Question

The cut end of a shoot is dipped in eosin solution. What will happen?
a) Ascent of sap does not occur.
b) Ascent of sap does not occur but the leaves remain fresh.
c) Leaves wilt but the ascent of sap continues.
d) Ascent of sap occurs and the tracheary elements get stained.

Answer 1

Eosin is a kind of chemical solution often used by histologists for dying (or staining) plant tissues. It is pink in colour and is generally used to dye protein content of cytoplasm of plant cells. These stains highlight the cell features and thus helps in its detailed study.

Complete answer
Eosin is an aqueous solution of Eosin salt along with $1\%$ of alcohol content. This solution acts like a sap (that is, water with some minerals) for shoot tissues. When a shoot is dipped into this solution then a concentration gradient (increase in number of particles on one side of the membrane) of Eosin molecules is created outside the shoot body. This concentration creates a transpiration force that pulls the solute molecules of the Eosin solution in upward direction through xylem tissues. Also, Eosin being a dying agent, would stain the tracheary tissues (the pathway of xylem tissues), vessels of xylem, pink in colour, through which these molecules were travelling inside the shoot. This process is used to track the pathway of xylem tissues that gets highlighted (pink in colour) by the action of Eosin. However, this sap won't affect the shoot leaves as is an aqueous solution. Therefore, ascent of sap occurs and the tracheary elements get stained without any wilting of leaves.

So, option D is the correct option.

Note:
In this process, phloem tissues are left unstained because in plants xylem transport sap (water and minerals) whereas phloem transport the food materials. Thus, xylem gets stained leaving the phloem tissues untouched.