PHOTOSYNTHESIS 500
“Ladies and gentlemen, start your chloroplasts!”
DST
Whether it’s NASCAR, Olympic luge, or the Tour de France, everyone loves a race. Today
we’re going to run a photosynthesis race! The race will take place in two solution filled syringes
between Ivy leaf disks. One syringe will be placed closer to the light than the other. You’ll put
10 disks in each syringe, create a vacuum to remove air from the disks and replace it with liquid
so that they sink. You’ll then put the syringes in front of a light to start up the photosynthetic
process. Photosynthesis will produce a gas that will eventually cause the disks to float towards
the “finish line” at the top of the syringe.
*****************DON’T GET ANY CLOSER THAN 10CM FROM A 90W BULB
1. What is the experimental variable being tested?
2. What “things” need to be controlled so that we will generate valid results, comparable
between groups? Shoot for a list of 10 (you can be picky!)
3. How many times will you need to repeat this in order to be confident of the results?
4. What gas produced by photosynthesis will cause the leaf disks to float?
5. Which syringe, closer or further, do you predict will win the race?
6. Why would a difference in distance from light affect the rate of photosynthesis? What
part of the photosynthesis process (light reactions or Calvin cycle) is being affected?
Please Explain
Materials
Per Team
 Two 10cc syringes
 Single hole punch SHARE THE ONES THAT ARE BACK WITH THE LEAVES
 Several Ivy leaves
 Light source AT THE LAB STATIONS
 Stopwatch
 Bicarbonate (H2CO3) and detergent solution (.75% bicarbonate, a little detergent)
POUR SOME INTO A BEAKER TO DRAW FROM THERE!
Procedures
1. Use the hole punch to make enough leaf disks to put 10 in each syringe.
2. Shake the leaf disks down to the end of the syringe with the hole. Try to get them to lie
flat.
3. Push the plunger down until it touches the leaf disks, but DON’T CRUSH THEM!
4. Draw up 5cc of the bicarbonate and soap solution into each syringe.
5. Invert each syringe (hole up) and tap to release air.
6. Push in each plunger just enough to remove all air from each.
7. Place your finger over the tip of the syringe and pull the plunger back to the 10cc mark.
Don’t go too far or the plunger will come out. This action creates a vacuum in the
syringe and will draw air out of the intracellular spaces in the leaf disks.
8. Hold the vacuum by keeping your finger over the tip and shake the syringe to release air
bubbles.
9. With the syringe still pointing up, release your finger from the tip and see if ALL the leaf
disks sink. If they do, stand the FAR syringe up no further than 30cm from your light and
the NEAR syringe no closer than 10cm from the light. If some are still floating repeat
steps 7-10 until they sink. If there are one or two stubborn disks, leave them
floating.
10. When both syringes are ready to go, turn on your light and begin timing.
11. Every couple of minutes rotate both syringes one turn to loosen any stuck leaf disks.
12. Keeping track of each syringe separately, record the time at which each of the first 5 leaf
disks reaches the top of the syringe.
13. The syringe that has five at the top first wins! BUT KEEP TRACK OF DATA UNTIL
BOTH HAVE 5 FINISHERS
14. Repeat the whole thing if time allows. After all an experiment with a
large _ _ _ _ _ _ _ _ z _ is better than a small one!
During /Post Lab Questions
7. What part of the photosynthetic process generated the gas that caused the disks to
float? I know you already answered this, but please humor me.
8. What molecule did the plant take in that provided the gas? What was the rest of that
molecule used for?
9. Where did those events (#8) take place? Be more specific than “chloroplast.”
10. What part of the photosynthetic process (see #6 for choices) made use of what the
Bicarbonate (H2CO3) supplied? Hint: the reaction shown below is what happens when
bicarbonate is put into water (the double arrow means that the reaction can go either
way).
H2CO3  H2O + CO2
11. Where does this part (referred to in #10) of the photosynthesis process take place? Be
more specific than “chloroplast.”
12. What is another testable variable that would affect the action of photosynthesis? Try to
think of something that would be do-able in ROOM 118.