Photosynthesis in Higher Plants

SYNOPSIS

• Synthesis of carbohydrates by green parts of plants in the presence of sunlight with the help of carbon dioxide and water is called photosynthesis.
• Chloroplasts are the site of photosynthesis.
• Pigments involved in photosynthesis are chlorophyll a, b, c, d and e.
  
  

• Absorption spectra of chlorophyll a and chlorophyll b reveal that these pigments absorb maximum wavelengths of the blue–violet and red light of the visible spectra.

• Maximum photosynthesis occurs in the blue–violet and red parts of light.

• The pigments are organised into two light-harvesting complexes or antennae within photosystem I and photosystem II.

• In PS I, the reaction centre chlorophyll a has an absorption peak at 700 nm, while in PS II, the absorption peak is at 680.

• Electron Transport Chain/Z Scheme
  
  
  

• The electrons that were removed from PS II during the electron transport chain are replaced by the photolysis or splitting of water.
  
  

• Light Reaction: The light reaction of photosynthesis occurs only in the presence of sunlight in the thylakoid membranes of grana and stroma lamellae.
  
  

• Dark Reaction: The dark reaction is the second phase of photosynthesis which occurs in the stroma of chloroplasts. It uses ATP and NADPH₂ for the fixation and reduction of CO₂ to form carbohydrates.

• Types of CO₂ Fixation
  
  
  
  

• The process of uptake of oxygen and the production of carbon dioxide in light by photosynthesising tissues is known as photorespiration.

• Factors Affecting Photosynthesis