Food and energy

Question 1

What is the simplest carbohydrate called?
State its formula.
State 3 properties.

Answer 1

Monosaccharide.
C6H12O6
Properties:
- referred to as sugars
- sweet tasting
- soluble in water

Question 2

How do fructose and sucrose relate to glucose? (2)

Answer 2

• Fructose and sucrose are isomers of glucose.

- They are all chiral molecules.

Question 3

How is a disaccharide formed?

What type of link is created?

Answer 3

Condensation reaction between hydroxyl groups on 2 monosaccharides.
A glycosidic link (ether) is formed.

Question 4

Name 3 disaccharides.

Answer 4

• sucrose
• lactose
• maltose

Question 5

Describe the three important polysaccharides.

Answer 5

• cellulose: major structural material in plants
• starch: acts as a store of glucose in plants and exists in 2 forms: amylose and amylopectin
• glycogen: acts as store of glucose in animals

Question 6

Compare glucose and fructose

Answer 6

Both are monosaccharides.
Both are soluble in water due to the presence of polar hydroxyl groups which form H-bonds with water.
Fructose is a 4 carbon aromatic ring whereas glucose is a 5 carbon ring.

Question 7

Compare sucrose and maltose.

Answer 7

Both are disaccharides.
Both are water soluble.
Sucrose is made up of glucose and fructose whereas maltose is only made up of glucose.

Question 8

Provide a description of starch.

Answer 8

A polysaccharide composed of ∂-glucose - molecules.
Exists in two forms:
- amylose: linear
- amylopectin: branched

Question 9

Provide a description of glycogen.

Answer 9

A polysaccharide composed of ∂-glucose molecules.
Highly branched material.
Acts as a store of glucose in animals.

Question 10

Provide a description of cellulose.

Answer 10

Polysaccharide composed of ß- glucose molecules.
Very large, straight-chain molecule.
Alternating nature of -CH2OH group allows for good alignment of -OH groups.
This results in strong H-bonds, thus the material is very strong and rigid.
Acts as a store of glucose in plants.

Question 11

How are carbohydrates digested?

Answer 11

By hydrolysis:
1. initially enzymes in mouth (amylase)
Bonds are split between every second pair of glucose units.
2. Digested in the stomach
In the small intestine, carbs are changed by enzyme are maltase, lactase and sucrase.

Question 12

Differentiate between simple and complex carbohydrates/

Answer 12

A simple carbohydrate contains less than 5 monomers, hence easily digested and energy is received quicker whereas complex carb is a polysaccharide, which takes longer to digest and receive energy.

Question 13

What is a triglyceride?

Answer 13

A triglyceride is an ester derived from glycerol and three fatty acids. Triglycerides are the main constituents of body fat in humans and other animals, as well as vegetable fat.

Question 14

How is a triglyceride formed?

Answer 14

Condensation reaction between glycerol and a fatty acid.

Question 15

What are the two different forms of starch?

Answer 15

• amylose: linear 30%

- amylopectin: branched 70%

Question 16

What are the steps used to calculate the energy content of food, using a bomb calorimeter?

Answer 16

1. add food to calorimeter
2. fill with water
3. passing energy into the system
4. measure rise in temp
5. igniting food sample
6. measure rise in temp again

Question 17

What is an antioxidant?

Provide an example.

Answer 17

Antioxidants are compounds that inhibit oxidation. Vitamin C acts as an antioxidant by being preferentially oxidised

Question 18

Discuss the similarities and differences between starch and glycogen.

Answer 18

Starch and glycogen are both comprised of a-D-glucose monomers however the structure of glycogen is much more branched than that of starch.

Question 19

Why is aspartame marketed as ‘low calorie’?

Answer 19

Aspartame is approximately 200 times sweeter than other sugars like sucrose and thus less aspartame is needed to provide an equivalent measure of sweetness.

Question 20

Compare the structure of fats and oils.

Answer 20

Oils, in terms of their structure, have a higher degree of unsaturation (double bonds), creating in kinks in the chain, preventing close packing. This results in a lower melting temp and thus oils are liquid at room temp. Whereas fats are solids at room temp since their structure is largely linear due to their saturation, thus allowing for closer packing.

Question 21

Why are polyunsaturated fats more prone to oxidative rancidity?

Answer 21

Polyunsaturated fats contain reactive c=c double bonds and are thus more prone to oxidative rancidity than saturated fats, which the only contain relatively stable c-c single bonds.