carbohydrates

Question 1

what is the empirical formula for carbohydrates

Answer 1

CH2O(n)

Question 2

what are monosaccharides

Answer 2

monomers from which different carbohydrates are made

Question 3

give three examples of monosaccharides

Answer 3

glucose, fructose, gelactose

Question 4

roles of monosaccharides

Answer 4

• used in respiration to release energy (ATP)
• monomers to form polymers
• building DNA/RNA
• chemical intermediate

Question 5

why can glucose hydrogen bond to water

Answer 5

it is polar and soluble

Question 6

what are disaccharides

Answer 6

two monosaccharide units liked together with covalent bonds

Question 7

are disaccharides polymers

Answer 7

no

Question 8

why are disaccharides not polymers

Answer 8

they are soluble and dont contain ‘many’ repeating units

Question 9

give three examples of disaccharides

Answer 9

maltose, sucrose, lactose

Question 10

how are disaccharides formed

Answer 10

by the condensation of two monosaccharides

Question 11

what monosaccharides form maltose

Answer 11

alpha glucose + alpha glucose

Question 12

what monosaccharides form sucrose

Answer 12

alpha glucose + fructose

Question 13

what monosaccharides form lactose

Answer 13

alpha glucose + galactose

Question 14

what bond forms disaccharides

Answer 14

glycosidic bonds

Question 15

describe how maltose is formed

Answer 15

a condensation reaction occurs between two molecules of alpha glucose, during this process water is released and a glycosidic bond forms between C1 from one glucose and C4 from the other

Question 16

maltose, sucrose and lactose: which is not a reducing sugar

Answer 16

sucrose (comes from plants)

Question 17

why is the benedict’s test a semi-quantitative test

Answer 17

as there are a range of positive results, they have no unit but you can make comparisons between them

Question 18

what forms benedicts solution

Answer 18

copper sulfate and dilute sodium hydroxide

Question 19

why does benedicts solution contain the alkali dilute sodium hydroxide

Answer 19

the solution only works in alkaline solutions

Question 20

what occurs in a positive result in benedicts test

Answer 20

reducing sugars donate an electron to the Cu2+ to form Cu+ ( the ion is being reduced)

Question 21

what does a higher concentration of reducing sugars do to the benedicts solution

Answer 21

more copper (II) is reduced, so a greater volume of precipitate is formed, the colour turning orange or brick red

Question 22

how do you make the benedict’s test fully quantitative

Answer 22

you can use a colourimeter or filter out the precipitate formed and measure its mass

Question 23

reducing sugars equation

Answer 23

Cu2+ (aq) -> Cu+ (ppt)
e-

Question 24

How to test for non-reducing sugars

Answer 24

• boil the solution you are testing in hydrochloric acid - hydrolysis will occur and it will release monosaccharides
• neutralise with alkali (eg. hydrogen carbonate)
• repeat benedicts test
• if goes ‘brick red’ then there was a reducing sugar

Question 25

what sugar type are all monosaccharides

Answer 25

reducing

Question 26

Cu2+ soluble or insoluble

Answer 26

soluble

Question 27

Cu+ soluble or insoluble

Answer 27

insoluble (produces a precipitate)

Question 28

name three polysaccharides

Answer 28

starch, glycogen, cellulose

Question 29

how is starch formed

Answer 29

condensation reaction forms many glycosidic bonds between the C1 and C4 of many alpha glucose monomers. water is eliminated in this process.

Question 30

how is amylose formed

Answer 30

extensive hydrogen bonds between monomers pull the starch polymer chain to a compact coil. this is amylose.

Question 31

amylose: soluble or insoluble

Answer 31

insoluble

Question 32

role of starch

Answer 32

store energy

Question 33

features of starch (3)

Answer 33

-consists mainly of polysaccharide amylose- - compact, so lots of energy can be stored in a small place - insoluble, so wont diffuse out of cells - insoluble, does not effect water potential of the cell

Question 34

how is starch used as an 'energy store'

Answer 34

hydrolysis of starch releases glucose, this is used in respiration to release energy in the form of ATP

Question 35

what solution tests for starch

Answer 35

potasium iodide solution

Question 36

chemical equation, testing for starch

Answer 36

I2 + K+ + I- -> I3-

Question 37

where can cellulose be found

Answer 37

walls of plant cells

Question 38

describe the formation of cellulose

Answer 38

a condensation reaction occurs between many beta-glucose monomers, forming man glycosidic bonds between the C1 and C4 of each monomer. every second alpha glucose is rotated 180 degrees, long straight chains are formed and water is eliminated

Question 39

how are microfibrils formed

Answer 39

extensive hydrogen bonding between parallel cellulose strands

Question 40

how are cellulose fibres formed

Answer 40

microfibrils are layered to form a larger macrofibril, macrofibrils are then layered to form cellulose fibres

Question 41

properties of cellulose

Answer 41

fibrous, strong, tensile

Question 42

what is the role of cellulose

Answer 42

- support plant cell walls - protects bursting by osmosis (prevents osmotic lysis- cell bursting)

Question 43

describe how to test for reducing sugars

Answer 43

mix solution with 2cm^3 of benedicts solution, heat in a water bath at 90degrees for 5 minutes. positive result will end in a colour change from light blue- green/orange/brick red

Question 44

what is the difference between alpha glucose and beta glucose

Answer 44

alpha glucose- on c1 and c4 hydroxide below the plane of the ring on both carbons beta glucose- hydroxide above the place of the ring on C1

Question 45

name the similarities between starch and glycogen (5)

Answer 45

- both polymers made from alpha-glucose - both compact - both insoluble - stores of energy for respiration - condensation reaction between monomers form glycosidic bonds

Question 46

how is amylose different to glycogen

Answer 46

- forms C1-C4 glycosidic bonds only - found in plants - forms unbranched, coiled chains

Question 47

how is glycogen different to amylose

Answer 47

- forms C1-C4 glycosidic bonds and C1-C6 branches - found in animals - heavily branched - more 'terminal ends'- more rapid hydrolysis of glucose