Question

During cell enlargement phase of growth, molecules of new cell wall material are inserted between the original molecules of the stretched wall. This process is known as
A. Intussusception
B. Apposition
C. Integration
D. None of the above

Answer 1

Hint: The cell wall expands at the time of growth because of the turgor and consequently, the microfibrils are disconnected at a few regions in the cell wall and a gap is formed. The gap produced as a result of this separation is filled through the deposition of new microfibrils.

Complete answer:
Intussusception is the process of growth by deposition of new cell wall materials inserted between the existing constituents of the stretched cell wall. Cell elongation takes place by the process of intussusception. Whereas, in the process of apposition, the new cell wall layers are laid i.e. the growth of cell wall in new cells takes place via apposition. The cellulose is inserted in between the spaces of the cell wall, this process of mending and refilling of the gaps in the cell wall and adding of the new microfibrils is known as Intussusception. This process leads to an increase in the cell portion. In the process of apposition, the deposition of the new microfibrils is generally centripetal. It takes place from the periphery and moves towards the lumen of the cell. The cell walls of many tissues usually follow the centripetal type of growth.
So, the correct answer is option A.

Note: The plant cell wall is typically composed of materials like carbohydrates, pectin, cellulose, hemicellulose and some small amounts of minerals. These materials form a clustered network together with the structural proteins and form the cell wall of the plant cell. The three primary layers of a plant cell wall are primary cell wall, middle lamella and secondary cell wall.