QCAA Biology Continuity of life on Earth
15 sample questions with marking guides and sample answers · Avg. score: 71.9%
Compare microevolution and macroevolution.
Reveal Answer
Both involve changes in allele frequencies, but in microevolution, this change occurs within a species, whereas for macroevolution, the change is at or above the species level. This means that in microevolution, the descendant is in the same taxonomic group as the ancestor, whereas in macroevolution, the descendant is in a different taxonomic group.
| Descriptor | Marks |
|---|---|
provides a similarity | 1 |
provides a difference | 1 |
states the significance | 1 |
The occurrence of atavism provides a possible piece of evidence for evolution. Atavism involves the reappearance of an ancestral genetic trait that has been lost over many generations of evolutionary change. One example in humans is a ‘caudal appendage’, where babies are born with a posterior tail made of cartilage and additional vertebrae.
The caudal appendage is an exterior extension of the coccyx. The coccyx itself is often considered an example of a vestigial organ.
Human colour blindness is considered another possible example of atavism in modern humans. It is believed that the colour blindness trait may have originated in early humans as a survival advantage. It is possible that the inability to distinguish some colours can improve the ability to view different textures and shades, providing a visual advantage in some habitats.
Consider the following hypothetical situation: An isolated island had a population of 300 people, 10 of which were colour blind. After 150 years, the island had a population of 400 people, none of whom were colour blind.
Identify one other vestigial organ of the human body.
Reveal Answer
Examples include (any 1 of the following):
appendix/male nipples/muscles to move ears/nictitating membrane/pointed canines/wisdom teeth/hair on body
| Descriptor | Marks |
|---|---|
appendix/male nipples/muscles to move ears/nictitating membrane/pointed canines/wisdom teeth/hair on body | 1 |
Explain how vestigial organs provide evidence for evolution.
Reveal Answer
Vestigial structures are structures that have a benefit in some species, but are present but not functional in other species. This indicates shared common ancestry.
| Descriptor | Marks |
|---|---|
Describes them as structures that have a benefit or normal function in some species | 1 |
States they are present but not functional in other species | 1 |
Explains that this indicates shared common ancestry or that at one point both species shared an ancestor who had the structure | 1 |
If colour blindness did provide a survival advantage, using the theory of natural selection, explain how colour blindness would have been maintained in early human populations.
Reveal Answer
Some individuals possess the colour blindness trait. Competition exists in the population, and those with colour blindness are more suited to the environment. They are more likely to survive to reproduce, so the allele is maintained or increased in the gene pool.
| Descriptor | Marks |
|---|---|
States that some individuals possess the colour blindness trait, the allele for colour blindness is present in the population, or there is variation in the population | 1 |
Identifies that competition exists in the population, there is a struggle to survive, or limited resources are present | 1 |
Explains that those with colour blindness are more suited to the environment or have better vision so are able to see predators better | 1 |
States that they are more likely to survive to reproduce or more likely to pass alleles onto offspring | 1 |
Concludes that the allele is maintained or increased in the gene pool | 1 |
If colour blindness did provide a survival advantage to this population, identify the name of the process that would provide the best explanation for the change in the population over time.
Reveal Answer
(Random) genetic drift
| Descriptor | Marks |
|---|---|
(Random) genetic drift | 1 |
Justify your response to part (c)(i).
Reveal Answer
This is due to the small size making it more likely to occur, and there is no gene flow evident with other populations. It must be a chance event, because if it does have a survival advantage it would be selected for in the population.
| Descriptor | Marks |
|---|---|
1 mark for each correct point (any 3 of):
| 3 |
Which of the following are all selection pressures which could reduce genetic variation in a population?
disease, increased competition and climate change
increased food availability, disease and climate change
increased competition, reduced environmental pollutants and disease
reduced land availability, increased food availability and climate change
Reveal Answer
disease, increased competition and climate change
Disease, increased competition, and climate change are all strong selection pressures that can cause significant mortality, eliminating disadvantageous alleles and reducing overall genetic variation.
increased food availability, disease and climate change
Increased food availability is a relaxed selection pressure that reduces competition, allowing more individuals to survive and typically maintaining or increasing genetic variation.
increased competition, reduced environmental pollutants and disease
Reduced environmental pollutants represents a relaxation of selection pressure, which allows a wider variety of phenotypes to survive rather than reducing genetic variation.
reduced land availability, increased food availability and climate change
Increased food availability relaxes selection pressure, meaning more individuals with diverse traits can survive, which does not reduce genetic variation.
A computer simulation was used to observe genotypic changes in the gene pool of 20 randomly selected rabbits. The simulation was set with these parameters:
- each rabbit's coat colour was either black or white
- black alleles were dominant; white alleles were recessive
- the number of rabbits was constant in each generation and breeding was random throughout the population
- an environmental factor was chosen in the simulation to provide selection pressure.
The table shows the results of the simulation at the start and after 20 generations.
| Initial population genotypes | Population genotypes after 20 generations |
|---|---|
| BB BB BB BB BB BB | BB BB |
| Bb Bb Bb Bb Bb Bb Bb Bb Bb Bb | Bb Bb Bb Bb Bb Bb Bb Bb |
| bb bb bb bb | bb bb bb bb bb bb bb bb bb bb |
Contrast the initial allele frequency with the allele frequency after 20 generations to draw a conclusion about the effect of the selection pressure on the rabbit population.
Reveal Answer
Initial allelic frequencies were B 0.55 and b 0.45.
Allelic frequencies after 20 generations were B 0.3 and b 0.7.
B decreased (from 0.55 to 0.3) and b increased (from 0.45 to 0.7).
This selection pressure was in favour of white rabbits as both genotype and allelic frequencies shifted toward the white phenotype and the white allele.
| Descriptor | Marks |
|---|---|
Provides the correct initial and final allele frequencies | 1 |
Identifies consequentially correct change in allele frequency | 1 |
States a consequentially valid conclusion | 1 |
The term ‘selectively-advantageous mutation’ means the mutation
provides a survival advantage in a particular environment.
will always be passed to the offspring.
is always changing to adapt to new environments.
provides a benefit to heterozygote individuals in populations.
Reveal Answer
provides a survival advantage in a particular environment.
A selectively advantageous mutation increases an organism's fitness, meaning it provides a survival and reproductive benefit specific to the environment the organism lives in.
will always be passed to the offspring.
Even highly advantageous mutations are not guaranteed to be passed on, as the organism might die before reproducing or the mutation might not be inherited due to random chance during meiosis.
is always changing to adapt to new environments.
Mutations are random changes in DNA and do not intentionally change or adapt in response to new environments; rather, the environment selects for beneficial mutations that already exist.
provides a benefit to heterozygote individuals in populations.
While heterozygote advantage is a specific phenomenon, a selectively advantageous mutation can provide benefits to homozygous individuals as well, not just heterozygotes.
A cat leg and a seal flipper are examples of
embryological structures.
vestigial structures.
analogous structures.
homologous structures.
Reveal Answer
embryological structures.
Incorrect. While these limbs develop during the embryonic stage, this term does not describe the evolutionary relationship between the adult limbs of different species.
vestigial structures.
Incorrect. Vestigial structures are anatomical features that have lost their original function through evolution, such as a human appendix. Both the cat leg and seal flipper are fully functional and actively used by the animals.
analogous structures.
Incorrect. Analogous structures share a similar function but have different evolutionary origins, like a bird wing and an insect wing. Cat legs and seal flippers actually have different primary functions but share a common evolutionary origin.
homologous structures.
Correct. Homologous structures share a similar underlying anatomy due to inheritance from a common ancestor, even if they have adapted for different functions. Both the cat leg and seal flipper are mammalian forelimbs with the same basic bone arrangement.
Speciation occurs when
the gene pool of an existing species becomes too small to support a viable population.
selection pressures cause significant changes to the allele frequencies of a population.
genetic drift is no longer occurring within populations.
gene flow is no longer occurring between populations.
Reveal Answer
the gene pool of an existing species becomes too small to support a viable population.
This scenario describes a population bottleneck or the path to extinction, rather than the divergence process required to form a new species.
selection pressures cause significant changes to the allele frequencies of a population.
While selection pressures drive microevolution by changing allele frequencies, speciation specifically requires reproductive isolation to separate a lineage into distinct species.
genetic drift is no longer occurring within populations.
Genetic drift is a constant evolutionary force in finite populations, and its cessation is not a mechanism for speciation.
gene flow is no longer occurring between populations.
Speciation requires reproductive isolation; when gene flow stops between populations, they can diverge genetically through mutation, selection, and drift until they become distinct species.
Koalas were once widespread in Australia. Due to a variety of factors, their population decreased and fragmented into small pockets, forcing them to inbreed. They have recently been hit by devastating epidemic diseases.
Explain why koalas face an increased extinction risk from disease.
Reveal Answer
High genetic diversity may allow for some members of the population to survive diseases and later reproduce and pass on their resistance to increase the survivability of the population.
However, inbreeding creates low genetic diversity, which makes koalas vulnerable to extinction due to disease.
| Descriptor | Marks |
|---|---|
Explains how genetic diversity can prevent extinction during rapid environmental change, e.g. disease | 1 |
Describes why koalas have low genetic diversity (inbreeding) | 1 |
States that koalas are more vulnerable to extinction due to low genetic diversity | 1 |
The Pacific Islands are made up of small, widely spread islands. Although migration between them has occurred, vast distances have historically made travel difficult for the inhabitants. As a result, genetic studies have shown that some of the island populations have distinctly unique gene pools.
Identify and explain the evolutionary mechanism that would have led to the populations in the Pacific Island countries being genetically different when compared to the original population from which they migrated.
Reveal Answer
The evolutionary mechanism is the founder effect/genetic drift.
The original population contains variation and a wide variety of phenotypes.
A small group of individuals moves to a new area and establishes a new population. This new group is not genetically representative and has a different allele frequency to the original population, resulting in decreased genetic variation in the new population.
There is no breeding between populations as the populations are isolated from each other. Over many generations, the ratio of allele frequency will differ to that of the original population, and these changes in allele frequency are non-directional or by chance.
Evolutionary mechanism
| Descriptor | Marks |
|---|---|
Identifies the evolutionary mechanism as the founder effect/genetic drift | 1 |
Explanation
| Descriptor | Marks |
|---|---|
States that the original population contains variation/wide variety of phenotypes | 1 |
Describes that a small group of individuals moves to a new area and establishes a new population | 1 |
Explains that the new group is not genetically representative/has a different allele frequency to the original population | 1 |
States that this results in decreased genetic variation in the new population | 1 |
Identifies that there is no breeding between populations/populations are isolated from each other | 1 |
Explains that over many generations, the ratio of phenotypes/allele frequency will differ to that of the original population | 1 |
States that changes in allele frequency are non-directional/by chance | 1 |
Define comparative genomics and explain how it is used to compare the genomes of different species.
Reveal Answer
Comparative genomics involves comparing the genome sequence of different species to determine relatedness.
DNA is sequenced to determine the order of nucleotides or bases. Over time, populations accumulate more and more differences in their genome. More similar DNA suggests species are more closely related and have a more recent common ancestor.
| Descriptor | Marks |
|---|---|
Defines comparative genomics as comparing the genome sequence of different species to determine relatedness | 1 |
States that DNA is sequenced to determine the order of nucleotides or bases | 1 |
Explains that over time, populations or species accumulate more and more differences in their DNA or genome | 1 |
Explains that more similar DNA suggests species are more closely related or have a more recent common ancestor | 1 |
Compare how nuclear DNA and mitochondrial DNA are used to provide evidence for evolution and migration.
Reveal Answer
Nuclear DNA is found in the nuclei of cells and is inherited from both parents. Due to recombination, migration is difficult to track; hence, it is used to trace evolutionary relationships between species.
Mitochondrial DNA (mtDNA) is found in the mitochondria and is only inherited from the mother. It has a high mutation rate; hence, it is used to trace migration routes between populations within a species.
Nuclear DNA
| Descriptor | Marks |
|---|---|
States that nuclear DNA is found in the nuclei of cells | 1 |
States that it is inherited from both parents | 1 |
Explains that due to recombination, migration is difficult to track | 1 |
Concludes that it is used to trace evolutionary relationships between species | 1 |
Mitochondrial DNA
| Descriptor | Marks |
|---|---|
States that mitochondrial DNA (mtDNA) is found in the mitochondria | 1 |
States that mtDNA is only inherited from the mother | 1 |
Identifies that mtDNA has a high mutation rate | 1 |
Concludes that it is used to trace migration routes between populations within a species | 1 |
If a geneticist is studying the amino acid sequence of haemoglobin, they are most likely looking for the possibility of
sickle cell anaemia or thalassemia.
Tay-Sachs disease or thalassemia.
thalassemia or malaria.
malaria or sickle cell anaemia.
Reveal Answer
sickle cell anaemia or thalassemia.
Both sickle cell anaemia and thalassemia are genetic disorders that directly affect the structure or production of haemoglobin chains, which can be identified by studying its amino acid sequence.
Tay-Sachs disease or thalassemia.
While thalassemia affects haemoglobin, Tay-Sachs disease is caused by a mutation affecting the enzyme beta-hexosaminidase A, which is unrelated to haemoglobin.
thalassemia or malaria.
Thalassemia is a genetic disorder affecting haemoglobin, but malaria is an infectious disease caused by a parasite, not a genetic mutation in the haemoglobin protein.
malaria or sickle cell anaemia.
Sickle cell anaemia is caused by a mutation in haemoglobin, but malaria is a parasitic infection, not a genetic disorder found in the amino acid sequence of haemoglobin.
The earliest fossils are of
protists from 3.5 million years ago.
protists from 3.5 billion years ago.
prokaryotes from 3.5 million years ago.
prokaryotes from 3.5 billion years ago.
Reveal Answer
protists from 3.5 million years ago.
Incorrect. Protists are eukaryotes that evolved much later, and 3.5 million years ago is far too recent for the earliest signs of life.
protists from 3.5 billion years ago.
Incorrect. While 3.5 billion years ago is the correct timeframe for the earliest life, protists are eukaryotes and did not appear until roughly 1.5 to 2 billion years ago.
prokaryotes from 3.5 million years ago.
Incorrect. Although prokaryotes are the earliest known life forms, they first appeared 3.5 billion years ago, not 3.5 million.
prokaryotes from 3.5 billion years ago.
Correct. The oldest widely accepted fossils are stromatolites, which were formed by single-celled prokaryotes (cyanobacteria) approximately 3.5 billion years ago.
Homologous structures are structures that are similar in related organisms because they were inherited from a common ancestor. An example of homologous structures is the
wings of birds and bats.
eyes of lizards and flies.
cell walls of bacteria and fungi.
fins of fish and squid.
Reveal Answer
wings of birds and bats.
The forelimbs of birds and bats share the same basic bone structure inherited from a common tetrapod ancestor, making them homologous structures, even though they evolved into wings independently.
eyes of lizards and flies.
The eyes of lizards (vertebrates) and flies (invertebrates) evolved independently to serve the same function. Because they do not share a recent common ancestor with this structure, they are analogous, not homologous.
cell walls of bacteria and fungi.
The cell walls of bacteria (made of peptidoglycan) and fungi (made of chitin) have different structural compositions and evolved independently, making them analogous structures.
fins of fish and squid.
The fins of fish and squid evolved independently in completely different lineages as an adaptation to swimming in water, making them analogous structures rather than homologous.
Scientists are investigating the mitochondrial genomes of different Aboriginal Australian populations. A purpose of these investigations is to reveal the pathways of migration of Aboriginal Australians who arrived from Sahul.
Mitochondrial DNA can be used for this purpose because it
contains genes that code for enzymes.
is always the same in specific populations.
is conserved through the maternal lineage.
is more structurally stable than nuclear DNA.
Reveal Answer
contains genes that code for enzymes.
While mitochondrial DNA does code for enzymes involved in cellular respiration, this functional characteristic does not help scientists trace historical migration pathways.
is always the same in specific populations.
Mitochondrial DNA is not identical within populations; in fact, the gradual accumulation of mutations over time creates distinct genetic markers (haplogroups) that scientists use to track migrations.
is conserved through the maternal lineage.
Mitochondrial DNA is inherited exclusively from the mother and does not undergo recombination, allowing scientists to trace unbroken maternal lineages back through time to map historical migrations.
is more structurally stable than nuclear DNA.
Mitochondrial DNA actually has a higher mutation rate than nuclear DNA due to its lack of protective histones and exposure to reactive oxygen species, so it is not more structurally stable.
The evolution of land plants from freshwater algae is an example of
macroevolution.
microevolution.
artificial selection.
natural selection.
Reveal Answer
macroevolution.
Macroevolution describes large-scale evolutionary changes over long periods, such as the emergence of entirely new taxonomic groups like land plants from aquatic ancestors.
microevolution.
Microevolution refers to small-scale changes in allele frequencies within a single population, rather than the major evolutionary transitions that create new groups of organisms.
artificial selection.
Artificial selection involves humans selectively breeding organisms for specific traits, which played no role in the ancient, natural transition of algae to land plants.
natural selection.
While natural selection is the underlying mechanism driving these changes, the specific term for the large-scale evolutionary event of forming a new major lineage is macroevolution.
Which of the following reduces genetic differences between populations?
genetic drift
gene flow
speciation
mutation
Reveal Answer
genetic drift
Genetic drift involves random changes in allele frequencies, which actually tends to increase genetic differences between isolated populations over time.
gene flow
Gene flow is the transfer of genetic material between populations. This mixing of alleles makes populations more genetically similar to one another, reducing differences.
speciation
Speciation is the process by which populations evolve to become distinct species, which requires an increase in genetic differences, not a reduction.
mutation
Mutations introduce new, random alleles into a population. Because they occur independently in different populations, they tend to increase genetic divergence rather than reduce it.