Lesson video

Hello and welcome to today's lesson.

So the lesson today is from the unit, Plant Nutrition and Photosynthesis.

And the title of today's particular lesson is Photosynthesis.

I'm Dr.

Mason, from the Oak National Academy.

We're gonna start by having a look at what the outcome of today's lesson is going to be.

So by the end of the lesson you are gonna be able to identify the reactants and the products of photosynthesis and we'll be having a look at how the plant obtains those reactants and what it does with the products of photosynthesis as well.

And we're gonna create a word summary to help us summarise the whole process and help you to remember it.

As part of today's lesson, there are a number of keywords that I want you to look out for.

It's really important that you know what these words mean and that you're able to use them correctly.

They are producer, chemical reaction, photosynthesis, carbon dioxide, and glucose.

So some really important words there that we need to be looking out for and making sure that we understand so that we can use those in our work.

Today's lesson is split into two parts.

So the first part is about how producers make their own food and that's through the process of photosynthesis.

And then we're gonna take a more detailed look in the second part by looking at the reactants and the products of photosynthesis.

So we're gonna get started with the first part and have a look at how producers make their own food.

Producers, like plants, make their own food, and because of this, they form the start of food chains and food webs.

The food that they make can be passed on through feeding relationships.

The food is made via a process called photosynthesis.

And photosynthesis takes place in the leaves and can also take place in other parts of the plant as well but they must be above ground and have access to light.

If we think about the word photosynthesis we can break it down into two parts.

So you've got photo, meaning requires light, and you've got synthesis, meaning to make.

So in order for plants to make food, it requires light.

You may also be able to think of other words that contain the word photo.

The obvious one that springs to mind for me is photograph, so requires light in order to take a picture.

Now I'm gonna check your understanding.

What I would like you to do is to select true or false to the following statement.

Photosynthesis happens in plant roots.

You can pause the video if you want to while you think about your answer.

Let's have a look at what you put.

Hopefully you ticked false.

So photosynthesis doesn't happen in plant roots.

So the statement above was false.

Now I want you to think about why you chose that answer and select either statement A or B.

So A is photosynthesis happens in plant leaves where it's light, and B is photosynthesis happens in all parts of a plant.

Again, you can pause the video if you want to while you think about choosing an answer.

Let's have a look at the answer.

The answer is A.

So photosynthesis happens in plant leaves where it's light.

And of course we know it doesn't happen in all parts of the plant because for example, it doesn't happen in the roots, and that's because they're below ground and don't have any access to light.

So we know that living organisms are made up of cells and plants are living organism and so are made up of cells.

So what we've got here on the screen on the left hand side we've got picture of a leaf, and then on the right hand side we've got a picture of what it looks like when you look down a microscope.

So you're seeing the leaf in much more detail.

And what you can see here are the cells and they're kind of elongated, rectangular blocks are what they look like.

Those are individual leaf cells and it's inside these cells that photosynthesis takes place.

What I'd like you to do now is to match one correct start of a sentence, which is on the left hand side of the screen, to one correct end of a sentence which is on the right hand side of the screen.

So you're just selecting one box from the left and one from the right that will make a complete, correct sentence.

Again, you can pause the video while you do this, and you'll probably want to, because there's quite a bit to read through.

Let's have a look at the correct answer.

So plant food is made inside plant cells by the process of photosynthesis.

So well done if you got that correct.

Photosynthesis needs light, and that light usually comes from the sun.

However, you could put a plant in a room that has no windows but has a light bulb, for example, the light from the light bulb will also provide the energy needed for photosynthesis.

So as we've just said, light transfers energy from the light source, which is usually the sun, but it could be artificial light as well, and it transfers it to the leaf, and in particular the leaf cells, and that's needed in order for photosynthesis to take place.

Without light, there will be no photosynthesis.

And if there's no photosynthesis then a plant cannot survive.

So it's vital that for this process and for plants to survive that they have access to light.

And different plants require different amounts of light.

Not all plants, for example, those that live on a forest floor require really bright light but they nevertheless do need access to some light because they need energy in order to carry out the process of photosynthesis.

So which of these statements about light and photosynthesis is true? So you just need to select A, B, or C.

So A is, light creates cells for photosynthesis, B, light is made by photosynthesis, or C, light provides the energy for photosynthesis.

You can pause the video if that's helpful while you select your answer.

Let's have a look at the correct answer.

So the correct answer is C, light provides the energy for photosynthesis.

So for example, B is definitely not true, light is made by photosynthesis.

No, the process of photosynthesis doesn't make light and light does not create cells, it just provides the energy for photosynthesis.

So well done if you got that correct.

Now we're gonna have a go at a practise question.

So, Izzy has a houseplant and she's had it for a very long time and it doesn't appear to be growing very well.

You can see it there on the screen, it's quite small, and she keeps it in a dim corner of the room, far away from the window.

So if it's far away from the window and it's in a dim corner, we can assume that it's not getting much light.

So Izzy decides to move her plant so that it's next to the window.

What I'd like you to do is explain why this will help the plant to grow bigger.

You'll need to pause the video while you write down your answer.

Now let's go and have a look at the answer.

So I'm gonna go through the answer, and what you can do is add to your own answer any bits that you didn't get, and perhaps you might want to tick the parts that you did get right.

So putting the house plant next to the window will help it to grow bigger because it will get more light from the sun.

And you can see there the sun beaming through the window in the picture, and light transfers energy from the sun to the plant's leaf cells.

And that provides energy for the process of photosynthesis to take place.

And photosynthesis makes the plant's food, and this food is used as a source of materials for growth and a source of energy for other life processes.

So now we've looked at how producers make their own food, we're going to move on and look at the reactants and the products of the process of photosynthesis in a bit more detail.

So photosynthesis is a series of chemical reactions that happen inside leaf cells.

So photosynthesis isn't just one reaction, it's actually a series of chemical reactions that take place inside the leaf cells.

And again, you can see here we've got a picture of the individual leaf cells and what they look like when you look at them through a microscope.

So what do we mean by chemical reactions? Well, in a chemical reaction you've got substances that are broken down, these are called reactants, and you've got new substances that are made, and these are called the products.

And so in any reaction you've got your reactants and you've got your products.

So reactants are what you start with at the beginning of the reaction, and your products are what you end up with at the end of the chemical reaction.

And so what we're gonna be having a look at here is what the reactants and what the products are of photosynthesis.

So we've got here the reactants, for photosynthesis, it requires water, and it requires carbon dioxide gas.

Carbon dioxide gas is an odourless, colourless gas and it forms part of the air around us.

So every time you breathe in you're taking in some carbon dioxide and that is required for photosynthesis.

And plants take in carbon dioxide through their leaves.

It also requires water, and plants take in water via their roots, which is why it's really important if you've got houseplant, for example, that you water them.

And we've got the products of photosynthesis and the products are glucose.

So that's the food that a plant makes and it uses that glucose to create other molecules that it can use for growth and other processes.

And then you've got oxygen gas, which the plant releases because it doesn't need it, back into the atmosphere.

So plants are really important for producing oxygen.

And of course if we think back to what we've just gone through, it's really important to have light, the process, the chemical reaction between carbon dioxide and water would not happen without light.

And we need the energy from light in order to make that process happen and produce our products, glucose and oxygen.

So as I've said, photosynthesis is not just one chemical reaction it's actually a series of chemical reactions and they all take place inside the cells of the plant.

And it's usually the leaves where this takes place.

In order to help us remember what's happening in photosynthesis, can be useful to have what we call a word summary.

So you can see we've got the reactants on the left hand side and we've got the products on the right hand side.

So we can say water plus carbon dioxide makes glucose and oxygen.

And I think that's a really nice way to summarise the process of photosynthesis to help you remember it.

So what I'd like you to do now is have a go at completing the word summary.

Again, if you pause the video while you do this.

Let's have a look at what you put.

So we've got carbon dioxide, it's in the air around us, and water that plant's take in via their roots produces glucose, and it produces oxygen.

And we'll have a look at each of those in a little bit more detail.

So we'll start with water.

You can see here we've got a plant in some water and you can actually see the roots of the plant there.

And it's in those roots where the water is taken in to the plant and the water goes in via the roots and then it's transported to the parts of the plant where it's needed.

So in this case, it's gonna go into the leaves because that's where photosynthesis will be taking place.

Next we'll have a look at carbon dioxide.

So carbon dioxide is present in small quantities, less than 1% of the air around us is carbon dioxide but plants need to obtain this in order to carry out photosynthesis, and it's taken in through the leaves.

So one of the products of photosynthesis is glucose and it's made inside the leaf cells.

I wonder if you know what glucose is or think about where you might have heard of that before, 'cause you might have come across it in everyday life.

Well, glucose is actually a type of sugar, and sugars are carbohydrates, and this is what the plant's food is.

And you might have heard of glucose, for example, sometimes people who are perhaps low on energy might have glucose tablets.

The glucose, once it's made, is transported around the plant to where it's needed and it's used by the plant for many different things.

It can be used as a source of energy, in respiration, and it also can be used to make other materials.

So you can join the glucose molecules together to make other types of carbohydrate which help make new cells and new tissues to help the plant grow.

And you can see there on the diagram that we've got the arrows showing that the glucose is being transported from the leaves to all the different parts of the plant where it's required.

Another product of photosynthesis, a waste product, is oxygen.

The plant doesn't need this and therefore releases it via its leaves into the air around us.

Oxygen is what we need from the air around us and it's a colourless and odourless gas.

Now let's check our understanding, and I want you to match each of the substance to its role in photosynthesis.

You probably want to pause the video while you do this.

Let's have a look at the answers.

So, carbon dioxide is used for photosynthesis.

Glucose is made by photosynthesis and that's the particular product that we're after here because that is the plant's food.

Oxygen is made by photosynthesis, but that's a waste product, the plant doesn't need that, and water is used for photosynthesis.

So again, like carbon dioxide, it's a requirement for photosynthesis to take place that it has those two materials.

Now what I'd like you to do is to match each substance to its correct description, so thinking of using more technical words here.

And again, you can pause the video if that's helpful.

Let's look at the answers.

So carbon dioxide is a reactant, glucose is a product, oxygen is a product, and water is a reactant.

So if we think back here to our word summary, remember, carbon dioxide and water are both reactants and glucose and oxygen are both products of photosynthesis.

So thinking about light, photosynthesis needs light, can be from the sun, can be from an artificial source.

However, we're gonna have a look here in a little bit more detail at light.

This is a really common misconception and something that a lot of people get wrong.

It's really important that we understand that light is not a substance, and that's why it's not part of the word summary that you can see across the top of the screen.

It's not a reactant, and it's not a product of photosynthesis.

Light provides the energy in order for the reactions to take place and in order for the reactants to undergo a chemical reaction and produce products.

A lot of people get this this wrong so it's really important that we understand the role of light and that we are not calling it a reactant, or a product, because it isn't, it simply provides the energy.

So glucose is a type of sugar.

You can see here we've got a bag of sugar from the shop, a 1 kilogramme bag of sugar.

I would like you to think how many bags, so how many kilogrammes of sugar do you think a large tree like the one in the picture can make in a sunny day? Again, you can pause the video if you want to have a think about this.

A large tree can produce around 90 kilogrammes of glucose in a day.

That's 90 bags of sugar, or equivalent to 90 bags of sugar.

It's also around the same mass as an adult human.

Where do you think most of that mass has come from? Well, most of that mass has actually come from carbon atoms. And if you have a look at the word summary across the top of the page, you'll see it's come from the carbon dioxide.

So the colourless, odourless gas in the air around us that forms a really small percentage of the air has actually produced that mass of glucose because the tree has taken it in, it's undergone the reactions of photosynthesis in order to produce that glucose.

I think that's absolutely amazing.

So what I'd like you to do now is complete the sentences about photosynthesis by filling in the missing words.

You'll need to pause the video while you do this and then we'll go through the answers together.

Right, let's go through the answers.

So if you got the answer correct, you can give it a tick.

If you didn't get it correct, if you just fill in the right answer so that you've got complete correct sentences that will help you to learn.

So the reactants of photosynthesis are carbon dioxide from the air and water from the soil.

Photosynthesis makes the type of carbohydrate called glucose that the plant uses to grow bigger.

Most of the mass of this carbohydrate is made up of carbon atoms, which were taken in from the air.

So well done if you've got those four correct, and as I say, if you didn't, just note down what the right answer is so you'll know it for next time.

Now we're gonna have a go at another practise activity.

So Lucas buys a small plant in a pot.

He keeps the plant in a sunny spot and he waters it whenever the soil is dry, After four months the plant is much bigger.

You can see in the diagram there that the plant has grown.

So what we'd like you to do is to write down what the plant has taken in to enable it to grow.

And then secondly, after four months, the mass of the plant had increased but the mass of the soil was the same at the start.

I'd like you to explain why.

You'll need to pause the video while you write your answer and then we'll go through the answers together.

Let's have a look at the answer.

So, first of all, we asked you to write down what the plant has taken in to enable it to grow.

So it took in water via its roots in the soil and carbon dioxide from the air around us, so carbon dioxide gas, and the plant also took in light to provide energy for photosynthesis.

After four months, the mass of the plant had increased but the mass of the soil was the same as it was at the start, explain why.

Well, the mass of the plant increased because it used carbohydrate from photosynthesis to make new cells and tissues.

So what's happened there is the plants has taken in the reactants of photosynthesis and it's used those to produce a carbohydrate, our glucose, and it's used the glucose to make new cells, new tissues, which is growth.

And most of that mass, as we say, when we looked at the tree and the amount of sugar that it produced actually came from the carbon dioxide in the air.

Most of the mass of glucose is carbon.

The plant takes in water from the soil, but the water was replaced so the mass of the soil didn't decrease.

So hopefully you've got those points.

If you're missing any of those, you might want to add them in to make sure that next time you get it right.

Well done if you've got them all correct.

Now we're gonna go through a summary of today's lesson.

So first of all, producers make their own food using a process called photosynthesis.

So producers remember, are those that form the start of food chains and food webs and quite often are plants, and they're called producers because they make their own food which they can then pass on through food chains and food webs via feeding relationships.

Photosynthesis only happens when it's light and obviously that's because the process of photosynthesis, the reactions require light energy or energy from light.

Photosynthesis is not one reaction, although we've summarised it in a word summary.

It's actually a series of chemical reactions, and they take place inside the plant cells.

The reactants of photosynthesis are water, which plants get by their roots, and carbon dioxide, which is a gas that they're taking from the leaves, from their leaves.

The products are oxygen and glucose.

Oxygen is a waste product, the plant doesn't need it, and releases it back into the atmosphere, so plants are good for the atmosphere, for Earth's atmosphere, and glucose is a sugar, a carbohydrate that the plant uses.

A word summary of the reactants and products of photosynthesis is water plus carbon dioxide makes glucose and oxygen.

And glucose is a really important product that's made and that's the plant's food.

And the plant will take the glucose and it can make it into other substances and use it for growth and creating new tissues.

That's it for today's lesson.

You can head on over and complete an exit quiz to really test your understanding.

And I would suggest that you do that just to check that you definitely understand everything that we've been through today, and hopefully you'll get full marks.

See you next time.