Sieve tubes are formed from sieve-tube members laid end to end.
2.
They have a narrower diameter and are more elongated compared to sieve tube members.
3.
Each companion cell is derived from the same mother cell as its associated sieve tube member.
4.
Experiments to demonstrate bidirectional movement in a single sieve tube are technically very difficult to perform.
5.
Organic compounds such as sucrose produced by photosynthesis in leaves are distributed by the phloem sieve tube elements.
6.
Some experiments indicate that bidirectional movement may occur in a single sieve tube, whereas others do not.
7.
Phloem is a nutrient-conducting tissue composed of sieve tubes or sieve cells mixed with parenchyma and fibers.
8.
The companion cells, connected to the sieve tubes via plasmodesmata, are responsible for loading the phloem with sugars.
9.
If the mechanism of translocation operates according to pressure flow hypothesis, bidirectional movement in a single sieve tube is not possible.
10.
Sieve cells are typically associated with gymnosperms, because angiosperms have the more derived sieve tube members and companion cells in their phloem.
