Why are xylem and phloem called complex tissues? How are they different from one other?

Soln

A complex tissue is the one which has more than one type of cells having a common origin which coordinate to perform a common function.

Xylem and phloem are made of different types of cells hence they are called complex tissues.

Xylem is made up of four different types of cells (elements), namely

• tracheids- Tracheids are elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts.

• vessels- A vessel element (trachea) is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are found in flowering plants

• xylem parenchyma- xylem live plant cells that are short, lignified and generally thin walled.

They surround conducting elements and assist directly or indirectly in the conduction of water upwards through vessels and tracheids, and also serve for food storage.

• xylem sclerenchyma (or fibre)- Xylem fibres are mainly supportive in

Phloem is also made of four different types of elements

• sieve tubes- Sieve tube, in flowering plants, elongated living cells (sieve-tube elements) of the phloem, the nuclei of which have fragmented and disappeared and the transverse end walls of which are pierced by sievelike groups of pores (sieve plates). They are the channels of food (mostly sugar) transport.

• companion cells- companion cell A type of cell found within the phloem of flowering plants. Companion cell are usually closely associated with a sieve Its function is uncertain, though it appears to regulate the activity of the adjacent sieve element and to take part in loading and unloading sugar into the sieve element.
• phloem parenchyma

• phloem fibre