The Chloroplast

Background of Chloroplast

The chloroplast was first discovered in 1905 by the Russian biologist, Konstantin Mereschkowski. However, Julius von Sachs is usually credited for discovering chloroplasts inside of plant cells.

Konstantin Mereschkowski discovered chloroplasts with an electron microscope.

Chloro” means “green” in biology terms. The chloroplast is a green structure, which also makes the plant cell green.
-plast” means a mix of “living substance”, “organelle”, and “cell”. The chloroplast is an organelle that is in the plant cell, which is a living substance.
Julius von Sachs
Julius von Sachs
Konstantin Mereschkowski
Konstantin Mereschkowski

The Chloroplast

Plants have the ability to conduct photosynthesis, which is one of the most important characteristics of plants.

The function of chloroplasts is to carry out this process in plant cells and some protists such as algae.

Chloroplasts are mainly in plant cells because without chloroplasts, plants would not be able to conduct photosynthesis. This would make the plant die because it would not get the energy from the sun that it needs.

Chloroplasts are also in some protists because some prokaryotes are photosynthetic such as cyanobacteria.

Chloroplasts are not in animal cells because animals obtain energy through different organelles instead of the chloroplast.
Animal cells use mitochondria to convert energy into food, while plant cells use chloroplasts to convert light into energy through photosynthesis.

Plants that actively conduct photosynthesis require large numbers of chloroplasts. This is because chloroplasts conduct the photosynthesis for the plant to stay alive, and the more chloroplasts the plant cell has, the more it can photosynthesize.
In a typical photosynthetic leaf cell, there are about 100 chloroplasts in each cell. Whereas in an algae cell, there is only one chloroplast.
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Photosynthesis - the process by which a plant uses the energy from the light of the sun to make its own food.

Plants make their own food by converting light energy into chemical energy.

The photosynthesis depends on the green molecules called chlorophyll in each chloroplast. This converts light energy of the sun into sugars that can be used by the cell.
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Anatomy of the Chloroplast
General Structure

  • Outer membrane - smooth outermost membrane of chloroplast that is freely permeable to molecules
  • Intermembrane space - the region between the inner membrane and the outer membrane a chloroplast
  • Inner membrane - the membrane which separates the chloroplast stroma from the intermembrane space.
  • Stromal lamellae - keeps all of the stacks of thylakoid sacs a safe distance from each other and maximizing the efficiency of the organelle.
  • Lumen - the chloroplast compartment bounded by the thylakoid membranes.
  • Thylakoid - membrane-bound compartment inside chloroplasts
  • Stroma - colorless fluid surrounding the grana within the chloroplast.
  • Starch/sugar - acts as the cell’s energy storage, and is a product of photosynthesis.
  • Granum - stacks of thylakoids. One thylakoid stack is called a granum.

Specialized Structure


Unlike many organelles, chloroplasts have two membranes: the outer membrane and the inner membrane.

The products of photosynthesis are used by the chloroplast to produce many organic molecules.
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Analogy of the Chloroplast

Solar Panels: House

Both solar panels and chloroplasts capture and store energy from the sun for the house and cell.

Chloroplasts: Cell


Like chloroplasts, solar panels convert sun energy into energy that the house (or the cell) can use.


Chloroplasts are the solar panels of the cell.
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Mitochondrion VS. Chloroplasts

The intermembrane space (IMS) is the region between the inner membrane and the outer membrane of a mitochondrion and a chloroplast. (Double Membrane Structure)

They both provide cells with energy.

They both contain own RNA and DNA

They have similar enzymes

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Chloroplast Review

Chloroplasts are organelles that are in plant cells. Their main role is to conduct photosynthesis in the cell, which is where chlorophyll in the cell captures energy from the sun and stores it. Cells need this to stay alive.

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