VCE Biology Questions Thread

Hey tubes!

1. Firstly radiometric dating is utilized to date igneous rock associated with (near) sedimentary layer that the index fossil is found within, percentage of parent isotope is compared to broken down products, hence using stratigraphy it can be inferred that the age of the index fossil = ____.

Here you must mention that calculations are made based on the half life of the particular radioisotope measured in the radiometric dating; otherwise, how does the ratio of parent to daughter nuclei help?

It might also be good to mention the type of radiometric dating technique you are referring to (i.e. K-Ar dating), as they all have ranges.

2. Using stratigraphy, the fossil found in the same strata is the same age as the index fossil, ____.

Yes, you are correct here as well, but because the unknown fossil is more often than not in another strata from the index fossil used, the index fossils are often used in conjunction with the principle of superposition (which states that rock strata are arranged in a order of progressing age, with the newest at top, in normal conditions). That is to say, if there is a fossil of unknown age and it is found below an index fossil, it can be inferred that the unknown fossil is older than a certain age (i.e. that of the index fossil); and vice versa.

So if the question asked whether using index fossils is absolute or relative (point 2) what would be say?

Relative - because the age of the fossil is being determined by using the index fossil nearby?

or Absolute - because the NUMERICAL value of the fossil is known because of the INDEX fossils whose NUMERICAL age is also known?

Relative. If an index fossil is used it is always relative. Because it is in relation -- or in other words, relative to -- the index fossil (also links back to my previous point that the unknown fossil is more often than not, in a different rock strata to the index fossil, so the approximate numerical age is not known anyway).

Hope this helps .

Hello again tubes

But in that VCAA question by determining absolute age of the igneous rock you could determine the absolute age of the ancient mollusk (as specified in the stem) by using relative dating techniques, since its found in the same stratum (after first using absolute dating techniques on the igneous rock),

You misinterpreted the VCAA question (/suggested answer).

Scientists take samples of igneous rock from igneous rock strata above and below the mollusc fossils. Then they use the ratio of Potassium-40 to Argon-40, and the half-life value of Potassium-40 to calculate the age of these igneous rock strata. Since the mollusc is in between these two strata of igneous rock scientists can kind of average the two values and get an approximate age* of the mollusc fossil. This is absolute dating.

*I know the name of the dating method would suggest that it yields an absolute value, but unfortunately it is not always possible to directly date a fossil.

tubes

No worries, it is mutually beneficial.

Hello hello tubes!

Ah, human evolution question! My [least] favourite!

I will try to give some tips, advice, and some suggested answers. However please note that I am not a teacher, so other advice (i.e. from your VCE Biology teacher) is highly recommended.

a) Which currently known hominin species is most likely the ancestor of Aboriginal Australians? Explain
your response by referring to the different species and other information presented in the article. (3 marks)

a) Homo heidelbergensis that evolved into Homo sapiens 300,000ya in Africa and then migrated to Australia 50,000 ya. Already present before the arrival of the ancestors of Indigenous Australians was Homo erectus - an earlier hominin- that had previously migrated out of Africa and had diverged into Homo floresiensis in Indonesia also coexisted with Homo sapiens.

• You should make it clearer which hominin species you are selecting for your answer (e.g. "Homo heidelbergensis, evolved into Homo sapiens...").

• The question stem specifically asks for an explanation using hominin species referenced in the provided article, you made a tangent which references hominins referenced in the article; these are very different things.

• In this question/example, Homo denisova would have been the best hominin species to reference in your answer, because we are told (presented information) that Aboriginal Australians share some common DNA with H. denisova. Even more compelling evidence presented in the article is that it specifically states no other currently known ancestral species shares similar nuclear DNA with Aboriginal Australians.

b) Comparisons of genomes of Aboriginal Australian populations on the west coast and east coast suggest
that there were two distinct pathways of migration across Australia.
Using supporting evidence from the article, explain likely reasons for the differences seen in the
genomes of the populations. (2 marks)

tubes b) Migration to Australia occurred in 2 distinct pathways, were one group reached and travelled along the East coast 40,000 ya and the 2nd group travelled across the western coast and settled 41000, because the 2 main groups were geographically isolated by Australia's mainland, gene flow was limited and hence different mutations occurred and accumulated in each population's genome

This is good, you have the main guts of it down; as you mentioned gene flow is limited and accumulation of different mutations lead to differences. I would only suggest polishing it up a little bit.

E.g.

• Migration to Australia, by who?
• Be more precise in how gene flow is limited, mainland is usually a means of gene flow.
• Also be more precise that a large amount of time has elapsed in order for the mutations to accumulate.

Overall pretty good answer for this part, goodjob ️

c) Analysis of mtDNA from Aboriginal Australians and phylogeographic patterns support the contention
that there was a continuous presence of distinct populations in discrete geographic areas for up to
50000 years.
i) Identify two types of artefacts that may be found in a particular geographic area if Aboriginal
Australians had lived in that area for long periods of time (thousands of years)? (2 marks)

i) Evidence of art (cultural evolution) such as cave paintings. The presence of stone tools.

• VCAA has specifically stated in their 2022 VCE Biology FAQs that "...ability to distinguish between biological evolution and cultural evolution is not required."
  So I think this is a typical case of VCAA blunder, and am not so sure you will encounter such questions on the end of year exam.

• However, in the case that it does show up, answers such as cave paintings, burial sites... etc. are perfectly fine, I think (stress "I think" ).

ii) Explain how mtDNA phylogeny provides evidence for the continuous presence of Aboriginal
Australian populations in discrete geographic areas. (3 marks)

ii) The large genetic variation in mtDNA indicates that a long time had elapsed since migration hence the time for mutations to accumulate, supporting a continuous presence in Australia as well as in discrete areas as many different mutations occurred in specific isolated population and hence accumulated because of the lack of gene flow leading to 111 mtDNA genomes to diverge

This is a hard question. I had to think about it for a while. What do they mean by continuous presence?

• The question asks for an explanation, you need to give a structured and logical line of thought in order to explain this.

• Perhaps you could say "When Aboriginal Australian populations formed in discrete geographic locations, they became isolated from other populations; which then limited gene flow between these populations. Consequently, over long (and continuous) periods of time, differences in their gene pools from mutations, natural selection and genetic drift accumulated. MtDNA phylogeny can serve as evidence of these differences, and hence the continuous presence of these populations."

• Or perhaps we can take a different angle of attack and say "Large differences between genetics of Aboriginal Populations of discrete geographical areas illustrated in mtDNA phylogeny, evidence that these populations have been established a very long time ago and have been continuously present. As those are the conditions required for these differences to arise, conditions required for factors such as lack of gene flow, different mutations, different natural selection pressures acting, and genetic drift to act on these populations; and create such differences."

• Feel free to add anything to these "suggested" answers (or dispute their validity), I feel like VCAA expects a fairly meaty answer for this type of question; perhaps some more information from the article can be utilised?

• Be careful, as it is very easy to fall into the trap of making an answer which uses false logic/circular reasoning for this sort of question, yuck .

Hope this helps!

(Apologies if I may have used harsh wording.)