Where does photosynthesis occur in plant ?

• Photosynthesis takes place in the leaves but photosynthesis is also reported in the stems in some special conditions.

• It is  both light independent and light dependent. The light dependent process uses light that has been absorbed by the thylakoids to convert into  chemical energy.

• This chemical energy is used by the CO2 for the synthesis of carbohydrates. 

• Chloroplasts are green plastids present in plant cells . The chloroplasts are  the site of photosynthesis in green plants or photoautotrophs. The leaves are the site of photosynthesis .

• Inside the leaves, chloroplast is generally present in mesophyll cells along their walls.

• Within the chloroplast there is a membranous system  in which a structure like the pile of coins is present called grana, the stroma lamellae and the fluid that is present in the chloroplast called  stroma.

👌👌Remember - The light and dark reaction of photosynthesis takes place in Grana and Stroma respectively.

• The membrane system is responsible for synthesizing light energy for the synthesis of ATP and NADPH.

• In stroma all the enzymatic reactions needed for formation of   ATP and NADPH takes places.

• The reaction in which light energy is absorbed by grana to synthesis ATP and NADPH is called  Light reaction. 

• Light reaction or photochemical phase includes the Light absorption, Water splitting, Oxygen release and the Formation of ATP and NADPH.

• Light reaction is followed by the dark reaction  of photosynthesis in which carbohydrates or glucose is synthesised. During a dark reaction , light is not necessary. Dark reaction is also called the biosynthesis phase. 

Pigments involved in Photosynthesis –

• Chromatographic separation  of leaf pigments reveals that Maximum absorption by chlorophyll a occurs in blue and red regions having higher rate of photosynthesis. So, chlorophyll a is the chief pigment.

• Other thylakoid pigments like chlorophyll b, xanthophyll and carotenoids are called accessory pigments that absorb light and transfer energy to chlorophyll a and protect them from photo-oxidation.

Photosynthetic Active Radiation (PAR)

• The surface of the leaf absorbs the blue and red wavelengths while the green light is absorbed by the internal part of plants Or leaves.

• This light that is absorbed by the chloroplasts used in photosynthesis and the conversion of energy.

• All the visible wavelengths are absorbed by the leaf but red, blue and green are the most important for photosynthesis.

• The light spectrum used by plants is known as Photosynthetic Active Radiation (PAR) ranging between 400 and 700 nm.

• Out of total solar radiation only 10 percent are used by the plant as Photosynthetic Active Radiation (PAR).