Cell Walls and their role in regulating plant cell shape Flashcards
what are the components in a Plant Cell
- nucleus
- golgi apparatus
- central vacuole
- mitochondria
- chloroplast
- cell wall
- plasmodesmata
What is the primary cell wall structure made of
- cellulose - a major structure
describe what cellulose is
- the most abundant organic macromolecule on earth
- glucose polymer
- highly ordered
- long, ribbon-like structures
what does cellulose form, also describe it
microfibers
- highly organized structures
- are strong and form major component of both primary and secondary cell walls
what is the 1st phase of the cell structure called
- crystalline Microfibrillar phase
- cellulose
what is the second phase called
- Noncrystalline Matrix
- makes pectin polysaccharides + hemicellulose polysaccharides
- also a network of Extensin
describe what hemicellulose is
is a heterogeneous group of polysaccharide.
- long chain of one type of sugar and short side chains form a rigid structure
describe what Pectin is
- is branched, negatively charged polysaccharides.
- they bind water and have gel-like properties
describe what extensin does
- the expansion of cells can be controlled by extension cross linking
- extensin cross-linking of pectin and cellulous dehydrates the cell wall, reduces extensibility and increases strength
what are the processes that happens during the synthesis of the primary cell wall
- coordinated synthesis and delivery
- exocytosis
what is the coordinated synthesis and delivery stage known for
1) cellulose microfibers at cell wall/plasma membrane
2) polysaccharides (pectin + hemicellulose) in the golgi apparatus are transported to the wall in vesicles
3) cell wall proteins (extensins) from the rough ER, the vesicles fuse to the membrane
what is exocytosis
- transports material out of the cell or delivers it to the cell surface
- CONSITUTIVE EXOCYTOSIS releases extracellular matrix proteins
what direction does the cellulose-producing rosettes move towards
- they move parallel to the cortical microtubules
what 3 functions does the cell wall do to regulate the cell shape
- influences cell morphology
- provides structural support
- prevents excessive water uptake
describe how cell morphology helps regulate the cell structure
- the orientation of the cellulose microfibrils influence cell morphology.
- randomly oriented : the cell will expand equally in all directions
- right angles to the ultimate long axis of cell: the cell will expand longitudinally along that axis
describe how it provides structural support
- the protoplast pushes against the cell wall. the cells become turgid and this maintains the plant structure
- wilting occurs when the protoplast is not pushing against the cell wall
- water loss from cells reduce the protoplast volume and the protoplast does not press in the wall, it will become flaccid
describe how it prevent excessive water uptake
- this is through osmosis
- as water enters the cell, the protoplast expands and pushes against the cell wall
- pressure from the cell wall limits the volume that can be taken up
- the amount of water in the cell determines the pressure in the cell
describe the structure of the vacuoles
- a vacuole of an organelle surrounded by a single membrane
- is highly selective, controlling much of what enters and leaves the vacuole
- water moves in the vacuole by osmosis
- typical nature plant cell has a single large vacuole
what functions does the vacuoles have to help regulate the cell shape
- there is a high concentration of solutes in the vacuole, resulting in water uptake into the vacuole by osmosis. the plant cell wall limits water uptake and prevents the cell bursting.
- the plant cells build up a larger internal pressure that contributes to plant structural support
what is osmosis
- the diffusion of water across a selectively permeable membrane
describe the secondary cell wall
- not all plant cells have this
- produced only after cell growth has stopped
- thicker and stronger than primary walls
- provides more structural support than primary cell wall
what are the chemical characteristics of the secondary cell wall
- more cellulose
- less pectin
- lost of lignin
describe what lignin is
- is the second most abundant organic macromolecule
- is a complex polymer
- confers strength, rigidity to the secondary cell wall and acts to exclude water
what does the secondary cell wall provide structural support for
- specific cell types, such as water transporting cells and for the whole plant
what is Plasmodesmata
- are intercellular connections, that enable cell to cell communication
describe plasmodesmata
- the plasma membrane is continuous
- small enough to prevent organelle movements - although endoplasmic reticulum is connected through plasmodesmata
- allows the free exchange of small molecules
