Question

2 write the experiment to prove sugar is
transported through phloem​

Answer 1

Answer:

Ernst Munch (1930), first proposed this hypothesis of solute transport in phloem tissue also called the pressure-flow hypothesis or the Munch hypothesis.

According to this theory, organic solutes are translocated through the sieve tubes from the source (leaves) to the consumption end or sink(is the part that stores the food). But, the source and sink may be reversed depending on the seasons or plant needs. Therefore the direction of movement in phloem can be bidirectional.

Movement of solutes such as sucrose through the phloem of a plant. Three Stages are involved namely,

A) Phloem loading - here sugar moves from the photosynthesizing cells into a chain of mesophyll cells, transfer cells, to the phloem of the vascular bundle.

B) Translocation -the pressure inside the sieve tubes is greatest at the source and lowest at the sink It pushes sucrose, etc, from source to sink.

C) Unloading - it is a passive transport mechanism. Unloading of the sieve tube takes place at the sink. The solute is removed for use, thus maintaining the pressure gradient in the sieve tubes.

Explanation:

Answer 2

1. Ringing or Girdling Experiment

In a healthy potted plant, all the tissue outer to the xylem including bark, cortex, and phloem is removed from a small portion of the woody stem (girdling). The upper and lower part of the plant is now attached only through the xylem.

After a few days, it is observed that the food material is accumulated just above the girdling. Also, the roots die first in the girdled plant. This may happen because the food is not transported to the roots. This experiment proves that phloem is responsible for translocation of organic material.

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