Why We Study the Cells and Its Components

Cells are structural and functional units of life. According to the cell theory all living things are composed of one or more cells. One-celled organisms are called unicellular organisms and those with more than one cell are called multi-cellular organisms. Virus particles do not have any cells and therefore, are termed as a cellular. No matter what type of cell we are considering, all cells have certain features in common: cell membrane, nucleic acids, cytoplasm, and ribosomes. Cells are small 'sacks' composed mostly of water. The 'sacks' are made from a phospholipid bilayer. The membrane is semi-permeable, allowing some things to pass in or out of the cell and blocking others.

Cells are 90% fluid (cytoplasm), which consists of free amino acids proteins, glucose, and numerous other molecules. The cell environment (i.e., the contents of the cytoplasm, and the nucleus, as well as the way the DNA is packed) affects the gene expression/ regulations, and thus is very important part of inheritance. Cells basically fall into two groups: prokaryotic cells and eukaryotic cells.

Prokaryotic cell include bacteria and blue-green algae (cyanobacteria). Simply stated, prokaryotes are molecules surrounded by a membrane and cell wall. Prokaryotic cells lack characteristic eukaryotic subcellular membrane-enclosed "organelles," but may contain membrane systems inside a cell wall as an extension or enfolding's of the cell membrane. The nucleus is not well-organized and is without any membrane.

Prokaryotic cells may have photosynthetic pigments, such as is found in cyanobacteria ("blue-green algae"). Some prokaryotic cells have external whip like flagella for locomotion or hair-like piled for adhesion. Prokaryotic cells come in multiple shapes: coccid (round), bacilli (rods), and spiral or spirochetes (helical cells). All prokaryotes are unicellular organisms and eukaryotes include both unicellular