Welcome to today's lesson.

I'm Mr. Jarvis and I'm gonna be taking you through the lesson today.

Today, we're gonna be planning an investigation.

We're going to be looking at the effect of light intensity on the rate of photosynthesis in algae.

This lesson comes from the unit photosynthesis, factors affecting the rate.

By the end of today's lesson, you should have planned an investigation into the effect of light intensity on the rate of photosynthesis in algae.

There are five key words to today's lesson.

They are rate, light intensity, hypothesis, variable, and control variable.

The definitions of the words are on the screen at the moment.

You can read through them if you want to, now by pausing the video, or wait until we go through the lesson where I'll explain the meanings of those words as we come to them.

Today's lesson is broken down into three parts.

First of all, we're going to look at light intensity and how this affects the rate of photosynthesis.

Then, we're going to move on to thinking about our aim, hypothesis, and variables for our investigation.

And finally, we're going to start planning the method that we're going to use.

So if you're ready, let's get started with our first section, which is all about how light intensity affects the rate of photosynthesis.

The word summary equation for the series of reactions within photosynthesis is water and carbon dioxide gives us glucose and oxygen.

Photosynthesis also needs light.

Photo means light and synthesis means to make, so the process of photosynthesis means to make using light and it makes glucose.

It makes food for the plants, for the producers.

So, light is absorbed by the chlorophyll within leaves.

However, it's really important to note that light is not a substance, it's not a chemical reactant in photosynthesis, and it's not turned into a product during photosynthesis.

It provides the energy for the series of reactions within photosynthesis to take place.

Here's a check.

Which of the following is a reactant in photosynthesis? Is it A, light, B, carbon dioxide, C, glucose, or D, oxygen? I'll pause for five seconds, and then we'll check your answer.

The correct answer is B.

Carbon dioxide is a reactant in photosynthesis.

The other reactant is water.

Remember, light is not a substance, light is not a reactant, and light is not a product.

The light provides the energy that's needed for the chemical processes within photosynthesis to take place.

Light transfers the energy needed for the chemical reactions of photosynthesis to take place.

Light is what we call a limiting factor of photosynthesis, and a limiting factor is a condition that when in short supply, slows down or limits the rate of a reaction, and the rate of a reaction is how quickly a reaction takes place.

When there's little or no light, photosynthesis will stop.

Think about the middle of the night.

There's very little light that's available to plants, so there's not enough energy to drive the reactions of photosynthesis.

The rate of photosynthesis will then increase as light intensity increases.

So, we can see that by the line that we've drawn on the graph.

And as the brightness or the light intensity increases, then rate of photosynthesis will also increase too.

Light intensity is the amount of light reaching a given surface in a period of time.

When light intensity is high, the rate of photosynthesis is usually limited by other limiting factors.

These include carbon dioxide concentration, temperature, and water availability, and we can see the point on the graph where other limiting factors are slowing the rate of photosynthesis down.

Farmers can use artificial light in greenhouses and this increases the light intensity, the amount of light that's hitting a given surface area in a given period of time, and this helps to produce crops faster.

They can also increase the temperature, increase the carbon dioxide concentration in the air, and provide plants with the water that they need, and this means that crops can be grown 24 hours a day and at all times of the year.

Here's a check.

I'd like you to look at the graph.

As light intensity increases, what happens to the rate of photosynthesis? Does it A, decrease, B, increase, C, increase to a maximum amount and then stay the same, or D, increase to a maximum amount and then decrease? I'll pause for a few seconds, and then we'll check your answer.

The correct answer is C.

It increases to a maximum amount and then stays the same, and that's because there are other limiting factors that slow down the rate of photosynthesis, and we looked at those as being carbon dioxide concentration, the temperature, or availability of water as three examples.

That brings us to our first task.

A farmer grows chrysanthemums in a greenhouse to sell the flowers to the public.

I'd like you, first of all, to write a short paragraph to explain how receiving more light could result in the plants producing more flowers per stalk.

And then, secondly, to suggest how else the farmer could increase the yield of flowers.

You'll need to pause the video at this point while you write down the answers.

And then, when you're ready, press play and we'll check to see how well you've done.

Good luck.

How did you find that? I hope you didn't find it too tricky, but let's see how you did.

First of all, I asked you to write down a short paragraph to explain how receiving more light could result in the plants producing more flowers per stalk.

You might have included that the higher light intensity results in an increased rate of photosynthesis, and that means that more photosynthesis produces more glucose, which can be used to provide the energy needed to produce more growth.

Well done if you got that.

Secondly, I asked you to suggest how else the farmer could increase the yield of flowers.

You might have included increasing one or more of the other limiting factors, such as increasing carbon dioxide concentrations in the atmosphere, increasing the temperature of the greenhouse, and making sure that the plants have the water available to them that they need.

All three of those things will increase the rate of photosynthesis, which means they will increase the amount of glucose that's produced, and that can be used to provide more energy for growth.

Well done if you've got any of those in your answer.

That brings us to the second part of the lesson today, and now, we're going to start thinking about the investigation on the effect of light intensity on the rate of photosynthesis in algae, and we're going to start writing our aim, hypothesis, and variables.

So if you're ready, let's move on.

When planning a practical, the first thing we need to decide is what the practical is aiming to achieve.

The aim of this investigation must be specific, concise, and accurate.

For example, for an investigation into the effect of light intensity on the rate of photosynthesis, an aim might be to measure the effect of light intensity on the rate of photosynthesis in algae.

Many algae are small photosynthetic organisms, and we can see some algae cells here under the microscope.

To investigate their rate of photosynthesis, we'll immobilise them in beads.

And to immobilise them, in essence, means to trap them, and that's done by mixing algae with alginate, which is a product from seaweed.

The algae are trapped in the beads but continue to photosynthesize.

Scientists usually state what they think will happen in an experiment and why they think it will happen.

This is what we call a hypothesis.

A hypothesis is an idea, for example, an idea about an outcome which is based on observations and scientific understanding.

Our aim is to investigate the effect of light intensity on the rate of photosynthesis in algae which are immobilised in algal beads, and we can see those algae that have been immobilised in algal beads in the picture on the screen.

Can you make a hypothesis based on the aim of this investigation? I'll pause for a few seconds, but you might want to pause the video while you perhaps either think or write one down.

So, for your hypothesis, you might have written something like this.

As the light intensity increases, the rate of photosynthesis in the algae will increase as the light provides the energy needed for chemical reactions of photosynthesis to take place.

Having written the hypothesis, we now need to think about how we can increase our confidence in it by carrying out an investigation.

Here's a check.

Which of the following are features of a hypothesis? A, it must always be right, B, it should be formed using your scientific understanding, C, it can always be tested by an investigation, or D, it can be based on observations, and there may be more than one of those answers that's correct.

I'll pause for a few seconds and then, we'll check your answer.

The correct answer is B, C, and D.

The features of hypothesis are that they should be formed using your scientific understanding, they can always be tested by an investigation, and they should be based on observations.

Well done if you've got all three of those answers.

When planning an experiment, it's important to firstly identify our variables and the variables are factors that can be changed during an experiment.

The independent variable is the factor that we decide to change.

The dependent variable is the factor that we decide to measure, and the control variables are the ones that we keep the same throughout the experiment.

The dependent variable is the factor that we measure.

Here, we've got water and carbon dioxide giving us glucose and oxygen as the summary equation for photosynthesis.

Water and carbon dioxide are reactants, and algae use the carbon dioxide for photosynthesis.

The more algae photosynthesize, the more carbon dioxide gas is used, and as carbon dioxide forms a weak acid in water, we can measure the level of carbon dioxide by using a pH indicator, and an indicator is a chemical that changes colour at different pHs.

The indicator that we're going to use in this experiment is hydrogen carbonate indicator, and it can be used to measure carbon dioxide levels.

It changes colour at different pHs.

We can see the hydrogen carbonate indicator chart on the screen.

The concentration of carbon dioxide in the indicator causes it to change colour, so we can see where there's on the left-hand side, increasing carbon dioxide in the indicator, and so, the solution turns more acidic, the solution turns a yellowy orange.

When there's reduced carbon dioxide in the indicator, turning it more alkaline, then the indicator turns more purple.

And if we link that to the actual process of photosynthesis, on the left-hand side of the indicator chart, when there's more carbon dioxide in the solution, so reduced photosynthesis, we would expect the indicator to be a yellowy orange.

And when there's reduced carbon dioxide in the indicator because the algae are going to be using that carbon dioxide to photosynthesize, then the indicator will be purple.

The independent variable is the factor that we're changing, and we're looking at the effect of light intensity on the rate of photosynthesis.

Light intensity, remember, is the amount of light that reaches a given surface area in a period of time, and this can be achieved by changing where the algae's placed.

We can, for example, move it closer to the light source to increase the light intensity and move it away from the light source to reduce the light intensity.

The control variables are the factors that we keep the same throughout the experiment.

What control variables, what factors are we going to keep the same for this experiment? I'll pause for a few seconds or if you want some more time, just click pause on the video now, and then restart it when you're ready.

Well, some examples of control variables for this experiment might include the time that we give the algae to photosynthesize.

We might think about the number of algal beads that we're using and keep that the same during the experiment.

The volume of indicator that we use and the starting pH of the indicator should be the same in each case.

And the temperature of the experiment needs to be kept the same, because we know that an increasing temperature will increase the rate of a reaction.

Well done if you've got any of those.

The light source may get hot and warm its surroundings, including the algae if it's close by, and this could affect the results because we know that temperature affects the rate of photosynthesis and other chemical reactions.

So, by placing a large beaker of water in front of the light source, it helps to shield the algae from changes in temperature.

We could also use an LED bulb, which doesn't get hot.

How will you control the other variables in the experiment, such as the amount of time over which the algae photosynthesize and the amount of algae that are present? I'll pause for a few seconds while you think of some answers.

Let's consider the variables in this experiment.

Our aim is to investigate the effect of light intensity on the rate of photosynthesis in algae.

What will your variables be? The independent variable is the variable that we change.

We're going to change light intensity.

The dependent variable is going to be the thing that we measure, and so, we are going to measure the change in pH.

And the control variables are the things that we keep the same, so the time for photosynthesis to take place, the number of algal beads, the volume and pH of the indicator, and the temperature are some examples of the things that we're going to keep the same.

Here's a check.

For each factor, I'd like you to identify the correct variable in the experiment which investigates the effect of light intensity on photosynthesis.

You need to answer either A, independent, B, dependent, or C, control.

We'll look at them one at a time.

So first of all, the volume of the indicator.

Is this the independent, the dependent, or the control variable? The answer is C, it's the control variable.

The volume of indicators stays the same throughout the experiment.

Well done if you got that.

What about our second factor, light intensity? Is this the A, independent, B, dependent, or C, control variable? I'll pause for a few seconds, and then we'll check your answer.

The correct answer here is light intensity is the independent variable.

Well done if you got that.

What about the change of pH over time? Is that independent, dependent, or control variable? The answer here is it's the dependent variable.

It's the factor that we're going to measure.

Well done if you got those.

That brings us to our second task.

You're planning the following investigation.

You're investigating the effect of light intensity on the rate of photosynthesis in algae.

I'd like you to, first of all, write an aim for this practical.

Secondly, I'd like you to clearly identify the variables for this practical and categorise them into independent, dependent, and control.

And thirdly, if you haven't already done so, I'd like you to write a hypothesis for the practical.

Remember, a hypothesis says what you think will happen and why you think it will happen.

You'll need to pause the video, write down your answers, and then when you're ready, press play and we'll check them.

Good luck.

I asked you to write a name for the practical.

Mine was to measure the rate of photosynthesis in algae at different light intensities.

Secondly, I asked you to identify the variables in the practical.

The independent variable, the variable that we're going to change, is light intensity.

The dependent variable, the one that we're going to measure is a change in pH of the indicator.

The control variables, those that we're going to keep the same, include the temperature of the indicator the algal beads are in, the mass or the number of algal beads, the volume of the indicator that we use, the starting pH of the indicator, and the time given for photosynthesis to take place.

And then, finally, I asked you to write a hypothesis for the practical.

Here's mine.

As the light intensity increases, the rate of photosynthesis in the algae will increase as the light provides the energy needed for the chemical reactions of photosynthesis to take place.

Hopefully, you've got a hypothesis that explains what you think might happen and why it might happen.

I hope that you got something similar to that in your answer.

That brings us to the third and final part of today's lesson, and here, we're going to plan our practical.

So if you're ready, let's move on.

We are now going to consider how to carry out the practical and the equipment that we're going to need.

As the algae photosynthesize, carbon dioxide will be used up.

This will result in a change of pH, and the indicator will change colour.

What will you need to measure the pH change? You're changing the light intensity in this experiment.

How will you do this? Remember, light intensity is the amount of light that reaches a given surface area in a period of time.

A method is a list of instructions to follow.

It should be written as a numbered list, starting with a verb, and be short and succinct.

Here's my exemplar method.

You can see, I've written it as a numbered list.

I've also highlighted the verbs in blue.

So, my exemplar method is one, place 15 algal beads into six bijou bottles.

That's 15 algal beads into each bottle.

Add five cubic centimetres of hydrogen carbonate indicator to each bijou bottle using a pipette and measuring cylinder.

Put the lids on the bijou bottles and record the starting pH.

Three, place a lamp on the bench.

Place a large beaker filled with water in front of the lamp to act as a heat shield.

Four, use the ruler to place a bijou bottle at 20, 30, 40, 50, and 60 centimetres from the lamp.

Five, wrap one bijou bottle in foil so that it's in the dark.

Place it next to the 20 centimetre bijou bottle.

Six, turn on the lamp.

Start a stopclock.

Leave the bijou bottles for at least 60 minutes.

And finally, seven, record the pH of the bijou bottle at the end of the experiment.

Here's a check.

How should a method be written? A, listed, starting with a verb, B, numbered, starting with a verb, or C, numbered, starting with then or next.

I'll pause for a few seconds, and then we'll check your answer.

A method should be written as a numbered list, starting with a verb.

That's B.

Well done if you got that.

The final aspect to consider when planning an experiment is hazards, risks, and how to limit them.

A hazard is something that may cause harm, a risk is the harm that the hazard may cause, and a limitation is an action that's taken to reduce the risk of the hazard.

It's really important to identify the risks of hazards in an experiment and put measures in place to reduce those risks.

For example, if we did an experiment to measure the rate of photosynthesis at different light intensities, the following hazards might be identified and methods put in place to limit the risk.

So, the hazard might be electricity use.

The risk is electrical shocks.

And the limitations, the things that we put in place to limit the risk, is that we check that there's no damage to cables before using any electrical equipment and keeping electrical outlets and liquids, such as beakers of water, away from each other.

Another risk is glassware use, and that can be a risk because it can cause breakages or cause cuts.

So the limitations that we have, the things that we put in place to reduce the risk is that we warn other people if we break something and we clear up broken glassware carefully, but also straight away.

And if we can't manage it ourselves, we get somebody to help us do that.

Here's a check.

True or false, it's important to minimise the hazards of risks.

Is that true or false? I'll pause for a few seconds.

The answer to that question is false.

Now, I'd like you to justify that answer.

Is it because A, a hazard is what can cause harm, and a limitation is what reduces the likelihood of risks occurring, and B, a risk is what can cause harm, and a limitation is how much harm that risk can cause.

Again, I'll pause for a few seconds while you decide on which answer's correct.

The correct answer is A.

A hazard is what can cause the harm, and a limitation is what reduces the likelihood of the risk occurring.

Well done if you got that.

That brings us to our final task, and we're going to be planning the investigation.

The investigation is investigating the effect of light intensity on the rate of photosynthesis in algae.

I'd like you to write a method for this experiment.

Write your method as a numbered list, starting with a verb, and use short, succinct sentences.

Then, I'd like you to list the apparatus that you would use.

And then, finally, I'd like you to identify the hazards and their risks, and then plan some appropriate limitations to manage and reduce the risks.

You might, at this point, want to use the table such as this on the screen where we've got the hazard, the risk, and the limitations.

You'll need to pause the video at this point, write down your answers to each of those three tasks, and then when you're ready, press play, and I'll give you some example answers for the tasks and we'll round up today's lesson.

So, here's an example method.

It's similar to the one we saw earlier in the lesson.

It's a numbered list and it starts each sentence with a verb.

I'm not gonna read through that method again.

If you want to read through it for yourself, just pause the video at this point, and then carry on when you're ready.

Next, I asked you to list the apparatus that you're going to need for this experiment.

Here's the apparatus that I'm going to need to carry out my method.

I'm going to need some pre-prepared, immobilised algal beads, at least 90.

I need some hydrogen carbonate indicator solution, at least 30 cubic centimetres, cherry red colour at 8.

4 pH.

I'm gonna need six bijou bottles, a graduated teat pipette, a 10 cubic centimetre measuring cylinder, a spatula, some kitchen foil, a light source, for example, a bench lamp, a large clear beaker filled with water to act as a heat shield, a metre ruler, a stopclock, and an indicator chart to determine the pH of the solutions.

And then, finally, I asked you to identify the hazards and their risks and plan some appropriate limitations to manage and reduce the risk.

Again, here are some limitations that I would put in place from my method.

So, electricity.

The risk is electric shocks, so I'm going to check that there's no damage to cables before they're being used, and I'm gonna keep the electrical outlets away from the beaker of water.

Glassware is another hazard.

Breakages can cause cuts.

So if there's breakage, I'm going to warn other people and clear up the glassware as quickly as I can.

Spilt liquids are also a hazard that can cause slips or falls.

So again, I'm gonna warn people if I spill anything and clean up the spilt liquid really quickly.

And use of chemicals is another hazard, and the risk is that those chemicals could get into my eyes or on my skin, so I'm going to wear safety goggles when I'm handling the chemicals and I'm going to wash my hands to make sure the chemicals are washed off.

That brings us to the summary of today's lesson.

Today, we've seen that photosynthesis needs light.

Light is not a substance, product, or reactant in photosynthesis.

It transfers the energy needed for the chemical reactions of photosynthesis to take place.

As light intensity increases, the rate of photosynthesis increases, and we can investigate the effect of light intensity on the rate of photosynthesis in algae by planning an experiment.

We can write a hypothesis that we'll test.

The hypothesis is an idea about the outcome, which describes how it will change and why.

And when planning an experiment, we need to identify the variable that will change, that's the independent variable, in this case, light intensity, the variable that we'll measure, that's the dependent variable, and in this case, it's the change in pH, and the control variables, ones that we keep the same.

So, the temperature, the number of algal beads, the amount of indicator in the solution, and the time that we allow the photosynthesis to occur over.

I hope you've enjoyed the lesson and I hope that you've enjoyed planning that practical.

I look forward to seeing you again soon.

Bye-bye for now.