2.2 - Biological Molecules

Question 1

What is a condensation reaction?

Answer 1

Reaction that occurs when two molecules are joined together with the removal of water

Question 2

Hydrogen bond def

Answer 2

A weak interaction that can occur whenever molecules contain a slightly negatively charged atom bonded to a slightly positive charged hydrogen atom.

Question 3

Hydrolysis reaction def

Answer 3

Reaction that occurs when a molecule is split into two smaller molecules with the addition of water

Question 4

Monomer def

Answer 4

A small molecule which binds to many other identical molecules to form a polymer

Question 5

Polymer def

Answer 5

A large molecule made from many smaller molecules called monomers

Question 6

Name of two monomers joined together

Answer 6

“Di” - mer, dimer

Question 7

What are condensation and hydrolysis reactions responsible for?

Answer 7

Condensation - linking of monomers with removal of water

Hydrolysis - splitting apart monomers with production of water

Question 8

Monomer and polymer for a carbohydrate

Answer 8

Monomer - monosaccharide

Polymer- polysaccharide

Question 9

Monomer and polymer for proteins

Answer 9

Monomer - amino acids

Polymer - Polypeptides and proteins

Question 10

Monomer and polymer for Nucleic acids

Answer 10

Monomer - nucleotides

Polymer - DNA and RNA

Question 11

What is a polar molecule?

Answer 11

Where a molecule has an uneven distribution of charge.

One side of the molecule is slightly negative, while the other side is slightly positive.

Question 12

What is a hydrogen bond?

How strong/weak is it?

Answer 12

A weak interaction which occurs wherever molecules contain a slightly negatively charged atom bonded to a slightly positively charged hydrogen atom.
The bond is weaker than a covalent bond.

Question 13

What is a covalent bond?

Answer 13

A covalent bond is the electrostatic attraction between a shared pair of electrons and the atom’s nuclei

Question 14

Properties of water

Answer 14

Liquid at room temperature
Ice is less dense than liquid water
It is a good solvent
Cohesion and surface tension
High specific heat capacity 
High latent heat of vaporisation
It is a metabolite(reactant in metabolic processes or reactions)

Question 15

Why is water a liquid at room temperature?

Answer 15

There are many hydrogen bonds between water molecules.
This makes it more difficult for them to escape to become a gas
It also has quite a low viscosity, so can flow easier.

Question 16

Uses of water being a liquid at room temperature.

Answer 16

• It can provide habitats for living organisms in rivers, lakes and seas.
• forms a major component of the tissues in living organisms
• provide a reaction medium for chemical reaction/acts as a metabolite
• provide an effective transport medium, e.g. in blood and xylem vessels

Question 17

Why is ice less dense than water?

Answer 17

At freezing point, because of its polar nature, the water molecules align themselves in a structure which is less dense than liquid water.

Question 18

Uses of ice being less dense than water

Answer 18

• Aquatic organisms have a stable environment in which to live in through the winter
• Ponds and other bodies of water are insulated against extreme cold, due to the layer of ice on top of the water reducing the heat loss from the rest of the pond/water body.

Question 19

Why is water a good solvent?

Answer 19

Is a good solvent for ionic solutes
As water is polar
So positive and negative parts of the water molecule are attracted to the negative and positive parts of the solute.
The water molecules will cluster around these charged parts of the solute molecule or ions, and will help to separate them and keep them apart.
They will dissolve at this point as a solution is formed.

Question 20

Benefits of water being a good solvent

Answer 20

• Molecules and ions can move around and react together in water. Many of these reaction happen in the cytoplasm of the cell, which is over 70% water.
• molecules and ions can be transported around living things whilst diddolved in water.

Question 21

What gives water cohesion?

Answer 21

Cohesion - Hydrogen bonds between water molecules pull them together.

Question 22

What gives water surface tension?

Answer 22

Water molecules at surface are all hydrogen-bonded to the mole.cues beneath them.
This means that they are more attracted to the water molecules beneath than to the air molecules above.
This means the surface of the water contracts(as molecules are being pulled inwards), and it gives the surface of the water an ability to resist force applied to it

Question 23

Benefits of cohesion and surface tension:

Answer 23

• Columns of water in plant vascular tissue are pulled up the the xylem tissue together from the roots due to cohesion.
• insects like pond-skaters can walk on water due to surface tension of water bodies.

Question 24

What is specific heat capacity?

Answer 24

Amount of heat required to raise the temperature of 1 gram of substance by 1 degree Celsius

Question 25

Why does water have high specific heat capacity?

Answer 25

Water molecules are held together quite tightly by hydrogen bonds.
Therefore you have to put a lot of heat energy to increase their KE and temperature.

Question 26

Benefits of water having high specific heat capacity:

Answer 26

• Living things, including prokaryotes and eukaryotes, need a stable temperature for enzyme-controlled reactions to happen properly
  Aquatic organisms need a stable environment in which to live

Question 27

What is latent heat of vaporisation?

Answer 27

The amount of energy required to transform a liquid substance into a gas or vapour.

Question 28

Why water has high latent heat of vaporisation

Answer 28

• The water molecules are held together by many hydrogen bonds, a large amount of energy is needed for water molecules to evaporate.

Question 29

Benefits of high latent heat of vaporisation of water:

Answer 29

• Water can therefore help to cool living organism and keep their temperature stable.
  E.g. mammals are cooled when sweat evaporates, or plants are cooled when water evaporates from mesophyll cells(transpiration)

Question 30

Benefits of water in reactions

Answer 30

• hydrolysis reactions - helps break apart polymers, like digestion of starch, proteins and lipids
• reactant in photosynthesis to produce ATP and transfer energy to plant.
• condensation reactions - used to synthesise large biological molecules

Question 31

Def of carbohydrates

Answer 31

A group of molecules containing Carbon, Hydrogen and Oxygen

Question 32

Def of glycosidic bond

Answer 32

A bond formed between two monosaccharides by a hydrolysis reaction.

Question 33

Uses of carbohydrates

Answer 33

• Source of energy(e.g. glucose)
• A store of energy(e.g starch in plants and glycogen in animals)
• structural units(e.g. cellulose in plants and chitin in insects).
• Can be part of other molecules, like nucleic acids and glycolipids

Question 34

What are the three main groups of carbohydrates?

Answer 34

• Monosaccharides
• Disaccharides
• Polysaccharides

Question 35

Importance of monosaccharides

Answer 35

• act as a source of energy
• well suited to this role as they contain large numbers of carbon-hydrogen bonds
• they are soluble in water, and insoluble in non-polar solvents.