Osmosis and water potentialAQA A-Level Biology: Flashcards

Exam questions on Osmosis and water potential

1. Cylinders of potato tissue were placed in sucrose solutions of different concentrations. Pure water has a water potential of 0 kPa and the potato cells have a water potential of −400 kPa.
   Explain why the mass of a potato cylinder placed in pure water increased.2 marks
2. A student has a stock solution of 1.0 mol dm⁻³ sucrose and distilled water. She makes a dilution series and measures the mass of potato cylinders before and after 30 minutes in each solution.
   Explain how a calibration curve of percentage change in mass against sucrose concentration can be used to find the water potential of the potato tissue.2 marks
3. A student recorded the percentage change in mass of potato cylinders after 30 minutes in sucrose solutions. In 0.0 mol dm⁻³ the change was +14.0%, in 0.2 mol dm⁻³ it was +6.0%, in 0.4 mol dm⁻³ it was −4.0%, in 0.6 mol dm⁻³ it was −11.0% and in 0.8 mol dm⁻³ it was −17.0%.
   Explain why the cylinder in 0.0 mol dm⁻³ sucrose gained mass and the cylinder in 0.8 mol dm⁻³ sucrose lost mass.3 marks