Download advice to examiners on the annotation of scripts

2801 Biology Foundation
January 2006
Mark Scheme
ADVICE TO EXAMINERS ON THE ANNOTATION OF SCRIPTS
1.
Please ensure that you use the final version of the Mark Scheme.
You are advised to destroy all draft versions.
2.
Please mark all post-standardisation scripts in red ink. A tick (ü) should be used for
each answer judged worthy of a mark. Ticks should be placed as close as possible
to the point in the answer where the mark has been awarded. The number of ticks
should be the same as the number of marks awarded. If two (or more) responses
are required for one mark, use only one tick. Half marks (½) should never be used.
3.
The following annotations may be used when marking. No comments should be
written on scripts unless they relate directly to the mark scheme. Remember that
scripts may be returned to Centres.
x
^
bod
ecf
con
sf
= incorrect response (errors may also be underlined)
= omission mark
= benefit of the doubt (where professional judgement has been used)
= error carried forward (in consequential marking)
= contradiction (in cases where candidates contradict themselves in the
same
response)
= error in the number of significant figures
4.
The marks awarded for each part question should be indicated in the margin
provided on the right hand side of the page. The mark total for each question should
be ringed at the end of the question, on the right hand side. These totals should be
added up to give the final total on the front of the paper.
5.
In cases where candidates are required to give a specific number of answers, (e.g.
‘give three reasons’), mark the first answer(s) given up to the total number required.
Strike through the remainder. In specific cases where this rule cannot be applied, the
exact procedure to be used is given in the mark scheme.
6.
Correct answers to calculations should gain full credit even if no working is shown,
unless otherwise indicated in the mark scheme. (An instruction on the paper to ‘Show
your working’ is to help candidates, who may then gain partial credit even if their final
answer is not correct.)
7.
Strike through all blank spaces and/or pages in order to give a clear indication that
the whole of the script has been considered.
8.
An element of professional judgement is required in the marking of any written paper,
and candidates may not use the exact words that appear in the mark scheme. If the
science is correct and answers the question, then the mark(s) should normally be
credited. If you are in doubt about the validity of any answer, contact your Team
Leader/Principal Examiner for guidance.
Mark Scheme
January 2006
1
(a)
(i)
/
;
NOT
R
()
___
ecf
AW
A
ora
Page 3 of 9
=
=
=
=
=
=
=
=
=
=
alternative and acceptable answers for the same marking point
separates marking points
answers which are not worthy of credit
reject
words which are not essential to gain credit
(underlining) key words which must be used to gain credit
error carried forward
alternative wording
accept
or reverse argument
Expected Answers
Marks
Abbreviations,
annotations and
conventions used in the
Mark Scheme
Question
2801
mitochondrion ; A mitochondria
1
(ii) aerobic respiration ;
ATP production ; A provides ATP
energy release ; A provides energy R produce / create / make / etc
AVP ;
e.g. Krebs cycle / regenerate NAD
oxidative phosphorylation
protein synthesis
lipid synthesis
oxidation of fats
ornithine / urea , cycle
2 max
(iii) (energy / ATP needed) for , movement / wafting (of cilia) ;
R flagellum / molecules
1
(iv) award two marks if correct answer (5) is given
award one mark for calculation
5;;
if answer incorrect, allow 1 mark for
100 +/- 2 (mm) or 10 +/- 0.2 (cm) ¸ 20000
(b)
2
low resolution ; ora
(close) points not easily distinguished ;
wavelength (of visible light) is too long ;
max resolution of light microscope = , 200 nm / 0.2 mm ; A anything close
no more detail visible than seen at , x1500 / x1000 ;
A comparative statements
R reverse arguments for points 2 - 5
2 max
[Total :
Mark Scheme
8]
January 2006
Question
2
2801
Page 4 of 9
Expected Answers
Marks
(a) do not credit if any incorrect answer included
(i)
(b)
fox ;
1
(ii) grass / clover / legume ;
1
(i)
1
nitrogen fixation / Haber (process) ; A reduction
(ii) lightning ;
(iii) denitrifying ;
A oxidation / combines with oxygen
A ‘lightening’
R thunderstorm / lighting
1
A correct e.g. (Pseudomonas)
R Nitrobacter / Nitrosomonas / Rhizobium
1
(iv) fixes nitrogen / provides fixed nitrogen or NH4(+) ; R ammonia
ref to, clover / legume / named legume , making , amino acids /
polypeptides / protein ;
(plant has) no need to rely on (fixed) nitrogen compounds in soil ;
R ref to fertilisers
free-living species provide , ammonium (ions) / fixed nitrogen , for nitrifying
bacteria / nitrification ;
[Total :
Mark Scheme
2 max
7]
January 2006
Question
3
(a)
2801
Page 5 of 9
Expected Answers
(i)
Marks
endocytosis / phagocytosis ; A bulk (transport)
R pinocytosis / exocytosis
(ii) enzymes / named enzymes / lysins ;
acid / low pH ;
digestion ; A breaking down
breaking , peptide / glycosidic / ester , bond ; R if in wrong context
hydrolysis ;
soluble / named , products ;
(b)
(i)
not enough points plotted / experiment not carried out at enough (different)
pH values ;
only 1 point between 3 + 4.3 / no points between 3.25 + 4.3 ;
don’t know / uncertainty of , rate between those points /
where peak should be / where optimum is ;
3.25 reading might be anomalous ;
cannot draw , curve / line of best fit ;
rises to , 3 / 3.25 , and falls after 4.3 ;
1
3 max
2 max
(ii) note ~ enzyme is completely inactive at pH 7
loss of tertiary structure / loss of 3D structure / (enzyme) denatured ;
(change in pH/[H+]) alters charge distribution on (enzyme) molecule ;
hydrogen / ionic , bonds affected ;
changes (shape of) active site ;
enzyme substrate complex cannot be formed /
substrate not attracted to active site /
substrate cannot bind to active site / AW ;
Mark Scheme
2 max
January 2006
Question
3
2801
Page 6 of 9
Expected Answers
(c)
Marks
mark each section (E, S and C) to max shown
E
1
2
3
4
S
1
2
enzyme concentration ~
reaction (rate) increases with increased enzyme ; A high / low
more active sites available ;
in excess substrate / as long as enough substrate (molecules
available to occupy active site) ;
(as reaction progresses) the rate will decrease as substrate ,
used up / becomes limiting ; R plateau
3
4
5
substrate concentration ~
reaction (rate) increases with increased substrate ; A high / low
more , molecules available to enter active site / ESC formed ;
A more successful collisions
reaches point where all active sites occupied ;
no further increase in rate / reaches Vmax ; A plateau / levels off
enzyme conc. becomes limiting / unless add more enzyme ;
C
1
2
3
4
5
6
7
8
competitive inhibitor ~
inhibitor has similar shape to substrate ;
can , fit / occupy , active site ;
for short time / temporary / reversible ;
prevents / blocks , substrate from entering active site ;
rate determined by relative concentrations ;
little inhibition / rate little reduced , if substrate conc. > inhibitor conc. ; ora
ref to chance of , substrate / inhibitor , entering active site ;
effects can be reversed by increasing substrate conc. ;
E
(3 max)
S
(3 max)
general points ~
10 drawing a suitable graph to illustrate point made with labelled axes ;
11 ref to optimum (rate) ;
C
(5 max)
9 max
QWC ~ legible text with accurate punctuation, spelling and grammar
[Total :
Mark Scheme
1
18]
January 2006
Question
4
Page 7 of 9
Expected Answers
(a)
(b)
2801
(i)
Marks
protein / polypeptide , with ,
carbohydrate (chain) / polysaccharide / sugar / glucose ;
(R) glycogen
1
(a) helix ;
1
R double helix
(ii) (b) pleat(ed) (sheet) ;
tertiary / 3o ;
(c)
(d)
1
(i)
1
restriction (enzyme) / endonuclease ;
A named e.g.
1
(ii) (DNA) ligase ;
(e)
1
(rough) ER has ribosomes ; R produces
for , protein synthesis / translation ;
ER transports protein through cell ;
forms vesicles ;
for transport to / forming , Golgi ;
(in Golgi) modification of protein / glycosylation ;
2 max
[Total :
Mark Scheme
8]
January 2006
Question
5
2801
Page 8 of 9
Expected Answers
(a)
Marks
look for shading in A on page 12
do not credit if more than 1 chromosome shaded
corresponding homologous chromosome correctly shaded on A ;
i.e. bottom one
1
(b) mark (i) and (ii) independently
(i)
metaphase ;
R ref to metaphase I or II
1
(ii) (individual) chromosomes align at ,
metaphase plate / equator / centre (of cell) ;
join to , spindle / microtubules ;
by centromeres ;
2 max
ref to bivalents / homologous pairs = max 1
(c)
C;
A;
2
[Total :
Mark Scheme
6]
January 2006
Question
6
solvent ;
liquid ; A same
dense ;
insulates ; A keeps warm
hydrogen ; A H / weak
surface tension / cohesion ;
(i)
Marks
R protects / warms
R H+ / H2
6
K;
1
(ii) (vacuole in cell K) has less water in it (than cell L) ;
(vacuole / cell K) has lost more water (than cell L) ;
lower, water potential / Y, outside cell K ; ora
(c)
Page 9 of 9
Expected Answers
(a)
(b)
2801
ora
ora
1
(iii) (cell wall is) freely permeable / permeable to salt (solution) ;
R partially permeable
1
(i)
1
- 1300 kPa ;
credit if clearly indicated as candidate’s choice
(ii) arrow drawn from -800 to -950 ;
arrow drawn from -800 to -1000 ;
arrow drawn from -1000 to -1250 ;
a continuous arrow from -800 to -1000 to -1250 = 2
additional arrow(s) = -1 for each arrow that goes from low Y to high Y
but do not award less than 0 for (c)(ii)
[Total :
Mark Scheme
3
13]