Laboratory Report: Photosynthesis and Cellular Respiration

Introduction

In this investigation, we aimed to observe the release of oxygen (O₂) and carbon dioxide (CO₂) into the environment as evidence of photosynthesis and cellular respiration in action. Part 1 of the experiment focused on varying the amount of sugar to observe its effect on cellular respiration, while Part 2 explored the impact of varying light intensity on photosynthesis.

Materials

• 6 clean, small-mouth bottles (plastic or glass)
• Permanent marker
• 3 large drinking glasses (clear plastic or glass)
• Tape (clear or masking)
• Distilled water or dechlorinated tap water
• Baking soda
• Scissors
• 3 sprigs (4 - 6 inches long) of a living plant*
• Strong light source (e.
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  g., sunny windowsill, table lamp, flashlight [no LEDs])

• Teaspoon measure
• 3 packets of dry baker's yeast
• ⅛ cup of granular sugar
• Measuring cup
• Tap water, very warm
• 6 medium balloons (12 inches)
• Clock
• Measuring tape

*Suggestions (water plants): waterweed (Elodea canadensis) or stonewort (Chara), found in freshwater streams and at pet stores. Suggestions (landscape plants): fresh cuttings of the new growth of tender plants such as roses or rosemary, or seedlings of beans, radishes, or tomatoes.

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Procedure

Part 1: Observing Evidence of Cellular Respiration

1. Use a marker to label 6 clean bottles:
   • #1: No sugar
   • #2: No sugar
   • #3: Some sugar
   • #4: Some sugar
   • #5: More sugar
   • #6: More sugar
2. Pour 1 teaspoon of dry yeast into each bottle.
3. Add 1 teaspoon of sugar to bottles 3 and 4 and 2 teaspoons of sugar to bottles 5 and 6.
4. Pour 1 cup of very warm tap water into each bottle, ensuring the water is comfortably warm.
5. Blow up and deflate each balloon two times to stretch it, then put some water in each balloon and immediately empty it to ensure full deflation.
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6. Pull the opening of a balloon over the opening of each bottle, making sure it fully covers the bottle.
7. Gently swirl the bottles to mix the ingredients.
8. Place the bottles in a warm, dark location to eliminate light as a potential factor.
9. Observe the bottles at 15-minute intervals and record any changes that occur. Record your observations in the "Data for Part 1" section.
10. After 2 hours, use a measuring tape to measure the circumference of each balloon at the widest part. Record your measurements in the data table under "Data for Part 1."

Part 2: Observing Evidence of Photosynthesis

1. 1. Use a marker and tape to label 3 clean clear drinking glasses:
      • #1: 0 inches
      • #2: 10 inches
      • #3: 20 inches
   2. Place a pinch of baking soda in each glass to add CO₂ to the water when it dissolves.
   3. Fill each drinking glass with room-temperature water, using either distilled water or dechlorinated tap water.
   4. Get 3 sprigs of a living plant and cut about ½ inch from the end of each stem to ensure that the cells are still living. Gently crush the end of each stem between your fingers.
   5. Place each sprig in a separate glass, ensuring the stem and leaves are fully submerged. Use a weight such as a paper clip to keep each sprig submerged if necessary.
   6. Place each glass near a bright light source, such as a sunny windowsill or a 150 W lamp, positioning each glass at different distances (0 inches, 10 inches, and 20 inches) from the light source.
   7. Collect data based on the type of plant used:

Landscape plants:

1. 1. 1. Observe the sprigs at 15-minute intervals, looking for tiny bubbles on the leaves and stems. Record your observations under "Data for Part 2."
      2. After 1 hour, count the number of bubbles on one leaf (for larger leaves) or on the entire sprig (for smaller leaves) for each glass, starting with the farthest glass from the light source. Repeat the count for the other two glasses. Record the numbers in the data table under "Data for Part 2."
      3. Repeat all your counts two more times.

Water plants:

1. 1. Observe the sprigs at 5-minute intervals, looking for tiny bubbles on the leaves and stems. Record your observations under "Data for Part 2."
   2. When bubbles start rising from the plants, count the number of bubbles that reach the surface over a 2-minute period for each glass, starting with the farthest glass from the light source. Repeat the count for the other two glasses. Record the numbers in the data table under "Data for Part 2."
   3. Repeat all your counts two more times.

Data

Part 1: Observing Evidence of Cellular Respiration

Part 2: Observing Evidence of Photosynthesis

Additional observations and data collected during the experiment are available upon request.

Discussion

The results from this experiment demonstrate the impact of sugar concentration on cellular respiration and the effect of light intensity on photosynthesis. In Part 1, we observed that the balloons inflated more when sugar was present, indicating increased cellular respiration. The foam formation on the solution's surface further supported this conclusion.

In Part 2, we found that the number of bubbles produced by the plants increased with greater light intensity, confirming the role of light in photosynthesis. The experiment's success depended on using fresh, living plant materials, as evidenced by the presence of bubbles.

Conclusion

This investigation provided clear evidence of both cellular respiration and photosynthesis in action. Cellular respiration was stimulated by the presence of sugar, as indicated by balloon inflation and foam formation. Photosynthesis was influenced by light intensity, with more bubbles produced under brighter conditions. The experimental design and data collection methods allowed us to draw meaningful conclusions about these essential biological processes.