Answer

Antibiotics affect the behaviour and biochemistry of bacterial cells.

(i) Give THREE ways in which antibiotics affect bacterial cells.

3 from:

Inhibit protein synthesis/ translation/ transcription;

Inhibit DNA replication;

Inhibit cell wall formation/ osmotic lysis;

Disruption of cell membrane function;

Reject destroy cell wall / digest cell wall

[ 3 ]

(ii) Antibiotic drugs are not given for viral illnesses. Give TWO reasons why this is the case.

Viruses have no metabolism / do not need nutrients / no ribosomes / named organelle / cell wall / not living; Antibiotics only active against (living) cells / viruses acellular; Viruses inside cell;

[ 2 ]

(iii) The graph below describes the growth curve of a population of bacteria. Identify ON THE GRAPH the stages shown by the letters A, B, C and D on the graph.

time

A = Resting Phase or acceptable equiv.

B = Exponential Phase

C = Stationary Phase

D = Death Phase

[ 4 ]

(iv) With reference to the graph, explain the shape of the curve

6 of:

A - equilibrating to / environment / getting used to / conditions; so no [overall] growth so almost straight curve; B - growth phase / doubling phase; numbers increase exponentially; so steep upward curve; C - growth at steady rate; no exponential increase in numbers; so levelling of curve; D - nutrients depleted so numbers fall; build-up of toxins; from dead cells causes growth rate to cease and cells to die; so steep downward curve.

[ 6 ]

[ Total: 15 ]

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