1 The Cell Wall Flashcards
label plant cell
see book
cell wall (3)
- gives plants strength and support
- made of insoluble cellulose
- usually freely permeable to everything that dissolves in water, does not act as a barrier
suberin
a waterproof chemical that impregnates cellulose cell walls in cork tissues and makes them impermeable (reduces permeability of cell wall)
lignin
a chemical that impregnates cellulose cell walls in wood and makes them impermeable (reduces permeability of cell wall)
middle lamella (3)
- first layer
- is made when a plant cell divides into two new cells
- mostly made of pectin
pectin (4)
- a polysaccharide that acts like glue and holds the cell walls of adjacent plant cells together
- has lots of negatively charged carboxyl groups that combine with positive calcium ions to make calcium pectate
- then calcium pectate binds to the cellulose on either side
- the cellulose microfibrils and the matrix build up on both sides of the middle lamella
primary cell walls (2)
- the first very flexible plant cell walls to form, with all the cellulose microfibrils orientated in similar direction
- gives mostly shape, and some strength
secondary cell wall (3)
- secondary thickening
- the cellulose microfibrils have built up at different angles to each other, making the cell wall more rigid and almost impossible to break
- function= gives strength
Hemicelluloses (3)
- poysaccharides containing many different sugar monomers
- holds together the layers so they don’t slide against eachother
- makes even harder
plant fibres
long cells with cellulose cell walls that have been heavily lignified so they are rigid and very strong
cellulose (4)
- similar to starch and glycogen
- consists of long chains of b-glucose joined by 1.4 glycosidic bonds, where one of the monomer units has to be turned around so the bonding can take place
- cellulose is very strong because many hydrogen bonds are made
- cellulose molecules do not coil or spiral, they remain strong straight chains
cross-linking (glucose) (2)
- because the hydroxyl groups stick out on both sides of the molecule (b-glucose), hydrogen bonds can be made between the partially positively charged hydrogen atoms of the hydroxyl groups and the partially negatively charged oxygen atoms in other areas of the glucose molecules
- holds neighboring chains firmly together
draw b-glucose
see book
compare and contrast cellulose with starch molecules (4)
- cellulose molecules do not coil or spiral and remain long, straight chains
- while starch molecules form compact globular molecules that are useful for storage
- cellulose made of b-glucose with only 1.4 glycosidic bonds
- while starch made up of a- glucose monomers with 1.4 and 1.6 glycosidic bonds
formation of cellulose fibrils (2)
- in the cell wall groups of 10 000- 100 000 cellulose molecules form microfibrils
- these are deposited in layers which are held together by a matrix of hemicelluloses and other short-chain carbohydrates
turgid (2)
- how cell is most of the time
- firm, swollen
flaccid (2)
- when water is in short supply
- floppy, soft
plasmodesmata (5)
- cytoplasm bridges between plant cells that allow communication between the cells
- produced as the cell divides (the two cells do not separate completely, threads of cytoplasm remain between them)
- these threads pass through gaps in the newly formed cell walls and signalling substances can pass from one cell to another through the cytoplasm
- cell walls are thinner in the region of the plasmodesmata
- secondary thickening (when hemicelluloses and lignin are deposited) does not take place in the areas around the plasmodesmata, leaving pits
symplast (2)
- the interconnected cytoplasm of the cells
- all of the material (cytoplasm, vacuole, etc.) contained within the surface membrane of a plant cell
pits (3)
- left because secondary thickening does not take place around plasmodesmata
- pits allow water to move between the xylem vessels
- important for maintaing a flow of water at even pressure through the plant
name the monomer that makes up cellulose
beta-glucose
how are the monomers in cellulose held together?
by glycosidic bonds in an unbranched chain
where can calcium pectate be found?
middle lamella
which properties can lignin give to cell walls in plants?
strength and waterproofing
