Carbohydrates - B2

Question 1

Are most carbohydrates monomers or polymers?

Answer 1

Polymers

Question 2

What 3 groups are carbohydrates split into?

Answer 2

Monosaccharides, disaccharides, and polysaccharides.

Question 3

What are monosaccharides?

Answer 3

-single sugars
-different ones contain different numbers of carbon atoms
can be made into di/polysaccharides

Question 4

Name 3 examples of monosaccharides.

Answer 4

Glucose, fructose, galactose

Question 5

What is the difference between alpha glucose and beta glucose?

Answer 5

Alpha- hydrogen on top, hydroxyl on bottom
Beta- hydrogen and hydroxyl on carbon 1 are swapped around
They are isomers.

Question 6

What does it mean if alpha and beta glucose are isomers of each other?

Answer 6

They are both molecules of glucose(same molecular formula), but the atoms have been arranged in a different way(different structure), giving them different properties.

Question 7

What are disaccharides?

Answer 7

A substance made from two monosaccharides.

Question 8

Give 3 examples of disaccharides.

Answer 8

Maltose, sucrose, lactose.

Question 9

What type of reaction bonds two monosaccharides together, and what is produced along with the disaccharide?

Answer 9

-Condensation reaction
-H2O is produced.

Question 10

What monosaccharides form:
a)sucrose?
b)maltose?
c)lactose?

Answer 10

a)alpha glucose, fructose
b)alpha glucose, alpha glucose
c)alpha glucose, galactose

Question 11

What reaction turns disaccharides(polymers) back into monosaccharides(monomers)?

Answer 11

Hydrolysis, add water.

Question 12

What is hydrolysis?

Answer 12

Polymers being broken down to constitute monomers.

Question 13

What is condensation?

Answer 13

Two monomers join together by a chemical reaction.

Question 14

What are three examples of polysaccharides?

Answer 14

Starch, glycogen, cellulose.

Question 15

What is the amylose structure of a starch molecule and what is it’s functions?

Answer 15

-Un-branched and highly coiled, it has C1-4 bonds.
-The coiled shape makes it compact and excellent for storage

Question 16

What is the amylopectin structure of starch and what is it’s function?

Answer 16

-C1-4 and C1-6 glycosidic bonds so it’s coiled. but also has branches.
-This increases the area for enzymes to hydrolise so it can be broken down quicker into glucose than amylose

Question 17

What is the function of starch being insoluble?

Answer 17

Doesn’t effect osmosis(presence of starch in solution will not lower water potential causing unwanted movement of water), doesn’t diffuse out of cells.

Question 18

What is the function of glycogen being more branched than starch and being coiled?

Answer 18

There are more free ends where glucose molecules can either be added or removed, allowing for condensation and hydrolysis reactions to occur more rapidly
- storage or release of glucose can suit demands of the cell
- more branched and coiled makes it more compact which helps them store more.

Question 19

Is glycogen also insoluble?

Answer 19

Yes.

Question 20

What is cellulose made from?

Answer 20

Beta glucose.

Question 21

What happens to the beta glucose in cellulose molecules because the hydroxyls don’t line up?

Answer 21

Every other glucose turns 180 degrees so that they match up and can form glycosidic bonds, also making it linear(the chains)

Question 22

Why are cellulose molecules strong?

Answer 22

The rows allow lots of hydrogen bonds to form between OH groups. This gives cellulose strength for cell walls. The OH bonds form between and within chains.
Thy hydrogen bonds are weak on their own, but the sheer amount of them makes them strong.

Question 23

Is cellulose branched or unbranched?

Answer 23

Unbranched as it only has C1-4 bonds.

Question 24

What are the different parts of the structure of cellulose?

Answer 24

-CH2OH group alternates
-doesn’t coil
-unbranched
-forms fibrils->lots of chains cause fibrils which add to strength beta glucose->cellulose fibres->microfibrils->macrofibrils->matrix

Question 25

What is the role of cellulose?

Answer 25

-Important structural molecule
-Major cell wall component

Question 26

What is a reducing sugar?

Answer 26

A sugar that give electrons(reduce) to other molecules.

Question 27

What are some examples of reducing sugars?

Answer 27

All monosaccharides and most disaccharides such as maltose and lactose.

Question 28

What happens in a chemical reaction with reducing sugars?

Answer 28

Reduce copper ions in copper sulfate which forms an orange/red precipitate copper oxide.

Question 29

What is a non-reducing sugar? Give an example.

Answer 29

A sugar that cannot give electrons. An example is sucrose.

Question 29

What is needed to be added in a non-reducing sugar chemical test?

Answer 29

You need to add HCl to conduct the test. This hydrolyses to produce monosaccharides.

Question 30

Which chemical test is for:
a)reducing sugar
b)non-reducing sugar
c)starch

Answer 30

a)Benedict’s
b)Benedict’s
c)iodine

Question 31

Explain the chemical test for a reducing sugar.

Answer 31

Benedict’s test:
-Add Benedict’s solution to 10cm^3 sample in test tube.
-Shake mixture and heat in a water bath for 3 mins(heat don’t boil)
-Observe colour change(precipitate): blue>green>yellow>orange>brick red

Question 32

Explain the chemical test for a non-reducing sugar.

Answer 32

Benedict’s test:
-Add 3cm^3 hydrochloric acid to the non-reducing sugar(sucrose)
-Heat in a water bath for 1 min
-Add one spatula of sodium hydrogen carbonate to neutralise
-Perform the Benedict’s test as completed for a reducing sugar
-Observe colour change: blue>green>yellow>orange>brick red

Question 33

Explain the chemical test for starch.

Answer 33

Iodine test:
-Place drops of iodine on a sample
-If present it will turn from a orange/brown colour to a blue/black