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A-level biology > carbohydrates > Flashcards

carbohydrates Flashcards

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1
Q

what is the empirical formula for carbohydrates

A

CH2O(n)

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2
Q

what are monosaccharides

A

monomers from which different carbohydrates are made

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3
Q

give three examples of monosaccharides

A

glucose, fructose, gelactose

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4
Q

roles of monosaccharides

A
  • used in respiration to release energy (ATP)
  • monomers to form polymers
  • building DNA/RNA
  • chemical intermediate
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5
Q

why can glucose hydrogen bond to water

A

it is polar and soluble

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6
Q

what are disaccharides

A

two monosaccharide units liked together with covalent bonds

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7
Q

are disaccharides polymers

A

no

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8
Q

why are disaccharides not polymers

A

they are soluble and dont contain ‘many’ repeating units

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9
Q

give three examples of disaccharides

A

maltose, sucrose, lactose

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10
Q

how are disaccharides formed

A

by the condensation of two monosaccharides

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11
Q

what monosaccharides form maltose

A

alpha glucose + alpha glucose

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12
Q

what monosaccharides form sucrose

A

alpha glucose + fructose

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13
Q

what monosaccharides form lactose

A

alpha glucose + galactose

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14
Q

what bond forms disaccharides

A

glycosidic bonds

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15
Q

describe how maltose is formed

A

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

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16
Q

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

A

sucrose (comes from plants)

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17
Q

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

A

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

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18
Q

what forms benedicts solution

A

copper sulfate and dilute sodium hydroxide

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19
Q

why does benedicts solution contain the alkali dilute sodium hydroxide

A

the solution only works in alkaline solutions

20
Q

what occurs in a positive result in benedicts test

A

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

21
Q

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

A

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

22
Q

how do you make the benedict’s test fully quantitative

A

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

23
Q

reducing sugars equation

A

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

24
Q

How to test for non-reducing sugars

A
  • 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
25
Q

what sugar type are all monosaccharides

A

reducing

26
Q

Cu2+ soluble or insoluble

A

soluble

27
Q

Cu+ soluble or insoluble

A

insoluble (produces a precipitate)

28
Q

name three polysaccharides

A

starch, glycogen, cellulose

29
Q

how is starch formed

A

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

30
Q

how is amylose formed

A

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

31
Q

amylose: soluble or insoluble

A

insoluble

32
Q

role of starch

A

store energy

33
Q

features of starch (3)

A

-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

34
Q

how is starch used as an ‘energy store’

A

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

35
Q

what solution tests for starch

A

potasium iodide solution

36
Q

chemical equation, testing for starch

A

I2 + K+ + I- -> I3-

37
Q

where can cellulose be found

A

walls of plant cells

38
Q

describe the formation of cellulose

A

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

39
Q

how are microfibrils formed

A

extensive hydrogen bonding between parallel cellulose strands

40
Q

how are cellulose fibres formed

A

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

41
Q

properties of cellulose

A

fibrous, strong, tensile

42
Q

what is the role of cellulose

A
  • support plant cell walls
  • protects bursting by osmosis (prevents osmotic lysis- cell bursting)
43
Q

describe how to test for reducing sugars

A

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

44
Q

what is the difference between alpha glucose and beta glucose

A

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

45
Q

name the similarities between starch and glycogen (5)

A
  • both polymers made from alpha-glucose
  • both compact
  • both insoluble
  • stores of energy for respiration
  • condensation reaction between monomers form glycosidic bonds
46
Q

how is amylose different to glycogen

A
  • forms C1-C4 glycosidic bonds only
  • found in plants
  • forms unbranched, coiled chains
47
Q

how is glycogen different to amylose

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

A-level biology (30 decks)

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