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  • Hi. It's Mr. Andersen and this is AP Biology Science Practice 1. What are

  • science practices? Well there are seven of them. And they're overarching skills and knowledge

  • that you should have to do well as a scientist. Why is that important in an AP Bio class?

  • Well if you're a teacher, if your'e an AP Biology instructor, practices are skills and

  • knowledge that you want to build in your students throughout the year. And if you're a student,

  • these are the practices that you want to pick up. Because when you take the AP Biology test

  • in the spring, they're going to ask you to apply the knowledge that you've picked up

  • throughout the year using science practices. And so you want to understand what a model

  • and what a visual representation is, because it's going to allow you to do better on the

  • test. And it could also allow you to do better as a scientist. And this right here is a picture

  • of DNA. So this is bacterial DNA under an electron microscope. And you might fool yourself

  • into thinking that we're looking at the double helix. That we're looking at DNA. But that's

  • not really what it is. If we zoom in as close as we can see, that's not what we see. In

  • fact the DNA is wrapped around histone proteins which are wrapped around more DNA and more

  • histone proteins. And we eventually get to something that looks like this. We call it

  • a fiber of DNA and that's what you're looking at in this picture. And so it's weird to think

  • that we've never seen a double helix. We've never seen DNA at this level, especially at

  • this level. And so how do we know that that's what it looks like? Through careful experimentation.

  • Watson and Crick developed a model. And a model is going to allow us to understand how

  • DNA works. It's a visual representation of what's going on inside the genetic material

  • of a cell. And so if I were to ask you, think about this, how is the DNA eventually become

  • a protein in a cell? Well in your brain you're going to start coming up with all of these

  • mental models of how the DNA maybe becomes messenger RNA and then is somehow translated

  • in the cytoplasm. That's your mental model. But it's still not a model. It's still not

  • a visual representation because it's not shared by everyone. And so once we have a picture

  • of how it works, now we're at the level of a conceptual model and that's what this science

  • practice is really about. And so throughout AP Biology, remember there are four big ideas

  • that we're going to talk about. Evolution, Free Energy, Information and then finally

  • Systems. And I came up with four models that would be typical in each of these different

  • big ideas. And so if we're talking about evolution, this is a nice model that shows natural selection.

  • So we've got bacteria, we've got a selective process when we're choosing these bacteria

  • and then this is a finally population. And maybe we're thinking about bacteria and so

  • this is resistance levels. And so the ones that are able to survive are going to be the

  • ones that have the highest resistance. And so by visually making natural selection apparent

  • to us, it's easier to deal with questions. Or let's say we're looking at free energy

  • and how free energy is transferred. This is a nice visual representation of photosynthesis.

  • So it shows the light reaction in the Calvin Cycle. It shows the reactants and the products

  • of each. And it also shows these carrier molecules of NADPH and ATP. What if we're looking at

  • information flow? Remember that deals with things like genetics and cell communication.

  • This would be a great example of a model. This shows you how an operon works. And so

  • this is going to be our RNA polymerase and we have a repressor here. Or maybe if we're

  • looking at systems a great model could be this pyramid of energy showing carnivores,

  • herbivores and plants. And so this gives you an idea of what a model looks like. And how

  • it can be applied in an AP Biology class. But they're asking that you can do five things

  • using models and visual representations. And so they first of all want you to be able to

  • create models and representations. And so you can think of each of these questions,

  • where's the first one, like a question you might experience on the AP Biology test in

  • the spring. In other words they're asking you to apply the knowledge that you've built

  • using a science practice. In this case you would have to build or create a model of representation.

  • And so you could pause the video, I've got five of these, and you could try to do this

  • and then you could watch me explain it. And so pause the video now and let me go through

  • it. So we've got a hypothetical population of beetles. There's wide variation in color

  • matching the range of coloration of the tree trunks. Create a graph that show how the beetle

  • population would change as a result in changes in the environment that darken the tree trunks.

  • And so what are some first things that I would look at? So we've got a beetle population.

  • There's differences in color. But they're saying that we have a variety of different

  • colors. And so we're going to represent that with a graph. We want to show the frequencies,

  • but we're going to have a normal distribution. In other words we could be put beetle color

  • here along the x axis, from light to dark and we're going to get a normal distribution.

  • In other words some of the beetles are really light. Some are really dark. But most of them

  • are going to be in the middle. What are they then asking us to do? They want to show us

  • evolution. They want to show us how they're changing as the bark becomes darker and darker.

  • So what's going to happen? Well as the bark becomes darker and darker, all of these lightly

  • colored beetles are going to die because the birds are going to see them. And they're going

  • to show up. And so they're going to die on this side of that curve. And so this would

  • be pre-evolution and then this would be post-evolution. And so what we're going to see is directional

  • selection. And so it's neat. I could look at that. We now have a visual representation

  • of a concept and this is what they're getting at. Can you build a model like this? Or, if

  • you were given four options in a multiple choice portion, could you choose the one that

  • reflects this hypothetical change? Let's go to the next thing they'd like you to be able

  • to do. They want you to be able to describe a model or a visual representation. Well here's

  • a question. What will happen to the water molecules in dissolved salts over time? So

  • we have a U-tube over here on the side. You could look right here that we've got water,

  • which is going to be this bluish color and we have these dissolved salts. And so they're

  • going to ask you what would happen over time? One other piece of evidence is that we've

  • got a semi permeable membrane down here. What does that mean? It's only going to allow certain

  • things through. In this case it's only going to allow water to go through. So what would

  • happen over time? Well we're now dealing with diffusion. And so these salt molecules are

  • going to be randomly bouncing around and they would always want to move from an area of

  • high concentration to low concentration. They would always want to move from the left side

  • of the U-tube to the right side of the U-tube. But they can't, because there's a semi permeable

  • membrane here. And so the water is the only thing that can move. So let's look at the

  • water now. Well the water is going to have a higher concentration of water on the right

  • side then the left side. And so the water is going to start flowing through this semi

  • permeable membrane. So the level of the water would magically move up on this side and it's

  • going to move down on this side. How long is it going to do that? Until the concentration

  • of salt molecules to water molecules is going to be the same on either side. Now does the

  • water stop moving? No. It's still going to move back and forth, it's just that it's going

  • to be at an equilibrium. So you can see now that I'm giving you a model and then I'm asking

  • you to describe the model or what's going to happen over time. The third thing they

  • want you to be able to do in this science practice is to refine a model or representation.

  • And so they could give you a model and then they could ask you questions based on that.

  • So I've got a model over here to the right and what I'm asking is how will changes in

  • the messenger RNA sequence effect the properties of the newly born protein? Okay now I'm asking

  • you to refine the model that I have given you. And so right here you can see that we've

  • got translation going on. So we've got messenger RNA. It's moving through a ribosome. And as

  • it does, we've got our tRNA. So the tRNA, which is going to be this molecule right here

  • is going to arrive at the A site and it's going to contribute it's one amino acid. And

  • so that would be just describing this model. But they want you to refine it. In other words,

  • what would happen if we would change the messenger RNA sequence? Well if we change that sequence

  • here, it's going to change the amino acids that come in and therefor it's going to change

  • the proteins. What's going to happen if we change the proteins? Well remember, or excuse

  • me, the amino acids? Every amino acids is going to be the same except for the R group

  • that hangs off to the side. And so if we change those R groups, we're going to change the

  • chemical interactions between all of those R groups and so we're going to get a protein

  • that folds differently. In other words its secondary and tertiary structure is going

  • to be different. And so now I'm not answering a question based on this model, I'm saying

  • if we could refine it what else do I know. Next thing they want you to be able to do

  • is use models and representations. And so right here they're saying the digram to the

  • right shows transduction in bacteria. How does genetic variation in bacteria result

  • from this process? So they're going to ask you to use the model. In this case we've got

  • a bacteriophage, remember it's a virus that's infecting a bacteria. But that's not what

  • the question is about. They're asking you to say how that would effect the genetic variation

  • in the bacteria. Now remember, bacteria don't have sex. They don't do meiosis and produce

  • sperm and egg. And so how could we get variation in it? Well let's look at what's going on.

  • So the bacteria is injected with DNA from the bacteriophage. That's basically programming

  • that bacteria to make more viruses. Except there's one thing going on right here. At

  • this point, instead of this virus being packaged with viral DNA that's created by the bacteria,

  • it's packaged with bacterial DNA. And so as these viruses spread out, this one virus is

  • injecting bacterial DNA into another bacteria. So it's transferring DNA from one bacteria

  • to another. What is that going to give that new bacteria? It's going to give it variation.

  • And so again I'm applying my knowledge to

  • a model or a visual representation. And then the last one is we need to be able to reexpress

  • models and representations. And so in this one we're looking at signal transduction.

  • So you can see right here that we've got an insulin receptor and then we've got glut or

  • we've got a glucose transport. So what's the question asking? How can changes in key elements

  • of signal transduction alter cellular response? And so again now they're asking you to apply

  • the knowledge that you have. In this case, why is insulin important? Insulin is going

  • to dock with an insulin receptor, but what it's really going to open up are going to

  • be these glucose transports. In other words it's going to open up this gate and so glucose

  • can get into the cell. And so what are some questions we can ask from that? Well let's

  • say there's no insulin. If there's no insulin here, there's going to be no signal transduction

  • and it's not going to open up and it's not going to allow glucose to come in. So if you're

  • a type I diabetic, if you don't have insulin, they you're out of luck. But let's say you're

  • a type II diabetic. Where's the problem going to be there? Now we've got a problem with

  • the insulin receptor itself. We're creating insulin but it's not docking properly with

  • the insulin receptor. What's that going to do? We still don't have a signal transduction.

  • We still don't have a glucose transport opening up. And so again these are all questions that

  • you might find on an AP Biology test in the spring. In other words they're asking you

  • to use models, create models. But models are neat. They allow us to make sense of a mental model. And lots of times it gets visual

  • and it gets much easier to understand. And they're used by scientists. What's the most

  • famous model of all? That model was developed by James Watson and Francis Crick, right here.

  • They're shaking hands with McCarty, who is one of the scientists who had figured out

  • that is was DNA that was actually doing the transforming inside bacteria. But they were

  • able to build a model. They were able to build a model because they knew what DNA was made

  • up of. They knew that it was made up of phosphates, sugar and then these nitrogenous bases. They

  • knew the ratio of the bases. But until they could physically build it, they couldn't visualize

  • it. And so models and visual representations are incredibly important. In AP Biology it

  • will help you do better on the test and I hope that was helpful.

Hi. It's Mr. Andersen and this is AP Biology Science Practice 1. What are

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