VCE Biology Question Thread

[geminii]

I know that, but what I'm asking is how the cell wall keeps it from bursting?

Did a bit of research and found that the cellulose in plant cell walls is very strong, and that's what keeps it from bursting. Once more and more water goes in, the cell wall simply cannot stretch anymore. It's simply the strength of the cellulose in the cell wall that keeps it from bursting.

[geminii]

Is the glycerol part of a triglyceride polar and hydrophilic, while the fatty acid tails are non-polar and hydrophobic? Or is that just in phospholipids?

[TheAspiringDoc]

Is the glycerol part of a triglyceride polar and hydrophilic, while the fatty acid tails are non-polar and hydrophobic? Or is that just in phospholipids?

phospholipids are amphipathic (partially polar, partially non-polar), but triglycerides are just non-polar pretty much.

phospholipids have a polar end due to the phosphate group.

[sunshine98]

Is the glycerol part of a triglyceride polar and hydrophilic, while the fatty acid tails are non-polar and hydrophobic? Or is that just in phospholipids?

A glycerol molecule by itself is highly polar (it has three OH groups that create this polarity). But when bonded to 3 fatty acid chains that are super non polar the whole molecule becomes more non polar than it is polar. And because the bond uses the OH bond (which created the polarity) the polarity of the molecule decreases. So no, we don't refer to triglycerides as having hydrophilic heads and hydrophobic tails. But we do for phospholipid's because the hydrophilic-ness/ polarity is increased by the phosphate molecule that is attached to the glycerol. 

[jk006915]

Sorry, this is a bit late, but thanks TheAspiringDoc for answering my question
I don't really understand photosynthesis.. specifically, what exactly are photosystems? what's the difference between I & II? and are they both part of the light dependent stage or something? confused...

[TheAspiringDoc]

Sorry, this is a bit late, but thanks TheAspiringDoc for answering my question
I don't really understand photosynthesis.. specifically, what exactly are photosystems? what's the difference between I & II? and are they both part of the light dependent stage or something? confused...

Here's a post from a while back

When photons hit photosystem II and I, their electrons become excited. This excitement 'reaches' the chlorophyll inside the photosystems which excites a chlorophyll electron. The excited chlorophyll electron is lost to an electron acceptor in the ETC, leaving the photosystems with a positive charge. The electrons lost from photosystem I combine with H+ from the stroma to form NADPH. Acting as a means of replenishment, the electrons lost from photosystem II move along the ETC to photosystem I. As they do this, H+ ions move against their concentration gradients into the lumen of the thylakoid. The electrons provide the energy for this to occur, as it is an active form of transport. H2O is split to form H+, O2 and e- (electrons). The electrons (e-) from the catabolism of water are used to replenish those that were lost from photosystem II. Oxygen is released from the exergonic reaction as a by-product. The H+ ions (or protons) released add to the H+ concentration forming in the lumen. These H+ then travel through ATP synthase, creating a concentration gradient which releases energy. I'm pretty sure that free electrons are also used in this process. ATP is formed as a result of this process.

[TheAspiringDoc]

The tiny water flea crustacean Daphnia has the most genes of any animal, some 31,000 (vs 25 000 for humans). Does this make it more complex? More evolved?

[vox nihili]

The tiny water flea crustacean Daphnia has the most genes of any animal, some 31,000 (vs 25 000 for humans). Does this make it more complex? More evolved?

Nope. It isn't the size that matters. It's how you use it.

[TheAspiringDoc]

If a point mutation occurs to a nucleotide, will its corresponding nucleotide be changed as well so as to be complementary, or will it just be it a bit of a mismatch?

[geminii]

If a point mutation occurs to a nucleotide, will its corresponding nucleotide be changed as well so as to be complementary, or will it just be it a bit of a mismatch?

I remember hearing my teacher telling us that if there is a defect in a nucleotide, the complementary nucleotide will simply not be able to bind to it, which is where the MHC Class 1 (or 2?) receptors fix it up. If they fail to pick up on around seven or eight of these defects, this is when cancer occurs.

Please know that I'm going off the top of my head! I can't really quite remember what she said but it was along these lines when we were learning about cancer and repair of DNA defects.

[vox nihili]

I remember hearing my teacher telling us that if there is a defect in a nucleotide, the complementary nucleotide will simply not be able to bind to it, which is where the MHC Class 1 (or 2?) receptors fix it up. If they fail to pick up on around seven or eight of these defects, this is when cancer occurs.

Please know that I'm going off the top of my head! I can't really quite remember what she said but it was along these lines when we were learning about cancer and repair of DNA defects.

Pretty well there, but a bit more complicated and not involving MHC molecules (they're involved in the immune system)

[geminii]

Pretty well there, but a bit more complicated and not involving MHC molecules (they're involved in the immune system)

Ah, thanks! Could you detail what the actual process is?

[Gogo14]

Guys, im really confused about exogonic,endogonic and exothermic and endothermic reactions? What are the differences? Also can someone explain teh difference between anabolic, metabolic and catabolic reactions?
Thanks

[geminii]

Guys, im really confused about exogonic,endogonic and exothermic and endothermic reactions? What are the differences? Also can someone explain teh difference between anabolic, metabolic and catabolic reactions?
Thanks

Hey, just a heads up, you misspelt exergonic as exogonic and endergonic as endogonic

Exergonic reaction: Releases energy. Example: cellular respiration.
Endergonic reaction: Takes in energy. Example: Photosynthesis.
Catabolic reaction: All catabolic reactions are also exergonic. Means that something is being broken down. (Big pieces into smaller pieces)
Anabolic reaction: All anabolic reactions are also endergonic. The same as an endergonic reaction. Means that something is being built up. (Small pieces into a large piece)

Don't know about exothermic, endothermic and metabolic reactions, sorry!

[TheAspiringDoc]

Guys, im really confused about exogonic,endogonic and exothermic and endothermic reactions? What are the differences? Also can someone explain teh difference between anabolic, metabolic and catabolic reactions?
Thanks

Ace more or less covered you, but I thought I'd add that endo/exothermic reactions are sorta equivalent to ender/exergonic reactions, it's just that the 'thermic' ones refer to temperature and are pretty much just referred to in chem. Metabolic reactions = umbrella term (i.e. all encompassing term) for life-sustaining reactions.