A3.1 Diversity of organisms
Practice exam-style IB Biology questions for Diversity of organisms, aligned with the syllabus and grouped by topic.
Question 1
What pattern of variation is shown when individuals have a range of intermediate values between two extremes?
A.
Continuous variation
B.
Binomial variation
C.
Hybrid variation
D.
Discontinuous variation
Question 2
What is the correctly written binomial for the lion?
A.
Panthera Leo
B.
*Leo panthera*
C.
*Panthera leo*
D.
*panthera Leo*
Question 3
What are the diploid chromosome numbers of humans and chimpanzees?
A.
Humans 23; chimpanzees 24
B.
Humans 46; chimpanzees 48
C.
Humans 44; chimpanzees 46
D.
Humans 48; chimpanzees 46
Question 4
A taxonomist groups organisms as one species because they share body shape, leaf arrangement and flower structure. What species concept is being used?
A.
Biological species concept
B.
Genomic species concept
C.
Ecological species concept
D.
Morphological species concept
Question 5
According to the biological species concept, what is required for organisms to be in the same species?
A.
They can breed and produce fertile offspring.
B.
They have the same common name in one language.
C.
They have the same chromosome number in every cell.
D.
They have identical DNA base sequences.
Question 6
Why is the biological species concept difficult to apply to organisms that reproduce only asexually?
A.
It depends on interbreeding and fertile offspring.
B.
It requires every organism to have an even chromosome number.
C.
It depends on measuring genome size only.
D.
It can only be used for extinct organisms.
Question 7
What is environmental DNA?
A.
DNA that lacks all mutations and alleles
B.
DNA collected from abiotic surroundings such as water, soil or air filters
C.
DNA produced only by extinct species
D.
DNA found only inside chloroplasts of plants
Question 8
Define a trait.
[1]
Distinguish between continuous and discontinuous variation.
[1]
Question 9
The scientific name of the grey wolf is Canis lupus.
State the genus of the grey wolf.
[1]
State two conventions used when writing a binomial name in typed text.
[1]
Question 10
Two isolated populations show gradually increasing differences in body size and song. Biologists disagree about whether they are separate species. What explains the disagreement?
A.
Non-interbreeding populations always remain the same species.
B.
All populations that differ in one trait must be different species.
C.
Species cannot diverge unless chromosome number changes first.
D.
Speciation usually occurs gradually, so the boundary can be arbitrary.
Question 11
What evidence is most useful for matching homologous chromosomes in a karyogram?
A.
Gene expression, protein folding and ribosome size
B.
Banding pattern, length and centromere position
C.
Gamete size, zygote mass and embryo age
D.
Cell membrane shape, cytoplasm colour and organelle number
Question 12
What is a single-nucleotide polymorphism (SNP)?
A.
A genome position where one DNA base varies between individuals and the less common variant is present in at least 1% of the population
B.
A complete set of chromosomes inherited from one parent
C.
A chromosome that has fused with another chromosome during meiosis
D.
A gene that is found only in members of one genus
Question 13
A gene for antibiotic resistance moves from one bacterial lineage to a distantly related lineage. What process has occurred?
A.
Vertical inheritance
B.
Discontinuous variation
C.
Binomial nomenclature
D.
Horizontal gene transfer
Question 14
Why may hybrids between closely related species with different chromosome numbers be infertile?
A.
Homologous chromosomes may fail to pair correctly during meiosis.
B.
Their gametes become diploid before meiosis begins.
C.
Their body cells cannot carry out mitosis.
D.
Their alleles are converted into proteins before fertilization.
Question 15
What is the best pair of alternatives for a step in a dichotomous key for local tree leaves?
A.
Plant is large / flowers are yellow
B.
Bark is rough / leaves smell strongly after rain
C.
Leaf is attractive / tree is common
D.
Leaf margin toothed / leaf margin smooth
Question 16
Why is chromosome number usually a shared trait within a sexually reproducing species?
A.
All species with the same chromosome number are equally closely related.
B.
Gametes contain two complete sets of homologous chromosomes.
C.
Meiosis requires homologous chromosomes to pair and segregate reliably.
D.
Diploid cells must always contain an odd number of chromosomes.
Question 17
What feature makes a DNA barcode useful for identifying species from eDNA?
A.
It is from a standard gene region with enough variation to distinguish species.
B.
It is a chromosome number counted in a karyogram.
C.
It is the complete genome sequence of every organism in a habitat.
D.
It is a visible body structure used in a key.
Question 18
State the biological species concept.
[1]
Explain one challenge in applying this concept to geographically separated populations.
[1]
State why producing offspring alone is not sufficient evidence that two organisms are the same species under this concept.
[1]
Question 19
Define speciation.
[1]
Outline why it can be difficult to decide whether two diverging populations are separate species.
[1]
Question 20
State the chromosome number in a typical human diploid cell.
[1]
State the chromosome number in a typical chimpanzee diploid cell.
[1]
Explain why diploid cells of plants and animals usually have an even chromosome number.
[1]
Question 21
Define genome.
[1]
Outline how members of the same species can show both unity and diversity in their genomes.
[1]
Question 22
Define horizontal gene transfer.
[1]
Explain why horizontal gene transfer makes the biological species concept difficult to apply to bacteria.
[1]
Give one example of a gene that may spread by horizontal gene transfer.
[1]
Question 23
Define clone in the context of asexual reproduction.
[1]
Explain why treating every long-lasting clone as a separate species may be problematic.
[1]
Question 24
The graph shows the frequency of shell width in a population of a freshwater snail and the frequency of shell colour categories in the same population.
| Shell width class / mm | Frequency / snails | Shell colour | Frequency / snails |
|---|---|---|---|
| 4.0–4.9 | 3 | Dark brown | 18 |
| 5.0–5.9 | 9 | Light brown | 34 |
| 6.0–6.9 | 17 | Yellow | 27 |
| 7.0–7.9 | 28 | Grey | 13 |
| 8.0–8.9 | 26 | White | 8 |
| 9.0–9.9 | 12 | ||
| 10.0–10.9 | 5 |
Identify the type of variation shown by shell width.
[1]
Identify the type of variation shown by shell colour.
[1]
Describe one feature of the shell width distribution that supports your answer to (a).
[1]
Suggest why variation is important for classification and natural selection.
[1]
Question 25
The graph shows changes in the time required and cost per sample for whole genome sequencing over several years.
Describe the trend in sequencing cost.
[1]
Describe the trend in sequencing time.
[1]
Suggest one current biological use made more practical by these trends.
[1]
Suggest one reason why a genome sequence alone may not accurately predict a person’s future health.
[1]
Question 26
A pond water sample contains a DNA barcode matching a fish species, but no fish are caught during trapping. What is the most cautious interpretation?
A.
The species may be present, but the DNA could also have been transported or contaminated.
B.
The species must be absent because trapping did not catch it.
C.
The species must be present in large numbers.
D.
The barcode shows the fish has become a new species.
Question 27
A simplified karyogram shows three unmatched chromosomes labelled X, Y and 7.
Identify two features used to match homologous chromosomes in a karyogram.
[1]
State the stage of cell division when chromosomes are easiest to observe for karyotyping.
[1]
Identify the sex chromosome combination expected in a typical human male.
[1]
Question 28
State what is meant by whole genome sequencing.
[1]
Outline one current use of whole genome sequencing.
[1]
Outline one potential future use of whole genome sequencing.
[1]
State one technological trend that has increased the use of whole genome sequencing.
[1]
Question 29
Two closely related plant species have diploid chromosome numbers of 14 and 16. A rare hybrid seedling is produced.
State the expected chromosome number in a body cell of the hybrid.
[1]
Explain why the hybrid may be infertile.
[1]
State the type of cell division affected.
[1]
Question 30
Four local leaf specimens have the following visible features: species P has needle-shaped leaves; species Q has broad leaves with smooth margins; species R has broad leaves with toothed margins and opposite arrangement; species S has broad leaves with toothed margins and alternate arrangement.
Construct the first dichotomous key couplet that separates species P from the others.
[1]
Construct a later couplet that separates species R from species S.
[1]
Question 31
A student writes this couplet for a dichotomous key: “1a organism is big; 1b organism is small”.
State one weakness of this couplet.
[1]
Suggest two improvements when developing a dichotomous key for local animal species.
[1]
Question 32
Define DNA barcode.
[1]
Outline how eDNA and barcodes can be used to identify species in a stream.
[1]
Question 33
eDNA surveys show that a native fish was detected in a wetland in 2019 and 2020 but not in 2023.
Suggest one ecological reason why the species may have gone extinct locally.
[1]
Suggest one reason why the species might still persist despite no eDNA detection in 2023.
[1]
State two factors that can increase the chance of persistence of a species in a habitat.
[1]
Question 34
Two populations of a bird occur on different islands. The table shows selected observations made after individuals were brought together in a controlled breeding programme.
| Observation | Island A | Island B | A×B trial |
|---|---|---|---|
| Mean beak length / mm | 12.4 | 16.1 | — |
| Breast plumage | spotted | plain | — |
| Male song type | rapid trill | slow whistle | — |
| Attempted matings / n | — | — | 30 |
| Hybrid offspring / n | — | — | 18 |
| F1 hybrid fertility | — | — | 14 of 16 fertile |
State which species concept is tested most directly by the breeding programme.
[1]
Identify one morphological trait that differs between the populations.
[1]
Describe the breeding evidence shown in the table.
[1]
Evaluate whether the two populations should be classified as one species using the biological species concept.
[1]
Question 35
A database was used to compare genome sizes and selected measures of organism complexity for several eukaryotes.
| Organism | Group | Haploid genome / Gb | Cell types / count |
|---|---|---|---|
| Yeast | Fungi | 0.012 | 1 |
| Paramecium | Protists | 0.087 | 1 |
| Arabidopsis | Plants | 0.135 | 40 |
| Onion | Plants | 16.0 | 35 |
| Paris japonica | Plants | 149.0 | 40 |
| Fruit fly | Animals | 0.18 | 60 |
| Human | Animals | 3.2 | 200 |
| Axolotl | Animals | 32.0 | 150 |
Identify the organism in the table with the largest genome size.
[1]
Compare the range of genome sizes in plants and animals.
[1]
State whether the table supports the claim that more complex organisms always have larger genomes.
[1]
Explain one reason why genome size may not match organism complexity.
[1]
Question 36
The table shows chromosome numbers and breeding outcomes for crosses among three closely related grass species.
| Cross | Parent 1 2n | Parent 2 2n | Hybrids produced / number | Fertile hybrids / % |
|---|---|---|---|---|
| Species A × Species B | 14 | 28 | 86 | 46 |
| Species A × Species C | 14 | 42 | 74 | 8 |
| Species B × Species C | 28 | 42 | 91 | 39 |
Identify the cross that produced the highest proportion of fertile offspring.
[1]
Describe the relationship between parental chromosome-number difference and hybrid fertility shown in the table.
[1]
Explain why a difference in chromosome number can reduce hybrid fertility.
[1]
Question 37
Students developed a dichotomous key for six local pond invertebrates and then tested it with preserved specimens. The table shows the intended species, features visible on the specimens and identifications made by the key.
| Specimen | Actual species | Legs visible | Shell | Antennae | Body segments | Key ID |
|---|---|---|---|---|---|---|
| A | Pond snail | 0 | Yes | Not visible | Not clear | Pond snail |
| B | Freshwater shrimp | Several pairs | No | Not visible | Clear | Water louse |
| C | Water louse | 7 pairs | No | Short visible | Clear | Water louse |
| D | Mayfly nymph | 3 pairs | No | Not visible | Clear | Dragonfly nymph |
| E | Dragonfly nymph | 3 pairs | No | Short visible | Clear | Dragonfly nymph |
| F | Bloodworm | 0 | No | Not visible | Clear | Bloodworm |
Calculate the number of specimens misidentified by the key.
[1]
Identify one feature that caused a misidentification.
[1]
Suggest one change to improve the key.
[1]
Evaluate why testing a dichotomous key with actual specimens is important.
[1]
Question 38
A rare amphibian is detected by eDNA in one of six pond samples.
State what the positive eDNA result suggests.
[1]
Evaluate two limitations of using this result alone to conclude that the amphibian is living in the pond.
[1]
Suggest one improvement to the sampling design.
[1]
Question 39
The figure compares human chromosome 2 with two separate chromosomes from a closely related primate.
Identify one feature used to compare the chromosomes in the figure.
[1]
Describe the relationship between the banding pattern of human chromosome 2 and the two primate chromosomes.
[1]
State one molecular feature predicted if human chromosome 2 formed by end-to-end fusion.
[1]
Evaluate whether the figure supports the chromosome fusion hypothesis.
[1]
Question 40
The table shows genome comparisons among four bacterial lineages isolated from different hospitals. One antibiotic resistance gene is present in lineages with otherwise different genome backgrounds.
| Lineage | Similarity to A / % | Similarity to B / % | Similarity to C / % | Similarity to D / % | NDM-1 gene |
|---|---|---|---|---|---|
| A | 100.0 | 98.7 | 92.4 | 86.1 | present |
| B | 98.7 | 100.0 | 91.8 | 86.4 | absent |
| C | 92.4 | 91.8 | 100.0 | 96.5 | absent |
| D | 86.1 | 86.4 | 96.5 | 100.0 | present |
Identify the lineage most genetically similar overall to lineage A.
[1]
Identify the lineages carrying the resistance gene.
[1]
Suggest why the distribution of the resistance gene is evidence for horizontal gene transfer.
[1]
Explain why this pattern complicates a simple tree-like view of bacterial species.
[1]
Question 41
Water samples from three sites along a river were analysed for eDNA barcodes of four fish species. The table shows barcode detections and field observations from netting.
| Site | Brown trout eDNA/net | Minnow eDNA/net | Bullhead eDNA/net | Atlantic salmon eDNA/net |
|---|---|---|---|---|
| Upstream | +/+ | –/– | +/– | –/– |
| Midstream | + /– | +/+ | +/– | –/– |
| Downstream | –/– | +/– | –/– | –/– |
Identify the site with the highest detected fish species richness by eDNA.
[1]
Compare eDNA detections with netting observations for one species.
[1]
Suggest one reason for a species being detected by eDNA but not by netting.
[1]
Evaluate whether the data are sufficient to conclude that an undetected species is extinct from the river.
[1]
Question 42
Outline the morphological species concept.
[1]
Compare and contrast the morphological species concept with the biological species concept, including one limitation of each.
[1]
Question 43
Define population and speciation.
[1]
Explain why divergence of non-interbreeding populations can make species boundaries difficult to decide.
[1]
Question 44
Outline why chromosome number is usually shared within a sexually reproducing species.
[1]
Explain how different chromosome numbers in closely related species can contribute to reproductive isolation.
[1]
Question 45
State two features of a well-made dichotomous key.
[1]
Evaluate how a student should develop and test a dichotomous key for local plant or animal species.
[1]
Question 46
An unknown eDNA barcode from a forest soil sample was compared with reference sequences in a database. The table shows percentage matches to several local mammals and the number of reference sequences available for each species.
| Candidate species | Match / % | Reference sequences / count | Known locally |
|---|---|---|---|
| European badger | 99.2 | 18 | Yes |
| Pine marten | 98.7 | 7 | Yes |
| Beech marten | 98.4 | 2 | No |
| Red fox | 91.6 | 32 | Yes |
| Wild boar | 89.8 | 15 | Yes |
| Roe deer | 88.9 | 24 | Yes |
Identify the most likely species detected from the barcode match.
[1]
Explain why percentage match alone may not be sufficient for a confident identification.
[1]
Suggest one additional database feature that would improve confidence in barcode identification.
[1]
State one conservation use of repeated eDNA barcode surveys in the forest.
[1]
Question 47
Describe how chromosomes are classified in a karyogram.
[1]
Evaluate the evidence for the hypothesis that human chromosome 2 arose by fusion of two ancestral primate chromosomes.
[1]
Question 48
Outline two ways in which eukaryote genomes vary.
[1]
Discuss the claim that genome size is a reliable measure of organism complexity, referring to genome databases and whole genome sequencing.
[1]
Question 49
Outline the biological species concept.
[1]
Evaluate the usefulness of the biological species concept for asexually reproducing organisms and bacteria that undergo horizontal gene transfer.
[1]
Question 50
Outline how DNA barcodes are used with environmental DNA to identify species in a habitat.
[1]
Discuss the strengths and limitations of using eDNA barcode surveys to investigate biodiversity, persistence and possible extinction of species.
[1]
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