VCE Biology Question Thread

[vox nihili]

I'm not certain as to why introns exist but do know they are certainly not 'junk DNA.' They may be involved in gene regulation but I'm not sure.

In alternate splicing, some exons are removed along with the introns

You don’t need to know what introns exist for, but your suspicions are quite right. Well done

[vox nihili]

Correct me if I'm wrong but I don't think the plasmid is integrated into the chromosome. The plasmid is just inserted into the plant cell. It replicates independently of the nuclear DNA but is still passed on to daughter cells in mitosis.

Nah it does become integrated into the chromosome. You don’t really need to know how that happens though.

If a plasmid didn’t become integrated into the chromosome, it wouldn’t be replicated. Only bacteria can replicate plasmids

[TheBigC]

Nah it does become integrated into the chromosome. You don’t really need to know how that happens though.

If a plasmid didn’t become integrated into the chromosome, it wouldn’t be replicated. Only bacteria can replicate plasmids

Just to add to this.

With A. tumefaciens-mediated uptake of genetic material, there is a T-DNA region on the A. tumefaciens plasmid. This segment is where the gene of interest is inserted, whereby the T-DNA (Transfer DNA) is 'transferred' into the plant cell. The plant cells is said to be transfected. This T-DNA then INTEGRATES itself into the plant cells genome (in the nucleus).

[Apricot]

In a question asking us to discuss humoral response (like in the sample exam) or even cell mediated response, would we be expected to discuss MHC markers in the process? None of the past vcaa exams seem to discuss MHC markers and neither do most practice exam companies. Could someone please clarify

[helpmepls112]

Hi guys,
I'm kind of stuck on weather my answer for exam 1 2011, question 5 is wrong.
It tells us to describe how antibodies and macrophages inhibit the spread of the bacterium disease, and I went on to write that the macrophages engulfs and destroys the bacteria by phagocytosis...presents the antigen on the MHC 2 markers. Then the MHC 2 markers bind T helper cell, which will generate B cells which will differentiate into plasma cells that secrete specific antibodies against the disease. The antibodies will then bind to the bacterium and cause agglutination.

Is it wrong to mention T helper cells and all that, because the answer was really simple and didn't mention any of that???

++ During the humoral response do we mention T cells at all  or is that wrong? (like T helper cells present antigen to naïve B cell etc..)

Thanks in advance!

[chrisjudd00]

Although they dont mention the T-helper cells specifically in the answers, the explanation of T-helper cells recognizing the antigens presented to them by the APC's and then stimulating the B-cells to proliferate (once the antibody binds to the antigen) into B-plasma and memory cells will be 100% fine. 

[banksduyvu]

Hey,
1) I don't quite understand how the further the population out from Africa, the more similar their mitochondrial DNA is. (Africa would have most diverse mtDNA)
2) Also, a question from NEAP exam states that the further out from Africa, the more genetic diversity, so African population would be more genetically similar.
(sorry for the clumsy wording)

Aren't those two ideas contradicting each other ?
Is it because 1) is referring to mtDNA and 2) is just their nuclear genes

[ezferns]

Is there such a thing as memory Tc cells and memory Th cells?
VCAA says T memory cells differentiate into Tc cells and Th cells.

[Jilian394]

To what extent do we need to know about neural transmission? We learnt about it in class for some reason but I can't see it on the study design right now.

[PhoenixxFire]

To what extent do we need to know about neural transmission? We learnt about it in class for some reason but I can't see it on the study design right now.

You just need to know the an action potential causes a neurotransmitter to be released by the prestmaptic neuron which then binds the the postsynaptic neuron (or target cell) causing an action potential. More detail was on the study design last year, but not there anymore.

[PhoenixxFire]

In a question asking us to discuss humoral response (like in the sample exam) or even cell mediated response, would we be expected to discuss MHC markers in the process? None of the past vcaa exams seem to discuss MHC markers and neither do most practice exam companies. Could someone please clarify

In humoral immunity yes. (Just that Th cells bind to their antigen presented on a MHC2 marker.

In the cell mediated response yes. (Just that Tc cells bind to peptide fragments presented on MHC1 marker)

You might get full marks without it, but it is more correct to mention it.

[Apricot]

In humoral immunity yes. (Just that Th cells bind to their antigen presented on a MHC2 marker.

In the cell mediated response yes. (Just that Tc cells bind to peptide fragments presented on MHC1 marker)

You might get full marks without it, but it is more correct to mention it.

For cell mediated, would i be expected to discuss co stimulation of the cytotoxic t cell by an APC and a T helper cell both releasing cytokines?

[PhoenixxFire]

Is there such a thing as memory Tc cells and memory Th cells?
VCAA says T memory cells differentiate into Tc cells and Th cells.

I have always been told yes. Found this on Wiki:

Memory T cells may be either CD4+ or CD8+ and usually express CD45RO.[2]

CD4 cells are Th cells and CD8 cells are Tc cells.

[PhoenixxFire]

For cell mediated, would i be expected to discuss co stimulation of the cytotoxic t cell by an APC and a T helper cell both releasing cytokines?

I normally mention it without any detail as they want to test your knowledge of cell mediated immunity not humoral. I would say something along the lines of .... the selected (or activated) Tc cell is stimulated to divide and differentiate by cytokines released from a selected (or activated) Th cell....

[PhoenixxFire]

Thank you for your answers! Just a quick question, how come a few years ago VCAA said that a hormone is "a chemical compound produced in a cell. It either acts within the cell or diffuses or is transported to other cells where it brings about a specific response," this implying paracrine autocrine and endocrine signalling?

The reason for the whole mess with hormones is that there is this other type (now called neurohormones) that are released from a neuron into the blood in the brain and are transported to another neuron nearby (paracrine signalling) these are now classified differently so you are fine to call hormones endocrine.