Chapters
In this article, we will discuss and carry out investigations using redox indicators. These investigations include DCPIP and methylene blue, and a suspension of chloroplasts to determine how the light intensity and light wavelength affect the rate of photosynthesis. Moreover, we will also discuss and carry out investigations using whole plants, which include aquatic plants, to know the effects of light intensity, carbon dioxide concentration, and temperature on the rate of photosynthesis. So, let us get started.
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1st lesson free!
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1st lesson free!
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£25
/h
1st lesson free!
Tomi
£50
/h
1st lesson free!
Andrew
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1st lesson free!
Juneyt (ma, msc oxford)
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1st lesson free!
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1st lesson free!
Investigating the Rate of Photosynthesis Using Redox Indicators
- There are two stages of photosynthesis: the light-dependent and the light-independent stage. The reactions in the light-dependent stage of photosynthesis occur in the thylakoid membrane and entail the high-energy electrons released from “chlorophyll a” molecules.
- The electron acceptors then pick up these high-energy electrons which are then transferred down the electron transport chain
- However, in the presence of the redox indicator such as DCPIP or methylene blue, the indicator picks up the electron instead of the electron acceptor
- Due to this, the indicator changes its colour. For instance, the oxidized DCPIP is blue in colour and the reduced DCPIP is colourless. Hence, accepting the electron makes it change its colour. Because of the green colour of the chlorophyll, the colour of the reduced solution may appear green.
- The rate at which the redox indicator alters its colour from its oxidized form to its reduced form can be employed to determine the rate of photosynthesis.
- In the presence of higher intensity light or preferable wavelengths of light, there is a rapid rate of photoactivation of an electron. Hence, the rate of reduction of the indicator is also quicker.
Procedure
Step 1:
Crush the leaves in a liquid called an isolation medium. It is done because of the following reasons:
- It generates a concentrated extract of the leaf that has a suspension of intact and functional chloroplasts
- This medium should have equal water potential as the leaf cells. The equal water potential will ensure that the chloroplasts don’t burst or shrivel. Moreover, the medium must have a buffer to keep the pH the same. To prevent the damage of chloroplasts and to maintain the structure of the membrane, the medium must be ice-cold.
Step 2:
- In the second step of this procedure, set up the tiny tubes with varying intensities, or varying colours, i.e. wavelengths of light shining from them.
- If you use different light intensities, then they should all be of the same wavelength, i.e. the same colour of light
- If you use different wavelengths of light, then all should be of the same light intensity
Step 3:
- In this step, DCPIP of methylene blue indicator is added to each tube along with the small volume of leaf extract
Step 4:
- In this step of this experiment, the time consumed by the redox indicator to go colourless is recorded.
- This time gives us the rate of photosynthesis
In the next section of the article, we will discuss and carry out investigations using whole plants, which include aquatic plants, to know the effects of light intensity, carbon dioxide concentration, and temperature on the rate of photosynthesis.
Investigating the Rate of Photosynthesis Using Aquatic Plants
- We can use aquatic plants to carry out experiments to determine the effects of light intensity, the concentration of carbon dioxide, and temperature on the rate of photosynthesis. These three factors are known as limiting factors of photosynthesis. For this purpose, we can use aquatic plants such as Elodea or Cabomba (They are types of pondweed
- We can investigate the effects of the limiting factors discussed above in the following ways:
-
- Light Intensity: Take a light source and change the distance (d) of a light source from the plant. Remember that (light intensity is proportional to 1/d2)
- The concentration of carbon dioxide: Add varying quantities of sodium hydrogen carbonate (NaHCO3) to the water that surrounds the plant. NaHCO3 will dissolve to generate carbon dioxide
- The temperature of the solution that surrounds the plant: For this, place the boiling tube that contains submerged plants in water baths of varying temperatures
- When you change one of these factors, make sure that the other two factors are constant
- For instance, if you are investigating the effect of light intensity on the rate of photosynthesis, place a glass tank between the lamp and a boiling tube that has pondweed so that it can absorb heat from the lamp. This can help you to avoid the solution from changing the temperature that surrounds the plant.
Procedure
Step 1:
- Before using water, ensure that it is aerated well. You can achieve this by bubbling air through the water.
- From this, you can ensure that oxygen produced by the plant during the experiment form bubbles and does not dissolve in water
Step 2:
- In this step, you need to ensure that the plant is illuminated sufficiently before use
- It is done to ensure that the plant has all the enzymes needed for the process of photosynthesis. Moreover, it will also help you to ensure that any changes in the rate are because of the independent variable
Step 3:
- In this step, you will finally set the apparatus for the experiment. Ensure to set up the apparatus in the darkroom
- Besides setting the apparatus in the dark room, you need to ensure that the pondweed is submerged in sodium hydrogen carbonate solution (1%). It will guarantee that the pondweed has a controlled supply of carbon dioxide gas. Remember that carbon dioxide is the reactant in the process of photosynthesis.
Step 4:
- Neatly cut the stem of the pondweed before placing it into the boiling tube
Step 5:
- Measure the gas volume that is accumulated in the gas syringe in a definite time period (For instance, 10 minutes)
Step 6:
- Change the independent variable, for instance, light intensity, the concentration of carbon dioxide, or temperature. (It depends on the limiting factor you are investigating)
- Repeat step 5
Step 7:
- Record the results in the form of a table and plot a graph of the volume of oxygen generated in a minute against the distance from the lamp.
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