Biological Molecules

Question 1

Explain five properties that make water important for organisms

Answer 1

• a metabolite in condensation/hydrolysis/photosynthesis/respiration
• A solvent so metabolic reactions can occur/ allows transport of substances
• High specific heat capacity so buffers changes in temperature
• Large latent heat and vaporization so provides a cooling effect through evaporation
• Cohesion between water molecules supports the columns of water in plants
• Cohesion between water molecules produces surface tension to support small organisms

Question 2

State and explain the property of water that can help to buffer changes in temperature

Answer 2

High specific heat capacity
Can gain/ lose a lot of heat/ energy without changing temperature

Question 3

Give two properties of water that are important in the cytoplasm of cells for each property. Explain its importance in the cytoplasm

Answer 3

1. Polar molecule
   Acts as a universal solvent
2. Universal solvent
   Metabolic reactions occur faster in solution
3. Reactive
   Takes place in hydrolysis/condensation

Question 4

A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution

Answer 4

• filter and dry precipitate
• find mass/weight

Question 5

Describe a biochemical test to show that a solution contains a non-reducing sugar

Answer 5

• heat with acid and neutralise
• heat with Benedict’s solution
• red precipitate for positive result

Question 6

Describe and explain 2 features of starch that make it a good storage molecule

Answer 6

1 - insoluble, doesn’t affect osmosis
2 - branched, more ends available for faster breakdown
3 - polymer of glucose, provides glucose for respiration
4 - large molecule, can’t pass cell membrane
5 - branched/coiled molecule, makes it compact

Question 7

Explain how cellulose molecules are adapted for their function in plant cells

Answer 7

• long, straight chains
• become linked together by many hydrogen bonds to form fibrils
• provide strength to cell wall

Question 8

Explain the difference in the structure of the starch molecule and cellulose molecule

Answer 8

• starch alpha, cellulose beta
• position of hydrogen and hydroxyl groups on carbon 1 inverted

Question 9

Suggest how the increase in temperature can cause the release of red pigment in a beetroot

Answer 9

1. Damage to (cell surface) membrane;
2. (membrane) proteins denature;
3. Increased fluidity / damage to the
   phospholipid bilayer;

Question 10

Describe the structure and function of the nucleus

Answer 10

Structure
1. Nuclear envelope and pores
OR
Double membrane and pores;
2. Chromosomes/chromatin
OR
DNA with histones;
3. Nucleolus/nucleoli;
Function
4. (Holds/stores) genetic information/material
for polypeptides (production)
OR
(Is) code for polypeptides;
5. DNA replication (occurs);
6. Production of mRNA/tRNA
OR
Transcription (occurs);
7. Production of rRNA/ribosomes;

Question 11

Scientists observe these APS on prokaryotes using a transmission. Electron microscope. They stain the aps using a monoclonal antibody with gold attached to it

Suggest how these techniques allowed. Observation of APS on prokaryotes

Answer 11

1. Antibody binds to AP
   OR
   Gold (present) where AP located;
2. (As antibody/tertiary structure is)
   complementary (to AP);
3. Gold interacts with electrons (in TEM);
4. (T)EM (used as it) has a high
   resolution;

Question 12

The scientists broke open the cells to produce a suspension of cell contents

Describe how the scientists would remove large organelles from this suspension of cell contents

Answer 12

1. Use centrifuge/centrifugation at
   slow/low/increasing (sequence of) speed(s);
2. Large/dense organelles (removed) in (first/early)
   pellet
   OR
   Less dense organelles (removed) in supernatant
   OR
   Small organelles (removed) in supernatant;

Question 13

Compare and contrast the structure of starch and the structure of cellulose (6 marks)

Answer 13

1. Both polysaccharides
   OR
   Both are glucose polymers
   OR
   Both are made of glucose monomers;
2. Both contain glycosidic bonds (between
   monomers);
3. Both contain carbon, hydrogen and oxygen/C, H
   and O;
4. Starch has α-glucose and cellulose has β-
   glucose;
5. Starch (molecule) is helical/coiled and cellulose
   (molecule) is straight;
6. Starch (molecule) is branched and cellulose is
   not/unbranched;
   7.Cellulose has (micro/macro) fibrils and starch
   does not;

Question 14

Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end

Answer 14

1. One amine/NH2 group joins to a
   carboxyl/COOH group to form a peptide
   bond;
2. (So in chain) there is a free amine/NH2 group
   at one end and a free carboxyl/COOH group
   at the other
   OR
   Each amino acid is orientated in the same
   direction in the chain;

Question 15

Formation of an enzyme-substrate complex increases the rate of reaction.
Explain how

Answer 15

1. Reduces activation energy;
2. Due to bending bonds