Organelles-Definition, Examples, Functions, and Types.


A cell is the smallest unit of any living organism. Many elements within a cell make help it to function maximally.

Organelles are small structures that perform different functions in the cells. There are many types of organelles, such as mitochondria and chloroplasts.

This blog post will give you an overview of what organelles are, how they function, and their importance to the cell! However, should you wish to skip this article due to reasons such as a busy schedule, our top writers are ready to cover you by acing that assignment for you. All you have to do is place an order with us.

Image: Organelles

What are Cell Organelles?

Cell organelles are the chemical components within a cell and outside the cell that function in different capacities. Some provide support, while others are for movement and much more.

Types of Organelles

Cell organelles are categorized according to their structures, functions, and location. Some organelles are endosomes, centrosomes, Golgi apparatus, and more.

The only organelle that is not classified according to structure or function is the nucleus of a cell. The main job of this organelle in plant or animal cells is to store DNA!

Cell organelles are grouped into three broad categories, namely:

  • Non-membrane Organelles
  • Single- membrane Organelles
  • Double- membrane Organelles
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Organelles Without A Membrane

One category of organelles is without a membrane. Non-membrane organelles are also called “intracellular” or “internal” organelles because they do not have a membrane around them. They are found in both prokaryotic cells and eukaryotic cells, and they include the cell wall, nucleolus, ribosomes, and cytoskeleton.

The Nucleolus

The nucleolus is made up of proteins to form an oval-shaped structure that can vary in size. This organelle is always found near the nucleus, and it produces ribosomes used by a cell for protein synthesis.

The Ribosome

Ribosomes are also composed of proteins, but their shape can vary depending on their type and the particular organism. Their main functions are:

  • Assembling amino acids to produce proteins in a process known as protein synthesis
  • Producing tRNA and rRNA
  • Taking part in DNA transcription to produce mRNA

The Cell Wall

Cell wall is another non-membrane organelle found outside the cell. It is made up of cellulose and other substances that help protect the cell.

Cellulose is a polysaccharide that provides protection and support as well. The cell wall is only found in plant cells, but animal cells have their membrane type, which does the same job.

The main functions of the cell wall are:

  • Provides the cell with a rigid outer layer
  • Protects cells from getting damaged and prevents them from bursting.


The cytoskeleton is made of microtubules and actin filaments. These features are important for movement within the cell. They also assist cell shape and cell division which is important for the production of new cells.

The microtubules consist of two different types of protein, namely tubulin and actin. Protein actin is the building block for the actin filament. They are very thin, and they form long chains. The tubulin filament consists of two proteins: alpha-tubulin and beta-tubulin.

The two types of filaments act together to provide the cell with movement, shape, and division. The cytoskeleton also aids in cell motility by intertwining actin filaments with microtubules.

Single-membrane Organelles

Image: Golgi apparatus and endoplasmic reticulum

Single-membrane organelles are the Vacuole, endoplasmic reticulum (ER), lysosomes and Golgi apparatus. They are only found in the eukaryotic cells.

The Vacuoles

A vacuole is a membrane-bound organelle that can be either large or small, depending on the type of cell that hosts it.

They are mainly found in plant cells and serve as a storage area for excess water and other nutrients that the plants may not need at that time.


Lysosomes are organelles found in animal cells, and they have a single membrane. They function as digestive vesicles that contain hydrolytic enzymes. The different functions of lysosomes are as follows:

  • Lysosomes are part of the lysosomal membrane system, which is important because it assists in the breakdown of materials that cells need.
  • They contain digestive enzymes important for breaking down carbohydrates, proteins, and lipids found in a cell.
  • Lysosomes are also involved in recycling materials that cells need, such as amino acids and nucleotides.
  • These single-membrane-bound organelles are constantly being broken down and reformed. This way, they provide the cell with a constant supply of hydrolytic enzymes.
  • Lysosomes are also involved in apoptosis and autophagy, which help keep cells functioning properly by removing unwanted materials.

Lysosomes are only found in animal cells, and they have a single membrane that surrounds them.

The Endoplasmic Reticulum

The endoplasmic reticulum is another single-membrane organelle found in animal cells. They usually have a rough or rugose appearance.

There are two types of Endoplasmic Reticulums:

The smooth Endoplasmic reticulum. It is common in cells that are involved with the production of lipids and steroids. This ER has a smooth surface.

The rough Endoplasmic reticulum is located in cells involved in producing proteins and has a rough surface.

The functions of these single-membrane bound organelles are as narrated below:

  • The endoplasmic reticulum helps get rid of unwanted proteins, and it also provides a site for protein synthesis.
  • The ER is involved in many cellular processes that make up the cell cycle, and it aids with protein production. Proteins are synthesized on the ribosomes and are then sent to the ER for amino acid activation.
  • These cell organelles are also responsible for synthesizing lipids, which are important because they help keep cells functioning properly.
  • The endoplasmic reticulum’s membrane is located near the nucleus, and it is also involved in membrane transport.

Golgi Apparatus

The Golgi apparatus has a single membrane that surrounds it and is only found in animals.

  • The Golgi apparatus helps to modify proteins that are useful to the cell, such as glycoproteins.
  • The Golgi is an organelle that has a very important function because it helps to load the proteins onto blisters, and these proteins are then sent to other organelles.
  • These organelles also help to package the cell’s secretions and aid in cellular immunity.
  • It is important because it modifies the proteins for use by the cell and packages secretions for transport.
  • The Golgi apparatus is mainly situated in an animal cell, and it has a single membrane.

Double-membrane Organelles

Image: double-membrane organelles

Double-membrane organelles are the nucleus, mitochondria, and chloroplast. They are only found in eukaryotic cells.


The nucleus is one of the most important organelles in the cell of any organism. Its functions are crucial to support life, growth, and the increase of all living things.

The main function of the nucleus in plant or animal cells, respectively, is to store DNA.

This cell organelle is found in the center of most cells and is contained by a membrane. The nucleus can vary in size depending on its function. For example, it may expand when increasing the number or copying DNA to create new cells.

The nucleus controls how much genetic material will be passed onto each daughter cell during mitosis: either all or only half. This figure is referred to as the chromosome number.

The nucleus consists of two regions:


Nucleoplast is the part of the nucleus that contains all the DNA and RNA that code for proteins. A membrane surrounds the nucleoplasm with tiny pores in it, allowing molecules to pass freely into or out of the cell!


The chromatin is the other region in a nucleus. It consists of DNA, histones, and proteins that are tightly packed together to form chromosomes!

Chromatin plays an important role in controlling how much genetic material will be passed onto daughter cells during mitosis: either all or only half. This process is called the chromosome number!


Mitochondria are double-membrane-bound organelles found in plant and animal cells. They have a small genome that is separate from the chromosomes in a cell’s nucleus.

Mitochondria are involved primarily with cellular respiration, and it produces energy for the cells to use.

These cell organelles have two membranes surrounding them, which are called the outer membrane or mitochondrial envelope. The inner side of the outer membrane is called the cristae.

Mitochondria have a role in cellular respiration. They use molecular oxygen to break down glucose and produce carbon dioxide and water as waste products.

These organelles produce energy that is stored in the form of ATP, which stands for Adenosine Triphosphate


Chloroplasts are double-membrane-bound organelles found in plant cells. They are also called green plastids because they contain a green pigment called chlorophyll. This pigment is necessary for photosynthesis to take place.

The chloroplast is involved in the whole photosynthesis process. It combines carbon dioxide and water with light to produce glucose which is converted into other sugars and oxygen.

These organelles are found in plant cells only, and there is a double membrane around them, which is called the chloroplast envelope. The inner side of this membrane contains a structure that looks like a stack of pancakes, and it has very thin membranes called thylakoids.

Other Organelles and their Functions


Image: nucleolus and nucleic acids

The cytoplasm is the fluid that surrounds organelles in a cell. It consists of proteins, biomolecules, and nucleic acids, which are the building blocks of life.

This cell organelle is a gelatinous fluid that fills up most of the cell and contains many organelles, such as the mitochondria and ribosomes.

The cytoplasm is mainly found around organelles, and it has many different functions, including:

  • Transportation of substances within the cell
  • Separation and division of cells during mitosis.
  • It also contains ribosomes that are responsible for making protein molecules.


Centrosomes are structures found in animal cells that play an important role during cell division. They help organize and position the microtubules, which are essential for cell division to take place, and they also play a role in the movement of chromosomes during mitosis.

Centrosomes consist of two primary parts: the centrosome body and the basal body. They are located in an animal cell’s nucleus, close to one another but not touching.

The centrosome body is a small spherical body, and it contains the centrioles, which are long wiry structures. The basal body consists of smaller parts, and it is the base for a centriole.

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Chromoplasts are organelles found in plant cells. They contain a pigment called carotene, which is important for photosynthesis to take place.

The carotene is used to capture the light needed for photosynthesis which takes place next to chloroplasts.

Chromoplasts are found in the cytoplasm of a plant cell and produce carotene pigment for photosynthesis.

Chromoplasts are similar to the mitochondria and ribosomes because they all have a double membrane that surrounds them.

Chromoplasts also contain enzymes like isoenzyme, which is an enzyme that does not need to be processed.


Image: leucoplasts

Leucoplasts are organelles found in animal cells. They contain a pigment called leucine, which is involved in the immune system.

Leucoplasts contain a protein called leukocyte, which is involved in the immune system, and they have many functions such as:

  • They are involved in the immune response and fighting infection.
  • They also help to destroy bacteria, viruses, or other foreign bodies which enter the body.
  • Leucoplasts also have a role in cellular defence mechanisms, and they work closely with the lymphocytes to make sure that these functions take place.

Leucoplasts are also known as white blood cells because they contain the leukocyte protein found in these organelles.

Cilia and Flagella

Cilia and flagella are similar because they both have the same function: moving substances in a cell. They can also be found in different cell types.

Cilia are small projections that can only be seen with a microscope. They work by beating back-and-forth in a special pattern, which can be very fast. These organelles have the same function as flagella except that they hit back and forth instead of side to side.

Flagella are thin hair-like projections usually found on the surface of an animal cell. They work by spinning in a circle, and this makes them move back and forth. Other animal cells like sperm have flagella which help them to charge toward the egg and fertilize it.

Cilia and flagella have a similar function, but they are different in some ways. They are small projections found in cells. They work by beating back and forth, so substances move away from them.

-Flagella are thin hair-like projections found in most cells, and they function by spinning. Cilia are located in different types of cells, such as the cell responsible for moving substances, while flagella are usually on animal cells.

Cell Membrane

The cell membrane is the outer layer of a plant or animal cell. It consists of lipids and proteins, which are different molecules.

This membrane is composed of a double layer made up of phospholipids and proteins held by cholesterol.

It is highly selective, allowing only certain substances that are important for the cell to enter and leave.

Cell membranes are important in plant and animal cells because they form the outer layer, which is selective to certain substances important for the cell.


The peroxisome is a small organelle that’s found in plant and animal cells. It contains the enzyme called catalase, which is important in breaking down substances poisonous to the cell.

The peroxisome breaks down molecules by using hydrogen peroxide. The enzyme catalase releases the latter.


Gerontoplasts are plastids that contain old chlorophyll. You’ll mostly find them in inactive plant cells that have stopped the production of chlorophyll. Their function is to store the old chlorophyll.

Functional Relationships of Cell Organelles

The cell wall and cytoskeleton

The cell wall provides structural support and protection for the cell. The cytoskeleton also helps maintain the shape of a single-celled organism and aids in cellular movement. These two organelles work together to keep the cell’s structure and allow it to move as desired.

Ribosomes, mitochondria, and Endoplasmic reticulum

Ribosomes are a part of both the endoplasmic reticulum and mitochondria because they carry out two important functions: protein synthesis and energy production. The endoplasmic reticulum is a membrane-bound network of tubes that functions in lipid, protein, and carbohydrate metabolism.

Mitochondria are the powerhouses of cells responsible for producing energy in a process called cellular respiration. The endoplasmic reticulum and mitochondria work together to provide the cell with the energy needed for necessary functions. Ribosomes are involved in protein synthesis, which is an essential function for the cell.

Protein synthesis allows cells to divide and grow as needed to keep up with their environment. When ribosomes start producing proteins, they use the endoplasmic reticulum to carry out this process.

Golgi apparatus and ribosomes

The Golgi apparatus packages and sends the proteins made in ribosomes to other parts of the cell.

Ribosomes are responsible for creating proteins. These proteins are then transported to the Golgi apparatus for packaging and distribution to the rest of the cell.

The ribosomes work together with the Golgi apparatus to create and ship proteins as needed in the cell.

Ribosomes and nucleolus

Ribosomes are a part of both the ribonucleoprotein particle and nucleolus. They carry out two essential functions: protein synthesis and gene production.

The ribonucleoprotein particle is also called the nucleolus. The latter is where genetic information is stored in ribonucleic acid (RNA). Ribosomes work together with the nucleolus to produce RNA for gene production.

Cytoplasm and centrosomes

The cytoplasm is the gel-like substance found inside cells, and it has many different functions.

Centrosomes are structures that help maintain the cell’s shape. The cytoplasm and centrosomes work together to give cells their structure.

The cytoplasm surrounds the centrosomes and provides a stable space for them to carry out their function.

Chloroplasts and chromoplasts

Chloroplasts are the green parts of plant cells, but they’re also in animal cells. Chromoplasts give leaves their colour in a process called photosynthesis.

Plant cells contain chloroplasts, which are responsible for carrying out the function of photosynthesis. In animal cells, chromoplasts are used for a different role: the production of carotenoids.

Chloroplasts and chromoplasts work together to produce different substances for the cell.

Cilia and Flagella

Cilia are tiny, hair-like structures that move fluid over a surface. Flagella help single-celled organisms swim by rotating like a propeller.

Cilia and Flagella work together to move substances over the surface of a cell or propel single-celled organisms through the water.

Flagella transport nutrients and other substances through the cell’s cytoplasm, while cilia aid in fluid movement across the cell’s membrane.

Similarities Between Animal and Plant Cells

They both:

  • Have cell membranes that surround the cell.
  • Contain genetic material inside the nucleus, which is surrounded by cytoplasm.
  • Have mitochondria to generate energy for the cell and ribosomes to build proteins.

Differences Between Animal and Plant Cells

Image: Animal cell and plant cell
  • Plant cells have cell walls, which animal cells don’t usually have.
  • Animal cells have larger nuclei
  • Animal cells have irregular shapes, while plant cells have a regular rectangular shape.
  • Plant and animal cells have different organelles because their functions differ. By comparing the differences between animal and plant cells, we can see that animal cells need ATP to survive while plants use photosynthesis.

You may be interested in Homologous and Analogous Characteristics

Bottom Line

Organelles are found in all cells, but their structures and roles vary depending on their type of organism. Some examples include mitochondria which produce energy for the cell to use, or chloroplasts which help make food. The points discussed here are not exhaustive but adequate to equip you for further research on cell organelles.

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