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 (1013) 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 later 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
1. 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.
7. 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
