Cell biology is the study of cells, including their structure, function, growth, reproduction, and genetics. A cell is the basic unit of life, composed of protoplasm enclosed within a membrane and containing a nucleus. The development of the cell theory began with early philosophers and microscopists observing plant and animal tissues as being made up of smaller units. In the 19th century, scientists such as Schleiden and Schwann formulated the cell theory stating that cells are the fundamental unit of structure and function in living things. The modern cell theory recognizes that all living things are made of cells, cells carry out metabolic functions, cells only arise from preexisting cells, and cells contain hereditary information.

1. CELL BIOLOGY
The biological science which deals with the study of structure, function, molecular organization,
growth, reproduction and genetics of the cells, is called cell biology or cytology.
WHAT IS A CELL?
Cell is an essentially functional unit (performing all the activities of life), comprising of protoplasm
limited by a membrane and containing one or more nuclei at some time in its life. Cell is considered
as the basic unit of life.
HISTORICAL ASPECTS
As is the case with all the important concepts, the cell concept has had an extensive background
of development.
 BEFORE THE INVENTION OF MICROSCOPE: Ancient Greek philosophers such as
Aristotle and Paracelsus concluded that “all animals and plants, however, complicated,
are constituted of a few elements which are repeated in each of them”. They were actually
referring to the macroscopic structures of an organisms such as roots, leaves, stem, in plants
and organs in animals.
 DURINH 16TH AND 18TH CENTURIES:
1. The first compound microscope was invented by Francis Janssen and Zachariais
Janssen.
2. Marcello Malpighi (1635-1694) use a microscope to examine the tissues of plants and
animals and suggested that they were composed of structural units that he called “utricles”.
3. The cell was first discovered and named by Robert Hooke in 1665. He remarked that it
looked strangely similar to cellula or small rooms which monks inhabited, thus deriving
the name.
4. The first man to witness a live cell under a microscope was Anton van Leeuwenhoek,
who in 1674 described the algae Spirogyra. He probably also saw bacteria.
He noted that the cell contain a central body (nucleus).
5. Nehemiah Grew published accounts of the microscopic examination of sections through
the flower, roots and stems of plants and clearly indicated that he recognized the cellular
nature of plant tissues.
 DURING 19TH CENTURY
1. In 1831, Robert Brown discovered and name the nucleus in the cell.
2. In 1838, Schleiden put forth his idea that the cells were the structure in plants. He also
described the nucleoli and appreciate the fact that each cell leads a double life-one
independent, pertaining to its own development and other as an integral part of a
multicellular plant.
3. In 1839, Schwann applied Schleiden’s thesis to the animals. He suggests that the living
things are made up of both the cells and the products or the secretion of the cells. He
also introduce the term metabolism which describe the activities of the cell.

2. Both of them thus formulated the basic and formal biological generalization, known as cell
theory or cell doctrine.
a. The cell is the unit of structure, physiology, and organization in living
things.
b. The cell retains a dual existence as a distinct entity and a building block in
the construction of organisms.
c. Cells form by free-cell formation, similar to the formation of crystals
(spontaneous generation).
4. In 1846, K. Nageli showed that the plant cells arise from the pre-existing cells.
5. In 1855, Rudolf Virchow confirmed the Nageli’s principle and stated that “omnis cellula
e cellula”.
6. In 1865, Virchow’s principle was experimentally proved by Louis Pasteur.
MODREN CELL THEORY
The modern version of cell theory states that
1. All living organisms are made up of one or more cells and cell products.
2. All metabolic reaction in unicellular and multicellular organisms take place in cells.
3. Cells originate only from other pre-existing cells.
4. The cell is the structural and functional unit of life.
5. Cells contains hereditary information which is passed from cell to cell during cell
division.
Kolliker applied the cell theory to embryology-after it was demonstrated that the new cell is
formed by the fusion of two cells-the spermatozoon and the ovum.
PROTOPLASM THEORY
Up to the middle of the 19th century greater emphasis was given to the cell wall and less to the
cellular contents. But soon biologist started to recognize the importance of juicy and slimy
contents of the cells.
 In 1835, Felix Dujardin termed the jelly like material with in the protozoans as sarcode.
 In 1835, H. Von Mohl describe cell division.
 In 1839, Czech Jepurkingi coined the term protoplasm to describe the contents of cell.
 In 1846, H. Von Mohl applied the name protoplast to the contents of embryonic cells of
the plants.
 In 1861, Max Schultze established similarity between sarcode and protoplasm of animal
and plant cells, thus, offering a theory which later on was improved and called protoplasm
theory by Ohertwig in 1892.
“All the living matter, out of which animals and plants are formed, is the protoplasm.”
The cell is an accumulation of living substances or protoplasm which is limited in space by an
outer membrane and possesses a nucleus. The protoplasm which is filled in the nucleus is

3. called nucleoplasm and that exists between the nucleus and the plasma membrane is called
cytoplasm.
DURING 20TH
CENTURY
20th century has witnessed great advancement in cell biological knowledge due to the following
two main reasons
 The increased resolving power of instrumental analysis due to the introduction of
electron microscopy and x-ray diffraction techniques.
 The convergence o cytology with the other fields of biological research (cytogenetic)
physiology and biochemistry.
ORGANISMAL THEORY
The organismal theory holds that the body of all multicellular organisms is a continuous
mass of protoplasm which remains divided incompletely into small centers. The cell for
the various biological activities. Thus a multicellular organism is a highly differentiated
protoplasmic in division differing with a unicellular protozoa only in size and degree of
differentiation of the protoplasm. The differentiation involves separation of the protoplast
into subordinate semi-independent compartments the so called cell.
CELL BIOLOGY AND OTHER BIOLOGICAL SCIENCES
1. CYTOTAXONOMY
Each plant and animal species has a definite number of chromosomes in its cells and the
chromosomes of the individuals of a species resembles closely with one another in shape and
size. This characteristics of the chromosomes help a taxonomist in determining the
taxonomical position of a specie. Further cell biology furnishes strong support to the manner
of origin of certain taxonomist position.
2. CYTOGENETICS
It is the branch of cell biology which is concerned with the cytological and molecular basis of
heredity, variation, mutation, phylogeny, morphogenesis and evolution of organism.
3. CELL PHSIOLOGY
The cell physiology is the study of life activities via nutrition, metabolism, excitability, growth,
reproduction or cell division and differentiation of the cell.
4. CYTOCHEMISTRY
It is that branch of cytology which deals with the chemical and physico-chemical analysis of
living matter.
5. MOLECULAR BIOLOGY

4. It is the most modern branch of biology in which the merging of cytology with biochemistry,
physico-chemistry and especially macromolecular and colloidal chemistry become
increasingly complex.
6. CYTOPATHOLOGY
The application of cell biology to pathological science has helped in understanding various
human diseases at molecular level. Because most diseases are caused due to disorder of
genetics codes in DNA molecule which alter the synthetic process of enzymes and ultimately
disturb the metabolic activity of the cell.
7. CYTOECOLOGY
It is the science in which one studies the effects of ecological changes on the chromosomes
number of the cell. The cytological studies on plants and animals have revealed that the
ecological habitat and geographical distribution have the correlation with chromosome
numbers.