Cell Organelle
A small organ-like structure present inside the cell is called a cell organelle. It has a
particular structural makeup and performs a specific function. Depending upon the
presence or absence of membrane, cell organelles can be classified into three
categories, namely:

Without membrane: Some cell organelles like ribosome are not bounded by
any membrane. They are present in prokaryotic as well as eukaryotic
organisms.

Single membrane-bound: Some organelles are bounded by a single
membrane. For example, vacuole, lysosome, Golgi Apparatus, Endoplasmic
Reticulum etc. They are present only in a eukaryotic cell.

Double membrane-bound: Cell organelles like mitochondria and chloroplast
are double membrane-bound organelles. They are present only in a eukaryotic
cell.
Structure and Functions of Cells
Structure and functions of different cell inclusions are as follows:
Cell Organelle
Cell
Membrane/
Plasma
Membrane
Occurrence/ Characteristic & Structure
Function

Present in both plant cell and animal cell.


Selectively Permeable: Allows the materials in
and out of the cell according to the requirement
of the cell.
Encloses the
contents of the
cell.

Provides shape:
animal cell.

Allows transport:
by Diffusion and
Osmosis.

Made up of bilipid layer and protein (Fluid
Mosaic Model)
Cell Wall
Cytoplasm
Nucleus
 Present only in a plant cell.
 Hard and rigid.
 Fully permeable.
 Made up of Cellulose in plant and peptidoglycan in
bacteria.
 Protection
 Gives shape and
turgidity.

Contains 80-90% water and many organic and
inorganic compounds.


Colloidal, Viscous, Jelly like fluid inside the cell.
Contains
enzymes
responsible for
all the metabolic
activity taking
place inside the
cell.

Covered by a double membranous nuclear
membrane in a Eukaryotic Cell.


Controls the
activity of the
cell.
Contains DNA, RNA, Protein, nucleolus, and
Chromatin network.

Starts cell
division.

It has the
chromosomes or
DNA which
controls the
hereditary
characters
(Director/
Brain of the
Cell)
*Double membranous structure.
*Autonomous body as contains its own DNA.
*Self-duplicates
*The main seat of respiration.
*Stores energy in the form of ATP molecules.
Mitochondria
(The Power
House of The
Cell / Storage
Batteries)
 Discovered by Camillo Golgi in 1898.
 Originates from RER.
 Contains Sac like Cisternae and Vesicles.
 Has two faces – cis face or receiving face and
trans face or supplying face.

Modification,
Packaging, and
transport of
materials

Synthesis of
lysosomes,
plasma
membrane

A network of membranes.

RER bears ribosomes and appears rough

SER does not have ribosomes
 Forms the
skeletal framework of
the cell.
 Transport of
materials from one
cell to other.
 Provides a
surface for the
synthesis of material
– Proteins in RER
and Lipids in SER.
 Formation of
lysosomes, Golgi
bodies and vacuoles
 Membrane
Biogenesis
 Detoxification of
harmful substances in
the liver.

Arise from ER and GB

Surrounded by tonoplast and filled with cell sap
Golgi Bodies
(Shipping
Department of
Cell)
Endoplasmic
Reticulum
(Framework of
Cell)
Vacuole
*Store cell sap which
may be liquid or solid
food, toxic byproduct.
*Provide rigidity and
turgidity to plant cell
Lysosomes
(Suicidal bags
of Cell,
natural

Membrane-bound organelles

Present in all animal cells and few plant cells

Intracellular
digestion of food
in unicellular
organisms.
 Tiny circular single membrane-bound structures
filled with digestive enzymes
scavenger,
cellular
housekeeper)
 Without a membrane
 Consist of two subunits – 60S and 40S
in eukaryote both made up of RNA

Synthesis of
Proteins
Ribosomes
(Protein
Factories)

*Double membrane-bound
Types:
1. 1. Leucoplast –Colourless plastid;
2. 2. Chromoplast –Coloured Plastid – blue, red, yello
3. 3. Chloroplast – Green plastid
 *Autonomous self-duplicating body
Plastids

Chloroplast –
Perform
Photosynthesis –
Helps in the release
of oxygen

Chromoplast
– impart colour to
flowers which help in
pollination

Leucoplast –
Storage

Amyloplast –
Store starch

Aleuroplast –
Store Protein

Elaioplast –
Store fat
The cell cycle and mitosis
Key terms
Term
Meaning
Cell cycle
The series of growth and development steps a cell undergoes between its
formation and reproduction
Interphase Phase of the cell cycle where the cell grows and makes a copy of its DNA
Mitosis
Phase of the cell cycle where the cell separates its DNA into two sets and divides,
forming two new cells
Cancer
A disease of uncontrolled cell growth
The cell cycle
In eukaryotic cells, the cell cycle is divided into two major phases: interphase and mitosis (or the
mitotic (M) phase).
Interphase is the longest part of the cell cycle. This is when the cell grows and copies its DNA
before moving into mitosis. During mitosis, chromosomes will align, separate, and move into new
daughter cells.
The prefix inter- means between, so interphase takes place between one mitotic (M) phase and
the next.
Interphase is composed of G1 phase (cell growth), followed by S phase (DNA synthesis), and
followed by G2 phase (cell growth). At the end of interphase comes the mitotic phase, which is
made up of mitosis and cytokinesis and leads to the formation of two daughter cells. Mitosis
precedes cytokinesis, though the two processes typically overlap somewhat.
Interphase
Interphase consists of three steps:

G_11start subscript, 1, end subscript phase: first gap phase; the cell grows larger and
organelles are copied

S phase: synthesis phase; the cell synthesizes a complete copy of the DNA in its nucleus

G_22start subscript, 2, end subscript phase: second gap phase; the cell grows more,
makes proteins and organelles, and begins to reorganize its contents in preparation for
mitosis
Cells that are meant to divide will complete G_22start subscript, 2, end subscript and enter
mitosis. Other types of cells that divide slowly or not at all may exit the G_11start subscript, 1, end
subscript phase and enter a non-dividing state called G_00start subscript, 0, end subscript. Some
cells remain here indefinitely, while others may re-enter division under the right conditions.
Mitosis (the M phase)
The process of mitosis, or cell division, is also known as the M phase. This is where the cell divides
its previously-copied DNA and cytoplasm to make two new, identical daughter cells.
Mitosis consists of four basic phases: prophase, metaphase, anaphase, and telophase.
Stages of mitosis
Early prophase. The mitotic spindle starts to form, the chromosomes start to condense, and the
nucleolus disappears.
Late prophase (prometaphase). The nuclear envelope breaks down and the chromosomes are fully
condensed.
Metaphase. Chromosomes line up at the metaphase plate, under tension from the mitotic spindle.
The two sister chromatids of each chromosome are captured by microtubules from opposite
spindle poles.
Anaphase. The sister chromatids separate from one another and are pulled towards opposite
poles of the cell. The microtubules that are not attached to chromosomes push the two poles of
the spindle apart, while the kinetochore microtubules pull the chromosomes towards the poles.
Telophase. The spindle disappears, a nuclear membrane re-forms around each set of
chromosomes, and a nucleolus reappears in each new nucleus. The chromosomes also start to
decondense.
Cytokinesis in animal and plant cells.
Cytokinesis in an animal cell: an acting ring around the middle of the cell pinches inward, creating
an indentation called the cleavage furrow.
Cytokinesis in a plant cell: the cell plate forms down the middle of the cell, creating a new wall that
partitions it in two.