October 18, 2019, 12:58:19 pm

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#### marangutan

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##### Re: VCE Biology Question Thread
« Reply #11520 on: February 04, 2019, 07:32:43 pm »
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Anyone know what limitations mean? I'm doing a scientific method and it's asking for that

#### darkz

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##### Re: VCE Biology Question Thread
« Reply #11521 on: February 04, 2019, 07:52:29 pm »
+3
Anyone know what limitations mean? I'm doing a scientific method and it's asking for that

I believe that limitations of an experiment would simply refer to factors which cannot be controlled by the experimental setup but would still affect the results
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#### Erutepa

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##### Re: VCE Biology Question Thread
« Reply #11522 on: February 04, 2019, 08:30:02 pm »
+6
Anyone know what limitations mean? I'm doing a scientific method and it's asking for that
To add to that, I would think that limitations may also be generally any disadvantages with an experimental design. This could include a experimental method that does not appropriately address the goal/research problem.
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#### DBA-144

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##### Re: VCE Biology Question Thread
« Reply #11523 on: February 04, 2019, 09:14:45 pm »
+5
To add to that, I would think that limitations may also be generally any disadvantages with an experimental design. This could include a experimental method that does not appropriately address the goal/research problem.

I suspect that it is also (although less) likely that limitations refer to the limits imposed by time, money, other resources such as the availability of a given material (eg. test tubes)

#### vox nihili

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##### Re: VCE Biology Question Thread
« Reply #11524 on: February 05, 2019, 02:44:35 pm »
+3
I believe that limitations of an experiment would simply refer to factors which cannot be controlled by the experimental setup but would still affect the results

You've gotta be careful with this definition. It's the right idea, but a limitation isn't something that "can't be controlled"...the whole purpose of discussing them is to try to get rid of them, which is usually possible.

To understand limitations, you need to understand what an experiment is for. An experiment is to show that A causes B. That's all it does. Really good experiments demonstrate that connection in such a way as to eliminate any doubt that A caused B. Bad ones leave open a lot of questions. A limitation is anything that makes us doubt that A caused B, so yes, it can be variable that wasn't properly controlled. It can also be something inherent in the design of the experiment, too.
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#### Chocolatemilkshake

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##### Re: VCE Biology Question Thread
« Reply #11525 on: February 07, 2019, 07:01:00 am »
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Hey everyone,

I know that the secondary structure of a protein (alpha-helices, beta-pleated sheets and random coils) forms spontaneously without the need of other proteins. However, my teacher said that it is still established in the Endoplasmic reticulum. Just wanted to confirm that if it was a free ribosome this secondary structure would not be established on the E.R would it?

Also, is the tertiary and quaternary structures established in the E.R or the Golgi Body?

Thanks

ChocolateMilkshake
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#### mrfredk

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##### Re: VCE Biology Question Thread
« Reply #11526 on: February 07, 2019, 09:22:28 am »
+1
Would it be correct to state that prokaryotes completely lack any membrane-bound organelles? I have a biology 3/4 teacher who is saying that VCAA states that ribosomes have a membrane and thus the statement is wrong, but my previous teacher and every single result on google is saying otherwise. Is there any official information I can find that confirms the correct answer?

#### Erutepa

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##### Re: VCE Biology Question Thread
« Reply #11527 on: February 07, 2019, 09:55:39 am »
+4
Would it be correct to state that prokaryotes completely lack any membrane-bound organelles? I have a biology 3/4 teacher who is saying that VCAA states that ribosomes have a membrane and thus the statement is wrong, but my previous teacher and every single result on google is saying otherwise. Is there any official information I can find that confirms the correct answer?

Ribosomes are not membrane bound and prokaryotes do lack membrane bound organelles.
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#### vox nihili

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##### Re: VCE Biology Question Thread
« Reply #11528 on: February 07, 2019, 11:16:52 am »
+3
Hey everyone,

I know that the secondary structure of a protein (alpha-helices, beta-pleated sheets and random coils) forms spontaneously without the need of other proteins. However, my teacher said that it is still established in the Endoplasmic reticulum. Just wanted to confirm that if it was a free ribosome this secondary structure would not be established on the E.R would it?

Also, is the tertiary and quaternary structures established in the E.R or the Golgi Body?

Thanks

ChocolateMilkshake

Re tertiary and quarternary structures: they can be established anywhere. Sometimes the ER helps them fold up into their structure. Sometimes they just do it on their own in the cytoplasm. Sometimes they need the Golgi to give them a bit of support, too.
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#### f0od

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##### Re: VCE Biology Question Thread
« Reply #11529 on: February 10, 2019, 09:22:08 pm »
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Would someone be able to explain to me how different pH values (2, 6 and 10) affect the structure of the cell membrane? Do both very acidic and very alkaline solutions denature the membrane structure or is it just very acidic solutions?

thanks!
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#### darkz

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##### Re: VCE Biology Question Thread
« Reply #11530 on: February 10, 2019, 09:30:19 pm »
+1
Would someone be able to explain to me how different pH values (2, 6 and 10) affect the structure of the cell membrane? Do both very acidic and very alkaline solutions denature the membrane structure or is it just very acidic solutions?
thanks!

Well firstly, we have to understand that pH measures the concentration of $H^+$ ions present. And therefore, because the secondary structure of proteins is completely formed via the hydrogen bonding interactions which occur in the backbone, if we increase the number of hydrogen ions/ decrease them, this can subsequently affect the secondary structure. Also, hydrogen bonds can form between R groups in the tertiary structure, so varying pH can affect them as well.

I'm pretty sure that both very acidic and alkaline conditions can denature a protein, but just remember, it must deviate significantly from the optimum pH, otherwise we don't consider it to be denatured.
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#### Erutepa

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##### Re: VCE Biology Question Thread
« Reply #11531 on: February 10, 2019, 09:41:11 pm »
+4
Would someone be able to explain to me how different pH values (2, 6 and 10) affect the structure of the cell membrane? Do both very acidic and very alkaline solutions denature the membrane structure or is it just very acidic solutions?

thanks!
While from some quick reading it seems that pH can have effects on the integrity of the phospholipid bilayer itself, For VCE biology, you would not need to know any of this. What you need to know is rather how proteins (like those interspersed within the bilayer) can be altered (as darkz has described above).
This standard relationship between enzyme activity (approximately indicating the integrity of the protein) might help you with your query
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#### Highway_end

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##### Re: VCE Biology Question Thread
« Reply #11532 on: February 11, 2019, 10:37:52 pm »
0
What are the different substances that can move across the plasma membrane via facilitated diffusion and active transport? Is the following list correct?

Channel-mediated Diffusion
• small, polar molecules- hydrophilic and uncharged e.g. glucose
• ions- charged e.g. Na+
Carrier-mediated Diffusion
• large, polar molecules- hydrophilic and uncharged
Carrier Pumps (Active Transport)
• small, polar molecules- hydrophilic and uncharged
• ions- charged
I would appreciate more detail (examples) and clarity regarding size, polarity, and charge. I'm a little confused
« Last Edit: February 11, 2019, 10:43:34 pm by Highway_end »

#### PhoenixxFire

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##### Re: VCE Biology Question Thread
« Reply #11533 on: February 12, 2019, 05:08:25 pm »
+5
What are the different substances that can move across the plasma membrane via facilitated diffusion and active transport? Is the following list correct?

Channel-mediated Diffusion
• small, polar molecules- hydrophilic and uncharged e.g. glucose
• ions- charged e.g. Na+
Carrier-mediated Diffusion
• large, polar molecules- hydrophilic and uncharged
Carrier Pumps (Active Transport)
• small, polar molecules- hydrophilic and uncharged
• ions- charged
I would appreciate more detail (examples) and clarity regarding size, polarity, and charge. I'm a little confused
Hey,
So you're looking at this a bit wrong, anything travelling by active transport will either travel via a carrier proteins or by bulk transport (endocytosis or exocytosis). The only things you'll really talk about as travelling via bulk transport for VCE will be proteins exported or imported into the cell, or other cells/cellular components engulfed by the cell (in immune reactions). Therefore every other type of molecule will travel via carrier proteins when it's going against the concentration gradient (when it's being actively transported) - regardless of whether it's polar, non-polar, small, large, or charged, if it's active transport it'll be going via a carrier protein.

In regards to facilitated diffusion, while some molecules can use either channel or carrier proteins generally for VCE we just refer to facilitated diffusion as being via channel proteins and active transport as being via carrier proteins. Best to check with your teacher for what they expect on SACs, but on the exam you don't need to separate what travels via channel proteins and what travels via carrier.

Note: Carrier proteins that allow facilitated diffusion of glucose are actually fairly well studied - however for VCE you don't need to know that they specifically travel via carrier proteins.

Simple diffusion
I'm going to start with this because some of the things you've listed above don't need to travel via facilitated diffusion - they still do sometimes though, particularly when a cell needs a lot of them (e.g. water can travel through aquaporins).
- Small, polar molecules (e.g. water) & non polar molecules (e.g. carbon dioxide).

Facilitated diffusion
- Large polar molecules (e.g. glucose)
- Charged molecules (anything represented with a + or - next to it)

Active transport (carrier proteins)
- Any molecules travelling against the concentration gradient (excluding extra large molecules as below)

Active transport (Bulk transport)
Concentration gradients are irrelevant for bulk transport, substances can be transported in either direction.
- Transport of very large molecules (e.g. proteins or cellular material) into or out of a cell.
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#### Erutepa

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##### Re: VCE Biology Question Thread
« Reply #11534 on: February 12, 2019, 10:13:20 pm »
+2
What are the different substances that can move across the plasma membrane via facilitated diffusion and active transport? Is the following list correct?

Channel-mediated Diffusion
• small, polar molecules- hydrophilic and uncharged e.g. glucose
• ions- charged e.g. Na+
Carrier-mediated Diffusion
• large, polar molecules- hydrophilic and uncharged
Carrier Pumps (Active Transport)
• small, polar molecules- hydrophilic and uncharged
• ions- charged
I would appreciate more detail (examples) and clarity regarding size, polarity, and charge. I'm a little confused
Simple graphics like this one may also help with remembering how things move across the membrane:

This image shows what substances can simply diffuse across the membrane itself. As PF mentioned above, those which can't diffuse by themselves, will need to have their diffusion facilitated by transport proteins (carrier and channel). However if any of these molecules are being moved against the concentration gradient (from low to high concentration), then this will have to be done via active transport facilitated by a carrier protein.
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