Isotonic Point of Potatoes

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Rushikesh Birewar Class 12 Biology HL

Isotonic Point of Potatoes – Biology Lab Report

Topic: Chemicals of Life

Research Question:

To find the isotonic point of potato (Solanum tuberosum) by varying the concentration (M) (+/- 0.06 M) (0.10,0.15,0.20,0.25,0.30 M) and measuring the change in length of potato strips (cm) (+/- 0.01 cm).

Background Information:

Isotonic Point: The isotonic point is the point where the concentration of the solution is the same as the concentration of the cell. It means that there are equal amounts of 'free' water (not bound to solutes) in the solution and the potato. 

Potato:  A plant tuber, Solanum tuberosum, eaten as a starchy vegetable, particularly in the Americas and Europe



  1. Concentration of Glucose solution (M) (+/- 0.06 M) (0.10, 0.15, 0.20, 0.25, 0.30)


  1. The change in mass and length of the potato chips (cm) (+/- 0.01 cm)


  1. Electronic Balance (+/- 0.01 g)
  2. Ruler (+/- 0.05 cm)
  3. 2 – 3 Potatoes
  4. A scalpel
  5. Glucose solutions of concentrations (0.10, .15, .20, .25, .30 M)
  6. 5 Petri dishes with a cover
  7. A few paper napkins
  8. Measuring Cylinder (+/- 0.05 cm3)
  9. Beakers (100 cm3)
  10. Permanent Marker Pen


  1. Cut the potato strips into a pre designated size so that their surface area is constant between the strips in the same sample
  2. Cut 5 potato strips for each sample into the same size as the other strips in the same sample.
  3. Measure the length and mass for each of these potato strips for all of the 5 samples using the electronic balance (+/- 0.01g) and the ruler (+/- 0.05 cm) provided
  4. Now pour 10.00 cm3 of the glucose solutions (0.10, .15, .20, .25, .30 M) into 5 different petri dishes using the measuring cylinder (+/- 0.05 cm3)
  5. Place 5 potato strips of consistent length, height and breadth (size) in each petri dish of a certain glucose concentration.
  6. After doing so, cover these petri dishes and place them in a corner, safe from any type of interference.
  7. After about a day, remove all these samples from the solutions, reweigh and re-measure the mass and length of the potato strips from each sample respectively.
  8. Make sure that these samples are kept in an airconditioned room where the temperature and pressure are kept constant.
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Raw Data Table:

Table 1: Shows the data collected for the potatoes in the 0.10 M solution (Glucose)

Table 2: Shows the data collected for the potatoes in the 0.15 M solution (Glucose)

Table 3: Shows the data collected for the potatoes in the 0.20 M solution (Glucose)

Table 4: Shows the data collected for the potatoes in the 0.25 M solution (Glucose)

Table 5: Shows the data collected for the potatoes in the 0.30 M solution (Glucose)

Qualitative Observations:

  1. The potatoes were ...

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