Biology Vol 2 Q pack Part 1

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Biology Vol 2 Q pack Part 1

Post by ragtaguzoo » Fri May 22, 2020 2:52 pm

1. Why did they say 5.5 uM for + end more than the - end?

2. Z line and I band are the only things affected by muscle contractions? Not the myosin of actin ( microtubules)? Just wanted to make sure my reasoning is valid.

8. I saw that the transcription inhibitor produced everything, but the translation inhibitor produced nothing, so I thought no proteins?

14. Isn't the GI tract, the abdominal cavity, so E coli would already be present there.

15. Why not Ans A (diarrhea)?

16. Isn't there more pressure, the deeper you go in water?

18. Is the cell membrane the same thing as the plasma membrane? Couldn't the answer be the cell wall, is it the plasma membrane (cell membrane) because it is the innermost structure?
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Re: Biology Vol 2 Q pack Part 1

Post by NS_Tutor_Mathias » Tue May 26, 2020 2:04 pm

1. Only when adding subunits can an end be said to be 'growing' at all. So for the same reason that the answer is "at concentrations greater than 1 uM" rather than "At all concentrations". In order to be growing faster, one has to be growing at all.

2. Only the distance between the Z-lines really changes, but none of the constituent proteins are changing significantly (this makes sense, since polymerization/depolymerization would be much too slow for muscle contraction to be effective). I-band and H-zone can also be said to be shrinking, but again, these are simply regions and don't denote changes in proteins in any way except their relative arrangement.

8. This is saying that if inhibition of translation results in a failure to signal, then the product of translation must be the critical ingredient in cell signaling. The product of translation is, of course, proteins. Therefore cell signaling must be occurring through proteins.

14. The abdominal cavity is not the GI tract. The abdominal cavity is everything in your abdomen, and consists of the space inside your body and all the organs inside that space. This is naturally sterile. The GI tract itself is outside of your body (as is your entire alimentary canal), and this is usually overgrown with various bacteria. Perforation of the GI tract therefore results in contamination of the abdominal cavity. This is largely an anatomy question: Still worth studying, but a little bit de-emphasized on the modern MCAT. Remember that AAMC QBank materials are fairly ancient!

15. You mean why not D? They want you to understand the gut as a simple biome, the way any other biome works: What sticks around is simply determined by what competes best, and competition is rather simply defined as 'producing the most viable offspring'.

16. You don't have to stand up in water, so you don't bear your weight. Instead the buoyant force aids in keeping you at your preferred elevation and orientation - and as a result, you also don't carry your entire weight on your bones.

18. Yes, those mean the same thing.

The cell wall doesn't provide a barrier capable of maintaining a concentration gradient, nor can ATP synthase be embedded in it. You are expected to reason by analogy here: Since ATP synthase and a concentration gradient are required for the final step of oxidative phosphorylation, the plasma membrane is the only viable place where this could occur. Also, the electron transport chain itself has to be embedded in some membrane. Prokaryotes mostly only have the one membrane available.
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