Question 1
A neuron and an intestinal epithelial cell in the same individual contain the same DNA base sequence but have different structures and functions.
What accounts for this difference during epigenesis?
A.
Each cell type changes cytosine into a different base permanently.
B.
Each cell type changes the genetic code used for translation.
C.
Each cell type deletes the genes it does not need.
D.
Each cell type expresses a different pattern of genes.
Question 2
A gene codes for an enzyme that converts a colourless substrate into a dark pigment. A cell has the normal DNA sequence for the gene, but no pigment is produced.
What is the most direct explanation for the absence of the pigment?
A.
The enzyme lowers the activation energy of transcription.
B.
The gene is not expressed to make a functional enzyme.
C.
The genotype has been changed by translation.
D.
The substrate prevents inheritance of the DNA sequence.
Question 3
A human mRNA molecule has a longer poly-A tail than another mRNA coding for the same polypeptide.
What effect is this most likely to have?
A.
The DNA sequence of the gene is methylated less often.
B.
The mRNA is degraded faster by ribosomes.
C.
The mRNA is more stable and can be translated for longer.
D.
The polypeptide contains a longer chain of adenine amino acids.
Question 4
A pancreatic cell and a skin cell are sampled from the same person at the same time.
Which comparison is most accurate?
A.
Their genomes differ because each cell expresses different genes.
B.
Their genomes, transcriptomes and proteomes are all identical.
C.
Their transcriptomes and proteomes differ more than their genomes.
D.
Their proteomes are identical because all mRNA is translated equally.
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 5
A cytosine base in the promoter of a gene becomes methylated.
What is the usual consequence for the downstream gene?
A.
The gene is translated directly from methylated DNA.
B.
The gene is transcribed at a lower rate without changing the base sequence.
C.
The gene mutates because methylated cytosine can no longer pair with guanine.
D.
The gene is transcribed at a higher rate because the promoter is activated.
Question 6
A liver cell divides during tissue repair. The daughter cells continue to express liver-specific genes and remain liver cells.
What mechanism best explains this continuity of cell phenotype?
A.
RNA polymerase copies histone amino acid sequences into DNA.
B.
Most liver genes are removed during cytokinesis.
C.
Epigenetic tags are maintained through mitosis.
D.
New alleles are produced in every mitotic division.
Question 7
Monozygotic twins are used to investigate environmental effects on gene expression.
What feature makes them useful for this purpose?
A.
They express all genes in every cell at the same rate.
B.
They always have identical epigenomes throughout life.
C.
They develop from two different eggs fertilised by two different sperm.
D.
They have essentially the same genome at the start of development.
Question 8
A gene in human liver cells codes for an enzyme involved in detoxifying alcohol.
State the name of the process in which an RNA molecule is synthesized from a DNA template.
[1]
Explain how expression of this gene can affect the phenotype of a liver cell.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 9
Cells in an early embryo become progressively specialized as development proceeds.
Define differentiation.
[1]
Distinguish between an epigenetic change and a mutation.
[2]
Question 10
An enhancer sequence is located many thousands of base pairs away from the promoter of a gene, but binding of an activator protein to the enhancer increases transcription of the gene.
What explains this effect?
A.
The activator changes the amino acid sequence of RNA polymerase.
B.
The enhancer is translated into an activator protein.
C.
The enhancer replaces the promoter as the RNA polymerase binding site.
D.
DNA looping can bring the bound activator close to the promoter.
Question 11
Histone methylation is detected in nucleosomes near a gene.
What conclusion can be made from this observation alone?
A.
The methylation proves that no transcription factors can bind anywhere in the gene.
B.
The methylation must stop all transcription of the gene permanently.
C.
The methylation may activate or repress transcription depending on the histone mark.
D.
The methylation changes the nucleotide sequence of the gene.
Question 12
Exposure to air pollution is associated with altered DNA methylation patterns in cells lining the airways.
What is the most likely biological consequence?
A.
Expression of some genes involved in cell responses may change.
B.
The genetic code in airway cells is replaced by a pollution-specific code.
C.
All genes in airway cells are expressed at the same rate.
D.
New alleles for airway proteins are produced by the pollutants.
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 13
In cells of the uterine lining, oestrogen increases expression of the gene coding for the progesterone receptor.
How does oestrogen produce this effect?
A.
It acts as a nuclease that degrades progesterone receptor mRNA.
B.
It binds an intracellular receptor, and the complex regulates transcription.
C.
It binds to extracellular cellulose and opens bacterial operons.
D.
It methylates every promoter in the genome to activate transcription.
Question 14
The diagram shows regulation of transcription of a eukaryotic gene.
State the role of the promoter in transcription.
[1]
Explain how an enhancer can increase transcription of the gene.
[2]
State one way in which a repressor protein can reduce gene expression.
[1]
Question 15
Human cells contain mRNAs that persist for different lengths of time before being degraded.
State the type of enzyme that breaks down mRNA.
[1]
Explain how rapid degradation of an mRNA can reduce production of its protein.
[2]
Question 16
A liver cell divides by mitosis during tissue repair. The daughter cells remain liver cells rather than becoming unspecialized cells.
Define epigenetic inheritance.
[1]
Outline how epigenetic inheritance can maintain the liver cell phenotype after mitosis.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 17
Cells lining the airways are exposed to fine particulates and nitrogen oxides from polluted air.
State one type of epigenetic tag that may be altered by exposure to air pollution.
[1]
Explain how air pollution can change the phenotype of airway cells without causing a mutation.
[2]
Question 18
Oestrogen affects cells of the uterine lining and increases expression of the gene coding for the progesterone receptor.
State why oestrogen can enter target cells.
[1]
Explain how oestrogen can increase transcription of a target gene.
[2]
Question 19
Cultured human liver cells were exposed to a signalling molecule. After 2 hours, researchers measured mRNA abundance, protein abundance and the activity of the enzyme product for four genes.
Gene | mRNA abundance / a.u. | Protein abundance / a.u. | Enzyme activity / a.u. |
|---|---|---|---|
A | 20 | 15 | 10 |
B | 40 | 60 | 50 |
C | 90 | 85 | 5 |
D | 30 | 25 | 20 |
Identify the gene for which translation has occurred but the protein product is least likely to be functional as an enzyme.
[1]
Calculate the ratio of protein abundance to mRNA abundance for gene B.
[1]
Explain how the data support the statement that gene expression affects phenotype.
[2]
Question 20
Genome sequencing, RNA sequencing and protein analysis were carried out on a pancreatic beta cell and a skin epithelial cell from the same person.
Gene | DNA fragment in both cells | Beta RNA / a.u. | Skin RNA / a.u. | Beta protein / a.u. | Skin protein / a.u. |
|---|---|---|---|---|---|
INS | ATG CCA GAA TTT GGC | 100 | 0 | 90 | 0 |
KRT14 | GCT TTA CCG AAG TCA | 0 | 95 | 0 | 85 |
ACTB | GGA TCT AAC CCG TTT | 55 | 55 | 50 | 50 |
PCSK1 | TTC GGA TTA CAG GAC | 70 | 70 | 65 | 20 |
State which of the genome, transcriptome and proteome is expected to be most similar in the two cells.
[1]
Using the data, distinguish between the transcriptome and the proteome of the two cells.
[2]
Suggest one reason why the proteome is not always a direct copy of the transcriptome.
[1]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 21
A liger is produced from a male lion and a female tiger, whereas a tigon is produced from a male tiger and a female lion. Ligers and tigons can differ markedly in body size.
What is the best explanation for the difference between the reciprocal hybrids?
A.
The hybrid with a lion father must express every lion allele dominantly.
B.
The two hybrids always inherit different numbers of chromosomes.
C.
Parent-specific epigenetic tags retained in gametes affect growth gene expression.
D.
The direction of the cross changes the base sequence of all growth genes.
Question 22
The table compares the genome, transcriptome and proteome of three cell types taken from the same person.
Cell type | Genome similarity to other cells / % | Transcriptome (mRNAs) | Proteome (proteins) |
|---|---|---|---|
Neuron | 99.99% | 7,850 mRNAs; SNAP25, MAP2, SCN1A | 5,900 proteins; synapsin, MAP2, channel |
Muscle cell | 99.99% | 8,120 mRNAs; ACTA1, MYH7, TNNT1 | 6,300 proteins; actin, myosin, troponin |
Hepatocyte | 99.99% | 7,960 mRNAs; ALB, CYP3A4, G6PC | 6,100 proteins; albumin, CYP450 enzymes, G6Pase |
State why the genomes of the three cell types are expected to be almost identical.
[1]
Explain why the transcriptomes of the three cell types differ.
[2]
Suggest why the proteome is not always a direct copy of the transcriptome.
[1]
Question 23
Methylation can occur at DNA promoters and on histone tails in nucleosomes.
State the chemical group added during methylation.
[1]
Compare the effects of promoter methylation and histone methylation on transcription.
[3]
Question 24
During gamete formation, most epigenetic tags are removed from DNA. Some tags may remain and cause genomic imprinting.
Explain why removal of most epigenetic tags from gametes is important after fertilization.
[2]
Outline how retained tags can help explain phenotypic differences between ligers and tigons.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 25
A study compared DNA methylation patterns in monozygotic twin pairs at different ages and in different environments.
State why monozygotic twins are useful for investigating environmental effects on gene expression.
[1]
Discuss what a decrease in methylation similarity between older monozygotic twins suggests.
[2]
State one limitation of using monozygotic twin studies to investigate gene expression.
[1]
Question 26
The lac operon in Escherichia coli regulates expression of genes needed for lactose uptake and breakdown.
Explain why the lac genes are not transcribed when lactose is absent.
[2]
Explain how lactose availability changes gene expression in these bacteria.
[2]
Question 27
A reporter gene was placed downstream of different regulatory DNA sequences from a human gene. The reporter protein gives fluorescence when the gene is transcribed and translated.
Construct | Fluorescence / a.u. |
|---|---|
Promoter only | 5 |
Promoter + enhancer, TFBS deleted | 12 |
Promoter + TFBS, enhancer deleted | 28 |
Promoter + enhancer + intact TFBS | 100 |
Identify the construct that produced the highest reporter gene expression.
[1]
Using the data, describe the effect of deleting the enhancer on reporter gene expression.
[2]
Explain how an enhancer can increase transcription of a gene even when it is not immediately next to the promoter.
[2]
Question 28
Researchers compared the stability of three mRNA molecules in human cells after transcription was stopped. One mRNA had a short poly-A tail, one had a long poly-A tail and one was tested in the presence of a nuclease inhibitor.
Estimate the half-life of the mRNA with the short poly-A tail.
[1]
Compare the stability of the mRNA with a long poly-A tail and the mRNA exposed to a nuclease inhibitor.
[2]
Suggest why rapid degradation of an mRNA can be useful in regulating translation.
[1]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 29
Stem cells were induced to differentiate in culture. At three stages, researchers measured expression of genes associated with unspecialised cells, neurons and muscle cells.
Stage | Unspecialised markers / a.u. | Neuron markers / a.u. | Muscle markers / a.u. |
|---|---|---|---|
Early | 9 | 2 | 1 |
Mid | 5 | 6 | 1 |
Late | 1 | 10 | 1 |
Identify the cell type that the stem cells are most likely differentiating into by the late stage.
[1]
Describe the change in gene expression during differentiation shown in the heat map.
[2]
Explain why this is an example of epigenesis rather than a change in genotype.
[1]
Question 30
Researchers measured promoter cytosine methylation, histone methylation near the promoter and transcription rate for three genes in the same cell type.
Gene | Promoter cytosine methylation (%) | Histone methylation near promoter (arbitrary units) | Transcription rate (arbitrary units) |
|---|---|---|---|
X | 80 | 7.5 | 2 |
Y | 45 | 4.0 | 9 |
Z | 10 | 1.0 | 17 |
Identify the gene most likely to be repressed by promoter cytosine methylation.
[1]
Describe the relationship between promoter cytosine methylation and transcription rate shown in the data.
[1]
Explain how methylation can act as an epigenetic tag affecting gene expression.
[2]
Question 31
A study compared monozygotic twin pairs of different ages. Some twin pairs had lived together for most of their lives and others had lived in different environments for many years. DNA methylation divergence was measured across many gene promoters.
Describe the overall relationship between age and DNA methylation divergence in monozygotic twins.
[1]
Compare the methylation divergence of twin pairs living together and living apart.
[1]
Explain why monozygotic twins are useful for investigating environmental effects on gene expression.
[1]
Suggest one environmental factor that could contribute to the divergence shown in the data.
[1]
Question 32
Cells from the uterine lining were grown with different concentrations of oestrogen. In one treatment, an oestrogen receptor antagonist was added. Researchers measured mRNA abundance for the progesterone receptor gene.
Identify the treatment with the highest expression of the progesterone receptor gene.
[1]
Calculate the fold increase in progesterone receptor mRNA abundance in the high oestrogen treatment compared with no oestrogen.
[1]
Explain how oestrogen can act as an external factor affecting gene expression in these cells.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 33
A population of cultured cells had a methylated promoter for gene P. Some cells were allowed to divide normally, while others were treated with a drug that reduced maintenance of DNA methylation during mitosis.
Cell sample | Promoter methylation / % | gene P mRNA abundance / a.u. |
|---|---|---|
Parent cell | 85 | 2 |
Untreated daughter cells | 85 | 2 |
Drug-treated daughter cells | 30 | 8 |
Identify the evidence that epigenetic information was inherited by daughter cells in the untreated culture.
[1]
Compare gene P expression in untreated and drug-treated daughter cells.
[2]
Distinguish this form of inheritance from inheritance of a mutation.
[1]
Question 34
A study investigated placental cells from pregnant individuals living in areas with different average concentrations of fine particulate air pollution, . Researchers measured methylation of the promoter of an inflammation-related gene and the abundance of its mRNA.
exposure / g m | Promoter methylation / % | Relative mRNA abundance |
|---|---|---|
5 | 70 | 1.0 |
15 | 60 | 1.4 |
25 | 50 | 1.9 |
35 | 40 | 2.5 |
Describe the relationship between exposure and promoter methylation shown in the data.
[1]
Calculate the percentage increase in relative mRNA abundance from the lowest to the highest exposure group.
[1]
Explain how altered DNA methylation could change the phenotype of placental cells.
[2]
Evaluate one limitation of using these data as evidence that air pollution causes the change in gene expression.
[1]
Question 35
Lion and tiger hybrids differ depending on the direction of the cross. Researchers compared expression of a growth-promoting gene and a growth-limiting gene in ligers and tigons.
Hybrid | Growth-promoting gene / relative level | Growth-limiting gene / relative level | Body growth / relative level |
|---|---|---|---|
Liger | 85 | 25 | 92 |
Tigon | 40 | 70 | 58 |
Identify the hybrid showing greater growth in the data.
[1]
Compare the expression of the two growth-related genes in ligers and tigons.
[2]
Explain how removal of most, but not all, epigenetic tags from gametes can account for differences between ligers and tigons.
[2]
Question 36
A culture of Escherichia coli was grown with different sugars. Researchers recorded whether the lac repressor was bound to the operator and measured expression of genes needed for lactose uptake and breakdown.
Condition | Repressor bound to operator? | Relative lac expression / a.u. |
|---|---|---|
Lactose absent; functional operator | Yes | 0.5 |
Lactose present; functional operator | No | 10.0 |
Lactose absent; operator mutant (cannot bind repressor) | No | 10.0 |
State the condition in which the lac genes are least expressed.
[1]
Explain the effect of lactose on expression of the lac genes.
[2]
Predict the expression of lac genes in an operator mutant that cannot bind the repressor, even when lactose is absent.
[1]
Suggest one advantage to the bacterium of repressing lac gene expression when lactose is absent.
[1]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 37
A mutation reduces the activity of an enzyme involved in melanin synthesis in a mammal. Cells of the skin still contain the gene for this enzyme.
I.
Outline how expression of the enzyme gene can affect phenotype.
[2]
II.
State why the DNA sequence of a gene is not itself the phenotype.
[1]
Explain why two skin cells with the same allele for the enzyme may contain different amounts of the enzyme.
[2]
Discuss how measuring mRNA and measuring enzyme activity could give different conclusions about expression of this gene.
[2]
Question 38
A neuron and an intestinal epithelial cell are isolated from the same adult human. Both cells are alive and functioning normally.
I.
Distinguish between the genome and transcriptome of a cell.
[2]
II.
State why the two cells would usually have very similar genomes.
[1]
Explain why the neuron and intestinal epithelial cell have different proteomes.
[3]
Discuss how these differences in gene expression contribute to epigenesis.
[2]
Question 39
Oestrogen affects cells of the uterine lining during the menstrual cycle. One effect is increased expression of the gene coding for the progesterone receptor.
I.
Explain why oestrogen can act inside target cells of the uterine lining.
[2]
II.
State why only target cells respond strongly to oestrogen.
[1]
Explain how oestrogen can increase transcription of the progesterone receptor gene.
[3]
Discuss why increased progesterone receptor expression changes the future behaviour of uterine lining cells.
[1]
Question 40
A researcher inserts a reporter gene into cultured human cells. The reporter gene has a promoter and a distant enhancer. Some cells also receive a plasmid coding for a transcription factor that binds to the enhancer.
I.
Describe the role of the promoter in transcription of the reporter gene.
[1]
II.
Explain how an enhancer can increase transcription even when it is distant from the gene.
[2]
Compare the expected reporter expression in cells with and without the transcription factor plasmid.
[2]
Evaluate whether reporter protein concentration alone is sufficient evidence that the transcription factor regulates transcription.
[3]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 41
Two mRNAs, A and B, code for proteins involved in a rapid stress response in human cells. The graph shows the relative amount of each mRNA remaining after transcription is stopped experimentally.
I.
Identify which mRNA is more stable and give a reason.
[1]
II.
Explain the role of nucleases in the change shown in the graph.
[2]
Suggest how shortening of a poly-A tail could change production of the protein encoded by mRNA A.
[2]
Discuss why rapid mRNA degradation may be advantageous for proteins involved in a stress response.
[2]
Question 42
A gene involved in cell adhesion is expressed in normal epithelial cells but is weakly expressed in some tumour cells. Analysis shows increased methylation of cytosines in the promoter and altered methylation of histone tails near the gene.
I.
State what is meant by an epigenetic tag.
[1]
II.
Explain how methylation of cytosines in the promoter may reduce expression of the cell adhesion gene.
[2]
Explain why methylated cytosine in the promoter is not a mutation.
[2]
Discuss why histone methylation is more difficult to predict than promoter cytosine methylation in this case.
[2]
Question 43
A population of liver cells divides repeatedly during tissue repair. The daughter cells continue to express liver-specific genes. In a separate study, some epigenetic tags are detected in gametes and in early embryos.
I.
Define epigenetic inheritance.
[1]
II.
Explain how epigenetic inheritance helps liver cells remain specialised after mitosis.
[2]
Compare epigenetic inheritance with inheritance of a mutation.
[2]
Evaluate the claim that epigenetic inheritance allows organisms to deliberately pass useful acquired characteristics to their offspring.
[2]
Question 44
Researchers compared cells from people exposed to low and high levels of fine particulate air pollution. They measured DNA methylation at promoters of genes involved in inflammation and measured mRNA from the same genes.
I.
Outline how air pollution can affect gene expression.
[2]
II.
State why a change in mRNA abundance is evidence for a change in gene expression.
[1]
Explain why altered gene expression can affect phenotype even if the DNA base sequence is unchanged.
[2]
Evaluate the use of this study as evidence that air pollution causes epigenetic changes in humans.
[3]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 45
Lion and tiger hybrids can differ in size depending on the direction of the cross. A liger has a male lion parent and a female tiger parent. A tigon has a male tiger parent and a female lion parent.
I.
State why most epigenetic tags are removed from gametes.
[1]
II.
Explain the consequence of some epigenetic tags not being removed from ovum and sperm.
[2]
Explain how genomic imprinting can lead to different phenotypes in ligers and tigons.
[3]
Distinguish imprinting from a simple Mendelian dominant-recessive explanation of hybrid size.
[1]
Question 46
The lac operon allows Escherichia coli to adjust gene expression according to lactose availability.
I.
State what is meant by an operon.
[1]
II.
Explain the role of the repressor when lactose is absent.
[2]
Explain how lactose changes expression of the lac genes.
[3]
Compare the lac operon response with oestrogen regulation of gene expression in human uterine cells.
[2]
Question 47
A longitudinal study follows monozygotic and dizygotic twin pairs from birth to age 60. The study compares methylation patterns and expression of genes associated with asthma in airway cells.
I.
Explain why monozygotic twins are useful for investigating environmental effects on gene expression.
[2]
II.
State why dizygotic twins are included as a comparison group.
[1]
Analyse the expected trend in methylation similarity with age in monozygotic twins living in different environments.
[2]
Discuss whether finding different asthma-related transcriptomes in monozygotic twins proves that asthma is not influenced by genes.
[3]
Question 48
A single genotype of a plant species can develop broad leaves in shade and narrow leaves in bright, dry environments. Researchers find differences in transcription factors, mRNA stability and DNA methylation between the two leaf forms.
I.
Define phenotypic plasticity in this context.
[1]
II.
Explain how transcription factors could contribute to the two leaf forms.
[2]
Compare regulation by mRNA stability with regulation by DNA methylation.
[3]
Evaluate the conclusion that the broad-leaf and narrow-leaf forms must be caused by different alleles.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
The Ultimate All-in-One
IB Platform
All content on this website has been developed independently from and is not endorsed by the International Baccalaureate Organization. International Baccalaureate and IB are registered trademarks owned by the International Baccalaureate Organization.