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AQA A LEVEL BIOLOGY PAPER 3 2021
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AQA A LEVEL BIOLOGY PAPER 3 2021
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A level Biology paper 31. RP01 - Rate of an Enzyme Controlled Reaction:
2. What are the factors that affect enzyme activity (4)?: 1. Enzyme
concentra- tion
2. Substrate concentration
3.Temperature
4. pH
3. How is a control set up in a practical measuring enzyme activity?:
Replace the enzyme solution with distilled water or boiled enzyme
solution.
4. How can the results of the practical measuring enzyme activity be used
to find the initial rate of reaction?: Plot your results on a graph of 'rate of
reaction' against 'time'.
Draw a tangent at time = 0 to find the initial rate.
5. Outline the practical procedure used to measure the effect of
temperature on enzyme activity, using trypsin and milk.: 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.
,6. How is the rate of reaction calculated from time?: Rate of reaction =
1/time
7. What is the effect of temperature on enzyme activity?: 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.
8. What is the risk and level of risk associated with handling enzymes?:
Stu- dents may have allergic reactions to enzymes, so avoid contact
with skin and eyes, wear eye protection.
Low risk.
9. RP02 Calculating Mitotic Index using Plant Cells:
10.Where in plants can cells undergoing mitosis be found?: Meristem
tissue at shoot and root tips.
11.What is the mitotic index?: The ratio of cells undergoing mitosis to
the total number of cells in a sample.
, 12.Outline the procedure to prepare a root tip slide.: 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.
13.State the formula for the mitotic index.: Mitotic index =
Number of cells with visible chromosomes /Number of cells in sample
14. State the hazards and precautions for reagents used in this procedure.-
: 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
15. RP03 - Investigating Water Potential:
16.What is the purpose of calibration curves?: They are used to
determine the concentration of an unknown sample by comparing it to
a set of standard values with known concentrations.
17. How is a calibration curve used to find the concentration of plant
tissue?-
: Plot a calibration curve of percentage change in mass against
concentration. Find the x-intercept where the plant tissue is isotonic to
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