Cells
Structure and functions
By
Priya tamang

What is cell?
• The cell is a structural and functional unit of all the
living organisms, and it is also known as building
blocks of life.
• The human body is composed of trillions of cells,
with their own specialized functions.
• The term cell was first coined by Robert hook in
1965.
• The cell is made up of water about two third of a
cell, and rest is a mixture of molecules(protein,
lipids, carbohydrates).
• Cells covert the raw materials in the food into the
molecules our body needs, using thousands of
different metabolic reactions.

Levels of Organization in
Living Organisms
• -Atoms (smallest unit of matter both living and non-living)
• -Molecules (building blocks of matter composed of two or
more atoms )
• -Organelles (parts of a cell that carry out a particular function or
role and are made of molecules)
• -Cell (is the smallest unit of life and the building block of all living
organisms)
• -Tissues (tissues are formed when cells combine to carry out a task.
Muscles used to move your eyes are tissues)
• -Organs (when two or more tissues combine and work together.
Examples are the heart or stomach organs)
• -Systems (Organs work together in systems, such as stomach, liver,
and pancreas that work together in our digestive system)
• -Organisms (Human beings are organisms that are composed of
many systems)

History
• 1595 – Jansen credited with 1st compound microscope.
• 1655 – Hooke described ‘cells’ in cork.
• 1674 – Leeuwenhoek discovered protozoa. He saw bacteria some 9 years later.
• 1833 – Brown descibed the cell nucleus in cells of the orchid.
• 1838 – Schleiden and Schwann proposed cell theory.
• 1840 – Albrecht von Roelliker realized that sperm cells and egg cells are also
cells.
• 1856 – N. Pringsheim observed how a sperm cell penetrated an egg cell.
• 1858 – Rudolf Virchow (physician, pathologist and anthropologist) expounds
his famous conclusion: omnis cellula e cellula, that is cells develop only from
existing cells [cells come from preexisting cells]
• 1857 – Kolliker described mitochondria.
• 1879 – Flemming described chromosome behavior during mitosis.
• 1883 – Germ cells are haploid, chromosome theory of heredity.
• 1898 – Golgi described the golgi apparatus.

• 1938 – Behrens used differential centrifugation to separate nuclei from
cytoplasm.
• 1939 – Siemens produced the first commercial transmission electron
microscope.
• 1952 – Gey and coworkers established a continuous human cell line.
• 1955 – Eagle systematically defined the nutritional needs of animal cells
in culture.
• 1957 – Meselson, Stahl and Vinograd developed density gradient
centrifugation in cesium chloride solutions for separating nucleic acids.
• 1965 – Ham introduced a defined serum-free medium. Cambridge
Instruments produced the first commercial scanning electron
microscope.
• 1976 – Sato and colleagues publish papers showing that different cell
lines require different mixtures of hormones and growth factors in
serum-free media.
• 1981 – Transgenic mice and fruit flies are produced. Mouse embryonic
stem cell line established.
• 1995 – Tsien identifies mutant of GFP with enhanced spectral
properties
• 1998 – Mice are cloned from somatic cells.
• 1999 – Hamilton and Baulcombe discover siRNA as part of post-
transcriptional gene silencing (PTGS) in plants

Cell theory
• The cell theory describes the basic properties of
all cells.
• The three scientists that contributed to the
development of cell theory are Matthias
Schleiden, Theodor Schwann, and Rudolf
Virchow. The cell theory states that:-
• All living things are composed of one or more
cells.
• The cell is the basic unit of life.
• All new cells arise from existing cells.

Modern Cell Theory
• All known living things are made up of cells.
• The cell is structural & functional unit of all living
things.
• All cells come from pre-existing cells by division.
(Spontaneous Generation does not occur).
• Cells contains hereditary information which is
passed from cell to cell during cell division.
• All cells are basically the same in chemical
composition.
• All energy flow (metabolism & biochemistry) of
life occurs within cells.

BASIC

CELL ORGANELLES

Contain all
the genetic
information
to produce
new cells and
controls all
the chemical
processes
that take
place in the
cell.
NUCLEUS

Respiration
takes place,
glucose and
oxygen are
changed into
energy.
MITOCHONDRIA

Cell membrane

GOLGI APPARATUS

Type of cells
• About 4.6 billion years ago, Earth was formed. In
the earth's history, there was a very hostile and
volcanic environment and is difficult to imagine
any life being viable in those types of conditions.
• It wasn't until the end of the Precambrian Era of
the Geologic Time Scale when life began to form.
• Several theories, about how life first came to be on
Earth. These theories include the formation
of organic molecules within what is known as
the"Primordial Soup", life coming to Earth on
asteroids (Panspermia Theory), or the first
primitive cells forming in hydrothermal vents.

Prokaryotic Cells
• The simplest type of cells were most likely the first type of
cells that formed on Earth. These are called prokaryotic
cells. They have a cell membrane surrounding the cell,
cytoplasm where all of the metabolic processes happen,
ribosomes that make proteins, and a circular DNA
molecule called a nucleoid where the genetic information is
held.
• They have a rigid cell wall that is used for protection. All
are unicellular, meaning the entire organism is only one
cell.
• All are asexual, meaning they do not need a partner to
reproduce. Most reproduce through a process called binary
fission where basically the cell just splits in half after
copying its DNA. This means that without mutations
within the DNA, offspring are identical to their parent.
• Archaea and Bacteria are prokaryotic organisms.

Eukaryotic Cells
• The other, much more complex, type of cell is called
the eukaryotic cell. Like prokaryotic cells, they have cell
membranes, cytoplasm, ribosomes, and DNA.
• There are many more organelles within eukaryotic cells
which include a nucleus to house the DNA, a nucleolus
where ribosomes are made, rough endoplasmic reticulum
for protein assembly, smooth endoplasmic reticulum for
making lipids, Golgi apparatus for sorting and exporting
proteins, mitochondria for creating energy,
a cytoskeleton for structure and transporting information,
and vesicles to move proteins around the cell. Some
eukaryotic cells also have lysosomes or peroxisomes to
digest waste, vacuoles for storing water or other things,
chloroplasts for photosynthesis, and centrioles for splitting
the cell during mitosis.
• Cell walls can also be found surrounding some types of
eukarotyic cells.

• Most are multi-cellular. This allows the eukaryotic cells
within the organism to become specialized. Through a
process called differentiation, these cells take on
characteristics and jobs that can work with other types of
cells to create an entire organism.
• There are a few unicellular eukaryotes as well. These
sometimes have tiny hair-like projections called cilia to
brush away debris and may also have a long thread-like tail
called a flagellum for locomotion.
• The third taxonomic domain is called the Eukarya Domain.
• This domain includes all animals, plants, protists, and
fungi.
• Eukaryotes may use either asexual or sexual
reproduction depending on the organism's complexity.
• Sexual reproduction allows more diversity in offspring by
mixing the genes of the parents to form a new combination
and hopefully a more favorable adaptation for the
environment.

Difference between Prokaryotic cell and Eukaryotic cell

Difference between plant cell and
animal cell