plant fibres & tensile strength

Question 1

whyre plant fibres strong

Answer 1

hollow
because cell contents have died
due to lignification of cell wall
doesnt allow contents into or out of cells
strenth exploited to by humans to make fabrics
cell wall also has microfibrils arranged in mesh like pattern
secondary thickening, secondary cell wall develops often containing lignin

Question 2

cellulose microfibrils

Answer 2

1,4 glycosidic bonds
strong due to many H bonds between

Question 3

which polysaccharides have 1,4 or 1,4 and 1,6 glycosidic bonds

Answer 3

amylose has only 1,4 alpha glucose, starch, not branched, helical structure so compact & good for storage, found in plants

amylopectin has both alpha glucose, starch, branched, many terminal glucoses so can be easily hydrolysed, found in plants

cellulose has only 1,4 beta glucose not starch, not branched found in plants

glycogen, found in animals, insoluble, good for storage, highly branched, more so than amylopectin easily hydrolysed

all insoluble (branching, many H bonds, folding)

Question 4

disaccaharides

Answer 4

lactose=glucose + galactose, 1,4

maltose=2 glucose monomers 1,4

sucrose= glucose + fructose joined by a 1,2 glycosidic bond

quick energy release, 2 monomers so easily broken down by enzymes in digestive system into monosaccharides and absorbed into the bloodstream

soluble due to large number of hydroxyl groups, hydroxyl groups form bonds with water

sweet in taste

Question 5

which organelles store amylopectin

Answer 5

amyloplasts

Question 6

identifying tissue types within stems

Answer 6

xylem towards centre of vasuclar bundle
phloem middle
sclerenchyma on outside of vascular bundle

cut very thin cross-section of stem using scalpel

transfer each section to a dish containing suitable stain & leave for 1 min

rinse off each section in water and mount onto microscope slide

lower cover slip slowly to avoid trapping in air bubbles which can be mistaken for plant tissues/structures

view & adjust focus to see a clear image

draw &label plant tissues

Question 7

which stain can be used and how will it make different sections of the stem appear?

Answer 7

toluidine blue O (TBO)

phloem pinky/purple
xylem and sclerenchyma bluey/green

Question 8

collenchyma

Answer 8

provide flexible, non-rigid support

cells are living and unlignified, contibute to plants ability to bend and flex without breaking

toward outside of the stem

Question 9

determining tensile strength:
what is the tensile strength of a fibre

Answer 9

maximum load it can carry without breaking

DV=the force or weight the fibre can withstand before breaking

Question 10

independent variable

Answer 10

type of plant used

or length of plant fibre

Question 11

CVs

Answer 11

-diameter and length of plant fibres used
-method of applying tension
-mass of weights used should be consistent and measurable if not added in a gradual and controlled manner fibres may break differently
-temp and humidity, high temps can cause fibres to degrade or swell

Question 12

method

Answer 12

-attach fibre to clamp on retort stand
-attach a weight on the end of the plant fibre
-gradually and carefully add weight until the fibre breaks
-record the mass at which the fibre broke (this represents tensile strength)
-to increase accuracy this should be repeated with more samples of same plant fibre
-use these values to calculate the mean which represents the tensile strength of the fibre