4. C1 IB Biology Review Video (new curriculum for 2025)

All right, folks. This is the super fast review of C1. Starting with enzymes and metabolism. Okay, enzymes have an active site that binds with the substrate. They are catalysts. They work to speed up chemical reactions by millions of times by lowering the activation energy needed for that reaction to occur. If we didn't have enzymes, these reactions would occur too slowly for life to be able to Exist. Okay, metabolism is the network of all of the chemical reactions that are occurring in your body. Sometimes they're in chain reactions and sometimes they're in cycles, but each of

these different steps would be driven by a different enzyme. Okay, enzymes are specific to a reaction. Uh you can see here that this substrate is only going to fit its specific enzyme. Okay, we have anabolic and catabolic reactions. Anabolic reactions are reactions that build. They're going to go from smaller to bigger molecules. Catabolic reactions break apart. They're going to go from larger to smaller. Now, note the way to remember this, okay? Anabolic reactions. Think of anabolic steroids where people take these to build muscle. So, they're building up smaller to larger. Catabolic reactions. Think of cats.

Cats destroy things. Cats Tear things up. Okay. Catabolic reactions break down larger molecules into smaller ones. Okay. Now, because we're building up smaller molecules, that's going to require energy. Whereas catabolic reactions release energy. An example of anabolic reactions are those condensation reactions. We've seen catabolic reactions. An example would be hydraysis reactions. Okay. We're going to be talking this unit about photosynthesis As an anabolic reaction. Okay. Where we're building glucose, catabolic reactions here, respiration, we're breaking down glucose. Okay. So, enzymes. Here's the active site. Here's a substrate. Here's an example of a catabolic reaction. Okay. The

substrate is going to bind to the active site. And they're only going to bind if they share two things. both the right shape and the right chemical Properties. In other words, we have to have charges that are going to attract each other as well as having a specific shape that's going to attract each other. Okay. Now, we have um an enzyme substrate complex that would be formed. Okay. The induced fit model says that they change uh the enzyme and substrate change shape very slightly when they bond. I think of it as like a big hug.

uh and when they form this enzyme product complex that then can drive the Reaction in this case catabolic reaction to split the initial substrate into two products. Those products are released and the enzyme can be used over and over and over again to complete the same reaction. Okay, so we've already talked about this is the induced fit that you can see that confirmational change occurring, okay, of both the substrate and the active site. All right, so movement, this is just going back to physics, is random of Particles. And so this substrate enzyme reaction is going

to be dependent on the random movement of molecules and the random collision of the substrate at the active site of the enzyme. As the temperature increases in a system, then all of those molecules are going to move more quickly because they have more kinetic energy and that's going to increase the rate of reaction. So, we're going to see a relationship between increasing temperature and increasing Rate of enzyme reaction up to a point. So, we'll get to that. All right. Um, so many enzyme reactions happen in the liquid of the cytoplasm. And so, that's going to

allow uh for this free movement in liquid. the substrate is usually smaller than the enzyme, so it moves more. Okay? But sometimes large substrate molecules are immobilized. An example of this is enzymes that move along and replicate or transcribe DNA. Okay? And sometimes the enzymes are Immobilized. For example, if they are within a cell membrane and the substrate has to move then to the enzyme. Okay. Shape and chemical properties allow substrate molecules to bind. We call that enzyme substrate specificity. Some enzymes are specific to one substrate. Others are less specific. Okay. Enzymes are proteins. So

they can be denatured. And remember that denaturation is permanent. So once the Enzymes denatured, the only way for this reaction to occur is for more enzymes to be made through protein synthesis. Okay? Remember pH is on this 1 to 14 scale. The lower end of the scale being more acidic. The higher end being more basic, seven being neutral. You can see some examples of different things that are different phes. Now, different enzymes are going to be adapted to a specific optimum pH depending on where they are adapted to Be used. Okay? For example, in the

stomach, we're going to have this more acidic optimum pH versus say in the large intestine. Okay? So, here we mentioned earlier as temperature increases molecules gain kinetic energy. those enzymes substrate collisions can happen at a faster rate. Okay? And so we see this increasing rate of reaction until we hit the optimum temperature beyond which the enzyme begins to denature Because of that high heat. And so we see that steep drop off in enzyme rate of reaction. Okay, pH. We're going to see a more regular bell normal distribution. Okay, where we have an optimum pH which

can be varied again depending on where that enzyme is adapted to be used. Okay, and then from there in either direction as the pH goes to um the more acidic or the more basic end, okay, ionic bonds are going to be altered because remember pH is just the number of hydrogen ions Or protons in the system. And so by having all of those charges, right, that can then disrupt ionic bonds which are bonds based on charge. Okay, we're going to see that as substrate concentration increases, the rate of enzyme reaction also increases. Okay, but eventually

we're going to uh begin to plateau, although we'd never reach a maximum. Uh and the reason is because more and more of those active sites become occupied um by substrates. And so we can keep adding more and more substrate, okay? But there's only so many enzymes and so um that reaction rate is going to slow. Okay, you should be able to identify some names of patterns. Here we're going to see that this is a positive correlation. The opposite here, this is a negative correlation. Okay. And we can say then also that there is no relationship

or no Correlation if we see a horizontal line pattern. Okay. If there's a positive relationship where we start at the origin, we can say that this is a directly proportional pattern. Okay. And if we see uh an inversely proportional pattern, it would look like this. Okay. We say this is an exponential pattern. All right. So, activation energy is required to reach the transition state during a chemical Reaction before the products are able to be produced. There's also going to be an energy yield when bonds are made to form the products of an enzyme catalyzed reaction.

Here we can see the activation energy that's needed to convert this substrate to the product. Okay, an enzyme works by lowering the activation energy needed. And so you can see here that when the reaction has an enzyme, the activation energy is much lower, okay, than the Activation energy without an enzyme. Okay, but we still have the same initial uh or substrate and final product energy levels. Okay, this is the end then of the SL content for this first slideshow. Moving on now to HL. Okay, intracellular versus extracellular enzyme catalyzed reactions. Okay, both of these are

synthesized by ribosomes, but enzymes that are inside the cell, okay, are Generally going to be made by free ribosomes in the cytoplasm, okay? versus the ribosomes attached to the rear are going to be for producing enzymes that are used outside of the cell. Okay. Examples of intracellular enzymes are enzymes used in glycolysis and the KB cycle, which we're going to get to in a bit. Extracellular enzymes might be released for chemical digestion in the gut. Okay. The conversion of energy from One form to another is never 100% efficient. Metabolic reactions the products contain less energy

than the reactants and that additional energy is converted to heat and this is why we say we are warm-blooded there our metabolic reactions are producing heat. So they're not 100% efficient. The rest of that energy becomes heat. Okay. And that helps us to maintain that constant body temperature. Okay. And sometimes we produce too much heat uh than we need. For example, during exercise, uh we're going to produce sweat then to remove extra heat through evaporative cooling. Okay. In contrast, in very cold conditions, okay, you can see these emperor penguins huddling here to maintain body heat.

But a lot of questions you're going to see the on the IB exam are going to be related to heat that is produced through metabolic activity. Okay. So metabolism, we're going to see here now some uh chain Reactions. Each step going from initial substrate to an end product requiring a different enzyme to go through a series of intermediates. So this here is just a little analogy for how we can go from one word to another by making a single change each time. And so we have these linear pathways, okay, where we can see uh multiple

steps, each one driven by a different enzyme. And then we also have cyclical pathways. Uh we'll look both at the KB cycle and the Calvin cycle of This video. All right. Now, non-competitive inhibition can occur where an inhibitor binds not to the active site but to an alisteric site, a site on the enzyme away from the active site. Okay. This though causes a confirmational change in the active site which prevents the substrate from being able to bind. Now, this binding is reversible. So if the non-competitive inhibitor uh unbinds from the alossteric site, the substrate Can

once again bind and the reaction can proceed. Okay, competitive inhibitors on the other hand bind directly to the active site of the enzyme. Okay, once again therefore directly preventing the substrate from binding. Uh these tend to be more structurally similar to the substrate because they have to fit into the active site. Um they are not converted into products though because they're inhibitors uh and remained bound therefore longer than the substrate Would. Okay. Statins are medicines that work by competitive enzyme inhibition. Okay. So an example of using competitive inhibition. Uh statins bind to the active site

of an enzyme uh that catalyzes a reaction used to synthesize cholesterol in liver cells. So as a result of lowering the rate of enzyme activity, less cholesterol is produced by the body. And so these can be used as a medication to reduce cholesterol. Okay. So, uh, competitive inhibition, uh, this graph is also one that you might even end up drawing, um, on your part B of, uh, or your paper two, uh, where you have your short answer questions. uh in competitive inhibition. Okay, as substrate concentration increases uh because we're directly competing uh for the active

site, the we will eventually be able to um get back up here to the normal enzyme rate of reaction as we just have more and more And more substrate. It's basically kind of out competing the inhibitor, you could think of it versus a non-competitive inhibitor, even if we keep increasing the substrate, we're still blocking off those active sites. So in competitive inhibition, the extent of inhibition will reduce until the enzyme is effectively uninhibited. With many more substrates than inhibitors, the substrates almost always arrive at the active site first and so we get back To this

normal rate of reaction versus non-competitive. Okay, even by increasing all these substrates, we're not going to be able to prevent the non-competitive inhibitor because it's binding not to the active site but the alossteric site. So, we're going to continue to have a somewhat inhibited rate of reaction even if we continue to increase substrate concentrate. Feedback inhibition. Many metabolic pathways use feedback Inhibition to produce enough of a substance but not too much. This allows us to regulate how much of a product is being produced, okay? By causing this end product to inhibit, okay, earlier in the

pathway, which means if we have enough end product, it acts as its own inhibitor because we don't want to make too much of it. So if the product is present, right, we're going to inhibit production of more of it. So if there's uh an enzyme that has an alossteric Site, okay, that end product can then bind to it. This is an example of non-competitive inhibition. If too much of that end products made, it increasingly inhibits that first enzyme in the pathway, switches off the whole pathway, prevents more synthesis of the end product. Okay? If there's

too little of it, there's minimal inhibition, and so we're going to produce more of the end product. This is very efficient. We don't want to allow too much of this end Product to accumulate. So it acts as its own inhibitor when there's a lot of it. Okay. And here's just an example of that. Okay. There's a metabolic pathway that converts the amino acid thrienine into isolucine. Okay. It's a series of uh five reactions. Okay. But then we're going to see that this isolucine ends up being an inhibitor, okay, of this very first reaction. And so

having a lot of this is going to slow down production of More of it because there's enough. Okay. Mechanism based inhibition as a consequence of chemical changes to the active site caused by the irreversible binding of an inhibitor. So this is going to be heavy metals such as mercury and lead. They're non-specific inhibitors of a wide range of enzymes. They bind irreversibly to the amino acid cysteine wherever it occurs. They're very toxic if they enter the body and they're dangerous pollutants of the Environment. Okay. Some irreversal inhibitors target one specific enzyme. Some are structurally similar

to the substrate. So they can bind directly to the active site. Okay. They would be converted to a product and released leaving the active site open if it was a substrate. But this is inhibitor and so these bind permanently. They're irreversible bindings of an inhibitor. Um this uh can never work as a catalyst again. And this is called mechanism Based inhibition. This can cause harm to an organism. Every molecule of inhibitor can permanently inactivate the enzyme and this could potentially kill the organism if that enzyme is vital and there's enough of that inhibitor to be

lethal. Okay. Some living organisms synthesize a mechanism based inhibitor in order to kill another organism. This is how penicellum works to kill grandpositive bacteria. Okay. they take an enzyme in this case specifically Transeptidase. Okay. And when the bacterial grow usually transeptidase causes uh remaking of the links in the back in the wall of the bacteria. Okay. And penicellum is going to bind irreversibly with the enzyme so that it can't anymore uh fix those breaks in the cross links and so the cell wall becomes weakened and that's how penicellin works to kill bacteria. Okay. Some chemical

weapons are mechanism based enzyme inhibitors And they're some of the most toxic substances ever discovered. All right, that takes us then to slideshow two of three on cell respiration. SL students should jump back in. All right, ATP stands for adenosine triphosphate. So here we can see that triphosphate. Okay, we're going to see that the important bond is this one right here between the second and third phosphate. The energy stored in that Bond can be used to drive chemical reactions throughout the cell. Okay? And so when that third phosphate gets broken off, that releases energy. Okay?

Drives chemical reactions. And the purpose of cell respiration is to take ADP, okay? And attach the phosphate to store energy in that bond. By making ATP, right, we're building up this energy currency. It's like making money, okay? that we can then use to drive chemical reactions and keep our cells Alive. Okay. Um, ATP is great for this temporary storage of energy and for energy transfer because it's soluble in water. So, it can move freely throughout the cytoplasm. It's stable at neutral pH levels. Okay. It cannot pass freely through the phosphoipid billayer and so it's controlled.

It's we are going to keep it in the place where we want it to be. Okay. The third phosphate group can easily be attached and reattached by hydrarolysis and condensation. Okay. And It's a relatively small amount of energy which is enough for many processes within the cell. If it was a larger amount, there would often be an excess which would be wasted by having to be converted to heat. Okay. Cells need energy for three main types of activity. synthesis of macroolelecules, anabolism, active transport across membranes and movement of the whole cell or cell components such

as chromosomes. All of these are Going to require ATP energy. Okay, energy again gets released by hydraysis, hydrolysis, licing or splitting, okay, by addition of water. Okay, that's going to convert it to ADP and release energy for those reactions. Okay. And vice versa, we can build up ATP by taking energy from the food we eat and we can then phosphorolate by adding that phosphate group to an ADP and making ATP. Okay. And uh this is just a summary Of what we've just said. Um excess energy gets transformed into heat. All right. So here's an overview

of cell respiration. Okay, in cell respiration, carbon compounds are oxidized to release energy and then we use that to make ATP. Okay, glucose and fatty acids are our principal substrates. A wide range of carbon compounds can be used and we'll be using glucose as an example as We talk through this process. Where do these initial carbon compounds come from? They come from the food that we eat. Okay, note importantly, plants also do cell respiration and they get their carbon compounds from photosynthesis. We also get our carbon compounds then from plants that do photosynthesis or from

something that ate a plant or something that ate something that ate something that ate a plant etc. Okay. So here is cell respiration. You should know both the chemical formula and the formula in words. So our two reactants are going to be glucose and oxygen. Just picture you know that you do cell respiration to get energy. Glucose you eat food. Glucos's molecular formula is C6 H1206 and you breathe in oxygen. A balanced equation is going to have six O2 molecules. Okay. Then through the process of respiration, you produce carbon dioxide. Again, a balanced equation are

going to be six Molecules of CO2. And lastly, water is produced. Also, six waters. Okay? And if you were to count up, you would notice there's the same exact number of atoms on either side of this balanced equation. For example, here we have C6. Six carbons on this side. And so there you can see we're going to have to have six CO2s. Six carbon dioxides are going to be produced, one for each of those carbons. Okay? And through the process of respiration, then we're going to be Making ATP. Okay? By combining this inorganic phosphate with

ADP. It's like a rechargeable battery. We can make ATP. We can then break off that phosphate. You spend that energy on some type of system like active transport. Okay? Okay. And so then it becomes ADP again and the cycle can continue uh like a rechargeable battery. Okay. Here's an overview of the process. Glucose is going to enter the cytoplasm of the cell. We're going to have this initial Reaction where we make a small yield of ATP as glucose is broken down into two pyrovates. Note that this initial reaction occurs in the cytoplasm. Then if oxygen

is present those pyrovates and oxygen can go into the mitochondria where a high yield of ATP can be produced. This high yield then produces carbon dioxide as a waste product which then exits the cell as well as water which can be used within the Cell. Okay, here's another uh image of that. Here's our initial reaction of glucose being broken into two pyrovates with that small yield of ATP. If oxygen is present then the pyrovates and oxygen in the mitochondria can make a large yield of ATP but producing CO2 as a waste product and water as

a product that could be useful. Okay, now that's aerobic cellular respiration if oxygen is present. But with anorobic respiration, Oxygen isn't needed. So in the absence of oxygen, cells can produce anorobic cellular respiration. Okay? And in humans usually we do aerobic cell respiration to get that high yield in the mitochondria. Sometimes however like if in strenuous exercise if you're sprinting around a track or doing heavy weightlifting in addition to maxing out your aerobic respiration okay you might be doing anorobic respiration in addition in your Muscles. Okay. So to supply rapid ATP over a short time

period, we have to maximize the power of muscle contractions and so we do anorobic respiration in addition to aerobic. The disadvantage is that the product of anorobic respiration is lactic acid or lactate and there's a limit to the concentration the human body can tolerate which is what's restricting how much anorobic respiration can be done. This is why you have a very short time Scale over which you can sprint not more than 400 meters at your top speed because you're limited by lactic acid buildup in your muscles. So after vigorous muscle contractions that lactate then has

to be broken down which requires oxygen. We call this demand the oxygen debt. And this is why after you cross the finish line, you huff and puff for a bit in order to try to repay that oxygen debt and break down the lactic acid. Okay. Um so aerobic respiration is Going to be that uh same formula we went over. Anorobic respiration okay in humans is just taking glucose lack of oxygen right anorobic but we produce lactate. Okay in yeast and other fungi though something special happens when they do anorobic respiration they produce ethanol and carbon

dioxide. Okay which we have been able to harness for use in things like brewing and in bread baking. So here's another nice overview. There's That initial reaction for a small yield in the cytoplasm. Okay. Now that small yield of ATP is what's being made when we do anorobic respiration. Now it's only a small yield but it can happen very quickly because it's not limited by oxygen supply. But remember that produces then that lactate or lactic acid in animals. Okay. If O2 is present, we can then have that high yield. Okay. Producing CO2 and water. Okay.

So, let's contrast aerobic versus Anorobic. Aerobic, just think of like those 80s ladies in the spandex doing aerobics, right? The whole idea is you're breathing deeply. Oxygen is needed. Anorobic, oxygen is not needed. Okay. In aerobic, you can use carbohydrates, lipids or amino acids as your input. Whereas in anorobic, only carbohydrates can be used. Aerobic produces CO2 and water as waste products. Anorobic either lactate for animals or ethanol and carbon dioxide as For yeast or other fungi. Okay. Aerobic we're going to have much higher yields of ATP more than 30 ATP per glucose. Okay. Versus

only two with anorobic. Okay. Remember aerobic initial reactions always in the cytoplasm with that small yield. Okay. But then we can go into the mitochondria. If oxygen is present for a high yield anorobic, everything's in the cytoplasm. Okay. Different uh rates of Cell respiration to determine uh if you want to measure this reaction, you can measure it either by the uptake or the use of one of the reactants or the production of one of the products. Okay. oxygen uptake is um going to be a good one to be able to be produced or to be

able to measure, excuse me, or production of CO2. Uh and one way that you can look at this is through a respter. This is a respter where we're measuring the respiration rate of these Seeds. This can also be done with small insects uh like shown here. So the idea here is we want to measure uh using looking at looking at gases. So, we know from here we're going to be using oxygen and producing CO2. And so, it's going to be hard to measure just one or the other unless we have a way to get rid

of one or the other. And in this case, we're going to see, okay, a potassium hydroxide solution with here a rolled filter paper to increase the surface Area. This is going to absorb CO2. So, if CO2 that's produced through respiration is absorbed by this solution, then we're going to be able to just look at gas um how much gas is consumed, and that's going to be our O2 consumption, and that's going to be able to give us a rate of respiration. And so, here we have a capillary tube filled with some type of liquid. Okay?

And as oxygen is consumed by these respiring seeds, okay, this level of the liquid is Going to move up the capillary tube and it's a grady a grady graduated tube, excuse me. So we're going to be able to then if we know the diameter of the tube, calculate the volume of air that is consumed over a set amount of time. This syringe is here to reset the experiment. More air can be added in order to push this liquid back. And so we can do multiple trials under uh multiple situations. For example, different temperatures um or

different Light levels or whatever it is that you're choosing to measure. Okay, here's a more simple resp. Okay, where the tip of the resperometer is simply placed under the surface of a liquid. Okay, but the same principle uh occurs of we're measuring O2 consumption and we have um some potassium hydroxide to absorb all of this CO2 so that we see the actual movement of say for example here a colored liquid okay into our tube with our organisms in it uh as a measure of Oxygen consumption. Okay. Uh temperature and pressure need to be controlled. It's

a good idea to be placing this resperometer within a water bath to uh seek to control temperature because we know the temperature affects the rate of respiration. Okay, this is the end of SL content for slideshow two. Okay, hang on with me if you're going on to HL. Let's begin. All right, oxidation and Reduction often referred to as redux reactions. Okay, oxidation occurs when there is a loss of electrons and reduction is the gain of electrons. So think of it as this acronym oil rig. Oxidation is loss, reduction is gain. These are reversible reactions. Okay.

And we're going to see electron carriers like NAD being used in this situation. Okay. Now this is the full reactions that is occurring but we are going to be just using a simplified form. We're Going to be talking about the electron carrier NAD being reduced to just reduce NAD and then oxidized back to NAD. Okay. So, what's actually happening is two protons and two electrons, okay, are going to be reduced with um from NAD+. We're going to make NADH plus having an extra proton. But again, we don't need to worry about this uh exact. We're

just going to use this simplified form for the purposes of this course. Okay. In summary, oxidation though, just think of That as electron loss. Remember oil oxidation is loss. Um, so redux reactions happen with both oxidation and reaction. We're going to see that we can't have oxidation without reaction because or excuse me without reduction because those electrons have to go somewhere. So we're going to break down cellular respiration into these five steps starting with glycolysis. Okay. Now in glycolysis that is what we talked about with the SL Students as that very uh first reaction that

occurs in the cytoplasm of the cell. And this is where we take um a glucose and we're eventually going to break it down into two pyrovates. But let's break that down into a few extra steps. We're going to start with an initial investment of 2 ATP. Okay. So the energy that's held within the second and third phosphate as that phosphate breaks off that energy is used. Okay. For this initial reaction, we're going To have phosphorilation occur. Okay? And we're going to have addition of two phosphates that serves to destabilize this glucose molecule. Okay? And allows

for the next step, lis to occur or splitting. So now we have two threecarbon molecules, each of which has that phosphate attached. And now we're going to see that oxidation reaction. Okay? We're going to have oxidation of those three carbon molecules. Okay, oxidation is Lost. So, they're going to lose electrons, but they have to then be passed somewhere. And so, we're going to reduce an NAD, an electron carrier. So, we're going to oxidize electrons, lose them to the NAD, which now gets reduced. Reduction is gain. So, we're left with reduce NAD. And this is going

to happen two times, one for each of these two threecarbon molecules. Okay? And along this process, we're going to have four ATP produced. So in total, we're going to have two pyrovates gained as we break down that glucose. So one sixcarbon molecule becomes two 3carbon pyrovates. We're going to end up with two reduced NADs. Okay? And we're going to have a net gain of two ATP because remember we invested two and we produced four. So we have a net gain of two. Okay? Now these reduced NADs are going to be used in a later step.

Okay. Um now we're going to take though our pyrovates and we're going to See what happens next. Okay. So note that if we have anorobic cell respiration and oxygen isn't present. Okay, those pyrovates then are going to be converted to lactate. Um but that's going to then take in order for that to happen our reduced NAD and we're going to oxidize it back to NAD. But remember that lactic fermentation that uh needs to then um be reversed. We can only handle so much lactate in our muscles and so we're Going to need to huff and

puff and breathe in lots of oxygen at the end of that um anorobic activity. Okay. And then here's just what it looks like then in yeast like we mentioned before. Okay. Pyrovate is going to be converted to ethanol and then ethanol. Okay. CO2 is produced and that ethanol um alcohol is also going to be produced and we can then use that anorobic cell respiration to be able to produce um alcoholic beverages through Brewing as well as the CO2 that's used uh here as we can see to allow for bread to rise through that production of

CO2. Ethanol of course is also produced but it does evaporate during baking. Okay, so that's step one. glycolysis. Those two pyrovates then are going to head over to the link reaction which links glycolysis to the KB cycle. So here's a pyrovate. We're just drawing one. So this link reaction is going to have to occur twice for each molecule of Glucose we started with. Okay, pyrovate is going to be decarboxilated meaning one car well one carbon is going to be removed in the form of carbon dioxide. So if one carbon's removed, we're down to two. Okay,

this is an oxidation reaction. So, we're going to oxidize pyrovate. Remember, we're going to lose electrons, which means we then have to reduce um our electron carrier NAD. So, then we end up with reduced NAD. This again is going to head to our later Reaction um for use there. Okay. And we're also going to have our co-enzyme A come along. co-enzyme A is just our helper enzyme that's then going to take this twocarbon acetal group to now in the form of acetal COA and that is going to head to the Krebs cycle the next step.

Okay. So our total uh at the end of our link reaction is going to be two acetal COAs. Okay, two reduced NADs and two CO2s because remember this process occurs twice. Okay, so now we've gotten to the KB cycle. Here we're going to have our acetto COAs enter here. This is a summary of the link reaction here, right? So we had that last step was our pyrovates going through the link reaction creating our acetal coas which are two carbon molecules. Okay, now this next step um also occurs in the mitochondrial matrix. Uh kind of missed

that going back here. Um so here we go. This also occurred in the mitochondrial Matrix with the link reaction. Sorry about that. All right, so let's jump into the KB cycle. Okay, so here uh we're going to have a fourcarbon oxaloacetate. Okay, this was produced at the end of the last KB cycle and so it's going to be then our input for this uh next round. So our acetto COA drops off our acetal group. Okay, which then is going to bind with our oxaloacetate to make a sixcarbon citrate molecule. That Co-enzyme A heads back to

the link reaction to pick up another acetal group to continue the process over and over again. Okay, our sixcarbon citrate is then oxidized. It's going to lose electrons. Okay, which means we're going to then reduce another NAD to reduced NAD. And we're also going to have a decarboxilation reaction occurs. So, we're going to have one carbon, okay, become carbon dioxide, and now we're down to five Carbons. Okay, we're then going to have the exact same processes occur again. Another oxidation of the 5carbon molecule, another reduction of NAD. Okay, another decarboxilation. So, now we're down to

a 4carbon molecule, but we need to regenerate that oxaloacetate. So, we call this last step rearrangement to get back to our initial starting 4carbon molecule. Along the way, we're going to produce an ATP. Okay. We're going to reduce another Electron carrier called FAD to reduced FAD and then another of our old friend NAD to reduced NAD. Okay. Here's an overview of the entire KB cycle. Okay. And it is going to occur over and over because we've re come up with our starting compound oxaloacetate. Okay. And we have a bunch of these now reduced molecules that

are going to head to our next step, our electron transport chain. Okay, so here's a summary of the Effects of one turn of the KB cycle. But remember, we have two turns for each glucose that we initially started this whole process with. Okay, it's time for the electron transport chain. Okay, the electron transport chain now is going to occur in the inner mitochondrial membrane. And this is one reason why the inner mitochondrial membrane has all of these infoldings. Um because the more surface area we have, the more electron transport chain we can Have. Uh I

just noticed this picture that I pulled from the internet is not a good one because the KB cycle doesn't occur in this intermembrane space. It actually occurs in the mitochondrial matrix which is here. So I just found a mistake. So the link reaction and the KB cycle should be drawn in over here. All right, but let's go ahead and zoom in on this inner mitochondrial membrane. Okay, so here is the matrix that very inside of both membranes. And Then this is that narrow intermembrane space that's in between the inner and outer mitochondrial membrane. Okay, so

first up, this is where all those reduced NADs that we've been making along the way, okay, are now going to be oxidized. Okay, they're going to be oxidized back to NAD. Remember, oxidation is lost. So, they're dropping off their electrons and protons. Okay, um and reducing this uh electron uh carrier that is within the Mitochondrial membrane. Okay. So, the electron that's being dropped off is going to power those protons being pumped against the gradient into the intermembrane space. That electron then is going to be passed down this electron transport chain within the inner mitochondrial membrane.

Okay, as that electron gets passed down, okay, we're also going to be taking some of those reduced FADS. Okay, and we're going to be then um Passing off their electrons and protons, okay, as well at this second point in the electron transport chain. And we're building up now a proton gradient. Remember that hydrogen ion and protons can be used interchangeably. Okay, a hydrogen is just made up of one proton and one electron. So if we have a hydrogen ion, that means it's lost its electron. So it's just a proton. So those terms proton gradient or

hydrogen ion gradient that's being built up are The same thing. Okay, so here we can see more protons being passed through. Okay, we've generated now a high concentration of hydrogen ions. Okay, this is the uh same reason why towns have water towers. Okay, we're building up potential energy by pumping all of the water up into a water tower. Okay, you can then let it just drain down into people's houses using gravity uh and potential energy. Okay, to pump that water into your sinks And faucets and showers. Okay, this is how chemiosmosis occurs by building up

this proton gradient just like the water at the top of a tower. Okay, we have all this potential energy, but then those protons are going to move back down the gradient, okay, through this special protein called ATP synthes. As protons move through ATP synthes, ATP synthes is going to rotate and it's going to be able to phosphorolate ADP into ATP. So, this is where our high yield of ATP is Going to occur. Okay. So, boom. We're getting all this ATP. This is great, but we have a problem because we've um got these electrons that are

still in that membrane. Okay? And we need to keep being able to pump more protons, but we can't do that unless we remove these electrons from the electron transport chain at the end to allow new ones to enter. So, the way that we do that is through oxygen. Oxygen is known as the terminal electron acceptor. Okay, oxygen Is going to be split. Okay, and each of those O's is going to become the O in an H2O. We're then going to be able to take protons that are being pumped back through um and we're going to

use those as well as the electrons that we're trying to remove from the system, okay? And that's going to not only help maintain that proton gradient by removing protons from this side and allowing that gradient to build up over here, but it takes care of those Electrons removal to allow for more electrons to enter the electron transport chain. And this is where that water is produced. Oxygen is used. Okay? If oxygen was to no longer be present, this entire process would grind to a halt. Okay? And aerobic cellular respiration would stop. and uh well you

would die. This is why you need to be breathing in oxygen constantly. Okay, one quick note on the differences between lipids and Carbohydrates as respiratory substances. Okay, both can be used in respiration but remember that anorobic respiration can only use carbohydrates um not uh any other of those substrates. Okay, carbohydrates do have a lower energy yield. Lipids have a higher energy yield because there's less oxygen. All right, final slideshow. SL students, we need your attention again. C1.3 photosynthesis. Photosynthesis is an Energy transformation, meaning it's changing forms from light energy to chemical energy. Okay, don't be

tricked with IB questions of having any other terms. It has to be light to chemical. that chemical energy is stored in the bonds of carbon compounds. Okay, the idea here is we are building glucose molecules and within the bonds of the glucose molecules is where that energy is stored that we are getting from the light in the sun. So that is chemical Energy stored within that molecule. Okay, this is the foundation of life. Photosynthesis, right, is what plants use to make glucose. But this is also where we are getting our glucose either directly from plants

or from animals that ate those plants or like I said earlier that ate the animals that ate the plants etc. So photosynthesis rather than trying to memorize a new equation remember that photosynthesis is the exact opposite process of respiration. And so whereas in respiration we produce CO2 and water, in photosynthesis we're going to use CO2 and water, plants take in carbon dioxide and you know you have to water them. Those are the two reactants in photosynthesis. Glucose and oxygen then are going to be produced. Glucose is our desired product. Oxygen is actually a waste product

for plants. But it's great because then it's our input and we need oxygen to fuel cellular respiration. This whole process again is driven by light. Okay. The first step is phototoysis. Photoysis is going to be licing or breaking thanks to photo energy. So light splitting. Okay. And we're going to be splitting specifically a water molecule. Okay. As we use that light energy to break up that water molecule, that's where our O2 is going to be produced. But we can then use those protons and electrons that are being used to power photosynthesis. Okay, cyanobacteria, algae, and

plants all do photosynthesis. Okay, proarotes of course did it first. Bacteria which don't have a nucleus that are much more simple came first in evolutionary time. Millions of years later, algae and plants begin carrying out photosynthesis using chloroplasts. Okay, oxygen again is a byproduct or waste product and it's released from the plant through the open stomata usually on the underside of Leaves. Okay. Uh so plants have many pigments. Chlorophylls tend to be the dominant pigment which is why most plants appear green. Okay. But we can use chromatography to separate the pigments. Most of which other

than chlorophyll tend to be uh covered up by chlorophyll. And this is why leaves change color in the fall because chlorophyll is usually the first pigment to exit um as the days get shorter. And so then we can start to See the other pigments that are there all the time that might be orange or yellow or red uh but that are usually hidden by the more dominant chlorophyll. So chromatography can be used to separate out those pigments. And you should be familiar um with chromatography. Okay. You should be able to calculate an RF value which

is basically a percent of how fast each pigment uh travels. So you would just take the distance that a particular Pigment traveled and divide that by the distance that the solvent traveled. Uh which is basically just a percent of how far the pigment traveled. Okay. So we have these different pigments. Uh white substances are not pigments. They reflect all wavelengths of visible light. Okay. Versus pigments that absorb all wavelengths of visible light appear black and they transform light energy into other forms of energy. mostly into Heat. Okay. So the reason that um leaves may appear

green to us is because the green light is what is reflected. These other colors of light can be used for photosynthesis. Okay. But the green light we see plants as green because that is actually going to have the lowest level of photosynthesis specifically with chlorophylls. Okay. So review of wavelengths of light. A photon is a particle of light. a specific amount of Energy uh is going to be needed to excite different pigments. Um here is our visible light. We're going to be concentrating here on how the longer wavelengths of visible light are the red end.

The shorter wavelengths are going to be the blue violet end. Okay? And each of those ends we're going to see have a higher amount of light that's be able to be absorbed. Here you can see um our two chlorophylls, chlorophyll A and B. Okay? They're going to have the Highest amount of light absorbed on the blue violet end. Okay. Then also quite a bit of uh light absorbed on the red end and low levels of light. Don't say none, but I'd say low levels of light uh of green light able to be absorbed. Note though

that corotenoid pigments like found in carrots that appear to give us our orange colored carrots are going to be absorbing light again away from that orange end because carrots appear orange or the reason carrots appear orange is Because the orange light is reflected. It's not absorbed uh by those carotenoid pigments. Okay. So here we see the absorption spectrum that we just looked at. The amount of light absorbed by different pigments. We're going to see a direct correlation with the action spectrum here. We're going to see for chlorophyll that we're going to have higher amounts of

photosynthesis. Okay, the highest at those blue violet end followed by this red end and lowest um But not zero at uh the green uh wavelengths. Okay. And here we can see them superimposed so that it's really clear that there's a direct correlation between the action and absorption spectrums. Okay. So, uh, looking at these three variables, we're going to see that as light intensity increases, the rate of photosynthesis is going to increase and then eventually plateau because there's some other limiting factor other than light. The same exact Thing happens for carbon dioxide. We're going to see

a sharp increase followed by a plateau when there's some other limiting factor in play. And then we're going to see that the temperature is going to have the exact same pattern as it does for the rate of enzyme reaction for the exact same reasons. Okay? Because this photosynthesis is driven by enzymes. We're going to see that as temperature increases. Okay? The rate of reaction is going to occur before Hitting an optimum after which we're going to see rapid dennaturation and a rapid sharp drop off. Okay. Um so we have two types of experiments. We have

enclosed greenhouse experiments where we have say two different green houses and we keep everything else controlled um other than the amount of carbon dioxide. And so if we have one with higher levels of carbon dioxide and one without, we can compare the growth of those two plants. And we Have found that plants that are given extra carbon dioxide have additional growth. And so it's now actually standard practice in green houses to pump additional carbon dioxide into those enclosed green houses. Uh and this can come from boilers that burn natural gas or most more sustainably from

compost where plant waste or animal manurses are decomposed by bacteria and fungi to produce CO2 through respiration. Okay. Uh we also have free Air carbon dioxide enrichment experiments you should be familiar with. Okay. And this is where we're looking at the effect of increased carbon dioxide in our atmosphere, but rather than in an enclosed laboratory setting, we want to see in a larger scale so that we can actually look at things like how biodiversity is going to be affected, which you can't do in an enclosed greenhouse as well. And so scientists have set up these

huge towers in these Circles, okay? Some of which just blow out normal air and some of which blow out carbon dioxide. Okay? and they're in circles so that only the ones that are upwind need to be blowing out carbon dioxide so that they're just targeting those um plants in this forest that are growing downwind of those particular towers. Then they compare things like growth biodiversity levels and on this large scale in the field to be able to determine what the effects are of Increasing carbon dioxide levels. All right, this is the end then of the

entire video for SL students. you guys are good to go. Uh let's go ahead though and talk about photosynthesis at the HL level. Okay. So photosystems are pigment protein complexes located in the philyloid membrane of chloroplast. So whereas in respiration we saw that the reaction occurred on the inner mitochondrial membrane. Chloroplast have Two membranes without infoldings. Okay. And these reactions occur instead along these little membrane pouches called philyloids. Now within that membrane, okay, we're going to see these photosystems which are made up of proteins with these pigments integrated. Okay, so these are molecular arrays. These

pigments are in a regular formation which is going to allow for the transfer of energy uh from whichever pigment is struck by light, okay, in Towards this special pair of chlorophyll molecules. Now when a photon enters it has to have a specific amount of energy in order to excite that particular pigment. When that occurs though the electron in an atom of the pigment becomes excited and it jumps to a higher energy level. So if it's the correct wavelength with the correct energy level it excites an electron. Okay. That energy then is going to be passed.

Okay. then funneled into this core complex Where we have this reaction center where there's a special pair of chlorophyll a molecules. Okay, which are able to donate pairs of excited electrons to electron acceptors. Okay, these emitted electrons carry the energy needed for later stages of photosynthesis. Okay, now there are two photos systems. Confusingly, photo system 2 comes first followed by photosystem one second. I know it's confusing, but they're named in the Order that they were discovered. So, first up, photosystem 2 are mostly going to be located in the philyloid membranes themselves. Photosystem ones tend to

be located on these stroma lamea that com um connect the philyloids together. Okay, photosystem 2, okay, is going to have this special pair of uh chlorophyll molecules called P680s because they have a peak like absorbance at 680 nmters versus in photosystem 1, okay, they have P700s as their primary electron donors because their peak like absorbance is 700 nmters. Okay, we're going to see in photos system 2, okay, that those um excited electrons from the P680s are going to be passed to plasticquinone, which is going to continue down this electron transport chain. Okay. Um photosystem 1.

Okay, they are going to be passing theirs to N the enzyme NADP reductase, which is going to be reducing a new electron Carrier called NADP. This is our electron carrier in photosynthesis, which is easy to remember because there's a P at the end of it for photosynthesis. Now, where are those replacement electrons going to come from? Okay, here we're going to see that photosis of water that we just talked about with the SL group happening uh to replace those electrons. And here we're going to see that electrons are coming From plasticin, okay, which are eventually

coming all the way down this electron transport chain. Okay, so let's jump in. How does a photo system work? Um, or we already actually kind of mostly talked about that photons of light are scattered. Photo systems have over a 100 pigment molecules, which increases the number of photons absorbed per second. They're only going to be able to absorb a narrow um range of wavelengths. And so we want to have a Variety of pigments so we can use a greater proportion of the energy in sunlight. Okay, here's that structural array which allows for that energy to

be passed from pigment to pigment down to the reaction center. Okay, so this is the stroma or the um liquid inside part of the chloroplast. This is the lumen of the philyloid. So this is a very small space inside of that little pouch, that little philyloid flatten pancake structure. All right. So, oxygen was not present in early Earth. Once photos system began, photo photosynthesis began though, we started seeing oxygenation of our atmosphere uh with immense consequences for living organisms. Okay, we can trace this um through rocks. We can see that um in early atmosphere we

had little or no oxygen. And so we can look at the banded iron formations uh which are often times under the sea but have also been pushed Up through plate tectonics. And we can see where oxygen arrived because we saw major oxidation of iron and other elements that were in the rock at this particular uh geological time. And so we can trace back and figure out how long ago uh oxygen began showing up uh in our uh planet. Okay. So once that occurred, we started producing more and more oxygen and we're currently at about 20%

oxygen. All right. So let's walk through The process. So we start with absorption of light by photosystem 2. Okay. This then remember is going to be if it's the right wavelength of light exciting an electron that energy gets passed to our P680 special chlorophyll molecules. They become oxidized and oxidation is lost. So they are going to lose or emit electrons to um our plasticquinone. Okay. They must then be replaced by our photosis. So phtolesis of water remember is going to produce Oxygen which becomes a waste product. But it's also going to produce electrons and protons.

Those electrons then can be used to replace the electrons that were um are being oxidized off of the P680. Okay. the protons begin to contribute to a proton gradient in this small philyloid lumen. Remember by having a narrow space that's an adaptation that allows that proton gradient to build up quickly. Okay. And then here we have Oxygen diffusing out as a waste product. Okay. So now we have our plastic quinone. Okay. Which is going to accept those electrons. Okay. By being reduced. Reduction is gain. So they're going to accept two electrons as well as two

protons from the stroma. Okay, it's then going to be able to pump those protons across the membrane and those electrons continue down this electron transport chain. Okay, this continues. The electrons are losing uh energy as They continue. Okay, until they eventually arrive at photosystem one um as low energy electrons. Now, we've built up this proton gradient though along the electron transport chain. And we're going to see the exact same chemiosmosis occur, okay, through ATP synthes. So, we're going to ATP synthes will rotate as protons move down the gradient, phosphorolating ADP into ATP and therefore producing

ATP. Okay. Again though, we have this New electron carrier called NADP, but it works the exact same way as NAD. Okay. where it gets reduced to reduce NADP as it gains electrons and that can be oxidized back as it drops them back off again. So now we're at this low energy electron level. Okay, but remember we have to get the electrons out of the chain. Okay, we're going to start by having those um low energy electrons uh be re-energized. So light is going to enter this second photo system, Photosystem one. Okay. uh that those electrons

then are going to be passed to NADP reductase which just like it sounds is an enzyme that reduces NADP. Okay. Now we have ATP and reduced NAT NADP which are our desired products of this these light dependent reactions. Those are going to head now to our light independent reactions. And remember just the other thing was that O2 produced as a waste product. So here's a summary of the light dependent reactions of Photosynthesis. Okay, note that there's also something called cyclic phosphorilation. And this is if we run out of NADP. If it's all been reduced, okay,

then we can actually take those excited electrons, divert them back to plasticquinone, and allow this electron chain to continue and more ATP to still be produced even if there's no other NADP available. Okay, note that this we're all talking About what happens in the chloroplast which are for uh our more complex green algae and land plants. Okay, but back in bacteria that are very simple and don't have organels, those philyloids are going to be just directly within the cyanobacteria themselves. Okay, here's just a really nice summary of all of that if you want to pause

and read through it. Okay, this is a summary of everything we just talked through. Okay, photos system two uh complexes are mostly going to be in the granana which are these actual stacks of philyloids. Okay, but photosystem one, okay, is going to be mostly again in these stroma lamea. Okay, and keep in mind that's because we've got this NADP that's going to need to be uh constantly available. Uh and so that allows for more easy availability by being uh closer uh in contact to the stroma rather than in the stacks of philyloids themselves. Okay, so

we just summed up the first half the light dependent reactions. Okay, we know that oxygen was released as a waste product and we know that ATP and reduced NADP were produced. So those are now going to head over to our second set of reactions, our light independent reactions. Note those are our two inputs as well as CO2 our other input for photosynthesis. Okay, so our first step in the light independent reactions known as the Calvin cycle is we're going to start with RUBP. This is a fivecarbon molecule and as we know just like we saw

with uh respiration, this is going to need to be regenerated at the end so that the cycle can continue. Okay, so the first thing is RUBP, okay, is going to have carbon fixation occur. Carbon fixation means we're taking gas carbon dioxide, which is a form that's not usable for uh organic animals, plants, anything, and we're putting it into a usable form. In this case, we're going to be eventually turning into glucose. Okay? And this is going to be driven by the most plentiful enzyme on Earth called rubiscoco. Now, don't be confused if you're like, "Wait,

enzymes end with ace. This doesn't end with ace." Rubiscoco is actually a shortened form of a very long word that does end with ace, I promise, but you just need to know it as rubiscoco. Okay, so in this first step, okay, we're going to have um The production of two glycerate 3 phosphates. So we're immediately going to have this now six carbon molecules split into two threecarbon molecules. Okay, from there, okay, our glycerate 3 phosphate is going to be converted into triosphosphate and it's going to happen using reduced NADP and ATP. Okay, so this is

being reduced this these three carbon molecules. So we're going to need to then reoxidize that reduced NADP. Okay, it's uh going to Then head back to the light independent reactions to be reduced again. Okay. Uh this process can only occur for a short time in the dark. Uh as ATP and reduced NADP are produced in the light dependent reactions quickly run out and that's why photosynthesis can only continue for a matter of seconds into the dark. Okay. But from there we know we need to regenerate RUBP. Okay. For every five molecules of triosphosphate, so three

turns of the Calvin cycle. Okay. We're going to have five of those three carbon molecules. Okay. which totals 15 carbons create three more RUBPS. Okay, which then allows for those next three turns to happen. But one of those six is then going to become half of our new glucose. Now note regeneration does cost one of those ATPs that we made in the light dependent reactions. Okay, now the math can be tricky on this one. So um we need to Just keep in mind so we're going to need a total let's go back to this whole

one of six CO2s to enter. So, we're going to need six turns of the carbon cycle to make one glucose. Okay? For every three turns, we're going to make half a glucose because for every three turns, we know we're going to generate a total of six triosphosphates. Five of which are going to become our three new rubps for those three turns. One of which becomes half Of the glucose. Okay? So, we're going to need six total turns to make a whole glucose. Now there's some great videos um on YouTube summarizing these uh that I recommend

you watch to see um that process animated. Okay. So what is the purpose of all this glucose making? Plants use glucose for cell respiration. Remember they do both photosynthesis and respiration. And then plants are made up Of cellulose and all of their cell walls which are chains of those beta glucoses that are up down up down up down which we've talked about before. Glucose is usually converted to sucrose for transportation. Sucrossse is also just what we know as table sugar. So that sucrose is what we use to mix in our coffee or to bake some

brownies. Okay. If glucose is produced more quickly than it can be transported, it gets converted to starch. And all of These dark colored circles are starch granules. Okay. That are produced inside chloroplast. And at night when photosynthesis stops because lack of light that starch then can be broken down and exported from the leaf and used to still power um respiration occurring through the night. Okay. All carbon compounds in photosynthesizing organisms are fixed in the Calvin cycle and we focus on glucose for simplicity. But just note that we Can have other compounds like glycerol, fatty acids

and amino acids. They're made by metabolic pathways that can be traced back to an intermediate in the cycle. But you don't need to know any details about that. Just know that all of our organic molecules are initially made through photosynthesis. Okay? So remember light dependent reactions can only occur for a few seconds. Um and because all of these products here are rapidly going to run Out and not be able to power the Calvin cycle any further. Okay. Um let's see in low light intensity therefore those the ATP and reduced NADP are our limiting factors. Um

so therefore because those are our inputs here um at this second step of the Calvin cycle the reduction of glycerate 3 phosphate is going to be our rate limiting step because we don't have ATP and reduced NADP to allow for this step to occur. Okay. In high light Intensity carbon fixation tends to be the rate limiting step. uh use of reduced NADP is restricted. So supplies of NADP therefore over here limit the light dependent reaction by preventing photosystem 2 from being able to function. In summary, a light a lack of light stops light dependent reactions

and a light a lack of CO2 produces photos system 2 from functioning. And we'll end here then with this nice summary. Thanks for listening.