3 — biological molecules

Question 1

Definition & composition of carbohydrates

Answer 1

Carbon:Hydrogen:Oxygen
(CnH2mOm)
H:O -> 2:1

Can be classified as sugars & complex carbohydrates

Carbohydrates r organic molecules made up of the elements carbon, hydrogen & oxygen. Hydrogen & oxygen atoms r present in 2:1.

Question 1

Define nutrients in food

Answer 1

• chemical substances in food that release energy and raw materials (to make protoplasm) needed by body

Question 2

Definition & composition of Fats

Answer 2

Carbon, hydrogen, oxygen
- Contains much less oxygen in proportion to hydrogen
- Proportions unfixed
Made up of
- 1 glycerol molecule
- 3 fatty acid molecules

Fats r organic molecules made up of elements carbon, hydrogen n oxygen & contains much less oxygen in proportion to hydrogen.

Tristearin -(lipase)-> glycerol + 3 stearin acid molecules

Question 3

Definition & composition of Proteins

Answer 3

Carbon, hydrogen, oxygen, nitrogen, Sulfur (may (not) be present)

Made up of amino acids (building blocks of protein) consisting of
- Amino grp
- Acid grp
- Side chain
Peptide bonds link up amino acids -> polypeptide chain (2 or more) -> (hydrogen bond to hold) 3 dimensional molecule: protein

Proteins r organic molecules made up of elements carbon, hydrogen, oxygen & nitrogen, Sulfur may be present.

Question 4

Functions of carbs (carbohydrates)

Answer 4

• Substrate for respiration to provide energy for cell activities (source of energy)
• Form supporting structures (cell wall)
• Converted into other organic compounds (amino acids & fats)
• Form part of nucleic acids (DNA)
• Used to synthesise lubricants & nectar in flowers

Question 5

Test for carbs

Answer 5

Benedict’s Test:Reducing sugars
1. Add equivalent amt of 2cm3 Benedict’s solution to 2cm3 of food sample in test tube
2. Shake the mixture
3. Heat the contents in boiling water-bath for 2-3mins
4. Record colour of solution
- Absent -> blue precipitate
- Present in trace/moderate/large amts -> green - red

Iodine test: Starch
1. Add 2cm3 of food sample to clean test tube
2. Add 2-3 drops of iodine solution to test tube
- Brown: absent
- Blue-black: present

Question 6

Function of fats

Answer 6

• Source & store of energy (contain 2x as much energy as carbs)
• Insulating material to prevent excessive heat loss
• Solvent for fat soluble vitamins & some hormones
• Forms main part of cell membranes
• Helps reduce water loss from skin surface

Question 7

Test for fats

Answer 7

Ethanol-emulsion test
1. If solid: (Crush solid sample into small pieces with mortar & pestle)
2. Add 2cm3 of ethanol to sample (liquid/solid) in test tube
3. Shake thoroughly
4. (Allow solid particles to settle)Decant ethanol into another test tube with 2cm3 of water & shake well
- Present: cloudy white emulsion observed
- Absent solution remains colourless & clear

Question 8

Function of proteins

Answer 8

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

Question 9

Test for proteins

Answer 9

Biuret test
1. + 2cm3 of NaOH solution to 2cm3 of food sample into a test tube
2. Shake mixture thoroughly
3. + 1% CuSO4 solution drop by drop, shaking mixture aft each drop

1. OR + 2cm3 of Biuret Reagent & shake the mixture thoroughly.

• Present: violet colouration observed
• Absent: solution remains blue

Question 10

Monosaccharides examples

Answer 10

• Basic unit of carbohydrates
• Can pass thru cell membranes + absorbed into cells
  (Single/reducing sugars)

Glucose
- Found in plants & animals
Fructose
- Common in plants, rare in animals
Galactose

Question 11

Disaccharides

Answer 11

• 2 single sugars joined tgt
• Can be split into 2 single sugar molecules via enzyme

Maltose
- G+G -> M
- M -(maltase)-> G+G
Sucrose
- G+F -> S
Lactose
- G+ galactose

Question 12

Polysaccharides

Answer 12

(Complex carbs)
Many similar molecules of single sugar joined tgt to form a large molecule

Starch
- Storage form of carbs in plants
- Found in plants’ storage organs
- Consumed + digested by animals -> forms glucose -> stored in animals as glycogen
Glycogen
- Storage form of carbs in mammal as in liver & muscles
- Digested to form glucose when needed
Cellulose

Question 13

Processes involved in conversion of monosaccharides to and from disaccharides

Answer 13

Condensation reaction (-H2O)
- A chemical reaction in which 2 smaller, simple molecules joined tgt to form a larger, complex molecule wif the removal of one water molecule

• 2 glucose molecules joined -> CR -> maltose formed

Hydrolysis (+H2O)
- Chemical reaction in which a water molecule is needed to break down 1 larger, complex molecule into 2 smaller, simpler molecules

• Maltose + water -(enzyme lactase)-> glucose + glucose
  In polysaccharide: Starch -(digested by amylase)-> maltose -(hydrolysed by maltase)-> glucose

Question 14

Complex carbohydrate: starch’s structure, role and occurrence

Answer 14

S: Several thousand glucose molecules joined tgt

R:
Storage form of carbohydrates in plants
Can be digested to glucose to provide energy for cell activities

O: Storage organs of plants
- potato tubers, tapioca

Question 15

Complex carbohydrate: cellulose’s structure, role and occurrence

Answer 15

S: Many glucose molecules joined tgt; bonds r diff from starch

R:
- Cellulose cell wall protects plant cells from bursting/dmg
- Cannot be digested
- Serves as dietary fibre -> prevents constipation

O: Cell walls of plants

Question 16

Complex carbohydrate: glycogen’s structure, role and occurrence

Answer 16

S: Many glucose molecules joined tgt; branched molecule

R:
- Storage form of carbohydrates in mammals
- Digested to glucose to provide energy for cell activities

O: Liver & muscles of mammals

Question 17

Why starch and glycogen r storage materials in cells

Answer 17

• Insoluble in water, does not change water potential (WP) in cells
• Large molecules that cannot diffuse thru cell membranes, won’t be lost from cell
• Easily broken down to glucose when needed (tissue respiration)
• Molecules hv compact shapes -> occupy less space than individual glucose molecules that make up a glycogen/starch molecule

Question 18

Process of breakdown of fats

Answer 18

Hydrolysis
- Fats can be digested/broken down into simpler substances via hydrolysis
- Produces fatty acids & glycerol

Fat molecule + 3 water molecules -(lipase enzyme)-> glycerol + 3 fatty acid molecules

Question 19

Types of fats

Answer 19

Saturated fats
Structure: Fatty acid chain is straight
Characteristic: Most r solid at room tempt (eg butter)

Unsaturated fats
Structure: Fatty acid chain has kinks
Characteristics: Liquid at room tempt (Eg olive oil)

Question 20

Condensation reaction definition

Answer 20

A chemical reaction in which 2 smaller, simple molecules joined tgt to form a larger, complex molecule wif the removal of one water molecule

Question 21

Hydrolysis reaction definition

Answer 21

Chemical reaction in which a water molecule is needed to break down 1 larger, complex molecule into 2 smaller, simpler molecules

Question 22

Compare and contrast between fats and carbohydrates. [4]

Answer 22

Similarities:
The first similarity is both are made up of the carbon, hydrogen and oxygen
elements.
The second similarity is both can serve as a source of energy / energy
storage.
Differences:
The first difference is fats do not have a fixed ratio between the hydrogen and
oxygen elements, but for carbohydrates, there is a fixed ratio between the
hydrogen and oxygen elements of 2:1.
The second difference is fats contain twice as much energy as carbohydrates.

Question 23

Define enzymes. [5]

Answer 23

It is a biological catalysts, that is made up of proteins [1]
It speeds up the rate of chemical reaction by lowering the activation energy required to start the chemical reaction. [1]
It remains chemically unchanged at the end of chemical reaction, and thus can be reused. [1]
Each enzyme will catalyse only one specific chemical reaction, as only the substrate with a specific three-dimensional shape that is complementary to the
enzyme’s active site can fit and bind to the active site. [1]
Sensitive to changes in temperature and pH OR can be denatured by extreme changes in temperature or pH [1]

Question 24

Describe and explain how enzyme functions are affected by temperature [4]
*note: must quote data if the question involves graphical / table result analysis

Answer 24

At low temperature, the rate of enzyme activity is low. Because the enzymes
are inactive. [1]
As temperature increases, the rate of enzyme activity increases. Because the enzyme and substrate molecules have a higher kinetic energy. This increases
the frequency of effective collision between the enzyme and substrate. Hence, increases the rate of enzyme-substrate complex formation. [1]
At the optimum temperature, the rate of enzyme activity is the highest. Because the enzymes are most active. [1]
Beyond the optimum temperature, the rate of enzyme activity decreases (until
zero). Because the enzymes are denatured. [1]