The cell is the basic unit of all living things in this world. It is often called the building block of life. In other words, we consider the cell to be a pretty fundamental structural aspect of life. There are two types of cells: eukaryotic and prokaryotic. Prokaryotic cells are usually independent, while eukaryotic cells are often found in multicellular organisms. Animal cells and plant cells are multicellular, but bacteria are made out of only one cell.
As most cells are so small, very small unit are used to measure them. The most common unit is the micrometre (µm) where 1 µm equal 1millionth of a metre. Because most cells are so small, we need a special device to see them, called the microscope.A typical cell size is 10 µm and the largest known cells are unfertilised ostrich egg cells, which weigh 3.3 pounds.
Prokaryotic cells are the cells that lack a membrane-bound nucleus are called prokaryotes. Prokaryotic cells have no nucleus. These cells have few internal structures that are distinguishable under a microscope. Prokaryotic cells differ significantly from eukaryotic cells. They don't have a membrane-bound nucleus and instead of having chromosomal DNA, their genetic information is in a circular loop called a plasmid. Cells in the monera kingdom such as bacteria are prokaryotes. Bacteria perform many important functions on earth. Bacterial cells are very small, roughly the size of an animal mitochondrion (about 1-2µm in diameter and 10 µm long). Prokaryotic cells feature three major shapes: rod shaped, spherical, and spiral. Instead of going through elaborate replication processes like eukaryotes, bacterial cells divide by binary fission. They serve as decomposers, agents of fermentation, and play an important role in our own digestive system. Also, bacteria are involved in many nutrient cycles such as the nitrogen cycle, which restores nitrate into the soil for plants. Unlike eukaryotic cells that depend on oxygen for their metabolism,...