Biological Molecules

Question 1

Define nutrients

Answer 1

Chemical substances in food that provide energy and materials needed by the body

Question 2

What are monomers and polymers of carbohydrates

Answer 2

Monomer: Glucose
Polymer: Starch, glycogen, cellulose

Question 3

Define condensation

Answer 3

A chemical reaction whereby two or more simple molecules are join to form a larger biological molecule with the removal of water

Question 4

Define hydrolysis

Answer 4

The splitting up of complex biological molecule into its component units with the addition of water molecules

Question 5

What are the characteristics of carbohydrates

Answer 5

Made of carbon, hydrogen and oxygen with hydrogen and oxygen atoms present in the ratio 2:1

Question 6

What are properties of monosaccharides

Answer 6

Same general formula C6H12O6 but atoms arranged differently, different chemical and biological properties
Still generally sweet-tasting, soluble in water, lower water potential of solutions

Question 7

What is the bond formed in disaccharides and polysaccharides

Answer 7

Glycosidic bond, -O-

Question 8

Describe the three types of disaccharides(in syllabus)

Answer 8

All have formula C12H22O11, different structure and properties
Maltose = glucose + glucose
Lactose = glucose + galactose
Sucrose = glucose + fructose

Question 9

Describe structure of starch

Answer 9

Formed from condensation reaction of large numbers of glucose molecules, can be in long straight chains or branched chains

Question 10

Describe structure of glycogen

Answer 10

Formed from condensation reaction of large number of glucose molecules, joined up in highly branched chains and found in liver and muscles of mammals

Question 11

Why are starch and glycogen suitable as storage materials

Answer 11

Insoluble in water so do not affect water potential in cells
Too large to diffuse through cell membrane
Compact shape, occupy less space than individual glucose molecules
Easily hydrolysed to glucose

Question 12

Describe structure of cellulose

Answer 12

Formed from condensation reaction of large numbers of glucose molecules, bonded differently compared to starch. Insoluble in water

Question 13

Describe structure and function of cellulose cell wall

Answer 13

Consists of cellulose fibres embedded in polysaccharide matrix. Fully permeable structure. Provides mechanical support for plant cell and plant, resist expansion when water enters by osmosis, ensuring integrity of plant cell and provides turgidity

Question 14

What are the general functions of carbohydrates

Answer 14

Glucose - substrate for respiration to release energy for cell activities
Deoxyribose sugars - formation of nucleic acids
Forms lubricants (e.g. mucus)
Forms nectar in flowers
Cellulose - supporting structure
Ready source of energy that can be easily utilised

Question 15

Describe Benedict’s test

Answer 15

It is test for reducing sugar
To 2cm^3 of food solution to be tested, add equal volume of BS
Shake mixture
Place test tube in boiling water bath for maximum of 5 minutes
Observe precipitate formation and color changes, if any

Question 16

Describe iodine test

Answer 16

It is test for starch, blue-black coloration observed in presence of starch
Place food substance on white tile. Solid foods may need chopping
Add -3 drops of dilute iodine solution to substance
Observe color changes, if any

Question 17

Describe structure of lipids

Answer 17

Organic compounds containing carbon, hydrogen and oxygen, with much less oxygen compared to carbon and hydrogen
Lipids insoluble in water but soluble in organic solvents

Question 18

Describe formation of triglyceride

Answer 18

Condensation reaction of 3 molecules of fatty acids and 1 molecules of glycerol with removal of three molecules of water. Fatty acids can be same or different

Question 19

Describe bond in triglyceride

Answer 19

Bond formed is ester bond
O
||
- O - C –

Question 20

How to differentiate fats and oils

Answer 20

Depends on state at 20degC
Solids for fats, liquid for oils

Question 21

Describe difference between oil and fats

Answer 21

Oil has unsaturated fatty acids but fat has saturated fatty acids
Presence of at least one carbon-carbon double bond in carbon atoms, relatively shorter fatty acid chains in oil
Lower melting point and molecular weight

Question 22

What are characteristics of fat and oil

Answer 22

Insoluble in water(both)
Fat stored as droplets inside specialised fat cells, adipose cells, as they are insoluble and do not affect water potential in cells

Question 23

What are functions of triglycerides

Answer 23

Energy storage, heat insulator, buoyancy in aquatic animals, protective layer, important component of myelin sheath, provides metabolic water, can act as a solvent for fat-soluble vitamins and other vital substances

Question 24

Describe energy storage of triglycerides

Answer 24

One gram of triglyceride yields twice as much energy as one gram of carbohydrate, half the mass for equivalent amount of energy stored, is light-weight energy source
Carbohydrates still most direct source of energy as they can be metabolised quickly

Question 25

Describe production of metabolic water by triglycerides

Answer 25

Oxidation of triglycerides release twice as much water as carbohydrates when oxidised. Metabolic water produced from respiration. Hydrogen atoms are used in formation of metabolic water during oxidation and triglycerides contain more hydrogen atoms than carbohydrates

Question 26

Describe phospholipids

Answer 26

Compound lipids containing two molecules of fatty acids, one molecule of glycerol and phosphate group. Hydrophilic phosphate group(face aqueous environment) attracted to water molecules and hydrophobic fatty acid tails(face inside of bilayer) repelled by water molecules. Major component of biological membranes

Question 27

Describe ethanol emulsion test

Answer 27

White emulsion will be formed in presence of fats
Add food solution/chopped food
Add 2cm³ of ethanol and shake thoroughly
(Allow solid particles to settle)
Decant ethanol mixture into another test tube containing 2cm^3 of water

Question 28

Describe structure of proteins

Answer 28

Made of elements carbon, hydrogen, oxygen and nitrogen
Each protein has unique 3D shape
When heated, weak bonds in protein are broken, denatured

Question 29

What are components of protein

Answer 29

At least one amino group(NH2)
A carboxyl group (COOH)
A hydrogen atom
A variable/R group

Question 30

Describe formation of polypeptide

Answer 30

Condensation reaction with removal of water molecules. Amino group one amino acid reacts with carboxyl group of another amino acid, with removal of water, covalent bond is formed is peptide bond
O=C-N-H

Question 31

Describe functions of proteins

Answer 31

Synthesis of new cells, growth and repair of worn-up cells
Biological catalysts - enzymes
Chemical messenger - hormones
Transport proteins - haemoglobin
Structural proteins - collagen-skin and bones, keratin-hair and nails
Defence of body - antibodies
Source of energy during starvation

Question 32

Describe kwashiorkor

Answer 32

A form of protein deficiency disease. Children with disease caused by malnutrition will have swollen stomachs, skins crack and become scaly

Question 33

Describe biuret’s test

Answer 33

In presence of copper(II) ions in alkaline solution, compound containing peptide bonds will form violet colouration
2 cm3 of food solution, add 1cm3 of sodium hydroxide solution
Shake thoroughly
Add 1% copper(II) sulfate solution, drop by drop until color change