A Level Edexcel Biology B Core Practicals Exam
Questions With Complete Solutions
How do you investigate the effect of sucrose concentration on the growth of
pollen tubes?
1. Make up solutions of sucrose between 0.2-2 moldm-3
2. Collect a petri dish for each sucrose concentration and place a moistened filter
paper on each
3. Collect one microscope slide per concentration
4. Place a few drops of sucrose plus mineral salt medium in the dip of each slide
5. Gently rub the point of a mounted needle over the mature anthers of a flower so
the pollen falls on the slide
6. Repeat for each sucrose solution and note the time at which the pollen was added
7. placate slides in the petri dish
8. Use a microscope at X100 magnification and a calibrated eye piece graticule to
observe the slides
9. Make observations quickly and return the slide to the petri dish to prevent drying
out
10. Once the pollen tubes have started to grow, measure the length of 4 or 5 tubes
at 3 minute intervals for 30 minutes
What are the controlled variables when investigated pollen tube growth?
Volume of sucrose solution, volume of mineral solution, time left in solution, pollen
source
What are the independent and dependent variables when investigating pollen
tube growth?
IV: Concentration of sucrose
DV: Length of pollen tube
Why must the pollen tube slides be kept in a moistened petri dish?
To prevent drying out
How often should you measure the length of pollen tubes?
Every 3 minutes for 30 minutes
What must be added to a sucrose solution before pollen?
, A mineral salt medium
How do you investigate the effect of temperature on membrane permeability?
1. Use a cork borer and knife to cut 1 cm lengths of beetroot
2. Place in distilled water overnight to remove dye, wash and blot dry
3. Place 8 boiling tubes in 8 water baths of different temperatures
4. Place a beetroot segment in each tube and leave for 30 minutes.
5. Remove the beetroot and shake the tubes to disperse the dye
6. Set colorimeter to % absorbance with a blue/green filter
7. Calibrate the colorimeter with distilled water
8. Calculate % absorbance for 2cm3 samples from each temperature
What are the controlled variables when investigating the effect of temperature
on membrane permeability?
Volume of distilled water, time left in water, size of beetroot piece, source of beetroot
How is dye removed from beetroot pieces when investigating the effect of
temperature on membrane permeability?
Placed in distilled water overnight to remove dye, washed and blotted dry
How is a colorimeter used when investigating the effect of temperature on
membrane permeability?
Set to % absorbance with blue/green filter
What is used to calibrate the colorimeter when investigating the effect of
temperature on membrane permeability?
Distilled water
How do you investigate the water potential of plant epidermal cells?
1. Take 5 thin sections of the red part of a red onion, as close to 1 cell thick as
possible
2. Label 5 watch glasses and add 5 different concentrations of sucrose solution
3. Add a piece of onion to each glass and leave for 20 minutes
4. Put a drop of each solution on separate slides and float each tissue on the
matching slides
5. Cover each section with a coverslip and observe under a microscope
6. Count 25 cells and record how many show plasmolysis
What are the independent and dependent variables when investigating the
effect of temperature on membrane permeability?
Questions With Complete Solutions
How do you investigate the effect of sucrose concentration on the growth of
pollen tubes?
1. Make up solutions of sucrose between 0.2-2 moldm-3
2. Collect a petri dish for each sucrose concentration and place a moistened filter
paper on each
3. Collect one microscope slide per concentration
4. Place a few drops of sucrose plus mineral salt medium in the dip of each slide
5. Gently rub the point of a mounted needle over the mature anthers of a flower so
the pollen falls on the slide
6. Repeat for each sucrose solution and note the time at which the pollen was added
7. placate slides in the petri dish
8. Use a microscope at X100 magnification and a calibrated eye piece graticule to
observe the slides
9. Make observations quickly and return the slide to the petri dish to prevent drying
out
10. Once the pollen tubes have started to grow, measure the length of 4 or 5 tubes
at 3 minute intervals for 30 minutes
What are the controlled variables when investigated pollen tube growth?
Volume of sucrose solution, volume of mineral solution, time left in solution, pollen
source
What are the independent and dependent variables when investigating pollen
tube growth?
IV: Concentration of sucrose
DV: Length of pollen tube
Why must the pollen tube slides be kept in a moistened petri dish?
To prevent drying out
How often should you measure the length of pollen tubes?
Every 3 minutes for 30 minutes
What must be added to a sucrose solution before pollen?
, A mineral salt medium
How do you investigate the effect of temperature on membrane permeability?
1. Use a cork borer and knife to cut 1 cm lengths of beetroot
2. Place in distilled water overnight to remove dye, wash and blot dry
3. Place 8 boiling tubes in 8 water baths of different temperatures
4. Place a beetroot segment in each tube and leave for 30 minutes.
5. Remove the beetroot and shake the tubes to disperse the dye
6. Set colorimeter to % absorbance with a blue/green filter
7. Calibrate the colorimeter with distilled water
8. Calculate % absorbance for 2cm3 samples from each temperature
What are the controlled variables when investigating the effect of temperature
on membrane permeability?
Volume of distilled water, time left in water, size of beetroot piece, source of beetroot
How is dye removed from beetroot pieces when investigating the effect of
temperature on membrane permeability?
Placed in distilled water overnight to remove dye, washed and blotted dry
How is a colorimeter used when investigating the effect of temperature on
membrane permeability?
Set to % absorbance with blue/green filter
What is used to calibrate the colorimeter when investigating the effect of
temperature on membrane permeability?
Distilled water
How do you investigate the water potential of plant epidermal cells?
1. Take 5 thin sections of the red part of a red onion, as close to 1 cell thick as
possible
2. Label 5 watch glasses and add 5 different concentrations of sucrose solution
3. Add a piece of onion to each glass and leave for 20 minutes
4. Put a drop of each solution on separate slides and float each tissue on the
matching slides
5. Cover each section with a coverslip and observe under a microscope
6. Count 25 cells and record how many show plasmolysis
What are the independent and dependent variables when investigating the
effect of temperature on membrane permeability?
