VCE Biology Question Thread

[Billuminati]

Water is formed during oxidative phosphorylation when oxygen combines with electrons and protons. Where does the oxygen come from?
A  molecular oxygen diffuses into the cell and then into the mitochondrion
B chemiosmosis
C electron transport chain
D glycolysis

Would this be a

Yes it’s A. None of the others explain where O2 comes from, and C is incorrect as although oxidative phosphorylation occurs during the ETC, the ETC itself doesn’t produce O2

[Chocolatepistachio]

So during lactic acid fermentation is the pyruvate reduced directly by NADH to form lactate or does lactate dehydrogenase converts pyruvate to lactate and the NADH is oxidised to NAD+. And then lactic acid is converted back to pyruvate through the cori cycle

[Billuminati]

So during lactic acid fermentation is the pyruvate reduced directly by NADH to form lactate or does lactate dehydrogenase converts pyruvate to lactate and the NADH is oxidised to NAD+. And then lactic acid is converted back to pyruvate through the cori cycle

Lactate dehydrogenase will convert the alpha ketone on pyruvate into an alcohol with the help of a proton donor ie NADH. Technically NADH is the reductant, however you do need lactate dehydrogenase to lower the activation energy in order for fermentation to occur rapidly at physiological pH. BTW, if you don’t mind me asking, why are you covering these pathways in this much detail? I reckon the questions you’ve been asking are at uni level

[Acegtr]

Hi,
I have two questions regarding the adaptive immune system; specifically at the lymph nodes.

1. When APCs travel to a lymph node, am I correct in saying that the MHC II markers on the APCs is recognised by a naive t cell, and this leads to the helper t cell-stimulating the naive t cell via cytokines, which leads to differentiation of the naive t cell into cyto toxic t cells and memory t cells?

2. In humoral immunity, do the b lymphocytes bind to the APCs and then the helper t cell binds to the APC which leads to clonal expansion? Or does a single non-self antigen travel through the lymphatic system to the node, and then attach to the b lymphocyte and start humoral immunity?

Thanks in advance!

[Bluebird]

Hi AN,

How does the body choose whether to use humoral or cell-mediated immunity? Or do they work together at the same time?

[Billuminati]

Hi AN,

How does the body choose whether to use humoral or cell-mediated immunity? Or do they work together at the same time?

They are activated at the same time as Th cells help activate both Tc and B cells.

Also to the other person asking about immunology, I'm sorry I don't remember because my immunology is very rusty

[-Lilac-]

Hi,
I have two questions regarding the adaptive immune system; specifically at the lymph nodes.

1. When APCs travel to a lymph node, am I correct in saying that the MHC II markers on the APCs is recognised by a naive t cell, and this leads to the helper t cell-stimulating the naive t cell via cytokines, which leads to differentiation of the naive t cell into cyto toxic t cells and memory t cells?

Not quite. The following is a simplified view as there is a lot happening during the activation of an immune response and many different interactions between all the cells involved.

There are two types of naive T cells in the lymph nodes; CD4+ (helper) and CD8+ (cytotoxic/killer). An APC that travels to the lymph node presenting antigen on MHC II will be recognized by a naive T helper cell. Then through further co-stimulation and cytokine release from the APC, the naive T helper will then be activated and there will be clonal expansion/differentiation. Activated helper T cells will then start producing cytokines etc. At the same time, an APC presenting antigen on MHC I will activate a cytotoxic T cell. Previously activated helper T cells can also help this activation of the cytotoxic cell occur. Some T cells will also become memory T cells and the effector helper and cytotoxic T cells will travel to the site of infection where further activation can occur.

2. In humoral immunity, do the b lymphocytes bind to the APCs and then the helper t cell binds to the APC which leads to clonal expansion? Or does a single non-self antigen travel through the lymphatic system to the node, and then attach to the b lymphocyte and start humoral immunity?

Thanks in advance!

B cells bind to what we call 'native or free antigen' which means antigen that has not been processed by the MHC antigen presentation machinery inside a cell. Therefore, the free antigen will drain to the lymph nodes and will be recognized by the B cell via it's B cell receptor. This usually is not enough to activate a B cell and T helper cell help will usually also be required. When the B cell receptor binds the antigen, the antigen actually ends up internalized within the B cell and the B cell can then present the antigen on MHC II. A previously activated T helper cell can then recognize that antigen bring presented on MHC II by the B cell and bind. Then the T helper can further activate the B cell leading to differentiation and clonal expansion.

[Chocolatepistachio]

Cystic fibrosis is a life threatening autosomal recessive genetic disorder. The normal gene (CFTR) determines the structure of a transmembrane ion channel that transports chloride ion channels. In approximately 66% of cystic fibrosis cases, a mutation of the CFTR gene results in a defective chloride ion channel, which may not even be inserted into the cell membrane. Lack of chloride ion channels in epithelial cells results in thick sticky mucus in the lungs, salty sweat and other serious symptoms. Assume that cells affected by the cystic fibrosis mutation cannot export chloride ions outwards across the cell membrane. Compared to normal cells, cells affected by the cystic fibrosis mutation accumulate higher concentrations of chloride and sodium ions. Assume that the NaCl concentration of body fluids is 9%. What is the net movement of water in a normal cell and a cell affected by cystic fibrosis mutation?
A water moves into and out of a normal cell at the same rate. More water moves into a cell affected by the cystic fibrosis mutation
B more water moves from inside a normal cell to outside. More water moves from inside to outside in a cell affected by cystic fibrosis mutation
C more water moves from outside a normal cell to inside. Movements of water into and out of a cell affected by cystic fibrosis mutation is equal
D more water moves from inside to the outside in both types of cell

Would this be b

[Billuminati]

Cystic fibrosis is a life threatening autosomal recessive genetic disorder. The normal gene (CFTR) determines the structure of a transmembrane ion channel that transports chloride ion channels. In approximately 66% of cystic fibrosis cases, a mutation of the CFTR gene results in a defective chloride ion channel, which may not even be inserted into the cell membrane. Lack of chloride ion channels in epithelial cells results in thick sticky mucus in the lungs, salty sweat and other serious symptoms. Assume that cells affected by the cystic fibrosis mutation cannot export chloride ions outwards across the cell membrane. Compared to normal cells, cells affected by the cystic fibrosis mutation accumulate higher concentrations of chloride and sodium ions. Assume that the NaCl concentration of body fluids is 9%. What is the net movement of water in a normal cell and a cell affected by cystic fibrosis mutation?
A water moves into and out of a normal cell at the same rate. More water moves into a cell affected by the cystic fibrosis mutation
B more water moves from inside a normal cell to outside. More water moves from inside to outside in a cell affected by cystic fibrosis mutation
C more water moves from outside a normal cell to inside. Movements of water into and out of a cell affected by cystic fibrosis mutation is equal
D more water moves from inside to the outside in both types of cell

Would this be b

I think this should be A. In a normal cell you want an isotonic solution ie no net movement because you don't want your cells to shrink or blow up in a hypertonic and hypotonic solution respectively. Since you're not able to remove solutes in your cell because your Cl- channels have been degraded by quality check mechanisms in the endoplasmic reticulum due to the mutation, your cell's osmolarity (solute ie Na+ and Cl- concentration) is higher, which means the concentration of water is lower. Hence water diffuses from a region of high concentration to low concentration (enters the cell by osmosis).

BTW there's a typo with the question, physiological osmolarity should be 0.9% not 9%

[Chocolatepistachio]

What does neural changes in blood pressure mean

Why are olfactory neurons called modified bipolar neurons

[Bri MT]

What does neural changes in blood pressure mean

Why are olfactory neurons called modified bipolar neurons

Hey,

I'm thinking that this question might be better suited to the uni area of the forums?
Probably in the biology or health sciences section, more specifically.

[Billuminati]

What does neural changes in blood pressure mean

Why are olfactory neurons called modified bipolar neurons

I agree with Bri that these questions are more appropriate for uni students (probably around 2nd year level), but I'm able to answer them for you cuz I'm doing biomed and have just completed anatomy and physiology units at 2nd year level.

Changes in blood pressure are detected by stretch sensitive neurons located in the carotid sinus and the aortic arch called baroreceptors. In response to low blood pressure, they decrease their rate of action potential generation, which tells your medulla oblongata to do something to increase blood pressure as you need to constantly supply your brain with enough O2 from circulation. Your CNS will decrease CN X (vagus nerve), or parasympathetic activity (remember parasympathetic nervous system = rest and digest = slows heart rate) and increase sympathetic activity to increase the rate and force of contraction in order to raise blood pressure. Sympathetic nerve activity will also cause vasoconstriction because noradrenaline will bind to adrenergic receptors on smooth muscles around arterioles which causes them to contract, in turn increasing total peripheral resistance and mean arterial pressure. Sympathetic activity will result in the release of vasopressin (I think you call it ADH in high school) to conserve blood volume which also helps to keep blood pressure up

As for the olfactory neurons, they're bipolar because they both project outwards towards your nose via the cribiform plate where they encode smells using the thin olfactory fibres, and they also project backwards to carry this info towards the olfactory cortex located in the temporal lobe where it's processed. Note that the olfactory neurons aren't like your typical sensory neurons, the olfactory nerve (CN I) isn't considered part of the peripheral nervous system as they're actually extensions of your cerebrum just like the optic nerve (CN II) and the retina, they even have their own meninges so that's why they're considered "modified"

[Chocolatepistachio]

Thanks

A mutation occurs in the liver cell of a dog before the dog reproduces. When the dog reproduces, how many of the puppies are expected to have the mutation?
A all of the puppies will have the mutation
B it depends if the mutation is dominant or recessive
C none of the puppies will inherit the mutation
D half of the puppies will have the mutation

Would this be b

[Sine]

Thanks

A mutation occurs in the liver cell of a dog before the dog reproduces. When the dog reproduces, how many of the puppies are expected to have the mutation?
A all of the puppies will have the mutation
B it depends if the mutation is dominant or recessive
C none of the puppies will inherit the mutation
D half of the puppies will have the mutation

Would this be b

A liver cell is a somatic cell.
Note the difference between somatic and germline mutations.

[Chocolatepistachio]

Oh ok so none will have the mutation