Carbohydrates and Lipids

Question 1

What is a monomer? (1)

Answer 1

A monomer is a small, identical molecule from which larger molecules called polymers are made via condensation reactions

Question 2

What is a polymer? (1)

Answer 2

Polymers are large molecules made from joining 3 or more similar monomers together

Question 3

What is a condensation reaction? (1)

Answer 3

removal of one water molecule which forms a bond

Question 4

What is a hydrolysis reaction? (1)

Answer 4

addition of one water molecule to break a bond

Question 5

Give 2 examples of monomers (2)

Answer 5

Alpha/Beta glucose
Nucleotides
Amino acids

Question 6

Give 2 examples of polymers (2)

Answer 6

Nucleic Acids
Cellulose
Starch
Protein

Question 7

Name the bond formed between two monosaccharides (1)

Answer 7

Glycosidic bond

Question 8

Draw the structure of alpha glucose (1)

Answer 8

https://www.google.com/search?q=structure+of+alpha+glucose&rlz=1C1VDKB_en-GBGB967GB967&sxsrf=ALiCzsa9otHIICek5tboH32WQ6Ai9k1dTA:1651412793402&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiUmLaHuL73AhWSX8AKHRSzAr0Q_AUoAXoECAEQAw&biw=1280&bih=601&dpr=1.5#imgrc=Od39dZJh972gdM

Question 9

Which monosaccharides form maltose and which enzyme is used to hydrolyse maltose? (2)

Answer 9

Alpha Glucose and Alpha Glucose
Enzyme - Maltase

Question 10

Which monosaccharides form lactose and which enzyme is used to hydrolyse lactose? (2)

Answer 10

Alpha Glucose and Galactose
Enzyme - Lactase

Question 11

Which monosaccharides form sucrose and which enzyme is used to hydrolyse sucrose? (2)

Answer 11

Alpha Glucose and Fructose
Enzyme - Sucrase

Question 12

Give three features of starch and explain how these enable it to act as a storage substance. (3)

Answer 12

Helical so compact
Insoluble so doesn’t affect water potential
Large molecule so does not leave cell
Branched chains (1:4 and 1:6 glycosidic bonds) so rapid hydrolysis to remove glucose for respiration

Question 13

The structure of cellulose is related to it’s role in plant cell walls. Explain how. (3)

Answer 13

Long straight unbranched chains of beta glucose monomers
Joined by MANY WEAK hydrogen bonds
Form microfibrils
Provide increased strength

Question 14

Hydrogen bonds are important in cellulose molecules. Explain why. (2)

Answer 14

Holds cellulose chains together
Provides strength
Many weak hydrogen bonds provide strength in large numbers

Question 15

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein (3)

Answer 15

Glucose and Galactose
Joined by condensation reactions
Forms glycosidic bond
Added to [polypeptide in Golgi Body

Question 16

Describe how the student would show that reducing sugars were present in a solution. (3)

Answer 16

Add equal volume of Benedict’s Solution
Heat to 95*C
Red/orange/green PRECIPITATE formed shows reducing sugar is present

Question 17

Describe how a student would show that a non-reducing sugar is present in the solution
(5)

Answer 17

Complete Benedict’s test and observe negative result
Add HCl to sugar solution AND heat to 95C
Neutralise with alkali
Add equal volume of Benedict’s solution
Heat again to 95C
Red/Orange/Green PRECIPITATE formed

Question 18

Describe how you would test a sample of food for the presence of starch. (2)

Answer 18

Add Potassium Iodide (KI) solution
Blue/Black indicates starch is present

Question 19

What is a triglyceride made from and what bond is formed between them? (1)

Answer 19

3 fatty acids bonded via an ester bond to one glycerol molecule

Question 20

What is a saturated fatty acid? (1)

Answer 20

Do not have double bonds between carbon atoms within the hydrocarbon chain

Question 21

What is an unsaturated fatty acid? (1)

Answer 21

Double bonds between carbon atoms within the hydrocarbon chain

Question 22

Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids. (3)

Answer 22

Crush the seed
MIX with ethanol and SHAKE
Add water AND shake
Forms cloudy white emulsion

Question 23

What is a structural difference between a phospholipid and a triglyceride? (1)

Answer 23

Fatty acid is removed and replaced with a phosphate group

Question 24

Compare and contrast the structure and properties of triglycerides and phospholipids. (5)

Answer 24

Both contain ester bonds
Both contain glycerol
Fatty acids on both may be saturated or unsaturated
Both are insoluble in water

Triglyceride has three fatty acids and phospholipids have two fatty acids plus phosphate group
Triglycerides are hydrophobic and phospholipids have hydrophilic and hydrophobic region
Phospholipids form bilayer but triglycerides don’t

Question 25

A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution. (2)

Answer 25

Filter and dry the precipitate
Find the mass

Question 26

Explain how the digestion of starch in the small intestine leads to an increase in the concentration of glucose in the blood. Details of co-transport are not required. (3)

Answer 26

Starch is hydrolysed by amylase
Produces glucose
Small enough to cross the gut wall into the blood

Question 27

Describe the structure of glycogen (2)

Answer 27

1. Polymer of alpha glucose
2. Joined by glycosidic bonds

Question 28

Suggest how glycogen acts as a store of energy (2)

Answer 28

1. Hydrolysed
2. Glucose used in respiration