Lesson video

<v Mrs. Waller>Hello and welcome to today's lesson from the Unit Growing Plants.

This lesson is called Plants Without Light.

Hi everyone, I'm Mrs. Waller and in this unit so far we've been growing plants from seeds and finding out what happens to them if we take certain things that they need away.

In the lesson today, you are able to find out and describe what happens to plants when they do not have light.

Let's take a look at the keywords we'll be using in the lesson today.

Plant, light, shade, compare and record.

Take a moment to think about what you might know already about these words and can you describe what any of them mean to somebody else? Today's lesson is in three parts.

In the first part we will be observing our plants that have been growing with no light.

And then we'll be learning a bit more about what happens to plants with no light.

And finally, we'll be thinking about how much light do plants need? Plants are living things.

Just like humans and other animals plants are alive too.

They need light to grow, stay alive and keep healthy.

Take a look at some of these plants growing in light from the sun.

We have our beautiful springtime flower, the crocus and we've got some lovely green healthy plant shoots and some wheat growing in a field under direct sunlight.

Now think about animals including humans.

Do they need light to? Can you think of some places where plants do not grow? The first idea that I've had is I'm thinking of somewhere really dark, maybe down under the ground.

Plants do not grow in places under the ground such as caves where there is no light.

Do you have any other ideas? How about deep down under the sea? Light from the sun cannot reach the bottom of the sea so no plants grow there because it's completely dark.

It's time for me to check your understanding of the first part of this lesson today.

Are you ready? Which statement below is true? Plants do not need light to survive.

Only some types of plants need light to survive or all plants need light to survive.

Are you ready? Yes, all plants need light to survive.

Moving on, true or false, plants do not grow at the bottom of the sea because the fish eat them.

Do you think that is true or do you think that is false? Yes, it is false.

Now can you explain why? You might want to choose from the following two statements.

Plants will only grow where there are no fish.

Or plants will only grow where there is light.

Yes, that's correct, it's B.

We know that plants will only grow where there is light and that's why we don't find plants growing in a deep dark cave in a tunnel or right down at the very, very bottom of the sea.

And now onto our science question for today.

Our science question is, what happens to plants when they do not get what they need? In this lesson, you will observe your plants that have been growing with no light.

I've been waiting for this one, have you? I'm really looking forward to making my observations.

But before we do what do you think will happen to a plant with no light? Just take a moment to think about it and you might want to share your ideas with someone before we look.

So you're going to observe your plants that have been growing with no light and you're going to compare those plants to the plants that have had everything that they need.

They've been growing with water and warmth and light.

Take a minute to remember what does a healthy plant look like? We're looking for a tall, strong stem.

We might be looking for green shiny leaves.

Can you think of anything else that makes a plant look healthy? Pause the video and off you go and make your observations.

Now, it's time to record what you've observed.

Remember scientists record their observations to remember exactly what they did and exactly what happened.

They also record to share their results with other people and maybe other scientists can have a go at the same investigation.

So I'm going to be using a chart to record my results and I've already put in my photographs of the plants growing at the very start of this investigation.

And then I've also added in the photographs of my plants after one week.

So let's just have another look at that plant growing with no light after one week in a cardboard box and the plant that's been growing with everything that it needs.

And we can already start to see some differences here, can't we? I'm so excited to see what's happened today.

I've got my two empty plant pots.

So it's time for me to add in my observations from today's lesson and also for you to add to your own method of recording.

You might be using a chart like mine, but don't forget you might have other ideas.

You might be drawing some pictures or you might be writing about what's happened to your plants.

I'm going to show you the photographs of the plants that I've been growing in my no light investigation.

Here is my poor plant that's been growing for quite a few weeks now in a cardboard box.

Don't forget it was still in a warm place.

I still remembered to water it every week.

And the one thing that was taken away from this plant was the sunlight.

And it certainly does look very, very unhealthy today, poor plant.

What can we notice about the plant? Well, it's certainly wilted and I'm thinking yes, it definitely looks a paler green maybe a little bit yellowy or a very, very light green in colour.

Now we're going to compare this to the plant that I've been growing with water warmth and light over several weeks.

Wow, what a difference.

So you can see that our healthy plant that's had everything that it needs has grown even taller this week.

If I look really carefully, I can even see some little buds and some flowers starting to grow at the top of the plant.

It's much taller, it's much stronger.

It certainly looks healthier and more green.

How about the results of your investigation? So I'm going to add in the results of my investigation into my chart.

I'm adding in my photograph of the plant that's had no light 'cause this is the end of the investigation now.

And also I'm adding in my photograph of the plant that's been growing with everything that it needs.

Are your results similar or different to mine? Take a moment to compare and think about it and maybe talk to somebody else about what's happened in your investigation.

So we're moving on now to the second part of this lesson is where we get a bit more time to think about what happens to plants with no light.

Take a look at this cress.

It's been growing in a dark room.

At first I observed that it had grown taller and thinner and it was almost as if it was growing to try to find some light.

After another week, I observed that the cress began to wilt because the stems could no longer stay upright.

This certainly does look like an unhealthy plant.

We know that plants need light from the sun to make their green colour.

Without light, their leaves and stem can change to a yellow or even a white colour.

Take a look at the photograph of this plant that's been growing in a dark place.

Can you see the leaves and some of the parts of the stem that have already started to turn yellow or a paler green colour? Have any of these things happened to your plant with no light? Some children grew grass heads by putting some soil and some grass seeds in some tights, tying a knot and keeping them damp with water.

Have you ever grown grass seeds in a pair of tights before? They're really fun to make.

Have a look at these grass heads.

So the grass seeds grow into grass and they push through the tights, the material of the tights and it looks like a funny little face.

You can put some eyes on and draw a smiley mouth but it looks like the head is growing grass hair and that's why we call them grass heads.

But have a look at the difference between the grass head on the left to the grass head on the right.

What do you notice? Which grass head do you think was grown in the dark? Yes, you can see that the pale yellow grass grew on the grass head on the right because this plant had no light so it was unable to make its green colour.

I'm going to ask you some quick checks now so I can see that you understand everything that we've covered in section two of today's lesson.

Plants need light from the sun to be able to make their leaves? Now which word do you think would go into the blank space? Is it to make their leaves yellow? Is it to make their leaves white or is it to make their leaves green? Yes, plants need light from the sun to be able to make their leaves green.

It's the plants that haven't had light that were starting to turn yellow.

And maybe after several weeks starting to turn white.

Take a look at this photograph of a cabbage.

Now the cabbage is being cut in half so that we can see the leaves on the inside of the cabbage.

And you'll notice that there's some different colours.

Why do you think the leaves on the inside of the cabbage are a pale yellow colour? Is it because the leaves on the inside get more warmth or the leaves on the inside get more light or the leaves on the inside get less light or the leaves on the inside are rotten? What do you think? It's because the leaves on the inside of the cabbage get less light.

So we can only see the leaves on the inside of this cabbage because it's been chopped in half.

But if you think about the cabbage usually, then the leaves are inside, are covered over they don't get to see any of the light and that's why those parts have been unable to make their green colour so they're a pale yellow colour instead.

Onto our practise tasks now.

I would like you to talk to someone about what you found out about what happens when plants grow with no light.

It would be really interesting if you could look back at your ideas from lesson three.

If you can remember, you might have drawn a picture of an unhealthy plant or a plant with no light or you might have written a description about it.

Were you correct? It would be great if you could draw another picture today to show what happens to plants when they do not have light.

You might also want to write a description of what happens.

Here are some ideas for you to look at.

So here's a drawing of a plant with no light and we can see that it's certainly wilted.

It definitely doesn't look so healthy anymore and it's got yellow thin leaves.

Is that the same as what you found out or if you've written a description you might include some of this information too.

At first, a plant with no light can grow taller and thinner as if it is growing to find some light.

Then the plant will wilt as the stem cannot stay upright.

Plants need light from the sun to make their green colour.

Without light, green leaves can change to a paler green or a yellow or a white colour.

I've got something else for you to think about now.

Izzy and her family went camping for a week.

As they were leaving, she took a photo of the grass where their tent had been.

Have a look really carefully at this photograph.

What has happened to the grass under the tent? Have you ever been camping before? Have you stayed in a tent? And when you've taken the tent down, you might have noticed that the grass under the tent has changed.

So what has happened to the grass under Izzy's tent? Can you talk to somebody about why you think this has happened? So we've got some answers here.

Grass that has been covered for a number of days will turn pale green or yellow or even white because it's had no light from the sun.

Have you ever left toys or anything out on the grass if you have a garden at home or on the school field and when you've moved them you might have noticed that the grass that's been underneath the toys has changed a different colour and it's gone lighter.

It's gone pale green or maybe yellow or white.

And that's because the light from the sun hasn't been able to reach the grass because the toys have been there covering it over just like the tent when Izzy has been camping.

So we know that a tent is made from a material that does not let the light through so the grass can't get the light.

So it can't make its green colour anymore.

Grass is a plant.

Without light from the sun grass cannot make its green colour.

Yes, I've been saying that haven't I? Is that similar to your ideas or do you have other ideas? Okay, so we're moving on to the final part of today's lesson and we're going to be learning about how much light do plants need.

Now we know that plants need light every day.

So what do you think happens to plants at night when it gets dark? It's an interesting one, isn't it? If you take a look at the photograph of this plant in the garden at night do you think it goes to sleep like we do? What do you think? Well, actually, plants can survive for short periods of time without light.

So they're okay overnight.

But if it was a lot longer period of time than that then we know that plants aren't able to stay healthy and stay alive without light, so they would die.

We know that plants stay alive and they actually keep growing at night even when there is no light.

But this is because it's just a very short period of time.

And if it was any longer the plant just would not be able to survive.

We know that all plants need light but different plants grow best with different amounts of light.

So for example, ferns are green plants that do not have flowers and they grow best in warm, damp places like forests where there's actually lots of shade from the sun.

Now here's a different example.

This is a corn plant and it grows from a seed and it doesn't grow very well in the shade, this one 'cause corn plants need about six to eight hours every day in the sunlight.

Corn seeds are planted away from large trees so we don't want them growing in the shade 'cause they could become unhealthy if the leaves from a large tree might block the light.

And that's the light that the corn plant needs to grow and to stay healthy.

Did you know that plants can become unhealthy if they've had too much light or not enough light? So here's the photograph of my plant that was growing with no light.

And can we just take a moment to think what do you think we could do to help a plant that is being growing with no light? Do you think it can become healthy again? Moving on now to some quick questions to check your understanding of the final part of this lesson.

Some plants grow best in the shade.

What does shade mean? Shade is where there is more light.

Shade is where the light has been blocked or shade is where there is bright light.

And the answer is B shade is where the light has been blocked.

So when I was talking about those corn plants they don't grow well if they're near to large trees with lots of leaves because that creates shade where the light has been blocked.

Now here's another type of plant.

It's called bamboo and it's the fastest growing plant in the world.

Which statement do you think is true? Bamboo grows fast in full sunlight because plants need light.

Bamboo grows fast in full sunlight because plants need dry weather or bamboo grows fast in full sunlight because plants need high temperatures.

Think really carefully about this one.

Which one do you think? Yes, bamboo grows fast in full sunlight because we know that plants need light.

My next question for you.

Plants die at night when there is no light.

Do you think that's true or do you think that's false? Yes, it's false.

And why do you think it's false? Have a think about your own ideas or you might want to choose from one of these.

Is it because plants stay alive through the day and the night? Or is it because plants do not need light from the sun? Are you ready? Yes, plants stay alive through the day and the night.

Yes, they do need light from the sun.

So it's certainly not B.

It's definitely A.

Onto our final practise tasks now.

What do you think will happen to a plant that you have been growing in the dark if you put it somewhere light? Can you record your ideas? So maybe you could draw a picture or you could write an explanation of what do you think about your plant.

Maybe it's been in a dark cupboard, maybe it's been in a box somewhere.

If you now put it somewhere with light what do you think will happen to it? Okay, now it's time to have a go at that.

So can you put that plant that's been growing somewhere dark? Can you put it in the light? And can you observe what happens to the plant? Definitely over the next few days, if you're really keen you could keep it growing over the next few weeks.

And could you talk to somebody about what happens to the plant? Here are some ideas for you to think about.

So I think when a plant has turned yellow and pale it is dead and it cannot be made healthy again.

Or maybe I think the light will make the plant stand tall again.

So have a think about those ideas or you might have some different ideas of your own.

I have a final question for you to think about now.

Have a look at this picture.

You should be able to see some plants that are growing near a fully grown tree.

Which plant do you think will grow best? And why do you think this? So do you think that plant A that is growing a little bit away from the tree will grow best? Or do you think that plant B that's growing directly underneath the tree will grow best? So take a moment to make up your mind and don't forget to think about why do you think this? So let's think about those plants.

Plant B is in the shade.

It's growing under the large tree.

It cannot get as much light from the sun can it, as plant A? So plant A will grow the best because it gets more light from the sun and plant B won't get as much light and water as plant A because it is growing under the big tree.

Is that the same as what you thought or do you have other ideas? Let's think about what we know from the lesson today.

Plants are living things that need light to grow, stay alive and keep healthy.

Plants without light can grow taller at first and then wilt.

Their leaves may change to a yellow or a white colour.

Can you remember those funny grass heads? Yes, have a look at the pale grass that was growing without light.

What else can you remember from today's lesson? All plants need light, but different plants grow best with different amounts of light.

The last thing for you to do now is have a go at the exit quiz.

Remember to think like a scientist and I will see you next time.