Plant cell

in ~ the chloroplasts of a plant cell, photosynthesis wake up in two key phases: the light-dependent and also light-independent reactions.

Download Photosynthesis lab Activities

Within tree cells, chloroplast are committed organelles that offer as the sites of photosynthesis. The reactions that comprise the procedure of photosynthesis have the right to be divided into light-dependent reactions, i beg your pardon take location in the thylakoids, and also light-independent reactions (also known as dark reaction or the Calvin cycle), i m sorry take place in the stroma.

You are watching: Difference between light dependent and light independent reactions

1. Chloroplasts have actually a complicated internal structure, and different reactions take ar in various parts the the chloroplast.

Understanding what the within of a chloroplasts looks like is key to visualizing where the various reactions that photosynthesis occur.


Surrounding the chloroplasts is a twin membrane, consists of an outer membrane and also an within membrane. This is comparable in structure to the twin membrane of mitochondria.

Interior come the chloroplast’s inside membrane and also surrounding the thylakoids is a fluid called the stroma. The light-independent reaction of photosynthesis take ar within the stroma. It contains enzymes that work-related with ATP and also NADPH come “fix” carbon native carbon dioxide right into molecules that can be used to build glucose. The chloroplast’s own hereditary material (separate from the of the cell) is additionally stored in the stroma.

The internal of the chloroplastic contains another membrane—the optical membrane membrane—which is urgently to form numerous associated stacks that discs. Every disc is a thylakoid and each ridge is a granum (pl. Grana).

The light-dependent reaction of photosynthesis take place within the thylakoids. This reactions occur when the colours chlorophyll, located within the optical membrane membranes, catches energy native the sun (photons) to initiate the break down of water molecules.

2. The light-dependent reactions transform light power into chemistry energy.


The score of the light-dependent reactions of photosynthesis is come collect power from the sunlight and breakdown water molecules to develop ATP and NADPH. These 2 energy-storing molecules space then supplied in the light-independent reactions.

Within chloroplasts, chlorophyll is the pigment the absorbs sunlight. It is save in the thylakoid membranes in protein complexes dubbed photosystem I and photosystem II. The series of light-dependent reactions begins when sunshine hits a molecule that chlorophyll, located in photosystem II. This excites one electron, which pipeline the chlorophyll molecule and travels follow me the optical membrane membrane via a series of transport proteins (known as the electron deliver chain).

Then, something remarkable happens—photosystem II splits a water molecule to gain back this shed electron and also fill the “energy vacuum” that has actually been created. This is a process humans haven’t been able come replicate exactly in a lab!

Each water molecule division down into two hydrogen (H) atoms and also one oxygen (O) atom. The oxygen is released together a rubbish product—oxygen atoms from disassembled water molecules sign up with up in bag to kind oxygen gas (O2).

The hydrogen ions develop up in high concentration in the lumen of the thylakoid. Castle pass with an enzyme referred to as ATP synthase, and their movement provides the power needed to add a third phosphate to ADP (adenosine diphosphate) to type ATP (adenosine triphosphate). This energy-storing molecule powers many cellular processes. In fact, the glucose made throughout photosynthesis is broken down to produce more ATP later, throughout cellular respiration.

Meanwhile, the electron exit from photosystem II come at photosystem I, which also contains chlorophyll. Energy from the sun excites the electron again, providing it enough power to pass throughout the membrane and into the stroma, whereby it joins v a hydrogen ion and an NADP+ to produce the energy-carrying molecule NADPH.

ATP and also NADPH relocate from the thylakoid into the stroma, whereby the power they keep is used to strength the light-independent reactions.

3. The light-independent reaction (Calvin cycle) use stored chemical power from the light-dependent reaction to “fix” CO2 and create a product that have the right to be converted into glucose.


The ultimate goal of the light-independent reaction (or Calvin cycle) is to assemble a molecule that glucose. This is the component of photosynthesis that calls for the CO2 the plant it s okay from the air.

Essentially, the plant needs the carbon indigenous the CO2 to develop the structure blocks for glucose. One enzyme in the stroma called ruBisCo combine a five-carbon molecule the RubP (ribulose biphosphate) with a molecule that carbon dioxide. This creates a six-carbon molecule the is broken down into two three-carbon molecule (3-phosphoglycerate). This component of the light-independent reaction is referred to as carbon fixation.

Then, the energy carriers from the light-dependent reactions make their contribution. ATP and NADPH offer each 3-phosphoglycerate a hydrogen atom, developing two molecule of the simple sugar G3P (glyceraldehyde-3-phosphate). Ultimately, these two molecules the G3P are supplied to build one molecule the glucose. This component of the light-independent reactions is commonly referred to as reduction (or reducing the sugar) because electrons room added.

See more: What Evidence Of A Chemical Change Is Observed When Rust Forms On Iron

It is vital to keep in mind that the Calvin cycle typically uses six molecules that carbon dioxide in ~ a time. This method that twelve molecule of G3P room generated. However, just two of them are supplied to create a molecule of glucose—the rest are recycled earlier into RubP so the the cycle deserve to keep running.