Biology: Discussion, Questions & Potential Solutions

[PhoenixxFire]

The question asks about things that prevent pathogens from getting in. By the googling I've just done (I know next to nothing about plants), phytoalexins seem to kick in once an infection has already occurred.
Likewise for abscisic acid.
I think it's really a matter of how anal VCAA is about this. That neither of these is really on the VCE course could make it harder to pick up the marks but it's hard to say. The moral of the story here is that it's always safest to stick with the simple things. There are no extra marks for showing off extra knowledge unfortunately!

For the part of the question about humans it specifies ways that pathogens are prevented from entering the environment, but for the part about plants it says chemical barriers, which seems to imply prevention of infection but then it says they'd be present in a plant 'that is protecting itself from an invading pathogen' so I don't think they're necessarily required to be barriers that stop infection. Also in the stem of the question it refers to plants developing chemical barriers to stop invading pathogens from causing significant damage rather than just to stop pathogens.

[vox nihili]

For the part of the question about humans it specifies ways that pathogens are prevented from entering the environment, but for the part about plants it says chemical barriers, which seems to imply prevention of infection but then it says they'd be present in a plant 'that is protecting itself from an invading pathogen' so I don't think they're necessarily required to be barriers that stop infection. Also in the stem of the question it refers to plants developing chemical barriers to stop invading pathogens from causing significant damage rather than just to stop pathogens.

I stand corrected...both of the above would be correct in that case, my apologies!

[dcassss]

could mtdna be used instead of the dna hybridization answer?

[Erutepa]

could mtdna be used instead of the DNA hybridization answer?

As long as you stated that the mtDNA sequences of each species would be compared to determine the degree of relatedness, I would assume this to be satisfactory. Stating mtDNA by itself would not have been enough to get the mark.

[vox nihili]

As long as you stated that the mtDNA sequences of each species would be compared to determine the degree of relatedness, I would assume this to be satisfactory. Stating mtDNA by itself would not have been enough to get the mark.

Agreed

[gab.r_se]

For the question that asks about the techniques to determine relatedness of a species, did it specifically say that we had to provide an example of a DNA method?

[Erutepa]

For the question that asks about the techniques to determine relatedness of a species, did it specifically say that we had to provide an example of a DNA method?

No. It asked for any two pieces of evidence. Although dna sequence comparison/dna hybridisation would have been an easy one to do.

[gab.r_se]

No. It asked for any two pieces of evidence. Although dna sequence comparison/dna hybridisation would have been an easy one to do.

Phew. Thanks heaps! Probably should have used those two, though.

[vox nihili]

Phew. Thanks heaps! Probably should have used those two, though.

Always best to use what you know and go with the simple stuff, but the stress of exams does funny things to all of us

[Erutepa]

Here are the completed answers that PhoenixxFire and I put together tonight.

These are the answers as we see them; however, we'd really welcome any discussion here and will stick around to answer any questions you have.

The answers contain:

-MCQ answers (checked off by Sine, too!)
-MCQ explanation
-SAQ answers and explanation

For the missing MCQ's, I have tried answering them below as I have come across a copy of the exam.
32. D
Explanation: This question dealt with modes of transmission. If a disease is primarily spread by airborne droplets, washing hands or clean needle programs will not prevent disease transmission. Isolation of infected individuals will. Also, vaccination of infected individuals will not prevent transmissions, in order for a vaccination to be effective in conferring immunity, it must be given before exposure to pathogen to allow stimulation of adaptive immune system and production of memory b and t lymphocytes.

33. B
Explanation: This question dealt with comprehension of the supplied table. If two diseases will both be transmitted to the same amount of people from each infected individual, then both diseases would have similar infection rates. By correctly reading other data on the graph, the other statements can be ruled out.

34. D
Explanation: This question dealt with comprehension of gel electrophoresis runs. The band contributing to a disease can be determined by identifying the band which is present in all affected individuals, but not in normal individuals. Therefore, any other individuals who possess the same affected band can be assumed to have that disease also.

35. B
Explanation: this question dealt with antibiotic resistance. It should be known that antibiotic-resistant diseases means antibiotics are less effective towards some bacteria. Exposure does not cause resistant mutation, instead, it selects for resistant phenotypes. Antibiotics affect bacteria, not viruses or humans.

36. D
Explanation: This question deals with the action of insect vectors in spreading disease. It should be known that sn insect vector will enable the protozoan parasite to enter the host.

I think these are all right, but please correct me if I am wrong or if my explanations are confusing/poorly written (I am in a bit of a rush)

[jsmith_1]

G'day Guys,
I was just wondering if the waxy cuticle could be considered a chemical barrier as well as a physical barrier because of the soluble wax component?
Thanks

[vox nihili]

G'day Guys,
I was just wondering if the waxy cuticle could be considered a chemical barrier as well as a physical barrier because of the soluble wax component?
Thanks

Maybe. I know that's a really annoying answer, but it potentially could be, but if they wanted to be harsher, potentially not. I'd be tending towards no, because the cuticle itself is not a chemical.

[jainamhs]

For the mass apoptosis question, wouldn't an answer of a localised mutation only affect one cell - as in, if a cell accidentally produces way too many caspases, wouldn't it only affect that cell?

Would a response including Th cells recognising a group of cells with similar antigens as foreign be an acceptable answers? Basically the extrinsic apoptotic pathway with some autoimmunity too - but is that a malfunction in apoptosis?

Thanks!

[vox nihili]

For the mass apoptosis question, wouldn't an answer of a localised mutation only affect one cell - as in, if a cell accidentally produces way too many caspases, wouldn't it only affect that cell?

Would a response including Th cells recognising a group of cells with similar antigens as foreign be an acceptable answers? Basically the extrinsic apoptotic pathway with some autoimmunity too - but is that a malfunction in apoptosis?

Thanks!

Genetic diseases are also diseases. It could be a mutation in a germ-line cell.

I think your idea of an immune mechanism is not unreasonable, but I think that talking about helper T-cells being central to this probably would lose you the mark. There are a few steps between helper T-cells and apoptosis. If you'd said cytotoxic T-cells you may have got the mark.

[Erutepa]

For the mass apoptosis question, wouldn't an answer of a localised mutation only affect one cell - as in, if a cell accidentally produces way too many caspases, wouldn't it only affect that cell?

Would a response including Th cells recognising a group of cells with similar antigens as foreign be an acceptable answers? Basically the extrinsic apoptotic pathway with some autoimmunity too - but is that a malfunction in apoptosis?

Thanks!

I'll add that since the question refers to malfunctions in program cell death specifically, I would feel inclined to stay away from the action of cytotoxic t cells. Excessive apoptosis in these scenarios would be more so considered due to malfunctions in the immune system rather than malfunctions in the process of programed cell death itself. But that's just my opinion, and I can't speak on behalf of vcaa.