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BIOLOGY, M3 EQ-Bank 3

"Natural selection is the architect of biodiversity."

Justify this statement. In your answer, describe how natural selection can lead to changes in a population and over time, increased biodiversity. Provide an example from the Australian ecosystems that demonstrates this relationship.   (5 marks)

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  • Natural selection is the architect of biodiversity as it drives the adaptation of populations to their environments, leading to the evolution of new species over time.
  • This process begins with genetic variations within a population, where individuals with traits better suited to their environment are more likely to survive and reproduce, passing these beneficial traits to their offspring.
  • Over generations, this can lead to significant changes in the population, potentially resulting in the emergence of new species adapted to specific environmental niches.
  • As populations adapt to different environments or ecological roles, the overall biodiversity increases.
  • Australian ecosystem example: the radiation of marsupials, such as the diverse kangaroo species.
  • From a common ancestor, natural selection has led to the evolution of various kangaroo species adapted to different habitats, from the large red kangaroos of the arid interior to the tree-dwelling tree-kangaroos of the rainforests.
  • Each fill a unique ecological niche and contribute to Australia’s biodiversity.
Show Worked Solution
  • Natural selection is the architect of biodiversity as it drives the adaptation of populations to their environments, leading to the evolution of new species over time.
  • This process begins with genetic variations within a population, where individuals with traits better suited to their environment are more likely to survive and reproduce, passing these beneficial traits to their offspring.
  • Over generations, this can lead to significant changes in the population, potentially resulting in the emergence of new species adapted to specific environmental niches.
  • As populations adapt to different environments or ecological roles, the overall biodiversity increases.
  • Australian ecosystem example: the radiation of marsupials, such as the diverse kangaroo species.
  • From a common ancestor, natural selection has led to the evolution of various kangaroo species adapted to different habitats, from the large red kangaroos of the arid interior to the tree-dwelling tree-kangaroos of the rainforests.
  • Each fill a unique ecological niche and contribute to Australia’s biodiversity.

BIOLOGY, M3 2015 HSC 30

The graph shows the history of the relative numbers of three varieties of bird \((X, Y\) and \(Z\) ) within a bird species, on a remote island in the Pacific Ocean.

The bird species arrived on the island in a migration event. Before migration, the bird species was not present on the island.

The graph record of bird numbers on the island is divided into two sections (1 and 2). Over the time data were recorded, the environment of the island did not change.
 

  1. What bird varieties originally migrated to the island?   (1 mark)

  2. Using the Darwin/Wallace theory of evolution, and making reference(s) to the data in the graph, explain the changes to the population of each variety of bird in
  3.   i. section (1) of the graph.  (2 marks)

  4.  ii. section (2) of the graph.  (4 marks)

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a.    Varieties \(Z\) and \(Y\).

b.i.  In section (1):

  • Variety \(Z\) is naturally selected as its numbers grow over time until they plateau when it reaches the limits of resources the environment can provide.
  • Variety \(Y\) is not naturally selected as it is not suited to the environment and becomes extinct as its numbers fall over time to zero.

b.ii. In section (2):

  • Variety \(X\) develops, likely from mutation.
  • Variety \(Z\) faces competition from variety \(X\) as the numbers of variety \(Z\) quickly fall as the numbers of variety \(X\) quickly grow. This  shows that variety \(X\) possesses characteristics which vary from \(Z\) and make it more suited to the island.
  • Variety \(Z\) population remains at low levels due to the difficulty of competing for resources with variety \(X\), yet they do not go extinct but instead become a minority variety in the species.
  • The numbers of variety \(X\) plateau off at a lower level than variety \(Z\) as it reaches the limits of resources the environment can provide for both variety \(Z\) and \(X\).
Show Worked Solution

a.    Varieties \(Z\) and \(Y\). 

b.i.  In section (1):

  • Variety \(Z\) is naturally selected as its numbers grow over time until they plateau when it reaches the limits of resources the environment can provide.
  • Variety \(Y\) is not naturally selected as it is not suited to the environment and becomes extinct as its numbers fall over time to zero. 
♦ Mean mark (b)(i) 47%.

b.ii. In section (2):

  • Variety \(X\) develops, likely from mutation.
  • Variety \(Z\) faces competition from variety \(X\) as the numbers of variety \(Z\) quickly fall as the numbers of variety \(X\) quickly grow. This  shows that variety \(X\) possesses characteristics which vary from \(Z\) and make it more suited to the island.
  • Variety \(Z\) population remains at low levels due to the difficulty of competing for resources with variety \(X\), yet they do not go extinct but instead become a minority variety in the species.
  • The numbers of variety \(X\) plateau off at a lower level than variety \(Z\) as it reaches the limits of resources the environment can provide for both variety \(Z\) and \(X\).
♦ Mean mark (b)(ii) 47%.

BIOLOGY, M3 SM-Bank 23

In 1926, T H Muller experimented with fruit flies (Drosophila sp.) by exposing them to X-rays. He found that their offspring showed new phenotypes not observed in the wild population.

Explain how the results of these experiments can provide support for Darwin's theory of evolution by natural selection.  (4 marks)

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→ He demonstrated that genetic mutations produced by X-rays in the lab, could be passed on to offspring.

→ As the X-rays could induce genetic diversity in the fruit flies, Muller’s experiments proved that genetic variation could be increased.

→ These findings bridged the gap between laboratory experiments and field observations, making evolution a rigorous experimental science

→ Muller’s work provided experimental evidence that genetic mutations could drive evolutionary change, aligning with Darwin’s theory.

Show Worked Solution

→ He demonstrated that genetic mutations produced by X-rays in the lab, could be passed on to offspring.

→ As the X-rays could induce genetic diversity in the fruit flies, Muller’s experiments proved that genetic variation could be increased.

→ These findings bridged the gap between laboratory experiments and field observations, making evolution a rigorous experimental science

→ Muller’s work provided experimental evidence that genetic mutations could drive evolutionary change, aligning with Darwin’s theory.

BIOLOGY, M2 2016 HSC 31

As altitude increases, the partial pressure of oxygen \( \text{(p} \ce{O_2)}\) in air decreases. 

Species A and B are closely related endotherms that live in different habitats in Asia. The minimum \( \text{p} \ce{O_2}\) required for 100% blood oxygen saturation differs in these species because of differences in their haemoglobin structure. Data related to these two species are shown below.

\begin{equation}
\begin{array}{|c|c|c|}
\hline \text { Endotherm species } & \text { Habitat altitude } & \text { Minimum } \mathrm{pO}_2 \text { for } 100 \%\ \mathrm{Hb} \text { saturation } \\
\hline \mathrm{A} & \mathrm{High} & 54 \\
\mathrm{~B} & \text { Low } & 80 \\
\hline
\end{array}
\end{equation}

Explain how the differences in these species could have arisen, using the Darwin/Wallace theory of evolution and your understanding of the adaptive advantage of haemoglobin.  (8 marks)

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  • Haemoglobin is a protein that provides a mechanism for transport of oxygen around the body. As it is a protein, it’s structure is dependant on the individual’s genotype.
  • Species A and Species B are able to reach 100% saturation at differing partial pressures of oxygen, meaning they have different DNA which codes for different haemoglobin structures.
  • Species A and B are likely to have diverged from a common ancestor because of differing environmental pressures resulting in two different species. Within the ancestral population there was variation which resulted from random mutations. One mutation would have resulted in haemoglobin that is able to reach 100% saturation at a lower partial pressure of oxygen.
  • When members of the ancestral species moved to a higher altitude the ability of their haemoglobin to reach saturation at a lower \( \text{p} \ce{O_2}\) gave them a survival advantage. These individuals were then more likely to reproduce and pass on their favourable genes.
  • For individuals living at lower altitudes, there is no survival advantage to being able to reach 100% saturation at lower \( \text{p} \ce{O_2}\) which means this trait was not selected for.
  • Over time, due to the isolation at a higher altitude a new species evolved.
Show Worked Solution
  • Haemoglobin is a protein that provides a mechanism for transport of oxygen around the body. As it is a protein, it’s structure is dependant on the individual’s genotype.
  • Species A and Species B are able to reach 100% saturation at differing partial pressures of oxygen, meaning they have different DNA which codes for different haemoglobin structures.
  • Species A and B are likely to have diverged from a common ancestor because of differing environmental pressures resulting in two different species. Within the ancestral population there was variation which resulted from random mutations. One mutation would have resulted in haemoglobin that is able to reach 100% saturation at a lower partial pressure of oxygen.
  • When members of the ancestral species moved to a higher altitude the ability of their haemoglobin to reach saturation at a lower \( \text{p} \ce{O_2}\) gave them a survival advantage. These individuals were then more likely to reproduce and pass on their favourable genes.
  • For individuals living at lower altitudes, there is no survival advantage to being able to reach 100% saturation at lower \( \text{p} \ce{O_2}\) which means this trait was not selected for.
  • Over time, due to the isolation at a higher altitude a new species evolved.
♦♦ Mean mark 41%.