Chloroplast Structure, Functions, and Processes

Chelsie Wheeler, Kristin Klucevsek
  • Author
    Chelsie Wheeler

    Chelsie has been a private tutor and a peer mentor throughout her ten-year career as an environmental and fisheries biologist. She also has experience educating the public through various programs via outreach with presentations, festivals, and set courses. She has a bachelor of science degree in environmental management from Columbia Southern University and a master of science degree in coastal and marine environments from the University of Ireland, Galway.

  • Instructor
    Kristin Klucevsek

    Kristin has taught college Biology courses and has her doctorate in Biology.

Learn about chloroplast structure and some of the important components of chloroplasts including chlorophyll, thylakoids, grana, and stoma. Updated: 12/01/2021

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Photosynthesis

Photosynthesis is a process where organisms use energy in the form of light to make food using carbon dioxide and water. This specialized process occurs in the chloroplasts of a plant cell.

Plant cells are eukaryotic cells meaning they have a unique membrane that surrounds them and a nucleus that regulates the functions of the cell. All plant cells contain chloroplasts which are specialized organelles that give plants their green color and it is also where photosynthesis takes place.

Each plant cell can contain anywhere from one to hundreds of little chloroplast organelles to help the plant create its own food. An organelle is a tiny organ-like structure that has specific functions it carries out to help the cell work properly. The below diagram shows the basic anatomy of a standard plant cell. Each item listed in the diagram performs a specialized function for each cell.

Term Function
Plasmodesmata allows flow or communications between cells
Plasma membrane regulates chemicals or supplies going in and out of the cells, also used for communication
Cell wall provides structure and protects the cell
Chloroplast contains the chlorophyll that makes plants green and is where photosynthesis takes place
Mitochondria specialized organelles that power the cell, synthesize ATP (energy) and other chemicals for the cell to use
Ribosomes decodes RNA, which are special codes used to operate the cells, and bonds peptides, which mainly provide protein support
Vacuole generally takes care of storage and waste for the cell
Filamentous cytoskeleton mainly help with shape and movement
Small membranous vesicles basically transport materials in and out of the cell
Cytoplasm fluid that suspends the contents inside the cell to protect them
Golgi vesicles transport different materials to and from the Golgi apparatus
Golgi apparatus membranes that pack and deliver synthesized particles in the cell
Rough endoplasmic reticulum produces protein for the cell
Nucleus holds DNA (instructions & genes) for the cell

The basic anatomy of a plant cell, although only one chloroplast is shown on this diagram there are usually multiple chloroplasts in every cell.

plant cell

Inside of the chloroplast, there are two structures that are where photosynthesis takes place, these are the thylakoid and the stroma. In the below diagram there is a close-up view of the process of photosynthesis happening in the thylakoid membrane of the cell.

There are two separate processes that take place during photosynthesis the first is called the light-dependent reaction process and the second is called the Calvin cycle.

The first process happens in the thylakoid during the light-dependent reaction process sunlight reaches the chlorophyll molecules, or pigment molecules, energizing the electrons to create an electron transport train. There are several different turns on this specialized train process and at each stop, the electrons are drained of some of their energy. The energy that is taken is turned into ATP, one type of molecule that holds or carries energy, and NADPH molecules help to power the second process. While the electrons are losing their energy, chlorophyll molecules will replace the missing electrons with Hydrogen (H+) electrons from the water (H2O) molecules. Eventually, what happens because Hydrogen is being taken from water is Oxygen (O2) is released from the process.

The second process happens in the stroma during the Calvin cycle which is also known as light-independent reactions. Energy is taken from ATP and NADPH to create three types of sugar (glucose). There are three main stages in the Carbon cycle which are Carbon fixation, reduction, and regeneration. Enzymes create reactions that ultimately make new compound elements, this is known as fixation. During the reduction stage, energy converts one compound into a compound and recycles some of the molecules back to the first process to be used again. Finally, some molecules leave this cycle to create complex sugars called glucose while others are regenerated to be pushed into a new cycle.

To summarize the process of photosynthesis:

  1. Photosynthesis happens inside of thylakoid membranes and the stroma that are located inside the chloroplasts
  2. There are two separate processes that happen during photosynthesis which are the light-dependent reaction process and the Calvin cycle
  3. During the light-dependent reaction process sunlight and water create energy in the form of ATP and NADPH which releases oxygen, this process happens in the thylakoid
  4. During the Calvin cycle the energy that was harnessed from the light reaction process is taken to make glucose, this process happens in the stroma

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  • 0:17 How Plants Make Food
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The chloroplast structure with a special diagram showing the process of photosynthesis, which occurs in the thylakoid membrane.

chloroplast

Chloroplast Structure

Chloroplasts are located in the cytoplasm of plant cells. The shape of chloroplasts tends to be oval and flat. The chloroplast structure is made up of the outer membrane, inner membrane, stroma, granum, thylakoid, lamella, and lumen.

Where is chlorophyll found in the chloroplast? Green chlorophyll is found in the thylakoid membranes inside of the chloroplast. Chlorophyll is a pigment that absorbs or attracts light into the chloroplast cell. There are a couple of different kinds of chlorophyll, Type A is the green-colored chlorophyll and is mostly responsible for photosynthesis in relation to the other pigment types.

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Frequently Asked Questions

What are stroma and grana?

Stroma is the aqueous fluid filling the chloroplast cavity, where the light-independent reaction process of photosynthesis takes place. Granum is stacks of thylakoids, which are also called grana. It is where chlorophyll is stored.

What's the stroma in a chloroplast?

Stroma is the liquidus material found throughout the cavity of the chloroplast. It is where the light-independent reaction process of photosynthesis takes place.

What is the role of the stroma?

The function of the stroma is to provide volume around the different structures inside of the chloroplast for protection. The stroma is where the light-independent reaction process of photosynthesis takes place, also called the Carbon cycle. After the Carbon cycle expels glucose, this specialized sugar stays in the stroma until it is needed.

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