Lesson 6 of 13 · 6 min
Cell wall
NCERT §8.5.2
Only the onion-peel slide holds still under Riya's cover slip without curling — because only it has a rigid wall around every cell.
The lesson in notes
In short
In plants and fungi a rigid, non-living cell wall covers the plasma membrane. Its jobs: giving the cell its shape, guarding against mechanical injury and infection, helping cells interact, and keeping out unwanted macromolecules.
Algal walls are made of cellulose, galactans, mannans and minerals such as calcium carbonate.
Walls of other plants contain cellulose, hemicellulose, pectins and proteins.
A young plant cell has a primary wall that can grow; this growth gradually slows as the cell matures.
The secondary wall is laid down on the inner side of the primary wall, that is, towards the plasma membrane.
The middle lamella, made mainly of calcium pectate, is the layer that glues neighbouring cells together.
Going outward from the cell: plasma membrane, secondary wall, primary wall, middle lamella. Plasmodesmata pass through the wall and middle lamella to join the cytoplasm of adjacent cells.