Question

Growth of cell wall during cell elongation takes place by
(A) Apposition
(B) Intussusception
(C) Both A and B
(D) None of the above

Answer 1

Cell wall of the plant is made up of cellulose, hemi cellulose etc. These cell wall materials are deposited on a cell wall either with the process of Apposition or Intussusception, based on the type of material deposited.

Complete answer:
Cell wall is the protective covering of the plant cell and bacterial cell. In the plant cell, it is made up of Cellulose, Hemicellulose, Pectin. Cutin, lignin and suberin may also deposit on the cell wall.
Cellulose, hemi-cellulose, pectin are synthesised in the golgi body.
Bacterial cell wall is made up of peptidoglycans while in fungi it is made up of Chitin.
Growth of the cell wall occurs with the help of two methods:

1. Intussusception: in this method cell wall material is deposited in the form of granules. Primary cell wall is formed by this method. Cell elongation occurs by the intussusception.
2. Apposition: in this, cell wall material deposits in the form of layers. Secondary cell wall is formed by both of these methods.

Hence the correct answer is OPTION(B)

Note: There are three structure of cell wall:

1. Primary cell wall: the cell wall of a young plant cell is the primary cell wall which is capable of growth and gradually diminishes as the cell matures.
2. Secondary wall is formed on the inner side (towards the membrane) of the cell.
3. The middle lamella is a layer made up of calcium (80%) and magnesium pectate (20%) which holds or glues the different neighbouring cells together. The cell wall and middle lamellae may be traversed by plasmodesmata which connect the cytoplasm of neighbouring cells.