Bio Experiment Light Intensity Essays

Bio Experiment Light Intensity Essays Bio Experiment Light Intensity Essay Bio Experiment Light Intensity Essay Research question : How does the different light intensity affect the rate of photosynthesis in plants? Objective : To investigate the relationship between different light intensity (by having the source of light at different distance to the plant discs which is at; 10cm, 15cm, 20cm, 25cm, 30cm, and 35cm ) and rate of photosynthesis of plant. Introduction : Photosynthesis is the process where light energy is absorbed by green plants to convert the raw materials (carbon dioxide and water) into sugars and oxygen (waste product). This conversion can be summarized into the equation below: Raw materials Products 6CO2 + 6H2O C6H12O6 + 6O2 (light energy) waste product Referring to the above equation, it can be seen that light energy plays the role as the source of energy stimulating the process of photosynthesis. The main pigment that absorbs light energy is chlorophyll which is the green pigment found inside chloroplasts. A green leaf cut out into discs of the same size are used in this experiment. This experiment is carried out to discover how different intensity would affect the rate of photosynthesis. Hypothesis : As light intensity increases, the rate of photosynthesis increases. Variables : Variables| Ways of controlling| Independent variable :The distance of the source of light energy to the plant discs (light intensity). | Use different distance in each experiment by measuring using a 1 m ruler. The different distance are 10cm, 15cm, 20cm, 25cm, 30cm, and 35cm. Dependent variable :Rate of photosynthesis | The rate of photosynthesis in each experiment is calculated by using the formula ;1tt = the time taken for each plant discs to float on the surface of 3% sodium hydrogen carbonate measured by using a stopwatch. | Controlled variable : * Number of plant discs used in each experiment * Concentration of sodium hydrogen carbonate solution * Volume of sodium hydrogen carbonate used * Size of plant discs * Source of light| Bu sing a cork borer, 5 discs measuring 8 mm in diameter each are cut out from the same leaf for each experiment. Each experiment uses a set of 5 plant discs). Use the sodium hydrogen carbonate solution of 3% concentration only for each experiment. Use only 10ml of sodium hydrogen carbonate in each experiment measured by using a 20ml syringe. The plant discs are cut out by using the same cork borer with each of them having the diameter of 8mm each measured with 15cm ruler. The same desk lamp and its bulb is used in each experiment. | Table 1 : List of variables and ways to control them Materials and apparatus : Materials and Apparatus| Quantity| Volume/size| Fresh green leaf| 1| 5 of 8mm discs for each experiment| 3% sodium hydrogen carbonate solution| 1 reagent bottle| 20ml for each experiment| Desk lamp| 1| -| syringe| 6| 20 ml| Stopwatch| 1| -| 1m ruler| 1| -| 15cm ruler| 1| -| Cork borer| 1| -| beaker| 66| 100ml50ml| White tile| 1| -| Measuring cylinder| 1| 100 ml| Table 2 : list of materials and apparatus, their quantities, and volume or size used in the experiment. Methodology: 1. The distance between the bottom of the light bulb (from the desk lamp) and the surface of the laboratory table is adjusted at 10 cm. The lamp was turned on, and all other source of light was turned off. 2. 20 ml of 3% sodium hydrogen carbonate solution was measured by using a 100 ml measuring cylinder and then was poured into a 100 ml beaker. 3. 10 ml of the 3% sodium hydrogen carbonate solution was transferred into a 20ml syringe. 4. 5 of approximately 8mm in diameter each plant discs were cut out from the same green leaf by using a cork borer. 5. A thumb or any finger was placed over the hole at the tip of the syringe to hold its content while the plunger is slowly pulled out. 6. The 5 plant discs are put into the syringe containing 10 ml of 3% sodium hydrogen carbonate solution. The plunger was then slowly pushed back inside the syringe while still keeping the finger or thumb over the hole at the tip of the syringe. 7. The finger was then removed to expel the excess air inside the syringe by pushing the plunger forward slowly. 8. Then, the finger was placed back again on the hole at the tip of the syringe, and the plunger is pulled in to compress the remaining content in the syringe. 9. The plunger was pulled slowly until it came out and the content in the syringe was poured into a 50 ml beaker. 0. The beaker was then quickly placed below the light bulb and a stopwatch was simultaneously started. 11. The time taken for each plant disc to float on the surface of the 3% sodium hydrogen carbonate solution was recorded. 12. Steps 1-11 were repeated with the distance of 15cm, 20cm, 25cm, 30cm, and 35cm. 13. All data were recorded, and tabulated. Results : * Quant itative data Distance between source of light energy to plant discs, cm ( ±0. 05 cm)| Time taken for plant discs to float on the surface of sodium hydrogen carbonate, s ( ±0. 1 s)| | Trial 1| Trial 2| Disc 1(reading 1)| Disc 2(reading 2)| Disc 3(reading 3)| Disc 4(reading 4)| Disc 5(reading 5)| Disc 1(reading 6)| Disc 2(reading 7)| Disc 3(reading 8)| Disc 4(reading 9)| Disc 5(reading 10)| 10. 00| 655. 0| 960. 0| 1170. 0| 1470. 0| 1835. 0| 1110. 0| 1280. 0| 1350. 0| 1370. 0| 1440. 0| 15. 00| 1212. 0| 1590. 0| 1490. 0| 1812. 0| 1856. 0| 1214. 0| 1350. 0| 1490. 0| 1710. 0| 1736. 0| 20. 00| 1530. 0| 1600. 0| 1610. 0| 1730. 0| 1950. 0| 1651. 0| 1700. 0| 1710. 0| 2026. 0| 2130. 0| 25. 00| 1720. 0| 1790. 0| 1820. 0| 1916. 0| 2066. 0| 1780. 0| 1950. 0| 2000. 0| 2410. 0| 2480. | 30. 00| 2110. 0| 2150. 0| 2240. 0| 2420. 0| 2750. 0| 2180. 0| 2250. 0| 2412. 0| 1570. 0| 2780. 0| 35. 00| 2411. 0| 2426. 0| 2483. 0| 2723. 0| 3057. 0| 2533. 0| 2566. 0| 2661. 0| 3503. 0| 3310. 0| Table 3 : Distan ce between source of light energy to plant discs, and time taken for plant discs to float on the surface of sodium hydrogen carbonate for trial 1 and 2. * Qualitative data 1. The leaf was green in colour, was quite thick, and felt a little spongy when discs were being cut out from it using a cork borer. 2. Sodium hydrogen carbonate solution is a colourless solution. 3. Bubbles were seen surrounding the plant discs when the plunger was being pulled to compress the contents in the syringe. 4. Bubbles were also seen forming during the wait for the plant discs to float as they were photosynthesizing. * Data processing Distance between source of light energy to plant discs, cm ( ±0. 05)| Light intensity(cm-2)| Uncertain-ty for light intensity| Average time taken for plant discs to float (s), ( ±0. 1s)| Overall average time taken for plant discs to float (s)( ±0. 1s)| Standard deviation| Rate of photosynthesis(s-1)| Standard error| | | | Trial 1| Trial 2| | | | | 10. 00| 1. x 10 | 5. 0 x 10 | 1218. 0| 1310. 0| 1264. 0| 3. 2 x 10 ? | 7. 9 x 10 | 6. 3 x 10 | 15. 00| 4. 4 x 10 | 1. 5 x 10 | 1592. 0| 1500. 0| 1546. 0| 2. 4 x 10 ? | 6. 5 x 10 | 4. 2 x 10 | 20. 00| 2. 5 x 10 | 6. 3 x 10 | 1684. 0| 1843. 4| 1763. 7| 2. 0 x 10 ? | 5. 7 x 10 | 3. 2 x 10 | 25. 00| 1. 6 x 10 | 3. 2 x 10 | 186. 40| 2124. 0| 1993. 2| 2. 6 x 10 ? | 5. 1 x 10 | 2. 5 x 10 | 30. 00 | 1. 1 x 10 | 1. 8 x 10 | 2334. 0| 2238. 4| 2236. 2| 3. 5 x 10 ? | 4. 5 x 10 | 2. 0 x 10 | 35. 00| 8. 2 x 10 | 1. 1 x 10 | 2620. 0| 2914. 6| 2767. 3| 3. 9 x 10 ? | 3. 6 x 10 1. 3 x 10 | Table 4 : Distance between source of light energy to plant discs, light intensity, uncertainty for light intensity, average time taken for plant discs to float, overall average time taken for plant discs to float, standard deviation, rate of photosynthesis, and standard error. * Light intensity (cm ) is calculated by using the formula: 1(Distance between source of light energy to plant discs)? For example on 10. 00 cm distance : = 110. 00? = 1. 0 x 10 (for the rest of the light intensity values, please refer to table 4) * Uncertainty for light intensity : ight intensity=1(Distance between source of light energy to plant discs)? ? light intensitylight intensity = ? Distance between source of light energy to plant discsDistance between source of light energy to plant discs+? 11 ? light intensity = ? Di stance between source of light energy to plant discsDistance between source of light energy to plant discs x light intensity For example on 10. 00cm distance : ? light intensity = 0. 05 cm10. 00 cm x 1. 0 x 10 = 5. 0 x 10 ( For the rest of the uncertainty of light intensity, please refer to table 4 ) * Average time taken for plant discs to float in trial 1 and 2 (s) : Average time taken in trial 1 = reading 1+ reading 2+ reading 3+ reading 4 + reading 55 Average time taken in trial 2 = reading 1+ reading 2+ reading 3+ reading 4 + reading 55 For example on 10. 00 distance : Average time taken in trial 1 = 655. 0 + 960. 0 + 1170. 0 + 1470. 0 + 1835. 0 5 = 1218. 0 s Average time taken in trial 2 = 1110. 0 + 1280. 0 + 1350. 0 + 1370. 0 + 1440. 0 5 = 1310. 0 s (for the rest of average time taken for plant discs to float in trial 1 and 2, please refer to table 4) * Overall average time taken for plant discs to float (s) : Overall average time take or plant discs to float = Average time taken in trial 1+ Average time taken in trial 22 For example on 10. 00cm distance : Overall average time take for plant discs to float = 1218. 0 +1 310. 02 = 1264. 0 s ( For the rest of the overall average time taken for plant discs to float, please refer to table 4) * Standard deviation : SD=reading 1-overall average2n-1+reading 2-overall average2n-1+†¦+(reading 10 -overall average2n-1) For example on 10. 00 cm distance : =655. 0-1264. 029+960. 0-1264. 029+†¦+(1440. 0-1264. 029) = 3. x 10? ( For the rest of the standard deviation, please refer to table 4 ) * Rate of photosynthesis (s ) : = 1(overall average time taken for plant discs to float, s) For example on 10. 00 cm distance : =1(1264. 0 s) = 7. 9 x 10 ( For the rest of the rate of photosynthesis, please refer to table 4) * Standard error : rate of photosynthesis=1overall average time taken for plant discs to float, s Rate of photosynthesis ? rate of photosynthesisrate of photosynthesis = ? overall average time taken for plant discs to floatoverall average time taken for plant discs to float+? 11 ? rate of photosynthesis = ? verall average time taken for plant discs to floatoverall average time taken for plant discs to float x For example on 10. 00cm distance : ? rate of photosynthesis = 0. 1 s1264. 0 s x 7. 9 x 10 = 6. 3 x 10 ( For the rest of the standard error, please refer to tab le 4) Graph 1 : graph of light intensity against rate of photosynthesis. Discussion : Photosynthesis is a process in which green plants use the energy of sunlight to produce sugars from the inorganic raw materials of carbon dioxide and water. In this experiment, we are trying to find the effect of light intensity on the rate of photosynthesis of plant. Theoretically, the rate of photosynthesis is directly proportional to light intensity up to certain point; as in graph below: Rate of photosynthesis X Light intensity Graph 2: Theoretical graph of relationship between light intensity and rate of photosynthesis As light intensity increases, the rate of photosynthesis increases up to a certain (point X) and then the graph will remain plateau. A further increase in light intensity (beyond point X) does not increase the rate of photosynthesis because of limiting factor such as concentration of carbon dioxide and temperature. However, this is not the exact case in this experiment. As we can see from the graph of light intensity against rate of photosynthesis, there is no constant reading (the readings continued to increase from 3. 6 x 10 s to 7. 9 x 10 s ) which means that the photosynthesis process in this experiment have not reached it’s the maximum point yet. When chlorophyll other pigments in the plant discs absorbs light, electrons becomes excited and the chlorophyll is also photoactivated. As more light is absorbed, more electrons can be boosted to higher level energy, and eventually the production oxygen is also vigorous. Hence, we can say that the rate of photosynthesis increases as chlorophyll absorbs more light. This explains why the first three points in the graph of light intensity against rate of photosynthesis produces a much steeper line. In this experiment, we can also see that although the plant discs were placed inside the sodium hydrogen carbonate at the same time, they still photosynthesize at different rate. This is because the discs are taken from taken from different part of the leaf. The side part of the leaf contains more spongy mesophyll cell and palisade mesophyll cell compared to the centre part of the leaf. The part which contain more spongy mesophyll cell and palisade mesophyll cell would have higher rate of photosynthesis as they are rich in chloroplast. As there are more chloroplast, there would be more absorption of light photons; leading t higher rate of photosynthesis when compared to the discs taken from the centre part of the leaf. As for the method of the experiment, air are expelled from the syringe containing the plant discs at the beginning of the experiment to ensure that each disc would have no gas in them initially; especially carbon dioxide. Once all plant discs are placed in the solution, the beaker containing them is put under the desk lamp, and a stopwatch is immediately started. When the plant disc starts to float on to the surface, it shows that photosynthesis has occurred and the presence of gas inside the cell causes the density of the disc to decrease; allowing it to float. The small bubbles seen are actually the release of oxygen gas as a result of photosynthesis. Limitations and suggestion : Limitation| Suggestion | The range between the 1st reading and the 10th reading of time taken for plant discs to float in each light intensity value varies with such great gap. | To avoid it, cut out the plant discs from the same area for all trials. Preferably, cut it out from the side of the leaf as that part contain lots of mesophyll cell (with lots of chloroplast; making it easier for photosynthesis to occur). | When expelling the air, some of sodium hydrogen carbonate tends to spill out too; leading to the decrease in volume of sodium hydrogen carbonate should be used. Hence the volume of carbon dioxide supplied which is supposed to be constant; became varied. | Expel the air on top of beaker containing the rest of sodium hydrogen carbonate solution so that when any of it inside the syringe leak out, it would drop inside the beaker itself; maintaining volume of carbon dioxide. | There is also presence of external source of light other than the desk lamp itself. The plant discs may have synthesized before they were put inside the beaker. This leads to unconvincing data. | All other source of light must be switched off before the experiment started. This will yield more accurate results. Some of the plant discs were stacked on each other when placed inside the beaker. Although this condition is already altered by moving them away from each other, the disc on top has received more light then the one below. | Before putting the beaker containing the plant discs under the desk lamp, make sure that the discs are not piled on top of each other by swirling the beaker a little. | Table 5 : limitations and suggestions Conclusion : From the experiment, it is proven that when light intensity increases, the rate of photosynthesis increases; while other factors remained constant. As light intensity increases, from 8. 2 x 10 cm to 1. 0 x 10 cm , the rate of photosynthesis of plant discs also increases from 3. 6 x 10 to 7. 9 x 10. The hypothesis is accepted. Reference : * MCB Biology HL students handbook (year 1) 2010 edition: page 192,193. * Alan Damon, Randy McGonegal, Patricia Tosto, William Ward : Heinemann Baccalaureate HL Biology,2007 for the IB diploma. * Biology for the IB DIPLOMA, by CJ Clegg,2008 by Hodder Education. * Biology Seventh Edition, by Neil A. Campbell and Jane B. Reece, 2005 by Pearson.