Photosynthesis By:isabelle

What is photosynthesis?

Photosynthesis is the process used by plants, algae and certain bacteria to make energy from light into chemical energy.

Light dependent reactions

In Light-dependent reactions, the energy from sunlight is absorbed by chlorophyll and converted into chemical energy. Light energy is utilized in Photosystem 1 (PS1) and photosystem 2 (PS2), both are present in the thylakoid.

Light-dependent reactions

First the light energy excites electrons in PS2. The light energy also causes a water molecule to split, releasing an electron in to the electron transport system, a hydrogen ion (H+)- also called a proton- into the thylakoid space, and oxygen as a waste product. This breakdown is essential for photosynthesis to occur.

The excited electron moves from PS2 to an electron-acceptor (NADP+ + H+) molecule in the thylakoid membrane.

Next, the electron-acceptor molecule transfers the electron along a series of electron-carriers to PS1

In the presence of light, PS1 transfers the electrons to a protein called ferrodoxin. The electrons lost by PS1 are replaces by electrons moved from PS2.

Finally, the electron transfers to the electron carrier NADP+, forming the energy storage molecule NADPH

Calvin Cycle ( Light independent )

Second phase of photosynthesis. Energy is stored in organic molecules such as glucose.

First step is called carbon fixation, six Carbon dioxide molecules are combined with 5 carbon compounds to form twelve 3-carbon molecules (3-PGA) The joining is called fixation

In the second step, chemical energy stored in ATP and NADPH is transferred to the 3-PGA forming high energy molecules called G3P. NADPH supplies hydrogen ions and electrons

In the third step, two G3P molecules leave the cycle to be used as glucose and other organic compounds.

The final step- An enzyme call rubisco converts the remaining 10 G3P into 5 carbon molecules called ribulose 1, 5-bisphosphate (RuBP) These combine to make new carbon dioxide to continue the cell.


Created with images by Arenamontanus - "Photosynthesis" • Kevan - "Photosynthesis"

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