Fig. 5.1 shows a photomicrograph of a transverse section through a dicotyledonous stem. Use label lines and labels to point out the phloem tissue and xylem tissue in Fig. 5.1.
Describe the route by which sucrose is carried in phloem sieve tubes from photosynthesising leaves to the rest of the plant.
Cyanide ions ($\text{CN}^-$) reduce the activity of an enzyme in respiration. Suggest why treating photosynthesising leaves with $\text{CN}^-$ leads to less sucrose being moved into phloem sieve tubes.
A student had to perform semi-quantitative Benedict’s tests on two solutions. Solution A was taken from the cytoplasm of cells in the mesophyll tissue of photosynthesising leaves. Solution B was taken from the phloem sap in phloem sieve tubes. The solutions came from the same plant, and all other variables were kept constant. For each solution, the student recorded how long it took before the first colour change appeared. Suggest which solution, A or B, would change colour in the shortest time. Explain your answer.