Cell Organelles Definition and Functions

Matthew Nesbitt
By Matthew Nesbitt, Writer and researcher. Updated: November 24, 2022
Cell Organelles Definition and Functions

All living beings have at least one cell. While they can differ in many ways, they are all morphological and physiological structures which have complex and specialized functions. Similar to how human beings have organs as part of their anatomy, cells have their own subunits which are used to carry out various processes. These subunits are known as organelles. Depending on the type of cell, they can vary greatly in size, shape composition and structure.

thedailyECO provides the cell organelles definition, as well as more background information on their functions. We look at examples of cell organelles in biology and how they act to carry out their functions in the cell.

You may also be interested in: Cell Types - Definition, Structure and Functions
  1. Definition of cell organelles
  2. Function of cell organelles
  3. Examples of cell organelles

Definition of cell organelles

Cellular organelles are membranous structural units with specialized functions. Referred to simply as organelles in biology, they are found inside cells and allow them to function properly. All cells have organelles, but not all have the same type of organelles, in the same proportion or at the same time.

There are organelles specific to the two main types of cell. These cell types are

  • Eukaryotes: cells that have a nucleus, the majority of which are multicellular.
  • Prokaryotes: cells that lack a nucleus. All prokaryotes are unicellular.

Different types of organelles are specific to animal, plant, fungal, protist, archaeal and bacterial cells.

All the organelles of a cell are found in their cytoplasm, the material within the cells walls which is not the nucleus. They are surrounded by a plasma membrane or cell membrane. This allows biologists to delimit and differentiate one cell and its organelles from another. In this way, each organelle is bound by its own membrane, allowing it to perform its functions correctly.

Function of cell organelles

Cellular organelles are responsible for carrying out all cellular processes. Without organelles, cells could not carry out their functions. In turn, multicellular organisms cannot continue their lifecycle, so they will die. Depending on the Kingdom, species and cell type, different organelles will be specially adapted to allow the cells to carry out their functions.

Without exception, all cells respire, feed, reproduce, synthesize compounds, communicate, interact with their environment and carry out various metabolic processes. These include catabolism (breaking down of molecules) and digestion (extracting nutrients from food). In the vast majority of cases, these general processes are carried out by the same type of organells. For example:

  • Cell nucleus or nucleoid: depending on whether we are talking about eukaryotic cells or prokaryotic cells, we speak of the cell nucleus or nucleoid, respectively. Both contain the DNA that allows the cell to reproduce.
  • Plasma membrane: allows nutrition, excretion, interaction with the environment and cellular communication.
  • Ribosomes: synthesize the proteins necessary for cell reproduction.
  • Cytosol or cellular cytoplasm: where all the substances and organelles vital to the cell are contained.

Cellular respiration

In eukaryotic cells, the most common type of respiration is aerobic respiration. In the cytoplasm of these cells are the mitochondria, which are organelles that synthesize ATP (adenosine triphosphate), provide energy and make cellular respiration possible.

In the case of prokaryotic cells, there is both aerobic and anaerobic respiration. In both cases, the ATP molecule provides energy to the cell and makes respiration possible. In the cytoplasm of prokaryotic cells are all the substances and mechanisms for obtaining the substances necessary for the synthesis of ATP.

More roles of cell organelles

Some processes are unique to certain cell types, such as photosynthesis, fermentation, chemosynthesis and nitrogen fixation. All processes that are not common to all cell types are carried out by specialized organelles specific to these cells. Each cell organelle are perfectly adapted to perform their function. Let's see some examples:

  • Chloroplasts: plant cells and autotrophic protist cells carry out oxygenic photosynthesis. For this biological process to work, chloroplasts are necessary. Chloroplasts are large organelles specific to photosynthetic eukaryotic cells whose main function is to facilitate photosynthesis.

  • Chlorosomes: green sulfur bacteria are anoxygen photosynthetic prokaryotic cells. To carry out photosynthesis, they need chlorosomes. These are organelles containing certain photosynthetic pigments essential to the process.

  • Woronin bodies: filamentous fungi form networks called hyphae. The fungal cells that make up the hyphae usually have more than one nucleus and possess a type of cell organelle unique to this type of fungus known as Woronin bodies. Their function is to separate the septa between each hyphal cell when necessary.

Examples of cell organelles

Depending on their cellular structure, the types of organelles they possess, the class of processes, the metabolisms they carry out, and the way they are grouped together and/or interact with other cell types and their environment, the cells can be either eukaryotic or prokaryotic. Prokaryotes are always unicellular and include certain algae, bacteria and mycoplasma. More complex organisms such as plants and all animals are eukaryotes.

Organelles in eukaryotic cells

Eukaryotic cells form eukaryotic organisms are far more complex than prokaryotic cells. They are characterized by their cell nucleus defined by an envelope and a nucleolus, in which the genetic material of the cell is located. Additionally, they have a wide variety of organelles that are not present in prokaryotic cells, such as mitochondria, Golgi apparatus and endoplasmic reticulates.

There are characteristic organelles of animal cells, such as centrosomes, centrioles, lysosomes, acrosomes and melanosomes. There are also characteristic organelles of plant cells, such as the cell wall, chloroplasts, leucoplasts and chromoplasts.

In eukaryotic cells, it is generally possible to find the following cell organelles:

  • Cell nucleus (with cell envelope and nucleolus)
  • Plasma or cytoplasmic membrane
  • Ribosomes
  • Mitochondria
  • Vacuoles
  • Golgi apparatus
  • Smooth endoplasmic reticle
  • Rough endoplasmic reticle
  • Peroxisomes
  • Centrosomes (in animal cells, fungal cells, and unicellular eukaryotic organisms)
  • Centrioles (in animal cells, fungal cells, and unicellular eukaryotic organisms)
  • Lysosomes (only in animal cells)
  • Cell wall (in cells of plants, fungi and protists)
  • Chloroplasts (in plant cells and eukaryotic photosynthetic cells)
  • Leucoplasts (in plant cells and eukaryotic photosynthetic cells)
  • Chromoplasts (only in plant cells)

Some of the representative structures of eukaryotic cells that are often confused with organelles are the cytoskeleton, cytoplasm, cilia and flagella.

Organelles of prokaryotic cells

Prokaryotic cells constitute the prokaryotic organisms and are much simpler than eukaryotic cells. They are characterized by the dispersion of their genetic material in their cytoplasm, in an area called the nucleoid. They possess certain organelles that are not present in eukaryotic cells, such as chlorosomes and gas vesicles.

In prokaryotic cells, it is generally possible to find the following cell organelles:

  • Plasma or cytoplasmic membrane
  • Ribosomes
  • Gas vesicles
  • Cell membran
  • Storage pellets
  • Chlorosomes (in some photosynthetic bacteria)

Some of the representative structures of prokaryotic cells that are often confused with organelles include cytoskeleton, cytoplasm, capsule, plasmids, carboxysomes, phycobilisomes, magnetosomes, pili, cilia and flagella.

If you want to read similar articles to Cell Organelles Definition and Functions, we recommend you visit our Biology category.

  • NHGRI. (2021). Organelle. Retrieved from:
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Cell Organelles Definition and Functions