Photosynthesis

• Photosynthetic rate


  The rate at which plants take in carbon dioxide, water and the energy from sunlight to produce glucose
• Chlorophyll


  A green pigment in plants that absorbs light energy used to carry out photosynthesis

  
• Role of enzymes


  Photosynthesis is an enzyme-controlled reaction where the enzymes are needed to convert carbon dioxide into glucose
• Temperature


  Increases the rate of reaction up to an optimum rate, after which the denaturation of enzymes will occur

  
• Sunlight


  Is needed as an energy source for photosynthesis to occur

  
• Carbon dioxide (CO2)


  Enters the plant through the stomata during gas exchange and is the source of carbon needed to make glucose

  
• Temperature effect


  Photosynthesis rate increases to an optimum and then decreases due to denaturing enzymes

  
• Light intensity effect


  Photosynthesis rate increases and then plateaus due to another limiting factor such as temperature or carbon dioxide

  
• Carbon dioxide concentration effect


  Photosynthesis rate increases and then plateaus due to another limiting factor such as temperature or light intensity

  
• Chlorophyll effect


  Plants with diseases or variegated leaves may have less chlorophyll which reduces the rate of photosynthesis

  
• Limiting factor


  An environmental factor that prevents photosynthetic rate from increasing

  
• Three main limiting factors


  Temperature, light intensity and carbon dioxide concentration

  
• Plateau


  Where a graph levels off and no longer increases past a certain point

  
• Inverse-square law


  Light intensity is inversely proportional to the square of the distance from a light source

  
• Inversely proportional relationship


  As the distance of light from a plant increases, the light intensity decreases

  
• Photosynthetic rate


  The rate at which plants take in carbon dioxide, water and the energy from sunlight to produce glucose and oxygen
• Light intensity


  A factor that typically increases the rate of photosynthesis

  
• Distance from light source


  The independent variable or factor that is changed in this experiment to investigate photosynthesis

  
• LED light source


  Is used as it releases less heat compared with other light bulbs

  
• Temperature


  A variable that should be controlled in this experiment to ensure the results are valid
• Sodium hydrogen carbonate


  Added to the water to supply the pondweed with a controlled source of carbon dioxide

  
• Pondweed


  A species of aquatic plant such as Cabomba or Elodea

  
• Acclimatise


  Allow the pondweed time to settle during each test before recording data to ensure results are valid
• Bubbles of gas

  The pondweed should release oxygen bubbles that can be counted as a measure of photosynthetic rate
• Number of oxygen bubbles


  The dependent variable or factor that is measured in this experiment to investigate photosynthesis

  
• Mean average


  The total sum of the data values divided by the number of times the data was recorded

  
• Volume of oxygen gas


  A more accurate experiment would be to collect the oxygen in an inverted measuring cylinder and record the volume

  
• Expected results


  As distance from the light source doubles, the number of bubbles per minute should decrease by a factor of four

  
• Inverse-square law


  Light intensity is inversely proportional to the square of the distance from a light source

  
• Inversely proportional relationship


  As the distance of light from a plant increases, the light intensity decreases

  
• Water bath


  A container of water heated to a given temperature for control purposes

  
• Examples of other control variables


  To ensure the results are valid the volume, concentration, external light and pondweed variety should be controlled
• Photosynthesis


  A process where plants and algae synthesise glucose from carbon dioxide and water, using light energy from the sun

  
• Photosynthesis word equation


  Carbon dioxide + water (+light energy) -> glucose + oxygen

  
• Balanced equation for photosynthesis


  6CO2 + 6H2O -> C6H12O6 + 6O2

  
• Glucose (C6H12O6)


  The main chemical product of photosynthesis that has many different uses in a plant, including respiration

  
• Oxygen (O2)


  A waste product of photosynthesis that leaves the plant through the stomata of the leaves or can be used for respiration

  
• Carbon dioxide (CO2)


  A reactant needed for photosynthesis to synthesise glucose, this gas enters the plant via gas exchange through the stomata of the leaves

  
• Water (H2O)


  A reactant needed for photosynthesis to take place, water is absorbed by the roots and is transported by the xylem to reach the leaves where photosynthesis occurs

  
• Endothermic reaction


  A chemical reaction where energy is taken in from the surrounding environment