Structure of Cell
There are two types of cells:
1. Prokaryotic cell
2. Eukaryotic Cell
Prokaryotic cell lacks a membrane bound nucleus and
membraned organelles e.g. bacterial cell while eukaryotic cell has a membrane
bound nucleus and membraned organelles e.g. cells of plants and animals.
With the help of light microscope and electron microscope, a typical Eukaryotic
cell shows the following structural details.
(Diagram)
1. Cell Wall
2. Cell Membrane
3. Nucleus
4. Cytoplasm
1. Cell Wall
It is the outer most boundary of plant cells. It is
rigid and non-living. It is chemically composed of Cellulose. The cell wall of
fungi is made up of Chitin. The walls of some cells are thick and walls of some
cells are thin. For example, in plants, xylem vessel elements and tracheids
(which transport water and minerals) have thick walls whereas as parenchyma
cells (which store water and food) have thin walls. The primary layer of cell
wall is known as primary walls which are further strengthened by an additional
layer called secondary wall especially in xylem vessels. Secondary wall is
thicker than the primary wall. Electron microscope studies reveal that
cellulose fibers in primary and secondary walls have a criss cross arrangement.
Functions
Cell wall provides a definite shape, rigidity, protection and support to
plant cell.
2. Cell Membrane
It is a thin membrane which is also called Plasma
membrane. It is present in cells of all plants and animals. It is outer most
boundary of animal cell while in plant cells; it is present inner to cell wall.
Both nucleus and cytoplasm are surrounded by cell membrane. According to fluid
mosaic model, cell membrane is composed of two layers of lipids in which
protein molecules are partially or completely embedded.
Functions
Cell membrane is selectively permeable membrane. It means that it allows
some things to pass through easily while some not. Thus, it controls the
movement of material inside or outside the cell.
3. Nucleus
It is most important and distinct part of the cell.
It is present in center of the animal cell while in plant cell it is pushed on
one side due to large central vacuole. It is also surrounded by a membrane
which is called membrane. Under microscope, it to be doubled and nuclear
electron appears porous.
1. The number of chromosomes is fixed for each species. This number is called
diploid number (2n). E.g human’s cell has 46 chromosomes, cell of Radish has 18
chromosomes, and cell of union has 16 chromosomes.
2. Chromosomes are composed of protein and DNA.
3. In the nucleolus (plural, Nucleoli) ribosomal RNA is formed which helps in
the formation of ribosome.
4. Cytoplasm
It is viscous opaque substance. It is present
between nuclear membrane and cell membrane. In a living cell, many types of
organelle of different sizes and shapes are found. It contains many insoluble
granules of storage substances. There are also present organic compounds like
carbohydrates, proteins, lipids (fats), enzymes and inorganic compounds like
water and salts.
Functions
Cytoplasm provides chemicals, site and environment for different
biochemical reactions.
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