Evolution, Ancestry & Biodiversity — Chapter quiz · Life Science: Biology, Grade 10

Explain population change and branching ancestry using independent evidence.

Problem 1

Which statement correctly describes the raw material that natural selection acts on?
  1. Heritable variation, which arises ultimately from mutation
  2. Traits that individuals build up through practice during their lives
  3. Identical traits shared by every member of the population
  4. Choices that organisms consciously make to improve themselves
Answer and explanation

Heritable variation, which arises ultimately from mutation

Natural selection requires heritable variation, and the ultimate source of that variation is random mutation. It cannot act on acquired traits or on a population with no variation.

Problem 2

A small, short-lived fish that leaves 40 surviving offspring has higher biological fitness than a larger, longer-lived fish that leaves 5. This is because fitness is measured by
  1. physical strength
  2. reproductive success (surviving, fertile offspring)
  3. body size
  4. lifespan
Answer and explanation

reproductive success (surviving, fertile offspring)

In biology, fitness means reproductive success — the number of surviving, fertile offspring — not size, longevity, or strength.

Problem 3

The matching bone arrangement in a human arm, a bat wing, and a whale flipper is BEST described as
  1. vestigial structures with no function
  2. acquired traits passed to offspring
  3. homologous structures, evidence of common ancestry
  4. analogous structures, evidence of convergent evolution
Answer and explanation

homologous structures, evidence of common ancestry

These limbs share the same underlying bone plan inherited from a common ancestor, so they are homologous structures — a key piece of anatomical evidence for evolution.

Problem 4

A bird's wing and an insect's wing both allow flight but are built on completely different plans. This similarity is an example of
  1. analogous structures produced by convergent evolution
  2. homologous structures showing recent common ancestry
  3. vestigial structures
  4. molecular evidence
Answer and explanation

analogous structures produced by convergent evolution

Structures that share a function but not an underlying plan are analogous, resulting from convergent evolution to a similar task — not from shared ancestry.

Problem 5

Scientists say the case for common ancestry is strong because it rests on multiple independent lines of evidence. Name three different lines of evidence and briefly explain why their agreement matters.
Answer and explanation

Three lines could be: the fossil record (including transitional fossils), comparative anatomy (homologous and vestigial structures), and molecular evidence (DNA and protein similarity); others include embryology and biogeography. Their agreement matters because they were discovered using completely different methods, yet they point to the same branching tree of life — independent confirmation makes the conclusion far more reliable than any single line alone.

Problem 6

Which mechanism of evolution tends to make two separate populations MORE genetically similar to each other?
  1. Genetic drift
  2. Mutation
  3. Reproductive isolation
  4. Gene flow (migration and interbreeding between them)
Answer and explanation

Gene flow (migration and interbreeding between them)

Gene flow moves alleles between populations, blending their gene pools and making them more alike. It works against speciation, which requires isolation.

Problem 7

A mountain range rises and splits a rodent population into two isolated groups, which over time become unable to interbreed. This is an example of
  1. allopatric speciation
  2. gene flow
  3. convergent evolution
  4. artificial selection
Answer and explanation

allopatric speciation

A geographic barrier isolating populations that then diverge into separate species is allopatric speciation ('other homeland').

Problem 8

In a population of 500 diploid pea plants, the allele for tall stems (T) has a frequency of 0.7. Since each plant carries 2 copies of the gene, how many copies of the T allele are present in the whole population's gene pool?
Answer and explanation

700 copies

500 plants x 2 copies each = 1000 total gene copies. 0.7 x 1000 = 700 copies of the T allele.

Problem 9

Which list correctly names the three domains of life?
  1. Domain, Kingdom, Phylum
  2. Bacteria, Archaea, Eukarya
  3. Animalia, Plantae, Fungi
  4. Prokarya, Eukarya, Protista
Answer and explanation

Bacteria, Archaea, Eukarya

All life is classified into three domains — Bacteria, Archaea, and Eukarya — based largely on Carl Woese's comparison of ribosomal genetic sequences.

Problem 10

Explain what biodiversity is and give one reason it is important to protect. Refer to at least one of the three levels of biodiversity.
Answer and explanation

Biodiversity is the variety of life at three levels: genetic diversity within a species, species diversity (the number of different species), and ecosystem diversity (the range of habitats). It is important because, for example, high genetic diversity makes populations more resilient to disease and environmental change; diverse ecosystems are also more stable and provide services like pollination, clean water, and medicines. Losing biodiversity reduces this resilience and these benefits.

Problem 11

Giraffes' long necks are best explained by
  1. individuals stretching their necks and passing the stretch to offspring
  2. longer-necked individuals leaving more offspring over many generations
  3. the environment creating a need that produced the trait
  4. a single mutation in one generation
Answer and explanation

longer-necked individuals leaving more offspring over many generations

Heritable variation in neck length existed; individuals with longer necks left more offspring in that environment, so the average shifted across generations.

Problem 12

A population of plants is sprayed with a herbicide and a few survive. Explain what will happen over several generations and what evidence would support your explanation.
Answer and explanation

The survivors carry heritable variation that allows them to tolerate the herbicide, so they reproduce while susceptible plants do not, and the tolerant form's frequency rises over generations. Supporting evidence would include showing that tolerance is heritable by growing the survivors' offspring and testing them without further selection, measuring the frequency of tolerant plants across several generations, and demonstrating that tolerant individuals were present in samples taken before the herbicide was ever applied. That last point distinguishes selection of existing variation from the mistaken idea that spraying induced tolerance.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 13

Independent chapter check: Equal groups of 20 parents of two heritable variants produce 40 and 70 surviving reproductive offspring under one condition. Compare per-parent output and explain why this does not prove a universal advantage.
Answer and explanation

Outputs are 2 and 3.5 offspring per parent; the second is 1.75 times the first here. Other environments, starting frequencies and interactions can change the result, so the advantage is conditional.

Outputs are 2 and 3.5 offspring per parent; the second is 1.75 times the first here. Other environments, starting frequencies and interactions can change the result, so the advantage is conditional.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 14

Which comparison would provide the strongest single piece of evidence that two species share a recent common ancestor?
  1. They live in the same habitat
  2. They are similar in size
  3. Their DNA sequences are highly similar across many genes
  4. They both have wings
Answer and explanation

Their DNA sequences are highly similar across many genes

Similarity across many genes is difficult to explain except by shared ancestry, whereas habitat, size, and wings can all arise independently.

Problem 15

A student argues that because dolphins and sharks have similar body shapes, they must be closely related. Evaluate the argument and name the evidence that settles it.
Answer and explanation

The argument confuses functional similarity with shared ancestry. Streamlined shape is advantageous for fast swimming, so it can arise independently in separate lineages, making it an analogous rather than homologous similarity. The evidence that settles the question comes from structures and sequences rather than outline: dolphins have mammalian skeletal structure, lungs, and milk production, and their DNA is far more similar to other mammals than to sharks. Relationship is inferred from inherited features, not from resemblance in form.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 16

Independent chapter check: Two organisms have similar flight function but different structural/developmental details, while other sequences support separate lineages. Explain how convergence differs from evidence of close ancestry.
Answer and explanation

Similar selection pressures can produce analogous functional resemblance through convergence. Close ancestry requires appropriate shared derived/homologous evidence, supported by independent records; function alone does not settle it.

Similar selection pressures can produce analogous functional resemblance through convergence. Close ancestry requires appropriate shared derived/homologous evidence, supported by independent records; function alone does not settle it.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 17

Mutation's role in evolution is to
  1. direct change toward useful traits
  2. supply new heritable variation without regard to usefulness
  3. prevent genetic drift
  4. eliminate harmful alleles
Answer and explanation

supply new heritable variation without regard to usefulness

Mutation is the ultimate source of new alleles and occurs without reference to whether the result will be beneficial; selection and drift then act on what arises.

Problem 18

Explain why speciation usually requires both isolation and time, using the mechanisms that cause populations to diverge.
Answer and explanation

Isolation stops gene flow, so alleles arising in one population are not shared with the other and differences can accumulate separately. Time is needed because the mechanisms that produce divergence act gradually: mutation introduces new alleles at a low rate, selection shifts frequencies over generations where environments differ, and drift alters them by chance. Reproductive barriers generally emerge as a by-product of accumulated differences rather than appearing at once, so neither isolation without time nor time without isolation is usually sufficient.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 19

Independent chapter check: A source population has 70 blue and 30 gold representatives. A stated random founder group has 2 blue and 3 gold. Compare gold fractions and explain what the change does not establish.
Answer and explanation

The source fraction is 30%, the founder fraction 60%. A random sample can yield that change; it does not alone demonstrate gold advantage, new mutation or completed speciation.

The source fraction is 30%, the founder fraction 60%. A random sample can yield that change; it does not alone demonstrate gold advantage, new mutation or completed speciation.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 20

Modern classification aims primarily to group organisms by
  1. similarity of appearance
  2. habitat
  3. evolutionary relationship
  4. usefulness to humans
Answer and explanation

evolutionary relationship

Groups are intended to reflect shared ancestry, which is why molecular evidence can require a group defined by appearance to be revised.

Problem 21

Explain why a loss of biodiversity can matter to an ecosystem even when the total number of organisms stays the same.
Answer and explanation

Different species contribute different functions — fixing nitrogen, pollinating, decomposing, controlling other populations — so replacing many species with a larger number of individuals of a few leaves those functions unperformed. Diversity also provides alternatives: if several species perform a similar role, a disturbance that removes one may be absorbed by the others, whereas a community dominated by one species has no such margin. Total abundance therefore does not measure what diversity contributes.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 22

Independent chapter check: Two equal-effort samples each contain five species. Counts are 8,8,8,8,8 versus 36,1,1,1,1. Compare richness and evenness and name one sampling limitation.
Answer and explanation

Both have richness five and total 40, but the first is more even. Detection, area, timing and effort can affect observed richness; unobserved species are not automatically absent.

Both have richness five and total 40, but the first is more even. Detection, area, timing and effort can affect observed richness; unobserved species are not automatically absent.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 23

On (A,(B,C)), which pair shares the most recent common ancestor?
  1. A and B
  2. B and C
  3. A and C
  4. The drawing cannot ever show ancestry
Answer and explanation

B and C

B and C meet at the recent node.

Problem 24

Why does rotating two branches around their shared node leave the relationship unchanged?
Answer and explanation

The connectivity and common ancestor are unchanged; only tip display order differs.

Problem 25

Independent chapter check: A rooted tree has topology ((A,B),C). A drawing is rotated to show B first, then A, then C. State the relationship and explain what is needed to estimate divergence time.
Answer and explanation

A and B remain sister lineages in that topology. Tip order does not alter their shared ancestor; time estimation needs a specified calibrated branch metric/model and uncertainty.

A and B remain sister lineages in that topology. Tip order does not alter their shared ancestor; time estimation needs a specified calibrated branch metric/model and uncertainty.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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