What are Cellular Organelles?
All cells contain cytoplasm, which is the substance on the inside of the cell.
Organelles are the structures within the cytoplasm.
Organelles consist of many different structures.
What are the Functions of Organelles?
Organelles relate to the cell as the organs relate to the human body.
For instance, some organelles have a digestive system which helps to break down complex molecules within the cell.
Of course, organelles have a completely different structure than bodily organs.
Classes of Organelles
Two classes of organelles are called mitochondria and plastids.
Mitochondria
Mitochondria are present in almost all types of eukaryotic cells.
From our post on cell structure, you will remember that eukaryotic cells contain a nucleus.
So, eukaryotic cells include both plant and animal cells.
The mitochondria in eukaryotic cells produce energy, oxidize glucose substances, and release adenosine triphosphate (also known as ATP).
Under an electron microscope, mitochondria appear as small rods.
Cells that need to expend large amounts of energy can contain unusually large numbers of mitochondria.
Plastids
Plastids are the granules and incisions found in the cytoplasm of the cell.
They are found in plant cells.
Plastids may be oval or spherical in shape.
The two main kinds of plastids are amyloplasts and chloroplasts.
Amyloplasts are the starchy grains in plants in which carbohydrate is stored.
Chloroplasts contain the green pigment chlorophyll, which is essential in the process of photosynthesis.
Organelles in Eukaryotic Cells
In addition to mitochondria and chloroplasts, eukaryotic cells can also contain the following organelles.
Endoplasmic Reticulum
There are two types of endoplasmic reticulum (also known as ER): rough endoplasmic reticulum and smooth endoplasmic reticulum.
Rough endoplasmic reticulum is studded with ribosomes and is responsible for the isolation and transportation of the proteins that have been synthesized by the ribosomes.
Smooth endoplasmic reticulum does not contain ribosomes. Smooth endoplasmic reticulum is responsible for the expression of lipids.
Both types of endoplasmic reticulum form channels through the cytoplasm and therefore help to distribute substances more quickly around the cells.
Flagellum
The flagellum brings locomotion and sensory aspects to the cell.
Many organisms move by means of flagella.
Golgi Apparatus
The Golgi apparatus is an especially dense part of the cytoplasm.
As proteins leave the ER, the move to the Golgi apparatus, where carbohydrate is added.
Thus, the functions of the Golgi apparatus are the sorting, packaging, processing, and modification of proteins.
So, protein is packaged and processed by the Golgi apparatus before it leaves the cell.
Questions on Organelle Function
- What are the two classes of organelles?
- What is the function of mitochondria?
- What is the difference between rough endoplasmic reticulum and smooth endoplasmic reticulum?
- What is the primary function of the flagellum?
- What are the functions of the Golgi apparatus?
Answers to Questions on Organelle Function
- The two classes of organelles are called mitochondria and plastids.
- Mitochondria produce energy, oxidize glucose substances, and release adenosine triphosphate.
- Rough endoplasmic reticulum is responsible for the transportation of the proteins that have been synthesized by the ribosomes, while smooth endoplasmic reticulum is responsible for the expression of lipids. Rough endoplasmic reticulum contains ribosomes, but smooth endoplasmic reticulum does not.
- The flagellum is responsible for locomotion or movement.
- The functions of the Golgi apparatus are the sorting, packaging, processing, and modification of proteins.
Other Organelles
The vacuole and the nucleus are also organelles.
The vacuole is essential for storage and transportation, and helps maintain homeostasis.
The nucleus supports DNA maintenance, controls all activities of the cell, and is crucial for RNA transcription.
For more information on the vacuole and nucleus, please see our post on cell structure.