3.1.2 Carbohydrates

Question 1

what are monosaccharides?

Answer 1

the monomers from which carbohydrates are made

Question 2

what are three common monosaccharides?

Answer 2

• glucose
• fructose
• galactose

Question 3

a condensation reaction between two monosaccharides forms a ___ bond?

Answer 3

glycosidic

Question 4

the condensation of two monosaccharides forms a…

Answer 4

disaccharide

Question 5

glucose + glucose –>

Answer 5

maltose

Question 6

glucose + fructose –>

Answer 6

sucrose

Question 7

glucose + galactose –>

Answer 7

lactose

Question 8

what is an isomer?

Answer 8

a molecule with the same molecular formula but a different structure

Question 9

what are the two isomers of glucose?

Answer 9

α-glucose and β-glucose

Question 10

what is the difference between α-glucose and β-glucose?

Answer 10

• in α-glucose the OH group bonded to carbon 1 is below the ring
• in β-glucose the OH group bonded to carbon 1 is above the ring

Question 11

where is glycogen found?

Answer 11

animal cells (especially liver and muscle cells)

Question 12

where is starch found?

Answer 12

plant cells

Question 13

where is cellulose found?

Answer 13

the cell wall of plant cells

Question 14

what is the basic structure of glycogen?

Answer 14

• polysaccharide of α-glucose
• branched structure due to 1,6 glycosidic bonds

Question 15

what is the basic structure of starch?

Answer 15

• polysaccharide of α-glucose
• amylose has a long unbranched structure which forms a coiled / compact shape
• amylopectin has a branched structure due to 1,6 glycosidic bonds

Question 16

what is the basic structure of cellulose?

Answer 16

• polysaccharide of β-glucose
• has long and straight chains
• contains lots of hydrogen bonds between straight chains which create microfibrils

Question 17

explain the structure of cellulose monomers compared to starch monomers

Answer 17

• starch formed from α-glucose but cellulose β-glucose monomers
• so position of hydrogen and hydroxyl groups on carbon atom 1 inverted

Question 18

what is the basic function of glycogen?

Answer 18

is an energy store

Question 19

what is the basic function of starch?

Answer 19

is an energy store

Question 20

what is the basic structure of cellulose?

Answer 20

acts as structural support

Question 21

how does the structure of glycogen relate to its function?

Answer 21

• branched structure provides a large SA so that it can be quickly hydrolysed by enzymes to release glucose for respiration
• is coiled in shape so can fit many molecules in small area
• is insoluble so has does not affect water potential of cell

Question 22

how does the structure of starch relate to its function?

Answer 22

• amylopectin’s branched structure provides a large SA so that it can be quickly hydrolysed by enzymes to release glucose for respiration
• amylose is coiled in shape so can fit many molecules in small area
• is insoluble so has does not affect water potential of cell
• large molecule so it cannot leave the cell

Question 23

how does the structure of cellulose relate to its function?

Answer 23

microfibrils provide strength to the cell wall

Question 24

what is the food test for reducing sugars?

Answer 24

• add Benedict’s solution and heat in water bath
• if sugar is present, colour change from blue to green / yellow / red

Question 25

how can you get quantitative data for reducing sugars in a food sample

Answer 25

• filter and dry the precipitate, find the mass
• remove the precipitate and use a colorimeter to measure the absorbance of the remaining Benedict’s solution

Question 26

what is the food test for non-reducing sugars?

Answer 26

• heat with acid and neutralise
• heat with Benedict’s solution
• red colour if non-reducing sugar is present

Question 27

what is the food test for starch?

Answer 27

• add iodine / potassium iodide
• colour change to blue / black