Lecture 7: Cell Walls and their role in regulation Plant Cell Shape Flashcards
What are the components of the cell wall?
Cellulose, Hemicellulose, Pectin and Extensin.
What is the crystalline microfibrillar phase made of?
Cellulose
What is the non crystalline microfibrillar phase made of?
Hemicellulose and Pectin
What is the purpose of extensin?
Extensin cross links the pectin and cellulose dehydrating the cell wall, reducing extensibility and increasing strength. Plant cells grow by expansion of the protoplast, eventually mature cells stop growing through the cross linking of extensin. Therefore the expansion of cells can be controlled by extensin cross linking.
How is the cell wall synthesised?
Cellulose microfibrils are made on the plasma membrane. The polysaccharides pectin and hemicellulose are delivered from the trans side of the Golgi apparatus in vesicles. Extensin is created in the rough ER and delivered via vesicles. All the components delivered via vesicles fuse to plasma membrane through constitutive exocytosis.
What are rosettes, and how does the orientation of microtubules result where cellulose is released.
The rosettes found on the plasma membrane attach to the cortical microtubules. This results in cellulose growing parallel to the microtubules. Therefore the orientation of microtubules determines where rosette releases cellulose as rosette runs along microtubules.
How does the orientation of microtubules influence cell morphology?
If the cellulose microfibrils are orientated randomly the cell will expand equally in all directions. If the cellulose microfibrils are oriented at right angles to the long axis of the cell the cell will expand longitudinally along that axis.
How does the cell wall provide structural support?
Protoplast pushes against the cell wall. The cells then become rigid and this maintains the plant cell structure. Wilting occurs when the protoplast is not pushing against the cell wall due to water loss removing pressure.
How does the cell wall prevent excessive water intake?
Water enters the plant cell via osmosis however the amount of water which can be absorbed is limited by the cell wall. As pressure from the cell wall limits the volume of water that can be taken up. Vacuoles are important in this process because they contain water and make up such a large portion of the protoplast.
What is the concentration of solutes within the vacuole?
High conc. of solutes within the vacuole so that water travels in via osmosis.
What is the secondary cell wall composed of?
The secondary cell wall has more cellulose less pectin and another molecule called lignin.
Do all plant cells have a secondary cell wall?
no.
How many layers does the secondary cell wall have?
Secondary cell wall is made of multiple layers which have different orientations of microfibrils resulting in more strength.
What is the purpose of plasmodesmata?
Plasmodesmata, intercellular connections that enable cell to cell communication. Plasma membrane is continuous from one cell to the other. The plasma membrane travels the plasmodesmata which allows free exchange of small molecules. But small enough to prevent organelles travelling between cells.
