factors that affect rate of photosynthesis experiment

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Photosynthesis Virtual Lab

This lab was created to replace the popular waterweed simulator which no longer functions because it is flash-based. In this virtual photosynthesis lab , students can manipulate the light intensity, light color, and distance from the light source.

A plant is shown in a beaker and test tube which bubbles to indicate the rate of photosynthesis. Students can measure the rate over time. There is an included data table for students to type into the simulator, but I prefer to give them their own handout ,

The handout is a paper version for students to write on as the work with the simulator. The document is made with google docs so that it can be shared with remote students.

There are several experiments that can be done in the lab that would complement this virtual experiment. For example, students can use elodea and measure the number of bubbles released when the plant is under a bright light. Algae beads can also be used to measure changes in pH as the plants consume carbon dioxide.

In experiment 2, students specifically look at light color to determine which wavelength of light increases the rate of photosynthesis. Students should discover that green light has a very slow rate. Their collected data is then compared to a graph of the absorption spectrum of light.

Shannan Muskopf

• Science is LIT

Explore How Light Affects Photosynthesis

Algae are aquatic, plant-like organisms that can be found in oceans, lakes, ponds, rivers, and even in snow. But don’t worry, if you’re not near a waterway, it can easily be ordered from Amazon or Carolina Biological. Algae range from single-celled phytoplankton (microalgae) to large seaweeds (macroalgae). Phytoplanktons can be found drifting in water and are usually single-celled. They can also grow in colonies (group of single-cells) that are large enough to see with the naked eye. The specific types of algae that can be used in this experiment are  Scenedesmus, Chlamydomonas, or  Chlorella , all of which are phytoplanktons or microalgae. 

Experimental variables

• Color filter paper
• Table/desk lamp
• Light bulbs (varying intensities and colors)

Laboratory Supplies

• Transfer pipettes
• Vials with caps
• Freshwater Algae ( Scenedesmus , Chlorella , or Chlamydomonas )
• Small beakers or cups

Laboratory Solutions

• 2% Calcium Chloride
• 2% Sodium alginate
• Cresol red/thymol blue pH indicator solution

Solution Preparations

2% calcium chloride (cacl 2 ).

• 20 g of CaCl 2
• Fill to 1000 mL with water

2% CaCl 2 is stable at room temperature indefinitely.

2% Sodium alginate (prepared in advance)

• 2 g sodium alginate
• Fill to 100 mL with water

It takes a while for the alginate to go into solution. We recommend to dissolve by stirring using a magnetic stir bar overnight at room temperature. Store at 4 °C for up to 6 months or use immediately.

Cresol red/Thymol blue pH indicator solution (10x)

• 0.1 g cresol red
• 0.2 g thymol blue
• 0.85 g sodium bicarbonate (NaHCO 3 )
• 20 mL ethanol
• Fill to 1L with fresh boiled water

Measure indicators and mix with ethanol. Measure sodium bicarbonate and mix with warm/hot water. Mix the solutions together and fill with remaining freshly boiled water up to 1L final solution. The 10x stock solution is stable for at least a year.

In preparation for doing the experiment, prepare 1x indicator solution by diluting the 10x indicator solution with distilled water (e.g. 20 ml 10x into 200 mL final solution).

Experimental Bench Set-Up

• ~10 mL of 2% CaCl 2 in a cup or beaker
• ~3-5 mL of sodium alginate in cup or beaker
• Cup with ~10 mL of water
• Empty cup or beaker that holds a minimum of 30 mL

Preparing Algae for Experiment

• Prepare a concentrated suspension of algae. Without centrifuge : leave ~50 mL of algae suspension to settle (preferably overnight), then carefully pour off the supernatant to leave ~3-5 mL of concentrated algae. With centrifuge : Centrifuge ~50 mL of algae suspension at low speed for 10 minutes and then carefully pour off the supernatant, leaving behind ~3-5 mL of concentrated algae.
• In a small beaker, add equal volumes of sodium alginate and then add in the concentrated algae. Gently mix algae and sodium alginate together using a transfer pipette until its evenly distributed.
• Using the transfer pipette, carefully add single drops of the algae/sodium alginate mixture into the CaCl 2 to make little “algae balls”
• Once all of the “algae balls” are in the CaCl 2 solution, allow them to harden for 5 minutes
• Place the strainer over the empty cup or beaker, and pour over the entire solution of “algae balls” and CaCl 2 into the strainer allowing the CaCl 2 to pass through, leaving just the algae in the strainer
• Keeping the strainer over the container, pour the water over the “algae balls” to rinse the remain CaCl 2
• Transfer your newly made “algae balls” to a new cup or beaker

Setting up Photosynthesis Experiment

• Distance from light (using ruler) – group can set up vials different distances from one light source
• Different color lights (using color filter paper or different color light bulbs) – group can set up by covering the vials with different colored films and arrange them the same distance away from the light source or set up 1 vial in front of a different colored lamp same distance away.
• With or without light – group places 1 vial in front of an illuminated lamp and another has the vial or lamp covered with black paper the same distance away

• When starting your experiment, be sure to take note of the time that you placed your vial in front of the light source. Vials should be left for ~1-2 hours.

What would happen if the algae photosynthesizes (increase O2) in a solution that started at pH8.2?

Analyzing photosynthesis results

• After 1-2 hours, return to the experiment. Without disturbing the vials, analyze and take pictures of results. Have students write down the time that their experiment ended.
• Using the color chart above, determine which pH matches your sample the closest.
• Have students determine if they got what they expected and discuss amongst their group members.

Explain how the rate of photosynthesis is affected by their different variables.

What were your conclusions from this experiment? If you were to repeat the experiment, what would you change and why? What’s the relationship with O2 and CO2 during the process of photosynthesis? Is there a “best” source of light that allowed the algae to photosynthesize better?

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Photosynthesis: Limiting Factors Affecting the Rate of Photosynthesis - (GCSE Biology)

Limiting factors affecting the rate of photosynthesis, single factors affecting rate of photosynthesis.

• Limiting factors affect the rate of a reaction. A limiting factor is a condition, that when in shortage, slows down the rate of a reaction. Light intensity, carbon dioxide concentration and temperature are limiting factors of photosynthesis. They all affect the rate of the photosynthetic reaction, but in different ways.

Photosynthesis Equation

The equation for photosynthesis is shown below in words. Factors affecting photosynthesis will affect the rate of reaction, will affect the amount of glucose and oxygen produced.

• Carbon dioxide + water + (light energy) → glucose + oxygen gas

Carbon Dioxide

• The higher the CO₂ concentration, the higher the rate until a certain point. As you increase the concentration of carbon dioxide (the reactant), the reaction is driven forwards.
• At high CO₂ concentration, rate levels off. until you reach a point at which the enzymes required are saturated. At this point, the carbon dioxide is no longer a limiting factor.

• You can prove the need for carbon dioxide in photosynthesis by placing a plant in a sealed bell jar with some soda lime. The soda lime will absorb any carbon dioxide present in the jar. After a while you can test the leaves of the plant for the presence of starch: 1. Dip the leaf in boiling water. This stops any further reactions in the leaf. 2. Place the leaf in a tube with ethanol. 3. Place the tube in an electric water bath and heat till it’s boiling. This removes any chlorophyll and turns the leaf a white colour. 4. Rinse the leaf with cold water and add drops of iodine solution. 5. Observe your results. The leaf won’t turn blue-black which means there is no starch present hence, no photosynthesis took place.

Light Intensity

• The higher the light intensity, the higher the rate until a certain point. If you increase the intensity of the light, more light can be trapped by the chloroplasts to provide energy to drive the photosynthetic reaction.
• At high light intensity, rate levels off. Again, this is up until a certain point, when the maximum amount of light has already been trapped. When you reach this point, light is no longer a limiting factor.

• You can prove the need for light by testing leaves of a plant left in the dark for 48 hours. You can test the leaves for starch in the same way as described above and will find that they won’t turn blue-black as no starch is present. The plant would have used up its starch stores without being able to make more due to the lack of light.

Temperature

• The higher the temperature, the higher the rate until a certain point. As the temperature increases, the enzymes gain more kinetic energy and so can catalyse the reaction at a greater rate. At the optimum temperature, the rate of reaction is the highest.
• At high temperatures, the rate falls as enzymes denature. When the temperature is greater than the optimum, the enzymes denature (change shape), so the reaction can no longer take place. This means the reaction is no longer feasible and so will not occur. This temperature is often around 45ºC.

Chlorophyll

• Chlorophyll can act as a limiting factor for photosynthesis. As the amount of chlorophyll increases, more light can be trapped by the chloroplasts in order to drive the reaction. However, once there is a certain amount of chlorophyll, it will no longer be a limiting factor and the values of other factors will limit the rate of the reaction. Infection and disease can reduce the amount of chlorophyll in a plant.
• You can prove the need for chlorophyll by testing variegated leaves. Variegated leaves are green and white – only the green areas contain chlorophyll so only they photosynthesise and produce starch. You can test the leaves for starch in the same way as described earlier. You will find that the areas of the leaf that were initially green (with chlorophyll) will turn black due to the presence of starch. The areas that were initially white (without chlorophyll) will remain orange.

Multiple Factors Affecting Rate of Photosynthesis

• Realistically, more than one factor is involved at a period in time. In the wild, plants are not kept under experimental conditions and so will be affected by different temperatures, carbon dioxide concentrations and light intensities.

Graphs can be used to map the effect of different limiting factors on the rate of photosynthesis at the same time:

Light Intensity and Temperature

• In the above graph, CO2 concentration is constant, so the effect of light intensity and temperature on photosynthesis is shown.
• As you increase light intensity, rate increases until we reach a plateau, after which light is no longer the limiting factor.
• As you increase temperature (shift from 20ºC to 30ºC), the rate increases. Also, the light intensity effect plateau’s at a higher level, so light intensity is a limiting factor for longer.

Light Intensity and CO2 concentration

• In the above graph, temperature is constant, so the effect of light intensity and carbon dioxide concentration on photosynthesis is shown.
• As you ice increase CO2 (shift from 0.05% to 0.5%), the rate increases. Also, the light intensity effect plateau’s at a higher level, so light intensity is a limiting factor for longer.

Canadian Pondweed Experiment

Setting up the experiment.

This test can specifically measure the effect of light intensity on photosynthesis. The rate of the plant’s oxygen production is proportional to the rate of photosynthesis .

• Place the plant in a boiling tube. Place the plant underwater in a boiling tube.
• Connect a gas syringe. Place the boiling tube on a clamp and add a capillary tube and a gas syringe. There should be an air bubble in the capillary tube.
• Use a ruler to measure movement of the air bubble. You can then use a ruler to see how much the air bubble moves. The amount the bubble moves is proportional to the rate of photosynthesis.
• Change the variables. You can now vary the light intensity, temperature and CO₂ concentration and observe the effect on bubble displacement (and hence rate of photosynthesis).

Investigating the Effect of Light Intensity

• Vary light intensity. Place a lamp at differing distances from the plant and observe the oxygen production through the movement of the bubble. This will give you an opportunity to see the effect of light intensity on the rate of photosynthesis.
• Control the other variables, and repeat for reliability. Control the temperature of the room and the time taken for the experiment. Make sure to repeat the experiment three times at each distance, then take a mean value in order to attain more reliable results.

Investigating the Effect of Temperature

• Vary the temperature. Place the boiling tube in different temperature water baths and observe the oxygen production through the movement of the bubble. This will give you an opportunity to see the effect of light intensity on the rate of photosynthesis
• Control the other variables, and repeat for reliability. Control the time taken for the experiment and the distance at which the lamp is placed. Make sure to repeat the experiment three times at each distance, then take a mean value in order to attain more reliable results.

Investigating the Effect of CO ₂ Concentration

• Vary the CO₂ concentration. Dissolve different amounts of sodium hydrogen-carbonate in the boiling tube. This releases carbon dioxide in water. You can dissolve different amounts into different boiling tubes to see the effect of differing carbon dioxide concentration on the rate of photosynthesis
• Control the other variables, and repeat for reliability. Control the temperature, distance of the lamp and the time taken for the experiment. Make sure to repeat the experiment three times at each carbon dioxide concentration, then take a mean value in order to attain more reliable results.

Photosynthesis takes place in plants to give them energy. Plants use sunlight, water and carbon dioxide to make food (energy in the form of sugars) and oxygen.

Photosynthesis takes place in chloroplasts, which contain chlorophyll. Chlorophyll is a pigment that gives plant leaves their green colour. This pigment absorbs the sun’s energy to use in the process of photosynthesis.

Chloroplast organelles are located inside the plant cell. Inside the chloroplast is a thylakoid membrane, housing a pigment called chlorophyll and this pigment absorbs the sun’s energy.

Photosynthesis is an endothermic reaction. This is because the sun’s energy is absorbed by the plant’s cells.

Plants absorb carbon dioxide and water from the air and soil. Inside the plant cell, the water is turned into oxygen. The carbon dioxide is transformed into energy (sugars in the form of glucose).

The rate of photosynthesis can be affected by various limiting factors such as light intensity, carbon dioxide concentration, temperature and water availability.

The rate of photosynthesis increases with an increase in light intensity until it reaches an optimal level. Beyond this level, an increase in light intensity will not increase the rate of photosynthesis.

The rate of photosynthesis increases with an increase in carbon dioxide concentration until it reaches an optimal level. Beyond this level, an increase in carbon dioxide concentration will not increase the rate of photosynthesis.

The rate of photosynthesis increases with an increase in temperature until it reaches an optimal level. Beyond this level, an increase in temperature will decrease the rate of photosynthesis.

Water is essential for photosynthesis, as it provides the hydrogen ions needed for the process. A shortage of water can limit the rate of photosynthesis.

Limiting factors are important in photosynthesis as they can determine the maximum rate of photosynthesis that can be achieved under a set of environmental conditions. Understanding these factors can help to improve plant growth and crop yield.

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Photosynthesis.

Plants make their own food – absorbing and converting sunlight energy into chemical energy stored in carbohydrates such as glucose and other biomolecules. Photosynthesis is vital for the life of plants and for all animals on the planet.

Explore the requirements for photosynthesis.

Experiments

• Identifying the conditions needed for photosynthesis
• Investigating photosynthesis using immobilised algae
• Investigating the light dependent reaction in photosynthesis
• Investigating factors affecting the rate of photosynthesis

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**iGCSE Biology Edexcel - FACTORS AFFECTING RATE OF PHOTOSYNTHESIS**

Subject: Biology

Age range: 14-16

Resource type: Lesson (complete)

Last updated

11 August 2024

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Factors Affecting Rate of Photosynthesis

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*iGCSE Edexcel Biology - Complete Plants**

Unlock the Secrets of Plant Biology with "Unit 8 - Plants" Are you looking to elevate your biology lessons with comprehensive, ready-to-use resources that engage students and save you precious planning time? Our "Unit 8 - Plants" teaching package is meticulously designed to align with GCSE curriculum standards, ensuring your students gain a deep understanding of plant biology through interactive and thought-provoking lessons. **What’s Included in the Unit?** LESSON 1: PLANT STRUCTURE & PHOTOSYNTHESIS: Dive into the fundamental structures of plants and the process of photosynthesis that fuels life on Earth. LESSON 2: THE USES OF STARCH: Explore how plants store energy in the form of starch and the significance of this process. LESSON 3: FACTORS AFFECTING RATE OF PHOTOSYNTHESIS: Understand the various environmental and biological factors that influence photosynthesis. LESSONS 4 & 5: INVESTIGATING THE FACTORS AFFECTING RATE OF PHOTOSYNTHESIS: Engage in hands-on experiments to explore how different conditions impact photosynthesis. LESSON 6: LEAF STRUCTURE - TISSUE & ORGANS: Examine the detailed structure of leaves and their role in plant function. LESSON 7: PLANT MINERALS: Learn about the essential minerals required for plant growth and how they are absorbed. LESSON 8: GAS EXCHANGE IN PLANTS: Delve into the processes of gas exchange and how plants manage oxygen and carbon dioxide. LESSON 9: INVESTIGATING THE EFFECT OF LIGHT ON NET GAS EXCHANGE FROM A LEAF: Conduct experiments to observe how light affects gas exchange in plants. LESSON 10: TRANSPORT OF WATER & SUGARS: Explore how plants transport vital nutrients and water throughout their structures. LESSON 11: TRANSPIRATION: Understand the process of transpiration and its importance in plant physiology. LESSON 12: FACTORS AFFECTING TRANSPIRATION: Investigate the various factors that influence the rate of transpiration in plants. LESSON 13: INVESTIGATING TRANSPIRATION: Engage in practical activities to measure and analyze transpiration rates. LESSON 14: COORDINATION & RESPONSE IN PLANTS: Discover how plants coordinate their responses to environmental stimuli. **Why Choose This Resource?** * Complete Lesson Plans: Whether you're a new teacher or a seasoned educator, our detailed lesson plans provide clear guidance to help you deliver impactful lessons. * Engaging PowerPoints: Our PowerPoints are designed to captivate students with clear, concise content and engaging visuals. * Comprehensive Summary Notes: Equip your students with summary notes that clarify key concepts and address common misconceptions. * Differentiated Questions: Each lesson includes at least 10 mixed/differentiated questions to ensure all students are challenged appropriately. * Ready-to-Use Worksheets: Printable worksheets reinforce lesson content and provide students with hands-on practice. This off-the-shelf, hassle-free resource package is designed to enhance your teaching and provide your students with the tools they need to succeed. With "Unit 8 - Plants," you can deliver lessons that are not only educational but also engaging and memorable. Transform your teaching today! Purchase "Unit 8 - Plants" on TES and bring plant biology to life in your classroom.

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Investigating the Rate of Photosynthesis ( AQA A Level Biology )

Revision note.

Biology & Environmental Systems and Societies

Apparatus & Techniques: Investigating the Rate of Photosynthesis

• Investigations to determine the effects of light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis can be carried out using aquatic plants , such as Elodea or Cabomba (types of pondweed )
• Light intensity – change the distance ( d ) of a light source from the plant (light intensity is proportional to 1/ d 2 )
• Carbon dioxide concentration – add different quantities of sodium hydrogencarbonate (NaHCO 3 ) to the water surrounding the plant, this dissolves to produce CO 2
• Temperature (of the solution surrounding the plant) – place the boiling tube containing the submerged plant in water baths of different temperatures
• For example, when investigating the effect of light intensity on the rate of photosynthesis, a glass tank should be placed in between the lamp and the boiling tube containing the pondweed to absorb heat from the lamp – this prevents the solution surrounding the plant from changing temperature
• Distilled water
• Aquatic plant, algae or algal beads
• Sodium hydrogen carbonate solution
• Thermometer
• Test tube plug
• This will ensure oxygen gas given off by the plant during the investigation form bubbles and do not dissolve in the water
• This will ensure that the plant contains all the enzymes required for photosynthesis and that any changes of rate are due to the independent variable
• Ensure the pondweed is submerged in sodium hydrogen carbonate solution (1%) – this ensures the pondweed has a controlled supply of carbon dioxide (a reactant in photosynthesis)
• Cut the stem of the pondweed cleanly just before placing into the boiling tube
• Measure the volume of gas collected in the gas-syringe in a set period of time (eg. 5 minutes)
• Change the independent variable (ie. change the light intensity, carbon dioxide concentration or temperature depending on which limiting factor you are investigating) and repeat step 5
• Record the results in a table and plot a graph of volume of oxygen produced per minute against the distance from the lamp (if investigating light intensity), carbon dioxide concentration, or temperature

The effect of light intensity on an aquatic plant is measured by the volume of oxygen produced

Results - Light Intensity

• The closer the lamp, the higher the light intensity (intensity ∝ 1/ d 2 )
• Therefore, the volume of oxygen produced should increase as the light intensity is increased
• This is when the light stops being the limiting factor and the temperature or concentration of carbon dioxide is limiting the rate of photosynthesis
• The effect of these variables could then be measured by increasing the temperature of water (by using a water bath) or increasing the concentration of sodium hydrogen carbonate respectively
• Rate of photosynthesis = volume of oxygen produced ÷ time elapsed

Limitations

• Immobilised algae beads are beads of jelly with a known surface area and volume that contain algae, therefore it is easier to ensure a standard quantity
• Immobilised algae beads are easy and cheap to grow, they are also easy to keep alive for several weeks and can be reused in different experiments
• The method is the same for algae beads though it is important to ensure sufficient light coverage for all beads

Light intensity – the distance of the light source from the plant (intensity ∝ 1/ d 2 )

Temperature - changing the temperature of the water bath the test tube sits in

Carbon dioxide - the amount of NaHCO 3 dissolved in the water the pondweed is in

Also remember that the variables not being tested (the control variables) must be kept constant.

Required Practical: Affecting the Rate of Dehydrogenase Activity

• The light-dependent reactions of photosynthesis take place in the thylakoid membrane and involve the release of high-energy electrons from chlorophyll a molecules
• These electrons are picked up by the electron acceptor NADP in a reaction catalysed by dehydrogenase
• However, if a redox indicator (such as DCPIP or methylene blue ) is present, the indicator takes up the electrons instead of NADP
• DCPIP: oxidised ( blue ) → accepts electrons → reduced ( colourless )
• Methylene blue: oxidised ( blue ) → accepts electrons → reduced ( colourless )
• The colour of the reduced solution may appear green because chlorophyll produces a green colour
• When light is at a higher intensity, or at more preferable light wavelengths, the rate of photoactivation of electrons is faster, therefore the rate of reduction of the indicator is faster

Light activates electrons from chlorophyll molecules during the light-dependent reaction. Redox indicators accept the excited electrons from the photosystem, becoming reduced and therefore changing colour.

• Isolation medium
• Pestel and mortar
• Aluminium Foil

Method - Measuring light as a limiting factor

• This produces a concentrated leaf extract that contains a suspension of intact and functional chloroplasts
• The medium must have the same water potential as the leaf cells so the chloroplasts don’t shrivel or burst and contain a buffer to keep the pH constant
• The medium should also be ice-cold (to avoid damaging the chloroplasts and to maintain membrane structure)
• The room should be at an adequate temperate for photosynthesis and maintained throughout, as should carbon dioxide concentration
• If different intensities of light are used, they must all be of the same wavelength (same colour of light) - light intensity is altered by changing the distance between the lamp and the test tube
• If different wavelengths of light are used, they must all be of the same light intensity - the lamp should be the same distance in all experiments
• DCPIP of methylene blue indicator is added to each tube, as well as a small volume of the leaf extract
• A control that is not exposed to light (wrapped in aluminium foil) should also be set up to ensure the affect on colour is due to the light
• This is a measure of the rate of photosynthesis
• A graph should be plotted of absorbance against time for each distance from the light
• This is because the lowered light intensity will slow the rate of photoionisation of the chlorophyll pigment, so the overall rate of the light dependent reaction will be slower
• This means that less electrons are released by the chlorophyll, hence the DCPIP accepts less electrons. This means that it will take longer to turn from blue to colourless
• A higher rate of decrease, shown by a steep gradient on the graph, indicates that the dehydrogenase is highly active.
• This experiment is not measuring the rate of dehydrogenase activity directly (through measuring the rate of substrate use or product made) but is instead predicting what the rate would be by measuring the rate of electron transfer from the photosystems
• It is therefore important to control the amount of leaf used to produce the chloroplast sample and also how much time is spent crushing the leaf to release the chloroplast
• It is also a good idea to measure a specific wavelength absorption by each sample on the colorimeter before and after the experiment so you can get a more accurate change in oxidised DCPIP concentration
• Results should also be repeated and the mean value calculated
• The time taken to go colourless is subjective to each person observing and therefore one person should be assigned the task of deciding when this is

In chemistry the acronym ‘OILRIG’ is used to remember if something is being oxidised or reduced. Oxidation Is Loss (of electrons) and Reduction Is Gain (of electrons). Therefore the oxidised state is when it hasn’t accepted electrons and the reduced state has accepted electrons.

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Author: Alistair

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

Rate of Photosynthesis

This experiment provides a low cost solution for investigating the rate of photosynthesis for students who are blind and visually impaired..

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This experiment provides a low cost solution for investigating the rate of photosynthesis for students who are blind or visually impaired. It could also be used with sighted students. 

A common experiment when studying plant biology is investigating factors affecting the rate of photosynthesis. Plants produce oxygen which is invisible and odorless, so the experiment is usually carried out with water plants; the bubbles of oxygen produced are observed. The experiment is usually carried out with a common pond weed, and sighted students are instructed to count tiny bubbles: the faster the rate of bubble production, the faster the rate of photosynthesis. 

This presents a problem for students with VI since the bubbles are often too small to see and therefore counting them and gathering valid results is not possible. A typical arrangement is shown in the photo on the top right, with a lamp and a beaker of water with pondweed in it.

As well as the pipette, students will also need a large beaker (1000ml) a transparent glass funnel, pond weed, sodium hydrogen carbonate and a desk lamp.

• Large beaker (1000ml)
• Transparent glass funnel
• Sodium hydrogen carbonate

Preparation

A pipette with a narrow end is required. Cut the end, and seal using a flame. This creates a tube sealed at one end. Then cut the other end of the pipette to create a large opening which can be placed over an upturned funnel.

This experiment can be adapted so that results can be gathered in 20 minutes or less. 

• Add sodium hydrogen carbonate to the water which introduces carbon dioxide to the water to speed up the rate, and fill the large beaker with this water. Use an aquatic plant such as elodea, but plants such as hottonia palustris also work well. Cabomba may be used in some countries, but it is restricted in the UK, due to it being an invasive species and a risk to local plant populations if it is released into the environment. 
• Place the pond weed under the funnel. Lower the funnel to rest on the lower surface of the large beaker, placing small pieces of putty to hold the funnel up to allow water to circulate.
• Fill the pipette with water and hydrogen carbonate in the large beaker and invert, so it rests on the funnel. It needs to be be full of water.
• Direct the light from the desk lamp onto the pond weed. As the plant produces oxygen, the bubbles with move up the funnel into the pipette and displace the water. The amount of water displacement allows students to investigate factors affecting the rate of photosynthesis.

The two layers of glass provides protection from the heat of the lamp, and the water level moves down rapidly as the gas is collected, making it possible to gather results in well under an hour.

NGSS Standards:

Hs.matter and energy in organisms and ecosystems.

• HS-LS1-5.    Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy.

By Will Stark

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