A2.1 Origins of cells
Practice exam-style IB Biology questions for Origins of cells, aligned with the syllabus and grouped by topic.
Question 1
What feature of the early Earth allowed more ultraviolet radiation to reach the surface than reaches the surface today?
A.
A lower concentration of methane than today
B.
A thick layer of photosynthetic microorganisms
C.
A lack of free oxygen and therefore little ozone
D.
A high concentration of atmospheric ozone
Question 2
What is the best reason for considering cells to be the smallest units of self-sustaining life?
A.
Cells are always visible with a light microscope.
B.
Cells are made only from organic compounds.
C.
Cells contain mitochondria that release energy.
D.
Cells can maintain internal organization using matter and energy.
Question 3
What property of fatty acids allows them to form vesicles in water?
A.
They contain a base sequence that can be copied.
B.
They are fully hydrophilic along the entire molecule.
C.
They are inorganic catalysts at high temperature.
D.
They are amphipathic, with hydrophilic and hydrophobic regions.
Question 4
What provides evidence for a last universal common ancestor of all living organisms?
A.
All organisms contain chloroplasts.
B.
The genetic code is nearly universal.
C.
All organisms have identical cell walls.
D.
The first cells left abundant body fossils.
Question 5
What is the significance of compartmentalization for the origin of cells?
A.
It proves that vesicles are living organisms.
B.
It requires oxygen-dependent respiration.
C.
It eliminates the need for any genetic material.
D.
It allows internal chemistry to differ from the external environment.
Question 6
Viruses contain genetic material and can evolve.
State one feature of viruses that is life-like.
[1]
Explain why viruses are usually considered non-living.
[1]
Question 7
Define LUCA.
[1]
State why LUCA was not necessarily the first living cell.
[1]
Question 8
Which requirement for the origin of the first cells is most directly described by the spontaneous organization of amphipathic molecules into larger structures?
A.
Self-assembly
B.
Self-replication
C.
Catalysis
D.
Heredity
Question 9
What conclusion is most strongly supported by the Miller–Urey experiment?
A.
Living cells can form rapidly from amino acids.
B.
Hydrothermal vents were the only sites where life could originate.
C.
Organic compounds can form from simpler chemicals under some early-Earth-like conditions.
D.
DNA was the first genetic material in protocells.
Question 10
Why is RNA considered a plausible first genetic material?
A.
RNA is found only in viruses, not in cells.
B.
RNA is more chemically stable than DNA and cannot fold.
C.
RNA is made only of amino acids and forms enzymes.
D.
RNA can store sequence information and some RNA molecules can catalyse reactions.
Question 11
What type of evidence can provide a minimum age for life when microbial activity is the most plausible explanation for a rock structure?
A.
A stromatolite-like structure in an ancient rock
B.
A laboratory vesicle formed from fatty acids
C.
A low concentration of ozone in the modern atmosphere
D.
A modern viral capsid sequence
Question 12
Which statement best distinguishes a virus from a self-sustaining cell?
A.
A virus maintains homeostasis by active transport.
B.
A virus always contains ribosomes and cytoplasm.
C.
A virus contains no genetic material.
D.
A virus lacks independent metabolism and replicates only in host cells.
Question 13
What was a major limitation of the Miller–Urey experiment?
A.
It proved that early Earth had the same atmosphere as today.
B.
It used no energy source in the apparatus.
C.
It produced amino acids but not living cells or genes.
D.
It showed that carbon compounds cannot form without enzymes.
Question 14
State one atmospheric condition on early Earth that differed from present-day Earth.
[1]
Outline how this condition could have favoured pre-biotic chemical reactions.
[1]
Question 15
Outline four requirements that had to be met for the evolution of the first cells.
Question 16
Explain how fatty acids can spontaneously form vesicles in water.
Question 17
Explain how the genetic code provides evidence for a last universal common ancestor.
Question 18
Distinguish between the origin-of-cells hypothesis and the discredited idea of spontaneous generation.
Question 19
Outline how carbon dioxide and methane could have influenced conditions on early Earth relevant to origins of cells.
Question 20
Explain why DNA is less likely than RNA to have been the first genetic material, even though DNA is the main genetic material in modern cells.
Question 21
A model estimates surface ultraviolet radiation reaching early Earth under different atmospheric oxygen concentrations.
Describe the effect of increasing oxygen concentration on ultraviolet radiation reaching the surface.
[1]
Explain the role of ozone in this trend.
[1]
Suggest why higher ultraviolet radiation could have both favoured and limited pre-biotic chemistry.
[1]
Question 22
Why are alkaline hydrothermal vents considered plausible sites for early cell evolution?
A.
They contain modern eukaryotic organelles preserved in rock.
B.
They prevent all mineral precipitation from occurring.
C.
They provide chemical gradients, mineral surfaces and porous compartments.
D.
They provide oxygen-rich air spaces and intense visible light.
Question 23
Why is heredity necessary before protocell populations can evolve by natural selection?
A.
Selection prevents molecules from self-assembling.
B.
Selection requires oxygen to form an ozone layer.
C.
Selection occurs only when all variants are genetically identical.
D.
Selection requires favourable variants to be passed to descendants.
Question 24
What modern cellular feature is evidence that RNA can have catalytic activity?
A.
Phospholipids in membranes catalyse codon recognition.
B.
RNA in the ribosome catalyses peptide bond formation.
C.
Cellulose in cell walls catalyses transcription.
D.
DNA in chromosomes catalyses ATP hydrolysis.
Question 25
What is a molecular clock used to estimate?
A.
The exact gas mixture used in the Miller–Urey experiment
B.
The temperature of a hydrothermal vent using isotope ratios only
C.
The rate at which fatty acids form vesicles in water
D.
The time since lineages diverged using accumulated sequence differences
Question 26
Why might other early forms of life not be represented among organisms alive today?
A.
They may have become extinct through competition with LUCA or its descendants.
B.
They could not have varied genetically.
C.
They all necessarily lacked carbon compounds.
D.
They must have evolved after modern animals appeared.
Question 27
Describe the role of the electrical spark in the Miller–Urey experiment.
[1]
State one organic product formed in the experiment.
[1]
Evaluate the extent to which the experiment supports hypotheses for the origin of life.
[1]
Question 28
State what is meant by a ribozyme.
[1]
Explain two reasons why RNA is a plausible first genetic material.
[1]
Question 29
Outline two approaches used to estimate dates for the first living cells or LUCA.
Question 30
Suggest why conserved sequences from genomic analysis support the hypothesis that LUCA lived near hydrothermal vents.
Question 31
A protocell model contains fatty-acid vesicles enclosing short RNA molecules.
Explain why enclosing RNA in vesicles could make protocells more likely to evolve by natural selection.
[1]
Question 32
Explain how porous mineral structures at alkaline hydrothermal vents could have acted as intermediate stages before fully developed cell membranes.
Question 33
Researchers repeated a Miller–Urey-type experiment using three gas mixtures and measured the relative yield of amino acids after the same time.
Identify the gas mixture with the highest amino acid yield.
[1]
Describe the relationship between reducing conditions and amino acid yield.
[1]
Suggest one reason why these results do not prove the actual composition of the early atmosphere.
[1]
Question 34
Fatty acids were mixed with buffered water at different pH values. The percentage of lipids observed in vesicles was recorded.
State the pH range in which vesicle formation is greatest.
[1]
Describe the trend in vesicle formation as pH moves away from this range.
[1]
Suggest why pH affects formation of fatty-acid vesicles.
[1]
Question 35
A rock formation has been proposed as evidence for early microbial life. The table summarizes three observations.
| Observation | Possible interpretation |
|---|---|
| Fine laminated domes resembling stromatolites | Layered sedimentary structures; could form by microbial mats or by non-living sediment processes |
| Carbon isotope values: δ13C = −28‰ | Strong enrichment in carbon-12 compared with typical marine carbonate |
| Recrystallized mineral grains and cross-cutting veins | Later heating and fluid movement altered parts of the rock |
Identify the observation that most directly supports biological activity.
[1]
Identify one observation that weakens the claim.
[1]
Evaluate whether the formation should be accepted as definite evidence of early life.
[1]
Question 36
Fluorescent molecules were placed outside fatty-acid vesicles. Their concentration inside vesicles was measured over time.
Describe the change in internal fluorescent molecule concentration over time.
[1]
Suggest what this indicates about the vesicle membrane.
[1]
Explain why partial permeability would be useful in protocells.
[1]
Question 37
A computer model simulated protocells with different combinations of three features: compartmentalization, RNA copying and catalysis. Persistence after many cycles was recorded.
Identify the combination with the greatest persistence.
[1]
Describe the effect of having compartmentalization without RNA copying.
[1]
Suggest why all three features together increase persistence.
[1]
Question 38
Carbon isotope ratios in some ancient rocks are interpreted as evidence consistent with early life.
State what is meant by an isotope.
[1]
Suggest why isotope evidence alone may be insufficient to prove early life.
[1]
Question 39
Several RNA sequences were tested for two properties: percentage copied after one hour and rate of catalysis of a model reaction.
| RNA sequence | Copied after 1 h / % | Catalytic rate / a.u. |
|---|---|---|
| RNA-A | 88 | 0.9 |
| RNA-B | 24 | 6.4 |
| RNA-C | 41 | 3.2 |
| RNA-D | 76 | 5.8 |
Identify the RNA sequence most likely to increase in frequency in a protocell population.
[1]
Explain your choice using both data columns.
[1]
Suggest why a sequence with high catalytic activity but very low copying percentage may not persist over generations.
[1]
Question 40
Genomes from early-branching bacteria and archaea were compared. The presence of selected conserved genes is shown.
| Gene / function | Aquificota (B) | Thermotogota (B) | Chloroflexota (B) | Methanobacteria (A) | Thermoproteota (A) | Archaeoglobia (A) |
|---|---|---|---|---|---|---|
| CODH/ACS; anaerobic CO₂ fixation | 1 | 1 | 0 | 1 | 1 | 1 |
| NiFe hydrogenase; H₂ metabolism | 1 | 1 | 1 | 1 | 1 | 1 |
| ATP citrate lyase; rTCA CO₂ fixation | 1 | 0 | 1 | 0 | 1 | 0 |
| psbA; oxygenic photosynthesis | 0 | 0 | 0 | 0 | 0 | 0 |
| G3P acyltransferase; ester lipids | 1 | 1 | 1 | 0 | 0 | 0 |
| GGGP synthase; ether lipids | 0 | 0 | 0 | 1 | 1 | 1 |
Identify the gene most likely to have been present in LUCA.
[1]
Give two criteria from the data that support this inference.
[1]
Suggest how the inferred gene set supports a hydrothermal vent origin for LUCA.
[1]
Question 41
A comparison of codon assignments in four organisms is shown.
| mRNA codon | Bacterium | Archaeon | Plant | Animal mito |
|---|---|---|---|---|
| AUG | Met | Met | Met | Met |
| UUU | Phe | Phe | Phe | Phe |
| GCU | Ala | Ala | Ala | Ala |
| GAA | Glu | Glu | Glu | Glu |
| UGG | Trp | Trp | Trp | Trp |
| UAC | Tyr | Tyr | Tyr | Tyr |
| UGA | Stop | Stop | Stop | Trp |
State the main pattern shown by the codon assignments.
[1]
Explain how this pattern supports LUCA.
[1]
Suggest why minor exceptions do not reject the LUCA hypothesis.
[1]
Question 42
Describe the structure of a fatty-acid vesicle.
[1]
Explain the importance of vesicle formation in hypotheses for the origin of cells.
[1]
Question 43
Define LUCA and state one type of evidence for it.
[1]
Discuss evidence for a last universal common ancestor and the possibility that other early life forms existed.
[1]
Question 44
Three methods were used to estimate dates relevant to early life: stromatolite fossils, carbon isotope ratios and molecular clocks.
| Method | Evidence | Age / Ga ago | Main strength | Main limitation |
|---|---|---|---|---|
| Stromatolite fossils | Layered microbial mats in rock | 3.43–3.70 | Physical structures in datable strata | Oldest known fossils may post-date earlier cells |
| Carbon isotope ratios | Low ¹³C/¹²C in ancient carbon | 3.70–3.95 | Can detect metabolism without body fossils | Abiotic processes can give similar ratios |
| Molecular clocks | DNA/protein sequence divergence | 3.80–4.20 | Can infer dates before fossils are found | Depends on calibration and mutation-rate models |
Identify which method provides a minimum age rather than a direct origin date.
[1]
Compare one strength of fossil evidence with one strength of molecular-clock evidence.
[1]
Evaluate why estimates for the first cells remain uncertain.
[1]
Question 45
Outline the main features of the Miller–Urey experiment.
[1]
Evaluate the contribution of the Miller–Urey experiment to hypotheses for the origin of cells.
[1]
Question 46
Outline why the spontaneous origin of cells is difficult to explain using cell theory.
[1]
Discuss how catalysis, self-replication, self-assembly and compartmentalization could have contributed to the evolution of the first cells.
[1]
Question 47
Outline two properties of RNA relevant to early genetic systems.
[1]
Compare and contrast RNA and DNA as possible first genetic materials.
[1]
Question 48
Outline two methods used to estimate dates for early life or LUCA.
[1]
Evaluate why dating the first living cells remains uncertain despite multiple lines of evidence.
[1]
Question 49
Describe two features of hydrothermal vents that could support early cell evolution.
[1]
Evaluate evidence for LUCA, or populations close to LUCA, evolving in the vicinity of hydrothermal vents.
[1]
Question 50
Outline early Earth conditions relevant to pre-biotic chemistry.
[1]
Discuss how non-living chemistry could progress towards cell-like systems capable of evolution by natural selection.
[1]
The Fast Track To Your
Best IB Coursework & College Essays
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.