Question

Which of the following statements is/are true?
I. Protoxylem and metaxylem is found in secondary xylem
II. In exarch condition, the protoxylem is towards the periphery
III. Tracheids are the chief water transporting elements in gymnosperms
IV. Companion cell is devoid of the nucleus at maturity

• A. I and IV only
• B. II and III only
• C. III and IV only
• D. II and IV only

Answer 1

The correct option is B II and III only

Endarch and exarch conditions are based on the position of protoxylem and metaxylem. Protoxylem and metaxylem are the two types of primary xylem. They are not seen in the secondary xylem. Protoxylem is the first formed primary xylem element. Metaxylem is the primary xylem that is formed after the protoxylem. In stem and roots, the protoxylem and metaxylem are arranged in two different ways. In roots, the protoxylem and metaxylem are present towards the periphery and centre, respectively. This is known as the exarch condition.


Xylem is a complex tissue and is made up of four different elements - tracheids, vessels, parenchyma and fibres. Tracheids and vessels are the major water-conducting elements in gymnosperms and angiosperms, respectively. Gymnosperms lack vessel elements and vessels are found only in angiosperms.


Companion cells are one of the components of phloem. They are specialised parenchymatous cells that are closely associated with the sieve tube elements in the phloem. The nucleus of companion cells controls the activity of the sieve tube element as sieve tube elements lack nucleus . It is a non-conducting element.