[BIO 11.1] E4 - Photosynthesis

• Plants are photoautotrophic. They produce their food in the form of glucose via photosynthesis. Plants use glucose in respiration or store it in the form of starch.
• Photosynthesis balanced equation:

  6CO2 + 6H2O –(light)–> C6H12O6 + 6O2

  Light triggers the chemical reaction of photosynthesis in chlorophyll
• Carbon dioxide is consumed in photosynthesis. The presence of carbon dioxide can be verified through the usage of an indicator, phenol red. It may also be verified through the production of oxygen air bubbles.
• First Experimental Setup

  Water was pre-boiled, removing all dissolved gases from the water. Once this cooled down, four test tubes were filled with the water. Phenol red was added to each test tube, and its colors based on pH were:

  Below 6.8: yellow

  6.8-8.2: yellow to pink

  Above 8.2: pink
• First Experimental Setup

  The experiment then proceeded as follows:

  Using a straw, carbon dioxide was blown into test tubes A and B.

  Carbon reacts with water to form carbonic acid:

  H2O + CO2 -> H2CO3

  Water thyme was placed in test tubes A and C.
• First Experimental Setup

  The color change in test tube A verifies the consumption of CO2 in photosynthesis, reducing the acidity of the solution.
• Second Experimental Setup

  One test tube was filled with pre-boiled water that had been cooled to room temperature, and the other test tube contained 1% sodium bicarbonate.

  A water thyme shoot was added to both test tubes.

  Photosynthesis uses the carbon dioxide from sodium bicarbonate via the following reaction:

  2NaHCO3 -> Na2CO3 + CO2 + H2O
• Second Experimental Setup

  Greater carbon dioxide therefore increases the amount of bubbles formed via photosynthesis.
• Cyclosis or cytoplasmic streaming is a process where chloroplasts move around the cytoplasm to optimize the photosynthetic process. The movement is constant and goes counter-clockwise in most plants.
• Effect of Light Exposure

  15% sodium bicarbonate and water thyme were added to four test tubes. Each test tube was placed in setups of varying light: darkly lit, 3 watts, 7 watts, and 11 watts.
• Effect of Light Exposure

  Greater light levels increase the rate of photosynthesis. This can be observed by increased bubble production in the setups with more wattage.

  However, photobleaching can happen if there is too much light. This damages the pigment, chlorophyll, slowing down or preventing photosynthesis.
• Oxygen Production in Photosynthesis

  Dumbcane has variegated leaves: their leaves have a green part, with chlorophyll, and a white part, without the pigment. Leaves of dumbcane were cut into leaf disks.

  The green and white disks were placed into separate syringes, and sodium bicarbonate was added.

  A finger covered the syringe while the plunger was pulled back The disks were then swirled for 30 seconds, and the plunger was released slowly. This extracted the gases in the leaves via vacuum boiling: most importantly, carbon dioxide was removed.
• Oxygen Production in Photosynthesis

  These disks were then placed into a beaker with a sodium bicarbonate solution placed under strong light.

  The white disks are supposed to sit at the bottom. They can still float, but it’s unlikely. This may be caused by their accessory pigment.

  The green disks are supposed to float to the top. Photosynthesis causes oxygen production, which is stored inside the cells of the plant. Similar to how humans can float better with filled lungs, this oxygen causes a buoyancy effect, letting the leaves float.
• Paper chromatography can separate the pigments based on their retention factor. Pigments exist to protect plants from light damage and to attract pollinators.
• Normal phase chromatography was performed, utilizing the nonpolar mobile phase of a 95% petroleum-ether acetone solution.

  • The green parts of dumbcane were crushed in a mortar and pestle, then acetone was added.
  • Using a capillary tube, three filter paper was blotted with the leaf extract.
  • The mobile phase was then added to the three flasks, then the chromatogram was placed and let sit for a sufficient time.
• The retention factor Rf was calculated with the following equation:

  Rf = (distance of pigment)/(distance of solvent)
• Carotenoids are accessory pigments colored red, orange, or yellow. They are for photoprotection: the absorption of excess light to prevent damage.

  Carotene: Rf = 0.99

  Xanthophyll: Rf = 0.40-0.68
• The pigment in the chloroplast is called chlorophyll.

  1.) Chlorophyll A: Rf = 0.3

  • The most important pigment, directly responsible for photosynthesis
  • Absorbs violet and orange light the most

  2.) Chlorophyll B: Rf = 0.13; green

  • Absorbs mostly blue and yellow light
  • An accessory pigment
• The relative polarities of the pigments are:

  (most polar) Chlorophyll B > Chlorophyll A > Xanthophyll > Carotene (least polar)