2015 AP Biology free response 2 c d

Part C: A researcher estimates that in a certain organism, the complete metabolism of glucose produces 30 molecules of ATP for each molecule of glucose. The energy released from the total oxidation of glucose under standard conditions is 686 kilocalories per mole. The energy released from the hydrolysis of ATP to ADP and inorganic phosphate under standard conditions is 7.3 kilocalories per mole.

Calculate the amount of energy available from the hydrolysis of 30 moles of ATP. Calculate the efficiency of total ATP production from one mole of glucose in the organism. Describe what happens to the excess energy that is released from the metabolism of glucose.

All right, I'm tired of squeezing things in between the questions, so let me go down here to get some real estate.

So, let's do the first part: Let's calculate the amount of energy available from the hydrolysis of 30 moles of ATP.

So I'll draw this: Hydrolysis of 30 moles of ATP. So I'll write this; I got the title right over there. So let's just take 30 moles.

30 moles of ATP times—They tell us how much energy is released when you hydrolyze that ATP per mole. They say the energy released from the hydrolysis of ATP... Let me underline that. The energy released from the hydrolysis of ATP to ADP and inorganic phosphate under standard conditions is 7.3 kilocalories per mole.

Since we have 30 moles, that's getting high. That is... that is... that is undergoing hydrolysis. So, 30 moles times 7.3 kilocalories per mole.

And what is that going to be equal to? Well, the moles cancel with the moles. The units are going to be kilocalories, which makes sense because I want units of energy.

And what is 30 times 7.3? See, 3 times 7.3 would be 21.9. So this is going to be 219... Since it's 30 times 7.3: 219 kilocalories.

All right, and now let's do the second part. Now, I'll do this in a different color. You're actually taking the test; you might not get the benefit of multiple colors, but this is for you to help me help you understand what's going on.

Calculate the efficiency of total ATP production from one mole of glucose in the organism. So I'll do that over here.

Efficiency... efficiency is actually... let me do it well. Efficiency is equal to energy... is going to be energy in ATP, the energy stored in ATP, over total energy, the total energy from oxidation... energy from oxidation of glucose.

So, they say, “Calculate the efficiency of total ATP production from one mole of glucose in the organism.” So this is going to be equal to... So they tell us what the energy production when you oxidize one mole of glucose. They say it is 686 kilocalories per mole. So the denominator here is 686 kilocalories.

And the numerator, the energy stored in ATP, will—For this particular organism, it is able to produce 30 ATPs. The complete metabolism of glucose produces 30 molecules of ATP. For every mole of glucose, it is producing 30 moles of ATP.

And we already figured that's going to be 219 kilocalories. So now we just have to do a little bit of math here to figure out what 219 divided by 686 is going to be.

Let me do it over here. 686 divided by... sorry, 219 divided by 686. This is going to be less than zero. So let me go straight to how many times 686 go into 2,190?

Well, this is a little bit less than seven hundred, and seven times three is twenty-one, so this looks like about three times; three times six is 18, three times eight is 24 plus 1 is 25, three times six is 18 plus 2 is 20.

Let me subtract it. Let's see, 90 minus 58 is 32, so I have 132. Then I can bring down another 0.

686, well, let's see, it looks like this might be one or two times. I see 2 times 686 would be 1,200; it's actually going to be one time. By feeling—well, maybe we'll round up; it sounds like.

So, one times 686 is 686. You subtract... All right, I will do some regrouping here, so I can make this a 10 and this a 1. So our 10 minus 6 is 4. Now I can make this a 2 and this a 1: 11 minus 8 is 3, and then 12 minus 6 is 6.

So 686 goes into 6,340; this is definitely going to be more than five times. So if we want to approximate, we would round up; this is going to be approximate. So there's going to be something else that is greater than five.

So, it's going to be approximately 32 percent. So I can write it; let me write it here. So this is approximately 32 percent efficiency.

So roughly 32 percent of the potential energy, or of all the energy that can be produced from the oxidation of glucose, actually ends up getting stored in ATP.

Now they say, “Describe what happens...” I'm just in another color for fun. Describe what happens to the excess energy that is released from the metabolism of glucose.

Yet, what happens to... What happens to the other 68 percent of the energy? So I'll do it over here. The rest of the energy is released as heat.

The rest of the energy gets converted or goes... is... is... is released... released as heat. And you could say it's also released as entropy, increasing the number of possible states of the cells, more things are bouncing around in different ways.

But this is the easiest way to think about it: it is released as heat, in general. When you think about any thermodynamic process, you think about the efficiency.

New thing: but where is all of that lost energy that wasn't captured? It's usually going to be... it's usually going to be heat.

All right, now let's do Part D. Part D: The enzymes of the Krebs cycle function in the cytosol of bacteria, but among eukaryotes, the enzymes function mostly in the mitochondria.

All right, mostly in the mitochondrion organelle. Pose a scientific question that connects the subcellular location of the enzymes in the Krebs cycle to the evolution of eukaryotes.

All right, well, and we've talked about it when we first discussed mitochondria on Khan Academy. But there is a theory that mitochondria are—or the ancestors of mitochondria—might have been independent prokaryotic organisms.

So we could say the scientific question could be: Were the ancestors of mitochondria once independent? Independent... independent because they even say, well, prokaryotic organisms, whose descendants—whose descendants became incorporated in eukaryotic organisms.

Whose descendants... descendants... the descendants became incorporated inside eukaryotes.

So, that's a scientific question and a really interesting one that, you know, if you look at any cell in the human body, you're actually going to see these mitochondria are actually in the great majority of cells and where their ancestors were once independent organisms that now have their—whose descendants now live in symbiosis with ourselves because they're so good at the Krebs cycle.