The cell is the smallest unit of the human body. Every cell has individual works, even the cell is the smallest unit but it has an unimaginable world. This article will be of great use to each of us to know about each member of the cell and its application.
Cells are enclosed by a cell membrane, also known as a plasma
membrane. It is a living, elastic and selectively permeable membrane. It
separates the outside environment of the cell from the inside of the cell.
Functions
It holds the protoplasm of the cell and provides mechanical
support to the cell.
Being selectively permeable, it allows only certain substances
to move in and out of the cell.
It provides a definite shape to the cell.
It helps in the removal of waste products inside the cell.
Cell Wall
The cell wall is a semi-rigid, freely permeable and
non-living part of a plant cell. It is made of a non-living substance called
cellulose.
Functions
It provides mechanical strength to the plant cell.
It provides a definite shape to the plant cell.
Differences between a
cell membrane and a cell wall
|
Cell membrane |
Cell wall |
|
It is the
outermost, living cover of the cell. |
It is the
outermost, non-living thick, protective cover of the plant cell. |
|
It is selective
and permeable in nature. |
It is highly
permeable and allows all substances to leave and enter the cell. |
|
It is found in
bacterial cells as well as in plant cells. |
It is found in
plant cells and animal cells. |
Nucleus
The nucleus is the largest and most important structure of a
cell. It is a dense, spherical body which lies in the centre of the cytoplasm.
The nucleus is enclosed by a double membrane called the nuclear membrane, which
separates the nucleus from the cytoplasm.
The nuclear membrane surrounds the dense, semi-fluid
substance called the nucleoplasm. It makes the body of the nucleus and contains
chromosomes. The chromosomes consist of a network of thread-like structures
called chromatin fibres.
Each chromatin fibre contains genes, the basic units of
parental characteristics. The nucleoplasm also contains one or more spherical
bodies called the nucleolus.
Functions
It controls all the vital activities of the cell therefore;
it also called is the brain of a cell.
It contains chromosomes which carry the parental characters
or genes to the offspring.
It plays an important role in cell division.
Cytoplasm
It is a viscous, homogeneous and granular protoplasm that lies
between the nucleus and the plasma membrane of a cell. It is a translucent,
gelatinous, semi-fluid substance which forms the main bulk of the cell. It
contains many living parts called cell organelles, and some non-living parts
called cell inclusions.
Functions
Cytoplasm stores many chemicals that are essential for life.
It supplies the proper nutrition to the cell organelles and
stores food in the form of starch grains.
Many vital metabolic reactions like protein synthesis take
place in the cell cytoplasm.
Cell Organelles
The discovery of the electron microscope revealed that the cells
contain many membrane-bound living structures scattered in the cytoplasm called
cell organelles. They have a definite shape and structure. They perform
definite functions.
Mitochondria (Singular:
Mitochondrion)
Mitochondria are tiny bodies of varying shapes (rods, round,
oval), distributed uniformly in the cytoplasm. Each mitochondrion is enclosed by
a double membrane.
The inner membrane is folded into finger-like projections
called cristae. A fluid filled in the inner membrane of the mitochondria is
called the matrix. Single cells have a few hundred to thousands of
mitochondria.
Functions
They perform the cellular respiration within the cells. Thus,
they are also known as the powerhouse of the cell.
Mitochondria are involved in the conversion of food into
chemicals. They convert the chemical energy contained in the food into a form
of energy that a cell uses to grow.
Endoplasmic Reticulum
(ER)
It is a network of tube-like structures scattered throughout the
cytoplasm. In some places, it connects the plasma membrane with the nuclear
membrane and transports useful substances within the cell. The endoplasmic
reticulum is of two types – the smooth endoplasmic reticulum and the rough
endoplasmic reticulum. The rough endoplasmic reticulum has many fine granules
called ribosomes.
Functions
They form the supporting skeletal framework of the cell.
They provide a pathway for the transport of nuclear material from
one cell to the other.
Golgi Complexes or
Golgi Bodies
Golgi bodies are flat, sac-like structures, usually found
near the nucleus of most of the cells. They are bound by smooth double
membranes. The main components of the Golgi body are – cisternae, vesicles and
vacuoles. The cisternae are stacked one over the other in parallel rows. The
vesicles are the budded outgrowths of cisternae and the vesicles are the large
membranous bodies.
Functions
Golgi bodies secrete hormones and enzymes.
It helps in the synthesis of a plant’s cell wall.
Lysosomes
The lysosomes are sac-like cell organelles, mainly found in animal cells.
Functions
It contains powerful enzymes which can break down many
substances.
It protects the cell from harmful foreign bodies like
bacteria.
Centrosome
The centrosome is a minute, non-membranous body found close
to the nucleus in the cytoplasm of animal cells. It contains to small and
bright granules called centrioles surrounded by aster (star-like cytoplasmic
microtubules). Plant cells do not contain centrosomes.
Function
Centrosome initiates the cell division in animal cells.
Vacuoles
They are membrane-bound, non-living, fluid-filled spaces
present in the cytoplasm of the cells. The membrane that binds a vacuole is
called the tonoplast. A large vacuole is generally found in the plant cell. If
vacuoles are present in an animal cell, they are very small and temporary.
Function
Vacuoles store excess water, pigments and waste products.
Plastids
The plastids are disc-shaped organelles found in plant cells
only. They are bounded by a double membrane and store pigments. There are three
types of plastids present in the plant cells namely leucoplasts, Chromoplasts
and Chloroplasts.
Leucoplasts
These are colourless plastids present in the cell of
underground storage parts like the tuber, corm and rhizome of the plant. The
leucoplasts store food prepared by the plant, in the form of proteins, starch and
fats.
Chromoplasts
These are the coloured plastids other than the green-coloured
ones. They are mostly present in the petals of flowers and pericarp of the
fruits and impart colour to them.
Chloroplasts
These are the green-coloured plastids, which contain a green
colour pigment, called chlorophyll. Chloroplasts trap the sun’s energy to
perform the process of photosynthesis.
The green colour of leaves and soft stems is due to the
presence of chloroplasts in them. A chloroplast has two parts – grana, a pile
of flat-green solid bodies and stroma, a liquid matrix.