Photosynthesis

• Chloroplasts


  They are found inside the cells of green plants and algae. There are often large amounts of chloroplasts near the top of the leaves.

  
  

  Chloroplasts contain the molecule chlorophyll that absorbs sunlight for photosynthesis.

  
• Photosynthesis is the process in which light energy is converted to chemical potential energy in the form of glucose.

  
• Photosynthesis

  • It occurs in the chloroplasts of plant cells (mainly those found in the leaf).
  • There are two main chemical pathways in which the reactants (water and carbon dioxide) are joined to produce glucose ( and oxygen as a waste product).
  • The source of energy is light energy (from the sunlight). Chlorophyll (a pigment) entraps the sunlight.
• Light Dependent Reaction (Photolysis)


  This reaction takes place on the thylakoid membranes of the grana stacks in the chloroplasts.

  
  

  Energy from the sunlight is used to split water molecules (H2O) into H atoms and O2 molecules. ATP is also produced. 

  
  

  2 H2O → O2 + 4 H
• Light Dependent Reaction (Photolysis)


  2 H2O → O2 + 4 H

  • The O2 is a waste product and is released into the atmosphere. The H atoms are transferred to the second chemical pathway via NADP (a carrier molecule).
  • This reaction depends on the light as it provides the energy.
  • Water enters the plant through the roots (via osmosis) and oxygen is released through the stomata of the leaf (via diffusion).
• Light Independent Reaction (Carbon Fixation)


  • This reaction is also known as the Calvin Cycle. This occurs in the liquid matrix of the chloroplast, the stroma.
  • CO2  and H atoms enter a complex biochemical cycle where rearrangement takes place, and glucose, C6H12O6 is formed.

  H + CO2  → glucose (C6H12O6)
• Light Independent Reaction (Carbon Fixation)

  word equation: H + CO2  → glucose (C6H12O6)

  • The ATP produced in the light-dependent reaction is used to run the cycle.
  • CO2 enters the leaf through the stomata, and H atom were produced in the first chemical pathway.
• Glucose From Photosynthesis

  The glucose produced is:

  • Stored as insoluble starch, typically in the cells of the roots
  • Used in respiration
  • Used to make other needed organic chemicals - e.g. fats, amino acids and cellulose.

  
• Factors Affecting Photosynthesis

  Similar to cellular respiration, there are also factors that affect the rate of photosynthesis.

  
  

  These include:

  • Temperature
  • Carbon dioxide concentration
  • Light intensity

  
• Reaction Graphs

  A) Light Intensity

  B) Carbon Dioxide Concentration

  C) Temperature

  
• Factors Affecting Photosynthesis - TEMPERATURE

  As temperature increases, the rate of photosynthesis also increases to an optimum temperature.

  
  

  Past the optimum temperature, the enzymes begin to denature and the reaction can no longer take place as fast.

  
• Factors Affecting Photosynthesis - CARBON DIOXIDE CONCENTRATION

  As the concentration of carbon dioxide in the air increases, so does the rate of photosynthesis to a certain point.

  
  

  The increase in the rate will level off due to another factor limiting the rate.

  
• Factors Affecting Photosynthesis - LIGHT INTENSITY

  As the light intensity increases, so does the rate of photosynthesis to a certain point.

  
  

  The increase in the rate will level off due to another factor limiting the rate.