Types Of Cells: Prokaryote Cells Versus Eukaryotic Cells

Background:

The cell is considered as the main functional and structural unit of all known organisms. There are two types of cells prokaryotic and eukaryotic cells

Prokaryotic cells are unicellular organisms with no nucleus. They contain non-membranous organelles Eukaryotic cells which may be unicellular or multicellular having a nucleus. Plant and animal cells are considered eukaryotic cells. They have similarities in their structures but they do not have the exact cell components and shape.

I-Prokaryote cells

Prokaryotic cells have no nucleus and with non-membranous organelles. Prokaryotes are divided into bacteria and archaea.

The structure of prokaryotic cells includes:

1. Cell wall: helps in the protection of the cell and gives the cell its shape.
2. Cell membranes: surrounds the cytoplasm and control the passage of different substances in and out of the cell.
3. Cytoplasm: matrix of the cell that contains all cell components
4. Ribosomes: responsible for DNA synthesis
5. Flagellum: aids the cell movement
6. Nucleoid: contains the single DNA molecule
7. Glycocalyx: glycoproteins that surround the cell membrane. (1)

II- Eukaryotic cells have a nucleus with multiple chromosomes.

The cell organelles are surrounded by a membrane. Typical organisms of eukaryotic cells include protozoa, algae, fungi, plants, and animals.(3,4)

Table (1): The main differences between prokaryotic and eukaryotic cells (6)

• Point of comparison Prokaryotic cell eukaryotic cell
• Membranes Cell membrane and membrane-bound organelles
• Type of nucleus Nucleoid Nucleus with double membrane
• Cell movement Flagella Flagella and cilia
• Mitochondria None Present
• Chloroplast None Present
• Cytoplasmic structure Very few structure Highly structured
• RNA and Protein synthesis Carried in cytoplasm RNA synthesis in the nucleus and protein synthesis in the cytoplasm
• Typical organisms Bacteria and archaea Plants, animals, fungi and protists

Typical organisms of eukaryotic cells

1- Plants

There are similarities between plant and animal cells , but they do not have the exact cell components and shape. As the plant cells are rectangular in shape and having a cell wall. While, the animal cells are more rounded in shape, having no cell walls.(6)

Plant Cells

• Cell wall: its main function is support and protection. The pores of the cell wall permit substances to come in contact with cell membrane.
• Vacuole: aids in the storage of water or other substances.
• Chloroplast: helps in creation of food and photosynthesis by using sunlight (present only in plant cells).

Plastids: They are structures forming pigment that provide color. (3,4,6)

2- Animals

Animal cells

Animal Cell Organelles and their functions are illustrated in the following table

Table (2): Functions of animal cell organelles. (6)

Animal Cell Organelle Function

The cell membrane controls the movement of substances in and out the cell.

Ribosomes are small, spherical structures that are the site of protein synthesis

Golgi Apparatus Helps in processing, packaging and secretion of proteins

Lysosomes They are considered as the digestive centres of a cell by the production of many different types of lysosomal enzymes

Endoplasmic Reticulum Functions in intracellular transport

Mitochondria They are main power generators in the cell as it converts oxygen and food into ATP

Fibrils & Microtubules Form cytoskeleton aids in transport and structural support

Nucleus Serves in genetic material storage, controls several cell activities such as growth, protein synthesis and cell reproduction

Centrioles Organize cell division

Figure (3): Comparison between the structure of plant cells and animal cells.(7)

3- Fungi:

Spore bearing organisms with no chlorophyll and can reproduce sexually and asexually. They act as decomposers. The fungus body is called a thallus which varies is single-cell microscopic yeast to multicellular moulds, macroscopic puffballs and mushrooms. (8,9)

a b c

Figure (4): Fungal Thalli. (6)

4- Protists

They are also known as protozoa. Protozoan can be defined as a motile eukaryotic unicellular protist. Protozoa have an important role in several aquatic food chains and webs. (10,11,12)

5- Algae

Algae is an organism carrying out oxygenic photosynthesis. It cannot be considered as a ‘higher plant’. It includes; (a) unicellular microalgae, e.g.diatoms and Chlorella. (b) multicellular forms, e.g. brown algae. (13, 14)

Conclusion:

• There are two types of cells; prokaryotic and eukaryotic cells.
• Prokaryotic cells are single cells that have no nucleus.
• Bacteria and archaea are prokaryotic cells.
• Eukaryotic cells may be unicellular or multicellular which contain a nucleus
• The typical organism of eukaryotic cells are Plants, Animals, Fungi, Protozoa and Algae
• These organisms have different structures and functions