Photosynthesis Essential to life

Photosynthesis is a process that that converts light energy from the sun into chemical energy for use by the plant cell. The two parts of photosynthesis are the light-dependent reactions and the Calvin cycle.

The first process included in photosynthesis is the light-dependent reactions, which changes light energy into ATP and NADPH.

This process begins when light energy from the sun excites electrons in what is called "photosystem II." A water molecule is also split, which causes an electron to release into the electron transport system and a hydrogen ion to release into the thylakoid space. This also creates oxygen as a waste product.

light dependent-reactions

The electrons are then moved from photosystem II to the electron-acceptor molecule, which is located in the thylakoid membrane.

The electrons are transferred to photosystem I. Light strikes the photosystem, and it transfers the elctrons to ferrodoxin, a type of protein.

light-dependent reactions

The ferrodoxin brings the electrons to NADP+, a type of electron carrier. Here is where NADPH, an energy-storage molecule, is formed.

Chemiosmosis occurs when protons (H+) are built up in the thylakoid space. This creates a concentration gradient.


Because of the concentration gradient, the H+ is able to diffuse out of the interior of the thylakoid through an ATP synthase. This is where ATP is formed.

The second part of photosynthesis is called the Calvin cycle, where the ATP and NADPH from the light dependent reactions are used to make glucose and other sugars.

In the first step of the Calvin cycle, carbon dioxide joins with other organic molecules (six 5-carbon compounds) to form twelve 3-carbon molecules, called 3-PGA

Next, the energy stored in the ATP and NADPH is used to form G3P. (glyceraldehyde 3-phosphates).

Two of the G3P molecules exit the cycle so they can be used to help produce glucose and other compounds.


In the final step, rubisco, an enzyme, converts the ten G3P that are left into RuBP (ribulose 1, 5-bisphosphates.) These are 5-carbon molecules. When these molecules combine with new carbon dioxide, the cycle continues.


Created with images by hajninjah - "photosynthesis green color" • gr33n3gg - "Sun" • Flower's.Lover - "Flower" • Conal Gallagher - "Flowers" • < J > - "Flowers" • Moyan_Brenn - "Sunset" • sherpas428 - "photosynthesis" • Freeimages9 - "banana beautiful botany"

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