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Class IX
Biology
Chapter: The Fundamental Unit of Life
Notes

Cell is Fundamental Structural and functional unit of life
*Cell is called structural unit of life because all living organisms are made up of one
or more than one cell*
*Cell is called functional unit of life because cell performs all life based functions
like respiration, reproduction, digestion, absorption, excretion etc in our body*

When number of cells come together they
form tissues
...
When tissues come together they form organs (
eg
...
Organs form organ systen ( eg
...
And then ultimately new organism is formed
...

(Cork is a substance which comes from bark of trees)
...

Examples: Bacteria, Paramecium and Amoeba

Multicellular Organisms: The organisms that are made from more than one cell are
known as multicellular organisms
...

>> Some cells have fixed shape(eg
...
Amoeba)
>> The cell is able to live, reproduce and perform all functions in
our body due to various cell organelle present inside the cell
>> Cell organelles are generally parts of cells
...
Similarly cell have also some specialised
parts to absorb, respirate, reproduce etc
...
Plasma Membrane Or Cell
Membrane:
>> It is the thin outermost covering present in
both plants and animal cells
>> It is known as selectively permeable membrane
because it allows entry and exit of some materials
in and out of cells
>> It is composed up of lipids and proteins
>> It is living cell organelle
...
Solid, Liquid, Gas)

from region of high concentration to low concentration until they
spread evenly is called Diffusion
...
The amount of oxygen is
greater outside cell and is lesser inside the cell
...
e high quantity to low concentration i
...
So oxygen will get inside cell
...
The concentration of carbon dioxide is
more inside cell than outside
...


There is one more process for entry and exit of
substance which is different from Diffusion and
that is OSMOSIS
OSMOSIS: The

movement of water molecules from region of

high water concentration to low water concentration through
selectively permeable membrane is known as osmosis
...


Types of OsmosisEndosmosis: The process in which water enters the
cell is known as endosmosis
...

Exosmosis: The process in which water leaves the
cell is known as Exosmosis
...


Types of solutions-

Hypertonic Solution: When we dissolve more solute
(eg
...

Or
When the solution has more concentration of solute
than solvent in beaker it forms hypertonic solution
...
So to make
equal concentration the water will move from a
region of high water concentration to low water
concentration through selectively permeable
membrane
...


Hypotonic solution: When we dissolve less solute
(sugar, salt) into solvent( water) it forms Hypotonic
solution
...


When we add few raisins (kishmish) (particularly
cell) into Hypotonic solution the medium
surrounding outside the cell has less
concentration of sugar and more concentration of
water than in cell (see definition)
...
As a result, water will be free to pass
in all directions, but more water will enter the cell
the cell will swell and this is called Endosmosis
...

Or
When the solution has equal concentration of solute
and solvent in beaker it forms hypertonic solution
...
So their is equal concentration of both
the items
...


2
...

>> It is composed up of cellulose
>> Cellulose is substance which provides strength
to plants
...

>> It is non living or dead
...
This is known as
Plasmolysis
...
This is because when cell
is kept in hypotonic solution cell contents
pressure against cell wall
...


3
...

>> It plays crucial role in cellular reproduction
and plays crucial part in determining the way the
cell will develop and what form will it exhibit at
maturity
>> It contains the following parts:
Nuclear Membrane : >> It is double layered
membrane which seprates nucleus from
cytoplasma
>> It has several nuclear pores which allow
exchange of materials between nucleus and
cytoplasm
...

Nucleolus: It is spherical body inside nucleus not
bounded by a membrane
...

>>During cell division, chromatin becomes highly
condensed, thick rod - like structures called
chromosomes
...
DNA contains the
information necessary for constructing and
organising cells
...


On the basis of nucleus presence their are two
types of organisms:
Prokaryotic Cells: The cells that lack nuclear
membrane
Or
The cells that have poorly defined nucleur region
and contain only nucleic acid (called nucleoid) are
called prokaryotic organisms or prokaryotes
Eg-Bacteria
Eukaryotic Cells: The cells that have a nuclear
membrane
Or

The cells that have well defined nucleur region are
called eukaryotic organisms or eukaryotes
...
Cytoplasma:
>> The fluid like substance present inside cell
Membrane is known as cytoplasma
>>It also contains many specialised cell
organelles
...

>> In prokaryotes besides the absence of defined
nuclear region, the membrane bound bound cell
organelles are absent
...

>> Viruses don't have any membrane and hence
do not show characteristics of life until they enter
enter a lining body and use its cell machinery to
multiply
...


5
...

>> Large and complex cells including cells from
Multicellular organisms, need a lot of chemical
activities to support their complicated function
and structure
...

Examples of Cell organelles are:

1
...

>>It looks like long tubules or round or oblong
bags(vesicles)
...

>> The ER also functions as a cytoplasmic
framework providing a surface for some
biochemical activities of the cell
...

Two types:
1
...

>> Has ribosomes attached to its surface
...

2
...

>> Does not have ribosomes attached to its surface
...


>> It plays crucial role in detoxifying many poisons
and drugs from our liver cells
...
So Endoplasmic reticulum helps
in building the cell membrane
...


2
...

>> It is system of membrane bound
vesicles(flattened sacs) arranged approximately
parallel to each other in stacks called cisternae
>> These membranes have connections with the
membranes of ER(Endoplasmic reticulum) and

therefore constitute another portion of complex
cellular membrane system
...

>> It's functions include the storage, modification
and packaging of products in vesicles
...

>> It also helps in formation of lysosomes
...
Lysosomes~
>> Lysosomes are membrane bound sacs filled
with digestive enzymes that are made by RER

>> They are kind of waste disposal from cell
...

>> Foreign materials entering the cell, such as
bacteria or food, as well as old organelles end up
in Lysosomes, which break complex cell into
simple substances
...
So they are
known as suicide bags of cells
...
Mitochondria~
>>Mitochondria is known as powerhouse of Cell
...

>>These folds increase the surface area for
ATP(adenosine triphosphate) -generating
chemical reactions
...


>> ATP is known as as the energy currency of the
cell
>> The body uses energy stored ij ATP for making
new chemical compounds and for mechanical
work
...
So, they
are able to make some of their proteins
...
Plastids~
>> These are present only in plant cells
...

>> Chromoplasts containing pigment chlorophyll
are known as chloroplasts
...


>> In leucoplast many materials such as starch,
oils and granules are stored
...
These are similar to
mitochondria in external structure
...


6
...

>>Animals have small vacuoles as compared to
plants
...

>> Vacuoles provide rigidity and turgidity to plant
cell
...

>> In Amoeba the food vacuoles contains the food
items that amoeba had consumed
...


Cell division~
>>The prpcces by which new cells are formed in
our body is called cell division
...

Two types of Cell division–
1
...

>> In this process each cell called mother cell
divides to form two identical daughter cells
...

>> It helps in growth and repair of tissues
...


2
...

>> They divide by a different process called
meiosis which involves two consecutive divisions
...

>> The new cells have half the number of
chromosomes that that of the mother cells
...


Chapter
Completed



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