Cells are the basic units of life and come in two types, eukaryotic and prokaryotic. Organelles are structures within cells that carry out specific functions to maintain cellular homeostasis. Membranous organelles are surrounded by membranes while non-membranous organelles like ribosomes are not. Organelles perform functions like energy production, protein building, waste destruction, and responding to signals. The plasma membrane forms the boundary of the cell and regulates what enters and exits.

1. CELL AND ITS ORGANELLES
CELL
Cells are the smallest units of life. They are a closed system, can self-replicate, and are the building blocks of
our bodies. The cells provide shape, structure, and carries out different types of functions to keep the
entire system active. There are 2 types of cells: eukaryotic cells, cells- that contain a nucleus and Prokaryotic
cells- cells that lack a nucleus, are structured differently. A cell consists of two major regions, the cytoplasm
and the nucleus. The nucleus is surrounded by a nuclear envelope and contains DNA in the form of
chromosomes. The cytoplasm is a fluid matrix that usually surrounds the nucleus and is bound by the outer
membrane of the cell.
Organelles are small structures within the cytoplasm that carry out functions necessary to maintain
homeostasis in the cell. They are involved in many processes, for example energy production, building
proteins and secretions, destroying toxins, and responding to external signals. Organelles are considered
either membranous or non-membranous. Membranous organelles possess their own plasma membrane to
create a lumen separate from the cytoplasm. This may be the location of hormone synthesis or degradation of
macromolecules. Non-membranous organelles are not surrounded by a plasma membrane. Most non-
membranous organelles are part of the cytoskeleton, the major support structure of the cell. These include:
filaments, microtubules, and centrioles.
Organelles without membrane: The Cell wall, Ribosomes, Microtubules, Actin filaments, Intermediate
filaments, Centrioles and Cytoskeleton are membrane-bound cell organelles. They are present both
in prokaryotic cell and the eukaryotic cell.
Single membrane-bound organelles: Vacuole, Peroxisomes, Lysosome, Golgi apparatus, Endoplasmic
Reticulum are single membrane-bound organelles present only in a eukaryotic cell.
Double membrane-bound organelles: Mitochondria, Vesicles and chloroplast are double membrane-
bound organelles present only in a eukaryotic cell.
CELL
ORGANELLES
STRUCTURE FUNCTIONS
CELL MEMBRANE/
PLASMA
MEMBRANE/
PLASMALEMMA
A double membrane composed of lipids
(cholesterol) and proteins [Phospholipid- lipid-
Phospholipid]. Present both in plant and animal
cell.
Provides shape, protects the
inner organelle of the cell
and acts as a selectively
permeable membrane.
CELL WALL
The cell wall is made up of cellulose,
hemicellulose, and proteins while in a fungal
cell, it is composed of chitin.
protecting and maintaining
the shape of the cell, helps
the cell withstand the turgor
pressure of the cell, initiates
cell division
CENTRIOLE
Cylindrical structure made with nine triplets
microtubules that surround the periphery of the
centriole while the center has a Y-shaped linker
and a barrel-like structure that stabilizes the
centriole.
Cartwheel is present in a centriole which is
made up of a central hub with nine
spokes/filaments radiating from it. Each of these
filaments/spokes is connected to the
microtubules through a pinhead.
forming spindle fibers,
formation of cilia and
flagella
CILIA AND
FLAGELLA
tiny hair-like projections from the cell made of
microtubules and covered by the plasma
membrane. Flagella are a filamentous organelle,
the structure of which is different in prokaryotes
and eukaryotes.
In prokaryotes, flagellin protein is wrapped
C/F- movement of the
organisms & movement of
various particles present
around the organisms.
C- In the blood vessels,
which helps in controlling

2. around in a helical manner creating a hollow
structure at the center throughout the length.
In eukaryotes, protein is absent and the structure
is replaced with microtubules.
the flow of blood
CENTROSOMES
Composed of Centrioles and found only in the
animal cells.
It plays a major role in
organizing the microtubule
and Cell division.
CYTOPLASM
A jelly-like substance, which consists of water,
dissolved nutrients and waste products of the
cell.
Responsible for the cell’s
metabolic activities.
CYTOSKELETON
A number of fibrous structures are present in the
cytosol that helps give shape to the cell while
supporting cellular transport.
Around three different classes of fibers make up
the cytoskeleton which is: microtubules,
microfilaments, and intermediate filaments.
These are separated based on a protein present
in them.
provide shape and
mechanical support to the
cell against deformation,
expansion and contraction of
the cell, intracellular and
extracellular transport of
materials.
MICROFILAMENTS
thinnest part of the cytoskeleton, and are made
of actin
Useful protein in cell
movement. In the heart,
contraction is mediated
through an actin-myosin
system.
MICROTUBULES
small tubes made from the protein tubulin,
found in cilia and flagella
cell movement, provide
pathways for secretory
vesicles, cell division part
INTERMEDIATE
FILAMENTS
Smaller than the microtubules, but larger than
the microfilaments, they are made of a variety
of proteins such as keratin and/or neurofilament.
They are very stable, and
help provide structure to the
nuclear envelope and anchor
organelles.
ENDOPLASMIC
RETICULUM [ER]
A network of membranous tubules, present
within the cytoplasm of a cell.
Forms the skeletal
framework of the cell,
involved in the
Detoxification, production of
Lipids and proteins.
ROUGH ER
The outer plasma membrane of rER is carpeted
with ribosomes, causing it to appear dotted under
a microscope, composed of cisternae, tubules,
and vesicles.
Protein production; in
particular for export out of
the cell
SMOOTH ER It lacks ribosomes and thus appears smooth under
a microscope and a storage organelle
Lipid & steroid production;
Detoxification
ENDOSOMES
Membrane-bound compartments within a cell
originating from the Golgi network and are
mainly composed of tubular structures.
Allow the sorting and
delivery of internalized
materials from the cell
surface and transport of
materials to the Golgi or the
lysosomes.
GOLGI
APPARATUS/
COMPLEX/ BODY
Membrane-bound, sac-like organelles, present
within the cytoplasm of the eukaryotic cells.
It is mainly involved in
secretion and intracellular
transport.
LYSOSOMES
A tiny, circular-shaped, single membrane-bound
organelles, filled with digestive enzymes.
Helps in the digestion and
removes wastes and digests
dead and damaged cells.
Therefore, it is also called as
the “suicidal bags”.
Irregular or pleomorphic; are surrounded by a plasma membrane repair, cell

3. LYSOZYME lysosomal membrane that contains the enzymes
within the lysosome and protects the cytosol
with the rest of the cell from the harmful action
of the enzymes.
signalling, and energy
metabolism
MICROVILLI
tiny finger-like structures that project on or out
of the cells. These exist either on their own or in
conjunction with villi.
increase the surface area of
the cell, allow the breakdown
of larger molecules into
smaller, act as an anchoring
agent in white blood cells
and in sperms during
fertilization
MITOCHONDRIA
An oval-shaped, membrane-bound organelle,
also called as the “Power House of The Cell”.
The main sites of cellular
respiration and also involved
in storing energy in the form
of ATP molecules.
NUCLEUS
A largest, double membrane-bound organelles,
which contains the entire cell’s genetic
information.
Controls the activity of the
cell, helps in cell division
and controls the hereditary
characters.
NUCLEOID
Nucleoid is a non-membrane, irregular shaped
cell organelle present in all prokaryotic cells.
They are the carrier of the
genetic material of a cell.
NUCLEOLUS
Within the nucleus is a small subspace known
as the nucleolus. It is not bound by a membrane,
so it is not an organelle.
responsible for making
proteins, assembling and exit
of Ribosomes
PEROXISOME
A membrane-bound cellular organelle present in
the cytoplasm, which contains the reducing
enzyme.
Involved in the metabolism
of lipids and catabolism of
long-chain fatty acids.
PLASMODESMATA
Tiny passages or channels that allow the transfer
of material and communication between
different cells.
Primary site for the
communication of two cells.
It allows the transfer of
molecules like proteins,
RNA, and viral genomes.
PLASTIDS
Double membrane-bound organelles. There are
3 types of plastids:
1.Leucoplast –Colourless plastids.
2.Chromoplast–Blue, Red, and Yellow colour
plastids.
3.Chloroplast – Green coloured plastids.
Helps in the process of
photosynthesis and
pollination, Imparts colour
for leaves, flowers and fruits
and stores starch, proteins
and fats.
CHLOROPLASTS
Present only in plant cells and contains a green-
coloured pigment known as chlorophyll.
Sites of photosynthesis.
CHROMOPLASTS
Present in certain photosynthetic eukaryotes. production and storage of
carotenoid pigments -
absorbing light energy &
protecting chlorophyll
GERONTOPLASTS
develops from the chloroplast
during senescence in foliage plants
salvaging nutrients and other
important material as a cell
dies
LEUCOPLAST
unpigmented organelles storage of starch
(amyloplasts), lipids
(elaioplasts) and proteins
(proteinoplasts)
RIBOSOMES
Non-membrane organelles, found floating freely
in the cell’s cytoplasm or embedded within the
Involved in the Synthesis of
Proteins.

4. endoplasmic reticulum.
STORAGE
GRANULES
Membrane-bound organelles, also called
zymogen granules storing cell’s energy reserve
and other metabolites & surrounded by a lipid
bilayer and are composed mostly of phosphorus
and oxygen.
Many prokaryotes and
eukaryotes store nutrients
Sulfur granules are
characteristic of prokaryotes
that utilize hydrogen sulfide
as a source of energy.
VACUOLES
A membrane-bound, fluid-filled organelle found
within the cytoplasm.
Provide shape and rigidity to
the plant cell and helps in
digestion, excretion, and
storage of substances.
VESICLES
Present inside the cell which are either formed
naturally during processes like exocytosis,
endocytosis or transport of materials throughout
the cell, or they might form artificially, which
are called liposomes. It contain liquid or cytosol
which is enclosed by a lipid bilayer
facilitate the storage and
transport of materials in and
outside the cell, exchange of
molecules between two cells,
allow temporary storage of
food and control the
buoyancy of the cell.
Actin - a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells. It is
both flexible and strong.
Cytosol - the proteins that enter the Golgi by mistake are sent back into the cytosol (imagine the barcode
scanning wrong and the item being returned).
Plasma membrane
The plasma membrane surrounds the cell to create a barrier between the cytosol and the extracellular matrix.
Plasma membranes also enclose lumens of some cellular organelles. The structure of the membrane
resembles a fluid mosaic made up of phospholipids, cholesterol, and membrane proteins. Phospholipid
molecules, the main structural components of the membrane, form an amphipathic bilayer.
An amphipathic structure is both hydrophilic and hydrophobic; part of the structure has a high affinity for
water and the other part is repelled by water. The inner surface of each layer is made up of lipid chains and
thus is hydrophobic. The outer surface of each layer is made up of the polar heads of the phospholipids and
is hydrophilic.
Proteins associated with the plasma membrane are either peripheral membrane proteins or integral membrane
proteins. Peripheral membrane proteins interact closely with the membrane through ionic
interactions. Integral membrane proteins are embedded within or pass through the lipid bilayer. There are six
broad categories of integral membrane proteins: pumps, channels, receptors, linkers, enzymes, and structural
proteins.
 Pumps - transport ions, sugars, and amino acids across membranes
 Channels - allow small ions and molecules to pass freely in and out of the cell
 Receptors - recognise and bind with ligands
 Linkers - anchor the cytoskeleton to the extracellular matrix
 Enzymes - have many roles, for example ATPases participate in ion pumping
 Structural proteins - form junctions with neighboring cells