Photosynthesis -Explained in English -Definiton ,Excitation of chlorophiles.Phtosystems,,C3 , C4 &CAM pathways.
---------------☀đģ Photosynthesis--------------------
đđŗPhotosynthesis is a metabolic process which light energy is trapped and coverted into chemical energy. This conversion from light to chemical energy fuels the organism and forms the base of most food webs, while also producing the oxygen essential for animal life..
), Carbon Dioxide (Co2
).
), Oxygen (O2
).
source-Wikipedia
The overall equation isđ
Carbon Dioxide + Water + Light Energy → Glucose + Oxygen,
Divied to two main reations :
Gas Exchange:light-dependent and light-independent
enters leaves through tiny pores called stomata, while
Importance
- Food Production: Creates organic compounds (food) for plants and, indirectly, all animals.
- Oxygen Supply: Releases the oxygen that sustains aerobic life on Earth.
- Energy Source: The fundamental process converting solar energy into usable chemical energy for ecosystems.
- Production of fossil fuel
- Maintenance of global temperature
- Fulfill both carbon and energy requirements of organisms.
The two Pathways of Photosynthesis.
1.C3 Pathway & 2.C4 Pathway.
Types (Adaptations)
- C3 Photosynthesis: e.g., rice, wheat.
- C4 Photosynthesis :e.g., corn, sugarcane
- CAM Photosynthesis: For extremely arid environments (e.g., cacti, pineapples) by opening stomata at night.
Light dependend reactions take place in the membrane system of thylakoids. While calvin cycle is done in the stroma
Stroma is a gel like structure.
Excitation of Chlorophiles.by photons.
When Chlorophyll molecules or other pigment absorbes photons and it boosts electrons to higher energy levels.
and those electrons are then travelled through several electron acceptors until to the final electron acceptor.
During this ,the chlorophylls get positively charged. So, it is oxidized and electron acceptor is reduced
Phtotsystems.
Chlorophyll molecules ,proteins and other organic molecules are arranged in complexes,in thylakoid membrane in chloroplasts.
Those are called Photosystems.
There are two photosystems ,there are PS 1(700 nm-means that it absorbs 700 nm photon rays more efficiently)
and PS 2 (680 nm-means that it absorbs 680 nm photon rays more efficiently.)
Light depended reactions -This image provides a good overview of the Z-scheme of electron flow, showing the involvement of Photosystem II (PSII) and Photosystem I (PSI) in the thylakoid membrane.
đ¯C3, and CAM pathways
In these pathways light depended reactions and calvin cycle is happened .
Calvin cycle convert carbon dioxide (CO_2) into sugar (glucose) and other organic molecules.It uses the energy stored in ATP and the reducing power of N ADPH—both generated by the light-dependent reactions of photosynthesis—to power the synthesis of carbohydrates.
Mainly co2 is connected with RUBP An enzyme called RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes the reaction,and then the cycle begins.Then it creates an unstable six-carbon compound that immediately splits into two molecules of a three-carbon compound called 3-phosphoglycerate (3-PGA).
Then it is converted to G3P(glyceraldehyde-3-phosphate.). it requires energy of ATP and NADPH
Only one G3P molecule (a three-carbon sugar) is produced for every three turns of the cycle
Examples-Rice ,Wheat and Soybeans-C3
CAM (Crassulacean Acid Metabolism) -It is done in Plants that exists in extremely arid environments .It is a water saving Photosynthetic method.where plants open Stomata at night to absorb Co2, store it as malic acid in and then release the CO2 for the Calvin cycle during the day with stomata closed, dramatically reducing water loss. It separates gas exchange (night) from carbon fixation (day) to thrive in hot, dry conditions, unlike standard C3/C4 plants.
Key Features -Essential for survival in deserts, conserving water while still photosynthesizing.
- Highly efficient due to closed daytime stomata, minimizing transpiration.
Examples- Cacti, orchids, pineapples, agave, and other succulents
đĨC4 Pathway
In c4 plants ,they have Kranze anatomy.Ther are twoorganized cells in the plants they are Mesophyll cells and bundle sheath cells.So in these C4 plants Carbon fixation is done twice.And the calvin cycle happens n Bundle Sheath cells.Mainly in Mesophyl cells The phosphoenolpyruvate is connected with co2 and converted to OAA (Oxaloacetate)-a 4-carbon acid. In bundle sheath cells the 4-carbon acid is transported here and is then BECOMES Malate (c4 Molecule) broken down (decarboxylated) to release CO2.This released co2 now highly concentrated around the enzyme RuBisCO, forcing it into the Calvin cycle to make sugar and preventing it from reacting with oxygen (photorespiration).
In conclusion C4 cycle acts as a CO2 "pump" to ensure the Calvin cycle runs efficiently, even when the leaf's stomata are partially closed to conserve water.
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