Eukaryotes and Prokaryotes.

Eukaryotic and Prokaryotic cells.

Animals and plants are composed of eukaryotic cells, whereas bacteria are simpler, prokaryotic cells. (Fungi and protoctistans (algae and protozoa) are also eukaryotic, since their cells have a nucleus). 

The main difference between Eukaryotic cells and prokaryotic cells is that prokaryotic cells have no nucleus or nuclear membrane. Their DNA is therefore not separated from the rest of the cytoplasm, but forms a single circular loop, sometimes called a bacterial chromosome. This DNA is not associated with proteins unlike that of Eukaryotic chromosomes. Bacteria also have smaller loops of DNA in the cytoplasm called plasmids. 

Prokaryotic cells are much smaller than eukaryotic cells and much simpler in their structure. They lack endoplasmic reticulum and membrane bound organelles like mitochondria and chloroplasts. 

Both types of cells have a cell membrane, a cytoplam, DNA and ribosomes. Prokaryotic cells lack any complex structures such as golgi body, cytoskeleton or lysosomes. 

Although bacteria has a cell wall, it isn't made up of cellulose but a substance called peptidoglycan. Outside the cell wall, some bacteria have a diffuse slime layer or thicker capsule. These are secretions of the cell which sometimes acts to stick the cells together they also act to protect the cell against attack from phagocytic white blood cells. Short protein rods called Pilli or Fimbriae project from the cells walls in some bacteria to help it stick to other cells and surfaces. 

Some species of the bacteria have one or many flagella, each consisting of a single rod of protein fibres rather than the hollow microtubule structure of the eukaryotic flagellum.

The cytoplasm of the bacterial cell contains scattered ribosomes, but these are not attached to membranes as with the rough endoplasmic reticulum of eukaryotic cells. They are also smaller than eukaryotic ribosomes. They are known as 70S ribosomes whereas eukaryotic ribosomes are called 80S ribosomes. The cytoplasm contains inclusions of glycogen granules for carbohydrate storage and lipid droplets.