question_answer 7)

Why are xylem and phloem called complex tissues?

Answer:

Xylem and phloem tissues are made up of more than one type of cells that is why they are known as complex tissues. (i) Xylem is composed of four different kinds of elements, namely?tracheids, vessels, xylem fibres and xylem parenchyma. Tracheids are dead tube-like cells which are thick walled, vessels are made up of large number of tube cells placed end to end. Xylem fibres are thick walled cells that may be septate and aseptate. Xylem parenchyma is living and thin walled cells. (ii) Phloem is composed of sieve tube elements, companion cells, phloem parenchyma and phloem fibres. Sieve tube elements are tube-like cells, whereas phloem parenchyma are living cells and phloem fibres are thick walled lignified cells.