carbohydrates

Question 1

describe carbohydrates (4)

Answer 1

● contain carbon, hydrogen and oxygen

● polymers

● source of energy for organisms

● made from monosaccharides

Question 2

what are monosaccharides? (2)

Answer 2

● monomers

● from which larger carbohydrates are made

Question 3

what are examples of monosaccharides? (3)

Answer 3

● glucose

● fructose

● galactose

Question 4

what is the molecular formula of monosaccharides?

Answer 4

C₆H₁₂O₆

Question 5

what type of sugar are monosaccharides?

Answer 5

hexose sugar

Question 6

what is a hexose sugar?

Answer 6

monosaccharide with six carbon atoms in each molecule

Question 7

what reaction joins monosaccharides together?

Answer 7

condensation

Question 8

what bond forms between two monosaccharides?

Answer 8

(1,4 or 1,6) glycosidic bond

Question 9

what is formed from the condensation of two monosaccharides?

Answer 9

disaccharides

Question 10

what are examples of disaccharides? (3)

Answer 10

● sucrose

● lactose

● maltose

Question 11

what two molecules form sucrose in a condensation reaction?

Answer 11

● glucose molecule

● fructose molecule

Question 12

what two molecules form lactose in a condensation reaction?

Answer 12

● glucose molecule

● galactose molecule

Question 13

what two molecules form maltose in a condensation reaction?

Answer 13

two glucose molecules

Question 14

what is the molecular formula of disaccharides?

Answer 14

C₁₂H₂₂O₁₁

Question 15

what are the two isomers of glucose?

Answer 15

● alpha (hydrogen above hydroxyl group)

● beta (hydrogen below hydroxyl group)

Question 16

draw the structure of alpha glucose

Answer 16

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Question 17

draw the structure of beta glucose

Answer 17

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Question 18

what is formed from the condensation of many monosaccharides?

Answer 18

polysaccharides

Question 19

what are examples of polysaccharides? (3)

Answer 19

● starch

● glycogen

● cellulose

Question 20

describe the structure of starch (3)

Answer 20

● storage polymer of a-glucose in plant cells

● 1-4, 1-6 glycosidic bonds

● mixture of amylose and amylopectin

Question 21

how is starch adapted to its function? (5)

Answer 21

● insoluble in water - doesn’t affect water potential so water does not enter cells by osmosis

● large - can’t diffuse out of cell (cross cell membrane)

● branched - allows enzymes to hydrolyse glycosidic bonds easily so glucose released quickly

● branched / coiled - compact

● polymer of glucose so easily hydrolysed

Question 22

what is amylose?

Answer 22

● long, unbranched chain of alpha glucose

● 1-4 glycosidic bonds only

Question 23

what is amylopectin?

Answer 23

● long, branched chain of alpha glucose

● 1-4 and 1-6 glycosidic bonds

Question 24

describe the structure of glycogen (2)

Answer 24

● storage polymer of a-glucose in animal cells

● 1-4, 1,6 glycosidic bonds

Question 25

how is glycogen adapted to its functions? (5)

Answer 25

● branched - allows enzymes to hydrolyse glycosidic bonds easily so glucose released quickly ● insoluble in water - doesn't affect water potential so water does not enter cells by osmosis ● branched / coiled - compact ● large - can't diffuse out of cell (cross cell membrane) ● polymer of glucose so easily hydrolysed

Question 26

describe the structure of cellulose (4)

Answer 26

● polymer of b-glucose ● 1,4 glycosidic bonds ● long, straight chain, unbranched molecule ● position of hydroxyl group and hydrogen group of carbon 1 are inverted (every other beta glucose molecule flips 180° to form glycosidic bond with next molecule)

Question 27

how is cellulose adapted to its function? (2)

Answer 27

● long, straight, and unbranched chains gives rigidity to plant cell walls - prevents bursting ● become linked together by many hydrogen bonds to form microfibrils - provides high tensile strength (to cell wall)

Question 28

which sugars are reducing? (2)

Answer 28

● all monosaccharides ● some disaccharides (maltose and lactose)

Question 29

describe the benedict's test for reducing sugars (5)

Answer 29

● add excess benedict's reagent (blue) to sample ● heat in water bath ● positive result: coloured precipitate will form ● colour of precipitate changes from blue - green - yellow - orange - brick red ● higher the concentration of the reducing sugar, further the colour change goes

Question 30

what is an example of a non-reducing sugar?

Answer 30

sucrose

Question 31

describe the test for non-reducing sugars (7)

Answer 31

● hydrolyse non-reducing sugar into their monomers ● add dilute hydrochloric acid ● heat in water bath ● neutralise with sodium hydrogencarbonate ● proceed with benedict's test ● positive result: coloured precipitate will form ● negative result: solution stays blue (doesn't contain any sugar)

Question 32

describe the test for starch (3)

Answer 32

● add iodine solution ● positive result: colour change from browny-orange to blue-black ● negative result: stays browny-orange

Question 33

describe how colorimetry could be used to give quantitative results for the presence of sugars and starch (6)

Answer 33

● make standard solutions with known concentrations ● record absorbance ● plot calibration curve: absorbance (y-axis), concentration (x-axis) ● record absorbance of unknown samples ● use calibration curve to read off concentration ● produces quantitative data

Question 34

how could you measure the quantity of a reducing sugar in a solution? (2)

Answer 34

● filter and dry ● find mass/weight

Question 35

what is the calculation to prepare a serial dilution?

Answer 35

(required conc / stock solution (mol) ) x final volume