• Focus Questions:a) Is light required for photosynthesis?

b) How does the rate of photosynthesis change as the amount of light changes?

Elodea and Photosynthesis Lab

• Background Information:– Photosynthesis Equation:

CO2 + water + light → glucose + oxygen

– Bromothymol Blue (BTB) – a chemical indicator used to detect weak acids and bases.

– BTB reaction:Blue BTB + CO2 → YELLOW BTBYellow BTB + oxygen → BLUE BTB

• Safety:

– Blow GENTLY through the straw to avoid splashing.

– Only submerse your straw into the liquid about ½ an inch to avoid splashing

• Materials available:– 2 test tubes– 2 rubber stoppers– Tap water– BTB solution (you only need a few drops)– 2.0-2.5 in. of Elodea– Straw– Dark environment (in the cupboard)– Strong Light environment (sunny window)

•Procedure:

1) Fill your test tube 1-2 way with water and add five drops of Bromothyml Blue (BTB) to your test tube. ( BTB is the small blue bottle at your table)

2) Use a straw to GENTLY blow bubbles into your test tube until your water turns Yellow (this will take 5-10 minutes)

•Procedure:

3) Take a 2 inch piece of Elodea from your plastic dish and place it in your test tube

4) Put a rubber stopper on top of your test tube.

• Procedure:

5) Label both of your test tubes with both you and your partner’s initials

6) Pick one test tube to go in the dark (Inside the cupboard labeled “DARK”), and the other test tube to go in the light (On the Test Tube Rack labeled “LIGHT”).

7) Place each LABLED test tube in the appropriate location:- one tube in the strong light from the sun lamp- one tube in the dark cupboard with no light

• Procedure:

8) Check your Elodea the next class and record in your data table the number that best matches the color in your test tube:

More CO2 CO2 = O2 More O2

6 7 8

Yellow Green Blue

• Procedure:

9) Make a Graph of the data you collected on your table. Be sure to include the following:

- A Title for your graph- Label and Units for X axis- Label and Units for Y axis- A bar for “high light” - A bar for “ dark/no light”

Effects of Different Light Exposures on Photosynthesis of Elodea

Light Dark

Test Tube TreatmentC

O2

conc

entra

tion

(BTB

col

or in

dica

tor n

umbe

r)

0

6

7

8

Please check your test tubes and use the data to complete your Data Table and Graph on the back of your Lab Sheet

1. What is the photosynthesis equation?

Answer:

CO2 + H2O + Sunlight O2 + Glucose

2. What gas was being made during photosynthesis that made the BTB turn from yellow to blue?

Answer: ___________ was turning the water _________

3. What gas were plants removing from the water that made the BTB turn from yellow to blue?

Answer:_____________ was removed, turning the water ____

4. If global warming is caused by the increase in CO2 in Earth’s atmosphere, would you predict an increase or decrease in photosynthesis due to global warming?

Answer:Global warming would cause _______________ __________________________________________

5. What effect did the presence of light have on the amount of photosynthesis?

Answer:Light caused __________________ to happen.

6. If Elodea is green, what color photons was Elodea absorbing in order to do photosynthesis?

Answer:Elodea was absorbing ____________________________ in order to do photosynthesis.

7. What would be the worst color light to put next to the Elodea if you wanted maximum photosynthesis?

Answer:___________ would be the worst color for a grow light.

8. Why would this be the worst color grow light?

Answer:_______ would be the worst color grow light because

plants are not able to ______ green light.

9. Besides light color and light amount, list two more factors that effect photosynthesis:

Answer:Amount of CO2Temperature (hot or cold)Amount of Chlorophyll in the leaf….

10. What is a pigment?

Answer:A pigment is _________________________

11. What is the name of the pigment involved in photosynthesis?

Answer:__________ is the pigment found in plants that allows them to do photosynthesis.

12. Describe a future experiment you could do to study some aspect of photosynthesis using Elodea (i.e. changing the color of the light, not blowing in the BTB, beforehand, etc).

Answer:Use your own brain on this one