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Light excites chlorophyll and energizes electrons that jump off the molecule. The energy liberated when these electrons escape is used in the phosphorylation of ADP, forming ATP. The enzyme that catalyzes the reaction is the ATP synthase.

The resulting ATP is then consumed in the next chemical stage of photosynthesis to energetically enrich carbon dioxide for the formation of glucose.

Raw Materials for Photosynthesis :

• Sunlight
• Chlorophyll → Sunlight absorbed by chlorophyll
• CO₂ → Enters through stomata and oxygen (O2) is released as by-product through stomata on leaf.
• Water → Water + dissolved minerals like nitrogen, phosphorus etc. are taken up by the roots of the soil.

NADPH acts as a reductant of carbon dioxide, it delivers highly energetic hydrogens to precursor molecules during the glucose formation process. ATP is an energy source for the reactions of the chemical stage.

The general equation of photosynthesis is:

6 CO₂ + 6 H₂O + light --> C₆H₁₂O₆ + 6 O₂.

Water molecules are also produced in the chemical stage of photosynthesis as the following complete equation reveals:

6 CO₂ + 12 H₂O + light --> C₆H₁₂O₆ + 6 H₂O + 6 O₂

Water molecules are present in the reagent side as well in the product side of the equation. Pure mathematical simplification of stoichiometric coefficients, however, leads to elimination of water from the product side and it then seems that 6 molecules of molecular oxygen (O₂), i.e., 12 atoms of oxygen, are made for each 6 molecules of water, i.e., 6 oxygen atoms, in the reagent side. Thus a false impression that 6 other oxygens come from carbon the dioxide is created.

“Dark reactions” is not a correct name for the chemical stage of photosynthesis since the reactions of the chemical the stage also occur in the presence of light.

Photosynthesis is divided into the photochemical stage, or light reactions, and the chemical stage.

The photochemical stage of the photosynthesis process occurs mainly on the thylakoids (the green part) and the chemical stage occurs in the stroma (the colourless framework) of the chloroplasts.

Light from the sun is transformed into chemical energy contained in organic material by the photosynthesis process. In photosynthesis light, water and carbon dioxide react and highly energetic glucose molecules and molecular oxygen is made.

The chemical equation of photosynthesis is the following:

6 CO₂ + 6 H₂O + light --> C₆H₁₂O₆ + 6 O₂

In autumn days become shorter and nights longer thus there is a reduction of the photosynthesis rate and some plants prepare themselves for the winter making nutrient stores. In this process, nutrients from the leaves travel towards storage sites: limbs, trunk and roots. With less chlorophyll produced in leaves the typical green color of the plant fades.

Free electrons, hydrogen ions and molecular oxygen is liberated, after the water photolysis.

The electrons will replace those electrons lost by chlorophyll molecules in photophosphorylation. The hydrogen ions will be incorporated into hydrogen acceptor molecules (NADP) and later will be used in the synthesis of glucose during the chemical stage. Molecular oxygen is liberated to the atmosphere.

In cyanobacteria, there are no chloroplasts and the chlorophyll layers are dispersed in the cytosol.

The chemical element that is central in the chlorophyll molecule is magnesium. One atom of magnesium is present in the centre of an amalgam of eight nitrogen-containing carbon rings. 

Chlorophyll molecules are placed in an organized manner in order to enhance the exposure to light on the thylakoid surfaces.

ATP is an abbreviation of adenosine triphosphate, a molecule made of adenosine bound to three inorganic phosphates. ADP is an abbreviation of adenosine diphosphate, two molecules of phosphate bound to adenosine. ATP is a molecule that stores energy for the cell. When ATP hydrolyzes and becomes ADP energy is liberated and then consumed by several metabolic reactions of the organism.

There are many beings (including all animals) that do not carry out photosynthesis. There are also autotrophic beings that do not perform photosynthesis but they perform chemosynthesis. Plants, algae and cyanobacteria are photosynthetic beings.

In plants and algae, light is absorbed by chlorophyll, a molecule present in cytoplasmic organelles called chloroplasts.

The sun, center of our planetary system and star of the milky way galaxy (our galaxy), is the source of the energy that is processed and consumed by living beings. Intense nuclear reactions in the sun liberate light and other energetic radiations into the surrounding space. Some of this energy reaches our planet.

Short notes on Significance of Photosynthesis:

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize food from carbon dioxide and water. Green plants absorb carbon dioxide from air and water from the soil. In the presence of sunlight and chlorophyll, they synthesize starch as food. They release oxygen as a by-product.
CO₂ + H₂O         --------> C₆H₁₂O₆   + O₂
Carbon dioxide + Water     -------------->  Glucose + Oxygen
Hence, photosynthesis provides food for most of the living organisms present on earth. Photosynthesis releases oxygen into the environment which is utilised by animals, human beings and many microbes in the process of respiration.

During photosynthesis carbon dioxide is energetically enriched with hydrogen from water. Water broken by photolysis is the hydrogen donor of the reaction. Glucose is made of carbon and oxygen atoms obtained from carbon dioxide and of hydrogen atoms obtained from water.

The described hypothesis is known as the endosymbiotic hypothesis about the evolutionary origin of mitochondria and chloroplasts. 

Mutualism is explained as mitochondria and chloroplasts can offer energy and nutrients to the cell in exchange for protection. The hypothesis is strengthened since those organelles have their own DNA, RNA and protein synthesis machinery and they divide themselves through binary division like bacteria do.

The experiment: Plants of same species and ages are placed each under (respecting their photoperiods) light sources emitting only one of the colours of the light spectrum (violet, anil, blue, green, yellow and red). The experiment is executed with each of the colours and after days each plant's development is compared. Those plants whose development was normal performed satisfactory photosynthesis while those with abnormal development underused the offered light. 

Chlorophyll is green because it reflects the green light frequency, i.e., it does not “use” the green range of the electromagnetic spectrum. Thus green light does not favour photosynthesis (curiously green is the light that plants “dislike”).

The complete chemical equation of photosynthesis is the following:

6 CO₂ + 12 H₂O + light --> C₆H₁₂O₆ + 6 H₂O + 6 O₂