A technician cuts similar-sized pieces from living, soft young plant stems. The pieces are placed in solutions P and R, which contain different concentrations of the same non-toxic dissolved substance.
Each piece is completely immersed throughout the investigation. All other conditions are kept the same. The pieces are gently blotted before their initial and final masses are measured.
| Solution | Concentration of dissolved substance in g per dm³ | Mean percentage change in mass after 4 hours in % |
|---|---|---|
| P | 40 | +7.2 |
| R | 240 | -6.4 |
Use the results to explain the different percentage changes in mass and predict which pieces would be less firm after a further four hours.
114 exam-style questions on OCR GCSE Biology 2.2 The challenges of size, covering 2.2.1 Exchange surfaces and surface area : volume ratio, 2.2.2 Substances transported in organisms, 2.2.3 The human circulatory system, 2.2.4 The heart and blood vessels, 2.2.5 Red blood cells and plasma, 2.2.6 Uptake of water and mineral ions by plants, 2.2.7 Transpiration and translocation, 2.2.8 Xylem and phloem, 2.2.9 Environmental factors and water uptake, and 2.2.10 Using a potometer. Each one has a worked solution and a mark scheme showing where the marks go.