www.studyguide.pk
NOVEMBER 2001
GCE ADVANCED SUBSIDIARY LEVEL
MARK SCHEME
MAXIMUM MARK : 50
SYLLABUS/COMPONENT : 8700/2
BIOLOGY
(STRUCTURED QUESTIONS)
http://www.xtremepapers.net
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1
Mark Scheme
AS Level Examinations – November 2001
Syllabus
8700
(a)
xylem vessel, transport of, water / ions;
1
(b)
no cross walls;
wide lumen / AW;
strengthened / lignified / thick cell wall;
no, cytoplasm / cell contents / organelles / hollow / empty;
pits;
3 max
(c)
companion cell;
movement of sucrose / other named substance;
into / out of, sieve tubes / loading / unloading;
through plasmodesmata;
provides energy;
active transport;
3 max
[Total:
2
Paper
2
7]
(a)
elastin / elastic fibres;
1
(b)
no recoil / alveoli do not recoil; (A) contract
air not forced out;
air not refreshed in alveoli;
concentration of oxygen, falls / not maintained;
less oxygen diffuses into the blood;
3 max
(c)
epidemiological evidence
increase in cigarette smoking, increase in cases / deaths from lung
cancer ~ 20 years later;
more men than women smoked in the past, linked to greater number of
cases / deaths among men; (A) anything similar to this
lung cancer rare / unknown, before cigarette smoking became common;
most people with lung cancer, smoke / have smoked;
lung cancer very rare in non-smokers;
lower incidence in smokers who do not inhale; (e.g. pipe and cigar
smokers)
ref to national differences in smoking and cancer / ref to developing
countries;
ref to studies involving British doctors;
ref to evidence from passive smoking;
AVP;
2 max
experimental evidence
experimental animals develop tumours similar to human lung tumours;
carcinogens have been isolated from tar;
when painted on animal skin induce tumours;
[Total:
1 max
7]
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Page 2 of 3
3
(a)
Syllabus
8700
amino acid;
1
(ii)
lose its shape / disrupted / uncoils / becomes straight chain;
denature;
hydrogen bonds break;
2 max
disulphide / sulphur bridges;
van der Waals / A/W;
hydrogen ;
ionic;
3 max
may be branched;
glycosidic links;
no R groups;
repeating unit structure / one monomer;
AVP;
2 max
three polypeptides twisted around each other;
hydrogen bonds between polypeptides;
covalent links between chains;
every third amino acid glycine, small so tight coil;
lay parallel to form fibrils;
ends staggered / fibrils overlap, so strong;
2 max
many –OH groups;
hydrogen bonds within the molecule;
hydrogen bonds between molecules;
straight chain (not helix) / unbranched / linear;
60-70 chains / associated to form microfibrils;
arranged in bundles to form, macrofibrils / fibres;
2 max
(c)
(i)
(ii)
[Total:
4
(a)
(b)
Paper
2
(i)
(b)
(d)
Mark Scheme
AS Level Examinations – November 2001
12]
(i)
serine;
1
(ii)
UAG;
1
(iii) codon;
1
(iv) phenylalanine, not isoleucine as next amino acid;
1
secondary structure / alpha helix / pleated sheet;
further folding / tertiary structure;
ref named bond(s);
transported in ER;
Golgi;
packaged / sugars added / trimmed;
vesicles;
exocytosis;
4 max
[Total:
8]
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5
(a)
(b)
(c)
Mark Scheme
AS Level Examinations – November 2001
A
B
C
D
Syllabus
8700
nucleus;
mitochondrion;
phagosome / vacuole;
lysosome;
half mark each
2
lower resolution in light microscope;
ref wavelength of light;
maximum is half wavelength;
200 nm;
many organelles / named example, smaller than this;
3 max
attachment to cell membrane;
receptors;
role of antibodies / opsonins;
folding inwards of cell membrane / endocytosis;
formation of vacuole / phagosome;
lysosomes fuse with vacuole;
toxins kill bacteria;
enzymes digest bacteria;
4 max
[Total:
6
(a)
Paper
2
statement
causative
organism is a
bacterium
causative
organism is
water-borne
transmitted
by an insect
vector
sexually
transmitted
cholera
malaria
HIV/AIDS
TB
ü
û
û
ü
ü
û
û
û
û
ü
û
û
û
û
ü
û
9]
one mark per row
4
(b)
people who are heterozygous / carriers;
resistant to malaria;
children of heterozygotes;
1 in 4 chance of inheriting sickle cell anaemia;
further detail of inheritance (e.g. Punnet square);
only attacks HbAHbA / healthy R.B.Cs;
3 max
[Total:
7]
Total mark for paper = 50