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What is the effect of light intensity on the rate of photosynthesis on the aquatic plant cabomba?Background information       Photosynthesis is a very important process, without it there would be no way for the environment to recover all the oxygen being used in processes of combustion and respiration. In addition the levels of carbon dioxide (CO2) in the atmosphere would rise. Hence, this reflects the importance of photosynthesis and how the atmospheric gases are kept stable by it.       Photosynthesis is the process in which plants, some partisans and some bacteria transform the energy from sunlight into potential chemical energy. The energy they obtain from sunlight is used to produce glucose from water (H2O) and carbon dioxide (CO2), this organic compound can be converted into pyruvate which discharges (ATP) adenosine triphosphate through cellular respiration and oxygen is also released through the process as a waste product.         The light energy is absorbed by chlorophyll, a photosynthetic pigment found in the chloroplast of plants and algae, during the time that the air holding oxygen and carbon dioxide enters the organism by way of the stomata which is a small pore used for gas exchange.        Glucose is a carbohydrate produced during the process of photosynthesis, plants use it as an energy source to build, flowers, leaves, seeds and fruits. Starch and cellulose (a major component of the structural material used in plant cell walls), which are more complex carbohydrates are formed when molecules of glucose integrate with each other.Photosynthesis can be outlined by the following word and chemical equation:       The rate of photosynthesis can be affected by several factors such as light intensity, concentration of carbon dioxide and temperature level. The rate of photosynthesis will normally increase when these elements are improved (the plant is more exposed to them). A limiting factor can strain the maximum rate of photosynthesis, preventing the rate from increasing above a particular level, controlling the highest attainable rate of the photosynthetic reaction. A plant cannot photosynthesise very fast without light, even if there is a large amount of carbon dioxide and water. Thus increasing the light intensity will increase the rate of photosynthesis. The concentration of carbon dioxide in the atmosphere can limit the rate of photosynthesis. A plant is not able to photosynthesise if there is deficient amount of carbon dioxide. Temperature affects the rate of photosynthesis by not being able to photosynthesise in very high temperatures and the rate of photosynthesis will also decline as the temperature decreases.      All plants, produce and use oxygen, aquatic plants and photosynthesizing algae are continually releasing oxygen into the water during a sunny day, so the dissolved oxygen in the water normally ample. Oxygen is surplus despite other organisms are using it as well. At night photosynthesis rate slows down due to the lack of light. The usual oxygen demands from organisms increase while aquatic plants and algae are also consuming it from the water. After several days of grey and cloudy weather, the oxygen in the water can exhaust and lead to a fish kill.      Even though the process of photosynthesis for aquatic and terrestrial plants is similar there are several differences, floating-leaved plants, terrestrial plants and emersed plants obtain carbon dioxide (CO2) from the air, while aquatic plants obtain it from the water. There is a lower exchange rate of gases underwater (104 times slower than in air) so it is harder for submersed plants to obtain carbon dioxide.       As stated earlier light effects in the rate of photosynthesis, when an aquatic plant is placed in a sodium hydrogen carbonate solution, if there is an appropriate amount of light, the plant will release bubbles of oxygen-containing gas. The bubbles serve as an indicator of the rate of photosynthesis when the light intensity increases the rate of bubbles being released should increase. If the light intensity is decreased, the bubbling should decrease.              Image demonstrates the effect of light intensity on the rate of photosynthesis (increasing the light intensity will increase the rate of photosynthesis)”GCSE Bitesize: Factors Affecting Photosynthesis.” BBC, BBC, www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_21c/life_processes/plantfoodrev5.shtml.  When light intensity is increased, an increase in the rate of photosynthesis will occur, more chemical energy will be released (ATP) because until a level of light intensity is attained where the rate does not increase since the light saturation point will have been reached and another circumstance (Carbon dioxide concentration or temperature) is limiting. Different wavelengths of light also affect the rate of photosynthesis, short wavelengths present a high frequency which results with more energy, while long wavelengths present a low frequency, resulting in less energy. The colour of light also affect the rate of photosynthesis, plants reflect green light, and chlorophyll found in them absorb more blue and red light. When exposed to red and blue light the rate of photosynthesis will be faster than when plant is exposed to green light.     An example of an aquatic plant is Cabomba, it is a pondweed found in dams, lakes, a weed of ponds and slow-moving waterways. It grows rapidly and generates a great amount of lat material which blocks waterways. Cabomba stems are often covered with a layer of “jelly-like” slime, it has a fan appearance since their leaves are deftly divided and it always bubbles when placed in a sodium hydrogen carbonate (NaHCO3) solution and its response to the light intensity is almost immediate.Image of a the aquatic plant cabomba “Cabomba Aquatica.” Cabomba Aquatica – Tropica Aquarium Plants, Tropica, tropica.com/en/plants/plantdetails/Cabombacaroliniana(015BDT)/4431. Hypothesis       When the light intensity is increased, the photosynthesis rate will increase, thus the cabomba will release more oxygen-containing gas bubbles. When light intensity is decreased, the rate of photosynthesis will decrease, the cabomba will release less oxygen-contained gas bubbles. As light intensity is increased, the rate of photosynthesis will rise because there will be more light available to prompt the reaction of photosynthesis, hence when light intensity decreases, the reaction rate of photosynthesis will decrease. As the light intensity is at a very high rate, the rate of photosynthesis won’t rise any more, since there will be other factors limiting the rate. A number of chlorophyll molecules that are absorbing the light is an example of a limiting factor, and at a very high rate of light intensity, photosynthesis rate will drop by the reason that light starts to injure the plant. During the process of photosynthesis carbon dioxide combines with water to produce glucose and oxygen is released as a gas. If a large amount of gas is released, photosynthesis is occurring promptly. If a small amount of gas is being released, photosynthesis is occurring gradually. Variables        My independent variable will be the light intensity, the distance from the light source to the test tube. The test tube will be positioned at four different distances from the light source. For the first position, the test tube will be placed 2 cm from the light source (a 60W desk lamp) which will be the distance with the highest light intensity. On the second position, the test tube will be placed 6 cm from the light source, in exposure to a lower light intensity. For the third position, the test tube will be 10 cm from the light source which will support a lower light intensity than the previous ones. Lastly, for the fourth position, the test tube will be placed 14 cm from the light source, this position will be the one with the lowest amount of light intensity, where it is expected for the cabomba to release the smallest amount of oxygen-contained gas bubbles.        My dependent variable will be the number of oxygen-gas bubbles released from the cabomba during the process of photosynthesis which will be counted. The variable will be measured by counting the oxygen-contained gas bubbles the cabomba will release at different light intensities (the distance from the test tube to the light source), each will be counted for two minutes and three trials will be made for each distance.The oxygen-gas bubbles released from the cabomba will be counted for three different distances, for each different placement of the test tube in relation to the light intensity (the distance from the test tube to the light source). The effect of light intensity on the rate of photosynthesis will be determined by a number of bubbles released by the cabomba at each distance from the light source.Controlled variable How it will be controlled Why it should be controlled1% sodium hydrogen carbonate temperatureThe sodium hydrogen carbonate (450 ml will be used for each trial and different distances)  temperature will be controlled by being measured (250C) before placing the cabomba in the tube by using a thermometer.The sodium hydrogen temperature should be controlled because temperature it is one of the factor that affects the rate of photosynthesis, disturbing the reliability of the experiment.Same lamp used for the experimentThe same lamp will be used throughout the experiment. (A 60W desk lamp)The same lamp should be used for the experiment because different lamps might have a different voltage, affecting the light intensity.Same aquatic plant specieThe same aquatic plant specie will be used (cabomba)The same aquatic plant specie should be controlled because using more than one species may affect data reliability, by not all species reacting the same to the solution and light. Some species can react more then others.Ex: release more gas bubbles and also be temperamental.Different piece of cabomba for each trial A different piece of cabomba will be used for each trial.A different piece of cabomba must be used for each trial during the experiment because it may affect the reliability of the data collected, by the plant not being “fresh”.Room lightningThe room will be dark at all times during the experiment.The room lightning must be controlled because varying ir may interfere on how the cabomba will react the the light sourceEx: may contribute to the light intensity and interfering in the amount of gas bubbles released. Apparatus Approximately 5-7cm long piece of Cabomba1 test tube1 Lamp (60W desk lamp)Example of a lamp used for the experiment”Globe Electric 35′ Heavy Base Architect Spring Balanced Swing Arm Desk Lamp, Black Finish, 5698601: Home Improvement.” Amazon.com: Globe Electric 35″ Heavy Base Architect Spring Balanced Swing Arm Desk Lamp, Black Finish, 5698601: Home Improvement, Amazon, www.amazon.com/Globe-Electric-Architect-Balanced-5698601/dp/B00RXSRQCC 1 Measuring tape1 Duct tape1 Timer1% sodium hydrogen carbonate (450ml)Thermometer1 500ml beaker1 funnelSet-up apparatus for the experimentAhmad, Zainal Haji. “BIOLOGY ORDINARY LEVEL NOTES.” PLANT NUTRITION PART 8: IS OXYGEN PRODUCED DURING PHOTOSYNTHESIS?, 1 Jan. 1970, aunibazilahbiologynotes.blogspot.com.br/2007/05/plant-nutrition-part-8-is-oxygen.html. MethodGather all your materials.Fill 450 ml of the beaker with 1% sodium hydrogen carbonate solution.Cut a 5-7 cm piece of Cabomba and place it at the bottom of the beaker (with the cut end up).Carefully place the funnel up side down on top of the cabomba. If there is still a portion of the beaker without 1% sodium hydrogen carbonate solution fill it up.Place the test tube on the top of the inverted funnel.Position a lamp (light source) in direction of the beaker.Fix a measuring tape with duct tape on your table so you can simply move the beaker throughout the experiment. Place the beaker at 2 cm along the measuring tape. Make sure the lamp is shining on the cabomba leaves.Time two minutes using a thermometer and count the amount of bubbles being released.Repeat this procedure for two more trials (three trials for each distance).Repeat the steps of the remaining distances (6 cm, 10 cm and 14 cm), starting from the shortest and making your way to the further away from the lamp.Throughout the experiment bubbles of gas should be released from the cabomba, if the plant does not release any bubbles, cut the end of the stem again to refresh it, only for the next trial.Safety       Students must be careful with the use of water and solutions near electrical equipment, they must ensure their hands are dry when using the lamps. Another safety measure that is very important is to dispose cabomba in household waste as it is a tropical plant meant for use in fish aquarium, it should not be disposed into ponds and lakes because it is not a native species.      Students must use safety goggles, gloves and aprons at all times since they will be working near light bulbs that can shatter. The bulbs will also get hot, students have to be very careful not to burn themselves, they should not touch the light bulb and move the desk lamp by its base at all times.