MEASURING THE RATE OF PHOTOSYNTHESIS

Transcription

1 MEASURING THE RATE OF PHOTOSYNTHESIS QUESTION: What factors affect the rate of photosynthesis in plants? BACKGROUND KNOWLEDGE Leaf disks float, normally. When the air spaces in the leaf are filled with a sodium bicarbonate solution, the overall density of the leaf disk increases and the disk sinks. The bicarbonate ion serves as the carbon source for photosynthesis. During photosynthesis, oxygen is released inside of the leaf which changes the buoyancy--causing the disks to rise. Since cellular respiration is taking place at the same time (remember plants have mitochondria too!), using oxygen, the rate that the disks float is an indirect measurement of the net rate of photosynthesis. MATERIALS: Sodium bicarbonate (Baking soda) Liquid Soap Plastic syringe Leaf material (spinach) Straw Plastic cups Timer Light source PROCEDURE: 1) Prepare the bicarbonate solution. Put 300 ml of tap water in a beaker, and add 1/8 of a teaspoon of baking soda a. The bicarbonate serves as a source of carbon dioxide for photosynthesis. 2) Add 1 drop of diluted liquid soap to this solution. Avoid suds. If your solution generates suds then dilute it with more bicarbonate solution. a. The soap helps the bicarbonate solution to be drawn into the leaf. 3) Use a straw to cut 10 leaf disks for each trial. Avoid cutting disks from any major leaf veins. 4) Remove the plunger and place the leaf disks into the syringe. 5) Replace the plunger being careful not to crush the leaf disks. Push on the plunger until only a small volume of air and leaf disk remain in the barrel. 6) Pull a small volume of sodium bicarbonate solution into the syringe. Tap the syringe so that the leaf disks are floating in the solution. 7) Holding a finger over the syringe-opening, draw back on the plunger to create a vacuum be careful not to pull the plunger out of the syringe. Hold this vacuum for about 10 seconds. While holding the vacuum, swirl the leaf disks to suspend them in the solution. 8) Let off the vacuum. 9) Repeat step 6 through 8 two or three times, OR MORE, until the leaf disks sink. 10) Remove the plunger and pour the disks and solution into a clear plastic cup. Add bicarbonate solution to a depth of 3 centimeters (use a ruler to measure this carefully!). 11) Place the cup under the light source and start your timer. At the end of each minute, record the number of disks that are floating in your data table until all disks are floating. 12) Clean up: when all of the disks have floated to the top, you may stop recording data. Dump the solution with leaf disks in the sink and return the cup to the appropriate area. DESIGN YOUR EXPERIMENT! Think about what variable you would like to change to see if it affects the rate of photosynthesis! You will conduct your own experiment using this technique, collect data, and write a conclusion about the lab. The experiment planner is on the other side of your data table.

2 Make a 3 line graph of your data (two controls and experimental) on the graph provided. CONCLUSION: Use the sentence starters below, your data, and your graphs to write a perfect conclusion! Remember, when writing a conclusion, you should write a PARAGRAPH!!! 1. The purpose of this lab was a. restatement of problem question 2. This was done by a. what was measured, calculated, found; summarize in one sentence b. Explain the purpose of the floating leaf disks. 3. Answer the lab question What factors affect the rate of photosynthesis in plants? 4. The data show a. Did the rate of photosynthesis increase or decrease due to the independent variable? b. Compare experimental results to control groups! 5. The hypothesis was a. was the hypothesis correct or incorrect; explain using the data as evidence. 6. The explanation for these results is a. Why did the independent variable cause the rate of photosynthesis to increase or decrease? 7. Possible sources of error in this lab were a. be specific - what could have affected the data? b. Do NOT include following the procedure incorrectly!!! 8. The accuracy of this lab could be improved by a. suggest ways to minimize the errors in the lab 9. This lab connects to photosynthesis because a. how could the results of this lab relate to photosynthesis as it occurs in nature? 10. A question for future research on this topic is.

3 MEASURING THE RATE OF PHOTOSYNTHESIS LESSON QUESTION: What factors affect the rate of photosynthesis in plants? Control 1 (soap and NaHCO3) Control 2 (soap only) Experiment Time (min) # floating disks Time (min) # floating disks Time (min) # floating disks

4 EXPERIMENT PLANNER My experiment plan has been approved by my teacher teacher initials

5 Title: CONCLUSION: USE A SEPARATE SHEET OF PAPER IF NECESSARY. USE THE SENTENCE STEMS (ON CLASS COPY) TO WRITE A PARAGRAPH.