PHOTOSYNTHESIS

What is the role of CO2 in photosynthesis?

Plants USE carbon dioxide to carry out photosynthesis.

We can determine the presence of CO2 in water by using an indicator called BTB (bromthymol blue). BTB is neutral (7).

If CO2 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 Continued5. 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

TUBE STARTING OBSERVATIONS

A

B

C

D

Water, CO2, Elodea, yellow

Water, CO2, yellow

Water

Water, Elodea, blue

HypothesisWhat 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 CO2…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 CO2…tube will be blue

TEST TUBE D

Nothing will happen…no plant…no CO2…this is CONTROL tube…still blue

The next day...

ConclusionTest Tube A:

Water is blue…

plant removed CO2…photosynthesized

Test Tube B:

Still yellow…

No plant present to remove CO2

Test Tube C:

Water is yellow…

plant released CO2…carrying out respiration

Test Tube D:

No change…control

ANALYSIS1. 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 MethodWhat was the independent variable?

What were some constants?

What affects the rate of photosynthesis?

Sunlight

Amount of CO2