Lesson video

Hello and welcome to this lesson from the Oak National Academy.

Today's lesson is taken from the unit Adaptations, Competition, Natural Selection and Evolution and the title of today's lesson is, A Model of Natural Selection.

Today is a practical lesson which I hope you're really gonna enjoy.

Hiya, I'm Mrs Wheate and I'm gonna be your teacher for today's lesson.

By the end of today's lesson you will be able to use a model of natural selection to make predictions about how population will change over time.

Let's have a look at our keywords.

So we have four keywords for today's lesson and they are natural selection, model, hypothesis and prediction.

Before I show you the definitions I just want to reassure you that you don't need to memorize all of these now.

I'm gonna be quiet for five seconds so you can read them through but if you want to copy them down or read them through more thoroughly I suggest pausing the video and then clicking play when you're ready to move on.

So here are our definitions.

Today's lesson is in three parts.

First of all we're gonna talk about how to use a model in order to demonstrate natural selection.

This model is gonna be using pretty everyday stuff that you can find.

We're gonna be using cocktail sticks and then in the second part of the lesson we're gonna explain what the different parts of the model mean, and then finally we're gonna use the model to make predictions but first of all let's talk about how do we use this model to demonstrate natural selection.

So before we talk about representing natural selection with a model, let's do a quick recap of what natural selection is.

So natural selection is a process through which organisms that are better adapted to the environment are more likely to survive, reproduce and then pass on their genes, their DNA, to their offspring.

It happens over many generations so you cannot see it happening in real time.

We're gonna talk about a really famous example of natural selection which was kind of documented, started being documented about 200 years ago and that's what these moths that I've got in my picture here.

So these moths are an example of natural selection in action.

So what happened was there was variation among the moths, some were light and others were dark, so the darker moths had an advantage, they were better adapted due to their camouflage.

The darker moths are much harder to see, they blend in with their surroundings, the tree bark, much much harder to see, than the white one that stands out a lot more obviously.

So the camouflage allowed the darker moths to successfully compete and avoid being eaten by predators.

Many dark moths survived, reproduced and passed on their genes, their DNA, to their offspring and over generations this trait became much more common.

So that's an example of natural selection, there being variation in a population, in a species, that then leading to an advantage for some of the individuals, that advantage allows them to compete successfully, that means they're more likely to survive than have babies reproduce and then over generations, that's a part of natural selection a lot of people miss out, this is something that takes a long time to happen, so over generations the ones that were more successful and reproduced and survived, their babies will be similar to them because of how inheritance works and then that can lead to changes within a species and sometimes it can lead to entirely new different species.

Okay, let's see if we understood that.

In the process of natural selection, which type of organism is most likely to survive?

Is it A.

the strongest, B.

the best adapted or C.

the fastest?

You can take five seconds now or if you want a bit more time, pause the video, click play when you're ready to see the answer.

Okay, let's look at the answer, so the answer is the best adapted.

We can get a bit fixated and maybe it's because when we talk about natural selection, we talk about this idea of survival of the fittest and that kind of makes it sound like it's this huge wrestling match where the strongest and the fastest are the ones that survived.

It's not always about being strong or being fast, although those things are very useful.

Being camouflaged can be a really good adaptation, being small and being able to hide can be a good adaptation, so it's not just about those kinds of features, it can be a number of different adaptations that are useful, so the most correct answer is the best adapted.

Well done if you got that right.

So one more thing before I introduce the practical, we're gonna talk about what a model is, because the practical is a model, a representation of natural selection.

So models are simple representations that can help us understand complex ideas such as natural selection, and science lessons that use models a lot because a lot of things we talk about in science are abstract or they're too small to see or too far away or too big to see and so we need to use simpler representations to help us to understand them.

So it'll be something you're already familiar with, so models can be a two-dimensional diagram or a description.

So in my picture here it's a model of a particle model of a liquid, this is how the particles and the liquid are arranged and again this is a very simple representation, particles aren't perfect circles but that's how it's represented in this diagram in order for help us to understand it.

So models can also be three-dimensional and physical, so this is an example of how the mammalian gas exchange system works, we've got a glass bell jar which is representing the rib cage, we've got balloons which are representing the lungs, we've got that rubber sheet at the bottom which is representing the diagram, so they can look like that.

Or models can also be analogies, you might have heard it said that the cells are like the building blocks that organisms are made of, so that analogy building blocks, that's something that we're familiar with or from childhood and we're using that to help us try and understand what cells are and how they work, so that's how models work.

Okay, let's check to see if that made sense, so a model is it A, includes every part in detail of the real thing, B is the real thing or C is a simpler version of the real thing.

Take five seconds or if you need a bit more time, pause the video, click play when you're ready to hear the answer.

Okay, what was the answer?

It is C, so a model is a simpler version of the real thing, great job if you got that right.

Okay, we're ready to start talking about how to set up the model, so we need the following, we need around 200 cocktail sticks, half need to be white so 100 white and 100 green, we need roughly a four meter by four meter square of astroturf or grass, we need a tape measure and we need a stopwatch.

So setting up the model, so first thing you need to do is on your playing field or on your astroturf wherever it is you are, you need to measure out an area of square roughly four meters by four meters.

And then once you've done that, you need to scatter the green and white cocktail sticks in this area, so like that in my photo, so over a four meter square trying to as randomly as possible spread out these cocktail sticks.

You don't need to do this perfectly, don't try and make sure that there's one cocktail stick in every single centimeter cubed, just kind of chuck them around this four meter square.

Okay, so that's it set up, really really simple.

Once you've done that, so this is for actually carrying out the model, so using a stopwatch to keep time, collect as many cocktail sticks as you can in 10 seconds.

Set the collected cocktail sticks aside and record how many you've collected in table one on your worksheet and then you're gonna repeat that, so in 10 second rounds collecting as many cocktail sticks as you can and then recording that number, you're gonna repeat step one and two about four more times, so you've done it for a total of five times.

Okay, let's see if you understand how to set up and how to carry out the practical.

Put these steps in the correct order to describe how to carry out this practical, so A, repeat the timing and collecting steps four more times, B, using a stopwatch collect as many cocktail sticks as you can in 10 seconds, C, scatter the green and white cocktail sticks over a four meter by four meter grassy area and D, set the collected cocktail sticks aside and record how many you've collected in a table.

So you can take five seconds now or you can pause the video if you want a bit more thinking time, click play when you're ready to see the correct order.

Okay, let's have a look at the correct order.

So the first step is C, scatter the green and white cocktail sticks over a four meter by four meter grassy area, then you need to B, using a stopwatch collect as many cocktail sticks as you can in 10 seconds, after that the next step is D, set the collected cocktail sticks aside and record how many you have in the table, and then A, repeat the timing and collecting steps four more times.

Great job if you got that right.

Okay, this is the first practice task of today's lesson, so number one, follow the method on the worksheet, A, set up the model, B, carry out the model experiment, and then C, complete table one on the worksheet.

So pause the video whilst you do all of that and click play when you're ready to continue with the lesson, good luck everyone.

Okay, so here's some sample data, this is when I did the practical, these are the results I got, so have a look and compare yours to mine.

Right, okay next question.

Question two, complete table two on the worksheet to show how many sticks were left on the grass.

So in my first round I collected three green cocktail sticks, there are a hundred cocktail sticks in total so I need to do a hundred minus three and that gives me 97.

So at the beginning of round two I had 97 cocktail sticks, in round two I collected two green cocktail sticks from the grass, until the end of round two I have 95 cocktail sticks, so hopefully that makes sense of how to do that, so you need to use table one in order to figure out table two.

Okay, after you've done that you need to do, so use table two, the one you've just filled in, to write a conclusion about the number of green sticks left on the grass compared with the number of white sticks left on the grass, so pause the video now to give yourself enough time to do that and click play when you're ready to see the answers.

Okay, so remember that my results will be very different to yours, these are just the results that I got when I carried out the practical, so this is what my table two looks like.

Right.

Okay, let's have a look at the answer to question three.

So question three was use table two to write a conclusion about the number of green sticks left on the grass compared with the number of white sticks left on the grass, so again this is using my table one and my table two, you might have gotten different data so this is a conclusion based on my data, so for my data there was nearly double the number of green cocktail sticks left on the grass than there were white cocktail sticks, great job everyone.

We've completed the first part for today's lesson, we've talked about what natural selection is, what a model is and then how to use a model to demonstrate natural selection.

Now we're gonna explain what each part of the model means.

So as the model demonstrates natural selection, here's another quick recap of natural selection, so the first step of natural selection is variation, due to random chance some individuals of a species have different traits or characteristics, then there's advantage, some traits can give individuals an advantage, competition, this advantage allows them to compete successfully, for survival this makes them more likely to survive and more likely to have offspring, that's reproduction, so now inheritance, so the ones that have survived and reproduced are now more likely to pass on their traits to their offspring and over generation these traits become more common.

So what does that have to do with cocktail sticks?

So the different parts of our model represent aspects of natural selection, so the sticks themselves they represent a prey animal like a worm or a mouse, so there is variation among the prey, the sticks, some are white and some are green, just like in natural selection variation is an important part of that.

So we've got their habitat which is the green grass or the astroturf, the green sticks are better camouflaged in their habitat, that gives them an advantage and means that they can compete hopefully successfully, and you, you were the predator, so you were eating the prey animal, the cocktail sticks.

So the predators you find it harder to see the green sticks, so more of the green sticks survive, that should have been what happened in your model anyway.

Okay, let's check to see if you understood that.

In this model of natural selection the cocktail sticks represent, is it A, prey, B, predators or C, habitat?

You've got five seconds now or you can click pause if you need a bit more thinking time, click play when you're ready to see the answer.

It is A, the cocktail sticks represented prey, well done if you got that right.

So models are really really important in science to help us to understand ideas that are too abstract, too big or too small or too far away to see, or maybe they take too long to happen in real time, but they're not perfect, they do have these things called limitations, things that make them imperfect and limit them.

So this means models are unable to include every single detail and every single part of the real thing, so in this example is natural selection, the whole entirety of natural selection is not being represented by this model, part of it is but not all of it.

So a limitation of this model, the cocktail stick model, is that it cannot fully demonstrate natural selection as there is no reproduction or no inheritance happening, that's a super super important part of natural selection, otherwise how are these characteristics then becoming more common in generations if there's no reproduction?

So hopefully that makes sense, and let's check to see if it did.

Which of these are not represented in the cocktail stick model of natural selection?

Is it A, variation, B, reproduction, C, advantage or D, inheritance?

We've got five seconds now if you want some more time, pause the video, click play when you're ready to see the answer.

Okay, let's take a look at the answers.

So which of these are not represented in the cocktail stick model of natural selection?

That is B, reproduction and D, inheritance.

Great job if you got that right.

We're ready for the second practice task of today's lesson.

Number one, explain how the model demonstrates each of the following parts of natural selection.

A, variation, B, advantage, C, competition and D, survival.

Then when you've done that, number two, this model is not able to demonstrate natural selection fully as it has nothing in it which represents reproduction and inheritance.

Suggest how it could be improved to show reproduction and inheritance.

So you need to pause the video to give yourself enough time to think about the question and to write your answer down.

Click play when you're ready to see the answer.

Okay, let's look at the answers.

Number one, explain how the model demonstrates each of the following parts of natural selection.

So A, the sticks were different colors, some were white, some were green, this represents variation.

B, the green sticks were the same color as the grass, this represents an advantage as they were camouflaged so they were harder to spot.

C, in the competition, to survive, green sticks had the advantage as they were harder to spot so fewer of them were picked up by the predators.

And D, more green sticks were left on the grass, this represents the green sticks' increased chance of survival.

Great job if you got that right.

Let's look at number two.

So number two, this model is not able to demonstrate natural selection fully as it has nothing in it which represents reproduction and inheritance.

Suggest how it could be improved to show reproduction and inheritance.

So after step two, the method which is putting aside the collected cocktail sticks, you could add a step which involves putting more cocktail sticks onto the grass.

So you should put more cocktail sticks of the color that was collected the least.

So which was probably green sticks, right?

If they're on the grass that means that they evaded predation and they survived more, so you should be adding more of those to the grass.

This represents that the cocktail sticks that were the least collected survived, reproduced and passed on their genes to their offspring.

Great job if you got that right.

We are on to the final part of today's lesson.

So we have talked about what natural selection is, we've talked about what a model is and we've talked about how to use a model to demonstrate natural selection.

We've explained what each part of the model means and now we're finally gonna talk about how do we use that model to make predictions.

We're gonna talk about two really important ideas in science.

We're gonna talk about hypothesis and prediction.

So starting with hypothesis.

Hypothesis is an idea based on observations about how something works.

So if we look at the context we've been doing in this lesson, a model about natural selection, hypothesis for that might be cocktail sticks which are camouflaged are less likely to be collected because they blend in with their surroundings.

So a hypothesis can always be tested using an experiment.

So there are statements that could be true which don't count as hypotheses because they're not testable.

So for example, aliens definitely exist.

That's not a hypothesis, there's not really any way of testing that.

The space is enormous, there's no way of knowing for certain unless an alien actually contacted us until we happen to stumble across and find some form of alien cellular life maybe.

But it's not testable with an experiment.

I can't myself conduct an experiment anyway to determine whether alien life definitively exists.

So it could be true but that's not a hypothesis.

Let's see if we understood that.

Which of the following is a feature of a hypothesis?

A, must be correct.

B, must be testable.

C, must be based on observations.

You've got five seconds or you can pause the video if you're ready to see the answer.

Okay, so the answer is, must be testable and must be based on observations.

Hypotheses don't need to be correct, they just need to be testable, something you can check out with an experiment, and they must be based on observations.

Great job if you got that right.

So predictions and hypotheses have some features in common.

Before we do a science experiment we can make a scientific prediction based on the hypothesis.

Let's look at our definition for prediction.

So it's a statement about what effect a change in a factor might have on an outcome.

So that's quite abstract, let's put it into some context.

So predictions are based on hypotheses, so let's take our hypothesis from before.

So our example hypothesis was cocktail sticks which are camouflaged are less likely to be collected because they blend in with their surroundings.

So let's now make a prediction based on that hypothesis.

So prediction might be if the model is being carried out on grass, so that's the factor that we can change in the experiment.

We can carry this out on grass, we can carry this out on a daisy field, we can carry this out on snow, not something that we can change.

So the prediction part is fewer green sticks will be collected.

I'm making a guess into the future, a prediction based on something that I have changed in the practical.

And then a really important feature of a prediction, which is the same as a really important feature of a hypothesis, is that a scientific prediction can always be tested using an experiment.

So just making random statements that you can't test, that are not testable, aren't predictions, they're not scientific predictions anyway, they're just guesses.

Okay, let's have a practice with that concept.

Make a prediction about what you would expect to happen to the number of green and white cocktail sticks if you conducted the experiment in spring when lots of daisies have grown in the grass.

So this is based again still on our example hypothesis that cocktail sticks which are camouflaged will be collected less.

So our prediction based on that for this example would be overall fewer cocktail sticks of both colors will be collected.

So the number of sticks left on the grass will remain higher for longer.

Okay, now you try.

So a different scenario, make a prediction about what you would expect to happen to the number of green and white cocktail sticks if you conducted the experiment in the summer when the heat has killed most of the grass.

So have a look at my example on the other side of the slide and think now about what's gonna happen to the green cocktail sticks in this scenario.

It's based on the same hypothesis that sticks that are better camouflaged are gonna be collected less.

You can take five seconds or you can pause the video if you want more time, click play when you're ready to see the answer.

Okay, let's have a look.

Overall more cocktail sticks of both colors will be collected.

The number of sticks left on the grass will decrease faster.

Well done if you got that right.

Okay, this is the final practice task of today's lesson.

So all these questions again are based on the example hypothesis I introduced at the start of this section.

That cocktail sticks which are camouflaged are less likely to be collected because they blend in with their surroundings.

So question one, students carried out the cocktail stick model on a grassy area and found that all of the white cocktail sticks had been collected and only green cocktail sticks remained.

Do these results support the above hypothesis?

Explain your answer.

So pause the video while you have a go at question one, click play when you're ready to see the answer.

Let's check your answer.

So these results do support the hypothesis.

The white cocktail sticks were not camouflaged and did not blend in with the surroundings as so more of those were collected.

The green sticks were camouflaged and blended with their surroundings and fewer of them were collected.

Right.

Let's try question two.

So same hypothesis still, cocktail sticks which are camouflaged are less likely to be collected because they blend in with their surroundings.

So question two, if the grass was frosty the results of the model experiment would be different, sorry might be different.

A, use the above hypothesis to make a prediction about how the population of cocktail sticks on the frosty grass would change after multiple rounds of picking them up and setting them aside.

And then B, explain why the results would be different on frosty grass compared to a normal grass.

So you'll need some time to have a go at that.

Pause the video to give yourself some time, click play when you're ready to see the answer.

Okay, let's check our answers.

So prediction, in each round of the model experiment more green cocktail sticks will be collected and set aside than white cocktail sticks.

After each round, white cocktail sticks will make up a bigger proportion of the population of cocktail sticks left on the grass.

Explain why the results would be different on frosty grass compared to normal grass.

So on frosty grass the green sticks are not camouflaged as so more of easier to be spotted by predators.

The white cocktail sticks are camouflaged and harder for the predators to spot.

Right.

Question three, final question.

So mountain hares live in Scotland and Northern England.

They are brown in the summer and most but not all have a completely white coat in the winter, so they change their coat, they change their coat color depending on the season.

Due to rising global temperatures there is less snow in the winter in the mountain hare's habitat.

Use what you have learned.

Carrying out the cocktail stick model of natural selection to suggest what will happen to the population of mountain hares.

Please explain your answer.

So again you'll need some time to have a go at that, pause the video and then when you're ready to check your answer click play.

Okay, let's check your final answer.

The mountain hares that change their coat color to white in the winter are no longer camouflaged.

This means they will be easier for predators to spot.

They are more likely to be eaten by predators so the population may decrease.

Mountain hares that don't turn completely white have an advantage and they're now camouflaged.

This means they will be harder for predators to spot.

They are less likely to be eaten by predators, so the population may increase.

Really great job if you got that right.

We have made it to the end of the lesson.

Let's summaries what we learned to help it stick in our memories.

Scientists use models as simpler representations of complex things and ideas.

We can use colored cocktail sticks to create a simple model to demonstrate natural selection.

This model can be used to make predictions about how a population will change over time or if environmental conditions change.

Great work today.

I really hope you enjoyed the practical.

Take a break now and I hope to see you back really soon for our next lesson.