Question

Transport of food material in higher plants takes place through
(a) Sieve elements
(b) Companion cells
(c) Transfusion cells
(d) Tracheid

Answer 1

The phloem carries the food materials from the place it is available to the places where it is needed. The food material is transported by the long tube-like structure which is arranged in distinct linear rows and has pores through which the food material moves.

Complete Step by Step Answer:
Phloem is made up of many cells called sieve tube elements or sieve- tube members. It is a long tube-like structure which is arranged longitudinally. These cells are arranged one above the other in distinct linear rows to form the sieve tubes. A mature sieve tube element possesses a peripheral cytoplasm and a large central vacuole but lacks a nucleus. The cytoplasm occurs in the form of a thin- living layer along the inner side of the cell walls. The end walls of the sieve tube elements are called sieve plates which are generally oblique. A sieve plate has numerous sieve pores through which the food materials move from one element to the other.
Function of sieve tube element: These are the food conducting elements of plants. The synthesized food translocates through sieve tube elements in the form of a continuous channel.

Additional Information:
- Phloem is a living complex tissue that transports the food material, usually from the leaves to the other parts of the plants.
Elements of phloem: It is a complex tissue and is composed of types of cells viz.
- Sieve tube elements
- Companion cells
- Phloem fibers
- Phloem parenchyma.
- In sieve tubes, the pressure gradient is maintained by the companion cells.
- Tracheids are the elongated cells with tapering ends. It is a component of complex tissue xylem and helps in the transportation of water and minerals from the roots to the stems and the leaves. They also provide mechanical support.
- Transfusion cells are found characteristically around the vascular bundles of Gymnosperms and carry water and found between the vascular bundles and the mesophylls.

So, the correct answer is, '(a) Sieve elements'

Note:
- Sieve tube elements are thin- walled living structures having cellulosic cell walls. However, their walls are thicker than surrounding parenchyma cells.
- The endplates are called sieve plates because they are perforated in a sieve- like pattern.
- Sieve tube elements are associated with companion cells. As mature sieve tube elements lack nuclei, the functions sieve tubes are controlled by the nucleus of the companion cells which are found closely associated with the sieve tube elements. Both the sieve tube element and companion cells are called “Sister cells”.
- Protophloem consists of narrow sieve tube elements whereas metaphloem has bigger sieve tubes.
- Sieve tubes are absent in the pteridophytes and gymnosperms. These plants have sieve cells in place of sieve tubes, which are not arranged distinctly in the linear rows.