AP BIOLOGY

Detailed explanation-1: -The phloem consists of sieve elements, companion cells, phloem parenchyma cells and phloem fibers. Other cell types may be found in the phloem of certain plant species. The functional units for long distance translocation and signal distribution are sieve tubes.

Detailed explanation-2: -The phloem is a complex tissue and is formed typically by three cell types, the sieve elements, the parenchyma cells, and the sclerenchyma cells (Figure 2a–d). Sclerenchyma cells might sometimes be absent in primary and/or secondary phloem.

Detailed explanation-3: -Both sieve cells and sieve tube members have parenchyma cells associated with them. Parenchyma cells associated with sieve cells are called albuminous cells; those associated with sieve tube members are called companion cells.

Detailed explanation-4: -The sieve tube is the conducting element of the phloem. It is formed from a vertical series of elongated cells, interconnected by perforations in their walls in areas known as sieve plates.

Detailed explanation-5: -Phloem is composed of various specialized cells called sieve elements, phloem fibres, and phloem parenchyma cells.