PHOTOSYNTHESIS

What is the role of CO 2 in photosynthesis? Plants USE carbon dioxide to carry out photosynthesis. We can determine the presence of CO 2 in water by using an indicator called BTB (bromthymol blue). BTB is neutral (7). If CO 2 is dissolved in water it will form carbonic ACID. BTB turns YELLOW in acids and GREEN in bases. Let’s demonstrate….

Procedure: 1.Label 4 test tubes A, B, C, & D 2.Fill each test tube1/2 full with water 3.Add 20 drops of Bromthymol Blue (BTB) indicator to each test tube What color is the water in the test tubes? What is the pH of the water? 4. Use a straw and gently blow into test tubes A & B What color do you think the water will turn after blowing into it? NOW LET’S TEST…

This is how it’s done…

Procedure Continued 5.Place a sprig of ELODEA in test tubes A & C. 6.Screw tops onto test tubes and let sit under a grow light for 24 hours. What process is the Elodea going to be carrying out?

STARTING OBSERVATIONS TUBESTARTING OBSERVATIONS A B C D Water, CO 2, Elodea, yellow Water, CO 2, yellow Water Water, Elodea, blue

Hypothesis What do you think will happen in each of the test tubes after 24 hours? Write your predictions on your data sheet. TEST TUBE A Plant will photosynthesize…use the CO 2 …tube will turn back blue TEST TUBE B Nothing will happen…no plant…tube will remain yellow TEST TUBE C Nothing will happen…plant present…water present…no CO 2 …tube will be blue TEST TUBE D Nothing will happen…no plant…no CO 2 …this is CONTROL tube…still blue

The next day...

Conclusion Test Tube A: Water is blue… plant removed CO 2 …photosynthesized Test Tube B: Still yellow… No plant present to remove CO 2 Test Tube C: Water is yellow… plant released CO 2 …carrying out respiration Test Tube D: No change…control

ANALYSIS 1.Write a conclusion about what you have learned about the relationship between carbon dioxide and photosynthesis. 2.In which tube did photosynthesis take place? What evidence supports your answer? 3.Explain what you think would have happened if test tube 1 were placed in the dark for 24 hours instead of the light. 4.Which test tube was the control tube? 5.Name 3 constants in the experiment 6.What was the independent variable in the experiment? (there were 2 different ind var)

The Scientific Method What was the independent variable? What were some constants?

What affects the rate of photosynthesis? Sunlight Amount of CO2