Floating Leaf Disk Assay - Mrs. Baur



Introduction:

Photosynthesis is a process that converts carbon dioxide into sugars such as glucose using energy from the sun. When light is absorbed by pigments in a leaf, the energy captured is used to incorporate the carbon dioxide into organic molecules in a process called carbon fixation.

The process of photosynthesis can be expressed by the following word equation and chemical equation.

Carbon dioxide + Water ( Glucose + Oxygen

6 CO2 + 6 H2O ( C6H12O6 + 6 O2

In this lab, you will be using leaf disks to compare the net rate of photosynthesis under various lighting conditions. Leaf disks normally float; however, when the air spaces are infiltrated with sodium bicarbonate solution, the overall density of the leaf disks increase and causes them to sink. In sodium bicarbonate, the bicarbonate ion acts as a carbon source for photosynthesis. As photosynthesis proceeds, oxygen is released into the interior of the leaf, which changes its buoyancy causing the disk to rise. Since cellular respiration is taking place at the same time in the leaf, the oxygen generated by photosynthesis is consumed. As a result, the rate that the disks rise is proportional to the net rate of photosynthesis.

Materials:

- Sodium Bicarbonate

- Liquid Soap

- Syringe (20 ml)

- Leaf

- Hole Punch

- Timer

- Light Source

- Stir sticks

- Plastic cups

- Beakers

- Tin Foil

Procedure:

Follow your teacher’s demo presentation carefully to set up your leaf disk apparatus and perform the experiment.

Predictions:

How will the different light conditions affect the rate of floating leaf disks?

| |

| |

| |

Data Collection:

Your group will only be able to fill out one of the columns in one of the following tables. For example, if you are assigned to the bright light variable, you will fill out one of the columns within the bright light table. You will get the rest of the class data when every group collects their data.

Individual Group Data

|Classroom Light | |Bright Light | |Dark |

|Time (min) |# of leaf disks floating per | |Time (min) |# of leaf disks floating per | |Time (min) |# of leaf disks floating per |

| |group | | |group | | |group |

|1 | | | | |

|Time (min) |# of leaf disks floating | |Time (min) |# of leaf disks floating | |Time (min) |# of leaf disks floating |

|1 | | |1 | | |1 | |

|5 | | |5 | | |5 | |

|10 | | |10 | | |10 | |

|15 | | |15 | | |15 | |

|20 | | |20 | | |20 | |

|25 | | |25 | | |25 | |

|30 | | |30 | | |30 | |

|35 | | |35 | | |35 | |

Analysis:

1. Graph the class average data for all three trials in the graph paper below. Label the graph, both axes and provide a legend to distinguish each trial.

Title: __________________________________________________________

2. What was the role of the sodium bicarbonate in this experiment?

3. Which trial resulted in all the leaf disks floating the fastest? Explain.

4. Explain the process that caused the leaf disks to rise.

5. Proteins within the leaf are necessary for photosynthesis to occur. If the leaf disks were boiled, what kind of result would you expect? Explain.

6. What is the name of the clusters of protein and pigment necessary for plants to capture light energy? Hint: they are found in the membranes of thylakoids

7. How does light intensity affect the rate of photosynthesis?

8. Which part of photosynthesis uses water? CO2?

9. Which part of photosynthesis produces O2? Sugars?

10. The same experiment was conducted where 10 leaf disks were placed in a sodium bicarbonate solution and placed in the light. Every minute, the number of floating disks were counted and recorded. After 14 minutes, the leaf disks were moved into the dark and the number of floating disks was recorded every minute. Below is a graphical representation of the data.

a. What are the 2 important processes that we need to consider when we talk about plant metabolism?

b. Why did the leaf disks begin to sink after being placed in the dark?

c. What could the rate of leaf disks sinking be correlated to?

d. Using your data, what can you deduce about the intensity of light used to obtain the data in the graph?

Conclusion: Write a 3-sentence conclusion of what you learned in this lab.

| |

| |

| |

| |

| |

-----------------------

Name _______________

Legend

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download