Why is glucose expressed as C₆H₁₂O₆ and not just CH₂O? Wouldn't that be simpler?
VCE Biology Questions Thread
Do we need to know about the electron transport chain for the exam? Or if we do, how much do we need to know?
Okay, I'm not sure if this question makes complete sense but: do plant cells store energy as ATP or starch? What about animals? Do either of them store it as both?
Again, not sure if this completely makes sense but: I thought one gene coded for multiple amino acids but isn't an operon made of multiple genes that code for one amino acid? So what happened there?
Can substances that aren't inhibitors bind to the allosteric site? And does everything that binds to the allosteric site inhibit substrate from binding to the active site? Or are there some things that can bind without inhibiting?
Does all the energy created by photosynthesis need to go through cellular respiration to become ATP or can some of it - being chemical energy (glucose) be used as is?
How can you tell if a reaction is anabolic or catabolic bc e.g. photosynthesis is anabolic but it also involves the destruction of materials which would mean catabolic right?
What is the main difference between C4 and CAM plants?
- Edited
Why is glucose expressed as C₆H₁₂O₆ and not just CH₂O? Wouldn't that be simpler?
The second formula that you have listed is an empirical formula, whereas the first is the molecular formula. It is the molecular formula that actually tells us the amount of carbon, hydrogen and oxygen atoms in a glucose molecule. You need to make sure that you write the molecular formula as it helps us identify that the molecule you are talking about is glucose, and must be used when writing equations for photosynthesis/respiration.
In the future, please post all your questions in the one post as it makes it easier to answer them all 
I'm don't get how C4 and CAM plants lack photorespiration? If someone could explain this simply I would be super grateful! Thank you!!
- Edited
chimichurri If a reaction uses small molecules like CO2 and H2O to build larger ones like C6H12O6, then it's anabolic
Vice versa if a reaction uses up big molecules to make smaller ones
- Edited
chimichurri
ATP can't be stored, it's generated on demand from oxidation of glucose. Plants store energy as starch (amylose or amylopectin) whereas animals store energy as glycogen
PS to admins, is there a way to reply to multiple comments within the same post?
- Edited
No, (Adaptive) Cell-Mediated Responses and Adaptive Humoral Responses can develop simultaneously -- they can be activated at the same time.
You got a trick question (or alternatively a bad question) 
. Because:
Any pathogen able to stimulate an Adaptive Immune Response, can in theory, stimulate both responses. (note the "in theory" bit)
HIV is specifically good at suppressing Adaptive Immune Responses. They do this by targeting cells with the CD4 co-receptor (i.e. Helper T Cells).
Actually, Helper T cells also somewhat assist in Innate Immune Responses once they are activated because they can heighten macrophage aggressiveness etc... so really the Innate Immune System is also affected by HIV, technically, anyways, so I don't think that second bit matters so much for VCE.
If a virus is named the 'Human Immunodeficiency Virus', there is probably a good reason for it 
.
chimichurri Do we need to know about the electron transport chain for the exam? Or if we do, how much do we need to know?
Yes, you will need to:
- Know that this is the final step (as far as VCAA is concerned anyways) of Cellular Respiration.
- Memorise it's inputs and outputs.
If a substance can bind to an allosteric site, it automatically makes that substance a non-competitive inhibitor.
It is just more efficient this way, especially in Eukaryotic cells with Mitochondria. In these Eukaryotes, glucose breakdown can be focused in specific areas of the cell.
Can you please group your questions together in one message next time? Or at least into groups with similar topics? It makes life easier for people on this thread that way 
.
C4 plants separate the initial carbon fixation stage and the rest of the Calvin cycle over space. In the mesophyll cells, a 4-carbon molecule called oxaloacetate is produced via the help of the enzyme PEP carboxylase. Oxaloacetate is then converted into another 4-carbon molecule called malate. Malate is then transported to the bundle-sheath cells and is broken down to release carbon dioxide, which can then enter the Calvin cycle in a similar manner to C3 photosynthesis light-independent processes. Therefore, C4 plants are more efficient than C3 plants in dry conditions because they can capture more CO2 in less time and the stomata can stay closed for longer to reduce water loss. PEP carboxylase also prevents photorespiration occurring as it has no affinity for binding with oxygen.
CAM plants separate the initial carbon fixation stage and the rest of the Calvin cycle over time. The stomata opens at night to bring in CO2. PEP carboxylase fixes the CO2 to form oxaloacetate, which is then converted into malate or another organic molecule. The molecule is then stored in the vacuoles until daytime. Once it is daytime, the stomata does not open (prevents water loss) but the plant can still photosynthesise by using the malate/organic molecule that has been transported out of the vacuole, which breaks down to release CO2. This CO2 then enter the Calvin cycle in a similar manner to C3 photosynthesis light-independent processes. Therefore, CAM plants are also more efficient than C3 plants in dry conditions because they can capture more CO2 in less time, and allow the stomata to open for effective exchange over night whilst ensuring that water is not lost during the day (due to increased temperatures during the day causing more water loss). PEP carboxylase also prevents photorespiration occurring as it has no affinity for binding with oxygen.
Why is water loss a problem? The stomata closes, meaning CO2 cannot enter and O2 cannot exit, causing photorespiration to increase. This is a problem for C3 plants who have no mechanisms to prevent this. C4 plants prevent this by capturing more CO2 in less time and therefore closing their stomata for longer (of course, stomata will still open to release O2, but since more CO2 is present anyway in comparison to O2, the rate of photorespiration will still decrease). CAM plants open their stomata at night to reduce water loss.
Not sure if this will be helpful because it's quite in depth. In summary, both C4 and CAM plants aim to prevent water loss by either separating carbon fixation and the rest of photosynthesis over space or time. This is to increase the amount of CO2 present, reduce water loss, and reduce the amount of O2 present (to therefore reduce photorespiration).
How do you explain the process of the lymphatic system in regards to drainage, flow and surveillance?
- Edited
Amadas_
Looks like good o'l Bio's changed.... sigh; Just my thought process here (idk if this is right, but hey - it might help):
- Surveillance sounds fairly obvious (it provides a sight for antigen presenting cells and lymphocytes to interact)...
- Flow might have something to do with how u need to contract mussels in order to 'squeeze' the lymph through (and how the one-way valves prevent it going backwards)
- Drainage could either mean where dead lymphocytes go - or how it drains from tissues into a lymph-node? I'm not sure about this.
I'm probably wrong tho (vcaa likes abstract terms)
7 days later
Hey guys if anyone has a copy of the edrolo textbook for 3/4 bio I would appreciate it so much, like people said it was kinda good, so I wanna try it out
Joseph41 added the VIC Units 3&4 Biology VIC Units 1&2 Biology tags .
heyyy everyone where is everyone up to in school with the content?
hi, does tissue / blood rejection (after transfusion) cause the humoral or cell-mediated response? i came across a vcaa question which says it's only cell-mediated but i don't understand why?
bioho4
Tbh this question is very similar to: Are viruses eliminated by the humoral response or the cell mediated response?
In theory both are activated.
But I think the more prominent one would be the cell mediated response. Because it seems more likely that the different markers on the transplant would be recognized as an intracellular threat rather than an extracellular threat, because its on a cell rather than in the blood (where the humoral response is more efficient), like you won't really have the donors cells floating around in the blood, though the humoral response would still be initiated.
Hence, I would talk about the cell mediated response rather than the humoral if no information is provided. However, VCAA is very specific in the language it uses for example in the sample exam 2022, 4c short answer, it specifically mentions the response against an intracellular pathogen (cell mediated) so I think if this question was to be asked there would be more context behind it to determine which pathway of the adaptive response needs to be mentioned.
Hey!
Just wondering what the difference between NADP+ and NAD+is?
And does glucose make ATP? Or does it get converted into ATP?
Hi bioho4! Can you please reference the particular VCAA question? Context is always useful.
The answer to your question actually depends on what is being transplanted/transfused.
- If it is a tissue transplant, the immune reaction to the tissue would be a Cell-Mediated response.
- If it is a blood transfusion, the immune reaction to the mismatched red blood cells would be a Humoral response.
That's not to say either won't induce both, though.
chimichurri
NADP+ has an extra phosphate group; and is used in photosynthesis.
NAD+ is used in cellular respiration.
Hey chimichurri!
I wouldn't worry about the specific chemistry involved.
Just know that they pretty much fulfil identical roles -- acting as electron/proton carriers/donors. With the difference being that NADPH is for Photosynthesis whereas NADH is for Cellular Respiration.
Also it seems like you should revise Cellular Respiration overall 
(Glucose is broken down to make energy to synthesise ATP)
Sorry there chimichurri I missed that second part! Moskva Is right!
In Photosynthesis: water is split using sunlight; and this releases electrons. These electrons are used to load NADP+ into NADPH. Also, hydrogen ions (H+) are released. These build up on one side of the membrane, creating a 'proton gradient'. (Since there is a lot of them on one side, they want to diffuse to the otherside). They then pass through this protein called ATP Synthase, which acts like a watermill; adding the third phosphate group to ADP; forming ATP!
This ATP is then used up in the light independent stage - which produces glucose.
So while photosynthesis does produce ATP; it's only in the first light dependent stage. There is none left over at the end!
This may sound similar to the Electron Transport Chain! In fact: it is! Except the direction of H+ ion flow is the opposite, and other reactions happen (Such as FADH, etc...) and the H+ ions come from the NADH/FADH produced in the krebs cycle etc... (instead of water).
Moving back a bit, during glycolysis (when glucose is split); it produces two 'pyruvate' molecules;
The thing is, it also takes two ATP to do this. So it is really a net 2 ATP produced (as it takes 2, but makes 4). Note that the atoms in glucose aren't being made into ATP; it's just the electrons!
Hence in photosynthesis: Sunlight & Water --> e- --> ATP....... --> Glucose
And in Cellular Respiration: Glucose --> e- --> ATP
So it's the electrons from ATP that are transferred. Not the ATP molecules!
I don't think you need to know all that btw... 
Secondary responses are extended cellular responses to an antigen utilising specified cells such as Phagocytes and Monocytes while primary responses are shorter lived and more often preventative toward antigens such, (skin, stomach acid etc).
7 days later
Hi, RBCs aren't nucleated therefore they don't have MHC 1 markers. So how are they identified as self/non-self? And how can blood transplants be rejected from the recipient's body?
- Edited
RBCs don't have MHC/HLA markers but some will have "red cell antigens". Most times these atigens will fall under either type-A or type-B (there are a few minor ones but they are very very uncommon so don't worry about it).
You may have heard of the term "blood type", which can be either O, A, B or AB (for all intents and purposes).
- People with type-O blood type have no red cell antigens on their red blood cells.
- People with type-A blood type have type-A antigens on their red blood cells.
- People with type-B blood type have type-B antigens on their red blood cells.
- People with type-AB blood type have both type-A and type-B antigens on their red blood cells
Ok, due to Immunological Tolerance, and the relatively conservative nature of these A and B antigens, people with a certain blood type will be able to accept any blood with the same or less antigens. Since they are recognised as self. That is to say, a person with type-A blood will be able to accept Type-O (no antigens, less) and Type-A (same) blood; but not Type-B or Type-AB blood.
Blood transplants are rejected is because the antigens in the transfusion are not recognised as self (i.e. foreign).
EDIT: just to be extra clear, this is quite a simplified view of blood types, as there are more red cell antigens types than just A and B; rhesus factors also need to be taken into consideration (which is technically just another type of antigen).
Ah ok I see,
The VCAA question explicitly states a tissue has entered the body; presumably transplanted but that doesn't really matter.
And, yes, MHC class 1 on the cells of the tissue is what allows Cytotoxic T Cells to recognise them.
Also, the cells themselves aren't considered pathogens, just foreign.