What's up, AP Bio Penguins? So today we are going to go live, and we're going to talk about Unit 3, which is on cellular energetics. So I'm Mrs. Jones from AP Bio Penguins. And so real quick, why are we penguins? Well, because of the fact that as AP Bio students, you are dressed for success.
And so AP Bio Penguins are, of course, dressed to success in their cute little tuxedos, all that good jazz. And as we go through this review session, you're welcome to go ahead and put your comments or your questions down into the chat. It's just me on here, but I'm happy to answer them as we go through each of the pieces of information.
And so real quick reminder, you already probably know about the resources, but just in case you don't, there's currently a daily review happening Monday through Friday on my Instagram page, so APBiopenguins. If you go to my website, my Weebly, I have a 374-page review guide in which I go through each of the topics in the CED. asking you little topic questions.
I give you ICANN statements. And then at the end of each unit, there is a multiple choice and free response questions to kind of help you to review, as well as there are explanations for all the multiple choice. And then there are scoring guidelines for all the free responses. I do an FRQ Friday every week.
So I've been currently posting four every weekend. And so the goal is to get through all the FRQs by the end of the review season. And then there's 120 Quizzes games on Weebly. So again, on my website, you'll get the access codes.
And so you'll go to Weebly, I'm sorry, you'll go to Quizzes.com. You'll type in that code and then you've got a game that you can use to review, as well as there's review PowerPoints. And all that is found on apbiopenguins.weebly.com. Or you can probably just Google apbiopenguins and you'll probably see it as like the first hit. So today's plan, we're going to work through enzymes.
We're going to talk about cellular respiration, photosynthesis. I've got some practice questions for you, two multiple choice and two free responses. Well, half of one of the responses. And then I'll open it up in case there's any kind of questions.
But of course, if you have questions as I'm going through this, go ahead and put them in the chat. Last week or I guess it was last weekend, individuals were kind of helping each other if I didn't see the question. There is a little bit of a lag between when I say it.
And then, of course, you hear it. And then whenever you have that moment to type it into the chat. So I may have moved on to the next slide, but I'm happy to go back. I can answer any questions as you have them. So let's go ahead and get started.
So before we get into enzymes, let's talk about free energy because this whole unit is about energetics and about the energy. So first thing, Gibbs free energy. So what is Gibbs free energy? Well, that's just the energy that's available to do work.
So whenever we talk about reactions in your cell, we're going to talk about them either releasing energy or them absorbing energy. which will be called energonic and exergonic reactions in a little bit. And yes, those terms are backwards.
So there's an equation. This equation is not on the formula sheet. It used to be on the formula sheet, but I don't believe you're going to have to calculate this. But just in case, I did want to show you the formula. So this delta G, because it was asked earlier this week, that delta G stands for change.
So it's just looking at your final minus your initial and how much the change in your free energy was. Equals the delta H, so the change in the enthalpy. or the change in the heat energy, minus your temperature, which is in Kelvin, times your delta S, which is your change in entropy, so the disorder, sort of the disorganization, the chaos, if you may.
And so with this, we've got another formula, that delta G equals your final Gibbs minus your initial Gibbs, which is where we're going to look at for our exergonic and our endergonic reactions. So with an endergonic reaction, this means that energy has to enter the system. So it has to be brought in. And so this kind of reaction, we're going to start with low free energy, and then we're going to gain energy, that delta G right here is going to be that we're going to have a positive change in free energy.
And so our products are going to have more energy than our reactants did. So this is going to be not spontaneous because it's not going to happen on its own. It's going to require that input of energy in order for this reaction to take place. It's going to absorb energy. An example of this would be ADP plus inorganic phosphate giving us ATP.
This is a endergonic reaction. You've got to have energy put in in order to be able to do this. And that's what the process of respiration is doing is it's releasing the stored energy of a glucose molecule or another molecule.
And that energy that gets released will be stored in the form of ATP. So exergonic reaction has to do with that the energy is going to exit the system. So here we see that our reactants have more free energy than our product. So our delta G is going to be negative because it's released that free energy.
I always tell students that EX for exit or the EN for enter. Okay, so exergonic reaction is releasing that energy. So this will happen spontaneously. Yes, there's going to be an energy of activation, so that activation energy is required to get a reaction started, but the overall process is, of course, going to release. You can put a stick of dynamite on your table, and sooner or later, that thing's going to explode.
That's why you always want to be careful with dynamite, you know, any kind of... movements, which you're not working with, so it's okay. And then the example would be ATP releasing that energy in the form of ADP. And that energy is not stored in that inorganic phosphate, it just has to do with the structure itself has less free energy as ADP than it does as ATP.
Enzymes. What are enzymes going to do? Well, these are just your biological catalysts.
And if you've had chemistry, you know that catalysts'job is just to speed up a chemical reaction. So these are biological catalysts. They're just things that are in your body that are going to speed up the reactions within your cells.
And their job is to reduce that activation energy. So we saw before that you have this energy of activation. It's the amount of energy that's required to get the reaction started. And so if you notice here, the purple line is higher than the green line. That is your...
uncatalyzed reactions. So if there's no enzyme in there or there's no catalyst, that's how much energy is required to get the reaction started. Versus if you have an enzyme, you have that catalyst.
It's just decreasing how much energy is required. It does this by binding to the different molecules and it can put them in the appropriate conformation so they can then, of course, react. It could kind of strain the bonds so that, of course, it helps to break that bond. And so they do a lot of things to help to decrease the amount of energy required to start.
Your delta G is going to be the same. So it's going to release the exact same amount of free energy, or it's going to absorb, like it's going to have the same energy. Delta G will be the same.
It cannot make a exergonic reaction endergonic, nor an endergonic reaction exergonic. Like it's not going to happen like that, okay? So important things to note is that these catalysts, they're proteins. So everything you learned about in unit one in terms of proteins applies to them, okay? They're still looking at the...
The conformational structure in terms of the primary, secondary, tertiary, and quaternary structures, it's the exact same thing we looked at before. So when we talk about denaturation, we're talking about proteins and how proteins break apart. They're not consumed by the reaction. So you can use an enzyme over and over and over and over, and it will never get used up. It will never go away.
The only way to get rid of that enzyme is, of course, to denature it. And as I said before, it has no effect on that Gibbs free energy. The free energy is the exact same whether You have double, triple, quadruple the amount of enzyme in there.
It's still going to have the exact same delta G. The reaction would just occur faster because you have more molecules to react to it. But you're not going to be able to, of course, change that delta G.
So how does an enzyme work? So we're going to have this little active site. That's the site at which our substrate is going to bind.
And once it binds, as you know with proteins, anytime you bond to a protein, it always changes shape. And so if we were to have this molecule here, right? It binds into my hand.
I'm not just going to let this kind of pen roll around, right? Naturally, when someone puts a pen in your hand, you close your hand, right? That's what's happening here is that substrate binds to the active site. It causes conformational shape change. And when that happens, of course, now it's putting all these molecules in the appropriate orientation.
So now they're going to be able to react. As I said before, decreasing that activation energy, okay? They react. It releases that product back out. And now the enzyme is ready to take the next substrate again.
again, go through the reaction, breaking apart the top from the bottom, and it goes on its merry way. As I said, it releases it. And so it's going to do this over and over and over again, repeatedly. Okay, so how can I stop it from happening?
Well, there are different things called inhibitors. So one thing is a competitive inhibitor. A competitive inhibitor is going to compete for the same active site. It has the same general structure. So here's our substrate, here's our competitive inhibitor.
It's going to to bond to the same places. It's going to have our same general shape, just like morphine and endorphins. Endorphins are natural in your body. But morphine, which is a drug that was made by a pharmaceutical company, has a similar structure to the endorphin, which allows it to bind to the same receptors, which gives you that same sense of euphoria and helps take away that pain that you might be feeling. Don't do it.
Yeah. And then we also have non-competitive inhibitors. Non-competitive inhibitors are going to bind to another side. So it's going to be an allosteric site. And when it binds to an allosteric site, what's happening is the enzyme changes shape, right?
The protein changes shape when you bind something to it. So now the active site is no longer the same shape to allow the binding of that substrate to it. And so when we look at this, we're looking at these competitive and non-competitive inhibitors.
They're going to bind and release, bind and release constantly. And so if we wanted to overcome an inhibitor, just increase the amount of substrate. We also find that sometimes your product can inhibit.
It's called product inhibition. And because the product was originally bound in that spot, it can bind again, which can inhibit. So if we're trying to increase our reaction rate, you can, of course, increase temperature slightly.
You can increase the amount of substrate or you can decrease the amount of product. All of that can help you to overcome that inhibitor. And so denitration. So if we increase our temperature too, too much, like it gets really, really high, that causes these bonds in our tertiary and our secondary and our quaternary structure to break.
They are covalent, they're ionic bonds, and those bonds can break because, of course, you have more vibrating, there's more kinetic energy as we increase that temperature. Also, pH. You know that the carboxyl group is acidic and the amine group is basic. And so because of the fact that you know that those groups are acidic and basic, they will, of course, donate and pick up hydrogens or protons from the reaction.
I'm sorry, from the solution. And so that can cause a conformational shape change. The shape will change if you change the pH. And so there's like a certain range, the optimal range.
So you might be asked questions where you're looking at a graph and wondering why is it coming off on both ends? Well, because of the fact that it's getting out of its optimal range. And so it's denaturing.
Why would I see this reaction slowing down? Because of denatured. And so oftentimes, it'll just give you some type of reaction that will make you see that, oh, this enzyme got denatured, which caused the reaction rate to either stop or slow down. You could also see that we have a change in salinity. The salinity can change the ionic structures, not ion structure, but it causes ions to be in there, which then changes the ionic bonding.
So then again, the enzyme can denature. So cellular respiration. So before we get into this.
I know that students have a hard time with cell respiration and photosynthesis. And it's because of the fact that you overwhelm it. Like you get put too much stress in knowing all 10 steps of glycolysis and knowing all eight steps of Krebs cycle and knowing every enzyme.
I didn't have to know any of that until I got to college in my biochem course. And I sat in the library for two weeks and I memorized it all. And do you think I still know it?
No, I do not because I haven't had to use it. So what I want you to remember is what goes in. What comes out, where does it take place, and why is it important?
And that's what we're going to focus on. So there are three steps to cellular respiration. You've got glycolysis, Krebs cycle, and then oxidative phosphorylation.
So glycolysis takes place in the cytosol. That means it will take place in a prokaryote as well as a eukaryote because it's just in that cytosol. It does not require a mitochondria for this process to take place.
And so this diagram is slightly wrong. This should be ADP and this should be ATP. But other than that, the diagram is correct. So we start out with glucose, and then in this process, we're going to make two NADHs. We make two pyruvates and then two ATPs.
Again, the diagram is wrong. It should say ATP, not ADP. Okay. So we start with glucose, and thinking about the name, glyco. Glyco means sugar.
Lysis, we know, means to break. So glycolysis means the sugar-splitting step, the step in which we're going to break glucose. So we take glucose, which is a six-carbon structure, and we break it into two. three carbon structures, okay? So at this point, I haven't lost any carbon dioxide.
So that's why I see I have the two NADHs, two pyruvates, and two ADPs, okay? So that pyruvate is going to go through pyruvate oxidation, and we're going to, of course, oxidize it, okay? So when we go through the oxidation process, we then are going to make this thing called acetyl-CoA.
Acetyl-CoA, acetyl group is two. So in the process of pyruvate oxidation, we lost one carbon dioxide, we made one NADH. And you're wondering why I'm doing this.
I tell my students that that H means to hold. So if I have NADH, it's holding an electron. If I have NAD+, it's not holding the electron.
And so it's a lie that I've told my students, but it works out for me. And so the acetyl group comes in. It loses the coenzyme A. The whole point of that coenzyme A was just as a placeholder.
So the acetyl comes in. It then binds to the molecule that's already in there, making the oxaloacetate. I'm sorry, it binds to oxaloacetate, making citrate.
Not important. Don't worry about it. And in this process, we go through this loop, and this is going to take place in the mitochondrial matrix. So we had to actually be in the matrix for this to take place. So when we talk about Krebs cycle, you have to have a mitochondria for this Krebs cycle, okay?
So the starting material, acetyl-CoA, and in one loop of the Krebs cycle, or one turn, we're going to have two carbon oxides. Remember, acetyl-CoA has two carbons, and then I make two carbon oxides, which means at this point, I've completely broken down the glucose. There is no more glucose left.
It's gone. Okay, I have three NADH. Again, they're holding those high energy electrons.
One FADH2, it's the same as an ADH, it's just a little bit weaker. It's still holding electrons. And then it makes one ATP.
Technically, it's a GTP, but that's okay. You can just know it as ATP. Now, glycolysis made two pyruvates.
But when I just gave you the explanation, there was only one acetyl-CoA. So you'll actually have to go through this cycle two times if you're talking about breaking down one glucose molecule, okay? So the next thing I have is... oxidative phosphorylation. So, as I said, prep cycle gone.
We already used up all of the glucose. It's all gone, right? So, all that's left are the high energy electrons. So, where is the oxidative phosphorylation taking place?
Well, let me sidetrack for a half second. And it's going to start out with these electrons. The NADH, the FADH2 that has all those electrons is going to bring it over here. Now, there's two steps. The first step is electron transportane.
That's what you see right here. This is our electron transport chain. It's found in the mitochondrial cristae. So if you remember, we had the mitochondria had the outer membrane, and the inner membrane was like highly folded, increasing that surface area, allowing for more of this to take place in there. And so in that cristae, we're going to drop off the NADH, and that electron is going to go through this chain and it's going to slowly drop in energy.
And as it slowly drops in energy, each time it releases energy, that energy is used to pump a proton. As you see right here, we have low protons here, high protons there. We're pumping the protons into the intermembrane space, okay?
So that's all that's happening with our electron transport chain. Protons are pumped into the I-M space. If you're wondering where the I-M space is, it's the space between the cristae, or the intermembrane, and the outer membrane.
So it's that intermembrane space is between there. And last time we talked about pH, and we mentioned that when the pH decreases, it means it's because there's an increase of H+. So the intermembrane space is actually really acidic, okay?
And so it generates this proton gradient. So there's a high concentration of protons on one side. And if you remember from unit two, when there's a high amount of protons, what it wants to naturally do is flow down its concentration gradient.
And so at the end of this whole thing, we, of course, have our oxygen. So why would I talk about the proton gradient? Because of chemiosmosis.
That's the second step of oxyphosphorylation. So these high protons, right, the protons that we have our gradient, it's going to flow down ATP synthase. It ends in A, so we know that's an enzyme.
This enzyme's job is to synthesize ATP. So it's going to use the energy, the potential energy that's stored in that high concentration. And as the protons move across the membrane, it's going to turn the turbine of ATP synthase, which is going to provide the energy needed to phosphorylate the ADP. Now, someone asked earlier this week on the review, where does the phosphate come from? It's just inorganic phosphate.
It's just floating around inside the cell. And so, as I said, there are two parts to oxidative phosphorylation, the electron transfer chain, okay? The whole point of electron transfer chain is to make the proton gradient.
There's no ATP made here. Chemiosmosis is the second step, and this is where ATP is made. So, hope that we've gotten cell respiration.
I don't see any questions happening in the chat. Remember, if you have a question as I'm going through this, go ahead and put it in the chat. It's just me, but I can answer them as I go. So, three steps.
You have glycolysis. We have Krebs cycle. We have oxidative phosphorylation.
So, making sure we know. Where does it take place? Cytosol, matrix, cristae.
What does it start with? It starts with glucose, the acetyl-CoA, and then the electrons of NADH and FADH2. Why is it important? It's important because it's making this NADH, this high-energy electron, it's making the materials needed to go into the next step.
It's creating a proton gradient. So I hope that were helpful. I don't really see any questions coming in, so I think I'm going to write a rule one. So...
I think it was 2015 or 2016. I can't remember the year exactly. This question was on the exam in which they gave you the picture. So those of you that are kind of freaking out like, oh my God, how do I remember all these steps?
They gave them a diagram and they just asked them to explain what they saw. Okay. So use the information, describe one contribution of each in the following of ATP synthase.
So here we see we have our glucose is again a mixed pyruvate and I can see that there's two ATPs made. So how are those ATP made? Well, they're made by substrate level phosphorylation.
Okay, so that's one way that we can make ATP. Another thing, look, I've got NADH. So I'm forming NADH that we know later on will go to the electron transfer chain to provide that gradient, right?
And the last thing I see is I've got this acetyl-CoA that ends here but starts there. So it's going to produce the acetyl-CoA that's needed for the Krebs cycle. Okay, so all you had to do was look at the picture.
A lot of these free responses, if you look at the diagram and really kind of interpret what you see, you can get a lot of points. OK, so the second step we're seeing here is how can I oxidize my intermediates of Krebs cycle and get it? Well, of course, I'm making ATP in the form of GTP. Again, substrate level phosphorylation. I can see that there's the NADH and the FADH2 that's also made that's going to go become the proton gradient.
And then it's producing high energy electrons. So, again, the diagram has the picture information for you. And the last thing is how does the proton gradient help us in the electron transfer stream?
That gradient is then going to provide the energy that's needed to move through ATP synthase to synthesize ATP. That wasn't nearly as easy because you're going to have to know a little bit about the process, but you could, of course, apply that. Okay, so that gets us to the end of cellular respiration. Are you ready for photosynthesis?
Okay, so photosynthesis is going to be made up of two steps. We have our light reactions and we have our Calvin cycle. The light reactions are going to take place in the thylakoid, okay? The same thing that we saw with cellular respiration.
We need to know what does it start with, what does it end with, where does it take place, and why is it important, okay? So it takes place in the thylakoid membrane. So if you remember the chloroplast, right, we have the outer membrane, we have the inner membrane. And then there are these little stacks. Those stacks were called grana.
And the stacks were made of these little stacks. And that was your thylakoid, okay? So it's in the membrane of that. And the reason why plants are, of course, green is because of the fact that there's chlorophyll within the membrane. That's what this P680 and the P700 is.
That's a molecule of chlorophyll. And actually, there's chlorophyll making up this whole reaction complex here. And those pigments are going to absorb that light energy.
And so the reason why it's green is because it's reflecting green back. Okay. And so your eyes see the green that's reflected.
So of course, if you saw there was an action spectrum, I think on the 2014 exam, in which they were looking at which one of these is the appropriate molecule for photosynthesis. And you would, of course, realize that the one that reflects in the green wavelength, you know, that was your... The chlorophyll.
They were comparing bacteridopsin and chlorophyll. Sorry, sidetracked. Sorry. So what does it start with?
It starts out with water. So right here, you see the water molecule is going in. It's getting broken down.
It's releasing that oxygen. So how interesting that in cellular respiration, we use oxygen as our final electron acceptor and it made water. But now water goes in and it acts as the way that we break the water and we get oxygen and our electrons back. So maybe a way to remember it. We also have photons coming in the form of light energy.
And so in our first reaction complex, this is actually photosystem two. OK, we're going to absorb that light energy. It then moves down this electron transport chain here. And oh, my gosh, we have an electron transport chain. What does that mean?
Again, we're going to see our protons moving against their gradient right there as the energy falls. Protons pump. So it's going to pump over here into the thylakoid space.
So instead of respiration, it was out into the intermembrane space. Now it's in the thylakoid. And so we can see that this is going to generate that gradient. And at the end, we see ATP synthase that's going to, of course, synthesize the ATP.
So this electron went through the electron transfer chain, then went into photosystem one, gained more energy, and then it's going to go to NADPH. The P stands for photosynthesis. Yeah, I know it's a lie, but that's OK.
And the H stands for holding. So when I have NADPH, that means that I am holding the electron in photosynthesis. And so the products ATP and NADPH, ATP is made because of this proton gradient here, and the NADPH is made over here.
There's a book, it's called As the Sun Shines, and it kind of gives a cartoonistic way. I did a video of this on my TikTok. I can see if I can share that later so you all can see this if you needed to, but I've got that for you. And so, as I said, protons are pumped against the aliquot space so we can create that proton gradient, okay? So there's two ways the electron can flow.
in photosynthesis. We have linear electron flow. That means I go photosystem two, electron transport chain, photosystem one, and ADPH. This is going to synthesize ATP and ADPH in a one-to-one kind of way, like you make equal amounts of each of them, okay, versus cyclic electron flow is going to go from photosystem one, and it doubles back, and it goes only through this electron transport chain.
So the function of this is going to allow us to make ATP without making an ADPH. You'll find out in a second why. but is allowing us to make NADPH without making the ATP, okay?
And so this is going to be important because in the Calvin cycle, we're going to need nine molecules of ATP and only six molecules of NADPH. So there's not that one-to-one that works, okay? So Calvin cycle taking place in the stroma.
In case you don't remember, the stroma is the kind of the cytosol of our chloroplast. And so we're going to use... three carbon dioxides, 9 ATPs and 6 NADPHs.
The CO2 is going to come in. It's going to bind to something called RUBP with the enzyme Robisco. It then goes through a whole big breakdown in which it's going to make something called G3P. If we had gone through all the steps of glycolysis, you would have seen that at step five, there's a molecule called G3P, glyceraldehyde 3-phosphate. And so that's what we're making here.
that G3P could then take two G3Ps, put them together, and you then make glucose again, okay? And then we have to regenerate the NAD, I'm sorry, the RUBP from that, okay? So the product is G3P. And so there was somewhere I was going to make sure I mentioned in this.
I can't remember what I was going to say. Somebody is asking, will you do fitness? So if you're thinking about fitness, there is a C4 and C3 in a camp plant in terms of photosynthesis. So the C3 is what we normally see.
So right here, it's going to break and make a three carbon structure. And so it's actually, I think, PGAL. But so it breaks up into this three carbon structure.
versus when we look at C4, it has to do with that there's going to be a four carbon structure. And so it kind of brings it in as some other thing, so it regenerates it. And the reason why we would need this is because of the fact that in arid conditions, in the leaf, we're going to have the stomata. not to be confused with stroma, the samadhi's little pores. And so the guard cells, when it gets hot, are going to close.
And so it decreases the amount of carbon dioxide that can come in because we are, of course, are losing that access point. And so C4 is going to be the adaptation that we're going to find in arid conditions. Can plants would be those that are going to use different organic molecules. And so at night, like a cactus. It's going to open up its stomata at night so that it doesn't lose all of its water during the day.
And so it can then bond, it can fix all those carbons in the form of organic molecules and organic acids. And then during the day when there's the sunlight present, that's when it releases the carbon from those organic molecules. So it's able to keep its stomata closed. And so the fitness would be that those individuals that live in this warmer environment have adapted and found a way to modify their C3, C4 plant.
Okay. In terms of specifics of the Calvin cycle, should we get the big picture or should we know the step-by-step? Again, big picture.
Okay. Carbon dioxide is binding, it's getting fixed. Okay.
We then are going to use some ATP, some NADPH to reduce. In case you don't remember, reduction is like oil rig, right? Oxidation is loss of electrons, reduction is gain.
So our carbon is going to gain electrons in the form of NADPH. Um, see right here, it releases it. And then I'm going to release carbon dioxide.
And then the last step is just regeneration or rearrangement. So just remembering fixation, reduction, rearrangement. We start with carbon dioxide.
I use nine ATP, six NADPHs, and I make one G3P. And it's easy to remember because there's three carbons in carbon dioxide and there's three carbons in one G3P. So again, it's the same amount going in as out.
Someone else said, should we memorize the amount of each product? Again, they're probably going to give you a diagram. But having a general idea to understand, oh, wow, there's more ATPs made than NADPH. Hmm.
That must be why we have to go through the cyclic electron flow. So kind of keeping those kind of things in mind. Okay. So I think I've answered all the questions in the chat.
So multiple choice question. Chemical reaction for photosynthesis. Here we see 6CO2 plus 12H2O plus light energy gives us glucose plus oxygen plus water. If the input of water was labeled with the radioactive isotope of oxygen.
then the oxygen gas released as the reaction proceeds is labeled with O2. So it's saying that this H2 over here is going to be labeled, I'm sorry, that this O2 right here is coming from this water, is what they're saying, which is always a likely explanation. So during the light reactions, water is split. Well, yeah, at photosystem two, I saw that my water got split releasing those electrons. And the hydrogen is combined with the CO2.
No, the CO2 is in the Kelvin cycle, so that's not right. and oxygen gas is released which that one is true because the water gets split releasing the ox so during the light reactions water split true removing electrons and protons and the oxygen gas is released that one's also true so so far i think the answer is b but let's just double check read through our other choices make sure we're good during the calvin cycle water is split nope that happened during the light reactions regenerating nad ph to nad plus um no way um and oxygen gas is released again oxygen release was during the light reactions during calvin cycle water split again no hydrogen atoms are added the intermediates of sugar no and oxygen gas release again no so a lot of times some of these answer choices might have things that are right but then also things that are wrong so don't get distracted when you look at your multi-choice questions kind of look through them if you need to make yourself some check marks as you go through it making sure things that are right or wrong um until you can kind of go back to figure out well which one is my right answer or at least can help you to narrow it down like oh A and B both sound right. And then you can have a 50-50 shot instead of a 25% chance.
And yes, there's always only four answer choices on your multiple choice. And so the answer is B. So in experiments measured rate of respiration in crickets and mice at 10 degrees versus 25 degrees was formed with a respirometer.
An apparatus that measures changes in gas volume. Respirometer was measured in milliliters of oxygen consumed per gram of organism over several five-minute trials, and the following data was obtained. According to the data, the mice at 10 degrees demonstrated greater oxygen consumption per gram of tissue than the mice at 25 degrees. This is likely explained by which of the following statements, okay? So we have to think for a second.
What's the difference between a mouse and a cricket? Well, a mouse is an endotherm, which means that it has going to be a warm-blooded organism. It's going to regulate its own temperature using metabolism, versus a cricket is going to be an ectotherm. Ectotherm meaning that it is a cold-blooded organism. It uses the environment to regulate its temperature.
You may have done an experiment like this looking at your peas and you put the peas in warm temperature versus cold temperature just to see what was going to happen in terms of which one respirated more. I mean, use a little respirometer. You may have done the experiment.
You may not have. Okay. Anyway, so we need to figure out, well, why would it respirate more at 10 degrees than 25 degrees?
So if we look through answer choices, A says the mice at 10 degrees had a higher rate of ATP production than mice at 25 degrees. Well, I'm going through more respiration, right? I've got a higher respiration rate. That means that there's more ATP that's being synthesized because of the fact that I went through the process of cellular respiration more frequently. So, so far, I think A sounds right.
B, the mice at 10 degrees had lower metabolic rate than the mice at 25 degrees. Well, if it had a lower metabolic rate, then I wouldn't see as much oxygen being consumed because there would be lower rates. So that's not true. C, the mice at 25 degrees weighed less than the mice at 10 degrees. Hmm, that sounds logical.
But the question told us that it was per gram of organism, which means that they've already accounted for maybe a difference in the weight. And the mice at 25 degrees was more active than the mice at 10 degrees. And if it was more active, it would have needed to respirate more. Okay. So A is our answer.
Does AP Bio cover the biology of skin coloration, melanin, et cetera? Some teachers do bring that in as like different forms of natural selection and adaptations that might have occurred. I know HHMI, Biointeractive, has an activity that they do.
There's like a video and a whole activity that they do in terms of the biology of skin coloration because the melanin historically, kind of looking evolutionarily, is found kind of at the equator regions. Individuals that live more in the equator have higher amounts of melanin because the melanin is going to break down the UV radiation, which is why they're of darker complexion versus individuals that kind of lives up at the poles are lighter complexion. And they had like the red hair, I believe.
And that was because of the, there wasn't direct radiation from the UV. Okay, so looking at a free response, we've got question 2021, number three. They hypothesize that there's a plant compound, resiferatrol, improves mitochondrial function.
To test the hypothesis, they dissolve this chemical into DMSO. The solution passes through cell membranes. They add the solution to the different muscle cells in a nutrient-rich solution that contains glucose.
They measure the ATP production at several time points after the addition of the solution and find an increase in ATP production by the muscle cells. So part A is asking us to describe the primary advantage for the cells using aerobic respiration over fermentation. Now, we didn't mention fermentation.
So let's talk about fermentation real fast about this. So fermentation is going through the process that takes place if the pyruvate is unable to get into the mitochondria or if there is no mitochondria for the pyruvate to go into. And so when you're talking about fermentation, we go through glycolysis first, and then we go through the process of fermentation.
Fermentation will regenerate the NAD+. So if you remember, there was the NAD+, that took the electrons when you broke down the glucose and glycolysis, and it held those electrons as NADH, taking them over to the electron transport chain. Well, if it can't get to the electron transport chain, I've got too many NADHs, and I don't have any NAD+, which means that I'm not going to be able to go through glycolysis, which is a problem. And so... When I do fermentation, I only go through glycolysis.
There was two molecules of ATP that was made in glycolysis. That's not a lot. Versus aerobic respiration is going to go through glycolysis, making two. Crab cycle, making two. And then goes through oxidative phosphorylation.
And in chemiosmosis step, there's, I think, 32 to 34-ish that are synthesized. And so we see that there is more. ATP that's synthesized in aerobic respiration than in fermentation.
So more ATP per glucose is produced by aerobic respiration. As a reminder, this is actually one of the newer free response questions. And so they always ask you in an A question about the biology.
Can you explain the biology of it? And so this is a straight biology question. Why is aerobic respiration better than fermentation? Or what's the advantage of one or the other?
So part B says to identify an appropriate negative control. Okay, so now we're looking at experimental. design, I mean, understanding what is a negative control and what is the point of it. Okay, so in terms of negative control, this is going to be something that is allowing us to see, does our independent variable actually have an effect?
So we're just basically isolating the variable to determine, was that actually the thing that did what we think it did in the experiment? So what is the negative control for the experiment? And that would allow research to conclude that ATP is produced in response to the reciprocal treatment.
Well, as a reminder, the reciprocal is in DMSO. So was it the DMSO that caused the effect or was it the resipiratol or whatever you say the word? Well, I don't know. So I need to test it again without the chemical.
And so I would say, okay, run it without the resipirol or run it so that it has just the DMSO alone. Okay, so I can take out the resipirol and say, okay, what would happen when the independent variable of the resipirol isn't there? Okay, so part C.
Predict the effect on short-term ATP production when it's treated in a medium that lacks glucose. Glucose. Wasn't that what I started glycolysis with? Well, if I don't have any glucose, can I go through glycolysis?
No, I don't have any glucose. So I would expect there to be no ATP made. But in case you've gone through this with your classes, you might know, okay, well, the glucose isn't the only thing that's broken down. We also can break down fats.
And so those different fats will be broken down into just like two carbon structures that go straight into the Krebs cycle. We can break down our proteins. The amino acids get broken down two different ways, and they end up going again into the Krebs cycle. And so I could also say that there is less ATP produced. And so no ATP produced or less ATP produced.
And then part D, the researcher found that this stimulated the different components of the electron transport chain. So if they then, of course. had, sorry, they said that the reciprocal would increase oxygen consumption and we need to justify that. Well, why would I see more oxygen consumed?
Oxygen is my final electron acceptor. And so if this is stimulating electron transport chain, that means I'm going to need more oxygen to take the electrons in electron transport chain, which means that I'm going to see that increase in that oxygen consumption. So more electrons can be transferred so that more oxygen is required as the final electron acceptor.
Okay. So. That's FRQ, and then we're done. So non-cyclic electron flow or cyclic electron flow are two major pathways of light-dependent reaction in photosynthesis. In non-cyclic electron flow, electron pass from photosystem 2, then the components electron transport chain, then photosystem 1, finally reducing NADP plus to NADPH.
In cyclic flow, they cycle back to photosystem 2, sorry, photosystem 1, and then the components electron transport chain. Okay, so what you're seeing here is that this right here is cyclic electron flow. It goes to the ferredoxin, and instead of going over here to NADP+, it comes back into the electron transport chain. So this diagram confused some students on the exam last year. And I think it's because that is not updated.
I should have said last year. I'm sorry. It is on last year's exam, 2023, number, I think, four. I didn't update this. I'm sorry.
And so it confused students last year because of the fact that they'd never seen this diagram before. So if you see a diagram that's confusing, just take a beat. And just make sure that you're following what's happening. Say, okay, it talks about this. Okay, cool.
I know that part. Okay. And then see what the difference is. Oh, they're cycling.
Well, this is my cyclic. And so really make sure that you understand what the diagram is saying. So part A, again, A always talks about the biology. What is the biology here? Describe the role of chlorophyll in the photosystems of plant cells.
Chlorophyll, chlorophyll. Oh, the chlorophyll is the pigment. And so it's going to absorb the solar radiation. It's then going to be the site where we saw the breaking of that water molecule to release the electrons from water.
You talk about absorbing the energy from light. And so you could say, OK, chlorophyll captures, absorbs light energy. Chlorophyll receives the electrons from the water. It receives electrons from electron transport chain or it receives electrons to the electron chain. So that what that thing is, OK, number one, we see electrons right here going to electron transport chain.
Again, use your diagrams. It shows you the electrons going in. OK.
You could also talk about that this electron went over into photosystem one. So that was the other place where we saw it. And then see the electrons being generated again.
So part B says based on figure one, here's figure one, explain why an increase in the ratio of NADPH to NADP plus will cause an increase in the flow of electrons through the cyclic plane. So if I have a lot of NADPH, That means it's holding the electrons and there's not a lot of NADP plus to accept those electrons. So that forces it to go through cyclic flow.
I'm unable to see NADP plus taking that electron. So explain why the increase would cause an increase in flow of electrons. Because there's less NADP plus to absorb that electron or to take the electron or to cure the electron. So less or no NADP to accept the electron. So electrons pass to the cyclic pathway or pass from ferredoxin to the cytochrome complex instead.
Use your diagram to explain. Now, part C and part D didn't actually have to do with Unit 3. So I cut them if you really want to know what's about biomass and how the biomass would change in a certain environment. So if there's any questions that you have about Unit 3, you can go ahead and put those into the chat while I kind of kill some time while I wait for, you know, y'all to catch up with me.
So don't forget. I am posting every day, Monday through Friday, on my Instagram to get you ready for the exam. I think yesterday, on Friday, we did 3.5, so we're currently going to be doing 3.6 on Monday. I also post those same questions on my TikTok, and I have a countdown on my TikTok. Not like you really want to see a countdown to the exam, but just in case you do.
And then you already know about the YouTube because you are here watching this live stream, or at least you're watching the recording of it. So, does anyone have... any questions before I log off.
Going once, going twice. So it doesn't look like anybody has any questions.