Investigating the Relationship between Light Intensity and the Rate of Photosynthesis Lab Activity

Aquatic plants can be used to demonstrate oxygen evolution in the process of photosynthesis. In theory, when an aquatic plant is placed in a solution containing a source of carbon dioxide (CO₂), in the presence of light of appropriate intensity, the plant will photosynthesize and produce bubbles of oxygen-containing gas. These bubbles can be counted and the rate of bubbling can serve as an indication of the rate of photosynthesis.

When the light intensity is increased, the rate of bubble production should increase. Decrease the light intensity and the rate of bubbling should decrease. Remove the light source altogether, or move it to a distance beyond which the energy levels are too small for photosynthesis, and the bubbling should cease.

Light is essential for photosynthesis. Green plants cells that are placed in the dark will not photosynthesize. An increase in light intensity will produce an increase in the rate of photosynthesis until a level of light intensity is reached above which the rate does not increase because the light saturation point has been reached and another factor is limiting. In this experiment, the light intensity is changed, by decreasing the light intensity. The rate of photosynthesis should decrease and therefore the amount of oxygen bubbles should decrease.

Photosynthesis Lab Activity Learning Objectives:

At the end of this laboratory activity, students are expected to:

• Observe the rate of photosynthesis in Elodea plants
• Determine the effect of light intensity on the rate of photosynthesis

Here are the Files Downloadable Files for the Photosynthesis Lab Activity

• 4-4 Laboratory Activity SE - Photosynthesis (Docx)
• 4-4 Laboratory Activity SE - Photosynthesis (PDF)
• 4-4 Laboratory Activity TE - Photosynthesis (Member Only Docx)
• 4-4 Laboratory Activity TE - Photosynthesis (Member Only PDF)

Photosynthesis Lab Activity Materials:

For each group of three to four students:

• Elodea plants
• Beaker
• Light source (lamp or flashlight)
• Ruler
• Stopwatch
• Sodium bicarbonate (baking soda)
• Distilled water

Safety Alert!

Safety measures should be observed, such as not looking directly at the light source and handling the sodium bicarbonate with care.

Photosynthesis Lab Activity Procedure:

1. Prepare a solution of 1% sodium bicarbonate by dissolving 1 g of sodium bicarbonate in 100 mL of distilled water. This solution provides carbon dioxide for photosynthesis.
   
2. Cut a small piece of Elodea plant and place it into a beaker containing 50 mL of the sodium bicarbonate.
   
3. Place the beaker under the light source at a distance of 5 cm.
   
4. Allow the plant to acclimate to the light source for 5 minutes.
5. Measure the initial length of the plant from the bottom of the beaker to the top of the plant.
   
6. Start the stopwatch and record the length of the plant every 5 minutes for a total of 30 minutes.
   
7. Repeat the experiment with different distances of the light source (10 cm, 15 cm, 20 cm).
   
8. Calculate the rate of photosynthesis by dividing the change in length of the plant by the time it took to occur.
9. Plot a graph of the rate of photosynthesis against the distance of the light source.

Plant Cells vs Animal Cells Lab Activities Result Sheet:

OBSERVATIONS: Complete the table with the structures that are visible during your investigation.

Table 1. Length of Elodea Plant in Varying Distances from the Light Source

Rate of Photosynthesis: __________________________

Discuss the following with your students about Photosynthesis Lab Activities:

1. How does the rate of photosynthesis change with increasing light intensity?
2. Why does photosynthesis require light?
3. How does the rate of photosynthesis affect the availability of oxygen and food for other living organisms?
4. How can the results of this experiment be applied to real-world situations, such as in agriculture or environmental management?

Here is your Free Content on Photosynthesis

Photosynthesis - PDFs

• 4-4 Vocabulary Worksheet TE - Photosynthesis (Members Only)
• 4-4 Vocabulary Worksheet SE - Photosynthesis (PDF)
• 4-4 Lesson Plan - Photosynthesis (PDF)
• 4-4 Slide Show - Photosynthesis (PDF)
• 4-4 Online Activities - Photosynthesis (PDF)
• 4-4 Laboratory Activity TE - Photosynthesis (Members Only)
• 4-4 Laboratory Activity SE - Photosynthesis (PDF)
• 4-4 Guided Notes TE - Photosynthesis (Members Only)
• 4-4 Guided Notes SE - Photosynthesis (PDF)
• 4-4 Exit Quiz TE - Photosynthesis (Members Only)
• 4-4 Exit Quiz SE - Photosynthesis (PDF)
• 4-4 Bell Work TE - Photosynthesis (Members Only)
• 4-4 Bell Work SE - Photosynthesis (PDF)
• 4-4 Assignment TE - Photosynthesis (Members Only)
• 4-4 Assignment SE - Photosynthesis (PDF)

Photosynthesis Worksheets - Word Docs & PowerPoints

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