Question

The cell functionally associated with sieve tubes is
A. Phloem fibres
B. Phloem parenchyma
C. Companion cell
D. Collenchyma

Answer 1

Plants are mostly multicellular, eukaryotic organisms. Plants depend on photosynthesis as a source of food production and the exchange of gases. Plants convert carbon dioxide from the environment into oxygen and release it into the environment.

Complete answer: Plants are composed of many parts, each of which has specific functions that facilitate the growth, strengthening, and development of the plants. Similarly, the plants are composed of different cells with different functions facilitating the growth, and development of the plant. Plants are composed of the following cells: parenchyma cells, collenchyma cells, sclerenchyma cells, xylem cells, phloem cells, meristematic cells, and epidermal cells. The leaves of the plant comprise of xylem tissues and phloem tissues. Xylem is present towards the adaxial surface of the leaf, whereas the phloem is present towards the abaxial surface of the leaf. Both xylem and phloem take part in providing the plant with nutrients for growth and development. Xylem functions by transporting water and other nutrients absorbed by the roots to various parts of the plant. The phloem on the other hand is responsible for transferring food absorbed by the leaves through photosynthesis, to parts of the plant body that are unable to photosynthesize such as roots and stem. The phloem is a vascular tissue and consists of major compounds such as the sieve elements, companion cells, phloem parenchyma, and phloem sclerenchyma. Sieve tubes are elongated cells present in the phloem of flowering plants and help in carrying out the phloem function, i.e. transportation of food.
Let's consider the options one by one-
-Phloem fibers: Phloem fibers are associated with the phloem tissue and responsible for providing tensile strength and flexibility in such a way so as to not limit flexibility.
-Phloem parenchyma: Phloem parenchyma cells also known as transfer cells in the transportation of food from the leaves to different parts of the plant that are incapable of carrying out photosynthesis.
-Companion cell: Companion cells are a type of cells present within the phloem. Though their exact function is unknown, they are determined to assist sieve tubes by providing them with energy to transport compounds to different parts of the plant. Companion cells also provide necessary signaling proteins to sieve tubes as well.
-Collenchyma: Collenchyma cells provide strength and rigidity to the cell. They appear to be polygonal in shape and have a thick deposit of cellulose in their cell wall.
Therefore, the answer is C, i.e., Companion cells.

Note: Phloem is equipped with structural elements such as companion cells, secretory cells, phloem parenchyma, and sieve tubes. Sieve tubes as discussed earlier are considered to be the conducting elements of phloem. The highest concentration of obligate bacterial parasites known as phytoplasma is present in mature sieve tubes.