The cell is the basic structural and functional unit of all living organisms. It is the smallest part of the body of an organism, capable of independent existence and able to perform all the essential functions of life. Cells vary in number (singlecelled: Amoeba; few-celled: Spirogyra, multi-celled: Man), size (smallest: Bacteria, longest: Nerve cell, largest: Ostrich egg) and shape (columnar: Epithelial cells).
The history of cell science began in 1665, with the observation of a thin section of a bottle cork by the English scientist Robert Hooke.
In 1838, Matthias Schleiden and Theodor Schwann proposed a basic cell theory.
The postulates of the modern cell theory are
- The cell is the smallest unit of structure of all living things.
- The cell is the unit of function of all living things.
- All cells arise from pre-existing cells.
- Also Read Tissues: Plant Tissues and Animal Tissues
Structural Organization Of a cell
|Content inside the
excluding the nucleus.
|Contains a mixture of water and soluble organic and inorganic compounds and various cell organelles.
|a. Centre of all metabolic activities.
b. Seat of occurrence of glycolysis (production of pyruvic acid).
Endoplasmic reticulum (ER)
|Irregular network of
|May be smooth (SER) or rough (RER).
|a. Supportive framework of the cell.
b. RER synthesises proteins, while
SER secretes lipids.
|Have varied shapes, but usually are sausage-like.
|a. Double-walled, inner wall thrown into folds, called
b. Contain their own
ribosomes and DNA, with several genes.
|a. Seat of aerobic respiration.
b. Synthesis of respiratory enzymes
and energy-rich compounds.
Golgi Apparatus (In animal cells)
Dictyosomes (In plant cells)
|Stacks of flattened
|Consists of a set of
membrane bounded, fluid-filled vesicles and vacuoles.
|a. Synthesis and secretion of enzymes, hormones etc.
b. Involved in the synthesis of plasma membrane, cell wall etc.
small granules, either scattered in the cytoplasm or attached to the outside of ER.
|a. Single-walled, dense, spherical bodies composed
mainly of RNA and proteins.
b. Not bounded by a membrane.
c. Two types: 70S and 80S
|Synthesis of proteins.
|Simple, tiny, single
|Contains 40 different types of enzymes.
|a. Intracellular digestion.
b. Destroy foreign substances.
Centrosome (In animal cells only)
the centrioles, located near nucleus.
|Contains one or two
centrioles that are
surrounded by radiating
microtubules to form an aster shape.
|Initiates and regulates cell division.
Plastids (In plant cells only)
|a. Have their own
|a. Double membrane,
proteinaceous matrix containing DNA.
b. Possess disc-like
structures called thylakoids, containing chlorophyll.
|a. Chromoplasts: Impart colour to
flowers and fruits.
b. Chloroplasts: Trap solar energy for photosynthesis.
c. Leucoplasts: Store starch.
|a. Mostly spherical and dense.
b. Surrounded by nuclear membrane with pores.
|a. Regulates cell functions.
b. Regulates cell cycle.
the nucleus of the cell.
|a. One or more in number.
|a. Produces ribosomes.
b. Participates in proteins synthesis
by forming and storing RNA.
the nucleus of the cell.
|Network of thread-like structures, made up of DNA.
|Chromosomes carry hereditary information or genes.
|Fluid-filled or solid-filled and membrane-bounded spaces.
|a. Non-living structures.
b. Larger in plant cells and fewer and smaller in animal
|a. Storage of water and other substances, food, pigments and
b. Gives turgidity to the cells.
c. Helps to maintain an osmotic pressure in a cell.
|Small particles, crystals or droplets.
|Starch (in plant cells), glycogen
(in animal cells) and fat-containing
granules serve as food for the cell.
Differences between plant and animal cells
|Presence of a definite cell wall, made up of cellulose
|Absence of a cell wall
|Present internal to the cell wall
|Forms the boundary of the cell
|Absence of centrosome
|Presence of centrosome
|Absence of centriole
|Presence of centriole
|Presence of one or more
|Presence of small and
|Presence of plastids
|Absence of plastids
|Usually larger with distinct
|Usually smaller with less distinct boundaries
|Not so dense
|Denser and more granular
|Only a thin lining of
cytoplasm which is mostly
pushed to the periphery
|Cytoplasm fills up almost
the entire cell
Differences between prokaryotic and eukaryotic cells
|Absence of a well-defined
|Presence of a well-defined
nucleus with a nuclear
|Presence of a single length of
|Presence of several lengths of DNA, wound around certain protein
|Presence of smaller
|Presence of larger
|Absence of other cell
|Presence of several other
cell organelles such as
mitochondria, ER, chloroplasts etc
|Cell division takes place by
fission or budding, but not by mitosis
|Cell division takes place by
mitosis or meiosis
|Bacteria, blue green algae
|Euglena, Amoeba, plants, animals
- All organisms grow due to the growth in size and increase in the number of cells. This growth is because of the production of more body substance and cell substance.
- Repair of an injury or regeneration of a lost part is because of cell division.
- Movement of the body is because of contractility of the cells or cellular parts.
- Feeding and nutrition have many steps, and each step is a result of cellular activities.
- Circulation of blood as well as the movement of other fluids in the body takes place through various forces that are set up due to the contraction of muscle cells of the heart and other parts of the body.
- Respiratory gases are transported from the lungs to different parts of the body by blood cells such as RBCs.
- Protection of the body from different germs and diseases occurs through cells called white blood cells (WBCs). These cells either devour the germs or give out antibodies or antitoxins, which destroy the germs and neutralize their effect.
- The sensation of touch, pain, heat, cold etc. occurs due to sensory cells. The brain orders the muscles to contract or glands to secrete through their cells.
- Thermoregulation or maintenance of our body heat also takes place through cellular activity.
- All living organisms reproduce through cellular activity.
- In plants, transportation takes place due to cellular activity