Couple of Bio questions...

<p>here are a couple of questions I came across that I think have errors, I just want to discuss with everyone.</p>

<li>In order to travel from the outside of a plant cell to the innermost part of one of its chloroplasts, a molecule would have to pass through a minimum of how many separate phospholipid bilayer membranes?
A. 1
B. 2
C. 3
D. 4
E. The Molecule would not have to travel through any phospholipid membranes</li>

<p>Answers A and E are clearly wrong. I put D because the molecule crosses the cell membrane first then the 2 membranes of the chloroplast and finally the thylakoid membrane which equals 4 total membranes.</p>

<p>The answer given was C and the explanation doesn’t seem to account for the thylakoid membrane.</p>

<p>So am I right with 4 or is the book right with 3?</p>

<li>Why were these amino acids a significant discovery? [preceding the question is a description of the Stanley Miller Experiment]
A. mRNA was formed in the chamber
B. Amino acids were the building blocks for living cells
C. It showed the spontaneous formation of ribosomes
D. The “primordial soup” was cellular cytoplasm
E. It showed that amino acids were present in Earth’s early atmosphere</li>

<p>A, C, D are clearly wrong. The answer given was B. I put E.
First of all, I don’t think amino acids are the building blocks for living cells (?).
Second, E seems more correct, but also seems wrong because the experiment showed that organic molecules spontaneously formed and not that amino acids were present.
So is B more right or E more right?</p>

<p>I know this was a mind-ful but Thanks for reading and responding.</p>

<p>q1. 3 is the correct answer. The thylakoid membrane is one of two membranes of the chloroplast. One plasma membrane and two chloroplast membrane</p>

<p>Q2. Amino acids make proteins. Proteins are the basic structural molecules of cells and the basis for enzymes that are crucial for maintaining homeostasis and life processes.</p>

<p>Both answers as given by the book are correct.</p>

<p>Hm...I just googled the first question and it seems I am right. Chloroplasts have an outer membrane, inner membrane and thylakoid membranes. If a molecules wants to go to the innermost part of the chloroplast, it needs to go inside the thylakoid. So it must cross the cell membrane and the 2 chloroplast membranes and 1 thylakoid membrane = 4 membranes!</p>

<p>Thanks BigIS, I guess your explanation makes sense for Q2.</p>

<p>Tell me something, will I encounter confusing questions/answers like this on the real SAT Bio?</p>

<p>Yes, you are indeed correct that the chloroplast has three layers of membranes. Now comes the tricky part. The phrase "innermost part" is ambiguous. Like you, my first interpretation would be that the thylakoid space would be the innermost part of the chloroplast. However, the innermost physical location may be the center of the stroma, without cutting across any thylakoids. I think you have a good argument, though, and I commend your scholarship. Nice work!</p>

<p>I would be interested in seeing the explanation the book gave for only three membranes.</p>

<p>Question 1 question would not have made it onto the SAT Bio test because of the ambiguity. Question 2 is an example of a question that will be on the SAT Bio test, asking about the "big picture" rather than a memorized detail.</p>

<p>I see what you are saying.</p>

<p>Here is the books explanation, BTW this is the Sparknotes test 3 #86</p>

<p>"In order to travel from the outside of the cell to the interior of a chloroplast, the molecule would first cross the plant cell membrane. It would then have to cross two membranes of the chloroplast: the outer membrane enclosing the organelle and the inner membrane within the chloroplast. (Mitochondria are also built of two membranes.) All membranes consist of bilayers of phospholipids."</p>

<p>thanks for all your help BigIS</p>