1.
In biology, cell theory is a scientific theory that
describes the properties of cells, the basic unit of
structure in every living thing. The initial
development of the theory, during the mid-17th
century, was made possible by advances in
microscopy; the study of cells is called cell biology.
Cell theory is one of the foundations of biology.
The three parts to the cell theory are as described
below:
All living organisms are composed of one or more
cells.
The cell is the basic unit of structure, function, and

2.
CELL The smallest structural unit of an organism thats
capable of independent functioning, consisting of one or more
nuclei, cytoplasm, and various organelles, all surrounded by a
semipermeable cell membrane.
CELL MEMBRANE The semipermeable membrane that encloses
the cytoplasm of a cell. Also
calledcytomembrane, plasmalemma, plasma membrane.
CELL WALL The rigid outermost cell layer found in plants and
certain algae, bacteria, and fungi but
characteristically absent from animal cells.
CHLOROPLAST A chlorophyll-containing plastid found in algal
and green plant cells.
CHROMOSOME A threadlike linear strand of DNA and

3.
CYTOPLASM The protoplasm outside the nucleus of a cell.
EUKARYOTES A single-celled or multicellular organism whose cells
contain a distinct membrane- bound nucleus.
GENE A hereditary unit consisting of a sequence of DNA that
occupies a specific location on a chromosome and determines
a particular characteristic in an organism. Genes undergo
mutation when their DNA sequence changes.
MULTICELLULAR Having or consisting of many cells.
NUCLELOUS A small, typically round granular body composed of protein
and RNA in the nucleus of a cell. It is usually associated with a
specific chromosomal site and involved in ribosomal RNA
synthesis and the formation of ribosomes.
ORGANELLES A differentiated structure within a cell, such as a
mitochondrion, vacuole, or chloroplast, that performs
a specific function.
ORGAN A differentiated part of an organism, such as an

4.
A microscope is an instrument used to
see objects too small for the naked
eye. An English scientist, Robert
Hooke, discovered the existence of
cells in 1665.Heis known for his book
Micrographia, and for first using the
word “cell” to describe the basic unit of
lSifcea. nning electron microscopes are used
to examine the external parts of various
organisms; It is a type of electron
microscope that images a sample by
scanning it with a high-energy beam of
electrons in a raster scan pattern. The
electrons interact with the atoms that
make up the sample, producing signals
that contain information about the

5.
The transmission electron microscope
(TEM) is used to view the internal structure
of a cell and its organelles. TEM is a
microscopy technique in which a beam of
electrons is transmitted through an ultra-thin
specimen, interacting with the specimen as it
passes through it. An image is formed from
the interaction of the electrons transmitted
through the specimen; the image is
magnified and focused onto an imaging
device, such as a fluorescent screen, on a
layer of photographic film, or to be detected
bOyr gaa sneisnmsosr t,h sautc ahr ea sm aa dCeC uDp coafm ae ra.
single cell and perform all their vital
activities, like reproduction, locomotion
and digestion, are
called unicellular organisms.
Unicellular organisms can be found
everywhere. The oldest forms of life,
unicellular organisms existed 3.8
billion years ago, if not longer.

6.
Organisms that are made up of
more than one cell are called multi-cellular
organisms. Most life that
can be seen with the naked eye are
multi-cellular, as are all animals and
pAlamnotse.ba uses small finger-like
projections, called pseudopodia, for
locomotion and to capture prey.
Pseudopods or pseudopodia are
temporary projections of eukaryotic
cells. Cells with these structures are
called ameboids.
Paramecium is a single cell, and is
built in such a way that can
perform all vital activities, like
reproduction, locomotion,
digestion, and so on.

7.
The White Blood Corpuscle (WBC) is
the only animal cell that changes its
shape. WBC’s are responsible for
protecting our bodies against invading
bacteria and harmful micro-organisms.
To find invading bacteria, they travel
along with blood in blood vessels.
Whenever they find invading bacteria,
they squeeze through the blood vessels
and intercellular spaces, catch the
bacteria and kill it. To perform this task,
WBC’s change their shape using
pseudopodia similar to those in an
amoeba.
The branched structure of
a neuron helps it transfer messages to
all parts of the body. A neuron, also
known as a nerve cell, is an electrically
excitable cell that processes and
transmits information by electrical and
chemical signaling.

8.
The black layer or scab (a hard
coating on the skin formed during
the wound healing reconstruction
phase) that you see on a wound is
a result of the aggregation of
dead Red Blood Cells (RBC’s).
The human respiratory system
consists of the nostrils, nasal
passage, internal nares, pharynx,
larynx, trachea, bronchi,
bronchioles and alveoli. Alveoli are
the functional units of the lungs.
All organ systems work together to
form a complex organism. Organ
systems include the digestive
system, respiratory system,
circulatory system, excretory
system and nervous system.

9.
Cytoplasm is a thick liquid in a cell
that holds the organelles, except for
the nucleus. All the contents of the
cells of prokaryote organisms are
contained within the cytoplasm. Within
the cells of eukaryotes organisms, the
contents of the nucleus are separated
from the cytoplasm.
The cell membrane is a biological
membrane that separates the interior of
all cells from the outside environment.
The cell membrane is selectively
permeable to ions and organic molecules
and controls the movement of
substances in and out of cells. It consists
of the phospholipid bilayer with
embedded proteins. Cell membranes are
involved in a variety of cellular
processes, such as cell adhesion, ion
conductivity and cell signalling, and serve

10.
The nucleus controls the activities of a
cell. The nucleus is a membrane-enclosed
organelle found in eukaryotic
cells. It contains most of the cell's genetic
material, organised as multiple long linear
DNA molecules to form chromosomes.
The genes within these chromosomes are
the cell's nuclear genome. The function of
the nucleus is to maintain the integrity of
these genes and to control the activities of
the cell by regulating gene expression.
The nucleus is, therefore, the control
centre of the cell.
Methylene blue is the stain placed on
plant and animal cells to differentiate the
nucleus under a microscope. Solutions of
this substance are blue when in an
oxidising environment, but will turn
colourless if exposed to a reducing
agent.

11.
Chromosomes are called the
vehicles of heredity because they
carry genes, and help in
the inheritance or transfer of
characteristics from the parents to
the offspring. A chromosome is an
organised structure of DNA and
protein found in cells. It is a single
piece of coiled DNA containing
many genes. Chromosomes also
contain DNA-bound proteins, which
serve to package the DNA and
control its functions.
Bacteria and blue-green algae that
contain nucleoids are
called prokaryotes.

12.
Organisms that have a well-organised
nucleus are called eukaryotes. The
defining membrane-bound structure
that sets eukaryotic cells apart from
prokaryotic cells is the nucleus, or
nuclear envelope, within which the
genetic material is carried. The
presence of a nucleus gives
eukaryotes their name, which comes
from the Greek eu, meaning "good",
andkaryon, meaning "nut" or "kernel".
Most eukaryotic cells also contain
oTthheer nmucelmeobirdanise a-bno iurrnedg uolragralyn-elles.
shaped region within the cell of
prokaryotes, which has nuclear
material without a nuclear
membrane.

13.
The nucleolus is a small,
spherical body in the nucleus. It
is a non-membrane bound
structure composed of proteins
and nucleic acids. Ribosomal
RNA is transcribed and
assembled within the nucleolus.
Chloroplast is a type
of plastid involved in
photosynthesis in plants. These
are specialised organelles found in
all higher plant cells. These
organelles contain the plant
cell's chlorophyll, providing the
green colour. They have a double
outer membrane. Within the
stroma are other membrane
structures,

14.
A vacuole is a membrane-bound
organelle present in all plant, fungal
cells, and some animal and bacterial
cells. Vacuoles are essentially
enclosed compartments filled with
water containing inorganic and
organic molecules, including
enzymes, in solution. In certain
cases, though, vacuoles may
contain solids that have been
engulfed. Vacuoles are formed by
the fusion of multiple membrane
vesicles, and are effectively just
larger forms of these. The organelle
has no basic shape or size, and its
structure varies according to the
needs of the cell.

15.
In 1665, a Englishman called Robert.
Hooke used a microscope which made by
himself to observe a cork, he then
discovered that it had many small holes,
just like honeycomb, so he named these
small holes be cells, which the original
meaning as small rooms. Robert Hooke
hadn't describe the things inside cells. He
just simply said that cells contain air and
liquid. Now, we know that the cells that
Hooke had discovered was only the cell
membrane of dead cell. Afterwards, many
scholars also discovered cells in different
living things. Plants and animals also
have cells, but these scholars hadn't
noticed the things inside the cells. In
1831,Robert Brown discovered nucleus in

16.
Born 28 July [O.S. 18
July] 1635
Freshwater, Isle of
Wight, England
Died 3 March 1703 (aged
67)
London, England
Nationality English
Fields Physics and
chemistry
Institutions Oxford University
Alma mater Christ Church,
Oxford
Academic advisors Robert Boyle
Known for Hooke's law
Microscopy
An artist's impression of
Robert Hooke.

17.
Question.1: Indicate True(T) or False(F)
a. Unicellular organisms have one-celled body.
b. Muscle cells are branched structures.
c. The basic living structure of an organism is an organ.
d. Amoeba has irregular shape.
Answer: a)T
b)T (spindle shaped structures)
c)F
d)T
Question.2: Make a sketch of the human nerve dell. What function
do nerve cells perform?
Answer: Functions of human nerve cell:
Nerve cells receive message from different parts of body.
They further transfer these messages to brain and accordingly brain
send commands for functioning of different organs of body.

18.
Question.3: Write short notes on the following:
(a) Cytoplasm (b) Nucleus of a cell
Answer:
(a) Cytoplasm: Cytoplasm is a jelly like substance which is present
between the cell membrane and the nucleus. Various
other organelles of cells are present in the cytoplasm. Cytoplasm is
made up of chemical substances like carbohydrates, proteins and
water. These chemical substances are present in cells of all types and
sizes. Cytoplasm contains many important tiny substances
called Organelles.
(b) Nucleus of a cell: Nucleus is the master of the cell. It commands
all the functioning of the cell. It is generally located in the center of the
cell and is spherical in shape. A membrane called nuclear membrane
separates it from cytoplasm. It contains the genetic material DNA and
RNA in it. This porous membrane allows the transfer of material in the
nucleus and cytoplasm. Nucleus contains a dense body called
Nucleolus which actually contains Chromosomes, the genetic material.
Question.4: Which part of the cell contains organelles?
Answer: Cytoplasm.

19.
Plant Cells Animal Cells
Cel
l
wal
l
Chloropl
They are usually larger than animal cells. They are generally small in size.
Cell wall is present. Cell wall is absent.
Vacuoles are larger in size. Vacuoles are small in size.
ast
Cell
Membrane
Vacuole
Nucleus
Cytoplasm
Cell
Membrane
Vacuole
Nucleus
Cytoplasm
Question.6: State a difference between eukaryotes and prokaryotes.
Answer: Prokaryotes do not have a well designed nuclear membrane while,
eukaryotes have a well designed nuclear membrane.

20.
Question.7: Where are the chromosomes found in cell?
State their functions.
Answer: Chromosomes are found in the nucleus of a cell. Their
function is to carry characteristic features of parent cells to the
daughter cell means, from parent to offspring.
Question.8: ‘Cells are the basic structural units of living
organism’. Explain.
Answer: In Biology, the basic unit of which all living things are
composed is known as ‘cell’. The ‘cell’ is the smallest structural
unit of living matter that is capable of functioning independently.
A single cell can be a complete organism in itself, as in bacteria
and protozoans. A unicellular organism also captures and
digests food, respires, excretes, grows, and reproduces. Similar
functions in multi-cellular organisms are carried out by groups of
specialized cells which are organized into tissues and organs
such as, the higher plants and animals. Hence, ‘cell’ is known as
the basic structural and functional unit of life.