First slide

Phloem Transport: Flow from Source to Sink

Question

Statement A: Transport of photosynthates through phloem is bidirectional.
Statement B: The sugars or sucrose loaded into the sieve tubes of leaf veins is transported towards the shoot apex as well as towards the root.

Easy

A

Statement A is correct and B is incorrect.
B

Statement A is incorrect and B is correct.
C

Both statements A and B are correct.
D

Both A and B statements are incorrect.

Solution

At the source or leaf, the sucrose formed in mesophyll cells is actively transported into the sieve tubes. Due to this, the osmotic pressure increases or water potential decreases. Water of leaf xylem is osmosed into the sieve tubes. In the sieve tubes, the turgor pressure builds up and the contents of the sieve tube are pushed upwardly towards the shoot apex and downwardly towards the root. Hence the movement of substances through phloem is upward as well as downward.

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