Cell walls & Their role in Regulating Plant Cell Shape Flashcards
What are the two sections of the plant cell?
The cell wall and the protoplast (plasma membrane and everything inside it)
What is the structure of the cell wall?
Cellulose (which is a highly ordered glucose polymer formed of long ribbon-like structures) forms a long strand called a microfibril.
What are the two phases of cell wall structure?
Phase 1: microfibrils (cellulose)
Phase 2: matrix (Pectin polysaccharides and hemicellulose polysaccharides, plus a network of extensin)
What is the structure of Hemicellulose?
(a heterogenous group of polysaccharides). A long chain of one type of sugar and short side chains to form a rigid structure
What is the structure of Pectin?
Branched, negatively charged polysaccharides. Bind water and have gel-like properties
What is the protein extensin?
It is a protein that cross links with the cell wall so that the expansion of the cell is controlled. Extensin cross linking with pectin and cellulose dehydrates the cell wall, reducing extensibility and increasing strength. It excludes water so that none is absorbed and it retains its structure.
What are the steps to synthesis of the cell wall?
A. Cellulose microfibrils at the plasma membrane.
B. Polysaccharides (hemicellulose and pectin) in the Golgi apparatus are transported to the wall in vesicles
C. Cell wall proteins (extensins) from the rough ER. The vesicles fuse to the plasma membrane.
The cellulose-producing rosettes move parallel to what?
The cortical microtubules.
The rosettes leave behind them a trail of cellulose microfibril that it has synthesised.
What colour is the middle lamella and what is it?
Blue. It is mostly made of pectin and it is a gel like substance that holds the cells together.
What are the cell wall functions in regulating the cell shape?
Influences cell morphology, Provides structural support, prevents excessive water uptake.
What is cell morphology?
The morphology is how it expands (in what directions due to the orientation of the cellulose microfibrils).
How does the cell wall provide structural support?
The protoplast pushes up against the cell wall. The cell then becomes rigid and this maintains the plant structure.
Water loss can cause the protoplast to lose volume and wilting of the plant will occur
How does the cell wall prevent excessive water intake?
As water enters the cell, the protoplast expands until it pushes up against the cell wall. That pressure against the cell wall prevents it from taking in any more water. (Vacuoles are important here because they take up water and make up a large part of the protoplast)
What is the structure of a vacuole?
It’s an organelle surrounded by a single membrane. It’s highly selective, controlling a lot of what enters and leaves the vacuole. Water moves into it using osmosis.
Typical mature plant cell has one large vacuole.
What is a vacuoles function in the regulation of cell shape?
They have high concentrations of solute in them which results in water uptake via osmosis. The cell wall limits the water uptake and prevents the cell from bursting.
