VCE Biology Question Thread

[TheBigC]

If an enzyme has an optimum temp of 38ºC, then what does this suggest about efficiency and collisions? I assume its maximum efficiency, but are there any other key terms/phrases?

At optimal temperatures, enzymes reach a state where their rate of reaction is maximised.

Reaction rate is affected by the following factors:
- Surface area
- Concentration
- Pressure
- Temperature
- Presence of catalysts

In relation to optimal enzyme activity, the discriminatory factor is temperature.

When temperature is increased, the frequency of collisions between enzymes and substrates are increased as particles move with greater rapidity due to possession of higher kinetic energy. Moreover, a greater number of successful collisions result. This occurs partially due to the increased frequency of collisions, but to a far more significant extent, consequentially to substrates' greater kinetic energies, which enables for a greater proportion to overcome the 'activation energy barrier'.

Thus, when an enzyme has reached an optimum temperature, a specific balance between frequency of collisions of substrates and enzymes, different particles' possession of sufficient energy to overcome the 'activation energy barrier' and maximised complementary nature of the enzyme's active site relative to its specific substrate exists.

You also delineate the concept of 'efficiency' within your question, though I am not sure that this appropriately pertains to any form of description of enzyme functionality. The only notion where I believe this might fit is when describing the energy input to produce a specific temperature in relation to the rate of reaction at that temperature (is this what you meant?).

[peachxmh]

I swear I'm posting on here a lot but lowkey stressing about bio because school is about to start! (yaaaayyyyy)

What is the mode of transmission of neurohormones? (i.e. are they autocrine, paracrine or endocrine?) I'm fairly certain that they travel through the bloodstream so they probably are endocrine but just wanted to get your opinions, thx :p

P.S. Also would love a description of how neurohormones are different to neurotransmitters + hormones as I think I kind of grasp it but not fully..

Side note: does anyone know when the AN lecture slides from last week's Bio lecture will be published (or their whereabouts if they've already been published and I'm living under a rock)

[Poet]

I swear I'm posting on here a lot but lowkey stressing about bio because school is about to start! (yaaaayyyyy)

What is the mode of transmission of neurohormones? (i.e. are they autocrine, paracrine or endocrine?) I'm fairly certain that they travel through the bloodstream so they probably are endocrine but just wanted to get your opinions, thx :p

P.S. Also would love a description of the differences between neurohormones and neurotransmitters..

Hey peachxmh,

All good - I'm pretty sure we're all feeling it haha :,)

Yep! The mode of transmission for neurohormones (in general) is typically endocrine as they travel in circulation.

Ah, the difference between neurohormones and neurotransmitters is that neurohormones are a wide range of things; they can act as neurotransmitters, but can also be secreted into the bloodstream and carried along to be received further away. Neurotransmitters are simply used to bridge the short gap between two nerve cells (synaptic gap), and the name 'neurotransmitter' is just specifying what kind of neurohormone we're talking about.
I also found an explanation from alondouek as to this. (They can explain is a lot better than I ever could!! I think my explanation above would be a bit dodgy without this.)

So, neurohormones are made by neurosecretory cells and are released into the blood. The significant difference between neurohormones and neurotransmitters is simply one of effect; neurotransmitters can only function as neurotransmitters, but neurohormones can function as both neurotransmitters, chemical messengers for the paracrine and autocrine systems as well as having a hormonal function (I.e. they have a systemic effect in the body).

Hope this helps!
~poet xx

edit: I am told they should be ready within the next couple of weeks.

[lazaward]

Hey,
I just wanted to clarify that my knowledge is correct in terms of photosynthesis. So, the CO2 comes from the atmosphere, goes through 2 rounds of the Calvin cycle and produces 1 molecule of glucose. The water comes from being an input in the light dependant stage of photosynthesis and as the water molecules are split oxygen is a by-product. Is this correct? Also I don’t really understand what RuBP is and if G3P is also PGAL? Thank you

[darkz]

Hey,
I just wanted to clarify that my knowledge is correct in terms of photosynthesis. So, the CO2 comes from the atmosphere, goes through 2 rounds of the Calvin cycle and produces 1 molecule of glucose. The water comes from being an input in the light dependant stage of photosynthesis and as the water molecules are split oxygen is a by-product. Is this correct? Also I don’t really understand what RuBP is and if G3P is also PGAL? Thank you

Hey,
So in VCE biology it's okay to say that two cycles of the Calvin cycle can produce one molecule of glucose - as there are a lot of textbooks which say that 3 carbon dioxide molecules enter the cycle at once, however it is also good to know that in reality, the Calvin Cycle actually only fixes one carbon dioxide molecule each cycle - so technically you'd need six cycles of the Calvin Cycle. And you're absolutely right in saying that water is an input of the light dependent stage, which is split and oxygen produced as a byproduct

You don't really need to know much about RuBP, G3P/PGAL as they're not within the study design, but RuBP is basically a molecule which reacts with carbon dioxide ("captures it") and uses the enzyme RuBisCO to catalyse the next few steps etc. And yes, PGAL is just another name for G3P

[TheBigC]

Hey,
I just wanted to clarify that my knowledge is correct in terms of photosynthesis. So, the CO2 comes from the atmosphere, goes through 2 rounds of the Calvin cycle and produces 1 molecule of glucose. The water comes from being an input in the light dependant stage of photosynthesis and as the water molecules are split oxygen is a by-product. Is this correct? Also I don’t really understand what RuBP is and if G3P is also PGAL? Thank you

Yes. You are correct. Each 'cycle' of the Calvin cycle takes up 3 molecules of CO2, ultimately producing 1 molecule of PGAL (also known as G3P: glyceraldehyde 3-phosphate or phosphoglyceraldehyde). After 2 cycles, 2 molecules of PGAL (3 carbon compound) are produced, which are utilised to produce glucose (6 carbon compound).

RuBP is ribulose 1,5-bisphosphate: it combines with CO2 during carbon fixation with the aid of the enzyme RuBisCO (ribulose bisphosphate carboxylase oxygenase) (first step of the Calvin cycle). After each 'cycle' RuBP is continually reproduced to enable for carbon fixation to perpetually occur (hence why the Calvin cycle is referred toward as a 'cycle').

[PhoenixxFire]

If anyone's reading the above and getting worried, you don't need to know any of it for VCE bio. You just need to know the inputs, outputs, and location.

[PhoenixxFire]

You just need to know the inputs, outputs, location (and a bit about chloroplasts) and factors that affect the rate of photosynthesis (e.g. temperature)

Yes you need to know the exact number of molecules, however you don't need to know the number of ATP produced in photosynthesis (but you do need to know how many are produced in each stage in respiration).

Study design dot points
Photosynthesis
• the purpose of photosynthesis
• chloroplasts as the site of photosynthesis, an overview of their structure and evidence of their bacterial origins
• inputs and outputs of the light dependent and light independent (Calvin cycle) stages of photosynthesis in C3
plants (details of the biochemical pathway mechanisms are not required)
• factors that affect the rate of photosynthesis, including light, temperature and carbon dioxide concentration.

When it refers to the purpose of photosynthesis, you just need to understand that oxygen is just a waste product, and that the glucose is intended to be used by the plant in its own cellular respiration.

We definitely don't expect you to read through all of these pages. Having said that I recently compiled all the questions that I thought are still relevant here. Your question isn't on there anyway though so don't worry about it

Also welcome the bio section is the best section of the forums

[darkz]

Hello,

I usually lurk around on this forum but today I've decided to ask a question. I'm sorry if this question has already been answered as I have not had the time to read this thread and I'm looking for a quick answer.

What is the level of detail required for VCE Biology Units 3 and 4 regarding photosynthesis?
Also, do we need to know the number of molecules (inputs and outputs) for both photosynthesis and respiration?

Thank you very much everyone.

For the actual processes, you just need to know the inputs, outputs, location and a general idea of what is happening in each stage - your level of detail doesn't need to be deep at all. For example, if the question asks you to describe what is happening in the light dependent stage or something along the lines of that, you generally just need to say

- Occurs in Thylakoid membrane of the grana
- Light energy is captured by the chlorophyll and used to split a water molecule
- Splitting provides electrons and hydrogen ions which are accepted by NADP+ to produce NADPH
- The splitting also produces oxygen which diffuses out as a byproduct
- ATP is produced from ADP +Pi (You can add in that ATP Synthase is the enzyme which catalyses this, but you don't need to know that)

And I don't really think you need to know the actual number of molecules for the inputs/outputs because I've never seen a past exam question ask for that.

Edit: Beaten by PhoenixxFire but I'll post it anyways

[PhoenixxFire]

The following is the dot point on the lymphatic system in the study design:

"The role of the lymphatic system in the immune response including the role of secondary lymphoid tissue (with reference to lymph nodes) as the site of antigen recognition by lymphocytes, and as a transport system for antigen presenting cells including dendritic cells."

What exactly should we know about the lymphatic system in relation to the immunity topic (what is relevant to the exam) and how much detail should we know?

This question is from a couple of days ago but it got missed so i'll answer it now.

That dot point describes pretty well what you need to know:
-Antigen recognition occurs in lymph nodes
      -T helper and B cells hang out in lymph nodes
-You should probably know the general location of lymph nodes (i.e. armpits, groin, neck)
-Immune cells travel through the lymph system

[Scribe]

For the actual processes, you just need to know the inputs, outputs, location and a general idea of what is happening in each stage - your level of detail doesn't need to be deep at all. For example, if the question asks you to describe what is happening in the light dependent stage or something along the lines of that, you generally just need to say

- Occurs in Thylakoid membrane of the grana
- Light energy is captured by the chlorophyll and used to split a water molecule
- Splitting provides electrons and hydrogen ions which are accepted by NADP+ to produce NADPH
- The splitting also produces oxygen which diffuses out as a byproduct
- ATP is produced from ADP +Pi (You can add in that ATP Synthase is the enzyme which catalyses this, but you don't need to know that)

And I don't really think you need to know the actual number of molecules for the inputs/outputs because I've never seen a past exam question ask for that.

Edit: Beaten by PhoenixxFire but I'll post it anyways

You just need to know the inputs, outputs, location (and a bit about chloroplasts) and factors that affect the rate of photosynthesis (e.g. temperature)

Yes you need to know the exact number of molecules, however you don't need to know the number of ATP produced in photosynthesis (but you do need to know how many are produced in each stage in respiration).

Study design dot points
Photosynthesis
• the purpose of photosynthesis
• chloroplasts as the site of photosynthesis, an overview of their structure and evidence of their bacterial origins
• inputs and outputs of the light dependent and light independent (Calvin cycle) stages of photosynthesis in C3
plants (details of the biochemical pathway mechanisms are not required)
• factors that affect the rate of photosynthesis, including light, temperature and carbon dioxide concentration.

When it refers to the purpose of photosynthesis, you just need to understand that oxygen is just a waste product, and that the glucose is intended to be used by the plant in its own cellular respiration.

We definitely don't expect you to read through all of these pages. Having said that I recently compiled all the questions that I thought are still relevant here. Your question isn't on there anyway though so don't worry about it

Also welcome the bio section is the best section of the forums

Wow that was a shockingly fast response   
Thank you very much for the time and effort!
If it doesn't bother you, I have two more questions.

Do we need to know the stages of the Calvin Cycle in detail? Is there a diagram that presents just enough information for the VCE level or are the diagrams on Google what we are supposed to memorise?
And what are we supposed to know regarding photosystems?

Thank you very much!

[darkz]

Wow that was a shockingly fast response   
Thank you very much for the time and effort!
If it doesn't bother you, I have two more questions.

Do we need to know the stages of the Calvin Cycle in detail? Is there a diagram that presents just enough information for the VCE level or are the diagrams on Google what we are supposed to memorise?
And what are we supposed to know regarding photosystems?

Thank you very much!

Nah, you don't need to know the Calvin cycle in detail. Just that CO2 is fixated/reduced into glucose would suffice and then touch on the other outputs/inputs and location of course. And you don't need to know the photosystems

[PhoenixxFire]

Do we need to know the stages of the Calvin Cycle in detail? Is there a diagram that presents just enough information for the VCE level or are the diagrams on Google what we are supposed to memorise?

You don't need to know any details at all. CO2 goes in, glucose comes out.
This is part of those biochemical pathways that have been removed from the study design, you may still see it appearing in tests up to 2016 though.

And what are we supposed to know regarding photosystems?

Thank you very much!

I didn't even know what photosystems are - seriously I had to google it so that should give you a clue haha. You don't need to know to know anything about them. Just know that there are lots of enzymes and other proteins involved but don't bother learning anything specific (unless you want to of course).

Edit: Beaten by darkdzn. Damn you are fast

[Scribe]

Thank you very much guys!

I guess my teacher was just going further in depth.

[peachxmh]

Hello again I did a quick search of the forum but couldn't find an answer to my question so I figured I'd ask it in case anyone else wanted to know as well. To what extent are we required to know about apoptosis? Do we need to know about Bcl-2 or Apaf-1? Many thanks!