Elodea Lab - Photosynthesis
 
Objectives 
The student will:
1.  Observe evidence of photosynthesis and respiration in elodea.
2.  Gather the equipment needed to measure the rate of photosynthesis in elodea.
3. Successfully set up and conduct experiment.
4.  Count bubbles (oxygen) given off by elodea to determine the rate of photosynthesis.
5.  Change the conditions of photosynthesis by altering light intensity and carbon dioxide amount. 
Then determine how this affects the rate of photosynthesis.
 
Materials Needed:
(For each group of four students)
4 cut pieces of elodea (material at teacher’s desk)                      
4 test tubes                                         
distilled water (boiled and brought to room temperature)        
sodium bicarbonate water(boiled distilled water w/ .5 g of baking soda)          watch                                      
test tube rack                               
metric ruler
4 stirring rods                              
8 small rubber bands
Plastic bottle with cap (to aerate distilled water-to shake distilled water to make it aerated)
Sunshine (or if cloudy, use overhead or 60 watt light bulb)
Pipette with 1 ml mark
Grease marker
2 pieces of aluminum foil (cut in pieces to totally cover sides of test tubes)
     
                    
Strategy:
 
1.  Obtain 4 sprigs of elodea in 12 cm long pieces. 
2.  Place one plant against one glass stirring rod.  Attach each end to the stirring rod by placing a rubber 
band on each end.  Keep elodea towards one end of the rod. Place a stirring rod with the elodea in each test tube.
3.  Place enough distilled water in each test tube to just barely cover elodea.
4. In two of the test tubes, place 1 ml of sodium bicarbonate water and mark as test tubes 1 and 3.
5. In the other two test tubes, place 1 ml of aerated water. Mark these as test tubes 2 and 4.
6. Place test tubes 1 and 2 in test tube rack.
7. Place aluminum foil around the sides of test tubes 3 and 4.
PART B. Running the Experiment
1.  Place test tube rack with test tubes 1 and 2 in sunshine (or alternate light source). 
2. Have two team members count the number of bubbles produced in each test tube for five minutes.
3. At the same time, two team members will be counting the bubbles produced in test tubes 3 and 4 for five minutes.  
Make sure that the test tubes are not exposed to much light.
4. After five minutes, the team reassembles to document the amount of bubbles in each test tube.  All members of 
the group should have the same information in their notes.
5. Clean up area and equipment.  
6. Replace clean and dried equipment in correct area.
7. Graph findings and answer the following questions.  Turn in to teacher before the end of class.
 
Performance Assessment:                                            
 
Answer these questions using specific values from your findings. Diagrams may be included.
 
1.  How does this lab demonstrate that plants give off oxygen during photosynthesis?  Explain your answer based 
on your observations.
2.  How does the rate of photosynthesis change with the different light sources?
3.  How does the rate of photosynthesis vary from the sodium bicarbonate water to the aerated water?  
4. Based on the type of experiment you just conducted, name one other variable that could be tested.