Growth & Development

Leaf Disc-o
Author(s): Kelly Castillo and Jocelyn Castro	Growth & Development Experiment SED 695B; Fall 2005

Research Question:

What is the effect of wavelength on photosynthesis?

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Standards addressed:

High School

1.The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism's cells. As a basis for understanding this concept:

f. Students know usable energy is captured from sunlight by chloroplasts and is stored through the synthesis of sugar from carbon dioxide.

Grade 7

1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As a basis for understanding this concept:

d. Students know that mitochondria liberate energy for the work that cells do and that chloroplasts capture sunlight energy for photosynthesis.

Independent variable

Dependent variables

Controls

Series

Time (minutes)

Number of floating leaf discs at any given time (as an indicator of photosynthesis rate)

Leaf discs will be placed in 0.2% bicarbonate solution.

A single hole punch will be used to keep leaf disc size the same.

Filter vs unfilter light

Materials

Procedures

leaves cut into discs
sodium bicarbonate
Blue Dawn dishwashing Detergent
Hole puncher
250mL beaker
Timer
Light source
Green cellophane

1. Collect leaves from the same plant.

2. Make leaf discs by hole punching the leaves.

3. Make 0.2% Sodium Bicarbonate solution my mixing 300ml of water with 1 teaspoon of sodium bicarbonate.

4. Make a diluted solution of liquid detergent. (3 drops of soap with 70ml of water)

5. Place 100ml of 0.2% Sodium Bicarbonate solution and add 1 drop of dilute soap solution together.

Use the syringe to add sodium bicarbonate solution into leaf discs.

6. Remove the plunger and place leaf discs into the barrel. Replace the plunger into the barrel leaving only a small amount air, but do not crush the leaf discs.

7. Pull a small volume of sodium bicarbonate solution. Create a vacuum in the syringe by covering the tip of the syringe with your finger while drawing back on the plunger.

8. While in the vacuum, swirl the solutions so that the discs are suspendend.

9. Release the vacuum so that the bicarbonate solution will enter the discs. Repeat the steps 3-5 times to get the discs to sink. If the discs do not sink, add more drops of soap.

10. Pour discs and solution into beaker. Add more solution into the beaker.

11. Place under the light sourcec and start the timer. Record the number of discs floating at the end of each minute.

***Repeat steps 6-11** For an experimental test, cover lamp with green cellophane**

Lab Tips:

Avoid wax-coated leaves; try using leaves from bagged spinach salad.
Syringe vaccuum is "tricky"; try using a vaccuum flask insead. The teacher may need to do this ahead of time.
Be sure that students are able to monitor data collection for an extended period of time. (aprox 45 min)

Extentions:

Try using different color filters to generate light of varying wavelengths.
Experiment with light intensity as well (be sure to account for differences in heat).

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Both data tables enable the student to record their observation. The primary observation made in this experiment is watching the discs floating in the solution.

The second data table shows the formula inputed into Excel so that students can easily calculate the percentages of discs floating

File formats

Excel

pdf

The graph shows a sample of the data observed during the experiment. The data is not the raw data, but the percentage of discs floating. The discs under regular light floated faster in comparison to the discs under the green light.

This graph shows the trend and pattern that occured betwen the unfiltered light and the green light. According to the graph more discs floated in the unfiltered light and it occured at a faster rate.

Sample File