12 Photosynthesis - part 01 - Chloroplasts

 

12 Photosynthesis - part 01 - Chloroplasts


Photosynthesis :

  • It is the only process on earth by which solar energy is trapped by green plants and converted into food. 
  • Defination : "Synthesis of carbohydrates ( glucose) from inorganic materials like CO2 and H2O with the help of solar energy trapped by pigments like chlorophyll."



  • Final light energy trapping process on which all life ultimately depends. 
  • Most massive chemical processes going on earth. 
  • Atmosphere contains only about 0.03 percent carbon dioxide by volume. This small percentage represents 2200 billion tons of CO2 in the atmosphere. 
  • The oceans contain over 50 times by amount of atmospheric CO2 in the form of dissolved gas or carbonates.
  •  From these two sources, about 70 billion tons of carbon is fixed by the green plants annually.

Chloroplasts :


  • Mainly located in the mesophyll cells of leaves. 
  • The CO2 reaches them through the stomata and water reaches them through veins. 
  • In higher plants, the chloroplasts are discoid or lens-shaped. 
  • Each chloroplast is bounded by double membrane.
  • Inside the membranes is found a ground substance, the stroma. 
  • Inside the stroma is found a system of chlorophyll bearing double membrane sacs or lamellae. 
  • These are stacked one above the other to form grana (singular, granum). 
  • Individual sacs in each granum are known as thylakoids.
  • All the pigments
  1.  chlorophylls
  2. carotenes and 
  3. xanthophylls are located in the thylakoid membranes. 
  • These pigments absorb light of a specific spectrum in the visible region. 
  • The pigments are fat soluble and located in the lipid part of the membrane. 
  • With the help of certain enzymes, they participate in the conversion of solar energy into ATP and NADPH. 
  • The enzymes of stroma utilize ATP and NADPH to produce carbohydrates.




  • All photosynthetic plants have these pigments that absorb light between the red and blue region of the spectrum. 
  • Carotenoids found mainly in higher plants absorb primarily in the violet to blue regions of the spectrum. 
  • They not only absorb light energy and transfer it to chlorophyll but also protect the chlorophyll molecule from photo-oxidation.

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