Chapter 3: Biological Molecules🧬

Question 1

Water’s role in the body

Answer 1

1. Structural: component of cell, lubricant for joints
2. Coolant: evaporation
3. Reactant: hydrolysis, photosynthesis
4. Solvent/ transport: blood, urine

Question 2

Carbohydrates definition

Answer 2

Organic molecules made up of carbon, hydrogen and oxygen (H and O atoms in the ratio 2:1)

Question 3

Carbohydrates function

Answer 3

Support: cell wall in plant (cellulose)
Reactants: glucose as substrate for respiration, formation of nucleus acids, to synthesise substances (eg lubricants, nectar)
Converted to other organic compounds (eg amino acids and fats)

Question 4

Types of carbohydrates

Answer 4

Simple carbohydrates:
1. Monosaccharides (single sugars)- energy source:
- glucose
- fructose
- galactose
2. Disaccharides (double sugars)- transport form:
- maltose
- sucrose
- lactose

Complex carbohydrates:
1. Polysaccharides- storage form:
- Starch
- Cellulose
- Glycogen

Question 5

Reducing sugars

Answer 5

All monosaccharides and disaccharides, except sucrose, are reducing sugars

Question 6

Monosaccharides

Answer 6

Sweet and water soluble
Can pass through cell membrane and be absorbed into cell
Molecular formula: C6H12O6
Impt egs:
Glucose: in plants and animals
Fructose: common in plants, rare in animals
Galactose: found in the milk sugar of mammals

Question 7

Disaccharides

Answer 7

2 monosaccharides bonded chemically
General formula: C12H11O6
Formation: condensation
Break down: hydrolysis

Question 8

Disaccharides: Forming

Answer 8

Condensation:
2 simple molecules chemically join together to form a larger molecule with the removal of 1 water molecule

glucose + glucose -> maltose + water
glucose + fructose —> sucrose + water
glucose + galactose —> lactose + water

Question 9

Disaccharides: Break down

Answer 9

Hydrolysis:
Water is used to break down a complex molecule into smaller molecules
(opposite of condensation)

Question 10

Polysaccharides

Answer 10

Many monosaccharides chemically bonded together
Impt egs: Starch, Cellulose, Glycogen

Question 11

Polysaccharides Structure

Answer 11

Glycogen: tree-like branches
Cellulose: even rows
Starch: loops or tree-like branches

Question 12

Polysaccharides Role

Answer 12

Glycogen: main storage of glucose in animals
Cellulose: Structural support for plants and dietary fibres to prevent constipation
Starch: Storage form in plants and digested to glucose for energy

Question 13

Polysaccharides Occurrence

Answer 13

Glycogen: Stored mainly in liver and muscles of mammals
Cellulose: Cell wall of plants
Starch: Storage organs of plants

Question 14

Glycogen and starch’s suitability as storage materials

Answer 14

• insoluble in water: does not change water potential in cell
• large molecules: cannot diffuse out of cell
• easily broken down to glucose
• compact

Question 15

Reducing sugars test

Answer 15

Benedict’s Test:
1. Add 2cm3 of Benedict’s solution to 2cm3 of food sample in a test tube.
2. Shake.
3. Heat contents in a boiling water Barth for 2-3 min.

Observe for colour changes

Question 16

Starch Test

Answer 16

Iodine Test

1. Add 2cm3 of food sample to a test tube.
2. Add few drops of iodine solution to test tube.
3. Observe for results: Brown to blue-black means starch is present

Question 17

Fats description

Answer 17

Type of lipid
Organic molecules made up of carbon, hydrogen and oxygen ( no fixed proportion but hydrogen is WAYYY more than oxygen )

Question 18

Fats use

Answer 18

• Energy storage: long-term as they have higher energy value than carbs
• Insulation (heat and water loss): secretes thin layer of oil that premiers heat and water loss
• Solvent for fat- soluble vitamins and hormones
• Synthesis of cell membrane

Question 19

Fat molecule and enzyme

Answer 19

Fat molecule —> 1 glycerol molecule + 3 fatty acid molecules

Enzyme: lipase

Question 20

Saturated vs Unsaturated Fats: Structure

Answer 20

Saturated fats: fatty acid chain is straight

Unsaturated fats: has kinks

Question 21

Saturated vs Unsaturated Fats: Physical State

Answer 21

Saturated: most are solid at room temperature
Unsaturated: most are liquids at room temperature

Question 22

Saturated vs Unsaturated Fats: examples

Answer 22

Saturated: butter, cream, cheese

Unsaturated: vegetable oil, nuts

Question 23

Fats: food test

Answer 23

Ethanol emulsion test

1. Add 2cm3 of ethanol to 2cm3 of food sample in a test tube
2. Shake contents vigorously
3. Add 2-3cm3 of water into test tube. Shake mixture.

Observation: if a white emulsion forms, fats are present

Question 24

Emulsion

Answer 24

Suspension of drops of one liquid in another liquid

Question 25

Protein

Answer 25

Organic molecules made up of carbon, hydrogen, oxygen, nitrogen and MAY have sulfur

Question 26

Protein function

Answer 26

• synthesis of new protoplasm for growth and repair
• synthesis of enzymes and hormones
• formation of antibodies to combat diseases

Question 27

Protein is made of?

Answer 27

Amino acids

Question 28

Amino acids are made of?

Answer 28

• An amino group
• An acid/carboxyl group
• side chain

Question 29

Condensation reaction: Protein (polypeptide)

Answer 29

Primary structure of protein: amino acids covalently bonded via a peptide bond to forms polypeptide chain

Question 30

Condensation reaction: Protein (protein molecule)

Answer 30

• 1 polypeptide chain chemically bonded in a specific 3D conformation
• 2 or more polypeptide chains chemically bonded together to form a specific 3D conformation

Question 31

Protein loss of structure

Answer 31

Weak bonds holding the 3D structure together are easily broken by heat or chemicals (denaturation)

Question 32

Protein breakdown

Answer 32

Hydrolysis

Question 33

Test for protein

Answer 33

Biuret test

1. Add 2cm3 of sodium hydroxide solution to 2cm3 of food sample in a test tube.
2. Shake mixture thoroughly.
3. Add 1% copper (ll) sulfate drop by drop. Shake mixture after every drop.

Observation: If the mixture turns from blue to violet/purple then protein is present.