CELS 191 Lecture 8 Flashcards
why are plant cells stronger than animal cells
because they have cell walls
why do plant need more adaptations for structure and strength (like the cell wall)
because they can’t move
what is the most abundant organic macromolecules on earth
cellulose
what is cellulose
the main component of cell walls - its composed of glucose polymers linked together in a highly organised fashion that forms long ribbon like structures that have lots of energy tied up in them
why isn’t cellulose a good energy course for humans
even though it is high ion energy we can’t digest it
what is a microfibril
many cellulose chains linked together to form one long rope like structure - these are highly organised and very strong
what are the two phases of the cell wall
phase 1 - microfibrils (crystalline phase)
phase 2 - matrix (non-crystalline phase)
what is phase 1 (microfibrils) of the cell wall made up of
cellulose
what is phase 2 (matrix) of the cell wall made up of
pectin polysaccharides
hemicellulose polysaccharides
plus a network of extension (a protein)
what is hemicellulose
a heterogeneous group of polysaccharides - a long cellulose chain with side chains that link up to microfibrils or other hemicellulose molecules
what is pectin
a branched, negatively charge polysaccharide - it binds with water and has gel like properties
when would a plant excrete extensin
when it needs to toughen up an area
how does the cell control expansion
with the protein extensin - extensin cross-linking of cellulose and pectin dehydrates the cell wall and reduces its extensibility and increases strength
what is needed for the synthesis of the cell wall and where are these components synthesised
cellulose microfibrils are synthesised at the plasma membrane
polysaccharides are synthesised in the Golgi and transported to the plasma membrane in vesicles
extensin is synthesised in the rER and transported via Golgi to plasma membrane in vesicles
what is exocytosis
the transport of materials out of the cell or the delivery of materials to the cell surface
what is constitutive exocytosis
the release of ECM proteins - this occurs constantly without the need for a signal or trigger
how is cellulose produced in the primary cell wall
in enzymes (protein complexes) arranged in rosettes (rings) that move parallel to the cortical (outer) microtubules. each enzyme in a ring produces a single strand of cellulose that joins together with the other strands in the ring to produce a microfibril
what is the polysaccharide pectin used for
to hold together cell walls which is why there is always a higher concentration of pectin between cells
what is the middle lamella of a cell wall
the space between cells that contains large amounts of pectin
what are the functions of the cell wall
influences cell morphology (shape)
provides structural support
prevents excessive water uptake
how does the cell wall influence the cell morphology (shape)
the orientation of the microfibrils - if the microfibrils are randomly orientated the cell will expand equally in all directions but if they are arranged 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
the protoplast pushes against the cell wall and the cell becomes more rigid which maintains the plants structure
when does wilting occur
when the protoplast is nit pushing against the cell wall. water loss from the cell reduces the protoplast volume
what is plasmolysis
when the plasma membrane pulls away from the cell wall (wilting) - this is the point at which the plant cannot recover
