Concept:Red ink acts as a visible tracer to show the path of water movement inside the stem tissues.
Explanation:The seedling was kept upright with its roots dipped in red ink solution.
For three hours, the plant absorbed the coloured water through its root hairs.
The ink moved upward inside the stem along with the absorbed water.
A thin transverse section of the stem was then cut and observed under the microscope.
The red stain was clearly visible only in the xylem vessels, not in the phloem.
This shows that the xylem is the specialised tissue responsible for conducting water upward from roots to leaves.
It is not about microelements, diffusion of the dye itself, or food transport because food moves through phloem and is not stained by red ink.
Therefore, the experiment is investigating the ascent of water through the xylem.
Answer:B. ascent of water through the xylem