -place the test tube into a test tube rack and then into the water bath at 80° and leave it for exactly 2 minutes, take the tube and place on the test tube rack.

  -observe the colour
• Benedict’s test for reducing sugars A ​blue colour is a negative result​ ​since this is the colour of the Benedict’s reagent, while ​colours closer to brick-red​ ​give a positive result ​with an ​increasing​ ​concentration of reducing sugar.
• Benedict’s test for reducing sugars

  Independent Variable: the concentration of the reducing sugar solutions

  Dependent Variable: the color of the solution after addition of Benedict’s Reagent
• Iodine test for starch

  Independent variable: the concentration of the starch solution

  Dependent Variable: The color of the solution after addition of iodine solution
• Iodine test for starch

  -pipette the test solution into a test tube and add 2 drops of potassium iodine solution
• Iodine Test for starch

  Negative Result: Brown color(no starch)

  positive result: Blue color (moderate amount) to Black color (high concentration present)
• Explain the role of the pollen tube in plant reproduction

  • it causes the tissues of the style to be digested
  • it transports the male gamers through the micropyl
  • then the male Gametes fuse with the egg nucleus and the polar nuclei
• Why do pollen tubes grow in the same direction from the stigma after pollination

  • the pollen tubes grow towards the micropyle due to the chemicals released by the embryo sac
• Why changes in temperature will affect investigations

  • it involves enzyme reactions, as the temperature increases the enzymes gain kinetic energy
  • however if temperature is higher than the optimum temperature the enzyme will begin to denature
• If results are based on observation they will be

  Semi-quantities and subjective
• How a investigation could he adapted to produce quantitative data

  • use a color meter to measure absorbance
  • carry out zeroing, use the same cuvette
• what is meant by biodiversity

  The number of different species of organisms living in an area and the genettc differences within species of living organism
• Describe how seeds are treated and then stored in a seed bank.

  The seeds are cleaned an screened using X-rays to ensure that they contain fully developed embryas.

  They are then dried to reduce the water content in them They are the stored at a low temperature of between -20 ~ - 40°c in a low oxygen environment
• How a test for reducing sugars is carried out

  Use Benedict’s reagent by heating in a water bath
• It was assumed that the extract contained all the reducing sugars from the food sample, how can this be tested

  Take the food residue from filter paper and test for reducing sugars
• What happens to DCPIP in the presence of vitamin C

  The color changed from blue to colorless because DCPIP was reduced
• Explain how this investigation should be carried out to give a semi-quantitative estimate of the concentration of the reducing sugars by comparing the colour of the precipitate with a colour chart.

  use the same mass for each food use the same volume of distilled water and standardize the test practice compare results with the colour chart
• Structure of heart

  A: right atrium

  B: aorta

  C: pulmonary artery

  D: coronary artery

  
• Describe the structure of sucrose.

  it is made up of glucose and fructose joined by glycosidic bonds
• Describe how the investigation could be modified to allow standard deviations to be obtained.

  repeat the experiment under the same conditions described
• Reducing sugars

  Positive: green>yellow>orange> brick red
• Factors effecting seed germination

  Water

  oxygen

  temperature

  light intensity
• Three membrane bound organelles found in plant cells

  RER, chloroplasts, mitochondria
• Water potential

  The tendency of free water molecules to move from one region of more free water molecules to a region of less free water molecules
• Placebo

  Used as a control to help eliminate the physiological effect of taking the drug
• Double blind

  Neither the doctor nor scientist or patient know if the new drug is given or not, it removes bias
• Two types of tissues found in fibers

  Sclerenchyma

  xylem
• Properties of sucrose that make them suitable for investigations 


  • They’re disaccharides so they’re metabolically inactive
  • dissolves in water
  • can’t cross cell membranes
• Explain why it would be better to measure the initial rate of reaction.

  the rate of reaction slows down so rates can be compared
• Describe how a suitable pH could be decided on experimentally.

  carry out experiment described at constant temperature at a range of pH

  choose which pH gives a time which is practical
• Explain how using a colorimeter allows valid measurements of light transmitted through the betalain solutions.

  • because the same light source used for all measurements
  • because calibrating
  • because objective measured
  • because no light lost
• Describe the difference between a semi-quantitative and a quantitative test.

  • semi quantitative test gives an estimate of concentration of a substance
  • quantitative test determines the exact concentration of a substance
• Describe how you could test for protein in this filtrate.

  add biruet reagent, it will turn purple
• Describe how the filtrates should have been prepared to allow a valid

  comparison of the protein content of these foods.

  use the same mass of sample same volume of water control the temperature
• Describe how you could use this apparatus to make a valid comparison of the tensile strength of fibres with different diameters.

  h

  • the length, mass, age and hydration levels should be the same
  • during the expenment, variables like humidity, temperature should be controlled
  • the distance between the stands should be the same during all experiments
  • mass should be added gently and one at a time until a speafic fibre breaks
• Describe a safe method, antibacterial properties

  • use aseptic techniques with sterilised equipment grow bacteria in a nutrient agar
  • filter discs soaked in plant extract on agar to keep extract volume controlled
  • use a dish lid
  • incubate at the same temp for a few days
  • measure the clear zone repeat experiment at similar conditions to calculate the mean
• devise a method to obtain the data for the pigment shown in the graph.

  cut even sized plant tissues.

  h

  • cut even sized plant tissues.
  • wash them thoroughly in distilled water until no more pigments pass through
  • set up I different concentrations of the chemical as used in the graph
  • Place the plant tissues into each solution
  • Measure the change in colour intensity using colorimetry and a suitable control for the same period of time
  • ensure that the temperature is constant
• Describe how a thin section of a stem could be prepared and viewed using a light microscope, in order to draw this plan.

  • Using a knife, cut through the stem horizontally
  • use dye to stain
  • Place the stained section on a slide glass and cover with a coverslip
  • observe the structure under low power and draw