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Cell Organelles

All organisms are composed of cells and there are many smaller structures in the cells called cell organelles. It can be called the division of labor among cells, which allows them to carry out their functions.

Cell organelles and their Structure


The nucleus is the largest organelle in the cell which is surrounded by a membrane called nuclear envelope. It contains all the hereditary information of the cell and is responsible for cell growth and reproduction. It contains a very dense structure called nucleolus within it which is responsible for the production of RNA and ribosomes which later on move out of the nucleus into the cytoplasm for protein synthesis. The nucleus is also called the control center of the cell. It contains nearly all of the genetic material of the cell on special strands called chromosomes.

Endoplasmic Reticulum

This organelle is found near the nucleus and is made up of flattened sacs called cisternae whose membrane is continuous with the nuclear envelope. There are two types of the endoplasmic reticulum: rough endoplasmic reticulum (RER) is so called because it has a lot of ribosomes on its outer surface and the smooth endoplasmic reticulum (SER) has no ribosomes on it. The RER transports proteins synthesized in ribosomes while the SER makes lipids.

Golgi Apparatus

Golgi apparatus (aka Golgi bodies) is the stack of membrane-bound sacs. They are responsible for the storage of proteins which are then transported to their destination via vesicles pinching off from the Golgi apparatus.


Lysosomes are the cell’s recycling center. They contain strong digestive enzymes which are able to break down almost any substance that crosses the membrane making the raw material available for the cell to use.


like lysosomes, peroxisomes are also responsible for digesting their contents. But unlike lysosomes which mostly digest proteins,  peroxisomes digest fatty acids.


Mitochondria is round shaped double membrane-bound organelle which is responsible for aerobic respiration of the cell. It is also called as “powerhouse” of the cell. Its inner membrane is folded to form cristae. ATP is produced by mitochondria during aerobic respiration.


It is the network of protein fibers within the cytoplasm which are responsible for stability and movement of the cell. It’s three major components are microtubules, microfilaments, and intermediate filaments.

Microtubules maintain the shape of the cell. They anchor the organelles and control their movement. They also play a key role in the synthesis of the cell wall in plants.

Microfilaments are the thinnest part of the cytoskeleton. They are made up of actin (a protein which is most abundant in eukaryotes). As actin is very flexible, so the function of microfilaments is in cell movement. The contraction of muscles is mediated through the actin-myosin system.

Intermediate filaments are smaller than microtubules but larger than microfilaments. They are composed of various proteins such as keratin. They anchor the organelles and provide structure to the nuclear envelope.


Ribosomes are small and spherical organelles which are made up of a larger and a smaller subunit. They are found on rough endoplasmic reticulum as well in the cytoplasm. They are responsible for the translation of genetic information in the form of mRNA into proteins.


Vacuoles are membrane-bound organelles which are found in all plants and fungi as well as some protists and animals. These are water-filled compartments which also contain enzymes. They are made of the many vesicles and are a larger form of these. Vacuoles function in disposing of the waste from the cell. They store the waste products which are then sent out of the cell.


These organelles are only found in plants and some protists like algae. They are the food factories of the cell. Their main function is to conduct photosynthesis. They contain a photosynthetic pigment chlorophyll which captures the light energy from the sun and converts it and stores it in the form of ATP and NADPH.

Next: Cell Division and its Types

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