VCE Biology Question Thread

[sophiie]

i know that when an antigen binds to a b cell its clonal selection,
but when an antigen binds to a t helper cell could that also be considered clonal selection?

[darkz]

i know that when an antigen binds to a b cell its clonal selection,
but when an antigen binds to a t helper cell could that also be considered clonal selection?

Just note that free antigens do not bind to T helper cells, rather, the antigens presented by APCs to a T helper cell can be regarded as clonal selection

[Hiea]

How would you define signal transduction?

I would say something like, "the internalisation and interpretation of an extracellular signal that leads to a cellular response", since mentioning second messengers would imply that the hydrophobic pathway is not an example of signal transduction. But would it be better to mention second messengers and a signal cascade after all (assuming the question isn't asking for a description of what comes after Reception)? I'm worried about being too vague with my answers.

[AISHAB]

Based on last year's exam and comparable SAC results roughly 55%

What are your sac averages for unit 3 and 4?

You could use the app study score predictor, but should know that it is just basing it off last years sac and exam marks, so your study score will vary, as they are unaware of your rank?

[LOL_ABC]

Im legit scared im midway my weak cohort and averaged 60% so what  exam mark i need

[AISHAB]

Im legit scared im midway my weak cohort and averaged 60% so what  exam mark i need

I'm not sure exactly, but try aiming for around 70% for the exam to achieve around 32

[persistent_insomniac]

What is the difference between validity and accuracy?

[PhoenixxFire]

What is the difference between validity and accuracy?

Validity: whether the experiment is measuring what it’s supposed to be measuring (ie. if it is actually measuring the effect of the IV on the DV)
Accuracy: how close your measurement is to the actual value of something (whether that be weight or length or whatever)

[AngelWings]

What is the difference/are the differences between genetic testing and genetic screening?

I've heard that genetic testing is done for one individual, whereas genetic screening is done for multiple (and that genetic testing only looks at one gene?). Is that correct?

Uh... kind of. The biggest reason is why you would choose genetic testing vs. genetic screening. If there's a history of genetic disease(s) in the family, you may as well get genetic testing, which, as you said, is generally more about diagnosing the individual. If it's just a routine check, then genetic screening is the way to go and screening is typically more general, usually made to check common mutations and such in the population. Another explanation can be found here.

How would you define signal transduction?

I would say something like, "the internalisation and interpretation of an extracellular signal that leads to a cellular response", since mentioning second messengers would imply that the hydrophobic pathway is not an example of signal transduction. But would it be better to mention second messengers and a signal cascade after all (assuming the question isn't asking for a description of what comes after Reception)? I'm worried about being too vague with my answers.

According to Heidi's VCAA approved biology definitions, signal transduction is "the series of events that occur after the receipt of a specific signal and which result in a response". I think your definition is mostly a reworded version of that, so a hesitant yes from me. (Hesitant, because I didn't do VCE Bio and haven't done molecular bio in a while.)

[randy123]

what score do u guys reckon is needed for a 40 study score from tomorrow (sac average A)

[Bri MT]

around 80

what score do u guys reckon is needed for a 40 study score from tomorrow (sac average A)

Around 80%

I used this
More info on study scores can be found in the Victorian Technical Score Discussion section of the forums

[Hirul1280]

To what temp do you cool in DNA-DNA Hybridisation?
Also, could someone explain to me the evolution models? Still confused to what they propose
- Multiregional
- Out of Africa
- Assimilation

Also, also do we need to know CRISPR & Micro Arrays?

[Owlbird83]

To what temp do you cool in DNA-DNA Hybridisation?
Also, could someone explain to me the evolution models? Still confused to what they propose
- Multiregional
- Out of Africa
- Assimilation

Also, also do we need to know CRISPR & Micro Arrays?

55 degrees for cooling.

OUt of Africa is that H. erectus evolved into H.sapiens, then some H. sapiens moved out and spread around the world.
Multiregional is that H.erectus moved out of Africa and then evolved into H.sapiens around the world, with gene flow between populations.
I don't know what assimilation is.

I don't think we need to know CRISPR or micro arrays

[cooperbailey14]

To what temp do you cool in DNA-DNA Hybridisation?
Also, could someone explain to me the evolution models? Still confused to what they propose
- Multiregional
- Out of Africa
- Assimilation

Also, also do we need to know CRISPR & Micro Arrays?

You don'd need to know the temperatures for DNA hybridisation, just the melting temperature (Tm), being that of which 50% of all bases separate. The out of Africa theory refers to the fact that the Homo species originated in Africa, and migrated elsewhere. Therefore African H. sapiens are found to have the lease amount of differences in their makeup compared to Australopithecus, in comparison to H. Sapiens present in other parts of the world. This is primarily due to the fact that there has less time for differences to occur in the DNA of the African populations in comparison to others such as Asian and European.
CRISPR and Micro Arrays, i believe, are not apart of the study design, but just understand that CRISPR is considered a form of genetic engineering as individual nucleotides can be substitued.

[PhoenixxFire]

1. To what temp do you cool in DNA-DNA Hybridisation?
2. Also, could someone explain to me the evolution models? Still confused to what they propose
- Multiregional
- Out of Africa
- Assimilation

3. Also, also do we need to know CRISPR & Micro Arrays?

1. 55 degrees Celsius (or thereabouts)

2. I don't know any of these particularly well, and I'm still not at all convinced that you need to know about them, but this is what I had in my notes:
Theories on the origin of modern humans
1. Out-of-Africa Hypothesis
This theory states that all humans (Homo sapiens) evolved from a discrete African population within the last 200,000 years and then migrated in relatively recent times throughout Africa, Europe, and Asia, displacing the more primitive H. erectus and H. ergaster populations. Also referred to as the replacement theory.

Mitochondrial DNA evidence – A comparison of mitochondrial DNA of native people around the world allows us to use a molecular clock to calculate the rate of mutation in mitochondrial DNA and therefore figure out where each group of native people came from and when. This traces it back to Africa 200,000 years ago. This theory is the one that is generally accepted.

2. Parallel evolution hypothesis
This theory states that the Homo sapiens line is older than 200,000 years, the theory is that Homo sapiens originated independently in different parts of the world from Homo erectus populations that had migrated from Africa around one million years ago, it was presumed that although there was some geographic isolation of populations there was some contact and hybridisation, and hence mixing of gene pools.

3. Nope