Cell biology
The cell can be defined as the basic functional and structural unit of life of an organism.
In other words, cell is the simplest, smallest and the basic unit of life. All living things (plants and animals) are made up if cells.
The cell is referred to as the basic unit of life because cell forms the building block of all living organism(plant and animal).
Classification of Living Organism based on the Number of Cell
Living organism are classified into two major groups based on the number of cells. They are:
- Unicellular organisms
- Multicellular organisms
Unicellular organisms
Unicellular organisms are organisms which consist of only one cell.
Examples of unicellular organisms
- Amoeba
- Chlamydomonas
- Euglena
- Paramecium e.t.c
Multicellular organisms
Multicellular organisms are organisms which consist of two or more cells. They are organisms that have several cells.
Examples of multicellular organisms
- Volvox
- Hydra
- Spirogyra
- Flowering plants
- Fish
- Bird
- Man e.t.c
Forms in which Living Cells Exist
- As independent or free living organism
- As a colony
- As a filament
- As part of a living organism
As independent or free living organism
Independent or free living organism are organisms which posess only one cell and they are capable of living freely on their own. Examples are Euglena, Chlamydomonas, Paramecium etc
Ameoba and it's structure
Ameoba has an irregular shape (shapeless) and changes constantly. The protoplasm is made up of cytotoplasm and nucleus. The food vacuole and the contractile vacuole are located in the cytoplasm. Ameoba moves by extending and retracting it's pseudopods.
Paramecium and it's structure
Paramecium is slipper shaped unicellular organism. The cytoplasm is made up of ectoplasm and endoplasm. Paramecium has two nucleus i.e micronucleus and meganucleus.The cytotoplasm also houses the food vacuole, contractile vacuole and cytostom. Paramecium moves with the aid of the cilia.
Chlamydomonas and it's structure
Chlamydomonas is a simple microscopic and unicellular plant having flagella, eyespots, food vacuole, contractile vacuole.
Euglena and it's structure
Euglena is a protist and a typical example of an organism sharing both the characteristics of plant and animal. It has flagellum, contractile vacuole, gullet, eyespots, pellicle which makes it an animal and chloroplasts, pyrenoids, granules which also makes it a plant.