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An Investigation to find out how Light Intensity affects Photosynthesis in Pondweed.

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An Investigation to find out how Light Intensity affects Photosynthesis in Pondweed. The investigation is intended to demonstrate the way in which photosynthesis in pondweed is affected by light intensity. I have read about photosynthesis in Illustrated Biology by B.S. Becket, as well as Biology, a fictional approach by M.B.V. Roberts, and this is my summery: Most plants are neither carnivores nor herbivores, they do not feed on complex organic molecules and can instead synthesis organic compounds from inorganic raw materials, this is called Autotrophic Nutrition. There are two different types of Autotrophic Nutrition: Chemosynthesis and Photosynthesis. The method used by all green plants is Photosynthesis. Photosynthesis can be summarised by: Light energy Chlorophyll 6CO2 + 6H2O ? C6H12O6 + 6O2 Carbon Dioxide Water Glucose Oxygen Energy from sunlight is trapped by chlorophyll contained in chloroplasts found mostly in the leaves of plants, and is used to combine carbon dioxide with water. Carbon dioxide is absorbed through pores called stomata which are usually located on the under surface of the leaves, and water is absorbed from the soil by the roots. The main product generated by photosynthesis is monosaccharide sugar (glucose). This can be converted into proteins for growth, broken down into carbon dioxide and water for energy production, or built up into starch for storage. A waste product of oxygen is also released. The structure of a leaf Plan Oxygen is the only gas released during photosynthesis. Therefore, to find out how light affects photosynthesis in pondweed, I will measure the volume of gas released from some Canadian pondweed (Elodea). I will record the volume of gas releases every minute, for six minutes, before changing the intensity of light the pondweed is exposed to, and repeating the procedure. The range of equipment available for me to use in school is limited, so this is what I shall be using: a. Lamp b. ...read more.


(to 1dp) Volume (ml) of Gas released during past 30 seconds (to 0dp) 0:00 9.7 0:30 9.4 -5 1:00 9.2 -3 1:30 9.0 -3 2:00 8.9 -2 2:30 8.9 0 3:00 9.0 2 3:30 9.2 3 4:00 9.5 4 4:30 9.8 5 5:00 10.1 5 5:30 10.3 4 6:00 10.6 5 Average volume (ml) of gas released every 30 seconds (0dp) 1 My trial experiment revealed several problems with my experiment: Firstly, for the first two minutes, the volume of the matter contained in the apparatus decreased, as if gas was being used up rather than produced. This was actually because I had placed the lamp next to the test tube while I had set the equipment up, and then had moved it away to a distance of approximately 15cm. The light was considerably hot and had heated up the test tube and it's contents. Therefore, when I moved the lamp away from the test tube, the contents of the equipment compressed as they cooled down, causing the ink bubble to register a decrease of volume. To compensate for this I will leave five minutes before taking any readings, leaving enough time for the contents of the equipment (i.e. the water, pondweed, and the air) to expand or decrease, to the present temperature. Secondly, my equipment proved to include several flaws: * The normal delivery tube proved to be too wide to sustain the ink bubble, so I replaced it with a 1mm wide equivalent. * Equipment was limited, and there was not a bent 1mm wide delivery tube, so I replaced the bent delivery tube with two straight delivery tubes and a rubber pipe. * I found it very hard to position the bubble. In the end, I found a syringe to be useful for the initial positioning. * The seal between the delivery tube and the rubber pipe was not totally air tight, so I added some Vaseline to maximise the seal. ...read more.


To account for these possible mistakes I should really repeat the experiment a many times and work out an overall average. This would ensure the data is reliable and not a fluke. In addition, I could use the following equipment to decrease the chance of any fault in my equipment: a. Fluorescent Lamp b. Clamp stand c. Meter ruler (cm) d. Bung with a hole in it e. Water containing Sodium Bicarbonate f. Scaled capillary tube g. 3 way tap h. Test tube i. Elodea (Canadian Pondweed) j. Ink bubble k. Syringe l. Stopwatch Ideally, the experiment would be carried out in the dark, with no light pollution at all so that I would have total control of the light intensity. The temperature of the lab would be controlled and constant so that my results would not show how temperature as well as light intensity affects photosynthesis in pondweed. In addition, a fluorescent lamp would be used. This is for two reasons, firstly, fluorescent lamps are incredibly more efficient than normal lumen incandescent lamps, meaning they give off less heat. This also would ensure that my investigation only records the effect of light intensity on pondweed and not temperature. Secondly, the light emitted from lumen incandescent lamps is not white light, it is made up of mostly red light, with some green light, and even less blue light. Since the objective of this investigation is to show how light intensity and not colour affects photosynthesis in pondweed, and plant life has evolved over millions of years to photosynthesise using sunlight, a lamp that emits light of daylight quality would be much more adequate. Also, a three way tap combined with a syringe would enable me to reset the ink bubble to 0 for each set of readings, along with the 1mm delivery tube with scale, this would decrease the chance of human error when reading the scale. ?? ?? ?? ?? Dave Burton 10FD An Investigation to find out how Light Intensity affects Photosynthesis in Pondweed. Page 1 of 2 ...read more.

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