How Plants Prepare Their Food

Plants and other photosynthetic organisms capture a tiny portion of the sun's energy, and in the process of photosynthesis convert it into chemical energy of organic molecule i.e, sugar. When photosynthesis occurs, oxygen is released and carbon dioxide is absorbed. Light, photosynthetic pigment, carbon dioxide and water play important role in the process of photosynthesis.

• Photosynthesis

Is the process through which plants converts poor energy containing inorganic molecules into high energy containing organic compounds. During the process of photosynthesis carbon dioxide gets reduce to sugar(glucose) and water oxidised to produce free molecule'r oxygen.

• Reactant's and product's of photosynthesis

The reactants of photosynthesis are water, carbon dioxide, and sunlight trapped by chloroplast pigments and on the other hand side products are sugar(glucose), water and free molecular oxygen. The oxygen released during photosynthesis is than used in cellular respiration to generate energy by breaking glucose. 

• Phases of photosynthesis

Photosynthesis is a series of complex redox reactions, which occurs in specific centers. These reactions of photosynthesis comprises of two phases:

The light-dependent reactions (light reactions) which use light directly and the light-independent reactions (dark reaction) which do not use light directly. 

• Light dependent Reaction

In chloroplast photosynthetic pigments are organised into clusters, called photosystems, for efficient absorption and utilization of solar energy in thylakoid membranes. Light dependent reactions constitute that phase of photosynthesis during which light energy is absorbed by chlorophyll and other photosynthetic pigment molecules and converted into chemical energy. As a result of this conversion, reducing and assimilating power in the form of NADPH2 and ATP, are formed, both temporarily storing energy to be carried along with H to the light independent reactions.

• Light independent reaction

During this phase of photosynthesis NADPH provides energised electron (and H+), while ATP provides chemical energy for the synthesis of sugar by reducing carbon dioxide, using reducing power and chemical energy of NADPH2 and ATP respectively, produced by light reactions. The energy is thus stored in the molecules of sugar. This phase of photosynthesis is also called dark reactions because these reactions do not use  light directly and take place equally well both in light and dark provided NADPH2 and ATP of light reactions are available.

• Chemiosmosis

In both cyclic and non-cyclic photophosphorylation, the mechanism for ATP synthesis is chemiosmosis, the process that uses membranes to couple redox reactions to ATP production. Electron transport chain pumps protons across the membrane of thylakoids in case of photosynthesis into the thylakoids space. The energy used for this pumping comes from the electrons moving through the electron transport chain. This energy is transformed into potential energy stored in the form of H+ gradient across the membrane. Next the hydrogen ions move down their gradient through several complexes called ATP synthase which are built in the thylakoid membrane. During this diffusion of H+ the energy of electrons is used to make ATP.