VCE Biology Question Thread

[infecthead]

Okay just to clarify, diploid number must always be positive but haploid number can be either positive or negative? Also, will organisms with a more expansive genome always show more genetic variation than those with a smaller genome?

Diploid number can be odd/even, humans have a diploid number of 23. A normal haploid cell should be even, because anything multiplied by two is even, however chromosomal abnormalities can alter this (trisomy-21 results in 47 chromosomes total for example).

And I don't think a bigger genome/more DNA is definitive proof of a more genetically diverse species. For instance, onions have more DNA than humans, and yet they're only onions.

[RazzMeTazz]

If you are given the genotype SsWw and and the question says that these two genes are linked, do you assume that the alleles on the chromosomes are linked in the combination of SW and sw ?

How would you know they aren't linked in this combination of alleles: Sw and sW?

(On one of my SACs during the year, we got a question like this and I didn't know which combination of alleles was on which chromosome, which is why I was wondering! )

[chekside]

Diploid number can be odd/even, humans have a diploid number of 23. A normal haploid cell should be even, because anything multiplied by two is even, however chromosomal abnormalities can alter this (trisomy-21 results in 47 chromosomes total for example).

And I don't think a bigger genome/more DNA is definitive proof of a more genetically diverse species. For instance, onions have more DNA than humans, and yet they're only onions.

You've got it around the wrong way. The human diploid number is 46 and the human haploid number is 23.

[sparkyblossom]

Diploid number can be odd/even, humans have a diploid number of 23.

That's enough bio for today!

[infecthead]

You've got it around the wrong way. The human diploid number is 46 and the human haploid number is 23.

Yeah I just realised that...damnit I need a break too .-.

[melons]

If you are given the genotype SsWw and and the question says that these two genes are linked, do you assume that the alleles on the chromosomes are linked in the combination of SW and sw ?

How would you know they aren't linked in this combination of alleles: Sw and sW?

(On one of my SACs during the year, we got a question like this and I didn't know which combination of alleles was on which chromosome, which is why I was wondering! )

In the questions I've seen you get a table with the number of offspring of each genotype or something... More offspring will have the parental combination.

So if the parents are SsWw x ssww and the ratio is not 1:1:1:1, the genes are linked. And the two most common genotypes will be the parental combination 

[soNasty]

Can someone give me a brief rundown of what occurs during bacterial infection?

[shivaji]

Can someone give me a brief rundown of what occurs during bacterial infection?

-immune system detects the bacteria as non-self (by macrophages engulfing bacteria and displaying its antigens  on surface)
-macrophages release interlukin-1 to stimulate t-helper cells, which bind to the antigens displayed on MHC-II markers by the APC
-t-helper cells secrete interleukin-2, which activates a specific b-cell that has specific antibody receptors on its surface for the bacterial antigen
-the stimulated b-cell rapidly divides via clonal expansion, producing memory b-cells and plasma b-cells
-plasma b-cells secrete specific antibodies into the general circulation, which then form antibody-antigen complexes  with the bacteria (agglutination)
- macrophages comes and engulf these complexes.
- bacterial infection is removed, excess immune cells die by apoptosis
- memory cells remain in circulation however, and will rapidly divide if they encounter the same antigen again
 

[Reus]

-immune system detects the bacteria as non-self (by macrophages engulfing bacteria and displaying its antigens  on surface)
-macrophages release interlukin-1 to stimulate t-helper cells, which bind to the antigens displayed on MHC-II markers by the APC
-t-helper cells secrete interleukin-2, which activates a specific b-cell that has specific antibody receptors on its surface for the bacterial antigen
-the stimulated b-cell rapidly divides via clonal expansion, producing memory b-cells and plasma b-cells
-plasma b-cells secrete specific antibodies into the general circulation, which then form antibody-antigen complexes  with the bacteria (agglutination)
- macrophages comes and engulf these complexes.
- bacterial infection is removed, excess immune cells die by apoptosis
- memory cells remain in circulation however, and will rapidly divide if they encounter the same antigen again

By stating 'cytokine' instead of 'interlukin-2, would this suffice? I feel like the specifics are too excessive.

[soNasty]

For some reason I thought that whole process only occurs for viral infections! When do Tc cells come into play? (And NK cells)?

[shivaji]

By stating 'cytokine' instead of 'interlukin-2, would this suffice? I feel like the specifics are too excessive.

yeh your right, cytokine is more than enough.

For some reason I thought that whole process only occurs for viral infections! When do Tc cells come into play? (And NK cells)?

i guess it happens for both. Tc cells and NK cells come into play for virus-infected cells, and cancer cells, and eukaryotic pathogens only.

[grannysmith]

Can someone give me a brief rundown of what occurs during bacterial infection?

Shivaji's answer was quite complex. Depending on the number of marks, the following should suffice:
•a B cell with specific antibodies binds to the antigens on the bacteria
•T-helper cells detect the antigens expressed on MHC II
•T helper cells release cytokines which stimulate the B cell to proliferate and differentiate into B memory cells and B plasma cells, which produce specific antibodies
•antibodies attach to antigens on bacteria, causing them to agglutinate/neutralising them/activating complement proteins
•phagocytes engulf and destroy bacteria

[vox nihili]

Shivaji's answer was quite complex. Depending on the number of marks, the following should suffice:
•a B cell with specific antibodies binds to the antigens on the bacteria
•T-helper cells detect the antigens expressed on MHC II
•T helper cells release cytokines which stimulate the B cell to proliferate and differentiate into B memory cells and B plasma cells, which produce specific antibodies
•antibodies attach to antigens on bacteria, causing them to agglutinate/neutralising them/activating complement proteins
•phagocytes engulf and destroy bacteria

This response is perfect, and is right on about what would be expected in VCE.

[dankfrank420]

Two things:

On 2013 exam question 2c, it says the tertiary structure is a 3d structure composed of secondary structures... isn't this wrong? Because there can be other random amino acid chains beside helices and pleated sheets?

Also can someone explain the process/initiation of apoptosis?

[mahler004]

Two things:

On 2013 exam question 2c, it says the tertiary structure is a 3d structure composed of secondary structures... isn't this wrong? Because there can be other random amino acid chains beside helices and pleated sheets?

Also can someone explain the process/initiation of apoptosis?

We had this discussion the other day, general consensus was yes (or at least 'not wrong but not really well-worded.')

Best definition is that the tertiary structure is the 3D structure of the protein, formed by interactions between side chains (hydrogen bonds, disulphide bonds, hydrophobic interactions, ionic bonds etc.)