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SCSA Biology Continuity of life on Earth

5 sample questions with marking guides and sample answers · Avg. score: 71.1%

Q24

2024

SCSA

1 mark

Q24

1 mark

Mutation is the ultimate source of genetic variation because mutation

results from errors in DNA replication.

can be caused by environmental factors.

can create new alleles.

changes allele frequencies.

Q28

2024

SCSA

1 mark

Q28

1 mark

The number of individuals in a frog population in an isolated swamp declined from 80 to 12 during a ten-year period. During this time, the population likely experienced

an increase in genetic diversity and no change in extinction risk.

a decrease in genetic diversity and an increase in extinction risk.

an increase in inbreeding and no change in extinction risk.

a decrease in inbreeding and an increase in extinction risk.

Q36

2024

SCSA

20 marks

Q36

Proteins are present in all living organisms and are essential to cell structure and function.

Q36a

10 marks

Describe the roles of DNA, messenger RNA (mRNA) and transfer RNA (tRNA) in protein synthesis.

DNA contains genetic information. mRNA is produced from DNA, and the genetic information or code is transferred to mRNA using complementary base pairing. The conversion of DNA to mRNA is called transcription.

The mRNA molecule transfers the genetic information from the nucleus to the cytoplasm, where the mRNA forms a complex with ribosomes. tRNA carries amino acids to the ribosome, ensuring the correct amino acid is added to the growing protein chain. One end of the tRNA molecule carries a specific amino acid, while the other end of the tRNA molecule, the anticodon, binds with the complementary mRNA codon. The amino acid on the tRNA is transferred to the protein chain, and different tRNAs add different amino acids. The conversion of mRNA to a protein is called translation.

Marking Criteria

Descriptor	Marks
1 mark for each correct point (any 10 of): States that DNA contains genes/genetic code/genetic information States that mRNA is produced from DNA Describes that genetic information/code is transferred to mRNA Identifies the use of complementary base pairing Identifies that the conversion of DNA to mRNA is called transcription Describes that the mRNA molecule transfers genetic information/code (from nucleus) to cytoplasm States that mRNA forms a complex with ribosomes Describes that tRNA carries amino acids to the ribosome/mRNA Explains that tRNA ensures the correct amino acid is added to the growing protein chain Describes that one end of the tRNA molecule carries a specific amino acid (determined by anticodon) Describes that the other end of the tRNA molecule (anticodon) binds with the complementary mRNA codon States that the amino acid on the tRNA is transferred to the protein chain Identifies that different tRNAs add different amino acids Identifies that the conversion of mRNA to a protein is called translation	10

Descriptor

Marks

1 mark for each correct point (any 10 of):

States that DNA contains genes/genetic code/genetic information
States that mRNA is produced from DNA
Describes that genetic information/code is transferred to mRNA
Identifies the use of complementary base pairing
Identifies that the conversion of DNA to mRNA is called transcription
Describes that the mRNA molecule transfers genetic information/code (from nucleus) to cytoplasm
States that mRNA forms a complex with ribosomes
Describes that tRNA carries amino acids to the ribosome/mRNA
Explains that tRNA ensures the correct amino acid is added to the growing protein chain
Describes that one end of the tRNA molecule carries a specific amino acid (determined by anticodon)
Describes that the other end of the tRNA molecule (anticodon) binds with the complementary mRNA codon
States that the amino acid on the tRNA is transferred to the protein chain
Identifies that different tRNAs add different amino acids
Identifies that the conversion of mRNA to a protein is called translation

Q36b

10 marks

Life on earth is very old.

Describe four characteristics of the oldest known life forms and explain how the fossil record and comparative genomics have helped to determine the characteristics of early life forms.

Early life forms were a type of bacteria that consisted of single cells. They were prokaryotes and anaerobic, dating back 3.5 billion years.

The fossil record provides preserved remains of organisms that show the morphological characteristics of organisms. From this, we can obtain evidence of their age from the type and location of the rock.

Comparative genomics involves the comparison of genomes of different species. This is done by collecting DNA from a broad range of organisms to identify conserved sequences of the genome. These conserved sequences are used to determine the genetic characteristics of early life forms and construct a phylogenetic tree. The tree is used to identify early life forms or close relatives, assuming that early life forms have similar characteristics to their closest living relatives.

Marking Criteria

Characteristics

Descriptor	Marks
1 mark for each correct point (any 4 of): Identifies them as a type of bacteria/archaea/cyanobacteria States they consist of single cells Identifies them as prokaryotes or lacking a nucleus/membrane-bound organelles States they were anaerobic/lived without oxygen Identifies they lived in aquatic/marine habitats States they are ancient/3.5 billion years old	4

Fossil record

Descriptor	Marks
1 mark for each correct point (any 3 of): Describes fossils as preserved remains/traces of organisms States that fossils show morphological characteristics (of organisms) Explains that evidence of age/habitat can be obtained Identifies that this evidence comes from the type/location of rock	3

Comparative genomics

Descriptor	Marks
1 mark for each correct point (any 3 of): Describes comparative genomics as the comparison of genomes/DNA/genes of different species Describes collecting DNA/genes/molecular data from a broad range of organisms/bacteria/micro-organisms/fossils Identifies the need to identify conserved sequences/genes/parts of the genome Explains using conserved sequences to determine genetic characteristics of early life forms Describes constructing a phylogenetic tree Explains using the tree to identify early life forms/close relatives of early life forms States the assumption that early life forms have similar characteristics to closest living relatives	3

Descriptor

Marks

1 mark for each correct point (any 3 of):

Describes comparative genomics as the comparison of genomes/DNA/genes of different species
Describes collecting DNA/genes/molecular data from a broad range of organisms/bacteria/micro-organisms/fossils
Identifies the need to identify conserved sequences/genes/parts of the genome
Explains using conserved sequences to determine genetic characteristics of early life forms
Describes constructing a phylogenetic tree
Explains using the tree to identify early life forms/close relatives of early life forms
States the assumption that early life forms have similar characteristics to closest living relatives

Q36

2023

SCSA

20 marks

Q36

The Montara oil spill, which occurred off the northwest coast of Western Australia in August 2009, is classed as one of the worse oil disasters in Australian waters. Oil spills are initially treated with detergents (to disperse the spill) and fire, but genetically-modified bacteria that can digest the oil are sometimes also used.

Q36a

10 marks

Describe how recombinant DNA technology is used to genetically modify bacteria to digest oil and discuss two advantages and two disadvantages of using a genetically-modified microorganism for environmental conservation.

To genetically modify bacteria using recombinant DNA technology, first isolate a suitable gene, which must be a gene that produces an enzyme that digests oil. Choose a suitable bacterium for genetic modification (one that can survive in aquatic environments). Use the same restriction enzyme to remove the gene from the host and insert it into a plasmid. Amplify the target gene in the plasmid or by polymerase chain reaction (PCR), and insert the gene into the target bacteria. Transform the bacteria using heat shock, and check the ability of the bacteria to reproduce and produce the gene product.

The advantages of this use include the ability to use genes from other species to achieve outcomes not possible via natural processes. After development, it is easy and fast to produce and supply transgenics in large quantities; and microorganisms are easy to transport, handle, and store.

However, disadvantages include that transgenic organisms could have a negative impact on other organisms or the environment, such as oil-digesting bacteria taking over and displacing natural bacteria. There is also the risk of gene transfer to other organisms.

Marking Criteria

Description of recombinant DNA technology used to genetically modify bacteria

Descriptor	Marks
1 mark for each correct point (any 6 of): Identifies the need to identify/isolate a suitable gene • States that it must be a gene that produces an enzyme that digests oil Describes choosing a suitable bacterium for genetic modification (one that can survive in aquatic environments) Explains the use of the same restriction enzyme to remove the gene from the host and insert it into a plasmid Describes amplifying the target gene (in a plasmid or by polymerase chain reaction (PCR)) States that the gene is inserted into the bacteria/target organism Describes transforming the bacteria using heat shock or another relevant method States the need to check the ability of the bacteria to reproduce/produce the gene product	6

Descriptor

Marks

1 mark for each correct point (any 6 of):

Identifies the need to identify/isolate a suitable gene • States that it must be a gene that produces an enzyme that digests oil
Describes choosing a suitable bacterium for genetic modification (one that can survive in aquatic environments)
Explains the use of the same restriction enzyme to remove the gene from the host and insert it into a plasmid
Describes amplifying the target gene (in a plasmid or by polymerase chain reaction (PCR))
States that the gene is inserted into the bacteria/target organism
Describes transforming the bacteria using heat shock or another relevant method
States the need to check the ability of the bacteria to reproduce/produce the gene product

Advantages of use

Descriptor	Marks
1 mark for each correct point (any 2 of): Explains that genes from other species can be used or outcomes not possible via natural processes can be achieved States that (after development) it is easy/fast to produce/supply transgenics in large quantities States that microorganisms are easy to transport/handle/store	2

Disadvantages of use

Descriptor	Marks
1 mark for each correct point (any 2 of): Explains that transgenic organisms could have a negative impact on other organisms/the environment or oil-digesting bacteria could take over/displace natural bacteria Identifies the risk of gene transfer to other organisms States that it is a fairly new technology, so there may be unknown effects, it may not be effective, or development can be very expensive	2

Descriptor

Marks

1 mark for each correct point (any 2 of):

Explains that transgenic organisms could have a negative impact on other organisms/the environment or oil-digesting bacteria could take over/displace natural bacteria
Identifies the risk of gene transfer to other organisms
States that it is a fairly new technology, so there may be unknown effects, it may not be effective, or development can be very expensive

Q36b

10 marks

Gene pools are dynamic, with changes in allele frequencies being caused by several factors, including mutation and genetic drift.

Describe how mutation and genetic drift change the frequency of alleles in a population and explain the significance of these changes.

A mutation is a permanent change to DNA that occurs at random. It changes one allele to another or creates new alleles.

The significance of changes made by mutation is that they can have deleterious effects on individuals. Mutations have a limited effect on allele frequencies because the rate of mutation is low, but they are the source of all genetic variation, alleles, and biological diversity. Other evolutionary processes are dependent on this variation, and populations cannot evolve without genetic variation.

Genetic drift involves the random death of individuals, leading to random or chance changes in allele frequencies. It has the biggest effect in small populations.

The significance of changes made by genetic drift is that it can result in the loss of advantageous alleles. This places populations at risk of extinction due to an inability to adapt.

Marking Criteria

Mutation

Descriptor	Marks
1 mark for each correct point (any 2 of): Describes mutation as a permanent change to DNA or a change in DNA structure States that it changes one allele to another or creates new alleles Identifies that it occurs at random	2

Significance of changes made by mutation

Descriptor	Marks
1 mark for each correct point (any 3 of): Explains that mutations can have deleterious effects on individuals, can result in the death of individuals, or can have neutral, advantageous, or disadvantageous effects (depending on the mutation) States that mutations have a limited effect on allele frequencies (because the rate of mutation is low) Identifies mutation as the source of all genetic variation/alleles/biological diversity • Explains that other evolutionary processes are dependent on this variation or that populations cannot evolve without genetic variation	3

Descriptor

Marks

1 mark for each correct point (any 3 of):

Explains that mutations can have deleterious effects on individuals, can result in the death of individuals, or can have neutral, advantageous, or disadvantageous effects (depending on the mutation)
States that mutations have a limited effect on allele frequencies (because the rate of mutation is low)
Identifies mutation as the source of all genetic variation/alleles/biological diversity • Explains that other evolutionary processes are dependent on this variation or that populations cannot evolve without genetic variation

Genetic drift

Descriptor	Marks
1 mark for each correct point (any 2 of): Describes genetic drift as the random death of individuals, selection of gametes, or founder effect States that it involves random/chance changes in allele frequencies Identifies that it has the biggest effect in small populations	2

Significance of changes made by genetic drift

Descriptor	Marks
1 mark for each correct point (any 3 of): Explains that it leads to a loss of diversity/alleles or can result in the loss of advantageous alleles States that it places populations at risk of extinction Explains that this risk is due to increased inbreeding, inability to adapt, or susceptibility to pathogens	3

Q31

2025

SCSA

20 marks

Q31

The cane toad (Rhinella marina) is an invasive species of amphibian that is spreading in Australia.

Adult cane toads excrete urea.

Q31d

In warm climates, cane toads are mostly active at night.

Q31a (i)

2 marks

Outline one advantage and one disadvantage of excreting urea compared to ammonia.

An advantage is that it requires less water to excrete than ammonia.

A disadvantage is that it requires more energy to produce than ammonia.

Marking Criteria

Descriptor	Marks
Identifies an advantage, such as requiring less water to excrete, being less toxic, or being able to be stored longer/more safely than ammonia	1
Identifies a disadvantage, such as requiring more energy to produce than ammonia	1

Q31a (ii)

2 marks

Outline one advantage and one disadvantage of excreting urea compared to uric acid.

An advantage is that it requires less energy to produce than uric acid.

A disadvantage is that it requires more water to excrete than uric acid.

Marking Criteria

Descriptor	Marks
Identifies an advantage, such as requiring less energy to produce than uric acid	1
Identifies a disadvantage, such as requiring more water to excrete than uric acid	1

Q31b

3 marks

Describe how cane toads thermoregulate.

They are ectotherms, which use the environment to heat or cool. They adjust their behaviour according to whether they want to heat or cool.

Marking Criteria

Descriptor	Marks
Identifies the organism as an ectotherm	1
Describes that they use the environment to heat/cool, rely on external heat sources, or that their body temperature fluctuates with the environment	1
Explains that they adjust their behaviour according to whether they want to heat or cool	1

Q31c

4 marks

Predict whether the energy requirements of a cane toad will be higher or lower than a mammal of equivalent size by circling the appropriate answer. Justify your answer.

higher $\quad$ or $\quad$ lower (circle your answer)
Justification:

The energy requirement is lower because toads do not need to maintain a constant internal temperature. Toads have a lower metabolic rate than mammals of the same size, and the lower the metabolic rate, the less energy is required.

Marking Criteria

Descriptor	Marks
States that the energy requirement is lower	1
Explains that toads/ectotherms do not need to maintain a constant internal temperature (or vice-versa for mammals)	1
States that toads/ectotherms have a lower metabolic rate than mammals of the same size (or vice-versa)	1
Explains that the lower the metabolic rate, the less energy is required (or vice-versa)	1

Q31d

4 marks

Explain how being active at night can help a cane toad to maintain water balance.

Water is lost through evaporation by breathing or through the skin.

The rate of evaporation is lower at night because (any 1 of the following):

the air temperature is cooler
the temperature difference between the cane toad and the environment is less
the cane toads are less likely to overheat.

Marking Criteria

Descriptor	Marks
Identifies that water is lost through evaporation	1
States that evaporation occurs by breathing or through the skin	1
Identifies that the rate of evaporation is lower at night	1
Explains that this is because the air temperature is lower/cooler, the temperature difference between the cane toad and environment is less, or the cane toads are less likely to overheat	1

Q31e

5 marks

Golden tree snakes prey on cane toads. Cane toads contain a toxin and a large cane toad has enough toxin to kill a snake that has eaten it. In areas the cane toads have invaded, the golden tree snakes have evolved a smaller head size such that they can only consume smaller cane toads.

Explain how natural selection could result in the evolution of a smaller head size in golden tree snakes in areas where there are cane toads.

There is variation in head size in the snake population. Snakes with small heads do not receive lethal doses of poison because they cannot eat large toads. Therefore, more individuals with small heads survive and reproduce. Snakes with small heads pass the alleles for a small head to their offspring, and over generations, the alleles for a small head increase in frequency.

Marking Criteria

Descriptor	Marks
Identifies that there is variation in head size in the snake population	1
Explains that snakes with small heads do not receive lethal doses of poison because they cannot eat large toads, or that snakes with large heads receive lethal doses when eating large toads	1
States that therefore, more individuals with small heads survive and reproduce (or vice-versa)	1
Describes that snakes with small heads pass the alleles for small heads to their offspring	1
Explains that over time/generations, the alleles for small heads increase in frequency	1

SCSA Biology Continuity of life on Earth

Characteristics

Fossil record

Comparative genomics

Description of recombinant DNA technology used to genetically modify bacteria

Advantages of use

Disadvantages of use

Mutation

Significance of changes made by mutation

Genetic drift

Significance of changes made by genetic drift

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