OCR – A-Level Biology Practicals Exam Questions and Mark Scheme – Revision
Notes (2025-2026)
*Practical 8: The effect of temperature on membrane permeability (beetroot experiment) -
✔✔✔-1. cut equal size pieces of beetroot and rinse them to remove any pigment released
during cutting.
2. Place the five pieces in five different test tubes, each with the same volume of water
3. Place each test tube in a water bath set at different temperatures for the same length of time
4 remove the pieces of beetroot from the test tubes, leaving just the coloured liquid
5. take the small volume of each coloured liquid and put it into covet for the colorimeter
*make sure to calibrate the colorimeter with a blank first
6. measure the absorbance rate of each liquid
7. the more absorbance (less light passing through) the more permeable the membrane was
* more transmission = less permeable the membrane
variables to control:
-temperature
-ethanol concentration
-No excess dye on cut sections of beetroot (rinse off)
-swirl liquid before putting in the cuvette for the
-time
-beetroot (age, same plant, same part)
-SA and/or mass of beetroot used.
** remember
,OCR – A-Level Biology Practicals Exam Questions and Mark Scheme – Revision
Notes (2025-2026)
judging colors by eye is not as good as using colorimeter because the results are judged
subjectively or by using a colorimeter
Computer modelling and data logging - ✔✔✔-COMPUTER MODELLING
advantages:
- Allows manipulation and measurements to be taken that couldn't be done with actual
molecules.
-Allows the potential to simulate interactions between a range of different molecules at the
atomic level.
-At a broader level computer modelling allows whole systems (e.g. metabolic pathways,
ecosystems, climate) to be investigated where experiments are not possible
-Models can make predictions about the impact of changes in the system that may not be
testable experimentally.
disadvatanges:
-Can require a large amount of data processing (high cost and too slow).
- Accurate and valid data needs to be collected to build a valid model
- Not all factors that affect a system can be included in a model which will affect validity.
-Predictions that models make are only valid if the assumptions of the model are true and if no
unforeseen changes occur in the future.
DATA LOGGING
advantages:
-Can be done remotely and continuously.
-Data can be easily stored for future analysis or transmitted elsewhere foranalysis.
-Often the equipment is more precise than alternative ways of measuring.
, OCR – A-Level Biology Practicals Exam Questions and Mark Scheme – Revision
Notes (2025-2026)
disadvantages:
-Equipment can be expensive
-If data is being collected remotely, and the data logger retrieved at the end of data collection
for downloading all the data could be lost if the data logger is lost or damaged.
DNA extraction - ✔✔✔-grind a sample in pestle and mortar
mix detergent with the sample - breaks down the cell membrane
add salt - break hydrogen bonds
add protease enzymes- brekadown histone proteins
add ethanol cause dna to precipitate out of the solution
DNA will be seen as white strands forming bewteen the layer of sample and layer of alcohol
Investigating the distribution of plant species along an abiotic gradient - ✔✔✔-
Investigating the rate of respiration of yeast under aerobic and anaerobic conditions - ✔✔✔-
AEROBIC
1. Put a known concentration of substrate solution (e.g. glucose in the test tube
Notes (2025-2026)
*Practical 8: The effect of temperature on membrane permeability (beetroot experiment) -
✔✔✔-1. cut equal size pieces of beetroot and rinse them to remove any pigment released
during cutting.
2. Place the five pieces in five different test tubes, each with the same volume of water
3. Place each test tube in a water bath set at different temperatures for the same length of time
4 remove the pieces of beetroot from the test tubes, leaving just the coloured liquid
5. take the small volume of each coloured liquid and put it into covet for the colorimeter
*make sure to calibrate the colorimeter with a blank first
6. measure the absorbance rate of each liquid
7. the more absorbance (less light passing through) the more permeable the membrane was
* more transmission = less permeable the membrane
variables to control:
-temperature
-ethanol concentration
-No excess dye on cut sections of beetroot (rinse off)
-swirl liquid before putting in the cuvette for the
-time
-beetroot (age, same plant, same part)
-SA and/or mass of beetroot used.
** remember
,OCR – A-Level Biology Practicals Exam Questions and Mark Scheme – Revision
Notes (2025-2026)
judging colors by eye is not as good as using colorimeter because the results are judged
subjectively or by using a colorimeter
Computer modelling and data logging - ✔✔✔-COMPUTER MODELLING
advantages:
- Allows manipulation and measurements to be taken that couldn't be done with actual
molecules.
-Allows the potential to simulate interactions between a range of different molecules at the
atomic level.
-At a broader level computer modelling allows whole systems (e.g. metabolic pathways,
ecosystems, climate) to be investigated where experiments are not possible
-Models can make predictions about the impact of changes in the system that may not be
testable experimentally.
disadvatanges:
-Can require a large amount of data processing (high cost and too slow).
- Accurate and valid data needs to be collected to build a valid model
- Not all factors that affect a system can be included in a model which will affect validity.
-Predictions that models make are only valid if the assumptions of the model are true and if no
unforeseen changes occur in the future.
DATA LOGGING
advantages:
-Can be done remotely and continuously.
-Data can be easily stored for future analysis or transmitted elsewhere foranalysis.
-Often the equipment is more precise than alternative ways of measuring.
, OCR – A-Level Biology Practicals Exam Questions and Mark Scheme – Revision
Notes (2025-2026)
disadvantages:
-Equipment can be expensive
-If data is being collected remotely, and the data logger retrieved at the end of data collection
for downloading all the data could be lost if the data logger is lost or damaged.
DNA extraction - ✔✔✔-grind a sample in pestle and mortar
mix detergent with the sample - breaks down the cell membrane
add salt - break hydrogen bonds
add protease enzymes- brekadown histone proteins
add ethanol cause dna to precipitate out of the solution
DNA will be seen as white strands forming bewteen the layer of sample and layer of alcohol
Investigating the distribution of plant species along an abiotic gradient - ✔✔✔-
Investigating the rate of respiration of yeast under aerobic and anaerobic conditions - ✔✔✔-
AEROBIC
1. Put a known concentration of substrate solution (e.g. glucose in the test tube
