Jan 2003 U4a

1.

(a) (b)

(c)

Cortex ; 1. Reference to high pressure {of blood / in glomerulus} ; 2. Because afferent vessel wider than efferent vessel ; 3. {Small molecules / molecules up to 70 000 MW} {forced / eq} out (through capillary wall) ; 4. {Larger molecules / protein / cells} remain in blood ; 5. Reference to basement membrane as a filter ; 6. Reference to {fenestrations / large pores} in capillary walls ; 7. Reference to {slits / pores} in {podocytes / cells lining capsule} ;

1

Glucose / amino acids ;

1

4 [6]

2.

(a)

Negative feedback ;

(b)

1. 2. 3.

(c)

1. 2. 3. 4. 5.

1

{Ovary / (target) organs / cells} have receptor {sites / molecules / proteins} ; On cell surface / plasma membrane ; Hormone binds with (receptor) {site / molecule} / hormone–receptor complex forms ;

2

Follicles develop over time / eq ; Hormone levels in the blood gradually build up ; Hormones present in blood for period of time ; Hormone effect lasts long time ; Nervous system co-ordinates {short term / immediate} responses ;

3 [6]

3.

(a)

{Equilibration / eq} / allow contents to reach temperature ;

1

(b)

1. 2. 3. 4. 5. 6.

{Red coloration / colour change} indicates reduction (of TTC) ; TTC reduced when it {accepts / eq} hydrogen ; Hydrogen {released / removed} by dehydrogenation ; Rate of reaction increases as temperature increases (up to 40°C) ; Rate slows above 40°C ; Indicating some denaturing of enzyme ; [ignore references to optimum temperature]

4

(i)

NAD / FAD / cytochrome oxidase / ethanal / oxygen ;

1

(ii)

Respiration / glycolysis / Krebs cycle / electron transfer chain / (alcoholic) fermentation ; [must be correct for the answer given in (c) (i)]

1

(c)

[7]

4.

(a)

(absorption is) {very quick / within 10 minutes} / reference to absorbed through stomach wall / eq ; {Volunteers who had the drug / B, C & D} all had slower reactions within 10 minutes ;

Edexcel Unit 4A January 2003 MS

2

1

(b)

1. 2. 3. 4. 5. 6.

(c)

1. 2. 3. 4. 5. 6. 7.

(d)

The drug increases reaction time ; The greater the {quantity / concentration} of the drug the greater the effect / eq ; Calculation of relative increase for at least two volunteers ; The greater the {quantity / concentration} of the drug the longer the recovery back to normal ; Volunteer B back to normal within 40 minutes but {C / D} still not back to normal after 60 minutes ; Reference to reaction time of A decreasing ; 3 Reference to the drug slowing down (rate of synaptic transmission) ; (drug has) {similar shape / mimics} {transmitter / acetylcholine} ; {Blocks / eq} receptors on postsynaptic membrane ; May affect {permeability / ion channels / eq} of (pre / post) synaptic membranes ; May {affect / inhibit} release of {neurotransmitter / acetylcholine} ; May bind to {transmitter / acetylcholine} ; Reference to effect on acetylcholinesterase ;

Age ; Gender ; Weight / BMI / eq ; Health / eyesight ; Whether other drugs used / e.g. tobacco / eq ; Previous exposure to this drug ; Fitness ; Time since eating / amount of food eaten ; Time of day / reference to tiredness ;

3

3 [11]

5.

Accept points in correct context only 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Pyruvate (from glycolysis) {passes / diffuses} into mitochondria ; Combines with {coenzyme A / coA} to form acetyl coenzyme A ; {NADH (+ H+) / reduced NAD} and carbon dioxide formed ; {Acetate / acetyl / acetyl coenzyme A} combines with {4C compound / oxaloacetate} to form {6C / citrate} ; Reference to Krebs cycle in the matrix ; Reference to Krebs cycle (as series of reactions) regenerating {4C compound / oxaloacetate} ; Reference to enzyme control (at any point) ; (more) {NADH (+ H+) / reduced NAD} and carbon dioxide formed ; ATP is produced (directly) ; {Electrons / hydrogen (ions)} from {NADH / FADH} pass on to {electron carriers / cytochromes / FAD} ; Reference to {cytochromes / electron carriers / ETC / oxidative phosphorylation} in {inner (mitochondrial) membrane / cristae} ; {H+ / protons} pumped out (of matrix) into intermembranal space ; ATP produced as {H+ / protons} flow back (into matrix) ; Through stalked particles ; Water formed as electrons and {H+ / protons} combine with oxygen ; [10]

6.

(a)

(b)

1.

(In latency) there is a delay between infection and {symptoms / lysis} / eq ; 2. (In latency) viral genetic material is incorporated into host’s DNA / eq ; 3. Reference to a trigger / eq ; Reverse transcriptase ;

Edexcel Unit 4A January 2003 MS

2 1 2

(c)

Makes DNA ; Using viral RNA as template / eq ;

2

(d)

2 HIV

TMV

1.

Polyhedral

Helical ;

2.

Enveloped

Non-enveloped ;

3. Contains reverse transcriptase

No reverse transcriptase ; [7]

7.

(a)

(b)

(i)

Endotoxin ;

1

(ii)

Salmonella releases {endotoxin / toxin} when it dies / eq ; Staphylococcus releases exotoxins immediately ; Reference to endotoxins needed in high concentrations ;

2

Salmonella would be {red / pink} ; Staphylococcus would be {purple / dark blue / violet} ;

2 [5]

8.

(a)

(b)

1. 2. 3. (i)

Substance produced by an {organism / microorganism / fungus} ; That {kills / inhibits} the growth of {bacteria / other organisms} ; (often) a secondary metabolite / produced {at end of exponential phase / during stationary phase} ; 1. 2. 3. 4. 5.

(ii)

1. 2. 3. 4. 5. 6.

2

The lag phase is longer with E.coli / L.bulgaricus begins to increase before E.coli ; The growth is more rapid (in growth phase) with E.coli ; Credit manipulated use of figures to compare growth rate ; The stationary period is reached earlier with E.coli / E.coli has a shorter exponential phase ; More cells per cm3 (maximum) in E.coli than in L.bulgaricus ;

3

Penicillin (affects growth of L.bulgaricus) because it is Gram positive ; Bacteriostatic / eq ; No effect during lag phase ; Starts having effect once bacteria in growth phase ; Only affects dividing cells ; Because it interferes with structure of {cell wall / mucopeptide} ;

4 [9]

9.

(a)

Culture {shaken / mixed} well OR counting chamber is dry ;

1

(b)

1. 2. 3.

3

Number of cells over 16 squares = 13 ; (13) ÷ 0.0004 OR × 2 500 ; × 200 (for dilution) ; [Max 2 marks for wrong answer]

Edexcel Unit 4A January 2003 MS

3

(c)

(i)

Optical methods / turbidity / dilution plating ;

1

(ii)

Turbidity Advantage: Quick / less subjective / continuous / no disturbance of culture ; Disadvantage: Problems with clumping / need to calibrate ; OR Dilution Plating – Advantage: Viable cell count ; Disadvantage: Labour intensive / not an immediate result ; 2

(iii)

Turbidity Lower ; Clumping / settling out / eq ; OR Dilution Plating Lower ; Because you may have counted dead cells in the counting chamber / only viable cells are counted by dilution plating ;

2 [9]

Edexcel Unit 4A January 2003 MS

4