pondweed photosynthesis experiment a level

Practical Biology

A collection of experiments that demonstrate biological concepts and processes.

Observing earthworm locomotion

Practical Work for Learning

Published experiments

Investigating factors affecting the rate of photosynthesis, class practical.

In this experiment the rate of photosynthesis is measured by counting the number of bubbles rising from the cut end of a piece of Elodea or Cabomba .

Lesson organisation

The work could be carried out individually or in groups of up to 3 students (counter, timekeeper and scribe).

Apparatus and Chemicals

Students may choose to use:.

Thermometer, –10 °C –110°C

Coloured filters or light bulbs

Push-button counter

Potassium hydrogencarbonate powder or solution (Hazcard 95C describes this as low hazard)

For each group of students:

Student sheets, 1 per student

Beaker, 600 cm 3 , 1

Metre ruler, 1

Elodea ( Note 1 ) or other oxygenating pond plant ( Note 2 )

Electric lamp

Clamp stand with boss and clamp

Health & Safety and Technical notes

Normal laboratory safety procedures should be followed. There is a slight risk of infection from pond water, so take sensible hygiene precautions, cover cuts and wash hands thoroughly after the work is complete.

Read our standard health & safety guidance

1 Elodea can be stored in a fish tank on a windowsill, in the laboratory or prep room. However it is probably a good idea to replace it every so often with a fresh supply from an aquarist centre or a pond. (It’s worth finding out if any colleague has a pond.) On the day of the experiment, cut 10 cm lengths of Elodea , put a paper-clip on one end to weigh them down and place in a boiling tube of water in a boiling tube rack, near a high intensity lamp, such as a halogen lamp or a fluorescent striplight. Check the Elodea to see if it is bubbling. Sometimes cutting 2–3 mm off the end of the Elodea will induce bubbling from the cut end or change the size of the bubbles being produced.

2 Cabomba (available from pet shops or suppliers of aquaria – used as an oxygenator in tropical fish tanks) can be used as an alternative to Elodea , and some people find it produces more bubbles. It does, though tend to break apart very easily, and fish may eat it very quickly.

3 If possible, provide cardboard to allow students to shield their experiment from other lights in the room.

Ethical issues

Look out for small aquatic invertebrates attached to the pond weed used, and remove them to a pond or aquarium.

Need help with Investigating Photosynthesis? Ask our AI Assistant

Review generated flashcards

to start learning or create your own AI flashcards

Start learning or create your own AI flashcards

StudySmarter Editorial Team

Team Investigating Photosynthesis Teachers

• 11 minutes reading time
• Checked by StudySmarter Editorial Team
• Bioenergetics
• Biological Molecules
• Biological Organisms
• Biological Processes
• Biological Structures
• Biology Experiments
• Cell Communication
• Cellular Energetics
• Chemistry of Life
• Communicable Diseases
• Control of Gene Expression
• Ecological Levels
• Energy Transfers
• Genetic Information
• Microbiology
• Organ Systems
• Plant Biology
• Reproduction
• Responding to Change
• Substance Exchange

Jump to a key chapter

Photosynthesis Refresher

Photosynthesis is the process by which Plants , and some other organisms, produce their own energy source , making them autotrophs or producers rather than Heterotrophs or consumers, which gather energy by consuming other Animals . They do this by harnessing light energy from the sun in the form of photons and converting it to chemical energy in the form of sugars. They then use these sugars not only for Respiration but also as a part of their structure, forming them into Polysaccharides such as cellulose and many other compounds.

The light energy is captured by chlorophyll contained within the chloroplasts of the plant and is only one of three things necessary for photosynthesis to occur. The other required elements are water and carbon dioxide .

Learn more about all these elements by taking a look at our Photosynthesis article

C a r b o n d i o x i d e + W a t e r → L i g h t e n e r g y G l u cos e + O x y g e n

6 CO 2 + 6 H 2 O → C 6 H 12 O 6 + 6 O 2

Photosynthesis does not occur at a constant rate regardless of external conditions, rather, its rate is dependent on several external conditions. These are explored further in our Rate of Photosynthesis article, but briefly, they are temperature, the light intensity the plant is exposed to and the level of carbon dioxide in the surrounding air.

Experimental Design

When conducting an experiment , it is important to remember how to design an experiment properly . This includes the formation of a hypothesis and the identification of variables . We must also ensure that the results are as accurate and precise as possible, along with the results being repeatable and reproducible .

Once we have the results, we must evaluate the presence of errors and the significance of the results.

Key Experimental Terms

Variables - A variable is a factor whose value may change, unlike a constant.

Constant - A constant is a factor whose value is fixed.

Experiments to Investigate Photosynthesis

We can perform many experiments to investigate photosynthesis , with some of the simplest involving simply changing factors impacting the Rate of Photosynthesis and observing its effect . A basic overview of this type of experiment would be picking the factor impacting the rate of photosynthesis you wish to observe and then maintaining the other two at a set level.

Investigating Photosynthesis Practical: Pondweed

One of the easiest practicals to investigate photosynthesis and the effect of varying limiting factors on the rate of photosynthesis is using Cabomba or Elodea plants, more commonly known as pondweed , within a boiling water tube . These aquatic plants are easy to grow and commonly available from aquarium shops.

These plants release oxygen bubbles from the cut end when undergoing photosynthesis, which can be used to gain insight into the rate of photosynthesis. This can be done in two ways:

Counting the number of bubbles produced within a set time frame, with more bubbles means faster photosynthesis.

By measuring the volume of oxygen produced within a set time frame using an inverted, water-filled measuring cylinder or syringe and delivery tube. A higher volume of oxygen produced means faster photosynthesis!

The use of aquatic plants allows for all variables of photosynthesis to be easily controlled, as the temperature can be moderated by heating or cooling the water, light intensity by regulating the amount of light the plant is exposed to within its tube and carbon dioxide levels can be modified by adding sodium carbonate to the water.

Investigate the Rate of Photosynthesis: Light Intensity And Pondweed

An example of an experiment using pondweed is varying light intensity. Below is an overview of the equipment and methodology to follow!

• Fill the boiling tube with sodium hydrogen carbonate solution and place it into the rack.
• Cut an 8 cm long piece of pondweed, then place it into the tube using the tweezers before immersing it gently with the glass rod.
• Position the light source five centimetres from the tube, turn it on and leave it for five minutes.
• Start the stopwatch and count the bubbles produced for one minute.
• Repeat steps 3 and 4 five times, recording the results each time in a table.
• Calculate the average number of bubbles produced in one minute at a 5 cm distance.
• Repeat steps 3 to 6 at different distances from the light source, ensuring that you adjust the length in consistent increments, such as 5 cm from the tube, 10 cm, 15 cm, and so on.
• Plot a graph of oxygen produced (number of bubbles) against the distance from the tube, remembering that the independent variable goes on the x-axis.

Effect of temperature & CO 2 : Pondweed Photosynthesis Investigation

The same principles of this investigation can also be applied to investigating the other two limiting factors of photosynthesis. The impact of temperature can be tested by maintaining the lamp at one distance and then varying the temperature using a water bath while keeping the 1% solution constant. The impact of carbon dioxide (CO 2 ) availability can be measured by keeping the temperature stable and maintaining the lamp at the same distance but varying the concentration of the solution used.

What each of these graphs is likely to look like is described further in our rate of photosynthesis article, but each of them will likely plateau at some point. This is where the factor being tested is no longer the limiting factor. By combining the results of each of these experiments, the theoretical maximum rate of photosynthesis can be achieved.

Photosynthesis Investigation Answers: Hydrogen Carbonate Indicator and Gas Exchange

If you immerse pondweed in a solution containing carbon dioxide , it will gradually deplete the carbon dioxide from the solution unless the carbon dioxide removed during photosynthesis is replaced somehow. This depletion of carbon dioxide can be visualised using hydrogen carbonate , an indicator which changes colour depending on the carbon dioxide present. These colours are outlined below.

As you hopefully know, photosynthesis can only occur in the light , as light-dependent reactions require energy gained from photons . This means that CO 2 is only absorbed by most plants when they are exposed to light. When a plant is in the dark , it ceases absorbing CO 2 for photosynthesis but continues to undergo Respiration . This means that the plant also ceases releasing oxygen into the environment and begins to absorb oxygen from the environment.

By placing the pondweed in a hydrogen carbonate solution that has had sodium hydrogen carbonate added until it turns yellow, we can see how light vs dark affects the rate of CO 2 uptake from the environment. By stoppering the tube, we can prevent CO 2 from entering the tube. We can then shine the light on the tube and watch the colours gradually change as photosynthesis occurs.

Repeating the experiment , but this time instead of exposing the tube to light, placing it in a dark place allows us to observe the impact of light vs dark on Gas Exchange for photosynthesis . After leaving it for the same length of time it took the light tube to turn purple, you should see a much higher CO 2 concentration.

Investigating Photosynthesis - Key takeaways

• Photosynthesis is used by plants to generate sugar from CO 2 and water in a reaction powered by light energy absorbed from photons.
• Experimental design necessitates the identification of independent, dependent and control variables, along with a hypothesis.
• The impact of each limiting factor on the rate of photosynthesis can be tested by controlling two and altering a third, with the rate of photosynthesis being measured by the number of oxygen bubbles produced within a set time period.
• The impact of light vs dark on Gas Exchange can be tested by using a hydrogen carbonate indicator to measure the amount of CO 2 present within a solution.
• Pondweed is an ideal plant choice for photosynthesis experiments, as its aquatic nature allows for easy control of the CO 2 levels, temperature and light intensity it is exposed.

Flashcards in Investigating Photosynthesis 1

Cabomba or Elodea plants (also known as pondweed)

Learn with 1 Investigating Photosynthesis flashcards in the free StudySmarter app

We have 14,000 flashcards about Dynamic Landscapes.

Already have an account? Log in

Frequently Asked Questions about Investigating Photosynthesis

How do you investigate photosynthesis? 

The rate of photosynthesis can be investigated by manipulating one of it's limiting factors, while controlling the other two. We can also use a co2 sensitive indicator to investigate the changes in gas exchange when the plant is in the light vs the dark. 

What are the needs for photosynthesis in this investigation? 

Photosynthesis generally requires co2, light and water to proceed. Light is provided by the lamp, water by immersion in it and co2 by sodium hydrogen carbonate. 

How does photosynthesis investigate the effects of carbon dioxide? 

By altering the level of carbon dioxide available to the plant, and controlling the temperature and light intensity it is exposed to, we can investigate the impact of different carbon dioxide concentrations on the rate of photosynthesis. 

how would you carry out an experiment to investigate photosynthesis?

You can conduct an experiment to investigate photosynthesis by picking an independent variable which has an impact on the process, controlling all other variables and then altering the independent variable to measure the changes caused in the dependent variable. 

what plants can be used to investigate photosynthesis?

Theoretically any plant could be used to investigate photosynthesis, but for ease of handling and control of variables, algae or pondweed are often used.

Discover learning materials with the free StudySmarter app

About StudySmarter

StudySmarter is a globally recognized educational technology company, offering a holistic learning platform designed for students of all ages and educational levels. Our platform provides learning support for a wide range of subjects, including STEM, Social Sciences, and Languages and also helps students to successfully master various tests and exams worldwide, such as GCSE, A Level, SAT, ACT, Abitur, and more. We offer an extensive library of learning materials, including interactive flashcards, comprehensive textbook solutions, and detailed explanations. The cutting-edge technology and tools we provide help students create their own learning materials. StudySmarter’s content is not only expert-verified but also regularly updated to ensure accuracy and relevance.

Team Biology Teachers

Study anywhere. Anytime.Across all devices.

Create a free account to save this explanation..

Save explanations to your personalised space and access them anytime, anywhere!

By signing up, you agree to the Terms and Conditions and the Privacy Policy of StudySmarter.

Sign up to highlight and take notes. It’s 100% free.

Join over 22 million students in learning with our StudySmarter App

The first learning app that truly has everything you need to ace your exams in one place

• Flashcards & Quizzes
• AI Study Assistant
• Study Planner
• Smart Note-Taking

Lesson 3 - Investigating the rate of photosynthesis

Pondweed, photosynthesis, rate, light intensity, temperature

Print RP sheet and Exam Questions

• Re-cap Questions
• Identify variables, Discuss risks and hazards
• Write a method
• Complete the experiment
• Draw graphs (different graph for F and H)
• Go through sources of error
• Apply knowledge to a 6 mark question with a different independent variable

Exam Question

Practical - Photosynthesis in pondweed

• 0.2% sodium hydrogen carbonate solution is low hazard. Refer to Hazcard 95C.
• Care should be taken when handling glassware.
• Care should be taken with the use of lamps that may get hot.
• To illustrate that the rate of photosynthesis declines as the light intensity gets weaker
• Leave the pondweed for a minute or two to adjust
• Take the water from the same tank as the pond weed. (already saturated with O2)
• Place a glass screen between the light source and the pondweed to eliminate any effect the heat from the lamp may have,
• Set up a test tube rack containing a boiling tube at a distance of 10cm away from the light source.
• 2. Fill the boiling tube with the sodium hydrogen carbonate solution.
• 3. Put the piece of pondweed into the boiling tube with the cut end at the top. Gently push the pondweed down with the glass rod.
• 4. Leave the boiling tube for 5 minutes.
• 5. Start the stopwatch and count the number of bubbles produced in one minute.
• 6. Record the results in your results table.
• 7. Repeat the count twice more. Then use the data to calculate the mean number of bubbles per minute.
• 8. Repeat steps 5‒7 with the test tube rack and boiling tube at distances of 20 cm, 30 cm and 40 cm from the light source.

Lesson 3 - Investigating the rate of Photosynthesis

• Name the 3 main things that limit plant growth
• Give the symbol equation for photosynthesis.
• Describe the optimum conditions for plant growth

How could this be achieved?

• Name the 3 main things that limit plant growth. Light intensity, carbon dioxide and temperature� ��

6CO 2 + 6H 2 O → 6O 2 + C 6 H 12 O 6 ���

• Describe the optimum conditions for plant growth.

For optimum plant growth high levels of carbon dioxide and light intensity would be required. The optimum temperature would be 40C for this process.

Check your answers

Learning objectives:

To investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed

Required Practical

Aquatic plants produce visible bubbles of oxygen gas into the surrounding water when they photosynthesise. ��

These bubbles can be counted as a measure of the rate of photosynthesis.

• The effect of light intensity on rate of photosynthesis can be investigated by varying the distance between pondweed and a light source. ��
• The closer the light source, the greater the light intensity.�

Required Practical - investigating the effect of light intensity on the rate of photosynthesis

Identify the independent, dependent and control variables�

IV: Distance between the pondweed and light source (light intensity)

DV: Number of bubbles produced in 1 minute

CVs: Mass of sodium hydrogen carbonate, temperature, size of pondweed/number of leaves on pondweed.

Task: Write a method for this experiment

Challenge: Why would an LED light source be a better option than a lamp?

Task: Write a method for this experiment, including a diagram of your equipment

• Read through the instructions on your practical sheet and add to your method
• Challenge: Why would an LED light source be a better option than a lamp? They don’t release much heat.
• Write a risk assessment on the back of your sheet using the table below:

❶ Place boiling tube in test tube rack 10cm away from light source.

Fill boiling tube with Sodium hydrogen carbonate solution.

❷ Add a piece of pondweed to the boiling tube. Push to bottom and leave for 5 minutes.

❸ Start the timer and record the number of bubbles produced in 1 minute.

• Repeat two more times
• Record all three results in your table
• Calculate a mean

❹ Repeat step 3, increasing the distance from the light source by 10cm each time.

Required Practical - Foundation

• Calculate the mean number of bubbles for each distance (Add together and divide by 3).
• Plot a graph of number of bubbles per minute against distance from light source.

Mean number of bubbles

Distance from light (cm)

Required Practical - Higher

• Plot a graph of number of bubbles per minute against light intensity.

Light intensity

What are the two main sources of error in this experiment?

How could they be overcome?

What are the two main sources of error in this experiment? B ubbles can be too hard to count, bubbles not always the same size.

How could they be overcome? Measuring the volume oxygen produced

A different independent variable?

Complete the 6 mark question

Logos / symbols

A-level set practicals – factors affecting rates of photosynthesis

• Share to Facebook
• Share to Twitter
• Share via Email

Age Ranges:

‘Factors affecting the rates of photosynthesis’ is an updated version of our popular ‘ algal balls ‘ resource is designed to support the use of practicals across various new 2015 A-level biology specifications (OCR, AQA, Edexcel and Eduqas).

Students conduct an investigation into factors affecting the rates of photosynthesis, using a colorimeter to record quantitative measurements.

Students will:

• use appropriate instrumentation (a colorimeter) to record quantitative measurements
• safely and ethically use organisms to measure plant responses to changing conditions
• use ICT such as computer modelling, or data logger to collect data, or use software to process data.

Materials include:

• Tested materials to support the A-level practical endorsement (CPAC)
• Support materials for teachers and technicians
• Student worksheet to help provide evidence for meeting the practical skills requirements
• Student revision materials to help prepare for exams

Support materials for other key practicals in A-level specifications can be found on the A-level set practicals main page.

What's included?

• SAPS - Light Intensity and the rate of photosynthesis - Learning Outcomes
• SAPS - Light Intensity and the rate of photosynthesis - Student Worksheet
• SAPS - Light intensity and the rate of photosynthesis - Student Sheet
• SAPS - Light intensity and the rate of photosynthesis - Grid
• SAPS - Light Intensity and the rate of photosynthesis - Technical and Teaching Notes
• Photosynthesis
• Respiration
• A-level set practicals

Related content

Teaching resources.

• A-level set practicals - investigating flower structure and function in primulas
• A-level set practicals - microscopy of root tip mitosis
• A-level set practicals - dissection and scientific drawing
• A-level set practicals - dissection and microscopy of a plant stem
• A-level set practicals - TLC of plant photosynthetic pigments