Like Schr6dinger\'s cat. you are locked in a room and before you can be let out
ID: 174604 • Letter: L
Question
Like Schr6dinger's cat. you are locked in a room and before you can be let out you need to determine the main direction (up or down) in which transport occurs in the xylem and in the phloem of a plant. You don't remember from your classes, and in this room there are no textbooks and no internet access. However, you do have access to a plant and all sorts of reagents, chemicals, measurement equipment and instruments. Describe one technique that you could use and how you would use it to resolve this question. (Luckily, you do remember that the xylem is closer to the center of a plant stem than the phloem.)Explanation / Answer
Xylem and phloem are the main vascular tissues of the plants. They are like the arteries and veins of the plant. The xylem transports water to the plants and the phloem transports food to the plant. Now we have to determine the direction of transport of xylem and phloem.
The most basic experiment to study the direction of transportation in xylem is color water experiment. In this when we place the small piece of plant in the colored water. It starts absorbing that water and when we cut it open we can see the flow of water occurs from bottom. So it is in upward direction. And as we know that xylem is closer to the center of a plant compared to phloem, the center tube is colored and not the adjacent sides. So it is proved that direction of transportation for xylem is in upward direction.
To study the direction of transportation of phloem is the ringing experiment, in this we take a plant and remove a part of phloem from the plant and not the xylem. Now the area from where we have removed the tissue we cover it with wax and leave it for 7-8 days. After 7-8 days the upper region of the epidermis becomes swollen and the adventitious roots start growing. This shows that the movement of food takes place in the downward direction. Hence we can say that xylem transports in upward direction whereas phloem transports in downward direction.
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