A Level BIology Paper 5 Past papers Solved and Marked

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f one brand of cleaning solution for c
8 1 1 shows the results of trials to find th . 'l
. f lion on the label of a bottle o tein from contact lenses. ontact len 1ab1 · ninQ solution at 35 °C. 8 tIrne taken I
The in orma which remove pro ses s1, 1or the COioured
that It contains enzymes ,q~ tne clea .
. solution state that Qetat,n 10 be removed by
The instructions for using the . . Table 1.1
ured into the cleaning pot provided up t trial
should be po . so Iut·ion for a.minimum
· . o the
The cleaning sol ut.ion I ft ·n the cleaning of I llla111
The contact lenses should be s~o~ld be washed in a sterile saline (SOdiurn c~ur ~OlJrs~d lev~. time/minutes
B tore using the lenses, they londe)
e soiuuon . e student noticed that there was a lar . 40
The contents of the solution are: . (a) Th k h t t ge variation ·
difficult to now w en o s op the stopwat h in the results To·
ith an optimum temperature of 1;>0°c and c· · is may be because it was
1. S_Ublilisin-A. a protease w - - -- - ~ an Optin,ul'll
suggest two problems in deciding when to
_7.Jt:Z.5. . h •ological solution with .the same 'balance of ions' PH 01 · th Ii,,

3. D1 Ium
~~;A
2. B._u, sod~rnd a/p7e~rvaiive.
,
as body fluids
· 1... \?.:\f.~5:'.1
~ \ . .•• i.~~/:'.:~~:: th
1; ; ~~tc~n is inve!gation.
,'·j!
~{e.._d ~ h(:Q·t
~~m,
.......................... \:~.~ ~\ the
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A student was asked to fi n
d out the actual concentration of the protease present .
in the c
·········-r····:....................... :'.: ..... <I~ °t'{"' ........................... I
I '1 1
lens cleaning solution. 0n1aQ I




; . . .. . \J
b site that gave ::,e concentration of subtilisin A in differ
The student fol und a swo~utions These range between 20 µg cm-3 and 100 µg crn-3 ent brands OI
contactlens c eaning · . · ·········································································• ...... .. ..
, ,

·····················•• .. ······························••l2l
t . lated a dirty contacflens using the protein gelatin and a thin transpa (b) The student made a sto~k cleani~g solution containi _ _ _ .• •
The s1uOden s~mu f the plastic sheet was dipped into melted gelatin containing a dye ~nt Plastic 3
EDTA and a buffered saline solution. The disOdium :r~t1lls1n A, disodium
sheet. ne s1 e o · 11Ie gelatin
was then allowed to set. 1 were the same concentrations as used in the trials. and th e buffered saline solution

Fig. 1.1 shows a simulated contact lens. This solution was u~ed. to r:nake a range of concentrations th .
concentration of subt1l1s1n A in the contact lens cleaning solution~! could be used to find the
layer of coloured gelatin on the
surface of the plastic sheet ~ -·'_-:,','}_ /
thin, transparent_ ~
plastic sheet
"~16t~f
· ,,
/
17 10mm



Fig.1.1

The student tested the activity of subtilisin A by recording the time taken for the coloured gelatin to
be removed, leaving the transparent plastic sheet.

Fig. 1.2 shows the apparatus the student used.

lid
line indicating
3
10cm on the pot:-VBMD:4---- cleaning solution
contact lens .ltt,:,~---simulated contact
cleaning pot --"i\/{?~V/] lens suspended in
the cleaning solution

Fig.1.2



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