The scientists used a radioactively labelled DNA probe to show that the cells of tobacco plant leaves contained the SUT1 gene.

Describe how they would do this.

Do not include PCR in your answer.

To study the role of SUT1 in tobacco plants, scientists reduced the expression of the SUT1 gene.

When the SUT1 gene is transcribed, the SUT1 mRNA produced is called 'sense' SUT1 mRNA. The scientists genetically modified plants by inserting an extra gene so that this also allowed the production of 'antisense' SUT1 mRNA.

The scientists had two types of tobacco plants:

• type A – plants that were genetically modified

• type B – plants that were not genetically modified.

Suggest how the production of 'antisense' SUT1 mRNA in type A plants would reduce the expression of the SUT1 gene.

The scientists hypothesised that lower rates of sucrose transport from leaves would cause reduced growth.

To test this hypothesis, the scientists provided leaves of type A and type B plants with labelled carbon dioxide (14CO2). To estimate sucrose transport out of leaves, they measured the percentage of 14C remaining in the leaves for 16 hours.

Figure 5 shows their results.

Calculate the ratio of percentage of 14C remaining in leaves of type B to type A plants 16 hours after providing 14CO2

Answer ______________

In type B plants, the percentage of 14C remaining in the leaves does not reach zero per cent, as shown in Figure 5.

Suggest two reasons why.

1

2

The scientists measured physiological differences between type A plants and type B plants.

Table 3 shows the scientists' results as they presented them.

Sucrose is able to inhibit the production and activity of rubisco in leaves of a plant.

Type A plants have decreased dry mass compared with type B plants.

Use all the information to suggest and explain how the physiological factors in Table 3 would contribute to the decreased dry mass observed in type A plants.