VCE Biology Question Thread

[Angelx001]

CAN SOMEONE PLEASE HELP ME? I'm sooo confused 
2003 VCAA exam 2:
Question 6b.
The differences between the mitochondrial DNA recorded are the result of base substitutions. There are 77 nucleotide differences between Human 1 and Chimpanzee 1. Explain why 77 nucleotide differences is a minimum number of base substitutions.
VCAA's answer: Mutations are reversible and some substitutions may reverse an earlier change making 77 nucleotides the minimum
number of base substitutions.

Can someone please explain it? I don't understand VCAA's answer

[The Usual Student]

CAN SOMEONE PLEASE HELP ME? I'm sooo confused 
2003 VCAA exam 2:
Question 6b.
The differences between the mitochondrial DNA recorded are the result of base substitutions. There are 77 nucleotide differences between Human 1 and Chimpanzee 1. Explain why 77 nucleotide differences is a minimum number of base substitutions.
VCAA's answer: Mutations are reversible and some substitutions may reverse an earlier change making 77 nucleotides the minimum
number of base substitutions.

Can someone please explain it? I don't understand VCAA's answer

Ok i don't know about everyone else but I CERTAINLY never learnt about mutations being reversible...
I don't think it is relevant to our study design so I would not fret, the logic kinda makes sense but the likelihood that another mutation counteracts the initial mutation is so small :/

[Angelx001]

Ok i don't know about everyone else but I CERTAINLY never learnt about mutations being reversible...
I don't think it is relevant to our study design so I would not fret, the logic kinda makes sense but the likelihood that another mutation counteracts the initial mutation is so small :/

I don't understand how the logic makes sense though, can you elaborate?

[carlyjames]

Do you guys think the exam this year is going to be hard?

Probably... considering it's the last of the study design!!

Hopefully it's of a relatively similar standard to last years (and not any harder lol)

[sweetcheeks]

I have answered this question before, so I will just post my response:

Quite a difficult question. What it is asking is why the difference of 77 nucleotides would be the minimum amount of mutations that have occurred. Over time, the mtDNA will undergo mutations. e.g going from ACACTG to ACATTG, but another mutation may occur reversing the initial mutation, ACATTG back to ACACTG, so the mtDNA may have had more mutations than the 77 different nucleotides, therefore 77 differences, which have been observed can be said to be the minimum (as more mutations may have occurred but they can't be detected).

Whilst we can observe that 77 is the number of base differences, many more substitutions may have occurred but subsequent changes may have reserved the changes, which we cannot determine.

[Butterflygirl]

Do you guys think the exam this year is going to be hard?

There's a slight pattern because I thought 2013 was harder, 2014 was easier, 2015 was harder...so maybe 2016 is easier?

Its all comparative, because exams are never easy

[thefrog]

Hi! Could someone help clarify: does radiometric dating involve comparing the amount of parent isotope to daughter isotope, or comparing the amount of isotope in the sample to fresh rock?

[AhNeon]

Do bacteria porduce pre-mRNA?

[Angelx001]

I have answered this question before, so I will just post my response:

Quite a difficult question. What it is asking is why the difference of 77 nucleotides would be the minimum amount of mutations that have occurred. Over time, the mtDNA will undergo mutations. e.g going from ACACTG to ACATTG, but another mutation may occur reversing the initial mutation, ACATTG back to ACACTG, so the mtDNA may have had more mutations than the 77 different nucleotides, therefore 77 differences, which have been observed can be said to be the minimum (as more mutations may have occurred but they can't be detected).

Whilst we can observe that 77 is the number of base differences, many more substitutions may have occurred but subsequent changes may have reserved the changes, which we cannot determine.

Thank you so much!

[HSPLegend]

Hey guys. What do you think are the chances of a 'Human Intervention' short answer question coming up on the 2016 exam? There was one in the 2013 exam, but none in the 2014 and 2015 exam, and I am not very confident in that area (sort of skipped over it because it was the last chapter).

[thefrog]

Does active transport involve lipid-soluble substances? (A little confused because aren't protein channels hydrophilic on the inside?)

[The Usual Student]

Does active transport involve lipid-soluble substances? (A little confused because aren't protein channels hydrophilic on the inside?)

well fi there is a higher concentration on the outside of the cell then on the inside, irrespective of the nature of the substance active transport will occur in order to go against the concentration gradient.

Protein channels are specific to the substance they channel or provide transport for, so I presume a protein channel ( more likely for A.T a protein carrier ) will be lipid soluble on the inside to allow for lipid soluble products to be transported against their concentration gradient.

[vox nihili]

Does active transport involve lipid-soluble substances? (A little confused because aren't protein channels hydrophilic on the inside?)

Not in any really huge way. Tbh I can't really think of one that does, so I'd say it's safe to assume that no, they don't.

[iconoclastic]

Yo, got a question from one of the free NEAP bio exams.

c) Some useful Brassica crops have evolved as the result of hybridisation between species. Hybridisation between the turnip Brassica rapa(2n = 20) and the black mustard Brassica nigra(2n = 16) initially produced a sterile hybrid (2n = 18). However, spontaneous chromosome doubling in the sterile hybrid has given rise to a new species, the brown mustard Brassica juncea(4n = 36).

ii) Explain why brown mustard plants are able to produce fertile seeds if the original hybrid was sterile.

The official answer from NEAP states that "In the sterile hybrid, the 10 chromosomes inherited from Brassica rapa could not form homologous pairs with the eight chromosomes inherited from Brassica nigra so gametes could not form. In the fertile polyploid hybrid B. juncea the chromosomes are able to form homologous pairs in meiosis. (Chromosomes will segregate normally into gametes which have n = 18)"

Could someone please explain this to me because I'm not understanding it despite having read this 10+ times. Cheers in advance xx

[geminii]

My teacher was telling us about reverse transcription involving reverse transcriptase making a DNA complementary copy of the mature mRNA. DNA polymerase then makes a complementary strand of DNA (cDNA) to the existing DNA strand. Specific restriction enzymes then cut the double stranded DNA at specific sites. The same restriction enzymes cut out a section of a plasmid and the gene is inserted into the plasmid. DNA ligase then sticks it all together. The gene is inserted into a plasmid and the plasmid is inserted into a bacteria. If the gene from the plasmid is expressed in the single circular chromosome in the bacteria, this reverse transcription is considered successful.

I was wondering what this process is used for? If the bacteria is then inserted into an organism, is it then considered a genetically modified organism, or a transgenic organism?