Question

Which is the outermost structure of the cell wall?
A. Primary wall
B. Secondary wall
C. Tertiary wall
D. Middle lamella, if present

Answer 1

Hint: The outermost structure of the cell wall acts as glue between different cells. It is the junction of contact between the cells. Moreover, the secondary cell is not present in every cell. It is only present in a few cells that are responsible for altering the growth of the primary cell wall.

Complete answer:
The cell wall is tough, flexible, and rigid. It is composed of cellulose microfibrils that are linked by a hemicellulosic network which is embedded in the pectin matrix. The most common hemicellulose present in the cell wall is Xyloglucan.
The cell wall of the plants and most algae consist of three important layers-
• The primary wall- is the outermost layer of the plant cell that is a thin, flexible, and extensible layer. The primary wall is generally covered with cutting and wax, forming a permeability barrier known as plant cuticle.
• The secondary wall- the wall is thick and is present inside the cell wall. The fibers which make up the wood are cellulose.
• The middle lamella- is a rich layer of pectin forming the plasmodesmata. It is a connection between two adjacent cell walls and glues them together.

Hence, the correct answer is option (D).

Note: The major function performed by the cell wall is-
• It provides a definite shape, strength, and rigidity.
• It protects cell constituents from mechanical injury, stress, and physical shock.
• It prevents bursting out of the cell due to an increase in vacuole size during turgidity.