First slide

Phloem Transport: Flow from Source to Sink

Question

A few drops of sap were collected by cutting across a plant stem by a suitable method. The sap was tested chemically. Which one of the following test results indicates that it is phloem sap?

Moderate

A

Acidic
B

Alkaline
C

Low refractive index
D

Absence of sugar

Solution

Phloem sap made up of non-reducing sugars, amides, ureides, PGR and little bit inorganic elements. Due to amides and ureides with very less electrolytes the overall pH of phloem sap is alkaline, because amides and ureides are rich of ${NH}_{2}$ groups. In contrast to phloem, in xylem Amides & ureides are present with huge amount of mineral elements so overall pH of xylem sap, even in presence of amides & ureides will not be alkaline. Hence alkaline pH is indictor of phloem sap.

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