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March 29, 2024, 02:16:46 am

Author Topic: VCE Biology Question Thread  (Read 3570633 times)  Share 

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vox nihili

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Re: VCE Biology Question Thread
« Reply #600 on: February 13, 2014, 10:29:49 pm »
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How do non-polar substances pass through the plasma membrane? I knot it's via diffusion, but does it occur as they are attracted to the phosphate head as they are non-polar, or are small enough to pass through the pores, and aren't repelled by the fatty acids as they too are non-polar?

Essentialy, how does non-polar substances get passed a negatively charged phosphate head?

It moves around and breaks a bit, so they just slide through like it's water. Non-polar substances don't go through the gaps though, it's incorrect to say this :)
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alchemy

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Re: VCE Biology Question Thread
« Reply #601 on: February 13, 2014, 10:39:41 pm »
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Essentialy, how does non-polar substances get passed a negatively charged phosphate head?

The only substances that can move across the membrane via 'simple diffusion' are lipid-soluble molecules such as steroids, or very small molecules, such as H2O, O2 and CO2. Larger molecules and lipid-insoluble molecules require the aid of a protein channel to move across the membrane.

vox nihili

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Re: VCE Biology Question Thread
« Reply #602 on: February 13, 2014, 10:59:50 pm »
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Just to make a few things clear for everyone (and if anybody does see some problems jump on them please, because it's been a little while).

As alchemy has mentioned, simple diffusion will involve small molecules or lipid soluble molecules. It's really important that you all understand this, but also understand why this is occurring. The plasma membrane is made of a phospholipid. Yes, this is an amphipathic molecule, but it probably is important to note that the major component is that lipid. The polar region is certainly much smaller. So, lipids can pass through by simple diffusion as well because it only needs to get past a pretty week polar barrier to make it into that nice, lipid environment.

Small molecules can get through because they're just that, they're small. The phospholipid bilayer can't pack in perfectly, and by virtue of the fact that the cell is at 37°C and not -273°C, the phospholipids will constantly move and jiggle around. For small molecules, they can just weave through, even if they are slightly charged. The effect of polarity isn't enough to knock them away either.

So the key points there:

-the effect of the phosphate heads' polarity will not be sufficient to deflect a lipid molecule; a phospholipid is a mainly non-polar molecule. The lipid will just barge through that tiny deflection.
-small molecules can get through for two reasons: there are tiny gaps because the packaging of phospholipids next to each other isn't perfect, and because the effect of polarity, likewise, isn't strong enough to knock them back.

Compare this last point with charged molecules. Whilst small, they bare a full charge, which would respond too much to the charge difference between itself and the phospholipid. The charge difference between an ion and a polar molecule is greater than the charge difference between two polar molecules. In this case, the difference will be great enough to keep the ions out.



The membrane is one of the most incredible things in Biology. Its design is absolutely perfect and its chemistry astounding. These systems that you're learning about, various types of transport across the membrane, reflect the complexity of its chemistry. That's why there's so much to learn, because you really are learning about an incredible structure.
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Tyleralp1

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Re: VCE Biology Question Thread
« Reply #603 on: February 13, 2014, 11:17:47 pm »
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IS the polymer of monosaccharides: Polysaccharides or Carbohydrates.
Is the polymer of glcuose: polysachharides or Carbohydrates
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alondouek

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Re: VCE Biology Question Thread
« Reply #604 on: February 13, 2014, 11:20:23 pm »
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IS the polymer of monosaccharides: Polysaccharides or Carbohydrates.
Is the polymer of glcuose: polysachharides or Carbohydrates

1. Polysaccharides
2. Complex Carbohydrates/polysaccharides

Would you like me to explain why? :)
« Last Edit: February 13, 2014, 11:35:56 pm by alondouek »
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Tyleralp1

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Re: VCE Biology Question Thread
« Reply #605 on: February 13, 2014, 11:22:28 pm »
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That would be very helpful if you did :)

Btw,  thank you to all who helped answer my frantic pre sac questions Really apappreciate it :D
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alondouek

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Re: VCE Biology Question Thread
« Reply #606 on: February 13, 2014, 11:34:37 pm »
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That would be very helpful if you did :)

Btw,  thank you to all who helped answer my frantic pre sac questions Really apappreciate it :D

Monosaccharides are monomer saccharides units, such as glucose. The plural of 'mono' is 'poly', and polysaccharides are a general term for many monosaccharides joined together by glycosidic bonds. (Between the levels of 'monosaccharide' and 'polysaccharide', there is a stage called 'oligossccharides'. You probably don't need to know this for VCE, so heads up).

Using glucose as our model carbohydrate monomer unit:

- monosaccharide --> one glucose unit
- (oligosaccharide --> between 2-10 joined glucose units)
- polysaccharides --> more than 10 joined glucose units



Glucose is a specific monosaccharide; polysaccharides are the polymer units of monosaccharides, so the best definition of a polymer of glucose is a complex carbohydrate (such as starch), i.e. A polysaccharide.
« Last Edit: February 13, 2014, 11:36:27 pm by alondouek »
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Paulrus

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Re: VCE Biology Question Thread
« Reply #607 on: February 14, 2014, 08:44:44 am »
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ok bear with me for a second cos this is probably a stupid question, but i'm not sure why my teacher marked this as wrong.
my reasoning was that the solution the cell has been placed in has a higher concentration of the solute (5%) than the inside of the cell (2%), making it a hypertonic solution. because the outside solution has a higher concentration of solute, i thought there would be net movement of water coming out of the cell in order to reach equilibrium. my teacher corrected it and drew an arrow going inwards and i'm not sure why.
what am i missing here? i have a sac on this later today and i'm feeling kinda panicked cos of this  :-\
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MagicGecko

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Re: VCE Biology Question Thread
« Reply #608 on: February 14, 2014, 10:40:49 am »
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mmhm osmosis is the net movement of water molecules across a semi-permeable membrane from a region of low concentration (high water concentration) to a region of high solute concentration (low water concentration). Knowing that, the water molecules would like you said, move out of the cell. So you're actually not missing anything, I'd say your teacher is wrong. Maybe he'she did this at midnight and wasn't thinking straight? Have you tried asking your teacher why he/she marked it as wrong?
 
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Re: VCE Biology Question Thread
« Reply #609 on: February 14, 2014, 12:13:55 pm »
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I have both tsfx and neap notes from the summer school lectures which one should i use primarily and which one is better and why?

masonruc

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Re: VCE Biology Question Thread
« Reply #610 on: February 14, 2014, 02:59:14 pm »
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I have both tsfx and neap notes from the summer school lectures which one should i use primarily and which one is better and why?

TSFX hands down!

-Notes reflect study design with tsfx, past experiences with neap is that they go way outside what is needed.
« Last Edit: February 14, 2014, 03:01:08 pm by masonruc »
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Paulrus

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Re: VCE Biology Question Thread
« Reply #611 on: February 14, 2014, 05:58:42 pm »
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mmhm osmosis is the net movement of water molecules across a semi-permeable membrane from a region of low concentration (high water concentration) to a region of high solute concentration (low water concentration). Knowing that, the water molecules would like you said, move out of the cell. So you're actually not missing anything, I'd say your teacher is wrong. Maybe he'she did this at midnight and wasn't thinking straight? Have you tried asking your teacher why he/she marked it as wrong?

i asked her earlier today and she apologised and said she was half asleep while marking haha
i'm glad i wasn't wrong, but man that confused me  :P
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KanMan

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Re: VCE Biology Question Thread
« Reply #612 on: February 14, 2014, 09:33:33 pm »
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Hi everyone, I'm new to forum so I do apologise if I've accidentally responded in the wrong section.  :D
I was wondering if anyone could clarify to me  two questions.
1) What is the difference between proteoglycans and glycoproteins?
2) Are there amino acids which have roles other than in the formation of proteins?

Thanks in advance!

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alchemy

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Re: VCE Biology Question Thread
« Reply #613 on: February 14, 2014, 10:00:23 pm »
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Hi everyone, I'm new to forum so I do apologise if I've accidentally responded in the wrong section.  :D
I was wondering if anyone could clarify to me  two questions.
1) What is the difference between proteoglycans and glycoproteins?
2) Are there amino acids which have roles other than in the formation of proteins?

Thanks in advance!

1) Firstly, you don't have to know this. I don't think you ever would have in the past. Even if you did, VCAA have toned down their study design so much over the years that there's no point in hoping this will show up on your exam. But if you are inquiring from interest, that's cool. From wider reading, I recall proteoglycans to be a special class of glycoprotein. Also, glycoproteins are referred to as a type of protein but proteoglycans are more often referred to as a type of carbohydrate as they consist mostly of polysaccharide (~95%) in comparison to glycoproteins.
2) I had this question before but forgot to ask it here. Amino acids tend to stabilise pH by removing excess H+ or OH- ions. They can act as neurotransmitters, and are also available as dietary supplements.

slothpomba

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Re: VCE Biology Question Thread
« Reply #614 on: February 15, 2014, 10:47:08 am »
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As alchemy said, both those are outside the study design and far outside VCE. They're more 2nd year biochemistry. Not sure where you got them but i'd use that less as a source in the future.

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