PHOTOSYNTHESIS:

 Photosynthesis is a proces in which the green parts of a palnt, mostly leaves manufacture food materials from carbon dioxide and water in the presence of sunlight. Photosynthesis is the ultimate source of food that we eat and the oxygen that we breathe.

Plants absorb water from the soil by root hairs and carbon dioxide through the atmosphere by stomata. Chlorophyll absorbs light energy from sunlight and intiates the process. The sun energy activates chlorophyll and the activated chlorophyll transfers the sun energy into chemical energy in the form of ATP and NADPH2. This chemical energy provides the energy for the second step of photosynthesis. The whole process of photosynthesis envolves a number of chemical reactions each under the action os a specific enzyme, leading finally to formation of glucaose and oxygen is released as a by-product. Photosynthesis is vital to life on earth since all animals are directly or indirectly dependentant on plants for their food and survival.

Thevolume of oxygen liberated has been found to be equal to the volume of carbon dioxide absorbed. But it is proved that all the oxygen liberated in the process is released from water and not form carbon dioxide gas.

Chloroplast- The Site Of Photosynthesis

Chloroplast is the site of photosynthesis. The first phase of photosynthesis(light reaction) occurs in grana of cholorplasts, wheres the second phase of photosynthesis(Dark reaction) occurs in stroma of chloroplasts. Chlorophyll pigment found in grana absrobs light energy from sunlight and intiates the process. The sun energy activates chlorophyll and the activated chlorophyll transfers sun enrgy into chemical energy.

Chloropasts are green plastids found in green parts of plant exposed in sunlight. They are small, green discoid or epipsoidal 4-10 nanometer in diameter and 1-3 nanometer in thickness. They are abundantly found in leaf parenchyma. A leaf parenchyma may contain 25-50 chloroplasts in each cell. The number may vary to a great extent in different cases. In moss(Mnium), an average of 106 chloroplasts are found in each cell.

Each chloroplasts is surrounded by a double layered membrane. The membrane is made up of lipids and proteins. It encloses the granular matrix of stroma. The stroma contains a complex system of double membraned lamellae. The lamellae run parallel to to one another along the length of chloroplast. At places, the lamellae form disc-shaped structures, the grana. In grana the lamellae are aompactly placed one above the other like a srack of coins. The lamellae, which are found in the grana region are called garna lamellae, while the rest of the lamellae are designated as stroma lamellae or ontergrana lamellae. The photosynthetic pigments mostly found in the grana are assicated with the thylakoid(lamellae) membranes.

The pigments of the chloroplasts pssess the power of transforming the radiant energy of the sun into chemical energy. The chloroplasts of higher plants contain four different pigments, two closely related green pigments, chlorophyll-a and chlorophyll-b and two yellow pigments, carotene and xanthophyll. Red and blue-green algae contain red and blue pigments phycoerythrin and phycocyanin in addition to chlorophyll and the yellow pigments.