Cell & Types

Cell & Types

1. Dr . Sonia Bajaj H.O.D Department of Zoology Cell   &Types of Cell

2. The  Cell  (from Latin  cella ,  meaning " Small Room ") is the basic Structural, Functional, and Biological unit of all known  Living Organisms . A cell is the  Smallest Unit  of life that can  replicate independently, and cells are often called the " Building Blocks of Life ". The study of cells is called  Cell Biology . Cells Consist of  cytoplasm enclosed within a membrane, which contains many  biomolecules  such as proteins and nucleic acids. Organisms can be classified as unicellular (consisting of a single cell; including bacteria) or multicellular (including plants and animals). While the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion (10 13 ) cells. Most plant and animal cells are visible only under a microscope, with dimensions between 1 and 100 micrometers.   Discovery of a cell Anton Von Leeuwenhoek  first saw and described a  Live Cell .  Robert Brown late r discovered the Nucleus .

3. Cell theory In 1838,  Matthias Schleiden , a German botanist, examined that plants are made up of large number of cells. Theodore Schwann (1839), a British Zoologist, examined that animals are also made up of cells. Later on, Rudolf Virchow explains that cells arise from pre-existing cell. This is known as  Omnis cellula-ecellula .   Characteristics of Cell Theory Cell is the structural and functional unit of life All organisms: plants and animals are made up of cells. All cells arise from the pre-existing cells.   Types of cell Prokaryotes Bacteria, blue green algae, mycoplasma and PPLO ( Pleuro Pneumonia like Organisms ) represents prokaryotes. The cell of prokaryotes is known as  Prokaryotic Cells . These cells are small in size and multiply at a faster rate. Prokaryotes have outermost covering known as  Cell Wall , except in mycoplasma. They are simpler and smaller than eukaryotic cells, and lack membrane-bound organelles such as a nucleus. The  DNA of a prokaryotic cell consists of a single chromosome that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid. Most prokaryotes are the smallest of all organisms ranging from 0.5 to 2.0 µm in diameter .

4. 2. Eukaryotes It includes protests, plants, fungi and animals. They have cell organelles separated by a membrane. They have well developed nucleus separated by a nuclear membrane. The main distinguishing feature of eukaryotes as compared to prokaryotes is compartmentalization: the presence of membrane-bound  organelles (compartments ) in which specific activities take place. Most important among these is a cell nucleus, an organelle that houses the cell's DNA. This nucleus gives the eukaryote its name, which means "true kernel (nucleus )".  

5. Other differences include: The plasma membrane resembles that of prokaryotes in function, with minor differences in the setup. Cell walls may or may not be present. The eukaryotic DNA is organized in one or more linear molecules, called chromosomes, which are associated with histone proteins. All chromosomal DNA is stored in the  cell nucleus , separated from the cytoplasm by a membrane. Some eukaryotic organelles such as mitochondria also contain some DNA. Many eukaryotic cells are ciliated with  primary cilia . Primary cilia play important roles in chemosensation ,  mechanosensation , and thermosensation . Cilia may thus be "viewed as a sensory cellular antennae that coordinates a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation." Motile eukaryotes can move using  motile cilia  or  flagella . Motile cells are absent in conifers and flowering plants. Eukaryotic flagella are less complex than those of prokaryotes.

6. Primary Function   1. They keep toxic substances out of the cell. 2. They contain receptors and channels that allow specific molecules, such as ions, nutrients, wastes, and metabolic products, that mediate cellular and extracellular activities to pass between organelles and between the cell and the outside environment . 3. They separate vital but incompatible metabolic processes conducted within organelles Cell Functions 1. Transport processes 2. Metabolism (i.e. chemical reactions) 3. Motility (i.e. spontaneous active movement that consumes energy) 4. Reproduction