Chapter – 6
The Fundamental unit of life – Cell
Q) What is cell?
Cell is the smallest structural and
functional unit of life.
Q) Who discovered cell?
Robert Hooke in the year 1665. He
observed a thin slice of cork under his microscope and observed small hexagon
boxes like that in a honey comb and he named this boxes as cells. He discovered
dead and fixed cells.
Q) Who discovered the free living cells for the 1st time?
Anton Von Leeuwenhoek, discovered the
free living cell in the pond water for the 1st time in the year
1674.
Q) Who discovered the nucleus in the cell ?
Robert Brown in the year 1831.
Q) Who coined the term “protoplasm”?
Purkinje in the year 1839.
Q) What is “cell theory”?
According to the cell theory, all the
plants and animals are composed of cell , and the cell is the basic unit of
life. It was proposed by two biologist – 1) Matthias Jacob Schleiden
(1838) 2) Theodore Schwann (1839)
It was further expanded by Rudolf Virchow
(1855) by suggesting that all cells arrives from the “pre-existing cells”.
Q) What made the observations of the ultra structure of the cell
possible?
The discovery of the electron microscope
in 1940 made it possible to observe and understand the complex structure of the
cells and its various organelles (on the basis of the no. of cells how
organisms are classified?)
Two parts – 1) Unicellular organisms –
Amoeba, Paramecium.
2) Multicellular organism
– Cells group together in a single body and assume different
functions in it to
form various body.
Q) Why the different cells present in the body of an organism looks
different?
The different parts of the human body has
different functions, Since They require the cells of different type in which
each type of cell organelles perform specific functions, Since the different
organ system are made up of different types of cells.
Q) Differentiate between unicellular and multicellular organism?
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S.No.
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Unicellular Organism
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S.No.
|
Multicellular Organism
|
|
1.
2.
3.
4.
5.
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Made up of single cell .
Simple organization.
They are primitive, came first on earth.
Singel cell perform all the activities, so there is no division of
labour.
Cell division always leads to reproduction.
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1.
2.
3.
4.
5.
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Made up of many cells.
Complex organization.
They are advanced, came later on earth.
Different Functions are performed by different cells, tissues,
organs, Since there is proper division of labour is seen.
May or may not be related to reproduction.
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Q) Differentiate between Prokaryotic and Eukaryotic cell.
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S.No.
|
Prokaryotic Cell (Organism)
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S.No.
|
Eukaryotic Cell (Organism)
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|
1.
2.
3.
4.
5.
6.
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Pro – primitive/first , karyon – nucleus. (false)
True nucleus is absent rather nucleus like structure called nucleoid
is present.
They originated first on earth.
They don’t have membrane bound cell organelles.
Eg.- Blue green Algae
The Cell division is very simple, mitosis and miosis, are absent.
Eg.- Eubacteria, Archae- bacteria.
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1.
2.
3.
4.
5.
6.
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Eu- New / true, karyyon – nuleus
True nucleus is present.
They originated later on earth.
They have membrane bound cell organelles.
Eg.- Mitochondria.
Mitosis and Meiosis are present.
Eg.- Protists and animals.
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Q) What do you mean by
organelle?
A specific living structure that performs
a specific jobs for cells and helps it to survive is called an organelle.
Q) What are chromosomes?
They are short, rod like structure formed inside the nucles at the time of cell
division from the chromatin threads.
Q) What are genes?
Genes are small functional segment of DNA
that codes for character.
Q) How does a cell performs various
activities for its survival?
There is an efficient division of labor
found inside the cells. The cells have tiny components inside it called
organelles, (miny organs) These organelles have a specific structure and each
one of them is specialized in performing
specific vitae activity such as making of new.
Q) Plasma Membrane!
It is a very thin, eleastic, dynamic,
semi-fluid membrane made up of lipo-protien that separete the cell from
external environment and gives identity to the cell. It is present in all types
of cell.
Q) Why plasma-membrane is called
selectively permeable?
The plasma membrane allows & permits
the entry of some material in and out of the cell. It also prevents the
movement of some other material out of the cell, Since, it is called a
selectively permeable membrane.
Q) What is Active & Passive
transport?
The plasma membrane allows 2 types of
transport, they are as follows:-
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S.No.
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Active
|
S.No.
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Passive
|
|
1.
2.
3.
|
It is a specialized process that needs energy
Substance move from lower to higher concentration
The substance moves against the concentration gradient
|
1.
2.
3.
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It is the normal process that does not allow the consumption of
energy
Substance move from heigher to lower concentration
The substance moves along the concentration gradient
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Q) Define “cell wall ”.
•
It is made up of
cellulose which is formed of very thin fibres of glucose along with “pectin”
•
Cellulose is a
complex substance and provide structural strength in the plant.
•
It is strong and
rigid
•
It is present in
plant cell only
•
It resist bursting
due to entry of excess water into the cell
•
In fungai, cell
wall is made up of “chitine”. And in bacteria, it is made up of “peptidoglycan
•
There are large
empty spaces present between the cellulose fibres, therefore it is freely
permeable.
Q) What is plasmolysis?
When a living plant cell looses water
through osmosis, there is a shrinkage or contraction of the content of the cell
away from the cell wall, this phenomenon is known as “plasmolysis”
However, only living cell and not the
dead cells are able to absorb slash, loose water by osmosis so are able to do
plasmolysis.
Q) Define “cell membrane”
•
Allows both active
and passive movement of molecules
•
Allows the
diffusion of oxygen and carbon dioxide
•
A living, semi
fluid and dynamic layer
•
It can control the
movement of materials IN and OUT of the cell.
Q) What is diffusion ?
Diffusion is a spontaneous movement of
substance from a region of high concentration to a region of lower
concentration.
It is a property of particles of solid,
liquid and gaseous particles due to their kinetic energy. diffusion plays an
important role in gaseous exchange. i.e. movement of carbon dioxide and oxygen
across the cell membrane between the cell as well as by its external
environment
Q) How water moves in and out of the cell
?
The movement of water molecules in plasma
membrane is a special type of diffusion called osmosis.
Osmosis is a passage of water from a
region of high water concentration through a semi-permeable membrane to a
region of lower concentration however osmosis is affected by the amount of
substance dissolved ( osmosis is potential in water).
OSMOSIS IS OF TWO TYPES :--
•
EX-OSMOSIS – loss
of water by a cell due to the shrinkage ( or which it shrinks)
•
END-OSMOSIS— gain
of water by a cell due to which it swells
Unicellular fresh water organisms and
most of the plant cell tend to gain water through osmosis. Absorption of water
by plant root is also an example of osmosis.
THREE TYPES OF SOLUTION WITH RESPECT TO
CONCENTRATION :--
•
Hypo-tonic solution
— if the medium surrounding the cell has a higher water concentration then the
cell, meaning that the outside solution is very dilute then such a solution is
known as hypo-tonic solution.
A cell will gain water by
osmosis, when placed in such a solution
Water molecules are free to pass across the cell membrane in both the
directions but more water would come into the cell than will leave. The net
result would be that due to more water
enters the cell, the cell is likely to swell up.
•
Hyper- tonic
solution — if the surrounding medium has a lower concentration. Meaning that it
has a very concentrated solution (having more solute) such a solution is known
as hyper-tonic solution.
A cell will lose water by osmosis, when
placed in such a solution.
Water crosses the cell membrane in both
direction but this time less water will leave the cell than enters, therefore
the cell will shrink
•
Iso-tonic — if the
surrounding has exactly the same water concentration as the cell is having,
then such a solution is known as a Iso-tonic solution
There will be no net gain or loss of
water across the cell membrane, when the cell is placed in such a solution
Water crosses the cell membrane in both
the direction but the amount of water going in is same as the amount coming
out. So there is no movement of water, therefore the cell size will remain the
same.
CYTOPLASM.
•
It is a jelly like
structure enclosed by the cell membrane, it is also known as the cell matrix
•
It provides a
medium for bio-chemical reaction to take place. It is made up of water and many
organic and inorganic molecules dissolved and suspended in it.
•
It provides
platform for all the organelles ( living and non-living). Eg chloroplast,
mitochondria, waste particles etc
NUCLEUS
•
It controls the
normal metabolic activities of the cell, this is why it is also known as the
brain of the cell.
•
It is bounded by
two nuclear membrane, both forming a nuclear envelope with lots of small pores
for exchange of materials with the cytoplasm.
•
It contains the
genetic material, i.e. “DNA” in the form of thread like structure called
chrmatins.
What is membrane bio-genesis?
Some of the proteins and lipid help in bulilding the cell membrane,
which is synthesid by ER, this process is known as bio-genesis.
Cell Organelles
•
The tiny structure
present inside the cell is called cell organelles
•
they all suspended
in the cytoplasm
•
Usually they are
membrane bound.
•
Exception-
Ribosomes & Centrioles.
•
they have specific
organizqaton and performs one or more vital functions.
•
Due to this there
is division of labour inside the Eukaryotic cell.
ENDOPLASMIC
RETICULUM
•
It is a network of
scattered inter-connected membrane bound tubes/chanels & vesicles that
mainly helps in the movement of various molecules. It consists of three main
components- 1) CISTERNE (hollow sac like structure) 2) TUBULES (long & hollow) 3) VESICLES (pouch like)
•
It increases the
inner surface area for efficient camical activity.
•
It helps in trafficing
of various molecules.
|
S.No.
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Rough ER
|
S.No.
|
Smooth ER
|
|
1.
2.
3.
|
More scattered.
It appears rough because of the presence of Ribosomes on its
surface.
Mainly associated with protein synthesis.
|
1.
2.
3.
|
Less scattered.
It appears smooth because Ribosomes are absent.
Mainly associated with lipid synthesis.
|
Function or ER:-
1.
It serves as
channels for the transport of materials between various region of th cytoplasm
or between the cytoplasm & the nucleus.
2.
It functions as a
cytoplasm framework providing a surface for some of the bio- chemical
activities of the cell
3.
In th live cells of
the vegetables, SER plays a crucial role in dedtoxifying many poisons &
drugs.
4.
It provides
internal support to the cell and helps to maintain the shape opf the cell.
GOLGI BODIES
•
It is discovered by
famous italian scientist Camillo Golgi.
•
It is made up of
sac like cisterns lying almost parallel one above the another, with two faces
forming an maturation which are convex & concave respectively.
•
Golgi is formed by
the transmition vesicles from ER containing mixed products.
•
From the maturation
face, sorted products are packed into vesicles , and sent to different targets.
•
The poorly
developed golgi in plants cell is better known as "Dictyosomes".
Functions:-
1.
It packs and
depatches materials from ER to various targets.
2.
It is associated
with storage, modification & packaging of products.
3.
Their the complex
sugar are made from simple sugar.
4.
Formation of
lysosomes takes place in Golgi bodies.
LYSOSOMES
•
These are a kind of
waste disposal system for cells that helps in the process of digestion, and
removal of debtis.
•
these are oval or
bound pouch like vesicles containing around 40 hydrolytic, digestive enzymes.
Q) How lysosomes helps in process of
cleaning & digestion?
Lysosomes helps to clean the cell by
digesting any foreign material as wll as wornout cell organelles. Foreign
material entering the cell, such as bacteria or food as well as old organelles
end up in the lysosomes which break them up into small pieces with the help of
digestive enzymes.
Q) Why lysosomes are called
"Suicidal Bags"?
Tjhe powerful digestive enzymes present
inside the lysosomes are capable of breaking down all the organic materials due
to te disturbance in the cellular matabolism eg.- When the cell gets damaged,
lysososmes may burst and the enzymes digest there own cell. "Therefore
lysosomes are also known as Suicidal bags".
MITOCHONDRIA
These are elongated, large, rod shaped
double membraneous organelles which is a center of cellular respiration.
•
The outer membrane
is smooth & porous while the inner membrane has got a no. of indolding
called "cristae" which increase the internal surface area for
efficient metabolic reaction.
•
The inner membrane
walls match-stick like particles called "oxysosomes" for "ATP
synthesis"
•
The jelly like
material filled inside is called "Matrix" that contain enzyme for
respiration.
•
Mitochondria ahs
its own "DNA and Ribosomes" and are able to produce some of the
required proteins & enzymes. It is "Semi- Autonomou Organelles".
Functions:-
1.
It is a place of
aelobic respiration where food is oxydised to release energy.
2.
It is a place of
ATP synthesis.
3.
Many entermidiate
compounds are synthesised inside the mitochondria which are used for different
cemical activities.
PLASTIDS
•
Its is double
membrane bound coloured organell found only in plant cell (and some microbe)
•
It is second
largenst organell in the plant cell
•
Plastids are of 3
types
1.
Chloroplast- Site
of photosynthesis. It is known as the "kitchen of the cell".
2.
Chromoplast-
Providesa colour to the different plants part. It helps in pollination.
3.
Leucoplast-
Envolves in foor storage. It stores starch, oils, protiens granulles.
•
Plastids are
semi-autonomous because they have their own DNA and Ribosomes so they can also
synthesize some of their protiens.
RIBOSOMES
•
It is the smalles
cell organells.
•
It is made up of 2
units and is chemically decomposed of RNA & protein.
•
It is smembrane less.
•
It is called the
"protien factory of the cell", because it synthesis various types of
protiens for varius types of protein (cellular activities)
VACUOLES
•
These are membrabe
- bound pouch like structure filled with some fluid. In planty cell there is a
large vacuole in the middle of each cell containing food materials.
•
In an animal cell
there are many small vacuoles scattered in the cytoplasm.
•
The vacuole are
full of cell cap and provide tergidity & rigedity to the cell.
•
Many important substance
are stored in the vacuole which include amino acids, sugar, various organic
acid and protein.
CENTROSOMES
•
It is cell organell
found in animal cell and cnsdist of two hollow rod like structure called
centrioles. Surrounded by a clear area.
•
Centrioles are made
up of protein and are located bear the nucleues.
•
It helps in the
process of cell division .
•
It sometime give
rise to flagella.
Q) Mention the role of vacuole in uni-cellular organism?d
In uni-cellulare organism, like amoeba the food vacuole contains food
items that amoeba has consume. In such organism, specialised vacuole also play
an imortant role in expelling exess water and some waste from the cell.
Q) How can we see the different parts of a cell when the cell is
almost transparent?
We can make different parts of cell visible by using specific colours
called stains. These are special colouring agent which are differently absorbed
by different cell organism (Organell) and produce proper contact due to which
the parts become prominently visible,some name of common stains are:-
•
Rosin - Cytoplasm
& The cell wall
•
Safeanine -
Cytoplasm & The cell wall
•
Haemotonylin -
Nucleus
•
Methylene Blue –
Microbes
|
S.No.
|
Plant Cell
|
S.No.
|
Animal Cell
|
|
1.
2.
3.
4.
5.
|
They are usually regular in shape.
It has an outer covering that is cell wall made up of cellulose in
addition to the cell membrane.
Plastids are present.
Vacuole are less in no. and bigger in size.
Centrioles are absent
|
1.
2.
3.
4.
5.
|
They are usually irregular in shape.
Cell wall is absent
Plastids are absent.
Vacuole are more in no. and are smaller in size.
Centrioles are present near to the nucleus.
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