exercises-07-micro-organisms.doc

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Section 7 - Health and Disease - Exercises and discussion

1 The drawings represent a bacterium, a protozoan and a plant cell (not to scale). Say whichis which and give reasons for your decision. (A)

2 Rewrite the following list in order of size starting with the smallest.red blood cell, virus, protein molecule, bacterium (R)

3 hich of the following is produced by the body in response to bacterial infection!(a) antibiotics (c) antigens(b) antibodies (d) antiseptics. (R)

4 "alaria is transmitted by(a) droplet infection (c) contaminated water

(b) mos#uitoes (d) houseflies (R)

5 $henyl%etonuria is caused by

(a) a gene deficiency (c) a blood disorder (b) a dietary deficiency (d) an allergy (R)

6 A microbiologist describes a new type of bacterium as follows&'t appears oval, about m long and *. m at its widest point. 't has a cell membrane about+.+* m thic%, surrounding its cytoplasm. utside the cell membrane there is a cell wall+.+- m thic%, surrounded by a layer of slime about +.* m thic%. $ro ecting from thesurface of the bacterium are several hundred fimbriae (fine cytoplasmic threads) aboutl m long, uniformly distributed and having their origin in the cytoplasm. Special stains showa region of /0A about +.1 m across, near the centre of the bacterial cytoplasm butwith no membrane round it.

2se a whole A3 sheet of paper to ma%e a labelled drawing of this bacterium, roughly toscale (where possible).hat is the magnification of your drawing! (* mm 4 +.++* m) (A)

7 /raw up a dichotomous %ey to help identify the different species of bacteria shown in thedrawing. (A)

A B C

A B C D E F G

56ercises and discussion 57.+*


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11 To try and find an effective and economical strength for a commercial disinfectant, a dilutionis made and tested against some bacterial colonies.

* cm - of disinfectant is diluted with = cm - of water in tube * so giving a *+B solution. * cm - of this solution is diluted with = cm - water in tube ?. The process is repeated for tubes -9 .

cm - solution from each tube was placed on separate agar plates containing e#ually densecolonies of bacteria. The figure below shows the method and the result.

(a) hich tube contained the most economical concentration that was effective against the bacteria!

(b) hat is the concentration of disinfectant in this tube!(c) 'f this is the most economical concentration, why donCt the manufacturers sell the

disinfectant in this form! (')

12 /isasters such as floods and earth#ua%es are often followed by epidemics of intestinaldiseases such as cholera, typhoid and dysentery. hy do you thin% this happens! (A)

13 The graph shows the level of antibody inthe blood after receiving the first and second(booster) in ection of a vaccine.

(a) hat is the ma6imum antibody level(i) after the first in ection, (ii) after the

booster in ection!(b) hat are the effects of the booster in ection!(c) Dow long does it ta%e for the antibody

level to reach its ma6imum after the booster in ection!

(d) hy, do you thin%, does the level of antibody fall slightly immediately after

the booster in ection! (') < $assmore and Robson

Section 7 - Health and Disease - Exercises and discussion (continued)

1cm 3

# cm 3

$ater

1 cm 3

disi!fecta!t

# cm 3 $ater

five ide!tical a%ar plates $it& bacterialcolo!ies

1 cm 3 fromtube 4

result after 24 &ours

a !

t i b o

d "

l e v e

l a r b

i t r a r " u !

i t s

$ee's

boosteri!(ectio!

result of si!%lea!tibod" i!(ectio!

56ercises and discussion 57.+3


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14 ne method of testing whether a person has antibodies to the D'E virus in his or her blood is carried out as follows& A D'E virus particles are bro%en up and made to stic% to the bottom of a plastic dish.

The particles will carry the virus antigens. 8 A sample of plasma, possibly containing

D'E antibodies from the patient, is added to the dish. The plasma is then washed away.@ Antibodies to the human D'E antibodies

are added. These antibodies have been combinedwith an enzyme which converts a colourlesssubstance CSC into a colour. The plastic dish is

washed again./ The colourless substance CSC is added to the dish. (')

(a) 2se the symbols above to show the result (i) with blood which contains no D'Eantibodies, (ii) with blood containing D'E antibodies.

(b) hat would you e6pect to see in each case!

15 An insurance office has a staff of -++. ne Tuesday, 3 people are absent with sic%ness anddiarrhoea which, investigations show, was caused by Salmonella typhimurium .The investigation found that ?-+ people on the staff, including 3+ of the affected people, hadta%en lunch in the office canteen on "onday. The choices had been meat and potato

pie (*++ servings), chic%en curry with rice (>+ servings) or pizza and chips ( + servings).-> of the affected people had chosen the chic%en.3+ of the affected people had been amongst 1+ who had attended an office party on the "ondaynight.

(a) hat evidence supports the possibility that the salmonella outbrea% was caused by thechic%en curry!

(b) hat is the evidence against this possibility!(c) hat further investigations would be necessary to find out the cause of the outbrea%! (AF')

16 ne way of testing the effectiveness of an antibioticagainst a species of bacterium is to soa% filter paperdiscs in the drug, place them on a plate of nutrient agar

elly which has been seeded with a culture of the bacteriaand incubate the plate at -7G@. The drawing shows theresults of such a test.

(a) hich antibiotics seem ineffective againstthe bacteria!

(b) hich antibiotic seems most effectiveagainst the bacteria!

(c) hy might the results not reflect the effectiveness of the drug in the body!(d) Dow would you design an e6periment to find

whether increasing concentrations of penicillin might be effective against the bacteria! ('F5)

Section 7 - Health and Disease - Exercises and discussion (continued)

A )irus particles bro'e! up a!d stuc' to plastic

B *+) a!tibodies i! plasma samples

C A!tibodies to *+) a!tibodies

D colourless substa!ce , e!."me colourcolour

e!."mee!."me

*+) virus a!ti%e!s

C - c&loamp&e!icol E - er"t&rom"ci!/E - tetrac"cli!e , - streptom"ci!G - sulp&ura.ole 0 - pe!icilli!

< Hohn Dumphries

56ercises and discussi on 57.+


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17 The e6periment in #uestion *1 compares theeffectiveness of different antibiotics against thesame species of bacterium. The e6periment in thediagram on the right tests the effectiveness of one,

antibiotic against different species of bacteria.The lines A95 represent strea%s made on the agarwith five different bacterial species.

(a) /raw what you would e6pect to see, after?3 hours incubation, if the antibiotic iseffective against species @ and 5 but notagainst the others.

(b) Dow might the choice of nutrient in the agaraffect the result! (AF5)

18 A student who has had a bad cough decides to see if his symptoms are caused by a pathogenic bacterium. De obtains a sterile petri dish with sterile agar containing a suitablenutrient. De removes the lid, coughs over the agar, replaces the lid and incubates the dishfor ?3 hours at [email protected] this time, he removes the lid, counts the colonies of bacteria and washes thecontents of the dish down the sin%.

(a) 56plain why the studentCs procedure is dangerous for him and his classmates.(b) This e6periment should not be carried out in school but, if carried out in a pathology

laboratory, could be made much safer. Suggest at least two safety measures that could be ta%en.

(c) Apart from the safety aspects, in what ways is the e6periment badly designed! (5)

trou%& cut i! a%ara!d filled $it&a!tibiotic solutio!

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exercises-07-micro-organisms.doc