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Lecture Comments (7)

2 answers

Last reply by: Apolonia Gardner
Tue Nov 24, 2015 1:23 PM

Post by Apolonia Gardner on November 24, 2015


I am a high school senior about to send off my applications for college. I am stuck on one thing – my intended major. Biology and chemistry have been my favorite courses throughout high school, and I would like to get a college degree that will enable me to perform research with viruses. My lifetime goal is to find a cure for a disease. From your experience, what undergraduate major should I shoot for? Biochemistry? Microbiology? Molecular Biology? Immunology? Chemical Biology? Organic Chemistry? Pharmaceutical Science? Any guidance is appreciated.

1 answer

Last reply by: Bryan Cardella
Mon Oct 13, 2014 12:27 AM

Post by Richard Meador on October 12, 2014

at 9:40, you stated pH of 7.4 for blood is slightly acidic.  

1 answer

Last reply by: Bryan Cardella
Fri Mar 14, 2014 3:24 PM

Post by Jacky Tumusiime on March 11, 2014

Fantastic course and a fantastic lecturer. I'd like to suggest yr lectures  be transcripted so that we get your lectur notes plz

Scientific Method

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Origins of the Scientific Method 0:04
  • Steps of the Scientific Method 3:08
    • Observe
    • Ask a Question
    • State a Hypothesis
    • Obtain Data (Experiment)
    • Interpret Data (Result)
    • Analysis (Form Conclusions)
  • Scientific Method in Action 6:16
    • Control vs. Experimental Groups
    • Independent vs. Dependent Variables
    • Other Factors Remain Constant
  • Scientific Method Example 13:58
  • Scientific Method Illustration 17:35
  • More on the Scientific Method 22:16
    • Experiments Need to Duplicate
    • Peer Review
    • New Discoveries

Transcription: Scientific Method

Welcome to, this is the lesson on the scientific method.0000

When we look at the origins of the scientific method and how it exists in today's society, it is not just from the western world.0005

It did not just originate in Europe hundreds of years ago.0013

You tend to hear that a lot, especially, if you are taking biology classes or other science classes in United States,0016

or in the westernized world, you are going to hear about what a bunch of dead white people did from hundreds of years ago.0021

But it is not just from that lineage, there is plenty of evidence that the scientific method came up independently in all different parts of the world.0027

For instance, in ancient muslim philosophy, there is plenty of evidence that they have their own scientific method,0036

a way of finding objective evidence, in terms of how things work in their world.0042

And that is really the whole point in the scientific method, is trying to find the empirical data that is not influenced by subjectivity.0048

It is getting to the facts and being able to replicate that particular experiment repeatedly with different people.0056

Biological study tends to trace its roots back to the work of Sir Francis Bacon,0065

in terms of post dark ages in Europe, getting into the scientific revolution.0070

And this particular gentleman, having a lot to do with influencing the modern day steps,0077

in terms of doing the scientific method effectively and in the right way.0083

It attempts at understanding of phenomena in nature by obtaining clear empirical evidence.0087

It involves a hypothesis and this is not just a random guess, this is an educated guess.0094

It is based on what you have observed already and it is really using your experience,0100

and being very clear about, hey I have observed A, B, and C, I am pretty sure that D will happen.0106

It is an educated guess, you obtain data in the experiment.0113

It could be quantitative meaning having to do with numbers or it could be qualitative.0116

Ideally, you want to go quantitative.0122

You want to have good numbers gathered in your experiment, measuring data with numbers.0124

In that way, any other person could measure the same numbers.0129

it is not really involved with much subjectivity or opinion.0134

But sometimes, quantitative data is not possible, based on whatever particular question you are asking.0138

Qualitative sometimes does work.0144

If you want to see how someone's mood is affected by a certain food or a certain drug,0147

qualitative data may actually be more meaningful then, because it has to do with observing the person0155

and recording what you notice about their mood in a qualitatively way, the quality of that person.0161

Both of these are reliable in different circumstances.0167

Of course, the forming of conclusions.0171

You want to get an answer, you want to figure out what did the data tell us, what does it tell us about our question?0174

Over time, you can get better and better answers, as you come up with better questions and getting into the heart of matter.0182

With the steps of the scientific method, depending on what source you look in,0189

you are going to see sometimes it is a slightly different order or different wording, in terms of how you go back doing this.0193

But this is a classic way to look at it.0199

First, you got to observe something in your environment that piques your interest.0202

That is interesting, that happened, I just observed that.0208

Let us take a circumstance that is not in a lab necessarily.0212

Let us say you are in your house or apartment, it is 9pm at night, all the power goes out.0217

You do not have any candles to light.0226

You go to the drawer where you keep your flashlight.0228

You take out your flashlight, you try to turn it on, it is not working.0231

You just observed flashlight not working.0236

You ask yourself a question, it might seem obvious, but the question is why is not my flashlight working?0239

Your hypothesis might be an educated guess that the batteries are dead.0247

Now, the batteries are no longer functioning that is why this thing would not turn on.0253

And that could be, not necessarily the answer but that is good educated guess, that is your hypothesis regarding this issue.0258

How are you going to obtain data?0266

Data is just a fancy scientific word for information.0268

Actually, most of you do not realize that the data is plural, a datum is the singular version of that word.0272

This is where we are actually experimenting.0281

The way that you could obtain data about this particular battery issue, you take out the old batteries,0283

and hopefully in the dark you could find where you keep the new batteries.0290

You put the new batteries in, you click the ON button, either it is going to work or it is not.0292

That is where you to interpret your data.0300

You interpret your data like let us say, you put the new batteries in and it still does not turn on.0303

You probably just proved your hypothesis false, that it is not the batteries.0310

Maybe it is the bulb, maybe it is the fuse, some other electrical wiring in the flashlight.0314

Depending on what your results are, that influences how you are going to continue.0324

If in this particular flashlight case, you realize it was the batteries because I put new batteries and it is on,0329

end of the story, problem solved.0335

Your conclusion was, it was the batteries, I fixed that problem, moving on.0338

But, if it was not the batteries, maybe I have to go back and redo the experiment by manipulating something else.0343

It is all a learning process.0352

If you know a lot about cars, and your car dies, and ends up on the side of the road,0353

you want to figure out what is going on with my car.0358

People use this without even realizing it.0361

You want to test all these different factors and see how they are affecting the whole system.0364

It is all about isolating the variables and doing it in a very objective sense.0369

We look at the scientific method in action, different group needs to be established.0378

Let us say, you have a goldfish at home, your goldfish is in its bowl.0383

Let me do it in black here.0398

Let us say, you are on your fifth goldfish.0412

You are like, every goldfish I have only lives few months.0416

I want to know how I can prolong the life of the fish.0423

Maybe it is the water, maybe just tap water is not the way to go.0426

Maybe it is something about the PH of the water, how acidic or how basic the water is, maybe that could affect the life expectancy of the fish.0431

A control group is in attempt to mimic the natural environment.0442

You want to get as close as possible to what the natural circumstances and variables are,0449

in that particular organisms existence in nature.0453

With this fish, it definitely has made of population of these gold fish that had been taken out of,0457

in order to give the people's pets.0464

If you could figure out, in this particular population of gold fish in the wild, it is fresh water and the PH is pretty close to a 7.0467

Maybe if the control group is the PH of the water is 7, you have your fish a bunch of fish ideally, not just one.0475

The more numbers you have, the more reliable your results generally are going to be.0484

You have a bunch of gold fish in water with the PH of 7, which means it is not acidic,0488

it is not basic, it is neutral, just real pure water.0492

But the experimental group is where you actually manipulate the PH, you then change the PH in other groups.0496

You will have some fish in, instead of 7.0, you will have some fish in 7.2, some fish in 7.4, and some fish in 7.6.0503

You want to go the other way too.0516

You are going to have some fish in 6.8, 6.6, 6.4 etc.0517

The more groups you can have, the more you can hit those different PH,0524

probably the more reliable your results are going to be, in terms of the specificity of your answer.0528

The reason why I only vary this by .2 increments is because PH is a logarithmic.0534

When you go all the way to an 8 from a 7, an 8 is 10 times more basic than a 7, a 9 is a hundred times more basic than a 7.0541

Going from 7 to 8 to 9 to 10, you are probably going to have a lot dead fish, if you do that.0551

It is the same reason on the side that is lower than a 7, you are in the acidity range there.0558

When you go from a 7 to a 5, a 5 is a hundred times more acidic than a 7, a 4 is a thousand times more acidic than a 7.0564

Just to give you an idea of how this impacts us.0572

With the PH of blood in humans, it is around 7.4, our blood is slightly acidic.0574

But back to our gold fish example, you want to have those experimental groups where just the PH has changed, nothing else.0582

Speaking of just the PH being changed, when you look at the variables, the independent vs. dependent variables.0589

This is how you actually would obtain your data, by looking at these particular parts of the experiment.0594

If you wanted to display it graphically, this would have a big impact on that.0602

The independent variable has to do with the question you are asking.0607

The question you are asking here is, what is the ideal PH for my goldfish, in terms of prolonging its life expectancy?0610

The independent variable is the PH, that is what our question asks to do with, that is what we want to manipulate.0617

In those experimental groups, the only thing that should be changing in those fish bowls0622

or fish tanks should be the exact independent variable, in terms of the quantitative value.0630

The temperature of the water should be the same.0638

The size of the bowls or the tanks should be the same.0640

You want one of the tanks to be a lot bigger because perhaps that fish being able to move around a lot more,0643

compared to its mates and the other particular tanks.0650

Maybe that one gets a little more exercise and that influence its life expectancy.0654

You want to keep all the other factors remain constant.0659

The dependent variable, literally depends on the independent variables.0666

That is how I keep it straight in my head, the dependent variable depends on the independent.0671

What depends on the PH is the success of the goldfish.0678

The dependent variable is a way that you measure the outcome.0683

Maybe, number of days or number of hours, if you want to be specific that the fish is alive.0687

If you could quantitatively measure something else about the fish’s health, that can be very revealing as well.0693

The dependent variable is how the independent variable affected the organism.0701

If you were to graph it, here is your Y axis, here is your X axis, here is our 0.0707

Typically, the independent variable is going to be down here.0717

Here is your independent variable on the X axis, and over here on Y is your dependent.0721

Just like with Math, if you said Y=2X, X is the independent variable and literally, Y depends on whatever you do with X.0728

If I put 2 in for X, of course Y is going to be 4.0741

If I put a 3 in for X, of course Y is going to be 6.0744

This really relates to math of course, science and math are quite related.0748

If we were talking about PH here, we have to adjust this 0 but we can have 7 be here, right here could be 8.0753

And if 6 were here, that is what I meant by adjusting where the 0 is.0768

My point is that, you would have different plotted points for how successful these fish are,0775

that corresponds to the dependent variable.0787

Here is the number of days or hours, or months whatever it might be that the fish is alive0789

and successful in that particular environment.0795

you would have an indication, based on this plotted points.0797

It turns out that, maybe it is 7.2 that could be the answer in terms of like,0802

that is the PH where the fish live the longest.0810

You notice that the way this is set up, it can be replicated, it can be duplicated by another party.0814

The scientific method is never, I got this answer and if you were there,0820

you would have seen it too, and that I swear that is how it happened.0825

It is going to be hard for you to replicate it, but I saw it.0827

The whole point of this is that you want it to be as objective as possible, measurable, and able to be duplicated.0830

Here is other example of the scientific method, this is actually based on a lab that I did in college.0839

The question is, what color or wavelength of light is most effective of providing energy in photosynthesis?0844

Which particular color of light in the spectrum of light is going to be best at making the plant healthy,0851

making it able to make sugar for all of its metabolic needs?0859

The hypothesis, based on your observations of plants, you might think plants are green,0865

I think it is going to respond best to green light.0870

And I know that there are definitely a lot of plants in nature that are not green,0873

but the majority of plants have a lot of green in them and that is because of chlorophyll.0876

But let us say our hypothesis is, I think green light is going to be the most effective.0882

We got to test it now.0889

The control, like we said before, it mimics the natural environment.0891

The control would be white light, light from the sun.0894

That is natural but definitely is mimicking the natural environment, that is what plants evolved in, white light.0898

They are used to absorbing all the different wavelengths, all the different colors of light.0905

The experimental groups should be the individual colors, by themselves, being shined directly on these different plants.0910

Red, orange, yellow, green, blue, indigo, violet, ROYGBIV, you see that down here with this illustration.0917

The ROY is over here to the G and the BIV.0925

And you could see the wavelengths of light, in terms of the nanometers.0928

Light is electromagnetic radiation and the wavelength from one way to the next,0933

this is the actual measurement that has been calculated for these different colors.0939

You could see that the wavelength is much smaller, when we get towards the violet.0944

This down here is zoomed in, on just this particular section.0947

But there you go, there is the ROYGBIV.0952

Ideally, we would have every part of the spectrum represented in the experimental groups.0954

The independent variable, what we are manipulating based on the question is the color of light.0961

That is the only thing you want to be different about those different boxes.0965

The reason why I say boxes, I will illustrate it for you on the next page.0968

You want to have the plant isolated from all the light in nature.0973

you do not want to have a bulb with a green light shining on the plant,0978

while all the other light in this room or outside is shining on it.0982

You want that plant to be isolated in just under that particular wavelength of light.0986

Otherwise, you are not going to know whether it is the green light that have that effect on the plant.0992

Of course, the dependent variable, you can measure it various ways.0996

If this is a plant that naturally keeps growing vertically,1000

the height of the plant could be directly related to how successful it is,1004

in terms of making sugar and being successful as an organism.1007

If it is something like moss which does not grow tall and just grows horizontally out,1012

then height of the plant would not be as effective in giving us a good measurable result.1019

The way that we did in college is, we actually measured amylase levels.1025

Amylase is an enzyme that has to do with the breakdown of sugars.1029

The amount of amylase that the plant was producing was directly related to its metabolic health,1035

in terms of the amount of sugar it is making.1041

It is only going to produce a lot of amylase if, it is in turn producing a lot of glucose or sugar through photosynthesis.1044

Height of the plant can be just as reliable, in terms of giving you an answer.1051

An illustration of how this works, here we go.1057

Here is the control and here is the experimental group.1071

The experimental groups you are going to have red, you are going to have yellow1087

which I know is harder to see, but that is what it says.1098

I do not have an orange marker, it is okay.1100

You are going to have green.1102

I will represent most of the colors here but not all of them, blue and of course violet.1105

Here are the plants, all in their separate little boxes.1122

Here is the control, here is the light in the box that is supposed to be white light.1128

This is a white background, it is hard to represent white light.1141

But whatever kind of bulb or lamp that you use in this, you do want to make sure that the wattage,1144

the power of the bulb, the amount of light that is being emitted from it is the same across the board.1150

You do not want this bulb to be stronger than this one.1157

The only thing you want to vary is that independent variable, and that is just the color of light.1161

Of course, you have got your red light here, you got your yellow light, and so on.1166

We want to make sure that all the other factors the same, the size, the pot, the soil, the amount of water you are giving them.1176

The area of the room you put them in should be the same because on one side of the room,1182

where you are doing this experiment, maybe the temperature is 1° difference.1186

Maybe light from the window is heating up the boxes and you are not even aware of it.1192

You want to try to control all those other variables as much as possible and that is going to make your answer more reliable.1198

You want to know just how the light is influencing the results.1204

After we did this, it turned out that with the green light that plant did not do very well.1210

As it turns out, the plant we used was not a θ plant but it was species similar to that.1224

it is very green plant, when you shine green light on it, it reflects green light.1232

The reason why a green plant looks green is because it is reflecting1236

that wavelength off of those chlorophyll molecules in the cells.1239

If you just shine green light on it, it will not have really anything to absorb, that plant did very bad, it died.1244

With yellow and violet, it did okay.1255

I am going to give violet, just sort of the medium face and yellow hard to see but there it is, medium face.1263

They did okay, the total height over the few months that we did this was pretty good.1274

In our case, the amylase levels per little unit inside the leaves were more decent.1279

But the winners were definitely red, red did very well, almost as good as the control, and blue did very well.1287

And of course, we had to graph all of our results, be very specific quantitatively1300

about how well they do relative to their control.1305

Our results were not surprising to our professors because it turns out that,1309

when you look at chlorophyll and its ability to absorb wavelengths of light, it is really good at absorbing reds and blues.1312

Those are the two big ones.1319

It does absorb some from the yellow, some from the violet, but not nearly as much as red and blue.1321

These wavelengths of light, these colors of light, very effective at allowing the plants to absorb that light1327

and have an energy source to make sugar.1333

Moving on more on the scientific method, it is okay if you make a mistake, it is a learning process.1337

In that particular course that I took, where students were designing their own experiment1342

and they were given a few months to do this.1347

Some of the groups actually had a big mess up, a big mistake, and they had to restart.1350

But you know what, when they made a mistake, they learned from it and they did not do it again.1354

That actually sometimes improved their setup the second time or the third time.1358

Speaking of mistakes, I have a picture here with little stamp commemorating Sir Alexander Fleming.1363

Alexander Fleming made a mistake that led to a huge discovery.1370

He was supposedly growing bacteria colonies on these pea tree dishes, these little plates.1374

He is exposing different conditions, etc, and he realize that on a plate, there was a whole region,1381

and he definitely put the bacteria on it, but there is a whole region that was devoid bacteria, nothing was growing there.1387

He said that it was odd, he took a sample from that region of the agar,1396

the medium that thee bacteria was supposed to be grown on.1399

He tested it and it turns out a fungus, a mold accidentally got in the plate and was inhibiting bacterial growth.1402

He did not like that to happen, but it did happen.1410

He realizes it turns out bacteria cannot grow in the presence of that mold.1413

You know what, that mold is how we got penicillin.1419

That particular mold species penicillium is the genus name.1422

We got penicillin from it and that has saved millions of lives.1427

A lot of people are allergic to it these days, you do not see this much in Emergency rooms1432

or in treatment of bacterial infections.1436

But nonetheless, this discovery that happens on accident really impacted the world in a positive way.1437

It is all a learning experience.1445

These experiments need to have the ability to be duplicated time and time again.1447

Like I mentioned before, the scientific method is not about like, I did this and I saw it happen and you just had to be there.1450

It is not about that, it has to be as objective as possible.1459

Quantitative is preferable, qualitative sometimes works, but you want to be able to duplicate this1463

in other lab with other scientists, over and over again.1470

If it can be duplicated time and time again with the same results,1473

you are on your way to having a decent theory or maybe, eventually a law regarding some kind of phenomenon in nature.1478

Peer review, the whole point is when you are a working scientists, you are in a lab doing this,1486

you want to be able to publish results and have other people look at them, and comment,1491

make suggestions, learn from that experience.1498

Because everybody has their own kind of encyclopedia of knowledge in their head,1500

in terms of what they have decided and what they bring to the table.1505

Scientists, it is supposed to be a team effort, in terms of we are just trying to get to the answers,1509

in terms of how the world works.1514

We all can learn from each other and expand upon previous results.1517

Adjustments need to be made with new discoveries.1523

As time goes on, you know there are new discoveries in terms of how cells work, in terms of what is going on in the brain.1526

If there is a new discovery that refutes a previous theory or refutes a previous information1535

that was gathered through the scientific method, that is okay.1541

It is not like with certain religions, for instance, there are certain dogmas that cannot be questioned,1545

you just have to believe those things and have faith about those.1552

But science is based on physical evidence.1556

If new physical evidence is refuting something from the past, it could be that,1558

the way it was discovered in the past was just not effectively done,1563

they were missing something, and maybe misinterpreting something.1567

New discoveries, they are welcome as long as we get objective empirical evidence1571

that tells about how the world works, it tells us about how life works.1577

Thank you for watching