2.1.2 Biological Molecules

Question 1

What is the importance of water?

Answer 1

• Reactant in lots of chemical reactions (incl. hydrolysis)
• Solvent as some substances dissolve in it
• Transports substances like glucose and oxygen around plants and animals
• Temperature control (thermoregulation)
• Habitat for organisms to survive and reproduce in
• Ice floats which forms an insulating layer

Question 2

How is water polar?

Answer 2

• It is polar due to the unevenly distributed charge
• The oxygen end acts negative
• The hydrogen end acts positive
• Water is polar as it has both positive and negative charge
• Overall, water is neutral

Question 3

How do hydrogen bonds form?

Answer 3

• Formed between a highly electro-negative atom of a polar molecule and a hydrogen
• One hydrogen bond is weak but many bonds are strong

Question 4

What is cohesion?

Answer 4

• It produces a surface film on the water (e.g. allowing insects to walk on water surface)
• Attraction between molecules of the same type due to polarity of the molecule
• Results in surface tension
• Water has a greater surface tension than most liquids because hydrogen bonds resist stretching or breaking of the surface

Question 5

What is adhesion?

Answer 5

• Attraction between two different substances
• Water will make hydrogen bonds with other surfaces (e.g. transpiration process which plants remove water from soil)

Question 6

What is the specific heat capacity of water?

Answer 6

• Water has a high specific heat capacity
• Water can absorb and release large amounts of heat energy with little change in the actual temperature due to the hydrogen bonds
• Water prevents temperature fluctuations and provides a stable thermal environment

Question 7

What is the latent heat of vaporisation of water?

Answer 7

• Water has a high latent heat of vaporisation (amount of energy to convert 1kg of water from a liquid to a gas)
• For water to evaporate, hydrogen bonds must be broken
• As water evaporates, it removes a lot of heat with it (cooling effect)
• This moderates Earth’s climate and prevents organisms from overheating

Question 8

What is the density of water?

Answer 8

• Ice is less dense as a solid than as a liquid
• Liquid water has hydrogen bonds that are constantly being broken and reformed
• Frozen water forms a crystal like lattice where molecules are set at fixed distances
• Prevents water from freezing from the bottom up
• Ice forms on surface first as freezing of water releases heat to the water below, creating insulation
• Makes transition between season less abrupt

Question 9

How is water a good solvent?

Answer 9

• Water is polar so the positive and negative parts are attracted to the negative and positive parts of a solute
• Water molecules cluster around the solute molecules and keep them apart so they can dissolve
• As water is a good solvent, molecules and ions can be transported around living things whilst dissolved and reactions can occur

Question 10

What is a monomer and a polymer?

Answer 10

A monomer is a single unit and a polymer is when many of the same monomers have been joined together

Question 11

What is a condensation reaction?

Answer 11

A condensation reaction occurs when 2 molecules are joined together with the removal of water

Question 12

What is a hydrolysis reaction?

Answer 12

A hydrolysis reaction uses water to split molecules apart

Question 13

What elements, monomers and polymers are in carbohydrates?

Answer 13

Elements - C, H and O
Monomers - monosaccharides (e.g. glucose)
Polymers - polysaccharides (e.g. starch)

Question 14

What elements, monomers and polymers are in proteins?

Answer 14

Elements - C, H, O, N and S
Monomers - amino acids
Polymers - polypeptides and proteins

Question 15

What elements, monomers and polymers are in nucleic acids?

Answer 15

Elements - C, H, O, N and P
Monomers - nucleotides
Polymers - DNA and RNA

Question 16

What elements are in lipids?

Answer 16

C, H and O

Question 17

What are the uses of carbohydrates?

Answer 17

• Substrate for respiration
• Energy store (starch and glycogen)
• Recognition of molecules outside a cell
• Structure (cellulose and chitin)
• Hereditary information

Question 18

What is the structure of an alpha and beta glucose ring?

Question 19

What is a disaccharide?

Answer 19

Formed from two monosaccharides joined by a glycosidic bond during a condensation reaction

Question 20

What are the monomers in different disaccharides?

Answer 20

Glucose + glucose = maltose
Glucose + galactose = lactose
Glucose + fructose = sucrose

Question 21

What is starch?

Answer 21

• Energy store in plants
• Excess glucose is stored as starch

Question 22

What is the structure of starch?

Answer 22

• Mixture of amylose and amylopectin
• Amylose is a long unbranched chain of α glucose and has a compact coiled structure
• It is good for storage and has 1-4 glycosidic bonds
• Amylopectin is a long branched chain of α glucose
• It has 1-4 and 1-6 glycosidic bonds
• Glucose can be released quickly as it is easier for enzymes to get to branches (more easily hydrolysed)

Question 23

What is glycogen?

Answer 23

• Energy store in animals
• Excess glucose is stored as glycogen
• Found in the liver and muscles

Question 24

What is the structure of starch?

Answer 24

• It is a polysaccharide of α glucose
• Lots of side branches for fast release of energy (easily hydrolysed)
• 1-4 and 1-6 glycosidic bonds

Question 25

What is cellulose?

Answer 25

• Structural support for cells (in cell wall) in plants

Question 26

What is the structure of cellulose?

Answer 26

• Long straight unbranched chains of β glucose
• Hydrogen bonds between chains forming microfibrils
• 1-4 glycosidic bonds
• Each alternate glucose molecule rotates 180° to allow bonding of hydroxyl groups
• Chains run parallel to each other (microfibrils) and are strengthened with cross-linkages (hydrogen bonds)
• Stability makes it difficult to digest

Question 27

What are lipids?

Answer 27

Macromolecules (not polymers) as they are made of different components
Insoluble as they aren’t polar

Question 28

What are triglycerides?

Answer 28

• Macromolecules
• Contain one molecule of glycerol and three fatty acid tails

Question 29

What are the functions of triglycerides?

Answer 29

• Energy source (secondary respiratory substrate)
• Energy store
• Insulation
• Buoyancy
• Protection

Question 30

What is the structure of glycerol?

Answer 30

• Made of 3 carbon atoms
• Each has a hydroxyl group attached to it on the right
• Hydrogen atoms occupy remaining positions

Question 31

What is the structure of fatty acids?

Answer 31

• Contains an acid group (COOH) attached to a hydrocarbon chain

Question 32

What are the types of fatty acids?

Answer 32

Saturated = every carbon atom is joined by a single C-C bond
Unsaturated = at least one C-C bond
Polysaturated = many double bonds

Question 33

What is the process of creating triglyceride molecules?

Answer 33

Esterification as an ester link/bond is formed

Question 34

What is the structure phospholipids?

Answer 34

• Contains a diglyceride, a phosphate group and a simple organic molecule (choline)
• One fatty acid tail is substituted
• Most commonly has 1 saturated and 1 unsaturated hydrocarbon chain

Question 35

What do phospholipids do in water?

Answer 35

• The phosphate group has a negative charge, attracted by water (hydrophillic)
• The fatty acid tails are non polar, repelled by water (hydrophobic)