Q. Select the wrong statements w.r.t. cell wall:
Solution:
Cell wall not only gives shape to the cell and protects the cell from mechanical damage and infection, but it also helps in cell-to-cell interaction and provides a barrier to undesirable macromolecules.
The cell wall is formed of the following layers (i) Middle Lamella (ii) Primary wall (iii) Secondary Wall (iv) Tertiary wall.
Middle Lamella is composed of pectin as calcium and magnesium pectate (mainly calcium pectate). It is absent on the outer free surface of cell and plasmodesmata.
The primary cell wall is elastic, permeable and thin, single-layered outermost wall layer of the plant cell. Cellulose, hemicellulose and pectin contents are roughly in equal amount in the primary wall. Root hairs, parenchymatous cells and meristematic cells are formed of only primary wall. It is capable of growth. Its growth takes place by intussusception (Addition of materials within the existing wall). It generally diminishes as the cell matures.
Secondary cell wall lies inside the primary wall, i.e. it lies towards the membrane side of the cell. Its growth takes place by accretion (deposition of materials over the surface of an existing structure). It consists of at least three layers-S1, S2, S3, this wall is made up of cellulose, hemicellulose and pectin.
Sometimes an innermost layer of the secondary wall is distinct both chemically as well as in staining properties due to the presence of xylans. It is called tertiary wall Eg. Tension wood in gymnosperms.
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