VCE Biology Questions Thread

Meep<3

Taaaa76 I think you should start off with the easier ones so that you can easily tell in which areas you need to focus on and to build up your confidence. After a few I think maybe you could start the harder ones.I'm not sure about which companies are better, I think its best to ask your teacher. Hope this helps.

btw how is everyone else going with exam prep??

Taaaa76

Meep<3
Haven't started practice exams yet, I have only just started revising the content from semester 1 and I have a trial exam tomorrow. yikes

Taaaa76

I have a question from AOS 1 unit 3: Is a silencer the same as an operator? or is an operator only in prokaryotes and a silencer in eukaryotes?

Seb

Taaaa76 From what I know, the operator is where the repressor binds in the trp operon to inhibit transcription (trp repression) and the silencer simply prevents transcription of an operon.

Taaaa76

For the polymerase chain reaction, what are the temperatures for each stage?? Every single source says something different
Edrolo says:
90-95 for denaturisation
50-55 for annealing
72 for elongation
TSSM says:
98 for denatureisation
60 for annealing
72 for elongation

Like what am I supposed to write in the exam????

Meep<3

Taaaa76 Question 2 on the 2022 exam is about PCR and asks about the different temperatures at each step. This is the answer to that question from the examiner's report, so I think you should go off this.

The stages are:
• Stage 1: denaturation occurs at e.g. 94°C; DNA strands separate
• Stage 2: annealing occurs at e.g. 55°C to allow the primers to join
• Stage 3: extension occurs at e.g. 72°C; optimal temperature of Taq polymerase and adding of nucleotides occurs.

hope this helps

Taaaa76

Meep<3
Thank you so much this definitely helped

Taaaa76

I was doing a TSSM exam and I came across this question:
Lithium hydroxide is a chemical that removes carbon dioxide by chemically reacting with it. During an experiment, a pot plant is placed into a sealed container that contains lithium hydroxide. Identify what will occur to the rate of photosynthesis. Provide a reason to support your answer. (1 mark)
The answer was:
The rate of photosynthesis will decrease. No mark awarded but must be stated. AND Carbon dioxide is an essential reactant in the process of photosynthesis. When it is a limiting factor there are insufficient carbon dioxide molecules to combine with the hydrogen ions. Less glucose is therefore produced.

I didn't understand this part: When it is a limiting factor there are insufficient carbon dioxide molecules to combine with the hydrogen ions.

Does carbon dioxide normally bind to hydrogen ions in photosynthesis? Is this referring to the Hydrogen ions that NADPH transfers??

prettypink1881

Taaaa76 I think they are talking about the carbon dioxide that binds with hydrogen and oxygen to make glucose (C6H12O6) but I'm not completely sure. it would makre sense though because it correlates directly to the fact that less glucose would be produced.

hope this helps!

Taaaa76

prettypink1881

Thank you!
Would a question like that come on the exam? As in should I expect to have to write that CO2 wouldn't be able to bind hydrogen to produce glucose if this question came in the exam?

prettypink1881

Taaaa76 personally I don't think so, because vcaa stated that

"Students should understand that a biochemical pathway is a series of steps (which may occur at different
locations within a cell or, in the case of eukaryotic organisms, in different cells) from initial reactants to a final
product and that each step is facilitated by enzymes and coenzymes. Students should understand the inputs,
outputs and cellular locations of the light dependent and light independent stages of photosynthesis within
chloroplasts in C3 plants. They do not need to understand the specific details of
the mechanisms that underpin biochemical pathways involved in photosynthesis and cellular respiration."-I belivee this means you don't need to know about which elements bind to other elements.
My teacher also told me that TSSM usually has much harder questions that have some content that isn't examined in the vce exam.

Taaaa76

prettypink1881

That's a relief. Thanks for letting me know so quickly

abbey1234321

Can someone please help me with this question? It is from the 2023 Northern Hemisphere exam, so there are no answers available.
DNA evidence from present-day humans shows that Homo neanderthalensis interbred with
H. sapiens while the two species coexisted in Europe. Fossil discoveries show that H. erectus
and H. sapiens coexisted in Indonesia about 143000 years ago.
Explain whether you would expect scientists to find DNA evidence to support the view that
H. erectus and H. sapiens interbred?

thanks 🙂

prettypink1881

abbey1234321

maybe modern day humans living in indonesia would have higher percentages of homo erectus dna than compared to other modern day human populations living in other countries- this would prove that homo sapiens and homo erectus coexisted and interbred in indonesia 143000 yrs ago.

I'm not sure if my answers correct but that's what I would say, hope it helps!

abbey1234321

prettypink1881
Thanks so much I really appreciate it!

Laila

Hey guys, could someone please explain to me why this answer wouldn't be allowed:
question: " Over the weekend, Morgan went to the movies with Alex and PAT. They all sat together and shared a drink. The next day Morgan had symptoms of the flu virus and the Doctor told Morgan that Morgan had been infectious when at the movies. Describe a component of the immune systems first line of defence that the virus overcame:"
answer: "The virus had to have overcome the intact skin barrier on Morgan"
On the answers, it doesn't mention anything about skin, only mucous, nose hairs and stomach acid.
Thanks in advance 🙂

HKS

Laila
Hi Laila, i think its because it is a flu virus and this is transmitted via air droplets, so the flu will enter the nose by 0inhaling the air particles or either thru contaminated food or water so stomach acid. and therefore intact skin would not be an appropriate answer for a question like this.

Laila

HKS Thank you so much 🙂

HKS

All good🙂

Taaaa76

I need help with this question:

A scientist wishes to make a recombinant plasmid into which they are going to insert gene X.
(I summarised what's Important from the table they showed):
EcoRI (sticky ends)
HindIII (sticky ends)
BamHI (sticky ends)
BalI (blunt ends)
HaelI (blunt ends)
SmaI (blunt ends)
The best option to do this is to
A. use BamHI to cut around the gene and through the plasmid.
B. cut around gene X with SmaI and cut the plasmid with SmaI.
C. cut around gene X with EcoRI and cut the plasmid with BamHI.
D. cut around gene X with HaeIII and cut the plasmid with HindIII.

The answer is A but I don't understand how. Can someone explain?

_sophiestudies_

Taaaa76 Remember that recombination works best with sticky end restriction endonucleases. This is because they create a specific overhang in the gene that can match the overhang created in the plasmid (blunt ends aren't specific enough, and any nucleotides could insert themselves. There's no hydrogen bonding between the complementary nucleotide overhangs to stabilize the formation of the vector/insert structure (i.e. the overhangs of the gene and plasmid can form hydrogen bonds, whereas that doesn't work with blunt ends). Therefore, B and D are incorrect (they're blunt end restriction endonucleases). C isn't correct either because you need to use the same restriction endonuclease for both the gene and plasmid, as they'll make a cut at the same base code (means they'll be complementary and can bind). A is correct because BamHI is a sticky end restriction endonuclease and is used to cut around the gene and through the plasmid (used for both).

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