AP Biology Practice 6 - Scientific Explanations and Theories

Summary

In this AP Biology science practice, Mr. Andersen discusses the scientific method, emphasizing the development and refinement of theories through evidence-based experimentation. He explains natural selection, its evolution with sexual selection, and how theories like Mendelian genetics are refined over time. The video also covers the importance of applying theories to new data, such as in genetic inheritance and environmental influences on gene expression, preparing students to analyze and justify scientific claims.

Takeaways

• 🔬 The scientific method involves asking questions, gathering data, analyzing it, and developing theories to explain how the world works.
• 🐦 Natural selection, developed by Charles Darwin, is a mechanism that explains evolution, using the example of finches in the Galapagos adapting to different food supplies.
• 💡 Theories in science start with an idea, are tested through experiments, and are refined or replaced as new evidence emerges.
• 🔄 The process of theory development is cyclical, involving constant feedback to ensure theories align with observed phenomena in the universe.
• 🌏 Before natural selection, the belief was that species were perfectly placed on Earth by a divine power, which was challenged by scientific evidence.
• 🛠️ Theories are modified to accommodate new evidence, such as the incorporation of sexual selection into the theory of natural selection.
• 📚 Understanding and applying theories is crucial in various scientific fields, including evolution, genetics, and systems biology.
• 🧬 The environment can influence gene expression without changes to the DNA itself, involving mechanisms like histone modification.
• 📉 College Board encourages the application of theories to understand phenomena like antibiotic resistance, feedback loops in blood glucose regulation, and epigenetic changes.
• 📝 The ability to justify claims with evidence, construct explanations, and make predictions about natural phenomena is essential in scientific reasoning.
• 🧬 Mendel's laws of inheritance were foundational but have been refined over time to accommodate exceptions like autosomal linkage and sex-linkage.

Q & A

What is the process of developing a scientific theory according to the script?

The process of developing a scientific theory involves coming up with a good question, gathering data, analyzing the data, and over time, developing theories that explain how the world works. If the evidence supports the idea, a theory is created to better understand the universe. The theory may be modified as new evidence is discovered to ensure it matches what's happening in the universe.

How does the script describe the concept of natural selection?

Natural selection is described as a mechanism that explains how evolution can occur. It is illustrated with the example of finches on the Galapagos, which had variations in their beaks and adapted to their specific food supply over time.

What is the significance of the feedback loop in the context of scientific theories?

The feedback loop is significant as it ensures that our theories match what is happening in the universe. It is a cycle of refining and improving theories based on new evidence and observations.

How did the understanding of species evolution change before the theory of natural selection?

Before natural selection, the prevailing idea was that God had placed all species on the planet, perfectly evolved to where they are. This belief was challenged and eventually revolutionized by the theory of natural selection.

What are the four big ideas in which the College Board expects students to apply theories?

The four big ideas are not explicitly listed in the script, but it can be inferred that they pertain to various aspects of biology such as evolution, genetics, regulation of biological processes, and the structure and function of biological systems.

How does antibiotic resistance in bacteria relate to the theory of natural selection?

Antibiotic resistance in bacteria is an example of natural selection in action. Bacteria that have genetic variations allowing them to survive in the presence of antibiotics will thrive, while those without such variations will be eliminated, leading to a population of antibiotic-resistant bacteria.

What is the role of histones and methylation in gene expression as mentioned in the script?

Histones and their methylation play a role in gene expression by controlling access to DNA. Methylation of histones can open up the chromatin structure, allowing for the expression of certain genes, which can be influenced by environmental factors.

What are the five ways the College Board wants students to deal with theories and explanations according to the script?

The script does not list all five ways but mentions justifying claims with evidence, constructing explanations based on evidence, and making claims and predictions about natural phenomena. The other two ways are not explicitly stated in the provided transcript.

How does the script explain the refinement of Mendel's Laws in genetics?

The script explains that Mendel's Laws, such as the law of segregation and independent assortment, were refined over time with the discovery of exceptions like autosomal linkage, sex-linkage, and polygenic inheritance, which do not follow straightforward Mendelian inheritance.

What is the example given in the script to illustrate the concept of genetic drift?

The script uses the example of a bottleneck in the northern elephant seal population or cheetahs to illustrate genetic drift, which occurs when a population size decreases, leading to changes in the genetic make-up of the population.

How does the script relate the process of artificial selection to the theory of natural selection?

The script relates artificial selection to natural selection by describing how humans can choose which individuals mate with whom, similar to how natural selection operates through environmental pressures and survival of the fittest.

What is the process described in the script for determining the genotypes of original parents in a genetic cross?

The process involves analyzing the data given for the F1 and F2 generations, working backward to determine the inheritance pattern, and identifying whether the trait is sex-linked recessive or sex-linked dominant, as illustrated with the example of a wild type male and white-eyed female.

Outlines

00:00

🔬 Scientific Theories and Natural Selection

In this paragraph, Mr. Andersen introduces the scientific method and the development of theories in science, using natural selection as a prime example. He explains how scientists start with a question, gather data, analyze it, and over time develop theories that explain natural phenomena. Charles Darwin's theory of natural selection is highlighted as a mechanism for evolution, illustrated by the adaptation of finches on the Galapagos Islands. The paragraph discusses the iterative process of theory development, where scientists propose ideas, test them with experiments, and refine or replace theories based on new evidence. The concept of a scientific revolution is also introduced, where a theory that doesn't fit with collected data leads to a significant shift in understanding, as was the case with the transition from the idea of divine creation to natural selection.

05:01

📚 Applying Theories to Understand Biological Phenomena

This paragraph delves into the application of scientific theories, particularly in the context of evolutionary biology. Mr. Andersen discusses how theories are tested and refined, using the example of Mendel's laws and how they have been expanded upon with the understanding of autosomal linkage, sex-linkage, and polygenic inheritance. The paragraph also addresses the expectations of the College Board for students to apply theories to various biological concepts, such as antibiotic resistance, blood glucose regulation, and gene expression influenced by environmental factors like histone modification. The focus is on the ability to justify claims with evidence, construct explanations, and make predictions about natural phenomena. The paragraph concludes with a discussion on the refinement of theories over time, using the germ theory as an example of how scientific understanding evolves with new evidence and experimentation.

Keywords

💡Scientific Explanations and Theories

Scientific explanations and theories are the backbone of understanding in the field of science. They are systematic statements that explain the causes of phenomena. In the video, Mr. Andersen discusses how theories like natural selection explain the process of evolution. The script emphasizes that theories develop through a cycle of questioning, data gathering, analysis, and refinement, as seen in the evolution of the idea of natural selection from Darwin's initial concept to its current understanding that includes sexual selection.

💡Natural Selection

Natural selection is a fundamental mechanism of evolution, first proposed by Charles Darwin. It refers to the process where organisms with traits that are better suited to their environment are more likely to survive and reproduce, thereby passing those advantageous traits to their offspring. In the script, Mr. Andersen uses the example of finches on the Galapagos Islands to illustrate how natural selection leads to adaptation over time.

💡Data Analysis

Data analysis is a critical step in the scientific method, where information is processed and interpreted to draw conclusions. The script mentions that after gathering data, scientists analyze it to see if it supports their initial ideas or hypotheses. This process is essential for developing and refining theories, such as natural selection.

💡Evolution

Evolution is the change in the characteristics of a species over several generations and is a central theme in biology. The script discusses evolution in the context of natural selection and how it can be observed in various phenomena, such as the variation in finch beaks or the development of antibiotic resistance in bacteria.

💡Antibiotic Resistance

Antibiotic resistance is a process where bacteria evolve to withstand the effects of antibiotics, posing a significant challenge in modern medicine. In the script, Mr. Andersen connects the concept of natural selection to antibiotic resistance, illustrating how the same evolutionary principles apply to the adaptation of bacteria to their environment.

💡Feedback Loops

Feedback loops are systems in which the output of a process is returned as input to the same process, either enhancing or inhibiting its operation. The script refers to feedback loops in the context of regulating blood glucose levels and how changes in the insulin receptor can affect this regulatory mechanism, emphasizing the interconnectedness of biological systems.

💡Genetic Information

Genetic information refers to the hereditary information stored in an organism's DNA. The script discusses how changes in genetic information can occur not only through alterations in the DNA sequence but also through mechanisms such as histone modification, which can influence gene expression without changing the DNA itself.

💡Histones and Methylation

Histones are proteins that help package and order DNA within the cell. Methylation is a chemical process that can modify histones, affecting how tightly DNA is packaged and thus its accessibility for gene expression. The script uses these concepts to explain how the environment can influence gene expression, which is a key aspect of epigenetics.

💡Macromolecules

Macromolecules are large molecules, such as proteins and nucleic acids, that are essential for the structure and function of cells. The script mentions the process of amino acids being added to proteins, which is a fundamental aspect of protein synthesis and affects the overall structure and function of the protein.

💡Genetic Drift

Genetic drift is a random change in the frequency of alleles in a population, often due to chance events that reduce the population size, such as a bottleneck. The script uses the example of northern elephant seals and cheetahs to illustrate how genetic drift can impact the genetic makeup of a population.

💡Artificial Selection

Artificial selection is the process by which humans selectively breed organisms with certain desirable traits. The script refers to the selective breeding of fast plants as an example of how artificial selection can influence the genetic makeup of a population, contrasting it with natural selection.

💡Mendel's Laws

Mendel's Laws, including the Law of Segregation and the Law of Independent Assortment, are fundamental principles of genetics that describe how traits are inherited from one generation to the next. The script discusses how these laws can be refined or modified in light of new evidence, such as the discovery of sex-linked traits or polygenic inheritance.

💡Germ Theory

The germ theory of disease is the idea that many diseases are caused by microorganisms, a concept that revolutionized medicine. The script contrasts the germ theory with the earlier Miasma Theory, highlighting the importance of scientific evidence and experimentation in the development of scientific theories.

Highlights

Introduction to scientific explanations and theories, emphasizing the development of natural selection by Charles Darwin.

Process of theory development from initial idea to experimental evidence and refinement.

Natural selection as a mechanism for evolution, illustrated with the example of finches' beak variations.

The importance of modifying theories in light of new evidence, such as the addition of sexual selection to natural selection.

Historical shift from the belief in divine creation to the acceptance of evolution through natural selection.

The scientific method as a feedback loop ensuring theories align with the universe's workings.

Application of theories to understand phenomena like antibiotic resistance in bacteria.

Exploring the impact of environmental changes on gene expression, such as histone modification.

Importance of understanding the order of molecular addition in macromolecules, like amino acids in proteins.

Five ways the College Board expects students to deal with theories and explanations in science.

Justifying claims with evidence as a key skill, demonstrated with an example question on metabolic strategies.

Constructing explanations based on evidence, using the example of antibiotic resistance in E. coli.

Articulating reasons for refining or replacing explanations and theories, as seen with Mendel's Laws.

Making claims and predictions about natural phenomena, such as genetic drift, migration, and artificial selection.

Analyzing genetic data to determine inheritance patterns, exemplified by a cross involving sex-linked traits.

The evolution of scientific theories over time, from Miasma Theory to Germ Theory.

The expectation to apply scientific theories to new data on the test, as a measure of understanding.

Transcripts

Hi. It's Mr. Andersen and this AP Biology science practice 6. It's on scientific

explanations and theories. So remember in science we come up with a good question. We

gather good data. We analyze the data. And then over time we start to develop theories

which explain how the world works. And so natural selection was developed by Charles

Darwin and it's been tested and tested over time. What is it? It's a mechanism that explains

how evolution can occur. In other words the finches on the Galapagos had variation in

their beaks and they each adapted to their specific food supply over time. And so how

does a theory develop? In other words, where do theories come from? Well they start when

a scientist comes up with an idea. They then preform experiments and they look, does the

evidence I'm collecting fit or support this idea? If it doesn't, then I go back. I had

a bad idea. I've got to get a good idea this time. So I come up with a better idea. Perform

more experiments. If the evidence does support the idea, then I can create a theory. And

that theory is used to better understand the universe. So natural selection is a great

example of that. What happens next, then we discover new evidence. And can we modify the

theory a little bit so it can explain this new evidence. And so natural selection had

to be modified when we started thinking about sexual selection. And so if we can, then we

improve upon the theory. And so this cycle occurs over and over and over again. It's

a feedback loop to make sure that our theory matches really what's going on in the universe.

If the theory doesn't match that, so before natural selection we had this idea that God

had simply placed all of the species on the planet, perfectly evolved to where they are.

And so if that theory doesn't fit with the data we're collecting, that leads to a revolution.

And so over time science gets better and better and better. Explanations get better and better.

So again the College Board want you to be able to look at theories and apply theories

in each of the four big ideas. So in evolution, not only should you understand how natural

selection works, but how antibiotic resistance or changes in bacteria as a resistance to

our antibiotics, how that fits into natural selection. Or maybe you understand how feedback

loops work. How we regulate the amount of blood glucose. But what if we have changes

to the insulin receptor? How would that effect our explanation? Or we all know that the genetic

information sits in the DNA. But how do we get changes that aren't related to changes

in the DNA? How can the environment change what genes we're going to express and that

has to do with remember the histones and methylation of the histones are opening up those histones

so we can get to the DNA. Of if we're looking at systems, how is that the order by which

molecules are added to macromolecules? For example the amino acids are added to proteins,

how is that going to effect the overall structure of the protein itself? And so I'm going to

go through the five ways they want you to deal with theories and explanations. And the

first one they would like you to be able to justify claims with evidence. And so which

of the following statements most directly supports the claim that different species

or organisms use different metabolic strategies to meet their energy requirements? And so

these are examples of questions you might find on the test. And so you may want to pause

the video and take a stab at each of these. So you may want to read through A, B, C and

D. As I worked through this, they all were good, but the only one that really got to

the root of changing metabolic strategies was D. So the right answer is D. They also

want you to construct explanations based on evidence. And so let me set this up. We've

got different plates of agar. On these ones there's no ampicillin in the agar. Ampicillin

remember is an antibiotic. On these we do have ampicillin. We have wild type e. coli.

Just regular e. coli. And then e. coli that we've transformed with an ampicillin resistant

plasmid. And so looking at this data, which of the following plates have only ampicillin

resistant bacteria growing? The right answer we would say is C or 4. Because we've transformed

some of these bacteria. Now we probably transformed them here, but they only show ampicillin resistance

in plate 4. Or let's go to the next one. State the conclusions reached my Mendel and his

work on the inheritance of characteristics. And explain how these following deviate from

this conclusion. So here we're trying to articulate the reasons that explanations and theories

are refined or replaced. And so again if I were to do Mendel's Laws I would first say,

the law of segregation. That alleles are going to segregate as we form gametes. And then

the second one is the idea of independent assortment. That genes are not going to effect

other genes. And then I could go through and look at autosomal linkage. Do genes ever assort

non-independently. They do if they're on the same chromosome. Or we could look at sex-linkage

or polygenic inheritance isn't going to follow straight Mendelian inheritance. And so again,

it's not that Mendel was wrong. It's that we had to refine his theory over time. So

this would be like an essay type question. They also want you to be able to make claims

and predictions about natural phenomena. So this would be another essay question. Explain

two of the following three processes using an appropriate example for each. And then

for each process discuss its impact on the genetic make-up of the population. So not

only are we explaining the phenomena, but we're saying you know for each of these how

is that going to impact the genetic make-up? Genetic drift remember is when we decrease

the population size. An example can be a bottleneck of the northern elephant seals or the cheetahs.

Migration would be movement into or out of an area. Artificial selection, like on our

fast plants, is when we're actually doing the choosing who mates with whom. And then

if we go to the last one, this is a pretty tough genetics question you may want to take

a stab at it. So here they're presenting you with a lot of data and then you come up with

alternative explanations. So you could pause the video and take a stab at this one. They

are telling you that we've got a dominant and a recessive allele. They aren't giving

the parental numbers here. It's a cross. They give you the f1 and the f2. And you have to

determine the genotypes of the original parents. So they're giving you the data and then you

have to work backwards to kind of figure out the inheritance pattern that's going on. This

is kind how I work through this. We looked at the parental cross. And so they gave us

a parental of a wild type male and white eyed female. I then kind of gave my two opportunities.

Number one, since we're getting differences in the females and the males we know it's

a sex linked trait. And now I have to figure out, is it sex linked recessive or sex linked

dominant? And so I said here is my wild type male. Maybe the wild type is going to be dominant

and the white eye is going to be recessive. And then here's my other one where the white

eyed females, maybe that's dominant as well. And so then I did all the possible f1s. And

so if we did these two parents, you could do this just as a punnett square. I could

end up having a male that is different than the male in the p generation. And same thing

here. So that fits. So we could have a white eyed male and a wild eye female being created.

But then in the other alternative, it just doesn't match up. And so again you're looking

at data. You're applying that. Seeing how it fits in with a theory or we have to refine

that theory. And so theories get refined over time. So, the germ theory didn't come about

until we could actually see germs and we could test them using the scientific method. So

before that, we thought you got sick using Miasma Theory. There was something like bad

air that moved around and caused us to get sick. And until Pasteur developed his Pasteur

flask and did experimentation on that, you know the germ theory shouldn't have been accepted.

Until we knew this, that air could move into the Pasteur flask, but the bacteria would

start to settle out here, did we know that it was germs rather than bad air that was

being passed on. And so again, theories get better and better over time. And on this test

they want you to be able to apply those theories to new data. And I hope that's helpful.