carbohydrates

Question 1

Define the term monomer

Answer 1

Monomers are small identical or similar molecules which can be condensed (joined/linked together) to make larger molecules called polymers.

Question 2

Define the term polymer

Answer 2

Polymers are large molecules made from joining many (3 or more) identical or similar monomers together.

Question 3

Describe hydrolysis and condensation reactions

Answer 3

A condensation reaction joins two monomer units together with the removal of one water molecule.

A hydrolysis reaction involves adding one molecule of water to break the bond between two monomers.

Question 4

State the elements found in carbohydrates.

Answer 4

The elements found in carbohydrates are Carbon (C), Hydrogen (H) and Oxygen (O).
H : O is 2 : 1 .

Question 5

name 3 monosaccharides

Answer 5

glucose and galactose and fructose.

Question 6

molecular formula of glucose

Answer 6

C6 H12 O6

Question 7

alpha glucose

Answer 7

penguin

Question 8

beta glucose

Answer 8

Egyptian mummy

Question 9

show how two glucose molecules join together by a condensation reaction to form maltose. Give the molecular formula for this reaction.

Answer 9

C6H12O6 + C6H12O6
——–> C12H22O11 + H2O

Question 10

Name the bond formed when two monosaccharides join together

Answer 10

The bond which forms between the two monosaccharides is called a glycosidic bond.

Question 11

look in booklet and identify fructose and galactose

Answer 11

fructose has only 5 carbons with a pointy head

galactose has both (OH) groups facing up

Question 12

glucose + glucose =

Answer 12

maltose and hydrolytic enzyme is maltase

Question 13

glucose + galactose =

Answer 13

lactose and hydrolytic enzyme is lactase

Question 14

glucose + fructose =

Answer 14

sucrose and hydrolytic enzyme is sucrase

easy way to remember - sucrose is found in fruit - fruit sounds like fructose

Question 15

carbohydrates into sugars

Answer 15

sugars into monosaccharide and then into ( glucose, fructose, galactose)

sugars into disaccharides and then into (sucrose, maltose, lactose)

Question 16

carbohydrates into polysaccharides

Answer 16

polysaccharides and then into storage molecules such as ( glycogen(humans)) and (starch(plants))

polysaccharides and then into structural molecules such as cellulose in plants

Question 17

describe starch? (alpha glucose)

Answer 17

starch is helical so it doesn’t take up much space
its a polymer of alpha glucose joined by glyosidic bonds
its insoluble so doesn’t effect the water potential
large so cant leave the cell
1 - 4 glyceridic bonds
can be branched or unbranched

Question 18

describe glycogen ( alpha glucose )

Answer 18

short chains
more highly branched
larger surface area
stored in muscles and liver
insoluble so doesn’t affect water potential
more short chains - glycogen being more readily hydrolysed into glucose for respiration

Question 19

structure of cellulose (beta glucose) - related to its function

Answer 19

long straight unbranched chains of beta glucose
joined by hydrogen bonds
forms microfibrils
provides strength and rigidity

Question 20

Identify alpha glucose is a reducing sugar and as such forms an orange precipitate when boiled with Benedict’s solution.

Answer 20

1. Add equal volumes of Benedict’s solution;
2. Heat to 95 ⁰C;
3. Red/orange/yellow/green precipitate (shows reducing sugar present);

@ Benedict’s test for reducing sugar (glucose, galactose, lactose, maltose, fructose)

Question 21

Identify sucrose and starch are a non-reducing sugars and as such do not form an orange precipitate when boiled with Benedict’s solution.

Answer 21

No colour change

Question 22

Explain that following hydrolysis by heating with acid into monomer units (non-reducing sugars) of sucrose form an orange precipitate when boiled with Benedict’s solution.

Answer 22

1. Add dilute hydrochloric acid (HCl) to sugar solution; - (to hydrolise glycocidic bonds)
2. Boil sugar solution;
3. Add sodium hydrogen carbonate (NaHCO₃) (alkali) to neutralise;
4. Add equal volumes of Benedict’s solution to the sugar solution;
5. Heat to 95 ⁰C;
6. Red/orange/yellow/green precipitate (shows reducing sugar present);

Question 23

Give test for starch as add drop of iodine solution, if starch is present solution will turn blue/black

Answer 23

1. Add potassium iodide(KI) solution to the food sample;
2. Blue/black/purple indicates starch is present;