June 2003 U4a

1.

(a)

(b)

1.

{Series / sequence / chain} of (chemical) reactions ;

2.

Controlled by enzymes / enzyme catalysed ;

3.

{Products / intermediates} formed by reactions become substrate for the next reaction ; 2

1.

{Control / maintenance / regulation} of internal environment ;

2.

Keeping it {constant / within limits / in dynamic equilibrium / balanced / eq} ;

3.

Even though external conditions change / independent of external environment ;

2

[mark points can be given in (a) and (b) if specific example described] [4]

2.

(a)

Relay / intermediate / connector / internuncial ;

(b)

Reference to impulse passing from sensory neurone to motor neurone ; Allowing other connections ;

(c)

1 2

1.

{Binds / eq} with receptors on postsynaptic membrane ;

2.

Sodium {channels / gates} open ;

3.

Sodium (ions) {go / flow / flood / diffuse} in (to post-synaptic knob / neurone) ;

4.

(ion changes result in) {depolarising / eq} of postsynaptic membrane ;

5.

Reference to depolarisation {triggering / reaching threshold for} action potential ;

4 [7]

3.

(a)

(b)

(c)

1.

Rate of production decreases {for / within} 10 minutes ;

2.

Starts to rise {after 10 minutes / by 15 minutes} ;

3.

Still not back to original rate {after 40 minutes / at end} / there is an overall decrease in rate of urine production ;

4.

Credit use of figures ;

1.

{Increased salt level / decreased water potential / eq} (in blood) detected by osmoreceptors ;

2.

In the hypothalamus ;

3.

(results in) increased ADH release from (posterior) pituitary ;

4.

(ADH causes) {walls / cells} of {collecting ducts / distal convoluted tubule} (in kidney) to become more permeable ;

5.

More water reabsorbed ;

6.

{Less / lower volume of} urine produced / rate of urine production decreases ;

7.

As {blood salt level / eq} decreases urine volume increases ;

3

4

Blood not going directly to {head / brain / hypothalamus / osmoreceptors} OR blood is going to the rest of the body ; Salt diluted by general circulation / salt removed by {kidney / sweating} / eq ;

2 [9]

Edexcel Unit 4A June 2003 MS

1

4.

(a)

(b)

1.

More insulin released ;

2.

Sharp / steep increase up to {7.5 / 10} mmol dm-3 ;

3.

Reference to {starting to level off / rate of increase has decreased} at 7.5 mmol dm-3 ;

4.

Reference to plateau at 10 mmol dm-3 ;

1.

Detected by {islets / cells} ;

2.

Reference to (glucose concentration being above) {a threshold / 2.5 mmol dm-3} ;

3.

As no other tissue present / only isolated {cells / tissues} used ;

2

2

(c)

Reference to {being within tolerance limits / below threshold} ;

(d)

1.

(Blood glucose concentration of 7.5 mmol dm-3) causes release of {more insulin / 104 a.u. of insulin} ;

2.

(insulin) increases glucose uptake into {liver / muscle} ;

3.

Reference to increasing permeability of membrane (to glucose) ;

4.

(because insulin) causes glucose to glycogen conversion / glycogenesis (in the liver / muscles) ;

5.

Inhibition of {gluconeogenesis / conversion of amino acids to glucose} ;

6.

When blood glucose reduced to {5 mmol dm-3 / normal} insulin release {much lower / 58 a.u.} ; 3

(e)

1

Adrenaline / epinephrine ; Glucagon ; Thyroxine ; Glucocorticoids / cortisol / cortisone ;

2 [10]

Edexcel Unit 4A June 2003 MS

2

5.

1.

Reference to glycolysis ;

2.

As {breakdown / conversion} of glucose to {pyruvate / pyruvic acid} ;

3.

Phosphorylation of glucose / glucose converted to glucose (6) phosphate ;

4.

Reference to use of ATP (for phosphorylation) ;

5.

Prevents glucose leaving cell / reference to activation energy / increased reactivity of glucose ;

6.

Formation of {glycerate-3-phosphate / GP / G3P / phosphoglycerate / phosphoglyceric acid / PGA} ;

7.

GP converted to pyruvate ;

8.

Results in {NAD+ to NADH / reduction of NAD+} and ATP ;

9.

Reference to (net) yield = 2 ATP per glucose molecule ;

10.

{Pyruvate reduced / NADH is oxidised} to maintain glycolysis ;

11.

Pyruvate converted to ethanol ;

12.

Reference to {acetaldehyde / ethanal} as an intermediate ;

13.

Reference to NAD being regenerated / NADH is oxidised ;

14.

CO2 produced (when pyruvate is converted to ethanol) ;

15.

Reference to involvement of {oxidoreductase / decarboxylase / dehydrogenase} enzymes ; [10]

6.

(a) Batch fermentation

Continuous fermentation

1.

{Substances / medium} not added during {fermentation / culture / process culture}

Medium added ;

2.

{Nothing / only waste gases} removed during culture / eq

{Spent medium / waste products} removed from culture ;

3.

Goes through all phases of growth / cells die when conditions are unfavourable

The growth is {maintained / kept at} {log / exponential / growth} phase ;

4.

pH is not adjusted

pH is kept constant ;

5.

(all) {product / eq} harvested at end

{Product / eq} harvested throughout ; 3

Edexcel Unit 4A June 2003 MS

3

(b) Cell infection (lytic) cycle

Latency

1.

Particles are made immediately

Particles are made later ;

2.

Genetic material is not incorporated

The genetic material is incorporated into the host genome / eq ;

3.

No reverse transcriptase present

Reverse transcriptase is needed if it is a retrovirus ;

4.

Cell is destroyed

Cell is not destroyed / no interference with cell function ; 3 [6]

7.

(a)

(b)

1.

Reference to germination ;

2.

As a result of incubation with water ;

3.

Amylase {activated / mobilised} ;

4.

Reference to starch (in barley) ;

5.

Broken down into maltose ;

3

Yeast would die because it is too hot ; Fermentation would not take place / no {alcohol / ethanol} produced ;

2 [5]

8.

(a)

(b)

1.

No {colonies / bacteria} found around disc A ;

2.

A {kills bacteria / is bactericidal} ;

3.

Disc B prevents colonies from increasing in size / eq ;

4.

B {stops growth of bacteria / is bacteriostatic} ;

5.

Reference to an appropriate mechanism for either A or B in correct context ;

1.

4

Target structures only found in {bacteria / prokaryotic cells} ; [Any two out of the following three marking points]

2.

E.g. cell wall ;

3.

E.g. 70S ribosomes ;

4.

E.g. membranes ;

5.

Interfere with {chemical reactions / enzymes} only occurring in {bacteria / prokaryotic cells} ; 3 [7]

Edexcel Unit 4A June 2003 MS

4

9.

(a)

(i)

Label the lag phase ;

(ii)

Cells {adjusting / eq} to conditions ;

1

Cells warming up ; New enzymes being synthesised ; (b)

(c)

1.

Up to 12 hours no difference in numbers ;

2.

Between 12 hours and 20 hours the cell numbers stay the same for the dilution plating but continue to rise for turbidity ;

3.

From 20 hours (to 24 hours) the numbers fall for dilution plating but {plateaus / stays the same / eq} for turbidity ;

4.

Credit correct manipulation of figures ;

3

Turbidity measures {viable and dead cells / total cells} ; Dilution plating measures only viable cells ;

(d)

2

2

1.

Serial dilutions described / e.g. in 10: 1 cm3 + 9 cm3 or in 100: 0.1 cm3 + 9.9 cm3 ;

2.

Range of concentrations plated out ;

3.

Reference to mixing cultures at either stage (marking points 1 and 2) ;

4.

Reference to the same volume plated ;

5.

Reference to {spreading technique / pour-plating technique} used ;

6.

Reference to aseptic technique ;

7.

Reference to counting colonies and a calculation of number in original solution ;

4 [12]

Edexcel Unit 4A June 2003 MS

5