AP Biology Science Practice 1: Models and Representations

Summary

This AP Biology Science Practice video introduces seven key scientific practices essential for success in the field. Mr. Andersen emphasizes the importance of models and visual representations in understanding complex biological concepts, such as DNA structure and natural selection. He illustrates how these tools can be created, described, refined, and used to explain phenomena like genetic variation and signal transduction. The video also highlights the famous DNA model by Watson and Crick, showcasing the significance of models in scientific discovery and AP Biology exam preparation.

Takeaways

• 🔬 Science practices are seven overarching skills and knowledge areas essential for success in scientific endeavors, including AP Biology.
• 👨‍🏫 For AP Biology instructors, these practices are the skills and knowledge to instill in students throughout the academic year.
• 📚 Students should aim to acquire these practices as they prepare for the AP Biology test, which assesses the application of accumulated knowledge.
• 🧬 Understanding models and visual representations is crucial for excelling in both the AP Biology test and as a scientist.
• 🌐 The DNA double helix is a misconception; DNA is actually wrapped around histone proteins, forming a fiber structure visible under an electron microscope.
• 🤔 Mental models are personal conceptualizations, but they need to be shared visually to be considered true models in scientific practice.
• 📈 AP Biology covers four big ideas: Evolution, Free Energy, Information, and Systems, each with its own representative models.
• 📊 Models like natural selection, photosynthesis, operon function, and energy pyramids are used to visually represent complex biological concepts.
• 🛠️ AP Biology students are expected to perform five tasks with models: create, describe, refine, use, and re-express them to answer test questions.
• 📉 An example task might involve creating a graph to show how a beetle population's color distribution changes in response to environmental shifts.
• 🔑 Watson and Crick's DNA model is a prime example of how visual representations can lead to groundbreaking scientific discoveries.

Q & A

What are the seven science practices mentioned in the AP Biology class?

The script does not explicitly list all seven science practices, but it emphasizes the importance of understanding and applying them in the AP Biology context, particularly in relation to models and visual representations.

Why are science practices important for an AP Biology instructor and students?

Science practices are important for an AP Biology instructor to build in students throughout the year and for students to pick up because they will be asked to apply this knowledge using science practices on the AP Biology test in the spring.

What is the significance of understanding models and visual representations in AP Biology?

Understanding models and visual representations is significant as it allows students to perform better on the AP Biology test and also enhances their ability to function effectively as scientists by providing a visual understanding of complex scientific concepts.

What does the electron microscope image of bacterial DNA reveal about DNA structure?

The electron microscope image reveals that DNA is not seen as a simple double helix at the microscopic level. Instead, DNA is wrapped around histone proteins, forming a complex structure known as a fiber of DNA.

Who developed the model of DNA and how did it contribute to our understanding of genetics?

James Watson and Francis Crick developed the model of DNA. Their model allowed us to understand the structure of DNA and how it works, serving as a visual representation of the genetic material inside a cell.

What is a conceptual model and how does it differ from a mental model?

A conceptual model is a visual representation of a process or system that can be shared and understood by everyone. It differs from a mental model, which is an individual's internal understanding or idea that is not necessarily shared or visualized.

What are the four big ideas discussed in AP Biology and how are they related to models?

The four big ideas discussed in AP Biology are Evolution, Free Energy, Information, and Systems. Each of these ideas can be represented and understood through specific models that illustrate key concepts and processes within them.

Can you provide an example of a model related to the concept of Evolution?

An example of a model related to Evolution is one that shows natural selection, illustrating how bacteria with varying levels of resistance are selected for in a population based on environmental pressures.

What is the purpose of creating models and visual representations in the context of the AP Biology test?

The purpose of creating models and visual representations is to apply the knowledge built throughout the year to answer questions on the AP Biology test, demonstrating an understanding of scientific concepts and processes.

How does the process of transduction in bacteria result in genetic variation?

Transduction in bacteria results in genetic variation when a bacteriophage injects bacterial DNA into another bacteria, transferring genetic material and introducing new genetic information into the recipient bacteria.

What is the role of insulin in the process of signal transduction as depicted in the script?

In the process of signal transduction, insulin plays a crucial role by docking with an insulin receptor, which triggers the opening of glucose transport channels, allowing glucose to enter the cell.

How can changes in key elements of signal transduction alter cellular response?

Changes in key elements of signal transduction can alter cellular response by affecting the ability of signals to be transmitted properly. For example, in type II diabetes, insulin may be produced but fails to dock properly with the insulin receptor, preventing glucose transport channels from opening and glucose from entering the cell.

Outlines

00:00

🔬 Introduction to Science Practices in AP Biology

Mr. Andersen introduces the concept of seven overarching science practices essential for success in AP Biology. He emphasizes their importance for both teachers and students, as they form the basis for understanding and applying scientific knowledge. The video aims to help students excel in the AP Biology test by understanding concepts like models and visual representations, exemplified by the DNA structure under an electron microscope. Mr. Andersen clarifies misconceptions about DNA's appearance and introduces the idea of a conceptual model as a tool for scientific understanding.

05:03

📊 Demonstrating Evolution and Osmosis with Models

This section delves into the application of models to demonstrate scientific concepts, specifically evolution and osmosis. Mr. Andersen uses a hypothetical scenario of beetles' color variation and tree trunks' darkening to illustrate directional selection and evolution. He guides the viewer to create a graph showing population changes due to environmental shifts. Similarly, he explains osmosis using a U-tube model with dissolved salts and a semi-permeable membrane, describing the movement of water molecules towards equilibrium.

10:07

🧬 Refining and Applying Models in Genetics and Cell Biology

The focus shifts to the refinement and application of models in genetics and cell biology. Mr. Andersen discusses how alterations in messenger RNA sequences affect protein synthesis, emphasizing the impact on amino acid sequences and protein folding. He also explores the concept of genetic variation in bacteria through the process of transduction, using a model of a bacteriophage infecting a bacterium and transferring DNA. This section highlights the ability to refine existing models and apply them to understand complex biological processes.

🚀 Signal Transduction and the Relevance of Models in Biology

In the final paragraph, Mr. Andersen discusses signal transduction, particularly the role of insulin and its receptor in glucose transport. He poses questions about how changes in signal transduction elements can alter cellular responses, using the model of an insulin receptor and glucose transport proteins. The paragraph ties back to the broader importance of models in making sense of complex biological phenomena, referencing the famous DNA model by Watson and Crick as a pinnacle example of the power of visual representation in scientific discovery.

Keywords

💡Science Practices

Science practices refer to the set of skills and knowledge areas that are fundamental to scientific inquiry and understanding. In the context of the video, these practices are crucial for AP Biology students and educators as they form the basis for the application of knowledge on the AP Biology test. The video emphasizes the importance of these practices in building a well-rounded scientific approach, including the ability to create and interpret models, which is a key aspect of scientific communication and understanding.

💡AP Biology

AP Biology is an advanced placement course and exam offered by the College Board for high school students. It is designed to provide a college-level understanding of biological concepts. The video script discusses the significance of science practices in the context of AP Biology, highlighting how these practices prepare students for the rigor of the AP exam and for future scientific endeavors.

💡Model

A model in science is a theoretical construct that represents a system or process. It helps in understanding complex phenomena by providing a simplified and visual representation. The video explains that models are essential in biology for visualizing concepts such as DNA structure and genetic processes. For instance, the script mentions the famous double helix model of DNA by Watson and Crick, which was crucial for understanding the molecule's role in heredity.

💡Visual Representation

Visual representation is any form of depiction that aids in the understanding of abstract concepts or data. In the video, visual representations are discussed as tools that complement models, making scientific ideas more accessible and interpretable. The script uses the example of an electron micrograph of DNA to illustrate how visual representations can sometimes be misleading without the context provided by a model.

💡DNA

DNA, or deoxyribonucleic acid, is the molecule that carries the genetic instructions for the development, functioning, and reproduction of all known living organisms. The video script delves into the structure of DNA, explaining how it is not typically seen as a simple double helix but is instead complexly wrapped around proteins called histones.

💡Histone Proteins

Histone proteins are a class of proteins that play a crucial role in the packaging of DNA into structural units called nucleosomes. The script mentions histone proteins to illustrate how DNA is organized within the cell's nucleus, which is vital for understanding the compact structure of chromosomes.

💡Natural Selection

Natural selection is the process by which certain heritable traits become more or less common in a population over successive generations. The video uses a model of natural selection involving bacteria to demonstrate how resistance levels can affect the survival and prevalence of certain traits within a population.

💡Photosynthesis

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll pigments. The script describes a model of photosynthesis to explain the transfer of free energy, highlighting the light-dependent reactions and the Calvin cycle.

💡Operon

An operon is a unit of genetic function in which a group of genes that are regulated by a single regulatory element are transcribed together. The video script uses the operon model to explain gene regulation and the flow of genetic information within a cell.

💡Energy Pyramid

The energy pyramid is a graphical representation that shows the flow of energy through different levels of a biological community, from producers to consumers. In the script, the energy pyramid model is used to illustrate the concept of systems in biology, showing the relationships between different trophic levels.

💡Signal Transduction

Signal transduction is the process by which a cell converts an external signal, such as a hormone, into an internal response. The video script discusses how changes in the elements of signal transduction, such as insulin receptors, can alter the cellular response, which is critical for understanding conditions like diabetes.

Highlights

Seven overarching science practices are essential for success in AP Biology.

Science practices are crucial for students to apply knowledge on the AP Biology test.

Understanding models and visual representations is key for excelling as a scientist and on the AP test.

DNA's structure under an electron microscope reveals a complex arrangement different from the classic double helix.

Models like Watson and Crick's help visualize and understand the genetic material within a cell.

Mental models are personal, but conceptual models are shared visual representations of scientific processes.

AP Biology covers four big ideas: Evolution, Free Energy, Information, and Systems, each with its models.

Natural selection can be visually represented to demonstrate evolutionary changes in a population.

Photosynthesis is a key model illustrating the transfer of free energy in plants.

The operon model explains the flow of genetic information in cell communication.

Energy pyramids are models representing the systems of energy transfer in ecosystems.

Students must be able to create, describe, refine, use, and re-express models and visual representations.

Creating a model involves applying knowledge to visualize hypothetical scenarios, like changes in beetle population due to environmental changes.

Describing a model requires explaining the process and changes over time, such as in a U-tube with dissolved salts.

Refining a model involves adjusting it based on new information or questions, like the effect of mRNA sequence changes on protein properties.

Using models to answer questions about genetic variation, such as the role of transduction in bacteria.

Re-expressing models involves applying knowledge to new scenarios, like how signal transduction changes can affect cellular response to insulin.

The famous DNA model by Watson and Crick demonstrates the importance of physical models in scientific discovery.

Transcripts

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.