CO2 Concentration & Photosynthesis. By Ellie Nir, Eliese Ottinger, and Zach Zatuchni

Transcription

1 CO2 Concentration & Photosynthesis By Ellie Nir, Eliese Ottinger, and Zach Zatuchni

2 Question The purpose of this experiment was to examine how the concentration of carbon dioxide affects the rate of photosynthesis in a C3 plant (spinach leaves).

3 Hypothesis More CO2 increases the rate of photosynthesis in a C3 plant (spinach) because it is an essential component of the Calvin cycle (it combines with RuBP at the first stage of the cycle.) However, at a certain concentration of CO2,the rate of photosynthesis plateaus because the Calvin Cycle can only move so quickly and utilize so much CO2 at once. Once the CO2 concentration causes the plant s rate of photosynthesis to reach its plateau, adding more CO2 will not have an effect on the rate.

4 Prediction The more CO2 that the C3 plant has access to, the higher the rate of photosynthesis will be. When the concentration is 8 grams of baking soda per 1 ml of water, all 12 leaf disks will float. When there is no baking soda, no leaves will rise.

5 Experimental Controls 1) 2) 3) 4) 5) 6) 7) The distance of the lamp was kept constant throughout all experiments at 3 cm The ph was altered with HCL so it was neutral (7.45) regardless of how much (basic) baking soda was added. The volume of water was kept constant at 1 ml The same light bulbs were used for each experiments (26 Watt) Spinach leaves only Same size leaf disks (hole punch) Same amount of dish soap (one drop)

6 Materials Scale Lamp Light bulb: 26 Watts; 175 Lumens 1 ml Graduated Cylinder Plastic Cup Syringe 12.7 grams Baking Soda 4 grams Water Spinach Leaf Disks 4 drops of Dish Soap Stirring Rods Lab Bench Rod ph Meter Hydrochloric Acid

7 Procedure First,.7 grams of baking soda was added to a plastic cup. Next, about 6 cm deep worth of water was added. After stirring to dissolve the baking soda, a drop of dish soap was added to the solution and stirred thoroughly, without making bubbles. Using a meter to measure ph, HCl was added until the (now basic) mixture returned to a normal ph (7.45). This mixture was divided into 2 cups (the other cup wrapped and saved for Monday). Next, leaf disks were prepared by hole punching spinach leaves, avoiding major veins. Then, 12 disks were poured into the bottom of a syringe (by the needle). The plunger was pushed into the barrel without crushing or damaging the disks. The tip was then placed into the solution and the plunger was pulled out until the barrel was filled 2/3 of the way. After that, a vacuum was created by pulling out the plunger while covering the tip with a finger, 4 times, until all disks

8 Procedure The infiltrated, sinking disks were placed in the cup of solution, the light was placed 3 cm above and directly over the cup and started timing. At one minute intervals, the number of leaf disks floating was counted and recorded in a table, stopping after 2 minutes. After that, a saturated solution was made, by adding 8 grams of baking soda to 1 ml of water until no more could dissolve. 12 leaf disks were infiltrated using this and the experiment was performed using a lamp clamped to a rod. The amount of leaves that rose to the surface was recorded each minute for twentyminutes. This procedure was repeated with 4 grams of baking soda and without baking soda.

9 Data Times. g.7 g 4. g 8. g Table. 1. This table shows the data collected. The amount of baking soda was altered while the amount of water was kept constant at 1 ml. The number of floating leaf disks was recorded at one minute intervals.

10 Fig. 1. This graph shows our data over time. This shows that the trials with no baking soda, and with a saturated solution resulted in no photosynthesis, and the trial with 4g of baking soda resulted in the highest rate of photosynthesis. No photosynthesis occurred in four minutes or less.

11 Data Amount of Baking Soda (Grams) per 1 ml of water Number of Floating Leaf Disks Table 2. This table shows how quickly photosynthesis occurred with each amount of baking soda by listing the total number of leaf disks that floated. The more leaf disks floating, the higher the rate of photosynthesis

12 Per 1 ml of water Figure 2. This graph shows the amount of baking soda vs the number of floating leaf disks (rate of photosynthesis). As the amount of baking soda increases, so does the photosynthesis rate until it reaches 4 grams. Then, the photosynthesis rate decreases until it drops back down to zero.

13 Discussion: Analysis The data collected in this experiment shows that the amount of carbon dioxide that is available dramatically affects the rate of photosynthesis. When the amount of baking soda was changed, the number of leaf disks that rose to the top also changed. When there was no baking soda, no leaf disks floated. With a pinch of baking soda, or.7 grams, four leaf disks floated. In a solution with 4 grams, all 12 leaf disks floated. However, in a saturated solution with 8 grams of baking soda, no leaf disks floated. The number of floating leaf disks shows the rate of photosynthesis in that more floating leaf disks at the end of 2 minutes indicated that the rate of photosynthesis is higher. By altering the amount of baking soda in this control experiment, the change in rate of photosynthesis was able to be observed.

14 Discussion: Analysis Figure 3. This graph shows what should happen as CO2 levels increase. The rate of photosynthesis should have increased, then plateaued.

15 Discussion: Analysis As seen in Figure 3, up until a certain amount, the rate of photosynthesis increases as the carbon dioxide. This is because CO2 is needed for plants to photosynthesize (make their own food). CO2 is used in the Calvin Cycle, and when it enters, it combines with RuBP, goes through a series of reactions. produces 1 G3P, and ends up as RuBP in its final step. The amount of CO2 affects the rate of photosynthesis. When there was less CO2 the Calvin Cycle doesn t move as much because there isn t as much CO2 to combine with RuBP. However, with a high concentration of CO2, the Calvin Cycle is always moving, and has a large supply of CO2 that it can use. When the concentrations is above a certain point, the Calvin Cycle is already moving as fast as it can, producing as many G3P as it possibly can, and no more CO2 will increase the rate because it is already at its maximum speed. This pattern is evident when plants are provided with pure CO2

16 Errors The data collected (as seen in graph on slide 12) is not what should have occurred if conditions were ideal. Instead of dropping back down to zero, the rate of photosynthesis should have plateaued. (See figure 3) There are multiple sources of error as to why this has occurred. The first is that 8 grams of baking soda were added to 1 ml of water in order to create a saturated solution. However, this high concentration of solute caused the water to become cloudy, which affected the amount of light which was able to reach the leaf disks that were sitting at the bottom. Also, not all of the baking soda has dissolved, leaving a few granules at the bottom of the cup which covered the leaf disks. This blocked light and prevented photosynthesis. These errors caused the rate of photosynthesis to stop, because the leaves were not given access to a vital component, light. Therefore, instead of the rate plateauing, it dropped to zero when 8 grams were used. These could be avoided by stirring thoroughly and adding slightly less baking soda to ensure that it fully dissolves.

17 Errors Lastly, baking soda is not pure CO2. While it is a source of carbon dioxide, it is also a chemical salt that also contains sodium. When high amounts of baking soda were added to the water (8 grams), more salt was added as well. Salt may have affected the rate of photosynthesis and the leaf disks. Since spinach is not an aquatic, saltwater plant it probably isn t used to high levels of salt, so it could have become dehydrated and not been able to photosynthesize. This caused the rate of photosynthesis to drop to zero when 8 grams were used. This could be prevented by using a different, more pure carbon source that did not contain chemical additives.

18 Conclusion The hypothesis claimed more CO2 increases the rate of photosynthesis in a C3 plant because it is an essential component of the Calvin cycle. This is due to the fact that it combines with RuBP at the first stage of the cycle. However, the rate of photosynthesis plateaus at a certain concentration of carbon dioxide because the Calvin cycle can only process so quickly and utilize so much CO2 at once. Because of this, adding more CO2 will not have an effect on the rate. This hypothesis was accurate and true. The trial with 4 grams of baking soda caused more leaf disks to float than the trial with.7 grams. Although the experiment produced partially unrealistic results in that the trial with a saturated solution produced floating leaf disks, further research on this topic helped to form and justify this hypothesis.

19 Conclusion This experiment was designed to test varying amounts of carbon dioxide on the photosynthesis of a C3 plant. Through this experiment, it was shown that more carbon dioxide is beneficial to photosynthesis to a certain point. However, the experiment was a partial failure. The other chemicals in the baking soda, and the fact that the solution was oversaturated corrupted the results of the trial with the most carbon dioxide. No photosynthesis occurred in that test, suggesting that too much carbon dioxide can be harmful. Through some research, it was discovered that as more carbon dioxide is added to the environment, the rate of photosynthesis in a C3 plant plateaus instead of decreasing because of the plant s limited capacity for CO2.

20 THE END