Question

Which of the following is made up of dead cells?
(a) Phloem
(b) Xylem parenchyma
(c) Collenchyma
(d) Phellem

Answer 1

Hint: These cells of meristematic cell layers of the stem of trees, develop outwards. These are also called cork cells which are dead at maturity because of slowly losing its protoplast.

Correct step by step answer:
Phellem is made up of dead cells present at the periphery of the bark. . These are the tissues found in many vascular plants as a part of the epidermis. These are present in one of the many layers of bark, between the layers of cork and primary phloem. Cork is a tough protective material produced by the cork cambium.
- The cork cambium is a lateral meristem and is responsible for the secondary growth that replaces the epidermis in roots and stems. These are found in woody and many herbaceous dicots, gymnosperms, and some monocots.
- Phellogen is the meristematic cell layer responsible for the development of the periderm. The periderm is consists of three different layers:
- Phelloderm: These are present inside of cork cambium and composed of living parenchyma cells.
- Phellogen or cork cambium: This layer of meristem gives rise to the periderm.
- Phellem or cork: These are dead at maturity and are mainly air- filled protective tissue on the outside or near the periphery of the stem.
- Growth and development of cork cambium vary between different species and are also highly dependent on age and growth conditions, as can be observed from the different surfaces of bark, that may be smooth, scaly, or flaking off.
So, the correct answer is, ’(d) Phellem’.

Note:
- Cork has been used for many purposes including wine bottle stoppers, bulletin boards, coasters, hot pads to protect tables from hot pans, insulation, sealing for kids, flooring, gaskets for engines, fishing bobbers, handles for fishing rods and tennis rackets, etc.
- It is also a high strength- to- weight/cost ablative material for aerodynamic prototypes in wind tunnels, as well as satellite launch vehicle payload fairings, reentry surfaces, and compression joints in thrust- vectored solid rocket motor nozzles.
- The function of phellem is to protect the plant from excessive evaporation, temperature fluctuations, penetration by microorganisms, and ingestion by animals. Soft phellem consists mainly of thin- walled cells that characterize chokeberry and fir; whereas the hard phellem is with cells having thick walls and is typical of willow trees.