VCE Biology Question Thread

[TheAspiringDoc]

Can somebody please clarify what exactly is needed to be studied for the immunology section of unit 3 (i.e. area of study 2)? The study design doesn’t exactly specify the depth of study that is required for this area of the course unlike area of study 1 which does a pretty good job. The textbook I am using goes into immaculate detail about pathogens and rambles on about different examples but I am not sure as to what I am supposed to actually look for in terms of exam preparation and note taking. Simply put, what concepts am I supposed to memorise and connect with the other area of studies?

hey!
I agree it's really hard to know what to know for this topic. For me, the most helpful thing was to use note-type resources rather than the textbook - which is notorious for its overwhelming complexity and detail. I liked using edrolo, douchy's bio podcast, ATARNotes notes, Connect education notes and A+ notes for this topic, but any one of them alone would suffice in my opinion.

Here is what I learnt for this topic:

In the immune system, antigen markers cause immune responses. The first immune defense is prevention of entry. In animals this can be physical (intact skin, mucus), chemical (lysozyme in tears/saliva, HCl in the stomach) or microbiological (healthy gut bacteria that outcompete bad bacterial growth, while in plants it can be physical (thick intact waxy cuticles) or chemical (defensins). The second level of animal defense is non-specific and responds to all infections in the same way. It mainly involves phagocytes that indiscriminately engulf pathogens, as well as mast cells (cause inflammation by releasing histamine), interferons, complement proteins and NK cells. Certain phagocytes may present pathogen antigens to specific lymphocytes of the third line of immunity. Different T lymphocytes coordinate specific responses or burst virus-infected self-cells. B lymphocytes release antibodies bind to and destroy pathogen antigens. All specific lymphocytes correspond to ONE specific antigen, and they clone when exposed and activated. Immunological memory occurs due to remaining lymphocytes specific to a particular antigen – allowing faster greater responses. Immunity can be natural or artificial (medical) and active (producing own antibodies) or passive (receiving antibodies – from breastfeeding). Immunisation can cause immunological memory.
Herd immunity is when most of the population is vaccinated so wont spread infection.
Autoimmunity is when the immune system attacks the host.
Immunodeficiency (e.g. HIV) involves weak immunity.
Allergies are a vigorous overreaction to harmless non-self antigens (e.g. pollen) due to B lymphocytes releasing IgE antibodies that sensitise mast cells to release histamine and cause inflammation.
Monoclonal antibodies are produced by fusing B cells and tumour cells to endlessly produce antibodies against cancer.

EDIT: as for links to other AoS's, this topic is largely governed by molecular specificity, which is an overarching theme in 3/4 biology. Also, enzymes pop up, as well as cell-cell signalling. As you will eventually see later in the year, immunology - like every other topic - links to evolution, as a stronger immune-system phenotype (and thus genotype) is favoured through natural selection. If you want you could even look at organelles etc. in relation to this topic, as cells such as phagocytes would contain many lysosomes for the purpose of degrading the pathogens.

EDIT₂: sorry, just realised the above quote doesn't mention the phagocytic process - which you do need to know: how the phagocyte encapsulates the pathogens in a phagosome, which fuses with a lysosome and forms a phagolysosome (know how to diagrammatically represent this)

[PhoenixxFire]

To add to the above in terms of pathogens, you need to know about different types (bacteria, virus, prions, parasitic worms). You just need to know their general structure, whether they are cellular or non-cellular and whether they are intracellular or extracellular.

[Phoenix11]

Hello guys!
I was just wondering what this meant?
"Bacteria are able to obtain energy from sunlight(photosynthesis) by reducing inorganic compounds such as sulfides or ferrous ion (chemosynthesis)." (Taken from the Heinmann Biology 1 5th Edition book).
I don't understand how there is a relation between the two as I thought they were completely different processes?
Thank you so much.
 

[Phoenix11]

Hello guys!
How are you?
I was just wondering why d) conversion of nitrites into by prokaryotes cannot be considered an example of chemosynthesis in this question below?
Which one of the following is an example of chemosythesis?
a) glucose production by plants.
b)methane production by methanogens
c)carbon dioxide production by organisms
d)conversion of nitrites into nitrates by prokaryotes

The correct answer is b) which is what I got.
However, I was wondering why d) conversion of nitrites into nitrates by prokaryotes wasn't an example of chemosythesis as I'm pretty sure that it correct?
Thank you in advance!
Your help is much appreciated!

[sweetcheeks]

I believe that chemosynthesis specifically refers to carbon containing compounds (formation of organic compounds). Converting nitrites into nitrates is more of a nitrification pathway rather than chemosynthesis.

[HighSchoolerRS]

Hi guys, I was hoping I could get some help writing hypotheses. I have to do the textbook review exercises for holiday homework and am struggling to formulate decent hypotheses for this question in the "if... then..." format.
Write a hypothesis for each of the following scenarios:
a. A student investigating algal blooms wondered whether Chlorella, a unicellular eukaryotic alga, carries out photosynthesis faster than Anabaena, a cyanobacterium.
b. A student on work placement at a dairy research station wondered whether dairy cattle with mastitis (a bacterial infection of the udder) would have  more white blood cells such as neutrophils in their blood to fight infection.
Thank you for your help!

[PhoenixxFire]

Hey! I’d rather avoid writing them for you, have a go at writing the independent and dependant variable and I’ll have a look at them, if you have that correct it’s pretty easy to work out from there.

Independent variable: the thing the experimenter changes

Dependant variable: the thing that is measured

[Monkeymafia]

Why would we need to ensure that potatoes (or any other material) are of the same size in an experiment? How is the response below:

- Having potato pieces of different sizes means there are pieces of varying SA:V ratios.
- Osmosis is dependent on SA:V ratio.
- This may skew the results.

If someone could recommend how I could improve my response/expression that would be great.

[TheAspiringDoc]

Why would we need to ensure that potatoes (or any other material) are of the same size in an experiment? How is the response below:

- Having potato pieces of different sizes means there are pieces of varying SA:V ratios.
- Osmosis is dependent on SA:V ratio.
- This may skew the results.

If someone could recommend how I could improve my response/expression that would be great.

You've got the right idea for sure

Here is my attempt:
-within an experiment all variables other than the independent variable should be kept constant so as to only test the effect of IV on DV (don't abbreviate)
-potato pieces of smaller sizes will mean that they have higher SA:V
-this will cause them to be subject to osmosis at a faster rate compared to their volume.
-thus they will produce different results due to their different sizes rather than the IV, so the experiment will not be controlled
-thus only pieces of the same sizes and SA:V should be used

^^not actually that good an answer by me as it is inconcise, but my point is maybe try to expand a bit more on your answer and be a bit more specific and use the scientific terminology

Good luck

[Mr West]

Hey guys,

I just need something cleared up regarding gene structure

in some textbooks i've read that repressor proteins bind to an operator which will decrease/prohibit transcription, but on edrolo Douchy says that repressor proteins bind to a silencer and that it also will decrease/prohibit transcription

are these the same things? would one term be better to used?

any help would be great. cheers

[PhoenixxFire]

In prokaryotic cells, repressors bind to the operator. In eukaryotic cells, they bind to the silencer.

[Calebark]

Hey guys,

I just need something cleared up regarding gene structure

in some textbooks i've read that repressor proteins bind to an operator which will decrease/prohibit transcription, but on edrolo Douchy says that repressor proteins bind to a silencer and that it also will decrease/prohibit transcription

are these the same things? would one term be better to used?

any help would be great. cheers

They're both correct. Operators are found on operons (bunch of genes controlled by a single promoter), which are found on prokaryotes.The silencer is a stretch on DNA in eukaryotic cells that have the same function of preventing transcription.

[randomnobody69420]

Question from activity 4 in Biozone

Why don't red blood cells in a 0.3 mol glucose solution haemolyse even though glucose is transported across the membrane?

My guess is that for some reason the glucose concentrations inside the cells never exceed the extracellular glucose concentration, which means water can never enter the cell via osmosis meaning the red blood cells can not haemolyse, but this is just an educated guess. Am I close?

[vox nihili]

Question from activity 4 in Biozone

Why don't red blood cells in a 0.3 mol glucose solution haemolyse even though glucose is transported across the membrane?

My guess is that for some reason the glucose concentrations inside the cells never exceed the extracellular glucose concentration, which means water can never enter the cell via osmosis meaning the red blood cells can not haemolyse, but this is just an educated guess. Am I close?

Good on you for having a guess first!!! Love this.

I'm actually not sure of the answer they're looking for here, so will defer to someone else. The true answer has to do with the means of glucose transport, but these details are well and truly beyond VCE so I highly doubt that's what they're after

[PhoenixxFire]

Question from activity 4 in Biozone

Why don't red blood cells in a 0.3 mol glucose solution haemolyse even though glucose is transported across the membrane?

My guess is that for some reason the glucose concentrations inside the cells never exceed the extracellular glucose concentration, which means water can never enter the cell via osmosis meaning the red blood cells can not haemolyse, but this is just an educated guess. Am I close?

Hey,

You’ve got the general idea, I think you are looking at the question slightly wrong though, as it specifically refers to glucose travelling across the membrane, not water. I can see four ways this question could be interpreted, either:

1. The solution is hypotonic to the cell, but as glucose can cross the membrane, it exits the cell (making the solutions isotonic) rather than water entering, therefore it doesn’t burst.

2. The solution is hypertonic to the cell, so glucose moves into the cell, however it is not enough volume increase to cause it to burst.

3. The solution is hypotonic to the cell, so water enters, however it is pumped out through active transport.

4. The solution and the cell are isotonic, so whilst glucose/water can cross the membrane, there is no net movement.

I would say that most likely to least likely is 4, 2, 1, 3 but I haven’t done biozone questions, so I don’t know what they expect.