Unicellular organisms are living things made up of just one cell. Unlike multicellular organisms that have many cells working together, these simple life forms carry out all their life processes within a single cell. Examples include bacteria, many protists, and some fungi.
There are many different types of unicellular organisms. Bacteria are prokaryotes without a membrane-bound nucleus. Amoeba are protists that move using pseudopods or false feet. Paramecium are protists covered in tiny hair-like structures called cilia. Yeast are single-celled fungi that reproduce by budding.
The key difference between unicellular and multicellular organisms is complexity. Unicellular organisms perform all life functions within a single cell, making them simple but efficient. Multicellular organisms have specialized cells that work together, allowing for greater complexity and size, but requiring coordination between different cell types.
Unicellular organisms reproduce through cell division. The process begins with DNA replication, followed by cell elongation and finally separation into two identical daughter cells. This simple reproduction method allows unicellular organisms to multiply rapidly under favorable conditions.
In conclusion, organisms that have only one cell are called unicellular organisms. These simple yet remarkable life forms include bacteria, many protists like amoeba, and some fungi like yeast. Despite having just one cell, they can perform all essential life functions and are the foundation of life on Earth.