Cell Walls Flashcards
What is the cell wall mainly composed of?
Cellulose
What structures does cellulose make within the cell wall?
Microfibrils
What are the two phases of a cell wall
- Crystalline Microfibrillar Phase
- Noncrystalline Matrix
What is the noncrystalline matrix composed of?
- hemicellulose
- Pectin
What is Hemicellulose?
- a heterogenous group of polysaccharides with one long chain of one type of sugar and short side chains
What is Pectin?
branched, negatively charged polysaccharides that bind water and have gel-like properties
What is the extensibility of plant cells controlled by?
Extensin cross linking
What does extensin cross linking do?
Dehydrates cell wall, reduces extensibility and increases strength
What are the steps of primary cell wall synthesis?
- cellulose myofibrils are synthesized at the cell membrane
- Polysaccharides (pectin + hemicellulose) in the Golgi apparatus are transported in vesicles to the cell wall
- Cell wall proteins (extensins) are transported from the rough ER
What is constitutive exocytosis?
exocytosis that releases extracellular matrix proteins
What are the functions of the cell wall? (3)
- influences cell morphology
- provides structural support
- prevents excessive water uptake
How does orientation of cellulose microfibrils influence cell morphology?
- randomly oriented leads to equal expansion in all directions (spherical cell)
- right angles to ultimate long axis of the cell leads to cell expansion longitudinally along that axis ( rectangle)
What is a protoplast
Name for entire plant cell excluding cell wall
when is the plant cell rigid?
when the protoplast pushes against the cell wall
When are plant leaves wilted?
when the protoplast is not pushing on the cell wall
What is a central vacuole?
An organelle surrounded by a highly selective single membrane
How does the central vacuole aid in regulation of cell shape?
- There is high concentrations of solutes in the vacuole
- result is uptake of water by osmosis
- cell wall limits uptake and prevents cell bursting
- pressure from vacuole means protoplast pushes on cell wall
What happens to an animal cell when put into hypotonic conditions?
It bursts - becomes lysed
What happens to an animal cell when it is put into hypertonic conditions?
It becomes shriveled
What happens to a plant cell when put in hypotonic conditions
It becomes turgid ( normal / good)
What happens to a plant cell in isotonic conditions
It becomes flaccid
What happens to plant cells under hypertonic conditions
Becomes plasmolyzed
What is the secondary cell wall
Thicker stronger cell wall that is produced once cell growth has stopped and provides more structural support than the primary cell walls
Do all cells have primary and secondary cell walls?
No
