Chap 3: Biological Molecules

Question 1

What are the 3 organic molecules?

Answer 1

• carbohydrates
• fats
• proteins

Question 2

Examples of foods where we can get carbohydrates?

Answer 2

Rice, noodles, etc

Question 3

Elements that make up carbohydrates?

Answer 3

carbon, hydrogen, oxygen
hydrogen to oxygen atom ratio
- 2:1

Question 4

Functions of carbohydrates?

Answer 4

• it is a substrate for respiration, provides immediate source of energy for cell activities
• used to form support structures eg cell wall in plants
• used for formation of nucleic acids eg DNA

Question 5

Different types of carbohydrates?

Answer 5

Simple sugars:
- glucose
- fructose
Double sugars:
- maltose
- sucrose
Complex carbohydrates:
- starch
- cellulose
- glycogen

Question 6

Name the 2 simple sugars and where they are commonly found

Answer 6

1. Glucose - both plants and animals
2. Fructose - mainly plants

Question 7

Name the 2 double sugars and where they are commonly found

Answer 7

1. maltose - plants
2. sucrose - plants

Question 8

Name the sugars that form:
1 - maltose
2 - sucrose

Answer 8

maltose: glucose + glucose
sucrose: glucose + fructose

Question 9

How can double sugars be split?

Answer 9

Using enzymes

Question 10

What are reducing sugars?

Answer 10

• glucose
• fructose
• maltose

Question 11

How to test for reducing sugars?

Answer 11

Benedict’s solution

Question 12

Procedure for benedict’s solution?

Answer 12

1. Place 2 cm^3 of food sample
2. Add 2cm^3 of benedict’s solution
3. Shake and place mixture in boiling water
4. Record observations

Question 13

What are the results for benedicts solution?

Answer 13

• solution remains blue: no reducing sugar
• solution turns green: traces of reducing sugar
• solution turns yellow or orange: moderate amount of reducing sugar
• solution turns red/red precipitate: large amount of reducing sugar

Question 14

What are the three types of complex carbs and where are they commonly found?

Answer 14

• starch: storage organ of plants
• cellulose: cell walls of plants
• glycogen: liver & muscle of mammals

Question 15

Role of starch?

Answer 15

• storage of carbohydrates in plants
• if needed, digested into glucose to provide energy for cell activities

Question 16

Role of cellulose?

Answer 16

• protects plant cells from bursting/damage
• it cannot be digested in intestines
• it is dietary fibre to prevent constipation

Question 17

Role of glycogen?

Answer 17

• storage form of carbohydrates for mammals
• if needed, it is digested to glucose to provide energy for cell activities

Question 18

Stores of glucose in plants and mammals?

Answer 18

Plants: starch
Mammals: glycogen

Question 19

Process of starch (in plants) to glycogen (in mammals)?

Answer 19

starch -> glucose -> glycogen

Question 20

Why is starch and glycogen suitable as storage materials?

Answer 20

• insoluble in water
• large molecules, cannot diffuse easily through cell membrane
• easily broken down to glucose if needed
• compact shape hence occupies less space

Question 21

What is the breakdown of starch?

Answer 21

• enzyme amylase digest starch to form maltase
• maltase breaks down and forms glucose

Question 22

How to test for presence of starch?

Answer 22

Iodine teste

Question 23

What are the different results from iodine test and what do the mean?

Answer 23

• solution turns blue-black: starch is present
• solution remains brown: starch is absent

Question 24

Procedure of iodine test?

Answer 24

1. Add few drops of iodine solution to sample
2. Record and observe

Question 25

List down foods that contain fats

Answer 25

butter, cheese, etc

Question 26

Elements that form fats?

Answer 26

carbon, hydrogen, oxygen (less oxygen in proportion to hydrogen)

Question 27

Function of fats?

Answer 27

- an insulating material that prevents excessive heat loss - source and long term storage of energy (higher than carbs) - part of cells, especially cell membrane

Question 28

What are the parts of a fat molecule?

Answer 28

- glycerol & 3 fatty acid molecules

Question 29

How to test for fats?

Answer 29

Ethanol emulsion test

Question 30

What are the results from the ethanol emulsion test and what do they mean?

Answer 30

- white emulsion formed: fats present - solution remains clear: fats absent

Question 31

Procedure of ethanol emulsion test for solids?

Answer 31

1. Crush sample 2. Add 2cm^3 of ethanol solution and shake 3. Decant and pour into mixture with 2cm^3 of water 4. Record and observe

Question 32

Procedure of ethanol emulsion test for liquids?

Answer 32

1. Add 2cm^3 of ethanol and shake 2. Add 2cm^3 of water and shake 3. Record and observe

Question 33

What does decant mean?

Answer 33

only pour out liquid and use it for the experiment

Question 34

What are some foods that contain protein?

Answer 34

eggs, milk, etc

Question 35

Elements that make up proteins?

Answer 35

carbon, hydrogen, oxygen, nitrogen, (sometimes sulfur)

Question 36

Functions of proteins

Answer 36

- synthesis of new cytoplasm - growth and repair of worn out cells - synthesis of enzymes and some hormones - formation of antibodies to combat diseases

Question 37

What are proteins made up of?

Answer 37

amino acids

Question 38

How do amino acids form proteins?

Answer 38

- amino acids form polypeptides - polypeptides folded together forms proteins

Question 39

How to test for proteins?

Answer 39

Biuret test

Question 40

What are the results of biuret test and what do they mean?

Answer 40

- solution turns violet: protein present - solution remains blue: protein absent

Question 41

What is the procedure of biuret test?

Answer 41

1. Add equal volume of biuret solution to food sample (2cm^3) 2. Shake well and let it stand for 5mins 3. Record and observe

Question 42

What are cellulose, glycogen and starch synthesised from?

Answer 42

glucose

Question 43

What are polypeptides and proteins synthesised from?

Answer 43

amino acids

Question 44

What are lipids (fats) synthesised from?

Answer 44

glycerol and fatty acids

Question 45

Another name for fats?

Answer 45

lipids