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The organelle where photosynthesis takes place in plants and algae.

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Photosynthesis: Chloroplasts

The Chloroplast

License: CC BY-NC 3.0


 Chloroplasts: Where the Magic Happens!

  • Chloroplasts are the organelles where photosynthesis occurs. Chloroplasts have a specific structure. The parts of a chloroplast includes:
  • Outer Membrane- a permeable membrane that lets water, carbon dioxide, oxygen and sunlight to freely pass into the chloroplast.
  • Inner Membrane: has transport proteins that allow the passage of molecules in and out of the chloroplasts like protein (into the chloroplasts) and sugar (out of the chloroplast).
  • Thylakoids: are folded membranes in the chloroplast that carry out the energy producing light reaction.
  • Grana: a stack of thylakoids.
  • Stroma: The fluid outside of the thylakoids but inside the inner membrane. 

You can take a video tour of a chloroplast at Encyclopedia Britannica: Chloroplasthttp://www.britannica.com/EBchecked/media/16440/Chloroplasts-circulate-within-plant-cells.

See the figure below!

License: CC BY-NC 3.0

The Chloroplast and Photosynthesis: The Magician's Secret!

 Remember, photosynthesis is the chemical process that is represented by the following equation:

                                      6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2

The chloroplasts take in materials such as carbon dioxide (CO2), water (H2O) and light to produce glucose (C6H12O6)  and oxygen (O2). Photosynthesis is composed of two reactions. They are the:

  • Light dependent reaction- In the thylakoids.
  • Light independent reaction (Calvin Cycle)- In the stroma


The light dependent reaction (a.k.a- the light reaction) happens in the thylakoids of the grana stacks. The light reaction produces energy carrying molecules adensosine triphosphate and NADPH that is needed for the Calvin Cycle. Here's the breakdown.

1. Water that is transported into the leave by the xylem moves into the thylakoid.

2. Sunlight strikes the thylakoids and splits the water molecules into hydrogen (H) and oxygen (O) atoms. This leaves oxygen to combine with other oxygen molecules that form O2. Oxygen diffuses out of the choloroplast to be used in respiration or to be released into the atmosphere.

3. NADP+ picks up a hydrogen (H) from the split water molecule to form NADPH. This will be used as energy in the Calvin Cycle. Adenosine diphosphate (ADP) picks up a third phosphate to make adenosine triphosphate (ATP).

See the figure below.

License: CC BY-NC 3.0

For your enjoyment, here is the chemical reaction that produces NADPH and ATP (you will not be required to know this portion of the ligh reaction)

This figure shows the light reactions of photosynthesis. This stage of photosynthesis begins with photosystem II (so named because it was discovered after photosystem I). Find the two electrons (2 e-) in photosystem II, and then follow them through the electron transport chain (also called the electron transfer chain) to the formation of NADPH. Where do the hydrogen ions (H+) come from that help make ATP?


The light independent reaction is called the Calvin Cycle. The Calvin Cycle was named after Melvin Calvin discovered this process in photosynthesis. The Calvin Cycle occurs in the fluid that surrounds the thylakoid called the stroma. It is this process that takes the ATP and NADPH energy, carbon dioxide and enzymes to fix carbon dioxide into glucose. Here's how Calvin (Cycle) goes to work!

1. NADPH and ATP are free floating in the stroma.

2. Carbon dioxide diffuses into the stroma of the chloroplast.

3. NADPH, ATP and carbon dioxide combine with enzymes and other organic molecules.

4. Gluose is produced.

See below!

License: CC BY-NC 3.0

Wrapping It Up

Watch the FIRST 9 MINUTES of the video explaining how photosynthesis works in the chloroplast. Thank you to Paul Anderson of Bozeman High School for this little gem.

Lesson Check

Please answer the questions in the Google form below. These questions review the main ideas of the lesson. You may LOOK BACK  in the reading or USE YOUR NOTES. 



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