Background

Plants use photosynthesis to make food (glucose). Photosynthesis produces oxygen as a gas. Humans and many other organisms cannot live without oxygen, since it is needed for cellular respiration. In this lab activity, you will record how plants absorb carbon dioxide in the chloroplasts during the process of photosynthesis, and release oxygen. In addition you will create a chemical equation for the photosynthesis reaction.

Materials

• Clear nail hardener
• Leaves from a variety of plants
• Microscopes and microscope slides
• Clear office tape
• Water plant called Elodea, Anacharis, or waterweed
• Eye Dropper
• Beakers
• Test tube
• Stopper
• Water
• Scissors
• Glue
• Images of carbon dioxide and water molecules
• Stopper
• Straws
• 1 flask
• Stop watch/clock
• Light source
• Ruler
• pH probe
• bromothymol blue

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Wash your hands thoroughly before leaving the lab.
• Follow instructions for clean-up of materials and disposal of any chemicals.
• Be careful when using glass, if any is dropped or broken notify teacher and follow clean-up directions.

Procedure

Station 1: Stomata

1. Using nail hardener, cover a fingernail sized spot on the underside of a leaf.
2. Wait for it to completely dry.
3. Cover the spot with a piece of tape, press firmly.
4. Place tape, sticky side down, on a microscope slide.
5. Focus on the slide using the course adjustment knob and on the 4x (red) objective lens, fine tune with the fine adjustment knob.
6. Switch to the 10x (yellow) objective and fine tune with the fine adjustment knob.

Clean up:

1. Return microscope to the 4x objective.
2. Completely lower stage to remove slide.
3. Remove your tape from the slide (CAREFULLY!) throw the tape away.
4. Make sure slide is clean.

Station 2: Carbon dioxide & pH
*Recommended that teacher complete steps 1-9.

1. Put 100 mL of water into a beaker.
2. Put the drinking straw into the beaker. Blow gently through the straw into the water for 3 minutes. This process will add a gas to the water. Throw away the straw.
3. Use a dropper to add 2.5 mL of bromothymol blue to the water. Swirl the beaker to mix.
4. Place a sprig of Elodea, cut end up, into a test tube.
5. Fill the test tube 2/3 full with the solution in beaker.
6. Fill a flask 2/3 full with water from the sink.
7. Use the ruler to position the bulb of your lamp exactly 12 inches away from the flask.
8. Put your test tube into the flask.
9. Carefully insert the pH probe into the test tube. While doing this, do not damage the Elodea sprig.
10. Measure the initial pH reading and record.
11. Measure the pH every 5 minutes and record in your data table.

Clean-up:

1. Leave for the next group as is.

Station 3: Chloroplasts

1. Pick off a small part of a leaf
2. Place the leaf in the middle of a microscope slide.
3. Using an eye dropper place 2 drops of water over the leaf.
4. Place a small cover slip over the leaf and drops of water.
5. Place the slide on the stage of the microscope.
6. Focus on the slide using the course adjustment knob and on the 4x (red) objective lens, fine tune with the fine adjustment knob.
7. Switch to the 10x (yellow) objective and fine tune with the fine adjustment knob.
8. Record observations.
9. NOTE: Make sure the aperture of the microscope is completely open, you may have to wait a minute or two.

Clean-up:

1. Dry off the water and leaf from the slide.
2. Dispose of your used leaf.

Station 4: Photosynthesis Equation

1. As a group, pick one sheet showing a carbon dioxide and water molecule.
2. Remember: Glucose (sugar) is C₆H₁₂O₆.
3. Determine as a group how many more CO₂ and H₂O molecules you need to draw to have enough atoms to make a complete glucose molecule.
4. Cut out your molecules and arrange the atoms to produce glucose and record the molecule left over (Hint: put them in pairs).

Station 5: Oxygen

1. Put one sprig of Elodea in a test tube.
2. Fill the test tube completely with water.
3. Put a stopper in the end of the test tube, the water should over flow and there should be no air in the tube.
4. Turn the test tube upside down; no air bubbles should appear at the top of the tube
5. Record observations

Clean-up:

1. Pour out the water and return the sprig to the beaker.

Results & Data

Station 1

1. What do you think the stomata are for?
2. Why do you think some are open and others are shut?

Station 2

Time	0 mins.	5 mins.	10 mins.	15 mins.	20 mins.	25 mins.
pH

1. What type of gas was blown into the beaker?
2. In this lab, how is the carbonic acid being formed?
3. Bromothymol blue is an indicator solution. In this lab what does it indicate?
4. If the plant uses the carbon dioxide in the water, what will happen to the amount of carbonic acid in the water?

Station 3

1. Record observations:
2. Did you see the chloroplasts move?
3. What is the job of the chloroplast in the plant cell?
4. Why do you think they move in a circular pattern around the cell?

Station 4

1. How many CO₂ and H₂O molecules do you need?
2. What are the reactants (ingredients for photosynthesis)?
3. What are the products of photosynthesis?
4. What is the complete chemical equation for the photosynthesis reaction?

Station 5

1. Record observations:
2. What happened inside the test tube?
3. Where are the bubbles coming from?
4. What gas is being released?