3.3-3.4 carbohydrates

Question 1

what are the 3 polysaccharides?

Answer 1

-starch ( amylase and amylopectin )
-cellulose
-glycogen

Question 2

which polysaccharides has 1,4 glycosidic bonds and/or 1,6 glycosidic bonds?

Answer 2

1,4:
-amylase
-amylopectin
-cellulose
-glycoge
1,6:
-amylopectin
-glycogen

Question 3

what is a condensation reaction in carbs?

Answer 3

the hydroxyl groups on two molecules of glucose react to produce a disaccharide bonded by a glycosidic bond and a water molecule

Question 3

how were the three disaccharides formed.

Answer 3

condensation reaction between:
-glucose + glucose = maltose
-glucose+ fructose = sucrose
-glucose + galactose= lactose

Question 4

what is a hydrolysis reaction in carbs?

Answer 4

when a molecule of water is added to break a glycosidic bond

Question 5

what is the formula for a carbohydrate?

Answer 5

Cn(H2O)n

Question 6

describe glycogen

Answer 6

-multi-branches due to 1,4 and 1,6 glycosidic bonds
-made up of alpha glucose
the branches have free ends
-compact molecule

Question 7

what are the functions of glycogen?

Answer 7

-free ends allow glucose to daily be added or removed allowing quick energy release
-main source of energy for animals
-due to being compact they are a good molecule for storage as they don’t take up a lot of space

Question 8

what are the two molecules in starch?

Answer 8

amylase and amylopectin

Question 9

describe amylase

Answer 9

-contains 1,4 glycosidic bonds so long unbranching chains
-10-30% of starch
-has a helix shape so is compact making is less soluble due to being stabilised by hydrogen bonds

Question 10

describe amylopectin

Answer 10

-contains 1,4 and 1,6 glycosidic bonds so has short branching chains
-makes up 70-90% of starch

Question 11

describe a property of starch

Answer 11

it is insoluble in water so doesn’t effect water potential in the xylem

Question 12

describe the structure of cellulose

Answer 12

-made up of long, unbranching, linear chains of beta glucose
-contains 1,4 glycosidic bods
-cellulose chains run parallel to one another and are joined by hydrogen bonds to form strong cross linkages

Question 13

why do cellulose chains run parallel to one another?

Answer 13

the hydroxyl group on carbon 1 and 4 are too far apart

Question 14

why does cellulose need strong cross linkages?

Answer 14

to prevent the cell from exploding due to osmotic pressure exerted inwards to stop the influx of water to keep the cell turgid

Question 15

what is a reducing sugar?

Answer 15

carbohydrates that can donate an electron to another molecule

Question 16

examples of reducing sugars

Answer 16

all monosaccharides, maltose and lactose

Question 17

example of a non-reducing sugar

Answer 17

sucrose

Question 18

how to test for reducing sugars?

Answer 18

-grind of the food with distilled water then filter out the door particles
-place 3cm2 of the food solution in a boiling tube and add 3cm2 of benedicts solution (blue)
-place the boiling tube in boiling water for 5 mins

Question 19

what makes benedicts solution blue?

Answer 19

copper 2+ ions

Question 20

what is a negative result for the reducing sugar test?

Answer 20

the solution remains blue

Question 21

what is a positive result for the reducing sugars test?

Answer 21

copper 1+ ions are formed which is red.
small amount of reducing sugars = been solution
large amount of reducing sugars = red solution

(green to yellow to orange to red )

Question 22

what type of data does the reducing sugars test give?

Answer 22

semi-quantitative

Question 23

how to test for non-reducing sugars?

Answer 23

-indirectly- use benedicts to test for the monosaccharide and note down any colour change
-take another 3cm2 sample of the solution and add 3cm2 of HCl and gently boil it for 5 minutes
-if a non-reducing sugar is present the acid will hydrolyse the glycosidic bond releasing the monossacharides
-then add a dilute alkali like sodium hydroxide and use pH paper to ensure the solution is alkali
-complete the benedicts test and note down any colour change

Question 24

what conditions does the benedicts test need?

Answer 24

alkaline

Question 25

what is a positive result for a non-reducing sugars test?

Answer 25

-the first benedicts test remains blue showing there are no reducing sugars present and the second benedicts test has a colour change -if the is an increase in reducing sugars between the first and second benedicts test

Question 26

what does a negative result of a non-reducing sugar test?

Answer 26

if the first benedicts test produces a red precipitate as we can't see a colour change