OCR Module Tests

Question 1

Glucose can be moved into cells by facilitated diffusion using proteins called GLUT proteins. These proteins expose a single binding site on one side of the membrane. Glucose binds to this site and causes a change in the shape of the protein. This change moves the glucose across the membrane and releases it on the other side.
(i) Explain why facilitated diffusion via GLUT proteins requires no metabolic energy.

Answer 1

particles have (their own) kinetic energy ✓ (movement) down concentration gradient

Question 2

Glucose can also be absorbed by an active process which requires metabolic energy. What is the immediate source of this energy in cells?

Answer 2

ATP

Question 3

Explain why glucose cannot pass through a cell membrane by simple diffusion.

Answer 3

phospholipids act as a barrier ✓ (glucose) molecules too large

Question 4

State what is meant by the resolution of a microscope

Answer 4

the ability to, see more detail / separate two objects ✓

Question 5

Amylase activity is increased in the presence of chloride ions.
State the name given to any inorganic ion that increases the activity of an enzyme

Answer 5

cofactor ./

Question 6

Outline how the process of DNA replication is completed, following the pairing of nitrogenous bases.

Answer 6

(involves) DNA polymerase ./
sugar-phosphate backbone (re)forms/condensation reaction between phosphate and sugar ./
DNA winds into double helix ./

Question 7

Why is DNA replication described as semi-conservative

Answer 7

(new molecule consists of) one old strand and one new strand ./

Question 8

At what stage of the life cycle does differentiation begin

Answer 8

mitosis ;

Question 9

State the correct term for communication between cells

Answer 9

cell signalling

Question 10

Describe two examples of communication between cells that occur during the life cycle of D. discoideum

Answer 10

1 attraction of cell(s) to folic acid from bacteria ;

2 attraction of cells to each other by cAMP ;

3 coordinated movement in grex ;

4 differentiation / described, of (grex / slime mould) cells in response to DIF ;

Question 11

The plasma membranes of the slime mould cells are specially adapted for communication.
Suggest how the plasma membrane of D. discoideum is adapted for cell communication.

Answer 11

contains , receptors / glycoproteins / glycolipids /
glycocalyx ;
for , folic acid / cAMP / DIF;

Question 12

In the past, beef was preserved by adding salt.

Explain how salting preserves food.

Answer 12

1 reduces , water potential / Ψ , outside , microbial / bacterial / fungal , cells ;

2 (microbes) lose water and cannot , reproduce / survive / carry out metabolic reactions / AW ;

3 water moves by osmosis

Question 13

(i) State the role of a gene

Answer 13

code for (one or more) polypeptide(s) ;

Question 14

State the name given to the sequence of amino acids in a protein molecule

Answer 14

primary structure

Question 15

State one function of haemoglobin

Answer 15

transport / AW , of, oxygen / O2

Question 16

Collagen is an important fibrous protein which forms part of the wall of blood vessels.
State one property of collagen that makes it a useful component of blood vessel walls.

Answer 16

strength / toughness / insolubility

Question 17

Phospholipid molecules are similar to triglycerides but they also contain the element phosphorus as part of a phosphate group.

Explain how the structure of phospholipids allows them to form the bilayer of a plasma membrane

Answer 17

(ii)

hydrophilic head and hydrophobic tails  hydrophobic part / tails , repelled / AW , by water head / hydrophilic part , forms H bonds with water  idea that medium outside / inside plasma membrane is aqueous  idea that hydrophobic nature of tails results in their facing towards each other

Question 18

The plasma membrane also contains proteins, which are made within the cell. Outline the process and organelles involved in the translation of these proteins from RNA

Answer 18

(m)RNA transported out of nucleus  (m)RNA transported to / associates with ribosome  translation / protein synthesis , occurs at ribosome  (t)RNA brings specific amino acids or (t)RNA described  peptide bonds form between adjacent amino acids or peptide bonds described  polypeptide / protein processed through Golgi apparatus

Question 19

Ponds provide a very stable environment for aquatic organisms.
Three properties of water that contribute to this stability are as follows:
• the density of water decreases as the temperature falls below 4 °C so ice floats on the top of the pond • it acts as a solvent for ions such as nitrates (NO3–) • a large quantity of energy is required to raise the temperature of water by 1 °C.
Explain how these three properties help organisms survive in the pond

Answer 19

ce floats (ice less dense because) molecules spread out ; molecules form, crystal structure / lattice / AW ; ice forms insulating layer / clearly described ; water (below ice), does not freeze / still liquid / remains water / kept at higher temperature ;

organisms do not freeze ; animals / organisms, can still, swim / move ; allows, currents / nutrients, to circulate ;

solubility ions / named ion, polar / charged ; ions /named ion, attracted to / bind to / interact with, water;

(named) organisms / plants / animals, uptake / AW, minerals / named mineral / nutrients ;

correct use of named, mineral / nutrient, in organism temperature stability many / stable, (hydrogen) bonds between molecules ;

at lot of energy to, force apart molecules / break bonds ; high (specific) heat capacity ;

temperature does not change much / small variation in temperature ;

effect of temperature on , enzymes / metabolic rate ;

gases remain soluble ;

Award once in any section hydrogen bonds ;

Question 20

the type of reaction that occurs when water is added to break a bond in a molecule

Answer 20

hydrolysis

Question 21

the phosphate group of a phospholipid that readily attracts water molecules

Answer 21

hydrophilic

Question 22

The primary structure of a protein consists of a chain of amino acids.
Describe how a second amino acid would bond to cysteine in forming the primary structure of a protein

Answer 22

The primary structure of a protein consists of a chain of amino acids.
Describe how a second amino acid would bond to cysteine in forming the primary structure of a protein

Question 23

Each amino acid has a different R group.

Describe how these R groups can interact to determine the tertiary structure of a protein.

Answer 23

1 some R groups, attract / repel ; 2 disulfide, bridges / bond ; 3 between, cysteine / SH / S (atoms) ; 4 hydrogen / H, bonds ; 5 ionic bonds between, oppositely charged / + and -, R groups ; 6 hydrophilic R groups, on outside of molecule / in contact with water (molecules) ; 7 hydrophobic R groups, on inside of molecule / shielded from water (molecules)

Question 24

Complete the table below to give three differences between the structure of glycogen and collagen

Answer 24

glycogen collagen

1
carbohydrate / polysaccharide 
protein / polypeptide 
;
2(alpha) glucose (units) amino acid (units) ; 3identical units different amino acid units ; 4glycosidic, bonds / links peptide, bonds / links ; 5branched unbranched / linear ; 6non-helical helical ; 7one chain (per molecule) three chains (per molecule) ;
8
no cross links cross links (between chains) 
;
9contains C H O contains C H O N

Question 25

Collagen is found in the ligaments which hold bones together at joints.
State two properties of collagen that make it suitable for this purpose

Answer 25

(high tensile) strength / strong ; does not stretch / is not elastic ; insoluble ; flexible ;

Question 26

State the components of a DNA nucleotide

Answer 26

deoxyribose (sugar) ; phosphate (group) ;

(nitrogenous / purine or pyrimidine) base / one correctly named base

Question 27

Describe how the structure of RNA differs from that of DNA.

Answer 27

has ribose ; uracil / U, instead of, thymine / T ; single stranded ; 3 forms / AW ;

Question 28

Before a cell divides, the DNA needs to be accurately replicated.
Describe how a DNA molecule is replicated

Answer 28

2 3

4

5 6 7

8 9 10

11 12 13
untwist / unwind ;

unzip / described ; H bond breaks ;

both strands act as template ;

(aligning of) free (DNA) nucleotides ; complementary, base / nucleotide, pairing ; C to G and T to A / purine to pyrimidine ;

hydrogen bonds reform ; sugar-phosphate back bone forms ; (using) covalent / phosphodiester, bond ;

semi-conservative replication ; DNA polymerase ; AVP ;

Question 29

Suggest how chloride ions have this effect on the rate of enzyme reaction.

Answer 29

(acts as a) cofactor ;

(Cl-) binds to, enzyme / amylase / amylose / substrate ;

enzyme substrate complex / ESC, forms more, easily / quickly ;

Question 30

Haemoglobin is a globular protein.

Describe the structure of a haemoglobin molecule

Answer 30

sequence / chain, of amino acids ; (amino acids) joined by peptide bonds ;

secondary alpha / α, helix ; small regions of, beta / β, pleated sheet / fold ; hydrogen / H, bonds ;

tertiary secondary structure / helix / polypeptide chain, undergoes further, coiling / folding ;

3 bonds / interactions from: disulfide / ionic / hydrogen / hydrophobic or hydrophilic ;

hydrophilic R groups on outside (of molecule) / hydrophobic R groups on inside (of molecule) ;

quaternary 4, polypeptides / subunits ;

2, alpha / α, chains and 2, beta / β, chains ;

1 haem (group) per polypeptide / 4 haems (per molecule) ;

prosthetic group (is) haem, (which) contains Fe2+ ;

Question 31

Describe the ways in which the structure of collagen is similar to the structure of haemoglobin.

Answer 31

collagen has) amino acid, chain / sequence ;

peptide bonds ;

helical / helix ;

3 bonds / interactions from: disulfide / ionic / hydrogen / hydrophobic or hydrophilic ; quaternary structure ;

more than one polypeptide / subunit ;

Question 32

Many of the physical properties of water arise as a result of these hydrogen bonds.
Describe ways in which the physical properties of water allow organisms to survive over a range of temperatures.
In your answer you should make clear links between the properties of water and the survival of organisms.

Answer 32

V1 high latent heat of vaporisation / large amount of energy required to change from liquid to gas / AW ;
V2 evaporation is (efficient) cooling mechanism / AW ; V3 example of cooling in living organism ;

H1 high specific heat capacity / large amount of energy needed to, raise / change, temperature ;

H2 (thermally) stable environment for, aquatic / named aquatic, organisms ; H3 (aquatic) organisms use less energy on temperature control ; H4 (internal) temperature of organisms changes only slowly ; H5 (biological) reactions / enzymes / metabolism, function(s) correctly ;

F1 ice, is less dense than water / floats ; F2 (surface of) ice provides habitat for, organisms / named organism I1 water (beneath ice), insulated / remains liquid / doesn’t freeze ;

I2 (aquatic) organisms, do not freeze / can still swim ; I2 IGNORE unqualified references to survival I2 ACCEPT gametes / AW, can be dispersed S1 (effective) solvent ; S2 medium for reactions / (internal) transport medium / able to dilute toxic substances ; C1 cohesion / adhesion ; C2 example of cohesion / adhesion, in living organism ; C2 e.g. transpiration stream / apoplast movement C2 ACCEPT descriptions T1 surface tension ; T2 habitat for (named) invertebrates ; T2 ACCEPT insects IGNORE animals P1 transparent ; P2 allows underwater photosynthesis ; P2 ACCEPT other example of transparency linked to survival, e.g. eyes
D1 idea of high density ; D1 IGNORE references to viscosity D2 allows flotation / support ; U not linked to a single property and so cannot contribute U organisms can still obtain, oxygen / (named) minerals / food / carbon dioxide, from water ;

Question 33

List three examples of where hydrogen bonds are found in biological molecules

Answer 33

protein secondary structure / α-helix / -pleated sheet ; (protein) tertiary structure ; between polypeptide chains in (named) quaternary structure ;

(between chains of) cellulose ; (between, strands of / bases in) DNA ; AVP ; ; ;

water

Question 34

State two roles of cholesterol in living organisms

Answer 34

egulates fluidity of / stabilises / AW, membranes / phospholipid bilayer ;

(converted to) steroid / named steroid, hormone(s) ; waterproofing the skin ; making Vitamin D ; making bile (salts) ;

Question 35

Identify one way in which the molecular structure of cholesterol is similar to the molecular structure of a carbohydrate.

Answer 35

contains C and H and O ;

has, OH / hydroxyl, groups ;

hex / 6-membered, ring ;

Question 36

In countries such as the UK, in which red meat forms a large part of the diet, people tend to have high levels of blood cholesterol compared with people in countries in which little red meat is eaten.
Suggest why diets with a high red meat content are associated with high blood cholesterol

Answer 36

(red) meat contains (large amounts of) saturated, fat / fatty acids ;

(meat / saturated fat) associated with / leads to, increased / large amounts of, LDLs ;

Question 37

Name a disease, other than atherosclerosis, for which high blood cholesterol is a risk factor.

Answer 37

(type 2) diabetes ; angina / coronary heart disease / CHD / stroke / hypertension / high blood pressure / obesity

Question 38

Enzymes are …………………………………… proteins and are therefore soluble. They alter the
rate of metabolic reactions and are described as biological …………………………………… .
Some enzymes, such as those found in cytoplasm, are described as
…………………………………… enzymes. Other enzymes, such as those that digest food in the
small intestine, are known as …………………………………… enzymes. Some medicinal drugs
reduce enzyme activity. These are called enzyme ……………………………………

Answer 38

globular ; catalysts ;

intracellular ; extracellular / hydrolytic ;

inhibitors

Question 39

Enzyme cofactors are often derived from vitamins and minerals in the diet.
Proteins are required in large amounts in the diet whereas vitamins and minerals are required only in small amounts.
Suggest why.

Answer 39

idea of cofactors / minerals , being , recycled / used again ;

idea that in enzyme action total mass of , cofactor / coenzyme , very small compared to total mass of protein ;

idea that proteins are used for purposes other than enzymes ;

proteins are not stored in the body but vitamins and minerals are ;

some enzymes don’t need cofactors ;

Question 40

Lipids are used for energy storage and as a respiratory substrate.
List three other roles of lipids in the human body

Answer 40

membranes ;

absorption of fat soluble vitamins ;

electrical insulation / insulation of , neurones / nerve cells / axons ;

(thermal) insulation ;

protection of organs ;

(source of) (steroid) hormones / named steroid hormone / named group of steroid hormones ;

(source of) cholesterol / LDL / HDL ;

waterproofing / skin suppleness / sebum ;

source of vitamin D ;

buoyancy ;

Question 41

Other than obesity, outline why a diet high in lipids might have a negative effect on the health of an individual.

Answer 41

(leads to) increased / AW , cholesterol / LDL ;

cholesterol / fat , deposited , in arterial walls / under endothelium ;

increase risk of / leads to , atherosclerosis / atheroma / plaque formation ;

narrowing / blocking , of artery lumen ;

increased risk of / leads to , CHD / angina / stroke / hypertension / high blood pressure / heart attack / myocardial infarction / gallstones ;

Question 42

Identify two differences and two similarities in the structures of triglycerides and phospholipids.

Answer 42

T:P 3 fatty acids 2 fatty acids ; 
difference 3 ester bonds2 ester bonds; 
difference 
absence of phosphate 
presence of phosphate 

similarities (contain) glycerol ; similarity (contain) fatty acids ; similarity (contain) ester bonds ;
similarity (contain elements) C,H and O

Question 43

The cells of living organisms require glucose.

State and explain two ways in which the glucose molecule is well suited to its function in living organisms

Answer 43

soluble so can be (easily) , transported / carried (around organism) ;

small (molecule) so can , be transported / diffuse , across (cell) membranes ;

easily / quickly , respired / oxidised / broken down , to , release energy / produce ATP ;

molecules can , join / AW , to produce , (named) disaccharides / (named) polysaccharides ;

Question 44

Deoxyribose is a pentose sugar that is a component of the double-stranded DNA molecule.
Describe the structural relationship between deoxyribose and the other components of the DNA molecule

Answer 44

part of nucleotide ;

bonded / joined / attached , to (named) base and phosphate ;

phosphate (joined) to C5 (and C3) / base (joined) to C1 ;

(deoxyribose is part of) backbone (of DNA) ;

idea of linking with (second) phosphate on adjacent nucleotide ;

nucleotide is , monomer / repeating unit , of DNA / polynucleotide

Question 45

Explain why the mRNA molecule is shorter than a DNA molecule

Answer 45

idea that only copies one, gene / section / part / AW, (of DNA) ;

idea that DNA comprises many, genes / alleles ;

Question 46

Suggest why DNA is not able to leave the nucleus.

Answer 46

too big to / does not, fit through pore (in nuclear envelope) ;

Question 47

State the meaning of the term primary structure

Answer 47

sequence / order, of amino acids ;

Question 48

When proteins are heated to a high temperature, their tertiary structure is disrupted.
Explain how this occurs.

Answer 48

increased kinetic energy ; (any part of protein molecule) vibrates ; hydrophilic / hydrophobic / hydrogen / ionic, bonds / interactions, break ;

change in, 3D shape / conformation (of protein) ;

denatures ;

Question 49

Explain the term biological catalyst

Answer 49

(enzymes are) proteins / used in metabolism / used in named metabolic pathway ;

alter rate of (chemical) reaction / lowers activation energy / provides alternative route for reaction / is not changed / is not used up ;

Question 50

Explain why glycogen makes a good storage molecule.

Answer 50

insoluble ; does not , change / affect , water potential / Ψ , of cell ;

can be , broken down / hydrolysed / built up , quickly / easily ;

lots of branches for enzymes to attach ; compact ; (therefore) high energy content for mass / energy dense / AW ;

Question 51

glycogen vs cellulose

Answer 51

glycogen cellulose  
no hydrogen bonding hydrogen bonding 
 α / alpha , glucose   β / beta , glucose   ; 1,4 and 1,6-glycosidic bonds or 1,6-glycosidic bonds present 1,4-glycosidic bonds (only)
 or 1,6-glycosidic bonds not present ;
branched  
not branched / linear / straight 
;
no , fibres / fibrils fibres / fibrils  ; granules     no granules   ; all glucose units in same orientation adjacent glucose units in opposite orientation

Question 52

Suggest why the lock-and-key and induced-fit explanations are termed models

Answer 52

idea of simple representation of the , process / structure or idea of showing people how it works ;

Question 53

Suggest why most scientists now accept the induced-fit model rather than the lock-and-key model.

Answer 53

supported by , more evidence / new research / more work ;

idea of fitting evidence more closely (than lock & key)

Question 54

Suggest how a more flexible structure might help this enzyme work faster at lower temperatures.

Answer 54

easier for / increased chance of , substrate, entering active site ;

more bonds can form / greater surface area for contact (between active site and substrate) ;

easier for active site to change shape (as part of induced fit) ;

the induced fit , will be easier / AW ;

Question 55

If species of Antarctic fish were to become extinct, their unique enzymes would be lost.
(i) Suggest why the loss of these enzymes might be undesirable.

Answer 55

enzyme could have potential / future , application ;

any example of potential application ;

Question 56

Describe the structure of the collagen molecul

Answer 56

peptide bonds , between amino acids / in polypeptide ;

every 3rd amino acids is , same / glycine ;

coil / twist / spiral / helix ;

left-handed (helix) ;

glycine / small R group , allows closeness / twisting (of polypeptide chains) ;

three polypeptide chains ;

hydrogen / H , bonds between (polypeptide) chains ;

no / few, hydrophilic (R) groups on outside (of molecule) ;

(adjacent molecules joined by) crosslinks ;

crosslinks / ends of molecules , being staggered ;

fibril ;

Question 57

Haemoglobin contains a prosthetic group known as haem.
Collagen does not contain a prosthetic group.
Describe three other ways in which the structure of haemoglobin differs from that of collagen

Answer 57

haemoglobin (has / is): globular ;

hydrophobic (R) groups on inside / hydrophilic (R) groups on outside ;

4 , chains / sub-units / polypeptides ;

idea that subunits are (two) different types ;

α / alpha , helix ;

idea that proportion of glycine similar to that , of other amino acids / in other proteins ;

Question 58

Suggest and explain why over-consumption of milk and beef can lead to malnutrition

Answer 58

contains , large amounts of energy / more energy than individual needs ;
2 increased , fat / lipid , deposition / storage ;

3 (associated with) obesity ;
4 (lots of meat and dairy in diet could mean) lack of other (named) food groups / AW