Nutrients

Question 1

Functions of water

Answer 1

• as a solvent for chemical reactions that take place
• a key component in cells, tissue fluid, digestive juices & blood
• helps to control body temp. through sweating - as water in sweat evaporate of skin surface, latent heat of vaporisation is removed, cooling down the body
• transport dissolved substances such as digested products & waste products

Question 2

Define carbohydrates

Answer 2

Carbohydrates are organic molecules made up carbon, hydrogen & oxygen (H:O atoms = 2:1)

Question 3

Monosaccharides eg

Answer 3

glucose, fructose, galactose

Question 4

Disaccharides eg

Answer 4

maltose, sucrose & lactose

Question 5

Define condensation reaction

Answer 5

A condensation reaction is a chemical reaction in which 2 simple molecules are joined tgt to form a larger molecule with the removal (release) of 1 molecule of water

Question 6

Define hydrolytic reaction or hydrolysis

Answer 6

Hydrolysis or a hydrolytic reaction is a reaction in which 1 water molecule is needed to break up a complex molecule into smaller molecules
- use an enzyme

Question 7

Test for reducing sugars

Answer 7

Carry out the Benedict’s test
- Add 2 cubic cm of Benedict’s solution to 2 cubic cm of food sample in test tube (1:1)
- Shake the mixture
- Heat contents in a boiling water bath for 2-3 minutes

Question 8

Determining amount of reducing sugar present

Answer 8

1. Solution remained blue: no RS
   Presence of…
2. Green ppt: Traces amnt of RS
3. Yellow or orange ppt: Moderate amnt of RS
4. Brick-red ppt: Large amnt of RS

Question 9

Why are glycogen & starch suitable as storage materials in cells?

Answer 9

• insoluble in water so they do not change the water potential in cells
• large molecules - cannot diffuse through CSM so they will not be lost from cell
• easily hydrolysed to glucose when needed
• molecules have compact shapes so they occupy less space than individual glucose molecules

Question 10

Functions of carbohydrates

Answer 10

• to provide energy for cell activities
• to form supporting structures such as cell walls (cellulose)
• to be converted into other organic compounds such as amino acids & fats
• to form nucleic acids in DNA
• to synthesise lubricants
• for nectar production in flowers

Question 11

Define fats

Answer 11

Fats are organic molecules made up of carbon, hydrogen & oxygen (much less oxygen in proportion to hydrogen)

Question 12

What is the result of hydrolysis of fats?

Answer 12

One fat molecule will be broken down into glycerol & 3 fatty acid molecules/fatty acid chains
- involves addition of 3 water molecules & enzyme

Question 13

What are the differences b/w saturated & unsaturated fats?

Answer 13

Saturated: fatty acid chain - straight, solid @ RT
Unsaturated: fatty acid chain - have kink/bent, liquid @ RT

Question 14

How do we test for fats?

Answer 14

ethanol emulsion test
1. Add 2 cubic cm of ethanol to 2 cubic cm of food sample in a test tube
2. Shake contents vigorously
3. Decant 2 cubic cm of water into test tube & shake the mixture

Question 15

Indication of presence of fats

Answer 15

A cloudy white emulsion is formed

Question 16

Functions of fats

Answer 16

• as a source & store of energy
• as an insulating material - prevents excessive heat loss
• as a solvent for fat soluble vitamins & hormones
• to form the main part of cell membranes (lipids)
• to help reduce water loss from skin surface

Question 17

What is amino acid made up of?

Answer 17

It is made up of an amino group, an acid group and a side chain, R group, which differentiates the different amino acids.

Question 18

Define proteins

Answer 18

Proteins are organic molecules made up of carbon, hydrogen, oxygen, nitrogen(+maybe sulfur)

Question 19

Formation of proteins

Answer 19

1. Amino acids are the building blocks of proteins
2. Peptide bonds (covalent bonds) link up amino acids to form a polypeptide
3. 2 or more polypeptide chains fold to form a 3D molecule called proteins

Question 20

How can we test for proteins?

Answer 20

Biuret test
1. Add 2cm3 of sodium hydroxide to test tube containing 2cm3 of food sample & shake well
2. Add 1% copper(II) sulfate solution drop by drop to test tube. Shake the test tube after each drop
3. Leave the test tube to stand for 5 minutes

Question 21

Indication of the presence of proteins

Answer 21

Biuret solution changes colour from blue to violet

Question 22

What are the functions of proteins?

Answer 22

• synthesis of new protoplasm for growth & repair of worn out cells
• synthesis of enzymes & some hormones
• synthesis of antibodies

Question 23

explain enzyme action in terms of the ‘lock and key’ hypothesis

Answer 23

• an enzyme has a specific 3D shape
• only substrate with a 3D shape complementary to that of active site can fit into the enzyme, forming an enzyme-substrate complex (the enzyme is like a lock and substrate a key; ‘lock-and-key’ hypothesis)
• while substrate is attached to the active site, chemical reaction occurs & substrate is converted into products
• products leave the active site, enzyme remains chemically unchanged

Question 24

explain the mode of action of enzymes

Question 25

explain the effects of temperature on the rate of enzyme catalysed reactions

Question 26

explain the effects of pH on the rate of enzyme catalysed reactions