1.1 chemical elements are joined together to form biological compounds

Question 1

Name the four key inorganic ions
in living organisms.

Answer 1

● Magnesium ions (Mg2+)
● Iron ions (Fe2+)
● Calcium ions (Ca2+)
● Phosphate ions (PO4 3-)

Question 2

What is the role of Mg2+ in plants?

Answer 2

Mg2+ is used to produce chlorophyll

Question 3

What is the role of Fe2+ in animals?

Answer 3

Fe2+ is found in haemoglobin and is
involved in the transport of oxygen.

Question 4

What is the role of PO4 3- in living
organisms?

Answer 4

PO4 3- is used to produce ADP and ATP.

Question 5

What is the role of Ca2+ in living
organisms?

Answer 5

Ca2+ is used to strengthen tissues such
as bones and teeth in animals and cell
walls in plants.

Question 6

Why is water a polar molecule?

Answer 6

O is more electronegative than H. O attracts
the electron density in the covalent bond
more strongly, forming δ- O and δ+ H.

Question 7

Describe hydrogen bonding between
water molecules

Answer 7

Weak intermolecular forces of attraction
form between a lone pair on a δ- O and a
δ+ H on an adjacent molecule.

Question 8

What is a metabolite

Answer 8

A molecule formed or used in metabolic
reactions.

Question 9

Describe the role of water as a
metabolite

Answer 9

Water is a reactant in photosynthesis
and hydrolysis reactions. Water is a
product in aerobic respiration and
condensation reactions.

Question 10

Why is water’s high specific heat capacity important for organisms?

Answer 10

Water acts as a temperature buffer, enabling
endotherms to resist fluctuations in core
temperature and to maintain optimum enzyme activity.

Question 11

Why is water’s high latent heat of vaporisation important for organisms?

Answer 11

When water evaporates, it has a cooling effect.
This is important in homeostasis

Question 12

Why is water an important solvent for organisms?

Answer 12

Water is a polar universal solvent. It enables
chemical reactions to take place within cells,
the transport of materials in the plasma and
the removal of metabolic waste.

Question 13

Why does water have a high surface tension?

Answer 13

Due to the ordered arrangement and
cohesion of molecules at the surface of
water.

Question 14

Why is the high surface tension of water
important for organisms?

Answer 14

● Enables the transport of water and nutrients through plants stems and small blood vessels in the body
● Allows small insects to ‘walk’ on water

Question 15

What is a monosaccharide?

Answer 15

single sugar

Question 16

Give some examples of monosaccharides.

Answer 16

● Glyceraldehyde
● Ribose
● Deoxyribose
● α- and β- glucose
● Fructose
● Galactose

Question 17

What is the name of the bond formed
when two monosaccharides react?

Answer 17

glycosidic

Question 18

What is a disaccharide?

Answer 18

Molecule formed by the condensation of two
monosaccharides, forming a glycosidic bond

Question 19

Give some examples of disaccharides and their monosaccharide constituents.

Answer 19

Sucrose (Glucose-Fructose)
Maltose (α-Glucose-α-Glucose)
Lactose (Glucose-Galactose)

Question 20

What is a polysaccharide?

Answer 20

A polymer of monosaccharides, formed
by many condensation reactions

Question 21

Give some examples of polysaccharides.

Answer 21

● Starch
● Glycogen
● Cellulose
● Chitin

Question 22

What is the function of starch?

Answer 22

energy storage in plants

Question 23

Describe the structure of starch

Answer 23

● Polymer of α-glucose monomers
● Two forms: amylose and amylopectin
● Amylose: α-1,4-glycosidic bonds, unbranched
● Amylopectin: α-1,4- and α-1,6-glycosidic bonds, branched

Question 24

What is the function of glycogen?

Answer 24

Energy storage in animals.

Question 25

How does the structure of glycogen relate to its function?

Answer 25

It is highly branched enabling the rapid hydrolysis of glucose molecules

Question 26

Describe the structure and function of cellulose.

Answer 26

● Linear polysaccharide that is the main component of the cell wall in plants ● Consists of many β-glucose molecules joined by β-1,4-glycosidic bonds ● Alternate glucose molecules rotated 180° allowing hydrogen bonds between parallel chains, forming myofibrils

Question 27

Describe the structure and function of chitin.

Answer 27

● Linear polysaccharide found in the exoskeletons of insects and crustaceans as well as fungal cell walls ● Consists of many β-glucose molecules (with amino acid side chains) joined by β-1,4-glycosidic bonds ● Alternate glucose molecules rotated 180° allowing hydrogen bonds between parallel chains, forming myofibrils

Question 28

Explain how a triglyceride is formed.

Answer 28

One molecule of glycerol forms ester bonds with three fatty acids via condensation reactions.

Question 29

Relate the structure of triglycerides to their functions.

Answer 29

● High energy-to-mass ratio - energy storage, high calorific value from oxidation ● Insoluble hydrocarbon chain - no effect on water potential of cells, used for waterproofing ● Slow conductor of heat - thermal insulation, e.g. adipose tissue ● Less dense than water - buoyancy of aquatic animals

Question 30

What is a phospholipid?

Answer 30

A type of lipid formed by the condensation of one molecule of glycerol, two molecules of fatty acid and a phosphate group

Question 31

Relate the structure of phospholipids to their functions.

Answer 31

Glycerol backbone attached to two hydrophobic fatty acid tails and one hydrophilic polar phosphate head: ● Forms phospholipid bilayer in water - component of cell membranes ● Tails splay outwards - waterproofing, e.g. skin

Question 32

What is the difference between saturated and unsaturated fats

Answer 32

● Saturated fats have no C=C bonds, and are solid at room temperature due to strong intermolecular forces ● Unsaturated fats have one or more C=C bonds, and are liquid at room temperature due to weak intermolecular forces

Question 33

Differentiate between monounsaturated and polyunsaturated fatty acids

Answer 33

● Monounsaturated fatty acids contain one C=C bond ● Polyunsaturated fatty acids contain more than one C=C bond

Question 34

What is meant by a low density lipoprotein (LDL)?

Answer 34

● Combination of triglycerides from saturated fats and protein ● Blocks receptor sites, reducing cholesterol absorption ● Known as ‘bad’ lipoproteins

Question 35

How do LDLs contribute to the risk of cardiovascular disease?

Answer 35

The high blood cholesterol level caused by LDLs leads to formation of atherosclerosis plaques

Question 36

Describe the general structure of an amino acid.

Answer 36

● Amine group (-NH2) ● Variable side chain (R) ● Carboxyl group (-COOH) ● H atom

Question 37

How are polypeptides formed?

Answer 37

Many amino acid monomers join together in condensation reactions, forming peptide bonds (-CONH-).

Question 38

What is the primary structure of a protein?

Answer 38

The individual sequence of amino acids in a protein

Question 39

Describe the secondary structure of a protein.

Answer 39

The local interactions of the amino acids in the polypeptide chain resulting in α-helices or β-pleated sheets. Hydrogen bonds hold the arrangements in place.

Question 40

Describe the tertiary structure of a protein.

Answer 40

The folding of a protein to make a three-dimensional structure. Held in place by various interactions and bonds: ● Disulfide bonds ● Ionic bonds ● Hydrogen bonds ● Hydrophobic interactions

Question 41

Describe the quaternary structure of a protein.

Answer 41

● Interactions of more than one polypeptide chain ● May involve addition of prosthetic groups, e.g. metal ions or phosphate groups

Question 42

Describe the quaternary structure of a protein.

Answer 42

● Interactions of more than one polypeptide chain ● May involve addition of prosthetic groups, e.g. metal ions or phosphate groups

Question 43

Describe how the structure of fibrous proteins relates to their function.

Answer 43

● Long polypeptide chains, folded in parallel ● Little tertiary/quaternary structure aside from cross-linkages for strength ● This makes them insoluble and good for structural roles

Question 44

Describe how the structure of globular proteins relates to their function.

Answer 44

● Spherical, compact, highly folded with complex tertiary/quaternary structures ● Hydrophilic R groups face outwards and hydrophobic R groups face inwards ∴ water-soluble ● Metabolic roles, e.g. enzymes

Question 45

What is the difference between a reducing and non-reducing sugar?

Answer 45

● A reducing sugar has a free aldehyde or ketone functional group so can act as a reducing agent ● A non-reducing sugar does not have a free aldehyde or ketone functional group so it cannot act as a reducing agent

Question 46

Describe the Benedict’s test for reducing sugars.

Answer 46

1. Add an equal volume of the sample being tested and Benedict’s reagent 2. Heat the mixture in an electric water bath at 100°C for 5 minutes 3. Observe the colour of the precipitate formed

Question 47

Describe the positive result for reducing sugars.

Answer 47

Colour change from green to yellow to orange to brown to brick red depending on the quantity of reducing sugar present

Question 48

Describe the Benedict’s test for non-reducing sugars

Answer 48

1. Negative test for reducing sugar 2. Hydrolyse non-reducing sugars with an equal volume of dilute HCl 3. Heat in a boiling water bath for 5 minutes 4. Add NaHCO3 to neutralise the acid 5. Re-test resulting solution with Benedict’s reagent 6. Observe the colour of the precipitate formed

Question 49

Describe the positive result for non-reducing sugars

Answer 49

Colour change from green to yellow to orange to brown to brick red depending on the quantity of non-reducing sugar present.

Question 50

Name the food test used to identify proteins.

Answer 50

biuret test

Question 51

Describe the Biuret test.

Answer 51

1. Add an equal volume of the sample to be tested and NaOH 2. Add a few drops of dilute copper (II) sulfate solution 3. Mix gently and record any observations

Question 52

Describe the positive result of a biuret test.

Answer 52

Colour change from pale blue to purple

Question 53

Describe the iodine-potassium iodide test for starch

Answer 53

● Add iodine-KI solution ● Colour change from orange to blue-black in the presence of starch

Question 54

Describe the emulsion test for fats and oils.

Answer 54

● Add ethanol to the sample and shake ● Allow the mixture to settle ● Add an equal volume of water ● Record any observations