Chapter 3: Biological Molecules

Question 1

Carbohydrates

Answer 1

organic molecules which contain elements carbon, hydrogen and oxygen,
hydrogen and oxygen atoms in ratio 2:1

glucose: C6H12O6
sucrose: C12H22O11

Question 2

test for reducing sugars

Answer 2

Benedict’s test:
blue: no RS
blue to green: little RS
blue to yellow/orange: moderate amt or RS
blue to red: large amt of RS

Question 3

starch

Answer 3

• made of several thousand glucose molecules joined tgt
• digested to glucose to provide energy for plant
• in storage organs or plants

Question 4

cellulose

Answer 4

• made up of many glucose molecules
• protects plant cells from bursting or damage
• dietary fibre: prevent constipation
• cell walls of plants

Question 5

glycogen

Answer 5

• many glucose molecules joined tgt
• storage form of carbs
• digested to glucose to provide energy for cell activities
• stored in liver & muscles cells

Question 6

test for starch

Answer 6

iodine test:
substance containing starch will produce blue-black colour
no starch- brown colour

Question 7

Fats

Answer 7

organic molecules made up of elements carbon, hydrogen & oxygen, contain much less oxygen than carbs

Question 8

functions of fats

Answer 8

1. source & long term energy storage: higher energy value than carbs
2. insulating material: prevents excessive heat loss, reduce loss of body heat
3. essential part of cells, esp cell membranes
4. reduce water loss from skin surface, glands secrete oily substance: oily substance forms a thin layer over skin surface, reduces rate of evaporation of water ; oily substance reduces heat loss from skin

Question 9

test for fats

Answer 9

ethanol emulsion test:
white emulsion- presence of fats
clear solution- absence of fats

Question 10

Proteins

Answer 10

organic molecules made of of elements carbon, hydrogen, oxygen & nitrogen
maybe sulcus

Question 11

functions of proteins

Answer 11

• synthesis of new cytoplasm, for growth and repair of worn out body cells
• synthesis of enzymes and hormones
• formation of antibodies to combat diseases

Question 12

test for proteins

Answer 12

[Biuret test]
violet: proteins present
blue: no proteins