Unit 4, Chapter 10: Relatedness of Species

Based on the information provided by and the structure of the Edrolo VCE Biology 3-4 Textbook (AI was not used to present any of the information)

Define the Fossil Record

The fossil record is made up of the information derived from fossils. It is arranged in chronological order and aids in mapping the history of life on Earth through evolutionary timelines.

Put the Following Events in Order (least to most recent):

• Cambrian explosion

• First multicellular organisms

• First animals on land

• First humans

• First prokaryotes

• First eukaryotes

• Widespread photosynthesis

• First flowering plants

• First mammals

1. First prokaryotes

2. Widespread photosynthesis

3. First eukaryotes

4. First multicellular organisms

5. Cambrian explosion

6. First animals on land

7. First mammals

8. First flowering plants

9. First humans

Define Fossils

A fossil is the preserved body, impressions or traces of a dead organism.

Define Fossilisation

Fossilisation is the process by which an organism becomes a fossil, rather than being consumed or decomposed.

Describe the Process of Fossilisation

1. Remnants of an organism are rapidly covered by sediment, preventing the remains from decomposition.

2. Over time, sediment layers build upon each other and compact until the pressure sements them together to form sedimentary rock.

3. Within this rock, fossilised remains are preserved.

Identify 5 Optimal Conditions for Fossilisation

• Physical protection from scavengers to decomposers

• Areas of rapid sediment accumulation

• Constant cool temperatures

• Low oxygen availability

• Low light exposure

Define Permineralised Fossils

Permineralised fossils are fossils formed when mineral-rich groundwater deposits minerals (eg. silica, calcite) into organic material, creating a mineral relic.

Define Mould Fossils

Mould fossils are fossils formed when a living this decomposes underneath sediment, creating a cavity in the shape of the dead organism.

Define Cast Fossils

Cast fossils are formed when the cavity of a mould fossil is filled with sediment.

Define Trace Fossils

Trace fossils are fossils or structures that provide indirect evidence of an organism’s existence by indicating their presence (eg. footprints).

Define Relative Dating

Relative dating is a dating technique used to determine the relative age of a fossil by comparing its position to other fossils or rock in surrounding rock strata.

Explain the Law of Fossil Succession

The principle that fossils of the same age will be found within the same layer of sedimentary rock, and fossils found in a higher or lower layer will be younger or older, respectively.

Define Geological Timescales

Informed by the law of fossil succession, we are able to assign seperate strata to particular periods of time (by first determining the age of the strata) to create a geological time scale.

Define Index Fossils

Index fossils are a group of widespread fossils which existed for a short period of with a known age and can thus be used to determine the relative age of another fossil.

Identify 4 Criteria for Index Fossils

• Physically distinctive

• Large population

• Inhabited widespread geographical areas

• Lived within a known short period of time

Define Transitional Fossils

Transitional fossils are fossils that show traits that are common to both its ancestral and descendant groups, and can thus be used to determine evolutionary changes between two related yet physically distinct species.

Define Absolute Dating

Absolute dating is a dating technique used to determine the absolute age of a fossil by measuring the relative amounts of radioisotopes to their stable products (radiometric dating).

Define a Half-Life

The half-life of a radioisotope refers to the time taken for half the mass of a sample to break down into its predictable, stable products.

Outline 3 Principles of Radiometric Dating

1. Radioisotopes are unstable elements that will break down over time into predictable stable products

2. On average, the rate of breakdown is constant and can be modelled (aided by calculating the half-life)

3. The half-life of a radioisotope can be used to determine how old something is by measuring the ratio of the remaining radioisotope to its product

Define the Dating Period

The dating period is the range of time since fossilisation in which a particular radioisotope series can be used to measure the age of a fossil. Beyond this period, too much of the radioisotope will have broken down, making it too difficult to estimate the age.

Identify the Dating Period of Radiocarbon Dating

1,000 to 50,000 years

Explain the Process of Radiocarbon Dating

1. All living things contain carbon, and the ratio of stable C¹² to radioactive C¹⁴ in an organism will be the same as the atmospheric ratio due to the constant cycling of carbon.

2. When the organism dies and begins to decay, C¹⁴ will begin to break down into stable N¹⁴ isotopes. Since carbon is no longer being cycled through the organism and the atmosphere, C¹² levels remain constant.

3. At any point within the dating period, scientists can compare the C¹⁴:C¹² ratio in the fossil to atmospheric ratios to ascertain how long the C¹⁴ has been decaying and thus approximate when the organism died.

Define Homologous Structures

Homologous structures are features present in two or more species that may look and function very differently but can be shown to have been derived from a common ancestor. They provide evidence for divergent evolution.

(eg. the bone structures of whale fins and cat legs)

Define Analogous Structures

Analogous structures are features present in two or more species that fulfil the same function but did not originate from a common ancestor. They provide evidence for convergent evolution.

(eg. the function of bat wings and dragonfly wings)

Define Divergent Evolution

Divergent evolution is the process in which a common ancestor evolves into two or more different species (descendant species).

Define Convergent Evolution

Convergent evolution is the process in which distantly related species evolve similar traits over time independently, due to the action of similar selection pressures.

Define Vestigial Structures

Vestigial structures are features that have lost all or most of their usefulness as a result of evolution by natural selection. They would have once served a purpose for an organism’s ancestors but, due to changed selection pressures, are no longer required for survival.

Define Molecular Homology

Molecular homology is the study of the similarities in the nucleotide sequences of DNA or amino acid sequences of proteins between organisms to establish degrees of relatedness.

Define Conserved Genes

Conserved genes are genes that have remained largely unchanged throughout evolution and are found across the genomes of many species.

Identify 2 Proteins Commonly used to Test Amino Acid Similarity

Haemoglobin (Hb) and cytochrome c

Identify 2 Advantages of mtDNA to Test DNA Sequence Similarity

1. mtDNA has a much higher mutation rate than nuclear DNA, meaning that for very closely related species, there will more likely be enough differences in DNA sequences to compare.

2. There is no recombination because mtDNA is only inherited from the mother. This means that mtDNA remains unchanged from generation to generation, making it easier to trace maternal lineages.

Explain why DNA Similarities are Often Analysed for Closely Related Species

Closely related species are likely to share very similar sequences for certain proteins. If only amino acid sequences were analysed, researchers would lack the nuance of DNA to reveal different nucleotide sequences and silent mutations that didn’t alter amino acid sequences due to the redundancy of the genetic code.

Explain why Amino Acid Similarities are Often Analysed for Distantly Related Species

Although DNA is more specific, amino acids are easier to interpret and are therefore used to determine relatedness between more distantly related species that are likely to have more differences.