Photosynthesis updated

Photosynthesis

Photosynthesis is the process by which all autotrophic organisms like green plants, algae and photosynthetic bacteria uses light energy to make sugar and oxygen gas from carbon dioxide and water. The term photosynthesis can be defined as a process in which all plants convert all inorganic raw materials into their organic compounds in the presence of sunlight. All forms of life in universe require energy for their growth and maintenance. Like we eat and gain energy, even plants require some energy for which they synthesize their energy by capturing the energy directly from the sun and use the energy for the synthesis of essential food materials.

Photosynthesis Diagram

Phases of Photosynthesis

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There are two phases in photosynthesis.

Photosynthesis Light Reaction
This reaction of photosynthesis requires light and it occurs in thylakoids membranes. In this reaction the light knocks the reaction centers of chlorophyll, which are found in the chloroplasts. The chlorophyll starts to vibrate, which results in the splitting of water molecule (H₂O) and oxygen (O) is released into air and the remaining molecules of hydrogen (H) from the water (H₂O) remains in chloroplast and gets attached to NADP. In this phase of photosynthesis there is a loss of energy along the electron transport chain to recharge ATP from ADP. In this process, light energy gets converted into chemical energy and finally ATP molecules are produced. This reaction is also called as light-dependent reaction.

An equation for light reaction is:

ADP + NADP + H₂O → ATP +NADPH + H ion + O_2.

Photosynthesis Dark Reaction
This reaction of photosynthesis does not require light and it occurs in the stroma. In this reaction the carbon dioxide (CO₂) present in the atmosphere gets combined with hydrogen (H) from water molecules to form glucose. In this process, produced ATP molecules are converted to simple sugars. In this phase of photosynthesis ATP and NADPH are used to produce energy and glucose sugar is synthesized from carbon dioxide and hydrogen. This reaction is also called as light-independent reaction.

An equation for dark reaction is:

ATP + NADPH + CO₂ → ADP + NADP + glucose.

Photosynthesis Reaction

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An overall chemical reaction involved in the process of photosynthetic is

6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ + 6O₂   

Plants Photosynthesis

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All photosynthetic organisms contain one or more organic pigments, which are capable of observing visible radiations and will initiate the photo chemical reactions of photosynthesis. Chlorophyll-A and Chlorophyll-B are the most important pigments which are involved in the process of plant photosynthesis.

1. Chlorophyll A is a pigment present in all photosynthesis organisms, which evolve oxygen. It is bluish green in colour
2. Chlorophyll B is a pigment present in leaves of all higher plants and in green algae. It is in yellowish green in colour.
3. The chlorophyll pigments present in bacteria are called as bacteriochlorophylls.

The absorptions of chlorophyll A and chlorophyll B pigments range from 643 to 660nm.

Function of Photosynthesis

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1. The photosynthesis is a process of converting radiant energy of the sun into the chemical energy of the plant tissues.
2. Evolves molecular oxygen, for use by other living organisms.
3. Maintains the level of atmospheric oxygen, which is continuously consumed by plants and animals during respiration.
4. Produces carbohydrates that are used by plants and animals to synthesize organic acids, proteins, fats, nucleic acids, pigments, hormones, vitamins, alkaloids and other metabolites.
5. Photosynthesis is the only process, which produces huge quantities of organic matter for sustaining the life on the earth. For e.g.: natural fibers, drugs, vitamins, gums, rubber, furniture, etc.

Calvin Cycle Photosynthesis

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Calvin cycle is the part of photosynthesis, which occurs in two stages. 

• In first stage the light energy is used to produce ATP and NADPH.

• In the second stage, carbon dioxide and water molecules gets converted into organic molecules. This reaction requires reduced NADP, which are produced from light-dependent reaction. The entire process in Calvin cycle takes place in dark.Hence it is also referred as dark reactions.

Calvin cycle occurs in the stroma of the chloroplasts and it synthesizes  sugar from carbon dioxide.During this reaction the  molecules of ATP, which is  generated in the  light reactions provides the energy for sugar synthesis and the  NADPH produced in the light reactions provides the electrons for the reduction of carbon dioxide to glucose

The overall chemical equation for the Calvin cycle is:

3 CO₂ + 6 NADPH + 5 H₂O + 9 ATP → glyceraldehyde-3-phosphate (G3P) + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi                    (Pi = inorganic phosphate)

Steps of Photosynthesis

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1. In all green plants, this process occurs in the leaves. 
2. Carbon dioxide and oxygen enter and exit the leaves through pores called stomata. 
3. Water gets delivered to the leaves from the roots through a vascular system. 
4. The chlorophyll, present in the chloroplasts of the leaf cells helps in absorbing sunlight.
5. Chlorophyll and other carotenoids help in transferring light energy.
6. Photosynthesis is carried out in two phases.
7. The light reactions produce carbohydrates by using ATP and NADPH 
8. The dark reaction synthesizes sugar from carbon dioxide with the help of ATP and NADPH.

Photosynthesis Flow Chart

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Below you could see photosynthesis flow chart