Both animals and plants are made
up of cells. Whether a cell belongs to an animal or a cell, every cell has three main components – Cell membrane, Nucleus and Nucleoplasm. Lets discuss about
the various components of a cell.
1. CELL MEMBRANE : The cell membrane of the cell is the outer layer of
the cell and it is basically a semi permeable membrane. The main function of
the cell membrane is to control the molecular activities between the cell &
its outer medium which interact with the cell. Cells are enclosed by a thin
film like membrane called plasma membrane, cytoplasmic membrane or plasma
lemma.
2. CYTOPLASM : It is a part of protoplasm lying between plasma
membrane and nucleus, Jelly-like fluid. It participates in the intracellular
distribution of nutrients, metabolites and enzymes.
3. CELL WALL : Cells of most fungi, prokaryotes (bacteria and
blue-green algae) and plants (except gametes) are surrounded by the cell wall.
It is absent in animals. In true bacteria and cyanobacteria, cell wall is of
peptidoglycan, in some fungi it is of chitin and in most of the algae and
higher green plants it is of cellulose.
4. NUCLEUS : It is discovered by Robert Brown. Every eukaryotic cell
consists of at least one, almost spherical, dense, highly specialized structure
called nucleus. Although, sieve tube element of mature phloem and RBCs of
mammals don’t have nucleus. It contains nucleoplasm (nuclear sap) which
contains chromatin. (Chromatin is composed of DNA mainly). Chromatin organizes
itself into thread like structures called Chromosomes. The function of
chromosomes is to carry genetic information from one cell generation to
another. Nucleolus is also present which helps in the production of ribosome. Nucleus
controls the metabolic activities of the cell by controlling the synthesis of
enzymes.
5. CHROMOSOMES : Waldeyer coined the term chromosome. Sutton and
Boveri proved that chromosome is the physical basis of hereditary. Each
chromosome is made up of DNA and this DNA by replication gives rise to
messenger RNA which carry the genetic information in the form of code. This
-RNA comes out of the nuclear wall into the cytoplasm where it helps to form a
particular kind of protein needed by the cell or body. Number is constant for a
particular species. In humans, the diploid number is 46. Of these, 23 are from egg cell and 23 from sperm cell.
6. MITOCHONDRIA : It is also called as Power house
of the cell or energy converting organelles,
as oxidation of food occurs in stepwise manner, resulting in the release of
chemical energy. This energy is stored in the form of ATP. From mitochondria,
ATP molecules are shifted to cytoplasm, which is the chief site of their utilization.
They are semi-autonomous organelles. They contain DNA, m-RNA, ribosome and can
synthesize some of their own proteins. Each mitochondria is enclosed by a
double-membraned envelope, outer and inner. Fluid (called matrix) is there
between these two layers
7. ENDOPLASMIC RETICULUM : It provides an increased surface area for various
metabolic activities within the cell. It provides mechanical support to the
cytoplasm. It is of two types: Rough and smooth. Both Smooth Endoplasmic
Reticulum and Rough Endoplasmic Reticulum form passages for transport of
secretary proteins, lipids and sterols. Rough Endoplasmic Reticulum collects
and stores the proteins synthesized by
its surface bound ribosome. Smooth endoplasmic reticulum also helps in detoxifying
any poisonous substance in the cell.
8. GOLGI COMPLEX : The
Golgi Complex (Golgi apparatus or Golgi body) is found in most eukaryotic cells.
The Golgi apparatus is a major collection and dispatch station of protein
products received from the endoplasmic reticulum (ER). The main functions of
Golgi bodies are the processing of proteins synthesized by ribosomes of the
rough endoplasmic reticulum, synthesis
of certain polysaccharides and glycolipids, and the packaging of secretory
materials that are to be discharged from the cell.
9. LYSOSOMES : These are also called Suicidal
bags. They contain powerful enzymes (acid
hydrolyses), rupture of lissome membrane releases these enzymes. They can digest
worn-out or unnecessary parts of the cell, or even whole cells by process
called ‘Autophagy’.
10. RIBOSOMES : These are found on Endoplasmic Reticulum. These are made of
RNA and proteins in equal amounts. They
act as sites of protein synthesis (Ribosome are inactive for protein
synthesis, but after combining with mRNA form polyribosome which play important
role in protein synthesis).
11. VACUOLES : These are found only in
plant cells. Membrane
surrounding the vacuole is tonoplast. There main functions are regulation of
water, osmoregulation, storage and indigestion.
12. PLASTIDS : They are found in plant
cells only. They are
of different types:
(i)Chloroplast: These impart green colour as they contains the
pigment chlorophyll. They contains
the matrix (fluid), stroma which has many flat membranous structures called
thylakoids
(ii)Leucoplasts: These are colourless, occur in large no in cells
of fruits, seeds, etc. They store
nutrients (eg, amyloplasts of potato store starch).
(iii)Chromoplasts: These are colored, containing fat soluble yellow,
orange and red pigments (chiefly carotinoids). These are found in flowers and
fruits.
13. CENTROSOME : These are found in animal cells and cells of lower plants (eg,
Algae) only. The first indication that the cell is about to divide is generally
given by the centrosome.
