Using the straw or hole punch, cut out 10 circles from your leaves see photos below. Straws work best with spinach; hole punches work best with ivy. Remove the plunger from the syringe, and remove the cover from the tip, if there is one.
Put the leaf disks into the barrel of the syringe, and tap them down to the tip. If you have a straw, you can blow the discs gently into the plunger see photos below. Replace the plunger into the syringe, being careful not to touch or damage the leaf disks see photo below. Pour mL of bicarbonate solution into the cup.
Try to avoid making suds. Draw about 6—8 mL of bicarbonate solution into the syringe. The leaf disks should float in the solution see photos below. Hold the syringe with the tip up, and expel the air by gently pushing on the plunger. Plug the tip of the syringe tightly with your finger, and gently pull on the plunger, creating a slight vacuum. You should see tiny bubbles coming out of the leaf disks. Hold the vacuum for a few seconds, and then release the plunger, letting it snap back see photos below.
Some of the disks should begin to sink. Repeat the previous step several times, until all of the disks have sunk to the bottom of the solution see photo below. You may need to tap on the plunger to release the bubbles in order to make all the leaf disks sink. When all the leaf disks have settled to the bottom of the solution, carefully remove the plunger and pour the disks and solution into the cup.
They should settle to the bottom of the cup see photos below. If any leaf disks float, remove them from the beaker. Set up your light fixture so that it is suspended about 12 inches 30 cm above the table. You may want to use a ring stand for this.
Place the beaker under the light fixture see photo below. To Do and Notice Turn on the light, start a timer, and watch the leaf disks at the bottom of the cup. Notice any tiny bubbles forming around the edges and bottoms of the disks. After several minutes, the disks should begin floating to the top of the solution.
Record the number of floating disks every minute, until all the disks are floating. How long does it take for the first disk to float? How long does it take for half the disks to float?
All the disks? When all the disks have floated, try putting the cup in a dark cabinet or room, or cover the cup with aluminum foil. Check the cup after about fifteen minutes. What happens to the disks? Plants occupy a fundamental part of the food chain and the carbon cycle due to their ability to carry out photosynthesis, the biochemical process of capturing and storing energy from the sun and matter from the air. Separate the two parts of the syringe, drop 10 of the spinach disks inside, reassemble the syringe.
Push the plunger almost to the bottom but don't crush the disks. Put a finger on the end of the syringe, and draw the plunger back slightly, creating a partial vaccum. Repeat until the leaf disks are suspended in the solution. This action forces the liquid into the interior of the leaf. Watch this video of the process to make sure you're doing it right. Pour the contents of control and treatment syringes into two labelled clear plastic cups.
Swirl the liquid to try to keep the disks from sticking to each other or the sides of the cups and then let them sit.
Turn on a bright light, and monitor the disks every minute. Count how many disks are floating during each of the next 15 minutes. After all or most of the disks are floating, put the cups in the dark a shoebox or a closet and monitor for the next 15 minutes.
Record how many disks remain floating after each minute until all or most of them have sunk. Watch this demonstration to see how to make the leaf disks sink. Results: In the light, you should expect to see the disks in the control solution water stay on the bottom, but the disks in the treatment solution baking soda should begin to rise as they use the CO2 to undergo photosynthesis and produce oxygen bubbles.Add a few drops of liquid dish soap to this solution and mix gently, trying to avoid making suds in the solution. When you put floating leaf disks in the dark, they will eventually sink. Straws work best with spinach; hole punches work best with ivy. Push on the plunger until only a small volume of air and leaf disk remain in the barrel Pull a small volume of sodium bicarbonate solution into the syringe. How does the detergent help the leaf disks to sink? All the disks? Add a few drops of liquid graduation speech bible school soap to this solution and mix gently, trying to avoid making. Resources This experiment was originally described in Steucek, Guy L. A control group is needed to make this a true experiment.
Remove the plunger from the syringe, and remove the cover from the tip, if there is one. When the air spaces are infiltrated with solution the overall density of the leaf disk increases and the disk sinks.
Continue as before. Record how many leaf discs reached the surface of the solution during every minute of your experiment. Avoid suds. Place the light source 12 inches away from the test tube and turn on the light.
Teaching Tips This experiment is extremely amenable to manipulations, making it possible for students to design investigations that will quantify the effects of different variables on the rate of photosynthesis. Some or all of the submerged disks should begin to float within about 15 minutes Questions: How does the suction help the leaf disks to sink?
Pour the contents of control and treatment syringes into two labelled clear plastic cups. You should see tiny bubbles coming out of the leaf disks. To Do and Notice Turn on the light, start a timer, and watch the leaf disks at the bottom of the cup.
They should settle to the bottom of the cup see photos below. Swirl the liquid to try to keep the disks from sticking to each other or the sides of the cups and then let them sit. If you have difficulty getting your disks to sink after about 3 evacuations, it is usually because there is not enough soap in the solution.
The bubbles should cause the disks to float. Some of the disks should begin to sink. Record the number of floating disks every minute, until all the disks are floating. You can try to identify the range of wavelengths of light used in photosynthesis by wrapping and covering the beaker with colored gel filters that remove certain wavelengths. To use the energy stored by photosynthesis, plants like all other organisms with mitochondria use the process of respiration, which is basically the reverse of photosynthesis. Using the straw or hole punch, cut out 10 circles from your leaves see photos below.
Why do the leaf disks in the baking soda solution treatment begin to float? Hold the vacuum for a few seconds, and then release the plunger, letting it snap back see photos below. Going Further Try changing other factors that might affect photosynthesis and see what happens.
For comparison purposes, each lab group that does this procedure should report the time at which half 5 of the disks is floating. While holding the vacuum, swirl the leaf disks to suspend them in the solution.