Hello, my name's Dr.

Warren, and I'm so pleased that you can join me for today's lesson on the effect of gravity on the growth of seedlings, practical lesson.

It's part of the Plant Growth and Development Unit.

I'm here to work with you throughout this lesson and support you all the way through it, especially the tricky parts.

Our learning outcome for today's lesson is, I can measure, record, and explain the growth response of seedlings placed in different orientations.

And here are our keywords.

Gravitropism, a plant response towards or opposing the direction of gravity.

Auxin, plant hormones that affect the growth of plants.

Scientific line drawing, a simple representation of a real object.

And conclusion, a summary of the results of an investigation with data and scientific explanations.

The effect of gravity on seedlings practical lesson has three learning cycles.

Firstly, we're going to look at the investigation itself and carry that out, then we're going to have a look at the results, and finally the conclusion.

So let's get started with our investigation.

Plants gain nutrition through photosynthesis.

So let's remind ourselves of the chemical equation.

Carbon dioxide plus water gives glucose plus oxygen, and it's really important to remember that we need sunlight to make that reaction work.

So plants grow in a way that increases their chances of taking in enough light and water for photosynthesis to occur.

And these responses are called tropisms. For example, gravitropism, which we are gonna be investigating today, is growth stimulated by gravity.

And with every tropism, we have two different types.

We have positive tropism, which is growth towards a stimulus, or negative tropism, which is growth away from a stimulus.

In plants, there are lateral roots and these grow out horizontally, and auxin builds up on the lower side of the root.

So when those meristem cells release the auxin, gravity pushes it down to the lower side of the root.

Auxin inhibits elongation of these cells on the lower side.

And the result of it is the roots grow downwards in the soil in the same direction as gravity.

And this enables them to reach the water needed for photosynthesis.

So in today's investigation, we're going to investigate the effect of gravity on the growth of newly germinated seedlings.

So to start with, we need to take 10 beans and soak them in warm water for 24 hours, and then arrange them on wet cotton wool and leave them to germinate.

So the setup for germination is similar to what you may have done in previous investigations.

You just take a Petri dish, put in some cotton wool with water, and then place your pre-soaked beans on the Petri dish and we'll leave them to germinate.

We'll know once they've germinated because we'll start to see shoots and roots growing from them.

Once they have germinated, select three beans and these are the ones that we are going to follow their growth and we're gonna place them in a bag.

But first of all, take a piece of kitchen roll and fold it and put it into a zipper bag.

Then place your three beans into the bag.

Now, we want to stop these beans from falling to the bottom of the bag.

And the way to do that is just to use a couple of staples, one at the base of where the bean is going and one at the side, and this'll stop them from moving around.

Finally, to complete our setup, we need to spray water into the bag and then seal, so the kitchen roll will be damp.

So here's our experimental setup, what it will actually look like.

We've got our germinated beans there and you can actually see the roots and shoots starting.

And we've got an example of the zipper food bag with the sprayed kitchen roll in there and how our germinated beans are in place with staples.

So really important that you get that all set up correctly.

So once we've got our setup, we then are going to pin the food bag to a notice board, and we're going to leave it there.

And we're gonna produce a scientific line drawing of the beans on day one.

Each day, we need to spray inside the bag to make sure that the kitchen roll remains damp so that the beans have got some water for photosynthesis.

After three days, we're going to observe the growth of the roots and the shoot and produce another scientific line drawing.

So you can see this investigation is gonna go on for quite a while while our beans start to grow.

So each day, we're gonna ask you to rotate the bag by 90 degrees and re-pin.

And when we've done this, again, produce a scientific line drawing of the bean, the root, and the shoot.

And again, each day, we need to spray inside the bag with water to make sure that kitchen roll remains damp.

After three days, observe the growth and produce another scientific line drawing.

So this investigation is kind of ongoing.

We've got our rotating of the bag.

We have got to make sure we keep the water, the kitchen roll wet, and do our line drawings, which is going to show our results.

So to make sure we've got this right, we've got some statements here.

Put the statements in the order to provide a method for this investigation.

So just pause the video now, read through the statements, and then number them one to four in the order which you would do them.

Okay, so number one, first of all, we're gonna soak the beans for 24 hours and then select three that have germinated.

Then we're going to secure them into a zipped food bag with wet kitchen roll.

Then number three, we're gonna pin up the bag and water daily.

And then finally number four, we're going to observe the growth of the seedling and produce a scientific line drawing.

So really well done if you got that order correct.

it's really important that these steps are taken in the right order when carrying out the investigation.

So this brings us to our first task.

Lucas and Jun are making predictions for the growth of the bean seedlings.

Let's have a look and see what they say.

Lucas says, "I predict that the roots will grow towards gravity, whichever way the bag is rotated." And Jun says, "I agree, as plants need to reach water for photosynthesis." So here are the questions.

First of all.

Number one, do you agree? Do you think Lucas and Jun are correct? Two, either add to their predictions with more detail or write your own.

And then finally, we'd like you to follow that method and set up your own investigation.

So pause the video while you do that.

Let's have a look at the answers.

So questions one and two.

So, "I predict the roots will grow down towards gravity, whichever way the bag is rotated as water is usually found in the soil.

The roots will grow to reach water for photosynthesis.

The shoots will grow against gravity as they try to reach sunlight.

This is the energy that is needed for photosynthesis." So if you agreed with Lucas and Jun and you managed to add some more information into those predictions, very well done.

So that brings us to the end of our first learning cycle, and hopefully you've set up that investigation and are ready now to look at the results.

So observations of living organisms can be recorded by making labelled scientific line drawings, as we mentioned in the previous learning cycle.

So here is a scientific line drawing of some muscle cells.

We've got to remember when we're doing a scientific line drawing, it does not look exactly the same as the original object.

We're not drawing in 3D, we are drawing in 2D because it is a clear and simple representation of what we observe.

So when we are drawing some scientific line drawings, we do have some rules that need to be followed.

So here are some simple rules that if we follow them, we'll get some great diagrams drawn.

So first of all, we want to have them a nice large size.

The lines need to be smooth and joined up.

They need to be continuous lines with no sketching.

We always want to have clear labels to the different parts of the diagram.

And on the diagram, no shading apart from some stippling that may be shown in some areas.

So we've got a couple of examples of drawings of a bean seedling, and hopefully your beans will be looking like this after a few days.

Which one do you think is the best? Well, let's have a look at the first one.

Well, in fact, this is a non-example of a scientific line drawing.

Why not? Well, first of all, the sketched lines, you can see those kind of sketchy lines.

There's also quite a bit of shading on the leaf on the shoot tip and actually the bean.

And there are no labels.

So when you are drawing your scientific line drawings, you don't want it to look like that.

Let's have a look at the second one, the one below.

And this is a good example.

Why is it a good example? Because it's smooth and continuous lines.

There's no shading, just a little bit of stippling, and it is labelled clearly, the bean, the shoot, and the roots are labelled.

So when you come to do your own drawings, please remember to include those features.

So select the correct scientific line drawing of a germinating bean.

A, B, or C.

Which is the correct scientific line drawing? Well done if you chose C.

We couldn't have A because there's shading.

And if we look at B, those lines are a bit sketchy, so we couldn't really have that one.

But when we get to C, we've got some good lines, we've got labels, and it's all continuous, and there's no shadings, so very well done if you chose C.

Right, here is our second task.

Draw four scientific line drawings for one of your beans.

You may also use the sample images.

So you can either use the sample images that we have here to do your drawings or your own results.

We have what it looked like at the start, after three days, immediately after rotation by 90 degrees, and three days after rotation.

So pause the video while you do your own line drawings.

So when you look at your scientific line drawings, you must check for the following that we've got smooth, continuous lines, we've got stippling, not shading, and we have got labels.

So make sure all those features are shown.

Right, now we're gonna move on to the final section in the learning cycle of today's lesson where we look at the conclusion to our investigation.

So when we have a conclusion, we need to remember it is a summary of what has been found out at the end of the investigation.

So we've got our results, and when we're starting to write a conclusion, it's always a good idea to have your results in front of you.

So we've got some images of what it looked like at the start, after three days, immediately after rotation by 90 degrees, and then again three days after rotation.

What could you conclude from the observations of these bean seedlings? So that's the first thing.

When we come to write a conclusion, we want to write down our observations, describe what we can see.

A conclusion also explains the findings of the investigation using scientific knowledge.

So here is an example.

First of all, we write down what we can see, describe, and then we can explain it.

So the shoot of the seedling grew upwards against the direction of gravity.

Auxin diffused down from the cells in the tip, causing cell elongation.

This allows the shoot to grow upwards to absorb more light for photosynthesis.

So we're using our scientific knowledge to explain our observations.

Quick check for understanding.

True or false.

Positive gravitropism is a growth response that is needed to aid photosynthesis.

True or false? True.

And why do you think that is? Positive gravitropism of roots means that they grow in the direction of gravity and this allows the roots to absorb more water for photosynthesis.

So very well done if you got that correct.

Right, we have a confidence grid here and you need to tick one box for each statement.

So just read those statements and then tick the box to say you're sure it's correct, you think it's correct, you think it's incorrect, or you're sure it is incorrect.

Okay, let's have a look and see what has been ticked.

So for the first one, this is incorrect.

Shoots use positive gravitropism, that's incorrect.

Also, roots use positive phototropism.

That's incorrect as well.

C, auxin inhibits cell elongation in root cells.

That is correct.

And D, auxin promotes cell elongation in shoot cells.

That is correct as well.

Okay, so what we'd like you to do now is correct and expand on each of the statements shown below.

Shoots show positive gravitropism.

Roots show negative gravitropism.

Auxin inhibits cell elongation in the root cells.

Auxin promotes cell elongation in the shoot cells.

So pause the video while you have a go at this question.

Right, let's have a look at the answers.

So first of all, shoots show negative gravitropism as they grow in the opposite direction to gravity to reach sunlight.

So well done if you got that.

What about the roots? Well, roots show positive gravitropism as they grow in the same direction as gravity.

That is they grow down into the ground towards the centre of the Earth.

So well done if you got both of those.

Auxin inhibits cell elongation in root cells.

Yes, this happens on the lower side.

So the cells on the upper side continue to elongate, making the root grow downwards.

So again, well done if you got that.

Auxin promote cell elongation in the shoot cells.

Well, auxin causes cell elongation in the shoot.

If one side is more shaded, it will diffuse unevenly so the cells on the shaded side elongate and the shoot grows towards the light.

So really well done if you got those explanations correct.

So finally, having gone through that, we'd like you to write a conclusion for the results of your own investigation.

Now remember in a conclusion, you need to include a description of the growth response observed, and also a scientific explanation of why this growth response took place.

In your conclusion, do use the following keywords: auxin, elongation, diffusion, and gravitropism.

And you may wish to use the sample images on the explanation slide to help you.

So pause the video while you have a go at this question, and then we'll have a look at some model answers together.

Okay, so let's have a look at an answer for a possible conclusion for the results of your investigation.

So you wanna try and include these points, and remember, when we're writing a conclusion, we need to put them in a logical order.

So it's good to start with a description first.

As the seedling grew, the roots grew out and down.

The auxin accumulated on the lower side of the root inhibiting cell elongation whilst the cells on the upper side continued to grow.

This caused the root to grow downwards demonstrating positive gravitropism.

The shoot grew out and up.

The auxin accumulated on the lower side of the shoot causing these cells to elongate.

This caused the shoot to grow upwards demonstrating negative gravitropism.

So very well done if you got all those points included in your answer.

Excellent work.

So this brings us to the end of our lesson today, and we're going to just have a quick look at the key learning points.

Beans can be used to investigate the response of germinated seedlings to gravity.

A plant's response to gravity is called gravitropism.

Scientific line drawings can be used to depict the growth response of the seedlings to gravity.

Observational data can be used to conclude the effect of gravity.

Observational data of seedling growth responses to gravity can be explained using ideas about auxin and gravitropism.

I hope that you have enjoyed today's lesson, and we look forward to seeing you again very soon.