Biology Unit 3 Questions Megathread

[Russ]

I don't do plant biology, but electrons will move to higher energy levels/subshells in order to "absorb" energy

[WhoTookMyUsername]

bump added a Q thanks russ

[Kaille]

why does the humoral response involve the MHC 2 marker, while the cell mediated response involves the MHC 1 marker?

[Russ]

why does the humoral response involve the MHC 2 marker, while the cell mediated response involves the MHC 1 marker?

MHCI is recognised by CD8 cells, which then destroy the cell they bind. That makes it directly cell mediated.
MHCII is recognised by CD4 cells, which are responsible for activating B cells, which produce antibodies. That makes it "humoral" because the antibodies are soluble in the serum etc.

Does  negative feedback work by simply causing a change in the variable being detected, or does it act directly on the gland (i'm sure its the first one but some sources imply otherwise) i.e. when drawing a negative feedback diagram, should i draw the feedback arrow to the stimulus, or the gland producing the hormone?

How does it cause a change in the variable/stimulus without affecting the gland? If there's too much sugar in the blood, you can't just magically reduce it, you have to stimulate the pancreas to produce insulin to insert GLUT4 into cell membranes to transport sugar out of the blood.

5) Do leukocytes phagocytose eukaroyttc pathogens? Neap says they do but Campbells  says otherwise

Depends what you mean by leucocytes and phagocytose. Eukaroytic pathogens generally aren't phagocytosed because they're too big...but phagocytes are involved in their clearance, as are other cells. Degranulation and oxidative burst to produce various toxic molecules are important clearance mechanisms.

q4 is biochem and i can't remember it clearly enough right now. google and wikipedia might help you out

[WhoTookMyUsername]

Thankyou

another question :S in addition to the remaining  ^ ones

- i remember someone talking about this before, but i couldn't find the exact page -

is it better to define an autoimmune disease as

the body is unable to distngush between self and non self

or

the body recognises self AS non - self cells

thanks

EDIT:
This may sound stupid


What does water do for the body, from a VCE biological standpoint?
Is it mainly just to provide solvent etc.
?
or does it directly participate in reactions (in addition to hydrolysis etc. ) integral to VCE Biology? (except photosynthesis)

thanks

[scocliffe09]

Thankyou

another question :S in addition to the remaining  ^ ones

- i remember someone talking about this before, but i couldn't find the exact page -

is it better to define an autoimmune disease as

the body is unable to distngush between self and non self

or

the body recognises self AS non - self cells

thanks

EDIT:
This may sound stupid


What does water do for the body, from a VCE biological standpoint?
Is it mainly just to provide solvent etc.
?
or does it directly participate in reactions (in addition to hydrolysis etc. ) integral to VCE Biology? (except photosynthesis)

thanks

Autoimmune disease is where the body attacks its own cells as it is unable to distinguish self from non-self. also be aware of the difference between immunodeficiency and autoimmunity.

Water acts as a solvent, transport and reaction medium, and also (occasionally but still significantly) as a reactant in some metabolic processes. Osmotic regulation is also a vital part of homeostasis because we lose control of everything if we become too dehydrated.

Just be careful - the body is not quite as black and white as your questions seem to make it out to be.

[WhoTookMyUsername]

hehe thanks

I often ask questions in that format just so i can get a more direct idea and more direct response

[Russ]

is it better to define an autoimmune disease as

the body is unable to distngush between self and non self
or
the body recognises self AS non - self cells

Both. The body recognises self as non-self because it is unable to distinguish between them. Worth bearing in mind that simply saying "the body cannot distinguish between self and non self" isn't correct (although VCE might let it slide). It is extremely rare that the immune system will simply target all self molecules as non-self...it's almost always a specific antigen or class of antigens

[shinny]

is it better to define an autoimmune disease as
the body is unable to distngush between self and non self
or
the body recognises self AS non - self cells

Although it's often said in the former way - that the body is unable to distinguish self and non-self - I think it's better said in the latter way. That's because the former could also be interpreted to not only mean that the body recognises self as non-self, but also vice versa. This would lead to an immunodeficiency of sorts where the body recognises foreign antigens as self. However, auto-immune diseases aren't associated with that, and it's purely a one way thing. So yeh, it's probably best to specify that the body recognises self as non-self.

[WhoTookMyUsername]

As always thanks for your great help


At VCE level , how is water produced in light independent reactions of photosynthesis?

I looked at both NOB and Campbells, and neither has water leaving the calvin cycle :S

EDIT:

Wiki says Natural Killer cells are lymphocytes, shoudl we describe as such or just avoid

[Russ]

Yes, they're one of the three types (T/B cells just get more press)

[Drunk]

As always thanks for your great help


At VCE level , how is water produced in light independent reactions of photosynthesis?

I looked at both NOB and Campbells, and neither has water leaving the calvin cycle :S

Pretty sure water's a reactant, isn't it?

[HERculina]

i suggest you look at this http://vce.atarnotes.com/forum/index.php/topic,40044.15.html
but dont think you need to really know how, just the fact that its both a reactant and a product in photosynthesis, i havent come across any questions that have asked

[jane1234]

Is a single amino acid considered a biomacromolecule? I thought not... but apparently it is?

[HERculina]

hmmm i think its an organic molecule but i wouldnt call it a biomacromolecule cause its not a big molecules like a protein.