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_level Biology paper 3 A+ Solutions.
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level Biology paper 3 A+ SolutionsRP01 - Rate of an Enzyme Controlled Reaction - ANS
What are the factors that affect enzyme activity (4)? - ANS-1. Enzyme concentration
2. Substrate concentration
3. Temperature
4. pH
How is a control set up in a practical measuring enzyme activity? - ANS-Replace the
enzyme solution with distilled water or boiled enzyme solution.
How can the results of the practical measuring enzyme activity be used to find the
initial rate of reaction? - ANS-Plot your results on a graph of 'rate of reaction' against
'time'. Draw a tangent at time = 0 to find the initial rate.
Outline the practical procedure used to measure the effect of temperature on enzyme
activity, using trypsin and milk. - ANS-Immerse equal volumes of trypsin and milk, stored
in different test tubes, in a water-bath for 5 minutes for the temperature to equilibrate.
Mix together and immediately start timing, record the time taken for the milk to be
completely hydrolysed (become colourless/ same as the control standard set up). Test at
least 5 temperatures, with at least 3 repeats at each temperature.
How is the rate of reaction calculated from time? - ANS-Rate of reaction = 1/time
What is the effect of temperature on enzyme activity? - ANS-As temperature increases,
kinetic energy increases so more ES complexes form. The rate of reaction increases up
to the optimum temperature.
Beyond that, bonds in the enzyme tertiary structure break, which changes the shape of
the active site. The substrate and enzyme are no longer complementary, so rate of
reaction decreases.
What is the risk and level of risk associated with handling enzymes? - ANS-Students
may have allergic reactions to enzymes, so avoid contact with skin and eyes, wear eye
protection.
Low risk.
, RP02 Calculating Mitotic Index using Plant Cells - ANS-
Where in plants can cells undergoing mitosis be found? - ANS-Meristem tissue at shoot
and root tips.
What is the mitotic index? - ANS-The ratio of cells undergoing mitosis to the total
number of cells in a sample.
Outline the procedure to prepare a root tip slide. - ANS-Warm 1M HCl to 60°C in a water
bath.
Cut a root tip using a scalpel and add to the HCl. Leave
for 5 minutes.
Remove from HCl and wash with distilled water.
Cut the tip of the root tip sample and place on a slide.
Add a few drops of stain to make chromosomes visible.
State the formula for the mitotic index. - ANS-Mitotic index =
Number of cells with visible chromosomes /Number of cells in sample
State the hazards and precautions for reagents used in this procedure. - ANS-HCl -
corrosive, avoid contact with skin, wear eye protection
Toluidine Blue O stain - irritant, avoid contact with skin, wear eye protection
Scalpel - cut away from fingers
RP03 - Investigating Water Potential - ANS
What is the purpose of calibration curves? - ANS-They are used to determine the
concentration of an unknown sample by comparing it to a set of standard values with
known concentrations.
How is a calibration curve used to find the concentration of plant tissue? - ANS-Plot a
calibration curve of percentage change in mass against concentration. Find the
x-intercept where the plant tissue is isotonic to the sucrose solution.
What occurs when plant tissue is placed in a hypotonic solution? - ANS-Water moves
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