carbohydrates

Question 1

define monomer + give some examples

Answer 1

a single sub unit that joins together with others to form a large molecule. eg amino acids, monosaccharides, nucleotides

Question 2

define polymer + give some examples

Answer 2

molecules formed when many monomers join together. eg proteins, carbohydrates, DNA/RNA

Question 3

what happens in a condensation reaction

Answer 3

a chemical bond forms between two molecules and a molecule of water is produced

Question 4

what happens in a hydrolysis reaction

Answer 4

a water molecule is used to break a chemical bond between two molecules

Question 5

name 3 hexose monosaccharides

Answer 5

all have formula C6H12O6
glucose galactose and fructose

Question 6

name the type of bond formed when monosaccharides react

Answer 6

1,4 or 1,6 glycosidic bond

Question 7

name 3 disaccharides and describe how they are formed, and their molecular formula

Answer 7

+ glucose = maltose
+ galactose = lactose
+ fructose = sucrose
formed by condensation, forms glycosidic bond
all have molecular formula C12H22O11

Question 8

draw the structure of a-glucose

Answer 8

-

Question 9

draw the structure of B-glucose

Answer 9

-

Question 10

describe the functions of starch and what it is made of

Answer 10

storage polymer of a-glucose in plants
insoluble - no osmotic effect on cells
large - does not diffuse out of cells
forms a-glucose which is easily transported and used in respiration
made of amylose and amylopectin

Question 11

describe the structure of amylose

Answer 11

a-glucose monomer
1,4 glycosidic bonds
straight chain helix with intermolecular H bonds - compact

Question 12

describe the structure of amylopectin

Answer 12

a-glucose monomer
1,4 and 1,6 glycosidic bonds
branched - many terminal ends for hydrolysis into glucose

Question 13

describe the structure and functions of glycogen

Answer 13

main a-glucose storage polymer found in animals and bacteria
1,4 and 1,6 glycosidic bonds
branched - many terminal ends for hydrolysis
insoluble - no osmotic effect and does not diffuse out of cells
tight coil- compact - much energy can be stored in a small space

Question 14

why is many terminal ends beneficial

Answer 14

for hydrolysis to form glucose monomers which are used in respiration. important to animals with a high metabolic rate rather than plants since they are more active

Question 15

describe the structure and function of cellulose

Answer 15

polymer of B-glucose in plant cells
prevents bursting under turgor pressure and holds stem up
1,4 glycosidic bonds
straight chain unbranched molecule
glucose molecules are alternately inverted
H bonds form crosslinks between parallel strands, forming microfibrils - high tensile strength

Question 16

what benefit does H bonds in cellulose provide

Answer 16

while each bond individually is weak, the sheer overall number of them makes a considerable contribution to strengthening cellulose, making it a valuable structural material. H bonds form between -Oh groups on adjacent parallel chains giving cellulose its structural integrity

Question 17

test for reducing sugars & colour change

Answer 17

(all monosaccharides and some disaccharides such as maltose)
grind or dissolve food sample
2cm3 food 2cm3 benedicts to test tube
5 min in hot water bath
if present blue to orange-brown

Question 18

which colours are associated with concentration of reducing sugar in benedicts test

Answer 18

blue - none
green - very low
yellow - low
orange - medium
red - high

Question 19

test for non reducing sugars

Answer 19

test for reducing sugars, no colour change
2cm3 food 2cm3 dilute HCl
water bath 5 min hydrolyses disaccharides into constituent monosaccharides
add sodium hydrogen carbonate slowly to neutralise HCl, benedicts will not work in acidic conds
test w pH paper to check it is alkali
retest by heating w 2cm3 benedicts 5 min

Question 20

test for starch

Answer 20

2cm3 food 2 drops iodine
presence of starch is indicated by a blue-black colouration