Exploring Photosynthesis with Spinach Leaves
Investigative Question: How does the distance of light received by
plants affect the rate of photosynthesis?
Background: Everyday green plants capture and convert sunlight into
chemical energy necessary for them to live and grow. This process is
called photosynthesis. Plants require sunlight, water (H2O) and
carbon dioxide (CO2) to produce glucose (C6H12O6) and oxygen (O2),
which is released back into the atmosphere. The balanced chemical
equation for this is:
↓
6CO2 + 6H2O → C6H12O6 + 6O2
Materials:
• Spinach Leaves
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•
Baking Soda (Sodium
Bicarbonate)
Single Hole Punch
•
•
Measuring Tape
•
•
•
35 mm film canister
(opaque)
10 mL syringe
Stopwatch or clock w/
second hand
Distilled water
Procedure:
1. Add enough baking soda to barely cover the bottom of the film
canister. Fill the canister with water, replace the lid, and shake to
dissolve the baking soda.
2. Using the hole punch, cut four leaf discs from the spinach leaves.
3. Remove cap from the tip of the syringe and pull out the plunger.
Gently place leaf discs into the syringe. Replace the plunger to the 1
mL line.
4. Draw 9 mL of baking soda solution into the plunger (stop at the 10
mL line). Hold the syringe with the tip facing up and gently push the
plunger to remove all the air. Be careful not to push out the liquid.
5. Put your finger over the tip of the syringe and pull the plunger
slightly to remove any excess air.
6. Turn the syringe so the tip faces down and the leaf discs are in the
solution. Release the plunger and remove your finger.
7. Turn the syringe back up and gently tap the side until all (or most)
of the discs sink toward the plunger.
8. Place the syringe, narrow end up, 5 cm from the light bank. Record
the time each disc takes to float to the surface. Occasionally tap the
side of the syringe to keep the discs from sticking. (As leaf discs
photosynthesize and produce oxygen, they will float to the top.)
9. After all the discs float, cover the syringe with the film can and wait
until they sink again.
10. Repeat Steps 8 and 9 twice.
11. Repeat Steps 8 and 9 twice more increasing the distances from the
light to 10 and 15 cm.
Questions:
1. Using the chemical equation provided at the beginning of this
activity sheet, explain how you know photosynthesis is occurring.
2. From what structure on the leaf do you expect the Oxygen to
escape? Where is this structure located on the leaf? Explain.
3. Explain why understanding the process of photosynthesis is
important to biology. In your explanation provide details utilizing the
chemical equation provided on the first page of this activity sheet.
4. Write down an investigative question and hypothesis using the
information and materials provided in this activity.