Question

Describe the differences in structure and function of sieve tubes, sieve elements and companion cells.

Answer 1

Ans.

Sieve elements -

• include sieve tube elements and sieve cells.
• Sieve tube elements are present in angiosperms but absent in gymnosperms while sieve cells are present in both angiosperms and gymnosperms.
• Sieve tube elements are more specialized for translocation of food while sieve cells are less specialized.

Sieve tube -

• sieve tube elements are placed one above the other forming a continuous tube called sieve tube.
• The sieve tube is found in angiosperms.
• Contain sieve plates
• Enucleated
• Contains fewer mitochondria
• Translocates food throughout the body.

Companion cells-

• Living cells usually associated with sieve tubes
• Don't contain sieve plates
• Nucleated
• High no. Of mitochondrial
• Responsible for regulating the activity of sieve elements.