Lesson video

Hello there, my name is Mr. Wilshire.

And in our lesson today, we are going to be looking at growing yeast and planning it.

Let's get started.

Our outcome for today is to plan an investigation to find out about food sources for microorganisms. There are some key words for our lesson today, so I'm going to say them, and I'd like you to repeat them after me.

The first key word is fungi.

Very good.

Our next key word is yeast.

Excellent.

Next up, carbon dioxide.

Well done.

Next is a fair test.

And finally, variable.

Excellent.

Hopefully, you know what some of those words are already, but if you're not too sure, have a little look at the definitions that are on this screen now.

You can pause the video here and continue when you're confident to do so.

Okay, so hopefully, you are ready to start our lesson.

Growing yeast, the planning stage.

The first part of our lesson is called yeast.

Now, microorganisms are a group of living things that are far too small for us to see with a naked eye.

We would need to use some specialist equipment in order to see them.

You can see here with these pictures that scientists are able to see them using things like microscopes.

Now, the group of microorganisms that we're talking about here include bacteria, viruses, and fungi.

Now, some types of fungus can grow large enough for us to see with a naked eye.

For example, mushrooms, you can see here, mould, and truffles.

I wonder if you've ever seen mushrooms that are not in a woodland or in the countryside.

You can see the mould on the bread there as well.

I wonder if you've ever pulled out a slice of bread to have your toast in the morning or maybe even to make a sandwich, and you found it's a bit green or black or spotty.

That's the mould.

You can see the truffles there, which are actually a bit of a delicacy, and some people like to eat them like that.

Not sure if I would.

Now, yeast is a type of fungus that we can sometimes see without the help of a microscope, as long as there's lots and lots of them that is.

You can see the picture of yeast there, and scientists have identified around 1,500 different species of yeast.

That is an awful lot, isn't it? Using the microscope, I'm sure they'd be able to identify which one is which.

I don't know if you'd be able to identify it just by looking at it like that in the picture though.

So let's stop here and recap.

What is yeast? Pause the video, have a discussion, and restart when you are ready.

Okay, yeast is a type of fungus.

Can you remember how many different types of yeast there was? Scientists predict that there's over 1,500.

Like other living things, yeast can reproduce, and many types of yeast will reproduce through a process called budding.

You can see there a picture of some budding yeast.

A new microorganism begins to grow on existing yeast and stays attached while it grows.

When it's fully grown, it detaches, and is now a fully formed microorganism itself.

So let's stop and think again.

How does a yeast reproduce? Does it do it by making seeds, by budding, releasing spores or dividing in two and splitting? Pause a video here and have a discussion.

Restart when you are ready.

The answer here is by budding.

You remember the picture on a previous slide.

You could see the yeast doing the process of budding.

Yeast needs moisture.

It needs to be warm, and it needs nutrition to grow and reproduce like any other living thing.

It can't make its own food, and it needs to take some nutrition from the environment that it's in.

Stop and think, which of these does yeast need to grow and reproduce? There's lots of options there.

Have a read of them.

Pause the video and discuss.

There's lots of answers here.

Warmth, nutrition, moisture.

Those are three of the things that yeast needs to grow and reproduce.

Now, when yeast takes in nutrition from food, it releases carbon dioxide gas and alcohol.

This process is called fermentation.

You can see here carbon dioxide bubbles on fermenting kombucha.

Now, we can sometimes see evidence of fermentation taking place when carbon dioxide bubbles form just like in the picture there.

This process of fermenting helps to create lots of things like alcohol or sometimes different types of bread.

Yeast is a really useful microorganism.

We can use fermentation to make food and drink products.

The fermentation of yeast is used to make beer and wine.

As you can see here, there's a beer fermentation tank.

They would mix all of the liquid and different flavours with the yeast and to help it to ferment.

Yeast is also very useful for baking as it consumes food during fermentation that releases carbon dioxide gas bubbles, and these bubbles can cause things to rise like dough.

You can see some air pockets in some baked bread there.

The air pockets or holes that we can see in the bread are all made by these carbon dioxide bubbles caused by the yeast as it ferments.

Without yeast, bread will be very flat and very doughy and sticky.

It's used in the making of many baked products including cakes, biscuits, and crackers.

So maybe the next time you eat some bread or a cracker or you're in the bakery section of a supermarket or even a bakery itself, have a little look at some of the products and see if you can see some of those air holes formed by the carbon dioxide bubbles.

So let's stop and think again.

Which of these food and drink products can be made with yeast? Lots of answers there.

Is it cake, bread, carrots, milk, or beer? Have a discussion.

Pause the video and restart when you are ready.

There's a few answers here.

Cake, bread, and beer are all things that need fermentation from yeast and be produced.

So here's your first task for the lesson.

Are these statements about yeast correct or incorrect? First one is yeast is a living thing.

Next one is yeast is a type of bacteria.

After that is yeast makes its own food.

Then fermentation by yeast is used to make bread, and fermentation by yeast produces oxygen.

What do you think? Are they correct or incorrect? The second part of your task there is to change the statements so that they are correct.

Pause the video here and continue when you've had a go at that task.

Good luck.

Right, let's have a look at some answers then.

Were the statements about yeast correct or incorrect? Yeast is a living thing.

Yes, correct.

It definitely is.

It reproduces and can breathe.

Next up, yeast is a type of bacteria.

Well, that's incorrect.

They're not.

They're actually a type of fungi.

Yeast makes its own food, incorrect.

It can't make its own food.

It needs nutrition to grow.

Fermentation by yeast is used to make some bread.

Yes, correct.

And fermentation by yeast produces oxygen, incorrect.

So hopefully, you've had a chance at changing some of these statements to be correct.

Yeast is a type of fungus.

Yeast takes in nutrients from the environment around it, it does not make its own food, and fermentation by yeast produces carbon dioxide, not oxygen.

Let's move on.

The final part of our lesson is investigating food sources for yeast.

Now, Lucas here has been making some bread, and he's mixed together all of his ingredients, including some yeast that's made a bread dough.

He's then left the dough in a warm place to raise for an hour.

And when he came back to his dough, it had doubled in size.

Why do you think this happened? I'd like you to pause the video here and have a discussion.

Why has this happened? Restart when you are ready.

Why has it happened? Whatever discussions you've had, I'm sure you've had some good answers.

Let's have a look.

Now, the yeast and the dough has fed on the other ingredients, and that's produced bubbles of carbon dioxide gas.

Lucas says, "Remember, yeast needs moisture, warmth, and nutrition to grow and reproduce." Yeah, he's right.

I can remember that from before.

Here, you can see a picture of some risen bread dough.

This often happens when you put it into the oven.

When it starts to warm up, it can begin to grow as well.

The bubbles get stuck inside the dough.

This makes it rise up and look bigger.

Let's stop and think.

Why has Lucas' bread dough risen? Is it because the yeast has photosynthesize or has it fermented? Has it breathed or is it frozen? Pause the video here and have a discussion.

Restart when you are ready.

Well, the answer here is because the yeast has fermented.

It definitely hasn't been breathing.

It definitely hasn't frozen, and it's not photosynthesized.

It's not a plant.

Now, Lucas thinks that the yeast must be feeding on the ingredients in the bread.

There's Lucas there, and he is got his list of ingredients for us.

There's a kilogramme of flour, 15 grammes of yeast, 10 grammes of sugar, 10 grammes of salt, and 30 millilitres of vegetable oil.

Lucas says, "I wonder which ingredient is the best food for the yeast?" Hmm, what do you think? And how could Lucas find out? Pause the video here, have a discussion, have a think, restart when you are ready.

Hopefully, in some of your discussions, you are able to decide on the best type of ingredient, but I wonder how we can find out for ourselves and make sure that we're scientific about it so that we get an accurate answer.

Lucas decides to plan a fair test of his own.

He wants to do this investigation to try and find the answer to this question.

What food source is the best for yeast? Here's Lucas here.

He says, "I know that yeast produces carbon dioxide when it consumes food, so I can measure how much carbon dioxide is produced when yeast is given different types of food." Hmm, very good, Lucas.

I wonder how he's going to do that investigation.

He plans to add some yeast, some warm water, and some different types of food into plastic bottles.

He says, "I'm using warm water because yeast needs moisture and warmth as well as food." Yeah, he's right again, isn't he? Then he's going to add a balloon to the top of each bottle to capture the carbon dioxide gas that is produced.

Look, here is his investigation.

He's put salt into one bottle, then sugar, after that is flour, and then he is got the veggie oil at the end.

He's used some different colour balloons there as well to help him remember which one is which.

But more importantly, he's labelled his bottles.

To make it fair, I can see that he's used the same amount of yeast mixture in all of the bottles there, so there's not going to be any discrepancies in his investigation.

He's then going to observe which balloon inflates the most.

Let's stop and think.

What's the name of the gas produced when yeast grows? Is it oxygen, nitrogen, carbon dioxide, or is it helium? Pause the video here, have a discussion, and restart when you're ready.

The answer here is carbon dioxide.

That's the name of the gas produced when yeast grows.

Stop and think again.

Why is Lucas putting a balloon on top of his bottles? Have a discussion and restart the video once you've discussed all these statements.

The answer here is to capture any carbon dioxide gas that is produced.

It's going to come out of the yeast and rise to the top of the bottle and then hopefully inflate the balloon.

Variables are the things that can have an effect on the results of a fair test investigation.

What variables might have an effect on how much carbon dioxide the yeast produces? Pause the video and have a quick discussion.

Restart when you're ready.

Okay, let's go through some different variables.

I wonder if you can spot any of the ones that you came up with as well.

Variables that could have an effect on the amount of carbon dioxide produced are the amount of food inside the bottle, the amount of yeast that's used each time, the amount of water in the mixture, the temperature of the water as well, the size and the shape of the bottles, and the time given for the yeast to ferment.

Lucas asked, "Can you think of any more variables?" Are there any on there that we've missed? Pause the video and have a quick discussion, restart once you've thought of a few more variables.

I wonder if you have been able to add any variables that we've forgotten about here.

Well, in a fair test inquiry, don't forget, all of the variables except for the one that's being investigated must be kept the same.

Lucas says, "So my question is, which food source is the best for yeast? So the one variable that I will change is the type of food." Of course, yes.

He's only allowed to change that.

That must mean that everything else stays the same.

This is so we know any differences we observe are not because of a variable that we're not investigating.

So if all of the bottles were different sizes, they would've different amounts of air stored inside, wouldn't it? And that wouldn't create a fair test because the amount of air escaping might not be the same as in a smaller bottle.

Let's pause and think.

Lucas is investigating which food source is the best for yeast.

Which of these variables will he need to keep the same to make sure that his results are reliable? There's a few different options there.

Read the statements and then pause the video, continue when you are ready.

The answer here, well, there's three different answers.

It could be the temperature of the water, the amount of each food, or the amount of yeast.

Look at the first part of Lucas's plan.

I wonder if you can see anything that needs to change here.

He's chosen four bottles that are the same size and type.

He's added labels to show what food source is going inside sugar, flour, oil, or salt, and he's making sure that they're in each one.

He's using a funnel to add 150 millilitres of warm water to each bottle.

He's then going to add one teaspoon of each food source to the bottles and add one teaspoon of yeast to the bottles as well with sugar and flour and two teaspoons of yeast to the bottles with oil and salt.

Is there anything there that he needs to change, do you think? Pause the video and continue when you've had your discussion.

Well, this is the step that needs to change, the fourth one.

Adding one teaspoon of yeast to the bottles of sugar and flour and two teaspoons of yeast to the bottles with oil and salt.

Lucas needs to make sure that he adds the same amount to each bottle because this is a variable that's going to affect his results.

Laura says, "If you put more yeast in some bottles, and they make more carbon dioxide, you won't know if this is because the food in those bottles is better than if there was more yeast in those bottles." Of course, yeah, he needs to keep it the same.

The same amount in each one.

Stop and think.

Look at the second part of Lucas's plan.

Can you see anything that needs to change here? Pause the video, have a read of those statements, and restart when you are ready.

There were lots of different things here to read, so hopefully you've had a good discussion about that and can see that number seven, "Putting one of the bottles above a radiator and one on a window sill," he needs to make sure they're all in the same place so they all have the same kind of temperature.

Otherwise, he's changing yet another variable.

Pause and think again.

Why is it important to keep all variables except one the same when carrying out a fair test? Pause the video here and restart when you are ready.

The answer here is C.

So we know that our results show the effect of the variable that we are investigating.

So here's the final task in our lesson.

It says, "Plan a fair test investigation to find out which of the ingredients in bread is the best food source for yeast.

Then you've gotta think about what kind of equipment you're going to need and write a list.

The variable that we are changing in each bottle is the type of food given to the yeast here.

So make sure that your plan explains how you are keeping all the other variables the same." Lucas down here says, "Your plan might be based on his ideas, or you might have some of your own," especially if you've been involved in those initial discussions.

Well, best of luck.

Plan your investigation, restart the video when you're ready to go through some answers.

Okay, so here is Lucas's plan.

It might be similar, it might be different.

He's using four identical 500 millilitre bottles.

He's got the same teaspoons.

He's got salt, vegetable oil, yeast, warm water, sticky labels and pens, a ruler and stopwatch.

He's also got some measuring jugs, funnels, four balloons, flour, and sugar.

This is his method.

He's first going to add a sticky label so he can remember what each one does.

He's then going to add 150 millilitres of warm water to each bottle using a funnel.

He's then adding two teaspoons of yeast to each bottle using a funnel.

He's adding one teaspoon of each of the different food sources.

Then he's giving the bottles a gentle swirl to mix the ingredients together.

He's then adding a balloon to the top of each bottle, putting 'em all together in a warm place, because remember, yeast needs warmth to grow.

Finally, he's going to make some observations of each bottle after 10, 20 and 30 minutes, and hopefully, he's not going to move those bottles at all.

Remember, you've only got to look.

So let's summarise our learning.

Yeast is a type of fungus, and it's a living thing that needs to get its own food from its environment around it that can help it to grow and reproduce.

When yeast takes in nutrition from food, it produces carbon dioxide gas and alcohol.

This makes it very useful in baking and in beer and wine making.

Scientists can investigate yeast with fair test inquiries in which they keep most variables the same to see the effect of changing one variable.

I hope that you go on to plan some of your own fair test investigations and find out what happens if you change one variable at a time.

I wonder if you'll use any of this knowledge for some of your science investigations in the future.

Best of luck for all your investigations.

I be Mr. Wilshire.

Thank you very much for listening.