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## Free-response questions: 2015 AP Biology exam

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# 2015 AP Biology free response, 2c-d

## Video transcript

- [Voiceover] Part c. A researcher estimates
that in a certain organism, the complete metabolism or
glucose produces 30 molecules of ATP for each molecule of glucose. The energy released from the
total oxidation of glucose under standard condition 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 let me write this. Hydrolysis. Hydrolysis of 30 moles of ATP. So I'll draw this, and we've
got the title right over there. So let's just take 30 moles, 30, 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. We have 30 moles, it's getting hyd, that
is undergoing hydrolysis, and so 30 moles times 7.3 kilocalories, 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, three times 7.3 would be 21.9, so this is going to be 219, since this is 30 times 7.3. 219 kilocalories. All right. Now let's do the second part. I'll do this in a different color. If you're actually taking the test, you know I might 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, energy stored in ATP, over total energy, total energy from oxidation, energy from oxidation of glucose. So they say calculate the efficiency of total AT production, 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, well, for this particular organism, it is able to produce 30 ATPs. The complete metabolism of glucose produces 30 molecules of ATP. So for every mole of glucose, it's producing 30 moles of ATP. And so we already figured that's going to be 219 kilocalories. 219 kilocalories. So now we just have to do
a little bit of math here, figure out what 219 divided
by 686 is going to be. Let me do it over here. 686 divided by 200, oh, sorry, 219 divided by 686. This is going to be less than zero. So let me go straight to, how many times would 686 go into 2,190? Well, this is a little bit less than 700 and seven times three is 21, so this looks, it's about three times. Three times six is 18. Three times eight is 24 plus one is 25. Three times six is 18 plus two is 20. Let me subtract it. Let's see. 90 minus 58 is 32. So I have 132 Then I can bring down another zero. 686, well, let's see. It looks like this might
be one or two times. Let's see, two times 686 would be 1,200, this is actually going to be one time, by feeling, or 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, this a one. So 10 minus six is four. Now I can make this a two and this an 11. 11 minus eight is three. And then 12 minus six is six. So, 686 goes into 6,340, this is definitely going
to be more than 5 times. So if we want to approximate,
we would round up. This is going to be approximate, so this going to be something else that is greater than five, so it's going to be approximately 32%. So I could write it, let me write it here. So this is approximately 32% efficiency. So roughly 32% 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 want this in another color for fun. Describe what happens to the excess energy that is released from the
metabolism of glucose. Yeah, what happens to, what happens to the
other 68% of the energy? So, I'll do it over here. The rest of the energy
is released as heat. The rest of energy gets converted, or goes, 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, if you think about the efficiency, and you think about,
well, 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
mitochondria, an 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, we've talked about it, when we first talk about
mitochondria on Khan Academy, but there actually is a
theory that mitochondria, or the ancestors of mitochondria, might have been independent,
prokaryotic organisms. So we could say, the scientific question, we could say, were the ancestors of mitochondria, mitochondria once independent, in-de, independent, independent, we could even say, well, prokaryotic, prokaryotic, kary-otic organisms whose descendants lived, learned, whose descendants became incorporated in euakaryotic organisms? Whose descendants, descendants, de, descend, descendants, whose descendants became, became incorporated, became incorporated, corp-or-ated inside eukaryotes, 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, you're going to see these mitochondria, or actually in the
great majority of cells, and were their ancestors
once independent organisms that now have, whose
descendants now live in symbiosis with our cells because they're so good
at the Krebs cycle?