Question 1
A mitochondrion contains DNA and can release energy from substrates. Why is it not considered the smallest unit of self-sustaining life?
A.
It has a membrane, so it must be non-living.
B.
It contains no genetic material of its own.
C.
It cannot maintain and reproduce itself independently of a cell.
D.
It cannot use chemical energy in reactions.
Question 2
What combination of conditions on early Earth would have favoured the pre-biotic formation of carbon compounds?
A.
Low methane, low and temperatures below freezing
B.
High ozone, low volcanic activity and no electrical storms
C.
Low free , little ozone and high ultraviolet radiation
D.
High free , a thick ozone layer and low ultraviolet radiation
Question 3
Early Earth is described as having allowed some chemical processes that do not now occur readily. What is the best explanation for this difference?
A.
Modern oxygen and ozone conditions reduce many pre-biotic reaction pathways.
B.
Modern lightning has less electrical energy than early lightning.
C.
Modern carbon dioxide levels are too high for carbon compounds to form.
D.
Modern oceans contain no dissolved inorganic ions for reactions.
Question 4
What feature is a reason that viruses are usually classified as non-living?
A.
They lack their own metabolism outside host cells.
B.
They are always smaller than bacterial ribosomes.
C.
They contain nucleic acid rather than protein.
D.
They evolve too rapidly to be organisms.
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Question 5
What is a valid conclusion from the Miller-Urey experiment?
A.
The exact atmospheric composition of early Earth is now certain.
B.
Amino acids can form from simpler chemicals under some simulated early-Earth conditions.
C.
DNA genomes must have existed before amino acids formed.
D.
Living cells can form spontaneously when methane and ammonia are mixed.
Question 6
What is the importance of compartmentalization in models of the first cells?
A.
It allows internal chemistry to differ from the external environment.
B.
It prevents any exchange of matter with the surroundings.
C.
It causes all enclosed molecules to replicate with perfect fidelity.
D.
It proves that a vesicle has a DNA genome and enzymes.
Question 7
What observation provides evidence for a last universal common ancestor?
A.
The earliest organisms left complete body fossils.
B.
All organisms use cellulose as their main energy store.
C.
All organisms have identical chromosome numbers.
D.
The genetic code is nearly universal among living organisms.
Question 8
A model of early protocells includes molecules that copy their own sequence, mineral surfaces that accelerate reactions, and lipid boundaries around reaction mixtures. What required feature of early cell evolution is still missing from this description?
A.
Self-assembly
B.
Catalysis
C.
Compartmentalization
D.
Self-replication
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Question 9
Why can fatty acids spontaneously form vesicles in water?
A.
Their covalent bonds are broken by water to form protein coats.
B.
Their hydrophilic chains face inward and their hydrophobic heads face water.
C.
Their amphipathic structure causes hydrophobic regions to be shielded from water.
D.
Their charged bases pair to form a double helix membrane.
Question 10
What property makes RNA a plausible first genetic material rather than DNA?
A.
RNA cannot fold into shapes, so it is copied without variation.
B.
RNA contains amino acids that form peptide bonds in its backbone.
C.
RNA is more chemically stable than DNA for long-term storage.
D.
RNA can store sequence information and some RNA molecules catalyse reactions.
Question 11
Why are alkaline hydrothermal vents considered plausible sites for the evolution of populations close to LUCA?
A.
They prevent all mineral precipitation, preserving only soft tissues.
B.
They contain modern eukaryotic cells that can turn directly into protocells.
C.
They provide mineral surfaces, chemical gradients and reduced compounds such as hydrogen.
D.
They provide abundant free oxygen and a protective ozone layer.
Question 12
Conditions on pre-biotic Earth differed from conditions on Earth today.
State one feature of the early atmosphere that allowed more ultraviolet radiation to reach the surface.
[1]
Explain how early Earth conditions could have promoted the pre-biotic formation of carbon compounds.
[2]
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Question 13
Viruses contain genetic material and can evolve, but they are usually not classified as living organisms.
State why a cell is regarded as the smallest unit of self-sustaining life.
[1]
Outline two reasons why viruses are considered non-living.
[2]
Question 14
Fatty acids can coalesce in water to form vesicles.
Identify the property of fatty acids that allows them to form membrane-like structures in water.
[1]
Explain why fatty acids form spherical bilayer vesicles in water.
[2]
Outline why vesicle formation was important in the evolution of cells.
[1]
Question 15
Polymerization is considered an important step in the transition from non-living chemistry to cell-like systems.
Outline why polymerization could have contributed to the origin of cells.
[2]
State one example of an emergent property of a polymer relevant to early life.
[1]
Question 16
The figure shows a model comparing selected conditions on pre-biotic Earth with present-day Earth.
Condition | Pre-biotic Earth / relative level | Present-day Earth / relative level |
|---|---|---|
Free oxygen in atmosphere | very low | high |
Atmospheric ozone | very low | high |
Ultraviolet radiation at surface | high | low |
Identify one condition in the model that would have increased the energy available for pre-biotic chemical reactions.
[1]
Explain how the concentration of free oxygen affected ultraviolet radiation reaching the surface of early Earth.
[2]
Suggest one reason why the same pre-biotic formation of carbon compounds is less likely under present-day surface conditions.
[1]
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Question 17
A biologist compared four biological entities using criteria associated with self-sustaining life.
Entity | Typical size / m | Cytoplasm present? | Genetic material present? | Independent metabolism? | Independent reproduction? |
|---|---|---|---|---|---|
Virus | 0.1 | No | Yes | No | No |
Mitochondrion | 1.0 | No | Yes | No | No |
Bacterial cell | 2.0 | Yes | Yes | Yes | Yes |
Amoeba | 100 | Yes | Yes | Yes | Yes |
State which entity in the table is the smallest unit of self-sustaining life.
[1]
Using the data, distinguish between the bacterial cell and the virus as living or non-living entities.
[2]
Explain why an isolated mitochondrion is not classified as self-sustaining life, despite containing genetic material.
[1]
Question 18
A very old rock contains layered structures similar to stromatolites, but the rock has been altered by heat and pressure. Carbon isotope ratios in the same rock are consistent with biological activity.
Observation | What was found | Main caveat |
|---|---|---|
Layered structures | Laminae resembling stromatolites were present in the rock | Heat and pressure can deform rock and produce stromatolite-like patterns without life |
Carbon isotopes | Carbon isotope ratios were in the range expected for biological activity | Metamorphism can alter isotope ratios, so the signal is not definitive |
A.
The rock proves LUCA lived after the stromatolite-like structures formed.
B.
The rock disproves biological activity because all isotope ratios are abiotic.
C.
The rock proves the exact date when the first cell divided.
D.
The rock gives possible evidence for early life, but the conclusion is uncertain.
Question 19
Explaining the origin of the first cells is challenging because modern cells are highly complex.
State the part of cell theory that creates a problem for explaining the origin of the first cells.
[1]
Explain why catalysis and self-replication were necessary requirements for the evolution of the first cells.
[2]
Suggest why origin-of-cell hypotheses are difficult to test directly.
[1]
Question 20
A simplified apparatus based on the Miller–Urey experiment is shown.
State the purpose of the electrical sparks in the apparatus.
[1]
State one type of biologically relevant product detected in the collection trap.
[1]
Evaluate the significance of the Miller–Urey experiment for hypotheses about the origin of cells.
[2]
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Question 21
RNA is often proposed as the first genetic material in protocells.
Outline two properties of RNA that support its proposed early role.
[2]
Explain why the existence of ribozymes in modern cells supports the RNA-world hypothesis.
[2]
Question 22
All living organisms share many molecular features, including a nearly universal genetic code.
State what is meant by LUCA.
[1]
Explain why the nearly universal genetic code is evidence for LUCA.
[2]
Suggest why LUCA may not have been the only form of early life.
[1]
Question 23
Several approaches are used to estimate dates for the first living cells and for LUCA.
State why a stromatolite-like structure in an ancient rock can provide only a minimum age for life.
[1]
Outline one limitation of using very ancient rocks to date the first living cells.
[1]
Compare carbon isotope evidence and molecular clock evidence as approaches for dating early life.
[2]
Question 24
Hydrothermal vents have been proposed as environments where populations close to LUCA may have evolved.
State two features of hydrothermal vents that make them plausible sites for early cell evolution.
[2]
Explain how genomic analysis can support the hypothesis that LUCA evolved near hydrothermal vents.
[2]
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Question 25
A Miller-Urey-type apparatus was run with different gas mixtures and energy sources. Organic products were measured after several days.
Gas mixture | Energy source | Organic yield / mg | Amino acid types / number |
|---|---|---|---|
vapour | none | 0.1 | 0 |
vapour | electrical sparks | 8.2 | 6 |
vapour | none | 0.0 | 0 |
vapour | electrical sparks | 1.3 | 2 |
State the role of the condenser in the apparatus.
[1]
Describe the effect of electrical sparks on the formation of organic products in the experiment.
[1]
Explain why the results support the possibility of pre-biotic formation of carbon compounds.
[2]
State one limitation of using this experiment as evidence for the actual origin of life on Earth.
[1]
Question 26
Fatty acids were mixed with water under different conditions and observed by microscopy.
Identify the condition in which vesicle formation was greatest.
[1]
Explain why fatty acids can self-assemble into spherical bilayers in water.
[2]
Suggest why the formation of vesicles was important in the origin of cells.
[1]
Question 27
The table compares properties of RNA, DNA and protein relevant to hypotheses about the first genetic material.
Feature | RNA | DNA | Protein |
|---|---|---|---|
Heritable information in base sequence | Yes | Yes | No |
Can be copied by complementary base pairing | Yes | Yes | No |
Catalytic role in cells | rRNA catalyses peptide bond formation | None | Many enzymes |
Using the table, state one property shared by RNA and DNA that is needed for heredity.
[1]
Explain why RNA is considered a plausible first genetic material rather than protein.
[2]
State one piece of evidence from modern cells that supports the RNA-world hypothesis.
[1]
Question 28
Researchers compared the genetic code and selected genes in bacteria, archaea and eukaryotes.
Type | Feature | Bacteria | Archaea | Eukaryotes | Note |
|---|---|---|---|---|---|
Codon | UUU | Phe | Phe | Phe | |
Codon | AUG | Met | Met | Met | |
Codon | GAA | Glu | Glu | Glu | |
Codon | GGC | Gly | Gly | Gly | |
Codon | UGA | Stop | Stop | Stop | rare mitochondrial Trp |
Gene | small-subunit rRNA gene | present | present | present | |
Gene | RNA polymerase beta subunit gene | present | present | present | |
Gene | ATP synthase beta subunit gene | present | present | present |
State the evidence in the stimulus that supports a last universal common ancestor.
[1]
Explain why a nearly universal genetic code is stronger evidence for common ancestry than for independent origins in each domain.
[2]
Suggest why the presence of minor exceptions to the genetic code does not falsify the hypothesis of LUCA.
[1]
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Question 29
A simulation compared the formation and concentration of carbon compounds in different pre-biotic environments.
Identify the environment in which carbon compounds became most concentrated in the simulation.
[1]
Explain why evaporation could increase the likelihood of further pre-biotic reactions.
[2]
Suggest why pre-biotic formation of carbon compounds may have occurred in localized settings rather than uniformly across Earth.
[1]
Question 30
For protocells to evolve by natural selection, their molecular systems would have needed heredity.
State one requirement, other than heredity, for protocells to evolve by natural selection.
[1]
Explain why heredity is essential for natural selection in early cell-like systems.
[2]
Question 31
Evidence from ancient seafloor deposits and from genomes has been used to evaluate hydrothermal vents as possible settings for the evolution of LUCA.
State one type of fossil evidence from hydrothermal vent environments relevant to the origin of cells.
[1]
Explain how porous minerals at alkaline hydrothermal vents could have acted as intermediate stages before fully developed cell membranes.
[2]
Identify one reason why the hydrothermal vent hypothesis remains uncertain.
[1]
Question 32
A model was used to test which combinations of properties allow protocell-like systems to persist over repeated cycles of growth and division.
System | Information copying | Compartmentalization | Persistence after 10 cycles / % |
|---|---|---|---|
A | No | Yes | 18 |
B | Yes | Yes | 86 |
C | Yes | No | 54 |
Identify the property missing from the system with the lowest persistence.
[1]
Explain why compartmentalization would increase persistence of a protocell-like system.
[2]
Suggest why the spontaneous origin of cells remains difficult to test scientifically, even with models such as this.
[2]
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Question 33
Several lines of evidence have been used to estimate the timing of the first living cells and LUCA.
Evidence line | Age / Ga | Interpretation / limitation |
|---|---|---|
Microfossils in sedimentary rock | 3.5 | Cell-like remains preserved in rock |
Stromatolite-like layered structures | 3.5 | Layered forms can also arise without life; rocks may be altered |
Carbon isotope ratios in carbonaceous rock | 3.8 | -depleted relative to |
First living cells (inferred) | 3.9 | Estimated from geochemical evidence |
LUCA (inferred) | 3.5 | Estimated from molecular-clock analysis |
Identify the type of evidence in the stimulus that gives a minimum age for life rather than an exact origin date.
[1]
Explain why stromatolite-like structures can be difficult to interpret as evidence for early life.
[2]
Suggest why carbon isotope ratios are described as evidence consistent with life rather than proof of life on their own.
[1]
State the relationship between the dates of the first living cells and LUCA.
[1]
Question 34
Evidence from ancient seafloor deposits and genomic analyses has been used to infer possible environments for LUCA or populations close to LUCA.
State one feature of hydrothermal vents shown in the stimulus that could have provided energy for early metabolism.
[1]
Explain how porous mineral structures at alkaline hydrothermal vents could have contributed to the origin of cells.
[2]
Using both types of evidence, evaluate the hypothesis that LUCA evolved near hydrothermal vents.
[2]
Question 35
A computer model investigated competition between early cell lineages with different genetic codes. One lineage had the code inferred to be ancestral to all living organisms.
State what LUCA represents in relation to organisms alive today.
[1]
Using the graph, suggest why the existence of LUCA does not mean it was the first living cell.
[1]
Explain why descendants of LUCA may have outcompeted other early forms of life.
[2]
Question 36
A researcher models possible pre-biotic environments on early Earth and compares them with present-day surface conditions.
The model includes atmospheric composition and sources of energy.
I.
State one atmospheric condition on early Earth that made pre-biotic carbon chemistry more likely than it is today.
[1]
II.
Explain how this condition could contribute to the spontaneous formation of carbon compounds.
[2]
Explain how higher concentrations of and could have affected the temperature of early Earth despite the young Sun being less bright.
[2]
Discuss why carbon compounds may have formed in localized environments rather than uniformly across the early Earth.
[2]
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Question 37
Some infectious particles contain nucleic acid and evolve over time, but they are usually not classified as living organisms.
Living systems are described as self-sustaining.
I.
Define self-sustaining life.
[1]
II.
Explain why a cell is considered the smallest unit of self-sustaining life.
[2]
Compare a mitochondrion with a whole bacterial cell as evidence that organelles are not self-sustaining life.
[2]
Discuss why viruses are considered non-living despite having genetic material and being able to evolve.
[2]
Question 38
Fatty acids added to water can coalesce into microscopic vesicles bounded by spherical bilayers.
The fatty acids have hydrophilic and hydrophobic regions.
I.
Define amphipathic molecule.
[1]
II.
Explain why amphipathic fatty acids form bilayers in water.
[2]
Explain why bilayers tend to close into spherical vesicles rather than remaining as open sheets.
[2]
Discuss why vesicle formation is important in hypotheses about the first cells.
[2]
Question 39
Researchers modelled protocells containing different RNA sequences. The protocells were supplied with fatty acids and monomers, then transferred repeatedly to fresh medium.
Describe the change in frequency of protocells containing RNA that catalyses membrane growth.
[1]
Explain how the model links RNA to natural selection in protocells.
[2]
Discuss whether these protocells should be considered living cells.
[2]
Question 40
Cell theory states that new cells arise from pre-existing cells, yet the first cells must have originated from non-living matter.
The origin of the first cells is difficult to explain using observations of modern cells.
I.
State the aspect of cell theory that creates a problem for explaining the origin of the first cells.
[1]
II.
Explain why this does not make hypotheses about the origin of cells unscientific.
[2]
Explain why catalysis and self-replication would both have been necessary requirements for the evolution of the first cells.
[2]
Explain how self-assembly and compartmentalization together could have produced systems on which natural selection could act.
[3]
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Question 41
A modified Miller-Urey apparatus is used to test whether organic products form from simple gases under simulated early Earth conditions.
The apparatus contains gases, water, a spark discharge and a condenser.
I.
Identify the early Earth energy source represented by the spark discharge.
[1]
II.
Explain the role of the condenser and collection trap in the experiment.
[2]
Explain how the detection of amino acids in the trap supports hypotheses about the origin of carbon compounds.
[2]
Evaluate the Miller-Urey experiment as evidence for the origin of life on Earth.
[3]
Question 42
The RNA-world hypothesis proposes that RNA had a central role before DNA genomes and protein enzymes became dominant.
RNA has properties relevant to both heredity and catalysis.
I.
State one property of RNA that allows it to act as genetic material.
[1]
II.
Explain how RNA can also act as a catalyst.
[2]
Compare RNA and DNA as candidates for the first genetic material.
[2]
Discuss how RNA-containing protocells could evolve by natural selection.
[3]
Question 43
Comparative studies show that most organisms use nearly the same genetic code and share genes involved in translation and basic metabolism.
The same codons usually specify the same amino acids in very different organisms.
I.
Define genetic code.
[1]
II.
Explain why a nearly universal genetic code is evidence for LUCA.
[2]
Explain how shared genes across all organisms provide further evidence for LUCA.
[2]
Evaluate the statement: LUCA was the first living cell on Earth.
[2]
Question 44
Hydrothermal vent systems have been proposed as plausible environments for the evolution of LUCA or populations close to LUCA.
Hydrothermal vents provide unusual physical and chemical conditions.
I.
Define hydrothermal vent.
[1]
II.
Explain why hydrothermal vents are plausible sites for early metabolism.
[2]
Explain how porous alkaline vent structures could have contributed to compartmentalization before modern cell membranes evolved.
[2]
Discuss how fossil and genomic evidence together support the hydrothermal vent hypothesis for LUCA.
[3]
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Question 45
The tree of life reconstructed from living organisms represents surviving lineages. It may not include all forms of early life that once existed.
LUCA is inferred from features shared by all living organisms.
I.
State what LUCA means.
[1]
II.
Explain why LUCA is inferred to have had translation machinery.
[2]
Discuss why the existence of LUCA does not exclude earlier or alternative forms of life.
[2]
Discuss how competition could have caused descendants of LUCA to replace other early forms of life.
[3]
Question 46
Scientists use several approaches to estimate when the first living cells and LUCA existed. Each approach has strengths and limitations.
Evidence line | Example result / age | What it indicates | Main limitation |
|---|---|---|---|
Layered stromatolite-like rock | 3.48 Ga | Possible microbial mat structures | May have abiotic look-alikes; dates the rock, so life must be older if biological |
Ancient carbon isotope pattern | 3.7 Ga; C-depleted carbon | Consistent with biological carbon fixation | Can be mimicked by non-biological processes or altered later |
Molecular clock from conserved genes | LUCA estimate: 3.8–4.1 Ga | Sequence differences among living organisms can date divergence | Depends on mutation rates and calibration points; different genes give different ages |
Fossil and geochemical evidence from ancient rocks is used to infer early life.
I.
State what a stromatolite is.
[1]
II.
Explain why ancient stromatolite-like structures can provide only a minimum age for life.
[2]
Explain how carbon isotope ratios can be used as evidence consistent with early life, and why this evidence must be interpreted cautiously.
[2]
Evaluate molecular clock estimates for dating LUCA.
[3]
Question 47
In a simulation, fatty acid vesicles sometimes enclose RNA-like polymers. Some polymers catalyse reactions that increase the production of membrane components inside the vesicle.
The simulation includes compartments, polymers and variation among vesicles.
I.
State one emergent property that can result from polymerization of monomers.
[1]
II.
Explain why enclosing polymers inside vesicles could increase the likelihood of protocell evolution.
[2]
Explain the conditions required for natural selection to act on the vesicles in the simulation.
[3]
Discuss why the simulated system should be described as a protocell model rather than a living cell.
[2]
Question 48
Two proposed pre-biotic settings are a warm shallow pool on a volcanic island and an alkaline hydrothermal vent on the seafloor.
Feature | Warm shallow pool on volcanic island | Alkaline hydrothermal vent on seafloor |
|---|---|---|
Main energy input | Sunlight / UV / lightning; surface heating | Geothermal heat; little or no sunlight |
Chemical conditions | Wet-dry cycles can concentrate dissolved monomers | Continuous supply of reduced chemicals and steep pH gradients |
Concentration of reactants | Evaporation can increase solute concentration | Fluid flow can deliver fresh reactants from below |
Compartment formation | Fatty acids can self-assemble into vesicles | Mineral micropores can act as natural compartments |
Catalysis / surfaces | Limited mineral surfaces compared with vent systems | Mineral surfaces and pores can catalyse reactions |
Environmental stability | Highly variable and temporary | Relatively stable and long-lasting |
Both settings could support the formation of carbon compounds.
I.
Identify one energy source that would be more available in a warm shallow pool than at a deep hydrothermal vent.
[1]
II.
Explain one advantage of a hydrothermal vent for pre-biotic chemistry.
[2]
Compare and contrast shallow pools and hydrothermal vents as sites for the emergence of compartmentalized systems.
[2]
Evaluate why scientists may investigate more than one setting for the origin of cells rather than choosing a single pathway.
[2]
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