Higher and Higher
Leaf disks float, normally. When the air spaces are infiltrated with solution the overall density of the leaf disk increases and the disk sinks. The infiltration solution includes a small amount of Sodium bicarbonate. Bicarbonate ion serves as the carbon source for photosynthesis. As photosynthesis proceeds oxygen is released into the interior of the leaf, which changes the buoyancy--causing the disks to rise. Since cellular respiration is taking place at the same time, consuming oxygen, the rate that the disks rise is an indirect measurement of the net rate of photosynthesis.
Purpose
Claim
After reading through the lab, create a claim about what will happen in the lab (it should relate to the leaf disks and light).
Materials
Methods
See tables in the lab procedure, or create your own.
Analysis
Leaf disks float, normally. When the air spaces are infiltrated with solution the overall density of the leaf disk increases and the disk sinks. The infiltration solution includes a small amount of Sodium bicarbonate. Bicarbonate ion serves as the carbon source for photosynthesis. As photosynthesis proceeds oxygen is released into the interior of the leaf, which changes the buoyancy--causing the disks to rise. Since cellular respiration is taking place at the same time, consuming oxygen, the rate that the disks rise is an indirect measurement of the net rate of photosynthesis.
Purpose
- Support or not support the idea that plants can go through photosynthesis.
- Determine what chemicals are needed and produced by plants photosynthesizing.
Claim
After reading through the lab, create a claim about what will happen in the lab (it should relate to the leaf disks and light).
Materials
- Sodium bicarbonate (Baking soda)
- Liquid Soap
- Plastic syringe (10 cc or larger)
- Leaf material
- Hole punch
- Plastic cups
- Timer
- Light source
Methods
- Pull the plunger out of the syringe.
- To cut out a disk, use a single hole punch. The disks will be captured in the trap on the hole punch, do not crush the disks when removing them
- Place each leaf disk into the syringe. You may need to tap the syringe case to cause them to fall to the bottom.
- After 10 leaf disks are in the syringe. Replace the plunger, making sure to not crush any of the disks.
- Place the syringe tip into your group's designated liquid (either baking soda solution or water). Pull the plunger back to fill the syringe to the 5-mL mark. (It will probably work best to overfill, tap the bubbles out, and then expel the extra until you reach 5 mL.)
- Put your thumb on the tip of the syringe, apply pressure, and pull the plunger back until you feel vacuum pressure. This vacuum will pull any air from the spaces within the tissue of the leaf disks. You may see air bubbles form on the disks as you create more negative pressure.
- Slowly release the plunger.
- Gently tap the syringe with your finger to remove the air bubbles from the disks.
- When you turn the tip of the syringe upward, the leaf disks should start to sink. You may need to repeat this process several times to get all 10 disks to sink. After the disks have sunk, fill the syringe to the 10-mL mark.
- If using bright light, place your syringe with its tip upward about 10 cm from a grow light, lamp, or flashlight.
- If using room lighting, place your syringe with its tip upward on a desk.
- If using no light, place your syringe with the tip upward away from direct light. You may need to cover your chamber to ensure that it is not exposed to light.
- After 2 minutes, tap the sides of your syringe and count how many leaf disks are floating. Continue to observe and record the results every 2 minutes for a total of 20 minutes.
- Record your own results on Table 1.
- After completing your experiment, compare your findings with other student pairs in your group and fill in Table 2 with this data.
- Graph your group’s results, making sure to include labels.
See tables in the lab procedure, or create your own.
Analysis
- What does a plant need for photosynthesis?
- What are the products of photosynthesis?
- What is a by-product of photosynthesis?
- Where does photosynthesis occur in a plant?
- Write a hypothesis that this experiment is designed to test.
- Which syringe serves as a control?
- What variables are tested in this experiment?
- Compare the test groups. Which syringe had the most leaf disks floating after 20 minutes?
- Were there any syringes without floating disks?
- How do floating disks correspond to the rate of photosynthesis?
- According to your data, does light intensity affect the rate of photosynthesis? Explain.
- How did the baking soda solution affect photosynthetic rates?
- Why is photosynthesis a light-dependent reaction?