AQA Biology A-Level Required Practical 3 - Investigating Water Potential - Preparation and Determination of Water Potential

Oct 20, 2026

Uploaded by Kyle

AQA Biology A-Level Required Practical 3 outlines how to produce a dilution series of sucrose, generate a calibration curve, and use it to determine the water potential of plant tissue. The method prepares sucrose solutions at defined molarities, measures potato mass before and after exposure, and calculates percentage mass change. A graph of mass change versus concentration identifies the isotonic point, linking solute concentration, osmosis, and direction of water movement. Includes equipment, risk assessment, and concluding interpretation.

LanguageEnglish

CategoryExam

FormatPDF

Pages4

Reading Time10 min

AccessFree to download

Equipment list

Method

Risk Assessment

Graph

Conclusion

AQA Biology A-Level Required Practical 3 Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue. Calibration curves are graphs used to determine an unknown concentration of a sample by comparing the unknown to a set of standard samples with known concentrations-they are also known as standard curves. A dilution series can be used to create a set of samples with known concentrations. A calibration curve can be used to determine an unknown water potential in a potato sample. Water potential is the tendency of water to diffuse from one area to another. Water molecules move from areas of high water potential to areas of low water potential by osmosis. The water potential is determined by the concentration of solutes. The movement of water in and out of cells is related to the relative concentration of solutes either side of the cell membrane. Equipment list ● Potato tuber ● Cork borer ● Scalpel ● Ruler ● Distilled water ● Sucrose solution (1M) ● Boiling tubes ● Boiling tube rack ● Timer ● Digital balance ● Paper towels Method 1. Make a series of dilutions of 1M sucrose solution. These should be at 0 .0, 0.2, 0.4, 0.6, 0.8 and 1.0M sucrose. Dilute using distilled water. 2. Measure 5cm3 of each dilution into separate test tubes. 3. Use a cork borer to cut out six potato chips and cut down the sections into identically sized chips. Dry each chip using a paper towel to remove excess water but do not squeeze. 4. Weigh each before the start of the experiment. 5. Place a potato chip in each test tube (one per sucrose concentration) and leave for 20 minutes. 6. Remove each potato chip, dry gently using paper towel, and weigh them in turn. 7. Calculate the percentage change in mass for each sucrose solution. Risk Assessment | Hazard | Risk | Safety Precaution | In emergency | Risk
Level | | --- | --- | --- | --- | --- | | Scalpel | Cuts from sharp object | Cut away from fingers;use forceps to hold sample whilst cutting, keep away from the edge of the desk | Elevate cuts; apply pressure; seek medical assistance | Low | | Broken glass | Cuts from sharp object | Take care when handling glass objects; keep glassware away from edge of desk | Elevate cuts; apply pressure; do not remove glass from wound; seek medical assistance | Low | Graph ● Plot a graph of change in mass against concentration of sucrose solution. ● The point at which the line of best fit crosses the x axis (zero change in mass) indicates the point at which the solution is isotonic. This is when the water potential of sucrose solution is the same as the water potential of the potato tissue, so there is no net movement of water in or out of the potato. Conclusion ● Potato chips in lower concentrations of glucose solution will increase in mass, whilst those in the higher concentrations of glucose solution will decrease in mass. ● In the dilute glucose solutions, the solution has a higher water potential than the potato, so water passively moves via osmosis to the area of lower water potential (the potato) . This causes the potato to increase in mass. ● In concentrated glucose solutions, water will move out of the potato, thus the potato will decrease in mass.

FAQs

What is the purpose of making a dilution series in this practical?

To create a range of sucrose concentrations with known values, which are then used to produce a calibration curve for comparison.

How do you determine the isotonic point from the graph?

Find where the line of best fit crosses the x-axis, indicating zero change in mass; this corresponds to equal water potential between the solution and potato tissue.

What happens to potato mass in dilute versus concentrated sucrose solutions?

Dilute solutions increase potato mass because water moves into the potato by osmosis. Concentrated solutions decrease potato mass because water moves out of the potato.

Oct 20, 2026

Uploaded by Kyle