Download Markscheme for sample questions File

1.
D
[1]
2.
D
[1]
3.
B
[1]
4.
D
[1]
5.
(a)
(b)
(c)
(i)
hydrogen
1
(ii)
covalent / phosphodiester linkage
1
DNA has deoxyribose, RNA has ribose;
DNA has base T/thymine, RNA has base U/uracil;
Do not accept double or single strands as chemical structure.
tRNA attaches to (specific) amino acid;
tRNA (with amino acid) moves to the ribosome;
anticodon of tRNA binds with codon of mRNA;
2
2 max
[6]
IB Questionbank Biology
1
6.
(a)
Award [1] for each pair of statements in the table and [1] for any
statement below the table.
Unique sequences
Highly repetitive sequences
occur once in genome
occur many times;
long base sequences
short sequences/5–300 bases;
(may be) genes
not genes;
(may be) translated / coding sequences
never translated;
small differences between individuals
can vary greatly;
exons (are unique sequences)
introns (may be repetitive);
smaller proportion of genome
higher proportion of genome;
satellite DNA is repetitive;
repetitive sequences are used for profiling;
prokaryotes do not (usually) contain repetitive sequences;
(b)
Award [1] for each of these structures clearly drawn and labelled.
four nucleotides shown in diagram with one nucleotide clearly labelled;
base, phosphate and deoxyribose (shown as pentagon) connected between
the correct carbons and labelled at least once;
backbone labelled as covalent bond between nucleotides correctly shown
as 3′ to 5′ bond;
two base pairs linked by hydrogen bonds drawn as dotted lines and labelled;
two H bonds between A and T and three H bonds between C and G;
adenine to thymine and cytosine to guanine; do not accept initials of bases
antiparallel orientation shown;
IB Questionbank Biology
5 max
5
2
(c)
DNA sample obtained;
from hair/blood/semen/human tissue;
DNA amplified / quantities of DNA increased by PCR/polymerase
chain reaction;
satellite DNA/highly repetitive sequences are used/amplified;
DNA cut into fragments;
using restriction enzymes/restriction endonucleases;
gel electrophoresis is used to separate DNA fragments;
using electric field / fragments separated by size;
number of repeats varies between individuals / pattern of bands is unique to the
individual/unlikely to be shared;
Award [5 max] for methods.
forensic use / crime scene investigation;
example of forensic use e.g. DNA obtained from the crime scene/victim
compared to DNA of suspect / other example of forensic use;
paternity testing use e.g. DNA obtained from parents in paternity cases;
biological father if one half of all bands in the child are found in the father;
genetic screening;
presence of particular bands correlates with probability of certain
phenotype / allele;
other example;
brief description of other example;
Award [4 max] for aims.
8 max
(Plus up to [2] for quality)
[20]
7.
(a)
DNA is double-stranded while RNA is single-stranded;
DNA contains deoxyribose while RNA contains ribose;
the base thymine found in DNA is replaced by uracil in RNA;
one form of DNA (double helix) but several forms of RNA (tRNA,
mRNA and rRNA);
IB Questionbank Biology
3 max
3
(b)
(c)
occurs during (S phase of ) interphase/in preparation for mitosis/
cell division;
DNA replication is semi-conservative;
unwinding of double helix / separation of strands by helicase (at
replication origin);
hydrogen bonds between two strands are broken;
each strand of parent DNA used as template for synthesis;
synthesis continuous on leading strand but not continuous on
lagging strand;
leading to formation of Okazaki fragments (on lagging strand);
synthesis occurs in 5´ → 3´ direction;
RNA primer synthesized on parent DNA using RNA primase;
DNA polymerase III adds the nucleotides (to the 3´ end)
added according to complementary base pairing;
adenine pairs with thymine and cytosine pairs with guanine;
(Both pairings required. Do not accept letters alone.)
DNA polymerase I removes the RNA primers and replaces them
with DNA;
DNA ligase joins Okazaki fragments;
as deoxynucleoside triphosphate joins with growing DNA chain,
two phosphates broken off releasing energy to form bond;
Accept any of the points above shown on an annotated diagram.
8 max
they increase rate of (chemical) reaction;
remains unused/unchanged at the end of the reaction;
lower activation energy;
activation energy is energy needed to overcome energy barrier that
prevents reaction;
annotated graph showing reaction with and without enzyme;
substrate joins with enzyme at active site;
to form enzyme-substrate complex;
active site/enzyme (usually) specific for a particular substrate;
enzyme binding with substrate brings reactants closer together to
facilitate chemical reactions (such as electron transfer);
induced fit model / change in enzyme conformation (when
enzyme-substrate/ES complex forms);
making the substrate more reactive;
7 max
(Plus up to [2] for quality)
[20]
8.
B
[1]
9.
A
[1]
10.
B
IB Questionbank Biology
4
[1]
11.
C
[1]
12.
(a)
(b)
(c)
(d)
(e)
(i)
(GMF) C
1
(ii)
(50  22)
× 100;
22
=127% ; (units required) (allow answers in the range of 127 to 127.3)
2
error bars show the range/variability/uncertainty of the data / OWTTE;
error bars/standard deviation about the same length for day 0 and day 11 /
spread of data (around the means) about the same;
overlapping bars indicate that there is no (significant) difference in the
data/ means;
68% of population within one standard deviation;
inversely proportional / the higher the tolerance, the less the
growth / vice versa
first name/Oryza for genus / second name/sativa for species;
(all) members of Oryza sativa share special/unique features;
two names make a unique combination to designate species / worldwide
recognizable nomenclature;
varieties (japonica and indica) have some (consistent) differences
(in tolerance);
(i)
Sub1C
(ii)
Sub1A is expressed strongly/the most / Sub1A produces the
most RNA;
Sub1B (always) has the lowest expression/produces least
mRNA;
Sub1A expressed/produces mRNA for the longest
time/days 1 to 10;
Sub1C expressed/produces mRNA for the shortest
time/days 3 to 7;
IB Questionbank Biology
2 max
1
2 max
1
2 max
5
(iii)
(f)
(g)
Sub1A only expressed/produces mRNA in indica / not/never
expressed/never produces mRNA in japonica;
Sub1C expressed/produces mRNA from day 1 in japonica,
but not indica;
Sub1B has lower expression/production of mRNA than
Sub1C in both varieties;
other accurate comparisons;
2 max
Sub1A;
is only expressed in indica;
indica is the variety showing submersion tolerance;
2 max
genetically modified rice/rice with Sub1A is more tolerant to
submersion;
can withstand seasonal flooding/torrential rain;
GMF/tolerant rice ensures greater harvest/provides more food
during flooding;
2 max
[17]
13.
(a)
name of component [1 max] e.g. plant cell wall/cellulose/interstitial matrix/
basement membrane/glycoprotein/bone matrix;
functions [3 max]
EITHER
e.g. (plant cell wall) strengthens/supports the cell/plant (against gravity);
prevents the entry of pathogens;
maintains the shape of plant cells;
allows turgor pressure/high pressure to develop inside the cell;
prevents excessive entry of water to the cell;
OR
helps cells to stick together/adhere;
needed to hold cells/tissues together / example of cells/tissues
holding together;
forms interstitial matrix / forms basement membrane to support single
layers of cells;
e.g. around a blood capillary;
forms (part of the) filtration membrane in the glomerulus;
IB Questionbank Biology
4 max
6
(b)
(c)
vesicles carry material to plasma membrane;
vesicle fuses with membrane;
(by joining of) phospholipid bilayers;
aided by the fluidity of the membrane;
material released/expelled from the cell;
membrane flattens;
name of example e.g. exocytosis of neurotransmitter / exocrine secretion/
endocrine secretion / hormone secretion / release of cortical granules;
outline of example: (in the presence of calcium), neurotransmitter vesicles
release their contents into the synapse / hormones released from one cell
have an effect on another cell etc.;
Accept these points if clearly made in an annotated diagram. [4 max] if
no example given.
5 max
translation involves initiation, elongation/translocation and termination;
mRNA binds to the small sub-unit of the ribosome;
ribosome slides along mRNA to the start codon;
anticodon of tRNA pairs with codon on mRNA:
complementary base pairing (between codon and anticodon);
(anticodon of) tRNA with methionine pairs with start codon / AUG is the
start codon;
second tRNA pairs with next codon;
peptide bond forms between amino acids;
ribosome moves along the mRNA by one codon;
movement in 5′ to 3′ direction;
tRNA that has lost its amino acid detaches;
another tRNA pairs with the next codon/moves into A site;
tRNA activating enzymes;
link amino acids to specific tRNA;
stop codon (eventually) reached;
9 max
(Plus up to [2] for quality)
[20]
IB Questionbank Biology
7