| Date | May 2017 | Marks available | 1 | Reference code | 17M.2.HL.TZ1.2 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | State | Question number | 2 | Adapted from | N/A |
Question
Nucleosomes help to regulate transcription in eukaryotes.
State the components of a nucleosome.
Nucleosomes help to regulate transcription in eukaryotes.
State a chemical modification of a nucleosome that could impact gene expression.
Markscheme
DNA and histone
methylation/acetylation/phosphorylation/epigenetic tags/modification of nucleosome tails/N-terminal tails
| Date | May 2016 | Marks available | 7 | Reference code | 16M.2.HL.TZ0.5 |
| Level | Higher level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Explain | Question number | 5 | Adapted from | N/A |
Question
Outline the action of enzymes.
Explain the roles of specific enzymes in prokaryote DNA replication.
Many genetic diseases are due to recessive alleles of autosomal genes that code for an enzyme. Using a Punnett grid, explain how parents who do not show signs of such a disease can produce a child with the disease.
Markscheme
Catalyse/speed up reactions
Substrate-specific
Lower the activation energy «of a chemical reaction»
Substrate collides with/binds to active site
Enzyme–substrate complex formed
OR
transition state formed
OR
bonds in substrate weakened
«DNA» gyrase/topoisomerase «II» prepares for uncoiling/relieves strains «in the double helix»
Helicase uncoils/unwinds the DNA/double helix
Helicase separates/unzips/breaks hydrogen bonds between the two strands of DNA
«DNA» primase adds an RNA primer/short length of RNA Accept RNA primase.
DNA polymerase III adds «DNA» nucleotides/replicates DNA/synthesizes complementary strand in a 5’ to 3’ direction
DNA polymerase III starts replication/adding nucleotides at the primer
DNA polymerase I removes the primer
OR
replaces RNA with DNA
«DNA» ligase seals the nicks
OR
links sections of replicated DNA
OR
links Okazaki fragments
DNA polymerase I/DNA polymerase III proofreads for mistakes
Key or text giving alleles with upper case for dominant allele and lower case for recessive allele/allele causing disease
Reject key showing a sex linked gene such as hemophilia.
Reject if X or Y chromosomes are shown with the alleles.
Accept Aa or any other upper and lower case letters.
Punnett grid showing that both parents can pass on either a dominant or a recessive allele in their gamete
For example row and column headings with A and a.
This mark can be awarded if X or Y chromosomes are shown but each parent has one recessive and one dominant allele as if for autosomal inheritance.
Four possible genotypes for child correctly shown on grid
AA, Aa, aA and aa for example.
This mark can be awarded if X or Y chromosomes are shown but the genotypes are correct for autosomal inheritance.
Double/homozygous recessive shown having the disease
Cannot be awarded with sex linkage.
25 % or 0.25 or 1/4 chance of inheriting the disease
This mark can be awarded if X or Y chromosomes are shown but the ratio is correct for autosomal inheritance.
| Date | November 2016 | Marks available | 8 | Reference code | 16N.2.HL.TZ0.7 |
| Level | Higher level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Explain | Question number | 7 | Adapted from | N/A |
Question
Angiospermophyta are vascular flowering plants.
Describe the transport of organic compounds in vascular plants.
The flowers of angiospermophyta are used for sexual reproduction. Outline three processes required for successful reproduction of angiospermophyta.
Growth in living organisms includes replication of DNA. Explain DNA replication.
Markscheme
a. phloem transports organic compounds/sucrose
b. from sources/leaves/where produced to sinks/roots/where used
c. through sieve tubes/columns of cells with sieve plates/perforated end walls
d. loading of organic compounds/sucrose into /H+ ions out of phloem/sieve tubes by active transport/using ATP
e. high solute concentration causes water to enter by osmosis (at source)
f. high (hydrostatic) pressure causes flow (from source to sink)
g. companion cells help with loading / plasmodesmata provide a path between sieve tubes and companion cell
h. translocation/mass flow
a. meiosis / production of male and female gametes
b. pollination / transfer of pollen from anther to stigma
c. fertilization happens after pollination / fertilisation is joining of gametes
d. seed dispersal / spread of seeds to new locations
Reject fruit dispersal.
a. helicase unwinds the double helix
b. gyrase/topoisomerase relieves strains during uncoiling
c. helicase separates the two strands of DNA/breaks hydrogen bonds
Accept unzips here but not for mark point a.
d. each single strand acts as a template for a new strand / process is semi-conservative
e. DNA polymerase III can only add nucleotides to the end of an existing chain/to a primer
f. (DNA) primase adds RNA primer/short length of RNA nucleotides
g. DNA polymerase (III) adds nucleotides in a 5’ to 3’ direction
h. complementary base pairing / adenine to thymine and cytosine to guanine
Do not accept letters.
i. DNA polymerase (III) moves towards the replication fork on one strand and away from it on the other strand
j. continuous on the leading strand and discontinuous/fragments formed on the lagging strand
k. DNA polymerase I replaces primers/RNA with DNA
l. ligase joins the fragments together/seals the nicks
| Date | May 2015 | Marks available | 4 | Reference code | 15M.2.HL.TZ2.5 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Outline | Question number | 5 | Adapted from | N/A |
Question
Outline the structure and functions of nucleosomes.
Explain how DNA is used to pass on genetic information to offspring accurately but also produce variation in species.
Accurate transmission of base sequences to offspring depends on successful gamete production. Describe how spermatogenesis occurs in humans.
Markscheme
Remember, up to TWO “quality of construction” marks per essay.
a. found in eukaryotes;
b. consists of DNA wrapped around proteins/histones;
c. histones are in an octamer/group of eight;
d. are held together by another histone/protein;
e. in linker region;
f. help to supercoil chromosomes / to facilitate DNA packing;
g. (function is to) regulate transcription / gene expression;
Remember, up to TWO “quality of construction” marks per essay.
a. DNA is replicated/copied semi-conservatively/from a template;
b. mutations can be a source of variation / resulting protein has new or different functions;
c. mutations/changes in the DNA may not result in changes in the amino acid for which the triplet codes;
d. genetic code is redundant;
e. genes occur as paired alleles which can be different;
f. crossing-over occurs;
g. recombines linked alleles producing new combinations;
h. random orientation of bivalents / homologous chromosomes (in metaphase I);
i. large genetic variation in (haploid) gametes / 2n / 223;
j. random recombination of alleles during fertilization (leads to variation);
k. different phenotypes among members of the same population;
l. natural selection may lead to enhanced survival of recombinants;
Remember, up to TWO “quality of construction” marks per essay.
a. germinal cells / spermatogonia undergo mitosis to keep a supply of germinal cells present;
b. some germinal cells / spermatogonia grow larger to become primary spermatocytes;
c. primary spermatocytes go through meiosis I;
d. to form secondary spermatocytes;
e. these secondary spermatocytes go through meiosis II;
f. to produce spermatids;
g. spermatids differentiate/grow a tail and reduce their cytoplasm
h. spermatids associated with nurse cells (Sertoli cells);
i. sperm detach from Sertoli cells and enter lumen of the seminiferous tubule;
j. testosterone stimulates sperm production;
| Date | May 2015 | Marks available | 8 | Reference code | 15M.2.HL.TZ1.5 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 5 | Adapted from | N/A |
Question
Outline the processes that occur during the first division of meiosis.
Prior to cell division, chromosomes replicate. Explain the process of DNA replication in prokaryotes.
Outline outcomes of the human genome project.
Markscheme
Remember, up to TWO “quality of construction” marks per essay.
a. (consists of) prophase, metaphase, anaphase and telophase;
b. chromosome number halved/reduced/(diploid) to haploid;
c. homologous chromosomes pair up/form a bivalent/synapsis in prophase;
d. crossing over between non-sister chromatids/chromatids of different homologues;
e. nuclear envelope breaks down (at end of prophase/start of metaphase);
f. tetrads/bivalents/homologous pairs move to/align on equator/cell centre/on metaphase plate in metaphase; (accept homologous chromosomes without pairs if pairing has already been described)
g. attachment of spindle fibres/microtubules to centromeres/kinetochores;
h. (homologous) chromosomes separate/pulled to opposite poles in anaphase;
i. nuclear envelopes reform/do not reform (because of meiosis II) in telophase;
Accept the above points in a series of annotated diagrams. Reject answers with single chromatids forming pairs in metaphase or separating or moving to opposite poles in anaphase.
Remember, up to TWO “quality of construction” marks per essay.
a. DNA replication is semi-conservative;
b. each (molecule formed) has one new strand and one from parent molecule;
c. helicase uncoils DNA;
d. helicase separates the two strands by breaking hydrogen bonds between bases; (reject unzips as an alternative to uncoils but accept as alternative to separates if breakage of hydrogen bonds is included)
e. RNA primase adds primer / primase adds (short) length of RNA;
f. DNA polymerase III binds to/starts at (RNA) primer;
g. DNA polymerase (III) adds nucleotides/bases in a 5’ → 3’ direction;
h. bases according to complementary base pairing / A–T and C–G;
i. (leading strand) built up continuously (towards the replication fork);
j. (lagging strand) built up in pieces/short lengths/Okazaki fragments;
k. DNA polymerase I removes RNA/primers and replaces them with DNA;
l. ligase seals gaps between nucleotides/fragments/makes sugar-phosphate bonds;
m. nucleoside triphosphates provide the energy to add nucleotides;
Accept the above points in annotated diagrams.
Remember, up to TWO “quality of construction” marks per essay.
a. complete human DNA/chromosomes sequenced;
b. identification of all human genes / find position/map (all) human genes;
c. find/discover protein structures/functions;
d. find evidence for evolutionary relationships/human origins/ancestors;
e. find mutations/base substitutions/single nucleotide polymorphisms;
f. find genes causing/increasing chance of/develop test for/screen for diseases;
g. develop new drugs (based on base sequences) / new gene therapies;
h. tailor medication to individual genetic variation / pharmacogenomics;
i. promote international co-operation/global endeavours;
| Date | May 2011 | Marks available | 2 | Reference code | 11M.2.HL.TZ2.2 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Compare | Question number | 2 | Adapted from | N/A |
Question
The diagram below shows two nucleotides linked together to form a dinucleotide.
Identify the chemical group labelled I.
State the type of bond labelled II.
Distinguish between the sense and antisense strands of DNA during transcription.
Compare the DNA found in prokaryotic cells and eukaryotic cells.
Markscheme
phosphate
covalent / phosphodiester
only the antisense strand is transcribed / the antisense strand is transcribed to mRNA and the sense strand is not transcribed/has the same base sequence as mRNA (with uracil instead of thymine)
To award [1], reference must be made to both strands and transcription.
Award marks for paired statements only. Answers do not need to be shown in a table format.
| Date | May 2012 | Marks available | 1 | Reference code | 12M.2.HL.TZ1.2 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Identify | Question number | 2 | Adapted from | N/A |
Question
The diagram below shows the process of transcription.
DNA replication involves a number of enzymes including DNA polymerase. Identify one other enzyme involved in DNA replication.
Explain the role of Okazaki fragments in DNA replication.
Label the sense and antisense strands.
Draw an arrow on the diagram to show where the next nucleotide will be added to the growing mRNA strand.
Markscheme
helicase / RNA primase / (DNA) ligase
DNA fragments/sections (formed) on the lagging strand;
because replication must be in the 5′ –3′ direction;
replication starts repeatedly and moves away from replication fork;
both strands clearly labelled
Check carefully whether the correct strand has been labelled if the labels are shown in helical parts of the DNA.
Reject if the sense strand label points to the mRNA.
a clearly drawn arrow pointing at the free 3′ end of the mRNA strand or to the first free nucleotide on the antisense strand to the left of the mRNA or to a nucleotide added by the candidate to the left hand end of the mRNA
| Date | May 2009 | Marks available | 3 | Reference code | 09M.2.HL.TZ1.6 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Distinguish | Question number | 6 | Adapted from | N/A |
Question
Distinguish between RNA and DNA.
Explain the process of DNA replication.
Outline how enzymes catalyse reactions.
Markscheme
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);
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.
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;
| Date | May 2009 | Marks available | 2 | Reference code | 09M.2.HL.TZ2.2 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Outline | Question number | 2 | Adapted from | N/A |
Question
Draw a labelled diagram showing two different complementary pairs of nucleotides in a molecule of DNA.
Outline the structure of nucleosomes.
Explain primary structures and tertiary structures of an enzyme.
Markscheme
The structures underlined must be labelled.
at least one nucleotide with deoxyribose linked to base and phosphate;{ Labels need not be on the same nucleotide. Do not allow sugar.
phosphate and deoxyribose linked C3 to C5;{ Position required, not label. Straight line from C4 to phosphate is acceptable. Do not penalize if the second strand is not antiparallel and the bonding is therefore incorrect on it.
(complementary) bases labelled with at least one of each of A, G, T and C correctly linked to C1;
hydrogen bonds between correct complementary bases;{ Bond numbers not required.
correct antiparallel orientation shown; (as seen by shape or orientation of sugar)
(eight) histone (proteins);
DNA wrapped around histones/nucleosome;
further histone holding these together;
Do not allow histone wrapped around DNA.
primary structure is (number and) sequence of amino acids;
joined by peptide bonds;
tertiary structure is the folding of the polypeptide/secondary structure/alpha helix;
stabilized by disulfide/ionic/hydrogen bonds/hydrophobic interactions;
tertiary structure gives three dimensional globular shape/shape of active site;
| Date | May 2009 | Marks available | 8 | Reference code | 09M.2.HL.TZ2.6 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Explain | Question number | 6 | Adapted from | N/A |
Question
Draw a labelled diagram showing the ultra-structure of a liver cell.
Distinguish between prokaryotic cells and eukaryotic cells.
Explain prokaryotic DNA replication.
Markscheme
Award [1] for each structure clearly drawn and correctly labelled. Whole cells not necessary.
(plasma) membrane – single line surrounding cytoplasm;
nucleus – with a double membrane and pore(s) shown;
mitochondria(ion) – with a double membrane, the inner one folded into internal projections, shown no larger than half the nucleus;
rough endoplasmic reticulum – multi-folded membrane with dots/small circles on surface;
Golgi apparatus – shown as a series of enclosed sacs with evidence of vesicle formation;
ribosomes – dots/small circles in cytoplasm/ribosomes on rER;
lysosome;
Award [0] if plant cell is drawn. Award [2 max] if any plant cell structure (e.g. cell wall) is present.
DNA replication is semi-conservative / each strand of DNA acts as template;
(DNA) helicase separates two strands/forms a replication fork;
new strand built / nucleotides added in a 5′ to 3′ direction;
(deoxy)nucleoside triphosphates hydrolysed to provide energy for nucleotide formation/base pairing;
on one strand DNA polymerase III builds continuous strand;
on other strand short chains of DNA/Okazaki fragments are formed;
each short chain starts with RNA primer;
added by RNA primase;
then remainder of chain of DNA built by DNA polymerase III;
DNA polymerase I removes RNA primer and replaces it by DNA;
DNA ligase joins DNA fragments together forming complete strand;
replication only occurs at a single replication fork;
Award credit for any of the above points clearly drawn and accurately labelled.
| Date | May 2010 | Marks available | 5 | Reference code | 10M.2.HL.TZ1.7 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Distinguish | Question number | 7 | Adapted from | N/A |
Question
Most of the DNA of a human cell is contained in the nucleus. Distinguish between unique and highly repetitive sequences in nuclear DNA.
Draw a labelled diagram to show four DNA nucleotides, each with a different base, linked together in two strands.
Explain the methods and aims of DNA profiling.
Markscheme
Award [1] for each pair of statements in the table and [1] for any statement below the table.
satellite DNA is repetitive;
repetitive sequences are used for profiling;
prokaryotes do not (usually) contain repetitive sequences
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;
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
| Date | November 2011 | Marks available | 8 | Reference code | 11N.2.HL.TZ0.7 |
| Level | Higher level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Explain | Question number | 7 | Adapted from | N/A |
Question
Define the terms chromosome, gene, allele and genome.
Compare the genetic material of prokaryotes and eukaryotes.
Explain the process of DNA replication.
Markscheme
chromosome: structure formed by DNA and proteins;
gene: a heritable factor that controls a specific characteristic;
allele: one specific form of a gene occupying the same gene locus as other alleles of the gene;
genome: the whole of the genetic information of an organism;
Responses do not need to be shown in a table format.
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;
hydrogen bonds between two strands are broken;
each strand of parent DNA used as template;
deoxynucleoside triphosphate provides energy;
synthesis continuous on leading strand but not continuous on lagging strand;
resulting in 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);
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/seals nicks (in sugar-phosphate backbone);
Accept any of the above points shown in a clearly annotated diagram.
| Date | November 2012 | Marks available | 8 | Reference code | 12N.2.HL.TZ0.7 |
| Level | Higher level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Explain | Question number | 7 | Adapted from | N/A |
Question
Draw a labelled diagram of the ultrastructure of a prokaryote.
Explain the process of DNA replication.
Outline how the structure of the ribosome is related to its function in translation.
Markscheme
Award any of the following clearly drawn and correctly labelled.
cell wall; (shown as a double line)
plasma membrane; (less than the width of wall) (reject inner surface of cell wall labelled as cell membrane)
nucleoid/(region containing) naked DNA (distinguished from rest of cytoplasm)
ribosome; (dots in cytoplasm)
cytoplasm;
flagella; (at least a quarter as long as the cell)
pili; (less than a quarter as long as the cell)
Award [3 max] if any specifically eukaryotic structure shown.
helicase uncoils DNA/splits DNA into two strands;
(RNA) primase adds short length of RNA/primer;
primer allows attachment of (DNA) polymerase;
DNA polymerase III copies DNA;
adds nucleotides in the 5′ to 3′ direction;
uses deoxynucleoside triphosphates/nucleotides that are free in cell;
two phosphates removed to release energy (required for the process);
(complementary base pairing of) adenine with thymine and guanine with cytosine; (reject A with T and C with G)
(leading) strand replication towards the replication fork;
short pieces of daughter DNA / Okazaki fragments (on lagging strand);
DNA polymerase I removes the RNA primers/replaces them with DNA;
(DNA) ligase joins short fragments/seals nicks;
by making sugar-phosphate bond;
translation is protein/polypeptide synthesis;
formed by (ribosomal) RNA and proteins; (both needed)
about 20nm/30nm / 80S in eukaryotes;
organized into a tertiary structure/globular shape;
a small subunit and a large one;
(three) binding sites for tRNA on/in large subunit;
A, P and E sites;
binding site for mRNA on surface/in small subunit;
two tRNA can bind at the same time;
ribosomal RNA catalyses formation of peptide bond;