Question

Mature sieve tube elements are devoid of------
A. Nucleus
B. Cytoplasm
C. Protein
D. Mitochondria

Answer 1

Hint: Sieve tubes are the major component of phloem. They consist of several sieve elements which are connected end to end and give a channel for conduction.

Complete answer:
Sieve tube element is an integral part of phloem and forms a channel like structure helpful for conduction. They are helpful in the translocation of sugars and complex carbohydrates in the whole body. They are necessary for the transportation of important molecules with the use of companion cells.
The vital function of the sieve tube is the transportation of carbohydrates, especially sucrose to the plant body . The interface of the tubes contains pores which play a major role in conduction. Each sieve tube element is joined with many nucleated companion cells, to which they are interconnected by plasmodesmata. Sieve tube elements are the relative type of phloem cells found in angiosperms.
Mature sieve tube elements are deep , tubular and do not contain nucleus in the cells with no secondary wall and terminal sieve plate. They lack nucleus at the maturity so that they are associated with companion cells for support. Their features are the same as prokaryotic cells. True sieve tube is not present in gymnosperms and pteridophytes.
Sieve tube members are found end to end which gives many tubular columns known as sieve tubes. These respond to the xylem vessels. The end wall or cross wall between the adjacent cell is an oblique and porous plate called sieve plates. The slightly depressing part of the sieve plate perforated by a cluster of sieve pores called the sieve area.

Note: The phloem comprises sieve compartments, companion cells, phloem parenchyma cells and phloem fibers. The sieve tubes are the enlarged living cells found in the phloem of flowering plants which are helpful for the conduction of food transport mainly glucose inside the plant body.