Lesson video

<v Instructor>Welcome to this lesson from the unit, Reproduction in Plants.

And the title of today's lesson is The Factors Affecting Seed Germination Practical.

And in today's lesson, you're going to be setting up practical if you are able, and we're going to be looking at how you can investigate different factors that affect seed germination.

It was an opportunity for you in this lesson to be able to make some choices in order to design your own investigation.

My name's Mrs. Barnard, and I'm going to be taking you through today's lesson.

So by the end of today's lesson, you should be able to plan and set up an investigation into the factors affecting seed germination.

So there's some key words for today's lesson, and those are germination, independent variable, control variables, dependent variable and method.

I won't go through the definitions, but we'll pause the video.

So if you want to write them down, then you can do.

So if you'd like to pause now.

So our lesson today is in two parts, and the first part of our lesson is variable.

So these are involved in planning our investigation and what we are going to investigate.

And then the second part of the lesson is writing a method.

So those are instructions for how you will carry out your investigation.

So let's start with the first part of today's lesson, which is variables.

We need to talk first about what we're going to be studying in our investigation and what we're gonna be studying is germination.

Now, cress seeds are one of the most useful seeds to be able to use in this investigation because they germinate quite quickly and they don't need a lot of conditions that are quite specific, but you can use other types of seed for this investigation too.

So germination is the growth of a plant from a seed, and you can see a real closeup here on this image of a seed germinating with the little sprout coming out of it there.

So seeds require a few things in order to germinate.

They need warmth and they need oxygen, and they need water, okay, for that process to start, because there's chemical reactions that take place inside those seeds that allow the germination to start, and those things are required for that.

And after a seed germinates, they continue to grow on, hopefully, if the conditions are correct, into a seed link and then into a new plant.

And this is the process below.

So first of all, we have germination, we have a sprout forming, they continue to grow, and then eventually we get a seed link.

So let's do a quick true or false.

So germination is the process of a pollen grain and an ovum fusing to make a seed.

Now, once you've decided whether that is true or false, decide which of those statements below would best justify your answer.

So pause the video while you decide and then we'll come back and we'll see how you've got on.

Okay, so germination is the process of a pollen grain and an ovum fusing to make a seed.

That is false.

That's actually fertilisation.

The statement, therefore that best justifies your answer is that a pollen grain and an ovum fusing is fertilisation.

Germination is the growth of a sprout from a seed.

So if you got that right, well done.

So let's go on to talk about the variables in this investigation that we're going to plan into germination.

So planning and investigation involves identifying variables.

So variables are factors that might have an effect on the process or the phenomenon that you are investigating.

So let's look at an example from everyday life.

So if you were planning an investigation to make the best cake, what variables do you think might affect the outcome? So maybe have a discussion with your partner on this one or list some of your ideas down.

What do you think would affect your ability to make the best cake? Okay, so the variables that I think could affect the cake, and you might have come up with some different ones, are the mass of the different ingredients that you might use.

So things like butter, flour, sugar.

Also the types of ingredients you might have included, for example, cocoa powder in your cake or you might not have done.

The temperature of the oven that you're going to cook it at, and then the time that that cake spends in the oven.

You might also have thought about different things like the shape of the cake or the size of the tins that you're going to use.

All of those things are factors that could affect whether you are going to make the very best cake.

So if we change the mass of the flour, so if that was the one we decided that we were going to change to see whether it affected the cake, then all of those other variables that you've come up with that you think would affect the cake need to be kept the same.

What we mean is you can only change one variable at a time in an investigation, and then you would have to set up another investigation in order to change a different variable.

So the different cakes then that were produced, we would know were due to the change in the mass of the flour, and we would know that because we kept all of the other factors the same.

So therefore we would know that the change in the cake was not due to any other factor.

The mass of the flour.

So that was the variable that we chose to change, is the independent variable.

And the independent variable is the variable that you choose to change or that you choose to investigate.

Okay, as part of a scientific investigation.

All of the other variables that you have listed that you thought would affect the investigation, must be kept the same.

And therefore those are called control variables.

So if we are changing the flour in our cake, then our control variables become all of the other things.

So for example, the mass of the other ingredients, so butter and sugar.

The types of ingredients.

So for example, what type of sugar are we using or are we using cocoa powder or not? The temperature in the oven and the time in the oven.

So all of those things must be kept the same if we're choosing to investigate the mass of flour.

So the dependent variable is what we measure to conclude on the effect that we've had by changing the independent variable.

So in this case, we were changing the flower, the mass of the flower, and we were keeping all of the other variables the same.

So now we have to decide how we are going to decide the effect of that change in mass of flour.

So what we could look at, for example, is the height of the rise.

So how high the the cake has risen.

We could have a look at the texture or the moistness of the cake, or we could look at the taste of the cake.

And all of those things could be our dependent variable.

So we are measuring those to see the effect of changing the independent variable.

You could say that that variable is dependent on the change that you made to the independent variable.

So the title of the investigation has to include both of the variables that we have chosen.

So for example, this investigation that I've been talking through with you would, the title would be an investigation into the effect of the mass flour on the height a cake rises, and you can see highlighted there are our independent variable mass of flour, and our dependent variable height of cake.

And the control variables would be massive sugar, massive eggs, massive butter, massive cocoa powder, temperature of the oven, time in the oven.

So these are all examples of control variables, and because they've all got measurements associated with them, it makes them much easier to control because we can keep them the same.

So let's have a go at looking at the title of an investigation together and identifying the variables from it.

So from this lesson title, we need to find the independent variable, the dependent variable, and suggest some control variables.

So the title is an investigation into the effect of age on running speed.

So we are looking at the effect of age on the dependent variable, running speed.

So our independent variable is age, our dependent variable is running speed.

So therefore the control variables that we would have to keep the same that could affect the investigation might be the terrain that you're running over.

So like whether it's hilly or it's uphill or downhill, how long you're running for, or the time of day, the sex of the person, so male or female, and the wind speed.

Now there's lots of other control variables that you might think about, but those are just a few examples.

So it's now it's time for you to have a go.

So same process.

So you're gonna look for the independent variable, the dependent variable, and suggest some control variables.

And you're looking at those for this investigation title, an investigation into the effect of temperature on the height of sunflowers.

So if you pause the video, well, you'll have a go at this and then we'll check back and we will see how you've got on.

Okay, let's see how you got on with this one then.

So our independent variable is temperature because that's what we're investigating, and our dependent variable is the height of the sunflower.

So that's what we're gonna measure to see what the effect of changing the temperature was, and therefore our control variables that we would have to keep the same.

So other things that may affect the height of sunflowers are the hours of sunlight, the volume of water, the concentration of minerals.

Now, you might also have thought about some other control variables, but those are just some examples.

So if you've got those right, then well done.

So it's time to now move on to another task.

I'd like to you to match up the name of the variable with its definition.

So we've got independent, dependent and control.

So pause the video while you do this, and then we'll check back and we'll see how you've got on.

Okay, so hopefully you managed that okay.

So the independent variable, then, is the variable that you are investigating.

So therefore the one that you change or choose to investigate.

And the dependent variable is the variable that you measure to conclude on the effects of changing the independent variable.

So the one that you measure at the end to see what's happened.

And the control variable is the variables that are kept the same during the investigation.

Okay, so if you've got all those right, then well done, and it's time to move on to another practise task.

So for your investigation, you are going to be investigating the factors that affect the germination of cress seeds growing on cotton wool.

So what I would like you to do is now that you've had a bit of practise at this, identify the variables which could affect the germination of cress seeds.

So use your knowledge of germination that we discussed at the start of the lesson, and also your general knowledge about the growth of plants, and decide which variables could affect how many cress seeds germinate.

Then identify variables you could measure.

So what could you measure to see the effect of germination? And then once you've identified all those variables, I'd like you to choose one independent variable, one dependent variable, and list the control variables for the ones that you will keep the same.

So this is a bit of an open choice here.

So we'll come back and I'll give you some examples after.

So pause the video for now while you do that.

Okay, so here are some examples of things that could affect germination.

So that may become our variables.

So temperature, light intensity, number of seeds, volume of water, type of seeds.

So identify the variables you could measure.

So what could you measure in terms of germination? You could measure the time taken for the seeds to germinate or the number of seeds that germinate in a given amount of time.

So if you chose to have temperature as your independent variable, and this is an example, you might have chosen one of the other ones.

And then if you chose to have as your dependent variable how many seeds germinate in one week, then your control variables would become all of those other factors that you said could have affected the germination of seeds in this investigation.

So in my example, light intensity, number of seeds, volume of water and type of seeds would have to be kept the same.

Now, there might be some others as well, but this is just an example.

Okay, so hopefully we're ready for you now to move on to thinking about the method for your investigation.

So the next part of our lesson is writing a method for your investigation.

A method is step-by-step instructions on how to carry out a scientific investigation.

A label diagram is used to show how the equipment should be set up, and the label diagram should be a line diagram using the correct drawings for apparatus drawn with a pencil.

It needs to be large and labelled, so it is easy to read.

In this particular investigation, the labelled diagram is quite simple, and here is an example.

So we've got a petri dish that's labelled cotton wool inside cress seeds and water.

It's large enough for somebody to see, and each of the points is labelled very clearly.

So why do we need to write a method? Because scientists make their method clear, so that others can follow it and get a similar outcome.

Each stage of the method could be carried out in different ways.

So scientists will choose the technique and the apparatus that they think is most suitable, and that is what they write down in their method.

The other reason for writing methods is because scientists will evaluate the work of others.

So one scientist will look at another scientist's investigation.

They'll look at how they carried it out in the method, and they'll identify some strengths and weaknesses of the way that that scientist has carried out the investigation, either to critique it or to repeat the experiment, but using a different technique to see if the outcomes are different.

So which piece of equipment do you think would be the best choice for measuring the growth of a seed link? So you've got metre ruler, tape measure, weighing scales, 30 centimetre rulers.

Gonna pause up and let you decide.

Okay, so the correct answer would be a 30 centimetre ruler.

That is the appropriate choice of apparatus equipment for this investigation.

So a method should include actions.

So for example, an action could be pour or way or count, and it should also include the names of apparatus and clear precise measurements.

So here's an example of a step in a method.

So it says count 10 cress seeds and place them one centimetre apart on the cotton wool in the petri dish.

And you can see I've highlighted in different colours the things that this statement should include.

So it's got an action, so count and place.

It's got measurements, so 10 cress seeds and one centimetre apart.

And it's got the names of scientific apparatus, cotton wall and petri dish.

So when you're writing your methods, you need to think clearly and carefully about including those things in each of the steps.

A method should also include how many measurements of the independent variable are being made and the values.

So in the first part of today's lesson, you decided what your independent variable was going to be.

So you also need to decide how many different values of that independent variable that you are going to investigate.

So for example, if your independent variable was temperature, the values that you may choose to investigate might be 10, 15, 20, 25, and 30 degrees C.

So you would measure five different values.

So in this investigation, you would have to set up five different petri dishes, all at different temperatures.

You may have chosen, whether it has water or no water.

And in this case, you would only be making two measurements of your independent variable.

You'd have one petri dish that had no water present, and one petri dish that does have water present.

So those are your two values of your independent variable.

So have a little think about your investigation that you've chosen.

What measurements will you take and how many values of those measurements will you take? So pause up while you decide.

Okay, hopefully you've made some decisions about your own investigation now and the number of different values of your independent variable that you will take.

So a method should also include repeat steps if you are going to be changing the values of your independent variable.

So for example, if your independent variable was light intensity, the method will include a step that states place the lamp five centimetres from the petri dish, but then the last step of the method will state, repeat all of the steps with another two petri dishes with the lamp 10 and 15 centimetres away.

So you don't need to write the whole method out again for the second independent variable value, you just need to have a line at the bottom that says you're gonna repeat all the steps and at what values you're going to repeat those steps.

So which of the following is the best example of a method step, bearing in mind what we have just discussed needs to be included.

So read through those and decide which one you think is the best.

Pause the video and we'll come back and we'll see if you're right.

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

So the correct answer is B.

It says measure, which is an action, 10 centimetres cubed of water, which is a measurement of value in a measuring cylinder piece of apparatus, and pour an action onto cotton wool apparatus into a petri dish apparatus.

So it's got all of the detail that we need in that step of the method.

So Lucas is carrying out an investigation like you are, into the germination of cress seeds.

He has chosen to have water volume as his independent variable.

He's drawn a diagram to start his method, and he has started writing step-by-step instructions.

So he's got his diagram there.

His petri dish and his cotton wall and his cress seeds, and he's labelled how far apart he's going to put them.

So his method starts like this.

Firstly, spread a layer of cotton wool over the bottom of three petri dishes.

Next, measure five centimetres cubed of water in a measuring cylinder and pour it into one of the petri dishes.

So this is just an example start to a method.

So you know how to start your methods, but obviously you are going to alter your steps based on what independent variable that you've chosen.

But this is a good example of how a method can start.

So for your investigation into the effect of a variable that you've chosen on the germination of seeds, use Lucas's method as a model to start your method.

And what I would like you to do is to complete the following.

So first of all, write a list of the apparatus you'll be using.

Draw a label diagram of how you will set up your equipment, and then write a method with clear and detailed steps for carrying out your investigation.

So this is gonna take you a little bit of time, so pause up the video and check back and we'll see how you've got on.

Okay, so let's see how you got on then.

So you are carrying out an investigation into the effect of a variable on the germination of seeds.

So what I've got here is an example, because yours will be dependent on what you've chosen, your variable, your independent variable to be.

So an example of the title would be investigating the effect of a light intensity, which is the independent variable on the germination of cress seeds, which is the dependent variable.

So my apparatus list for this one would be three petri dishes, cotton wool, 10 centimetre cube measuring cylinder, cress seeds, a lamp and a ruler.

You may have a different apparatus list.

In most cases you'll have petri dishes and cotton wool and cress seeds, okay, and a ruler and a lamp, but you might have a few other things depending on what you are changing.

And then this is my diagram.

So we can see a simple diagram with it labelled.

And then for the method, this is again an example method.

So your method will be different, but each step should include actions and apparatus and clear measurements.

So for mine, take one petri dish and cover the bottom with cotton wall.

Measure 10 centimetres cubed of water with the measuring cylinder and pour water evenly over the cotton wall in the petri dish.

Place nine cress seeds one centimetre apart on the cotton wall, and then place the lamp 10 centimetres from the petri dish and turn it on.

And then leave the seeds for seven days, and then count the number that have germinated.

Repeat these steps for two more petri dishes with the lamp at 50 centimetres and a hundred centimetres away.

So that will let me be able to conclude on the effect of light intensity on the number of cress seeds that have germinated in seven days.

So if you have a method that looks like this, then well done.

And it's time to carry out your investigation.

So it's time for a summary of today's lesson.

So some seeds will germinate on cotton wall in the right conditions.

Planning an investigation includes identifying the variables and then selecting the independent dependent and control variables.

The variable that is changed or chosen is the independent variable, and the values of this variable to investigate are selected.

The variable that is measured to conclude on the effect is called the dependent variable.

All the other variables that could affect the investigation are kept the same.

These are called control variables.

A method is a clear and detailed set of instructions that include apparatus, measurements, and actions.

Well done for your work today.

I hope you get your practical investigation set up.

So in our next lesson, we can have a look at your results.