VCE Biology Question Thread

[Calebark]

Cholera is a diarrhoeal disease that continues to ravage the developing world. It is caused by the bacterium Vibrio cholerae, which is transferred in water contaminated by faeces.

V.cholerae causes diarrhoea by producing a toxin that binds to a receptor on the intestinal mucosa. Binding to the receptor increases the production of cAMP in the cell, which in turn activates the CFTR chloride channel.


1.What is the role of cAMP in this pathway?
2.Explain how opening of CFTR can cause diarrhoea

1. cAMP acts as a signalling molecule which activates the CFTR chloride channel.
2. -Chloride channel opens
    -Chloride will leave cell via facilitated diffusion
    -The cell is now hypertonic to the extracellular environment
    -Water will leave the cell via osmosis
    -Increased water in small intestine causes diarrhoea

Edit: Ahh, didn't see Butterflygirl just beat me to it

[Butterflygirl]

I have a question... For VCE biology, do we need to know about T-memory cells? I only learnt about B-memory, B-plasma, T-helper, Cytotoxic T cells and suppressor T cells.

Just making sure >.<

[HasibA]

I have a question... For VCE biology, do we need to know about T-memory cells? I only learnt about B-memory, B-plasma, T-helper, Cytotoxic T cells and suppressor T cells.

Just making sure >.<

better to know it, should be very similar to B memory cells

[Mapleflame]

Could someone tell me the exact/required terms that I need to include for the definition of species?
Thanks.
~A.H

[vox nihili]

a) cAMP acts as a secondary signalling molecule that stimulates a signal cascade to then activate the CFTR chloride channel.
b) If the chloride channel opens, then chloride will move out of the cell via facilitated diffusion. This will then cause water to move out of the cell via osmosis from a low solute concentration (inside the cell) to a high solute concentration (outside the cell). The water levels in the intestine will increase, causing diarrhoea.

Maybe? Maybe not? I don't know 

1. cAMP acts as a signalling molecule which activates the CFTR chloride channel.
2. -Chloride channel opens
    -Chloride will leave cell via facilitated diffusion
    -The cell is now hypertonic to the extracellular environment
    -Water will leave the cell via osmosis
    -Increased water in small intestine causes diarrhoea

Edit: Ahh, didn't see Butterflygirl just beat me to it

#smashedit perfect answers

A tricky one:


Palmaris longus is a muscle found in the forearm of the majority of people. The body of palmaris longus is very thin and its tendon blends with connective tissue in the wrist, meaning that the muscle isn't able to move anything. Why do humans have this muscle?

[HasibA]

Could someone tell me the exact/required terms that I need to include for the definition of species?
Thanks.
~A.H

not sure if its exact, but pretty sure you have to mention it being an organism, producing fertile offspring etc.
ill try find a biol definition for it if i can hahah thats pertinent to high school
edit: beaten by solution

[solution]

Could someone tell me the exact/required terms that I need to include for the definition of species?
Thanks.
~A.H

Species are a group of individuals who can interbreed and produce viable offspring.

[Calebark]

Palmaris longus is a muscle found in the forearm of the majority of people. The body of palmaris longus is very thin and its tendon blends with connective tissue in the wrist, meaning that the muscle isn't able to move anything. Why do humans have this muscle?

-The palmaris longus once served an evolutionary purpose
-As people evolved, this purpose was no longer needed
-No selection pressure was present to keep or remove it, so natural selection did not occur, and it remained in the gene pool
-The tendon became vestigial over time

Not exactly pertinent to the question, but I guess such a purpose was from when we were arboreal?

[ezferns]

I've got an osmosis question:
Say there's a bag that's permeable to water and saccharides and it has high glucose concentration. If it's placed in a solution of low solute concentration, why doesn't the glucose diffuse into the surrounding solution?
Whenever I come across this type of question, the answer is always that the volume of the bag increases. I understand this for a membrane in which the solute can't diffuse but why is this the case when the solute can diffuse?

Thanks

[Calebark]

I've got an osmosis question:
Say there's a bag that's permeable to water and saccharides and it has high glucose concentration. If it's placed in a solution of low solute concentration, why doesn't the glucose diffuse into the surrounding solution?
Whenever I come across this type of question, the answer is always that the volume of the bag increases. I understand this for a membrane in which the solute can't diffuse but why is this the case when the solute can diffuse?

Thanks

My guess would be that as glucose cannot simply diffuse, it must use transport proteins. As water can diffuse across the entire membrane, but glucose must use transport proteins, the water will diffuse at a faster rate, so there will be a net increase of water into the bag, which will increase the volume.

[vox nihili]

-The palmaris longus once served an evolutionary purpose
-As people evolved, this purpose was no longer needed
-No selection pressure was present to keep or remove it, so natural selection did not occur, and it remained in the gene pool
-The tendon became vestigial over time

Not exactly pertinent to the question, but I guess such a purpose was from when we were arboreal?

Perfect.

Not entirely sure what PF did to be honest, but that seems to be a reasonable guess.

[plsbegentle]

My guess would be that as glucose cannot simply diffuse, it must use transport proteins. As water can diffuse across the entire membrane, but glucose must use transport proteins, the water will diffuse at a faster rate, so there will be a net increase of water into the bag, which will increase the volume.

Remember that osmosis is diffusion! Its the movement of water from a high to low concentration, usually across a semi-permeable membrane.

[AhNeon]

Hey, is it better to write answers in full sentences paragraph or do dot points suffice?

[HasibA]

Hey, is it better to write answers in full sentences paragraph or do dot points suffice?

i reckon dot points can suffice, and are probs better for complex questions where clear answers are required

[vox nihili]

Hey, is it better to write answers in full sentences paragraph or do dot points suffice?

Dot points are particularly good if you're prone to waffling








Malaria is called by a variety of species of the genus Plasmodium, with the most severe form of malaria being the result of infection with P.falciparum.

Plasmodium species infect red blood cells. Once inside a red blood cell, the Plasmodium parasite produces proteins that it exports into the red blood cell to alter the cell to its specifications. One of these exported proteins, PfEMP1, is placed on the surface of the red blood cell. It is used to anchor the infected red blood cells to vessel walls, thereby preventing the red blood cell from moving in the blood to the spleen.

1. Suggest one reason why Plasmodium has developed a mechanism to prevent red blood cells infected with it from going to the spleen.

P.falciparum has about 60 different genes that code for PfEMP1, though only one of these genes is expressed at a time.

2. Suggest why P.falciparum has 60 genes that code for PfEMP1

Plasmepsin is an enzyme produced by Plasmodium species. It helps to mediate the export of proteins from Plasmodium into the red blood cell.

3. How many genes do you think there would be for plasmepsin? Why?