Cells of a freshwater alga can move nitrate ions across their cell membranes.
A scientist separates identical algal cells into four treatments. At the start, the concentration of nitrate ions in the cytoplasm of every cell is 12 arbitrary units. The scientist keeps the nitrate ion concentration in the surrounding water constant for 30 minutes.
All four treatments are kept in darkness to prevent photosynthesis.
| Treatment | Concentration of nitrate ions in surrounding water in arbitrary units | Oxygen in the water | Concentration of nitrate ions in cytoplasm after 30 minutes in arbitrary units |
|---|---|---|---|
| A | 3 | present | 30 |
| B | 3 | absent | 8 |
| C | 24 | present | 36 |
| D | 24 | absent | 22 |
Calculate the percentage increase in the concentration of nitrate ions in the cytoplasm of the cells in treatment C.
Explain the results for all four treatments. Your answer should name the processes involved.
194 exam-style questions on OCR GCSE Biology 2.1 Supplying the cell, covering 2.1.1 Transport across cell membranes, 2.1.2 Mitosis and the cell cycle, 2.1.3 Importance of cell differentiation, and 2.1.4 Stem cells. Each one has a worked solution and a mark scheme showing where the marks go.