3.1.2 │ CARBOHYDRATES

Question 1

what are monosaccharides

Answer 1

monomers from which larger carbohydrates are made

Question 2

what are the three monosaccharides

Answer 2

glucose, fructose, galactose

Question 3

how are disaccharides formed

Answer 3

condensation reaction with two monosaccharides

Question 4

how is maltose formed

Answer 4

condensation reaction between two glucose molecules

Question 5

how is sucrose formed

Answer 5

condensation of a glucose molecule and a fructose molecule

Question 6

how is lactose formed

Answer 6

condensation of a glucose molecule and a galactose molecule

Question 7

what is an isomer

Answer 7

compounds with the same molecular formula but a different arrangement of atoms

Question 8

what are the two isomers of glucose

Answer 8

α-glucose and β-glucose

Question 9

describe the difference between the structure of α-glucose and β-glucose

Answer 9

OH group is below carbon 1 in α-glucose
but above carbon 1 in β-glucose

Question 10

how are polysaccharides formed

Answer 10

many monosaccharides joined together with glycosidic bonds formed by many condensation reactions, releasing water molecules

Question 11

what is the bond formed between monosaccharides

Answer 11

glycosidic

Question 12

what is the function of starch

Answer 12

energy store in plant cells

Question 13

what is the function of glycogen

Answer 13

energy store in animal cells

Question 14

describe the structure of starch

Answer 14

polysaccharide of α-glucose
amylose - 1,4-glycosidic bonds → unbranched
amylopectin - 1,4- and 1,6-glycosidic bonds → branched

Question 15

describe the structure of glycogen

Answer 15

polysaccharide made of α-glucose
1,4- and 1,6-glycosidic bonds → branched

Question 16

explain how the structure of starch relates to its function

Answer 16

helical → compact for storage in cell
large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane
insoluble in water → water potential of cell not affected (no osmotic effect)
branched → compact / fit more molecules in small area
branched → more ends for faster hydrolysis → release glucose for respiration to make ATP for energy release

Question 17

explain how the structure of glycogen relates to its function

Answer 17

branched → compact / fit more molecules in small area
branched → more ends for faster hydrolysis → release glucose for respiration to
make ATP for energy release
large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane
insoluble in water → water potential of cell not affected (no osmotic effect)

Question 18

what is the function of cellulose

Answer 18

provides strength and structural support to plant/algal cell walls

Question 19

describe the structure of cellulose

Answer 19

polysaccharide of β-glucose
1,4-glycosidic bond → straight, unbranched chains
chains linked in parallel by hydrogen bonds forming microfibrils

Question 20

explain how the structure of cellulose relates to its function

Answer 20

every other β-glucose molecule is inverted in a
long, straight, unbranched chain
many hydrogen bonds link parallel strands
(crosslinks) to form microfibrils (strong fibres)
hydrogen bonds are strong in high numbers
so provides strength to plant cell walls

Question 21

what test is used for reducing sugars

Answer 21

benedict’s

Question 22

give three examples of reducing sugars

Answer 22

monosaccharides, maltose, lactose

Question 23

describe the test for reducing sugars

Answer 23

add Benedict’s solution (blue) to sample
heat in a boiling water bath
positive result = green / yellow / orange / red precipitate (increasing quantity of sugar)

Question 24

describe the test for non-reducing sugars

Answer 24

do Benedict’s test and stays blue / negative
heat in a boiling water bath with acid (to hydrolyse into reducing sugars)
neutralise with alkali
heat in a boiling water bath with Benedict’s solution
positive result = green / yellow / orange / red precipitate (increasing quantity of sugar)

Question 25

give an example of a non-reducing sugar

Answer 25

sucrose

Question 26

suggest two methods to measure the quantity of sugar in a solution

Answer 26

1. carry out benedict's test, then filter and dry precipitate find mass/weight 2. make sugar solutions of known concentrations (eg. dilution series) heat a set volume of each sample with a set volume of Benedict’s solution for same time use colorimeter to measure absorbance (of light) of each known concentration plot calibration curve - concentration on x axis, absorbance on y axis and draw line of best fit repeat Benedict’s test with unknown sample and measure absorbance read off calibration curve to find concentration associated with unknown sample’s absorbance

Question 27

describe the test for starch

Answer 27

add iodine dissolved in potassium iodide (orange / brown) and shake / stir positive result = blue-black