Question 4

In an investigation into the transport mechanisms of tomato plants, scientists applied localized steam treatment to a section of the stem. Control plants did not receive this heat treatment. They then supplied carbon dioxide containing radioactively-labelled carbon, $14C^{14}\text{C}$ , to a leaf situated above the treated stem section.

After 5 hours, they:

Identified the position of the radioactively-labelled carbon in each plant.
Recorded the water content of the leaves above the treated section.

The results showed:

In control plants, the radioactively-labelled carbon was found throughout the plant (including roots and lower leaves).
In heat-treated plants, the radioactively-labelled carbon was only detected in the leaf that was supplied with $14CO2^{14}\text{CO}_2$ and did not pass the treated section.

The leaf water content data are presented in the table below:

Plant group	Leaf water content / % of maximum ( $±2\pm 2$ standard deviations)
Heat-treated	$(±9.5)81.5\ (\pm 9.5)$
Control	$(±8.0)88.2\ (\pm 8.0)$