1.1. Some scientists investigated the uptake of magnesium ions in rice plants. They divided the plants into two groups and placed their roots in solutions containing radioactive magnesium ions.

   Group Y: plants had a substance that inhibited respiration added to the solution    
Group Z: plants did not have the respiratory inhibitor added to the solution

The scientists calculated the total amount of magnesium ions absorbed by the plants every 5 minutes. Their results are shown in the graph in Figure 1 below:

Figure 1 

Calculate the ratio of the mean rate of uptake of magnesium ions in the first 20 minutes to the mean rate of uptake of magnesium ions in the second 20 minutes for group Z plants. Show your working.

1.2. Consider the graph in Figure 1. Explain the results of the students’ investigation.

1.3. Using the graph in Figure 1, calculate the rate of uptake of magnesium ions for group Y plants during the investigation. Give suitable units.

1.4. State the names of three other substances that would not be absorbed into the group Y plants.