1.1. A scientist investigated two substances, X and Y,  which may affect the growth of new roots from a cut plant stem.

They used a ringing experiment to investigate the transport of substances X and Y through the plant stems taken from a grapefruit plant. A length of stem was cut from each grapefruit plant and a small block of agar was placed at the top of each stem. Substance X or Y was added to some of the agar blocks.

Figure 1

The stems were grown in the same environmental conditions for 5 weeks and then the number of roots per stem was recorded. The roots grew at the opposite end to where the agar block was located.

Table 1 below shows the results of the experiment. 

Table 1

 Agar delivers substances X and Y in treatments 2-5.

Suggest one other reason why agar is present in all of the treatments.

1.2. State what can be concluded about the action of substance Y in plants from Figure 1 and Table 1?

1.3. The movement of substances through the phloem can be explained using the mass flow hypothesis.

Evaluate whether the data from this experiment supports the mass flow hypothesis. No statistical analysis is required.

1.4. Upon further research it was discovered that substance Y could be sprayed onto the leaves of a plant and it would be absorbed into the phloem sap.

Using this information, discuss the mechanism by which substance Y could act as weed control.