Investigation 5: Photosynthesis
If the leaf disks are treated in a way you know increases the net rate of photosynthesis, should they start to float faster or slower? Why?
If the leaf disks were bathed in a red light source, then the rate of photosynthesis would increase than leaf disks that are bathed in a regular light source because chlorophyll absorbs red pigment and reflects green pigments. Therefore, shining a red light source onto the leaf disks would cause them to absorb more light, increasing the rate of photosynthesis. Background context:
Plant leaves are known to have a spongy mesophyll layer which usually contains CO2 and O2 gases within it, due to this leaves and leaf disks usually float in water. If leaves are placed in an alternate source of carbon dioxide in the form of bicarbonate ions, then photosynthesis can occur. When photosynthesis occurs, oxygen will accumulate in the air space of the mesophyll, causing the sunken leaf to become buoyant again. Cellular respiration occurs at the same time as photosynthesis in plant these, countering the processes and affecting the accumulation of oxygen in the air spaces. Therefore the buoyancy of leaf disks is an indirect measurement of the net rate of photosynthesis. Photosynthesis can be summarized into an equation: 6CO2 + 6H2O + Energy –> C6H12O6 + 6O2 Cellular respiration can be summarized into an equation as followed: C6H12O6 + 6O2 –> 6CO2 + 6H2O + Energy Abstract:
The objective of this study was to figure out how different light colors affected the rate of photosynthesis in spinach leaves. This was done by taking leaf disks, removing the CO2 and sinking them in beakers. One beaker filled with regular water, the other filled with a mixture of water and sodium bicarbonate. The beakers were then placed in front of the light sources and the amount of disks floating was recorded every minute. In our study the disks exposed to the red light started to float sooner than the disks exposed o the regular light. However both tests had all of their disks floating at the same minute mark. The significance of these findings is that the color of the light isn’t a very large factor in photosynthesis and is not important in the long run. Procedure:
1) Prepare 300ml of 0.2% (0.6g) bicarbonate solution for each experiment being conducted. The bicarbonate solution will act as a source of CO2 2) Pour the bicarbonate solution into a clear plastic cup to a depth of approximately 3 cm. Label this cup “with CO2.” Fill a second cup with only water, this will be used as a control for this experiment and label it “Without CO2” Throughout the rest of the procedure you will be preparing materials for both cups, so do everything for both cups at the same time. 3) If the leaf disks do not sink, add one drop of dilute liquid dish soap into your solution. This will act as a “wetting agent” or surfactant, allowing the solution to enter the leaf and causing the disks to sink. 4) Use a hole puncher to cut 10 or more uniform leaf disks for each cup. You will require 20 leaf disks in total.
Avoid major leaf veins. (The choice of plant material is perhaps the most critical aspect of this procedure.) The leaf surface should be smooth and not too thick. 5) Draw the gases out of the spongy mesophyll tissue and infiltrate the leaves with the sodium bicarbonate solution by performing the following steps. a. Remove the piston or plunger from both syringes. Put 10 leaf disks into each syringe barrel. b. Replace the plunger, but be careful not to crush the leaf disks. Push in the plunger until only a small volume of air and leaf disk remain in the barrel (