Chloroplasts – Cell Facts

What are chloroplasts?

There is a specific structure that is critical to one type of cell, and is not included at all in another kind of cell. That structure is the chloroplast, and they are found in plant cells, but not animal cells. They are extremely important organelles for the survival of plant cells.

The primary function of a chloroplast is to convert rays of sunlight into energy that plants can feed off of, in a process called photosynthesis.

Chloroplasts visible in the cells of Bryum capillare

What is the structure of a chloroplast?

Chloroplasts are organelles found in the cytoplasm of a cell, just like ribosomes and mitochondria. They have some features in their structure that are very similar to other organelles, and they have some features in their structure that are very different to other organelles.

Features of a chloroplast include an outer membrane, an inner membrane, a stroma, thylakoids, and pigments, among other things that they have in common with other organelles. The outer membrane of a chloroplast is a smooth shell, much like the outer membrane of mitochondria.

The inner membrane of a chloroplast is much like a cell membrane, in that it regulates what substances can and cannot pass through into or out of the chloroplast and the cytoplasm.

The stroma of a chloroplast is the liquid that fills the inside of the inner membrane, much like the cytoplasm of a cell. Inside the stroma are thylakoids, or small sacs of a substance called chlorophyll granum.

The many chlorophyll granum are linked together by little structures shaped into disks, called lamella. Pigments in chloroplasts are what give color to plants. As you can guess, the most common pigment found in chloroplasts and on plants is green.

Chlorophyll is a specific substance that helps in the process of photosynthesis, or creating energy from sunlight. Chlorophyll is also indigestible for humans, which is why human beings cannot live by eating grass (although, of course, there are many plants humans can eat).

Other structures that chloroplasts have that are similar to other organelles are proteins and DNA, similar to mitochondria and ribosomes.

Chloroplasts Structure

How does photosynthesis work?

As mentioned before, chloroplasts are specific plant cell organelles with the responsibility of converting sunlight into food or energy. The most important part of the chloroplast for this function is the chlorophyll, which absorbs and stores light energy in the form of ATP.

ATP is adenosine triphosphate, and it’s the same type of energy molecule that mitochondria use to produce energy for animal cells. In animals, ATP is combined with oxygen to produce energy; in plants, ATP is combined with carbon dioxide and water to produce glucose (sugar) as energy.

This means that, while animal cells engage in respiration by taking in oxygen for energy and releasing carbon dioxide, plant cells engage in respiration by taking in carbon dioxide for energy and releasing oxygen.

Additional information about chloroplasts

Like many other cell structures, chloroplasts have a primary function, but they can also engage in other kinds of functions. For instance, in addition to energy production, the chloroplasts of a plant cell help the cell’s immune system functioning.

four membraned chloroplast


  1. What is a chloroplast?
  2. What is the primary function of a chloroplast?
  3. What is the most important structure of the chloroplast?
  4. What molecule is involved in the energy production of the chloroplast?
  5. What type of cell does not have a chloroplast?



  1. A chloroplast is a plant cell organelle that helps photosynthesis.
  2. The primary function of a chloroplast is to convert sunlight into energy.
  3. The most important structure of the chloroplast is the chlorophyll.
  4. Adenosine triphosphate is involved in the energy production of the chloroplast.
  5. Animal cells do not have chloroplasts.