Question

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

Answer 1

Hint: In this process, the primary wall is extended and secondary wall materials will be deposited. By this application, the secondary wall material is deposited in the form of thin layers.

Complete step by step answer: Cell wall growth includes both surface area growth and thickness growth. Normally, the entire cell wall is rising. Localized development occurs in fibres, root hairs, tracheids and pollen tubes. A new primary wall is rising in the surface area. The wall extends due to the turgor pressure exerted by the protoplast on the walls. Turgor pressure is caused by a protoplastic propensity to absorb water by osmosis. It forces the protoplast outwards towards the wall, and the wall begins to stretch out from a plastic manner. New cell wall materials such as matrix polysaccharides and cellulose microfibrils are deposited over the expanding wall.
Microfibrils of cellulose are produced between both the plasmalemma and the outer envelope. This is shown by an isolated protoplast culture where the initial development of the cell wall is not associated with cytokinesis. Preston is of the opinion that tiny granules are present on the outer face of the plasmalemma.
Earlier, there were two hypotheses to explain the development of the cell wall in relation to the deposition of wall materials. In one perspective, growth occurs via intussusception, where new microfibrils are interwoven between the existing microfibrils of the expanding wall. The other view, that is more prevalent, is that growth occurs by apposition. So, the addition of new cell wall particles to the current one is intussusception.
Hence, the correct answer is option A, 'Intussusception'.

Note: The void, thus formed by the separation, is then filled by the accumulation of new microfibrils by either apposition or intussusception. Growth hormones and enzymes present on the cell wall are suggested to be involved in the process.