S3T1: Nutrients

Question 1

Starch test

Answer 1

Add 2-3 drops of iodine to sample (solid - cut into small pieces/mortar and pestle)
Positive: iodine solution turns from yellow brown to blue black

Question 2

Reducing sugar test

Answer 2

Benedict’s Test
- Add equal volume of Benedict’s solution to sample solution, shake thoroughly (solids: cut, mash, decant after adding water…)
- Immerse test tube in boiling water bath for 3-5 minutes
Positive: Brick red precipitate formed from blue solution
*All monosaccharides and disaccharides are reducing sugars except sucrose

Question 3

Proteins test

Answer 3

Biuret test
Add equal volume sodium hydroxide to sample and shake well
Add 1% Copper (II) Sulfate to solution, shaking after each drop
Positive: mixture turned from blue to violet/lilac

Question 4

Fat test

Answer 4

Ethanol-emulsion test
Add 2cm3 of ethanol, shake well (solid: cut into small pieces/mortar and pestle, add into test tube with ethanol)
Add 2cm3 of water (For solids, decant into a new test tube) and shake well.
Positive: cloudy, white emulsion formed from clear solution.

Question 4

Fat test

Answer 4

Ethanol-emulsion test
Add 2cm3 of ethanol, shake well (solid: cut into small pieces/mortar and pestle, add into test tube with ethanol)
Add 2cm3 of water (For solids, decant into a new test tube) and shake well.
Positive: cloudy, white emulsion formed from clear solution.

Question 5

Explain the formation of 3 disaccharides: maltose, lactose and sucrose

Answer 5

Glucose + Glucose -> Maltose
Glucose + Fructose -> Sucrose
Glucose + Galactose -> Lactose

Question 6

How are polymers formed?

Answer 6

Monomers (monosaccharides) joined to form polymers (large molecule with repeating units) through polymerisation

Question 7

List 3 differences between saturated and non-saturated fats

Answer 7

Straight chains vs bent/kink chains
Solid vs liquid (at rtp)
Single bond vs double bond
Cholesterol found (coronary heart diseses) vs do not cause heart diseases (plant/vege)

Question 8

Equation for fats

Answer 8

Fats + 3H2O -(hydrolysis)-> glycerol + 3 fatty acids

Question 9

State 3 functions of fats

Answer 9

Source of energy + storage of energy
Stored under adipose tissue in skin -> insulator, minimise heat loss
Surround internal organs to protect them from shock and injury

Question 10

Describe formation of protein molecules

Answer 10

Amino acids (absorbed in body) joined together by peptide bonds
Link up to form long chain (condensation) -> polypeptides
Polypeptides coil together with weak hydrogen bonds (broken easily) to form protein molecule

Question 11

State 4 functions of proteins

Answer 11

Synthesis of protoplasm
Form structures in body and synthesize enzymes and some hormones
Source of energy
Formation of antibodies to combat diseases (eg. lymphocyte)

Question 12

List 7 properties of water

Answer 12

Thermal property (high heat capacity)
Important part of tissues
Solvent for chemical reactions
Metabolic reactions (photosynthesis in plants, hydrolysis, condensation)
Transport dissolved substances
Lubricant
Support (incompressible: eg turgor pressure)

Question 13

What is hydrolysis and condensation?

Answer 13

Hydrolysis: big molecule broken down to form small molecules with the addition of water
Condensation: small molecules join together to form big molecule with the release of water