8 CELL- THE UNIT OF LIFE
CHAPER NO.8
CELL:THE UNIT OF LIFE
A80
INTRODUCTION:Dear
students today we are going to discuss about cell. In Biology cell is the basic
structural, functional and biological unit of all known organisms. The study of
cells is called cell biology. The word cell is derived from a Latin word
cellula which means small room. Cells are the smallest units of life, and hence
are often referred as the building blocks of life. The study of cells is called
cell biology, Mor WE. The cell is a small membrane bound compartment that
contains all the chemicals and molecules that help to support an organism's
life.
DISCOVERY OF CELL In 1665, scientist Robert Hooke examined a thin slice of cork under his microscope and found a structure like a honey comb having hollow compartments. He named them cells. He wrote a book named Micrographia.He is known as Father of Cytology.
Anton Von Leeuwenhoek first saw and described a living cell. Robert Brown later discovered the nucleus. The invention of the microscope and its improvement leading to electron microscope revealed all the structural details of cell.
In 1838 Matthias Schleiden, a German botanist examined a large number
of plants
and observed that all plants are composed of
different kinds of cells which form the
tissue of the plant.
THEODORE SCHWAN British Zoologist reported that cells have a thin outer layer which is today known as plasma membrane.
Matthias Schleiden and Theodore Schwan together formulated the
Cell Theory. This theory did not explain as to how new cells were formed. In
1855 Rudolf Virchow
explained that cells divide and new cells are formed
from pre- existing cells (omnis
cellula-e-cellula) and gave the cell theory a final
shape.
TYPES OF CELL
There are two types of cells: iS anc
Prokaryotic cells lack a membrane bound nucleus.
These cells are represented by
bacteria, blue green algae. mycoplasma and PFPLO {Pleuro Pneumonia like Organisms}. They are generally smaller and multiply more rapidly than the eukaryotic cells. They may vary greatly in shape and size.The four basic shapes of bacterial cell are: Bacillus (rod like), Caccus (spherical),Vibrio (Comma shaped) and (spiral).
Most
prokaryotic cells, particularly the bacteria cells have a chemically complex
cell envelope that consists of a tightly bound a three layered structure
glycocalyx. Each layer of envelope performs distinct functions. They act
together as a single protective
unit. Prokaryotes have fluid matrix filling the
cell, the cytoplasm. There is no well-
defined nucleus. The genetic material is basically
naked. 70 s ribosome and flagella
are also present in prokaryotes.
Eukaryotic cells possess an organized nucleus.
They include all the protists, plants,animals and fungi. In these cells there
is an extensive compartmentalization of cytoplasm, through the presence of
membrane bound organelles. In addition these cells have locomotors and
cytoskeleton structures. Their genetic material is organized into chromosomes.
All eukaryotic cells are not identical. Plant and
animal cells are different, as plantcells possess cell walls, plastids and a
large central vacuoles, which are absent in animal cells. On the other hand
animal cells have centrioles which are almost absent in plant cells.Eukaryotic
(plant and animal) cells possess the following organelles:Cell membrane, cell
wall(in plant cells), ribosomes , endoplasmic reticulum ,golgiapparatus ,
lysosomes , vacuoles , mitochondria , plastids ( in plant cells ) ,centrioles
(in animal cells), nucleus , cilia and flagella ( in anima! cells), centrioles
and centrosomes ( in animal cells) and microbodies.
A. MULTIPLE CHOICE QUESTIONS:
1. Who discovered
the cell?
a) G.N. Ramachandran
b) Robert Hooke
c) A.V. Leeuwenhock
d) None of these
2. Which
scientist formulated cell theory?
a) Matthias Schleiden
b) Theodore Schwann
c) Both A and B
d) Robert Brown
3. ‘Omnis
cellula-e-cellula’ means;
a) Cell is a basic unit of life
b) All organisms are composed of cells.
c) New cells are formed from preexisting cells.
d) None of these.
4. Prokaryotic
cells are represented by;
a) Bacteria
b) Blue green algae
c) Mycoplasma
d) All of the above
5. Which
organelle is absent in plant cells?
a) Centriole
b) Plastids
c) Cell wall
d) Golgi apparatus
B. FILLIN THE BLANKS
1. discovered the nucleus.
2. The genetic material in eukaryotic cells is
organized into...................
3. Well organized nucleus is a unique character
of......................cells.
C. TRUE AND FALSE
1. Prokaryotic cells lack a well organised nucleus.
2. Plastids are present in animal cells.
3. All eukaryotic cells are not identical.
A. MULTIPLE CHOICE QUESTIONS:
1. b (G.N. Ramachandran worked in the field of
protein structure and A.V.
Leeuwenhoek described a live cell.
2. c ( Robert brown discovered the nucleus)
3. c (cells divide and produce new cells)
4. d (All these represent prokaryotic cells)
5. a ( Rest three organelles are found in plant
cells)
B.FILL IN THE BLANKS
1. Robert Hooke
2. Chromosomes
3. Eukaryotic cells
C. TRUE AND FALSE
1. True
2. False(Plastids are found in plant cells)
3. True
PART-B SHORT ANSWER TYPE QUESTIONS
1. What are four basic shapes of bacterial cells?
2. Describe the structure of glycocalyx.
3. What are the main differences between prokaryotes
and eukaryots?
PART-C LONG ANSWER TYPE QUESTIONS
1. Write a note on prokaryotic cells.
2. Give an account of eukaryotic cells.
A81
INTRODUCTION:Eukaryotic
cells appeared on earth long = after Prokaryotic cells but they are much more
advanced.Eukaryotic organisms unlike prokaryotic can be
unicellular or multi-cellular.
Eukaryotic Cell Definition :-“Eukaryotic cells are
the cells that contain a membrane bound nucleus and organelles.”
What is a
Eukaryotic Cell?
Eukaryotic cells have a nucleus enclosed within the
nuclear membrane and form large and complex organisms. Protozoa, fungi,
plants,and animals all have eukaryotic cells. They are classified under the
kingdom Eukaryota.They can maintain different
environments in a single
cell that allows them to carry out various metabolic
reactions. This helps
them grow many times larger than the prokaryotic cells.Characteristics
of Eukaryotic Cell The features of eukaryotic cells are as follows:-The cell
has mitochondria.Flagella and cilia are the locomotory organs in a eukaryotic
cell.
A cell wall is the outermost layer of the eukaryotic
cells.The cells divide by a process called mitosis.The eukaryotic cells contain
a cytoskeletal structure.Eukaryotic cells have the nucleus enclosed within the
nuclear membrane.The nucleus contains a single, linear DNA, which carries all
the
genetic information.Eukaryotic Cell structure The
eukaryotic cell structure comprises the following:-
1. Plasma Membrane
The plasma membrane separates the cell from the outside
environment.It comprises specific embedded proteins,
which help in the exchange of substances in and out of the cell.
2. Cell Wall
It is composed of cellulose, hemicellulose, pectins, proteins, etc.
It provides shape to the cell and helps in
cell-to-cell interaction.It is a protective layer that protects the cell from
any injury or pathogen attacks.A cell wall is a rigid structure present outside
the plant cell. It is,' however, absent in animal cells.
3. Cytoskeleton
The cytoskeleton is present inside the cytoplasm, which consists of
microfilaments, microtubules, and fibres to provide perfect shape to the cell,
anchor the organelles, and stimulate the cell movement.
4. Endoplasmic Reticulum
It is a network of small, tubular structures that divides the cell surface into
two parts: luminal and extraluminal.Endoplasmic Reticulum is of two types:Rough
Endoplasmic Reticulum contains ribosomes.Smooth Endoplasmic Reticulum that
lacks ribosomes and is therefore smooth.
5. Ribosomes
These are the main site for protein synthesis and are composed of proteins and
ribonucleic acids.
6. Lysosomes
They are known as “suicidal bags” because they possess hydrolytic enzymes to
digest protein, lipids, carbohydrates, and nucleic acids.
Eukaryotic Cell Structure
7. Nucleus
Ribosome production also takes place inside the nucleus.The nucleoplasm
enclosed within the nucleus contains DNA and proteins.The nuclear envelop
consists of two layers- the outer membrane and the inner membrane. Both the
membranes are permeable to ions,molecules, and RNA material.
8. Golgi
Apparatus It is made up of flat disc-shaped structures called cisternae.
They are arranged parallel and concentrically near the nucleus.It is absent
in red blood cells of humans and sieve cells of plants.It is an important site
for the formation of glycoproteins and glycolipids.
9. Mitochondria
They help in the regulation of cell metabolism.These
are also known as “powerhouse of cells” because they produce
energy.it consists of an outer membrane and an inner
membrane. The inner membrane is divided into folds called cristae.
10. PlastidsThese
are double-membraned structures and are found only in plant
cells.Plastids are of three types:
Chloroplast that contains chlorophyll and is involved = in photosynthesis.Leucoplasts that are colourless and store oil, fats, carbohydrates, or proteins.: Chromoplast that contains a pigment called carotene that provides the plants yellow, red, or orange colours.
Eukaryotic Cell Diagram Eukaryotic cell diagram mentioned below depicts different cell organelles present in eukaryotic cells. The nucleus, endoplasmic reticulum, cytoplasm, mitochondria, ribosomes, lysosomes are clearly mentioned in the diagram.
Eukaryotic Cell Cycle The eukaryotic cells divide
during the cell cycle. The cell passes through different stages during the
cycle. There are various checkpoints
between each stage.
1. Quiescence
(GO)This is known as the resting phase, and the cell does not divide
during this stage. The cell cycle starts at this
stage. The cells of the liver, kidney, neurons, and stomach all reach this
stage and can remain there for longer periods. Many cells do not enter this
stage and divide indefinitely throughout their lives.
2. Interphase
In this stage, the cells grow and take in nutrients to prepare them
for the division. It consists of three checkpoints:
Gap 1 (G1) Here the cell enlarges. The proteins also
increase.Synthesis (S) DNA replication takes place in this phase.
Gap 2 (G2) Ther cells enlarge further to undergo
mitotic division.
3. Mitosis
Mitosis involves the following stages:-
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
On division, each daughter cell is an exact replica
of the original cell.Examples of Eukaryotic Cells Eukaryotic cells are
exclusively found in plants, animals, fungi,protozoa, and other complex
organisms. The examples of eukaryotic cells
are mentioned below:
1. Plant Cells
The cell wall is made up of cellulose, which provides support to
the plant. It has a large vacuole which maintains
the turgor pressure.The plant cell contains chloroplast, which aids in the
process of photosynthesis.
2. Fungal Cells
The cell wall is made of chitin. Some fungi have holes known as
septa which allow the organelles and cytoplasm to
pass through them.
3. Animal Cells
These do not have cell walls. Instead, they have a cell membrane. That is why
animals have varied shapes. They have the ability to perform phagocytosis and
pinocytosis.
4. Protozoa Protozoans are unicellular organisms.
Some protozoa have cilia
for locomotion. A thin layer called pellicle
provides supports to the
cell.
Let us know what we have Learnt!
PART: A VERY SHORT ANSWER TYPE
QUESTIONS:
MCQ’s Prokaryotic Cells
1) Which of the
following is not true of a Eukaryotic cell?
a. The cell wall is made up of peptidoglycans
b. 80S ribosome’s is present in the cytoplasm
c. Mitochondria contain circular DNA
d. Membrane bound organelles are present
2) Which one of
the following is absent in eukaryote?
a. Nucleolus
b. Plastid
c. Mesosomes
d. Ribosomes
3) Which of the
following are not Eukaryotic?
a. Plants
b. Fungi
c. Protests
d. Moneras
4) Which of these
are absent in plant cell?
a. Large central Vacuole' cc. Centriole
b. Cell wall d. Plastid
5) What is the
name of fluid part of the cytoplasm of Eukaryotic cells?
a. Protoplasm
b. Cytokine
c. Cytoplasmic Inclusion
d. Matrix
6) Which of the
following is not available in animal cells?
a. Plastid
b. Mitochondria
c. Lysosomes
d. Centrosomes
Fill Ups
1) Eukaryotic cell is with nucleus.
2) Eukaryotic cellhas envelops organisition.
3) The functions of eukaryotic cell organellesto
generate sig.
4) Eukaryotic cells have a well developed membrane.
5) slis the empty space in the cell.
True/False
1) Flagella is used for cell motility in eukaryotic
cells.
2) The eukaryotic cell is the earliest type of cell.
3) Cytoplamic matrix is also called hyaloplasm.
PRT: B SHORT ANSWER TYPE QUESTIONS:
1) Which of the following is not true for a
eukaryotic cell?
2) Write short note on eukaryotic cells?
3) Where is DNA located in eukaryotic cells?
4) Write shirt note on RNA Polymerases of eukaryotic
cells?
PART: C LONG ANSWER TYPE QUESTIONS:
1) Give the salient features of eukaryotic cells?
2) When & how might the eukaryotic cell have
arisen?
MCQ’s Fillups True/False
1) a 1) Organised 1) False
2) a 2) Two 2) False
3) d 3) Energy 3) True
4) c 4) Nuclear
5) d 5) Vacuole
6) a
A82
INTRODUCTION:Prokaryotic
cells were here first and for billions of years were
the only form of life on Earth. All prokaryotic
organisms are unicellular.
Prokaryotic Cell Definition :-
“Prokaryotic cells are the cells that do not have a
true nucleus and membrane-bound organelles.”D.N.A. is naked, without
Histone Proteins.
What is a
Prokaryotic Cell?
Prokaryotic cells are single-celled microorganisms
known to be the earliest on earth. Prokaryotes include Bacteria and Archaea.
The photosynthetic prokaryotes include cyanobacteria that perform
photosynthesis.A prokaryotic cell consists of a
single membrane and therefore, all the reactions occur within the cytoplasm.
They can be free- living or parasites.
Characteristics of Prokaryotic Cell
Prokaryotes are the simplest type of cell.
Oldest type of cell appeared about four billion
years ago.The largest group of organisms.Unicellular organisms that are found
in all environments.They lack a nuclear membrane.Mitochondria, Golgi bodies,
chloroplast, and lysosomes are absent.The genetic material is present on a
single chromosome.The cell wall is made up of carbohydrates and amino acids.The
plasma membrane acts as the mitochondrial membrane carrying respiratory
enzymes.They divide asexually by binary fission. The sexual mode of '
reproduction involves conjugation.The histone proteins, the important
constituents of eukaryotic
chromosomes, are lacking in them.
PROKARYOTIC CELL STRUCTURE:A
prokaryotic cell does not have a nuclear membrane. However,the genetic material
is present in a region in the cytoplasm known as the
nucleoid. They may be spherical, rod-shaped, or
spiral. A prokaryotic cell
structure is as follows:-
Capsule :-
it is an outer protective covering found in the bacterial cells, in addition to
the cell wall. It helps in moisture retention, protects the cell when engulfed,
and heips in the attachment of cells to nutrients and surfaces.
Cell Wall :-
It is the outermost layer of the cell which gives shape to the cell.
Cytoplasm :-
The cytoplasm is mainly composed of enzymes, salts, cell
organelles and is a gel-like component.Cell This
layer surrounds the cytoplasm and regulates the entry
Membrane :-
and exit of substances in the cells.
Pili :-
These are hair-like outgrowths that attach to the surface of other bacterial
cells.
Flagella :-
These are long structures in the form of a whip, that help
in the locomotion of a cell.
Ribosomes :- These are
involved in protein synthesis.
Plasmids :- Plasmids are
non-chromosomal DNA structures. These are not involved in reproduction.Nucleoid
it is the region in the cytoplasm where the genetic
Region :-
material is present.A prokaryotic cell lacks certain organelles like mitochondria,endoplasmic
reticulum, and Golgi bodies.Prokaryotic Cell Diagram
The prokaryotic cell diagram given below represents
a bacterial cell. It depicts the absence of a true nucleus and the presence of
a flagellum that differentiates it from a eukaryotic cell.
COMPONENTS OF PROKARYOTIC CELLS:
The prokaryotic cells have four main
components:-Piasma It is an outer protective covering of phospholipid
Membrane :-
molecules which separates the cell from the surrounding environment.
Cytoplasm :- it is a jelly-like
substance present inside the cell. All the cell organelles are suspended in it.
DNA :- It is the
genetic material of the cell. All the prokaryotes possess a circular DNA. It
directs what proteins the cell creates. It also regulates the actions of the
cell.
Ribosomes :-
Protein synthesis occurs here.
Some prokaryotic cells possess cilia and flagella
which helps in locomotion.
REPRODUCTION IN PROKARYOTES:
A prokaryote reproduces in two ways:-
Asexually by binary fission Sexually by conjugation
BINARY FISSION:
The DNA of an organism replicates and the new copies
attach to the cell membrane.
The cell wall starts increasing in size and starts
moving inwards.A cell wall is then formed between each DNA, dividing the cell
into two daughter cells.
RECOMBINATION:In
this process, genes from one bacterium are transferred to the
genome of other bacteria. It takes place in three
ways:CONJUGATION, TRANSFORMATION, AND TRANSDUCTION.Conjugation is the process
in which genes are transferred between
two bacteria through a protein tube structure called
a pilus.Transformation is the mode of sexual reproduction in which the DNA from
the surroundings is taken by the bacterial cell and incorporated in its
DNA.Transduction is the process in which the genetic material is transferred
into the bacterial cell with the help of viruses.Bacteriophages are the virus
that initiates the process.
Examples of Prokaryotic Cells:
The examples of the prokaryotic cells are mentioned
below:
Bacterial Cells
Archaeal Cells
Bacterial Cells These are unicellular organisms
found everywhere on earth from soil to the human body.They have different
shapes and structures.The cell wall is composed of peptidoglycan that provides
structure to the cell wall.Bacteria have some unique structures such as pili,
flagella and capsule.They also possess extra chromosomal DNA known as plasmids.
They have the ability to form tough, dormant
structures known as endospores that helps them to survive under un-favourable
conditions.The endospores become active when the conditions are favourable
again.
Archaeal Cells Archae bacteria are unicellular
organisms similar to bacteria in shape and size.They are found in extreme
environments such as hot springs and
other places such as soil, marshes, and even inside
humans.They have a cell wall and flagella. The cell wall of archaea does not
contain peptidoglycan.The membranes of the archaea have different lipids with a
completely different stereochemistry
Learnt!
MCQ’s Prokaryotic Cells
i. Which of the
following is the typical feature of a Prokaryote cell
a. Abrence of DHA
b. Abrence of Nucleus
c. Abrence of RNA.
d. Abrence of cellwall
ii. The cell wall
of enbacteria is made up of
a. cellulose
b. Peptidoglycan
c. Phospholipids
d. chitin
iii, Ribosomes in
prokaryote cells are
a. 80s
b. 70s
c. 60s + 40s
d. 50s+Nos
iv. Extremely
fine extracellular structures involved in cell to cell
contact is
a. Flagella
b. Cilia
c. Pili
d. Spinae
v. In some
bacteria there is slimy layer outside to cell wall considered
as virulence factor is called
a. Capsule
b. Plasmid
c. Outer layer
d. Fimbriae
vi. What is the
name of the region where double-strandel single circular DNA is found in
Prokaryotic cell.
a. Protonucleus
b. Nucleus
c. Nucleoid
d. Nucleoplasm
vii. The two
domains to which prokaryotics are classified into are
a. Bacteria & Protista
b. Bacteria & Archaea
c. Archaea & Eukarya
d. Eukarya & Monera
Fill Ups:
i. cell does not have a nuclear membrane.
ii, The nuclear region of prokaryotic cell is called
iii, Cells were discovered by Robert Hooke in .
iv. Prokaryotes are organisms
v. Prokaryotes proper us.nucle
True/False
i. True nucleus is seen in Prokaryotre cell.
ii, The example of a Prokaryotic cell is Blue-green
algae.
iii, Bacteria & Algae are Prokaryotic cells.
iv. Circular genetic material of Prokaryotes are
Plasmids.
v. Prokaryotes divide to reproduce by binary
fission.
Short Q/A
i. What are the characteristics of Prokaryotic cell?
ii. How Prokaryotic cell is differs from eukaryotic
cell?
iii, What is Mesosome in Prokaryotic cell? Mention
the function that it performs.
iv, What are cell inclusions in prokaryotic cell?
Long Q/A
i. What are the differences between prokaryotic cell
& Eukaryotic
cells?
ii. Differentiate Gram +ve & Gram -ve bacteria?
ANSWER- KEY: PART-A
Mca: Fill ups:
i. Absence of Nucleus i. Prokaryotic
ii. Peptidoglycan iit Nucleoid
iii, 70s iii, 1665
iv. Pili iv. Unicellular
v. Capsule v. Lack
vi. Nucleoid
vii, Bacteria & Archaea
True/False:
i. False
ii. True
iii. False
iv. True
v. True
A83
INTRODUCTION:Cell
is the basic unit of life; structural as well as functional. The various
structures present inside the cell are known as the Cell Organelles.Today in
our topic we will discuss about Cell membrane, cell wall and endomembrane.
CELL MEMBRANE / PLASMA MEMBRANE:The
cell membrane, also called the plasma membrane, is found in all cells and
separates the interior of the cell from the outside environment. The cell
membrane consists of a lipid bilayer that is semipermeable. The cell membrane
regulates the transport of materials entering and exiting the cell.
The plasma membrane, or the cell membrane, provides
protection for a cell. It also provides a fixed environment inside the cell,
and that membrane has several different functions. One is to transport
nutrients into the cell and also to
transport toxic substances out of the cell. Another
is that the membrane of the cell, which would be the plasma membrane, will have
proteins on it which interact with other cells. The cell membrane also provides
some structural support for a cell. There are different types of plasma
membranes in different types of cells.
PLASMA MEMBRANE or CELL MEMBRANE:
STRUCTURE
Biological membranes have three primary functions:
(1) They keep toxic substances out of the cell;
(2) They contain receptors and channels that allow
specific molecules,such as ions, nutrients, wastes, and metabolic products,
that mediate cellular and extracellular activities to pass between organelles
and between the cell and the outside environment; and
(3) They separate vital but incompatible metabolic
processes conducted within organelles.
STRUCTURE OF PLASMA MEMBRANE:Membranes
consist largely of a LIPID bilayer, which is a double layer of phospholipid,
cholesterol, and glycolipid molecules that contains chains of fatty acids and
determines whether a membrane is formed into long flat sheets or round
vesicles. Lipids give cell membranes a fluid character,with a consistency
approaching that of light oil. The fatty-acid chains
allow many small, fat-soluble molecules, such as
oxygen, to permeate the
membrane, but they repel large, water-soluble
molecules, such as sugar,
and electrically charged ions, such as
calcium.Embedded in the lipid bilayer are large PROTEINS, many of which
transport ions and water-soluble molecules across the membrane. Some proteins
in the plasma membrane form open pores, called membrane
channels, which allow the free diffusion of ions
into and out of the cell.Others, known as carrier proteins bind to specific
molecules on one side of amembrane and transport the molecules to the other
side. Sometimes one protein simultaneously transports two types of molecules in
opposite directions.Most plasma membranes are about 50 percent protein by
weight, while the membranes of some metabolically active organelles are 75
percent protein.
Attached to proteins on the outside of the plasma
membrane are long carbohydrate molecules.The R.B.C. membrane is composed of 52%
proteins, 40% lipids and 08%
cabohydrates.The cell membrane is primarily composed
of a mix of proteins and lipids. |
Phospholipids are a major component of cell
membranes. They form a lipid bilayer
in which their hydrophilic (attracted to water) head
areas spontaneously arrange to
face the aqueous cytosol and the extracellular
fluid, while their hydrophobic (repelled by water) tail areas face away from
the cytosol and xtracellular fluid.Cholesterol is another lipid component of
animal cell membranes. Cholesterol molecules are selectively dispersed between
membrane phospholipids. This helps to keep cell membranes from becoming stiff
by preventing phospholipids from being too closely packed together.
Glycolipids are located on cell membrane surfaces
and have a Carbohydrate sugar
chain attached to them. They help the cell to
recognize other cells of the body.
PROTEINS: The cell membrane contains two types of
associated proteins.Peripheral membrane proteins are exterior to and connected
to the membrane by interactions with other proteins.Integral membrane proteins
are inserted into the membrane and most pass through the membrane.
FLUID MOSAIC MODEL OF PLASMA MEMBRANE
In the above model the quasi-fluid nature of the
lipids, enables lateral movement of proteins within overall bilayer. Singer and
Nicolson proposed this model.
CELL WALL:Cell
wall is NON-LIVING rigid structure present outside the plasma
membrane of FUNGI and PLANTS.
It gives shape and
protection from mechanical damage and infection.It helps in cell to cell
interaction through plasmodesmata.It provide barrier to undesirable
macromolecules.The plant cell wall is made up of CELLULOSE,
HEMICELLULOSE,PECTIN
and PROTEINS.The Algal cell wall consists of
CELLULOSE, GALACTANS, MANNANS and
MINERALS.FUNGAL cell wall is made up of CHITIN.In
young plant cell the wall is living and can grow. Later secondary wall is
formed.The middle lamella is layer made of CALCIUM PECTATE, which holds the
neighbouring cells together.
ENDOMEMBRANE:The membranes of different organelles are different in terms of structure and function. The membranes of many organelles considered as ENDOMEMBRANE SYSTEM because their functions are coordinated.
The ENDOMEMBRANE SYSTEM includes Endoplasmic reticulum, Golgi
complex, Lysosomes and Vacuoles.The other organelles
are not coordinated with above, so they are not the part of endomembrane
system.
LET US KNOW WHAT WE HAVE LEARNT!
PART: A VERY SHORT ANSWER TYPE
QUESTIONS:
MCQs:
Q1. Who proposed
the fluid mosaic model of the plasma membrane?
a.) Benda
b.) Schleiden and Schwann
c.) Singer and Nicolson
d.) Robert Brown
Q2. Which of the
following statements is not true for plasma membrane?
a.) itis present in both plant and animal cell.
b.) Lipid is present as a bilayer in it.
c.) Proteins are presently integrated as well as
loosely associated with lipid bilayer.
d.) Carbohydrate is never found in it.
Q3. Which of the
following are covered by a single membrane?
(a) Mitochondria
(b) Vacuole
(c) Lysosome
(d) Plastid
Q4. Cell wall of
which one of these is not made up of cellulose?
(a) Bacteria
(b) Hydrilla
(c) Mango tree
(d) Cactus
Q5. The organelle
that helps in the membrane biogenesis is:
(a) lysosome
(b) Golgi bodies
(c) endoplasmic reticulum
(d) ribosome
FILL IN THE BLANKS:
1. The function of endomembrane system is
2. The fungal cell wall is made up of
TRUE/FALSE:
1. Plasma membrane is a selective permeable
membrane.
2. Middle lamella is made up of calcium pectate.
3. Mycoplasma has cell wall.
4. The cell wall of certain fungi is made of lignin.
ANSWER KEY: PART-A
MCQs:
1. C(Singer and Nicolson)
2. D (carbohydrate is never found in it)
3. C(lysosome)
4. A(bacteria)
5. C (endoplasmic reticulum )
FILL IN THE BLANKS:
1. Coordinated
2. Chitin
TRUE/FALSE:
1. True
2. True
3. False: Mycoplasma has NO cell wall, it is bound
by plasma
membrane only.
4. False: The cell wall of certain fungi is made of
CHITIN.
PART: B SHORT ANSWER TYPE QUESTIONS:
Q1. Give the biochemical composition of the plasma
membrane. How are
lipid molecules arranged in the membrane?
Q2. Write the functions of the Cell wall and Cell
membrane.
PART: C LONG ANSWER TYPE QUESTIONS:
Q1. Discuss structure of cell wall and cell wall
depositions.
Q2. Differentiate between primary wall and secondary
wall.
A84
INTRODUCTION:MITOCHONDRIA
were named by Carl Benda in 1898 from his study of cell
internal structure and the first recorded
information of mitochondria in plants in
cells was created by Friedrich Meves in 1904. In
1908, Friedrich Meves and
Claudius Regaud showed that they contain lipids and
proteins.“Mitochondria are membrane-bound organelles present in the cytoplasm
of all eukaryotic cells, that produces adinosine triphosphate (ATP), the main
energy molecule used by the cell.”
PLASTIDS:Plastids
are double-membrane organelles which are found in the cells of plants and
algae.
What are
Mitochondria?
Popularly known as the “Powerhouse of the cell,”
mitochondria (singular:
mitochondrion) are a double membrane-bound organelle
found in mos eukaryotic organisms. They are found inside the cytoplasm and
essentially functions as the cell"s “digestive system.” They play a major
role in breaking down nutrients and generating energy-rich molecules for the
cell. Many of th biochemical reactions involved in cellular respiration take
place within th mitochondria. The term mitochondrion is derived from the Greek
words “mitos’and “chondrion” which means “thread” and “granules-like”
respectively. It wa first described by a German pathologist named Richard
Altmann in the yea 1890.Characteristics of Mitochondria:
The features of Mitochondria are as
follows:-Mitochondria are organs of special importance. These organelles are
absolute requirements to sustain the physiological
activities of the cells.
Typically sausage shaped or cylindrical shaped.Each
mitochondrion is a double membrane - bound structure with the oute
membrane and the inner membrane dividing its lumen
distinctly into two compartments, l.e., the outer compartment (perimitochondrial space) and the inner
compartment matrix).They are present in almost all the cells of the body except
in Red Blood Cells.They are freely floating in the cytoplasm and stay in the
regions of high energy requirement.Mitochondria are self-replicable i.e. they
can multiply on their own withou the requirement of cell to divide. Its
characteristic feature helps replacemen of old, worn out and damaged
mitochondria with new and healthy
mitochondria.Mitochondria have their own genetic
material as single stranded DNA.
The mitochondria have many enzyme complex which in
series help in formation of energy i.e. adenosine tri-phosphate (ATP).
Mitochondria Diagram The diagram of mitochondria
below illustrates several structural features of mitochondria.
Structure of Mitochondria:The structure comprises
the following:-The mitochondrion is a double-membrane, rod-shaped structure
found i both plant and animal cell.
Its size ranges from 0.5 to 1.0 micrometre in
diameter.The structure comprises an outer membrane, an inner membrane, and a
gel like material called the matrix.
The outer membrane and the inner membrane are made
of proteins and phospholipid layers separated by the inter membrane space.The
outer membrane covers the surface of the mitochondrion and has a larg
number of special proteins known as porins. It is
freely permeable to ions,
nutrient molecules, energy molecules like the ADP
and ATP molecules.
1) Cristae
The inner membrane of mitochondria is rather complex in structure. It has many
folds that form a layered structure called cristae, and this helps in
increasing the surface area inside the organelle. The cristae and the proteins
of the inner membrane aids in the production of ATP molecules. The inne
membrane is strictly permeable only to oxygen and to
ATP molecules.number of chemical reactions take place within the inner membrane
o mitochondria.
2. Mitochondrial Matrix
The mitochondrial matrix is a viscous fluid that contains a mixture of enzymes
and proteins. It also comprises ribosomes, inorganic ions,
mitochondrial DNA, nucleotide cofactors, and organic
molecules. The enzymes present in the matrix play an important role in the
synthesis of ATP molecules.Functions of Mitochondria The most important
function of mitochondria is to produce energy through
the process of oxidative phosphorylation. It is also
involved in the following
process:-Regulates the metabolic activity of the
cell.Promotes the growth of new cells and cell multiplication.Helps in
detoxifying ammonia in the liver cells
Plays an important role in apoptosis or programmed
cell death Responsible for building certain parts of the blood and various
hormones like testosterone and oestrogen Helps in maintaining an adequate
concentration of calcium ions within the
compartments of the cell It is also involved in
various cellular activities like cellular differentiation,"cell
signalling, cell senescence, controlling the cell cycle and also in cell
growth.
PLASTIDS:
What are
Plastids?
Plastids are double-membrane organelles which are
found in the cells of plants and algae. Plastids are responsible for
manufacturing and storing of food. These often contain pigments that are used
in photosynthesis and different types of pigments that can change the colour of
the cell.
Types of Plastids:There
are different types of plastids with their specialized functions. Among them, a
few are mainly classified based on the presence or absence of the Biological
pigments and their stages of development.
Chloroplasts
Chromoplasts
Gerontoplasts
Leucoplasts
1. Chloroplasts:Chloroplasts
are biconvex shaped, semi-porous, double membrane, cel
organelle found within the mesophyll of the plant
cell. They are the sites fo
synthesizing food by the process of photosynthesis.
2. ChromoplastsChromoplasts
are the name given to an area for all the pigments to be kept and synthesized
in the plant. These can be usually found in flowering plants, ageing leaves and
fruits. Chloroplasts convert into chromoplasts. Chromoplasts hav
carotenoid pigments that allow different colours
that you see in leaves and fruits. The main reason for its different colour is
for attracting pollinators.
3. Gerontoplasts
These are basically chloroplasts that go with the ageing process. Geronoplast
refer to the chloroplasts of the leaves that help to convert into different
othe organelles when the leaf is no longer using photosynthesis usually in an
autumn month.
4. Leucoplasts
These are the non-pigmented organelles which are colourless. Leucoplasts ar
usually found in most of the non-photosynthetic parts of the plant like
roots.They act as storage sheds for starches, lipids, and proteins depending on
the need of the plants. They are mostly used for converting amino acids and
fatty
acids.Leucoplasts are of three types:
Amyloplasts — Amyloplasts are greatest among all
three and they store and
synthesize starch.Proteinoplasts — Proteinoplasts
help in storing the proteins that a plant needs and can be typically found in
seeds. Elaioplasts - Elaioplast helps in storing fats and oils that are needed
by the plant.
Inheritance of Plastids:There are many plants which
are inherited from the plastids from just a single parent. Angiosperms inherit
plastids from the female gamete while there are many gymnosperms that inherit
plastids from the male pollen. Algae inherit plastids from one parent only. The
inheritance of the plastids-DNA seems to be 100% uniparental. In hybridisation,
the inheritance of plastid seems to be more erratic.
LET US KNOW WHAT WE HAVE LEARNT!
MCQs:
Q1.Cristare in
mitochondria serves as sites for?
a. Oxidation reduction reaction
b. Protein Synthesis
c. Macromolecules breakdown
d. Flavoproteins are phosphorylated
Q2. Which of the
following cell organelle can be viewed by a light
microscope?
a. Ribosome
b. Golgikodies
c. Endoplasmic Reticulum
d. Mitochondria
Q3. Mitochondria
in the human sperm cell are occupied at which part?
a. Sperm head
b. Mid piece
c. Sperm Tail
d. Mitochondria in the Sperm
Q4. Leucoplasts
are a type of:
a. Plastids
b. Endoplasmic reticulum
c. Nucleus
d. Golgi Apparatus
FILL IN THE BLANKS:
1. Mitochondria are of the Cell.
2. helps in storing fats and oils that are needed by
the plant.
TRUE/FALSE:
1. Mitochondria are not membrane bound.
2. Yellow colour of mango is due to chloroplasts.
ANSWER KEY: PART-A
MCQs:
1. a (Oxidation reduction reaction)
2. d (Mitochondria)
3. b (Mid piece)
4. a(Plastids)
FILL IN THE BLANKS:
1. Power House
2.
Elaioplasts
TRUE/FALSE:;
1. False: Mitochondria are double membrane bound
cell organelles.
2. False: Yellow colour of mango is due to
chromoplasts.
PART: B SHORT ANSWER TYPE QUESTIONS:
1. What are 3 facts about mitochondria?
2. | Why mitochondria are called the power house of
the cell?
3. Write a short note on Plastids.
PART: C LONG ANSWER TYPE QUESTIONS:
Q1. Write down the structure and functions of
Mitochondria?
A85
INTRODUCTION:The organelles
are present inside the cell and they are performing specific function that
regulates the cell activities.Let us discuss some important organelles.
A. Claude (1941), first observed ribosomes and
called them as microsomes.
B. Robinson and Brown (1953) first discovered
ribosomes, in plant cells (roots of Vicia).
C. Palade (1955) isolated ribosomes from animal
cells and detected RNA.
D. Roberts (1958) coined the term ribosome.
The ribosome word is derived from — ‘ribo’
ribonucleic acid and ‘somes’ from
the Greek word ‘soma’ which means ‘body’.
The location of the ribosomes in a cell determines
what kind of protein it makes. If the ribosomes are floating freely throughout
the cell, it will make proteins that will beutilized within the cell itself.
When ribosomes are attached to endoplasmic reticulum,it is referred to as rough
endoplasmic reticulum or rough ER. Proteins made on the rough ER are used for
usage inside the cell or outside the cell.
On average in a mammalian cell, there can be about
10 million ribosomes.
FUNCTIONS OF RIBOSOMES:
1. They assemble amino acids to form specific
proteins, proteins are essential to carry out cellular activities.
2. In the process of production of proteins, the DNA
produces mRNA by the
process of DNA transcription.
3. The genetic message from the mRNA is translated
into proteins during DNA
translation.
4. The sequences of protein assembly during protein
synthesis are specified in
the mRNA.
5. The mRNA is synthesized in the nucleus and is
transported to the cytoplasm
for further process of protein synthesis.
6. In the cytoplasm, the two subunits of ribosomes
are bound around the polymers of mRNA; proteins are then synthesized with the
help of transfer RNA.
7. The proteins that are synthesized by the
ribosomes present in the cytoplasm
are used in the cytoplasm itself. The proteins
produced by the bound ribosomes are transported outside the cell.
Cilia and Flagella are complex filamentous
cytoplasmic structures which grow
through a cell wall.They are minute, especially
differentiated appendices of the cell.Flagella (singular = flagellum) are long,
hair-like structures that extend from the plasma membrane and are used to move
an entire cell.Cilia (singular = cilium) are short, hair-like structures that
are used to move a cells (Such as paramecia) or substances along the outer
surface of the cell (for example, the cilia of cells lining the Fallopian tubes
that move the ovum toward the uterus, or cilia lining the cells of the
respiratory tract that trap particulate matter and move it toward the
nostrils).The terms cilium (meaning an eyelash) and flagellum (meaning a whip)
are often used simply.Generally, cilia are shorter than flagella (<10 um
compared to >40um).Cilia are present on the surface of the cell in much
greater numbers (ciliated cells often have hundreds of cilia but flagellated
cells usually have a single flagellum).The real difference, however, lies in
the nature of their movement. Cilia row like oars. The movement is biphasic,
consisting of an effective stroke in which the cillum is held rigid and bends
only at its base and a recovery stroke in which the
bend formed at the base passes out to the
tip.Flagella wriggle like eels. They generate waves that pass along their
length,usually from base to tip at constant amplitude.Thus the movement of
water by a flagellum is parallel to its axis while a cilium moves water
perpendicular to its axis and, hence, perpendicular to the surface of the cell.
STRUCTURE OF CILIA AND FLAGELLA:
Despite their different pattern of beating, cilia
and flagella are indistinguishable
structurally.All cilia and flagella are built on a
common fundamental plan:
1. A bundle of microtubules called the axoneme which
is covered by a membrane
that is part of the plasma membrane.
2. The axoneme is attached with the basal body which
is an intracellular granule
lying in the cell cortex and which originates from
the centrioles.
3. Each axoneme is filled with ciliary matrix, in
which are embedded two central
singlet microtubules, each with the 13
protofilaments and nine outer pairs of
microtubules, called doublets. This is known as the
9 + 2 array.
4. Each doublet contains one complete microtubule,
called the A sub fiber,
containing all the 13 protofilaments. Attached to
each A sub fiber is a B sub fiber with 10 protofilaments.
5. Subfibre A has two dynein arms which are oriented
in a clockwise direction.
Doublets are linked together by nexin links.
6. Dynein is an ATPase that converts the energy
released by ATP hydrolysis into
the mechanical work of ciliary and flagellar
beating.
7. Each sub fiber A is also connected to the central
microtubules by radial spokes
terminating in fork-like structures, called spoke
knobs or heads.This regular arrangement of microtubules and associated proteins
with the nine-way pattern is also seen in centrioles. But unlike centrioles,
cilia and flagella have a central pair of microtubules, so that the overall
structure is called the 9 + 2 axoneme.
IMPORTANT POINT:
Eukaryotic flagella diverge from prokaryotes in composition.
Flagella in eukaryotes contain far more proteins and
bear some similarity to motile
cilia, with the same general motion and control
patterns.WORKING OF CILIA AND FLAGELLA:In eukaryotes The ATP produced are used
by mitochondria near the base of the cilium or flagellum as fuel, the dynein
arms push on the adjacent outer doublets, forcing a sliding movement to occur
between adjacent outer doublets. Because the arms are activated in a strict
sequence both around and along the axoneme and because the amount of sliding is
restricted by the radial spokes and inter-doublet links, sliding is converted
into bending.
In prokaryotes Bacterial flagella use a different
method. Like the propeller of a boat, the motion of the bacterial flagellum is
completely driven by the rotary motor at its base. The bacterial flagella
itself is a specialized piece of extracellular cell wall, made of one protein
named as flagellin that different from tubulin or dynein. Cilia and flagella
are full of cytosol all the way to their tips and use the ATP in that cytosol
to generate
force all the way along their length.
FUNCTIONS OF CILIA:Cilia
are used for locomotion in unicellular organisms, such as protozoans (e.g.,
Paramecium).
Motile cilia use their rhythmic undulation to throw
away substances, as in clearing
dirt, dust, micro-organisms and mucus, to prevent disease.Cilia
play important roles in the cell cycle as well as animal development, such as
in the heart.
Cilia selectively allows only some proteins to
function properly.Cilia also play a major role in cellular communication and
molecular trafficking.Non-motile cilia serve as sensory apparatus for cells,
detecting signals. They play crucial roles in sensory neurons. Non-motile cilia
can be found in the kidneys to sense urine flow, as well as in the eyes of the
hotoreceptors of the retina. They also provide habitats or living areas for
symbiotic microbiomes in animals. Cilia have also been reported to participate
in vesicular secretion of ectosomes.
FUNCTIONS OF FLAGELLA:Flagella
are generally used for locomotion of cells, such as the spermatozoon and Euglena
(protozoan).It has an active role to help the cell for feeding and eukaryotic
reproduction.In prokaryotes such as bacteria, flagella serve as propulsion
mechanisms; they're the chief way for bacteria to swim through fluids.It also
provides a mechanism for pathogenic bacteria to aid in colonizing hosts
and therefore transmitting diseases.
It also function as bridges or scaffolds for
adhesion to host.as Centrosome is an organelle that contains two cylindrical
structures called centrioles.Both are composed of two centrioles arranged at
right angles to each other, and
covered by a dense, highly organized mass of protein
which is known as the
pericentriolar material (PCM). The PCM contains
proteins responsible for
microtubule nucleation and anchoring — including
y-tubulin, pericentrin and ninein
(these are the names of proteins).
FUNCTIONS OF CENTROSOME:Centrosomes
arrange the microtubules, so it is also called the microtubules organizing
center. The centrosomes duplicate before cell division.
CENTRIOLE:Eukaryotic
cells contain two cylindrical, rod-shaped, microtubular structures,called
centrioles, near the nucleus.They lack a limiting membrane and DNA or RNA and
occur in most algal cells ,
moss cells, some fern cells, and most animal
cells.They are absent in prokaryotic cells, red algae, yeast, cone-bearing
(gymnosperms) and flowering plants ( angiosperms)
and some non-flagellated or
non-ciliated protozoans (such as amoebae).
Centrioles form a spindle of microtubules, the
mitotic apparatus during mitosis or
meiosis and sometimes get arranged just beneath the
plasma membrane to form
and bear flagella or cilia in flagellated or
ciliated cells.When a centriole bears a flagellum or cilium, it is called the
basal body
STRUCTURE OF CENTRIOLE:
1. Centrioles and basal bodies are cylindrical
structures which are nearly 0.16-0.27 um in diameter usually 0.28—0.69 um in
length.
2. They are visible under a light microscope, but
the details of the centriole structure were seen only under an electron
microscope.
3. Each cell has a pair of centrioles in the
centrosome, a region near the nucleus.
The members of each pair of centrioles are at right
angles to one another.
4. They are small -sub-microscopic microtubular sub
cylinders with a configuration of nine triplet fibrils and the ability to form
their own duplicates, astral poles and basal bodies, without having DNA and a
membranous cover.
5. A centriole consists a whorl of nine peripheral
fibrils. Fibrils are absent in the center. The arrangement is, therefore,
called 9 + 0. Fibrils run parallel to one
another but at an angle of 40°. Each fibril is made
up of three sub-fibers. So, it is
called a triplet fibril.
6. Each sub-fiber has a diameter of nearly 25 nm.
From outside to inside the three
sub-fibers of a triplet fibril are named as C, B and
A. Sub-fibre A are complete
with 13 proto-filaments while B and C sub-fibers are
incomplete due to sharing of
some microfilaments.
7. The adjacent triplet fibrils are connected by C—A
proteinaceous linkers. The
center of centriole possesses a rod-shaped
proteinaceous mass known as the
hub. The hub has a diameter of 2.5 nm. From the hub,
develops 9 protein strands
towards the peripheral triplet fibrils. They are
Known as spokes.
8. Each spoke has a thickening called X before
uniting with A sub-fiber. Another
thickening known as Y is present nearby. It is
attached both to X thickening as
well as C —A linkers by connectives.
9. The presence of radial spokes and peripheral
fibrils, the centriole gives a
cartwheel type shape in T.S.
FUNCTIONS OF CENTRIOLE:Centrioles
are mainly involved in the formation of the spindle, which functions during
cell division(or cell reproduction)
The absence of centrioles causes divisional errors
then there is delay in the
mitotic process.A single centriole makes the anchor
point, or basal body, for each individual cilium or flagellum.Basal bodies
direct the formation of cilia and flagella
LET US KNOW WHAT WE HAVE LEARNT!
PART: A_ VERY SHORT ANSWER TYPE
QUESTIONS:
MCQs:
1. Centrosome is
found in:
(a) cytoplasm
(b) chromosome
(c) Nucelus
(d) Lysosomes
2. Two
cylindrical rod shaped structures present in Eukaryotic cell:
(a) centrioles
(b) genes
(c) chromosomes
(d) ribosomes
3. Who coined the
term ribosome?
(a) Robert Brown
(b) Roberts
(c) Robert Hook
(d) Leeuwenhoek
4. Centriole
Takes Part in the Formation of:
(a) Nucleus
(b) Spindle
(c) Cell plate
(d) To start cell division
5. Bacterial
flagella are made up of protein:
(a) tublin
(b) flagellin
(c) chitin
(d) None of these
FILL IN THE BLANKS:
1. Centrioles are involved in the formation of the .
2. Flagella are generally used for of cells.
TRUE/ FALSE:
1. Nucleus controls the hereditary characteristics
of an organism.
2. A bundle of microtubules called the axoneme.
ANSWER KEY: PART-A
MCQs:
1. a) Cytoplasm
2. a) Centrioles
3. b) Roberts
4. b) Spindle
5. b) Flagellin
FILL IN THE BLANKS:
1. Centrioles are involved in the formation of the
spindle apparatus.
2. Flagella are generally used for Locomotion of
cells.
TRUE/ FALSE:
1. TRUE
2. TRUE
PART: B SHORT ANSWER TYPE QUESTIONS:
1. What are the functions of Ribosomes?
2. What are the functions of centriole?
3. What is the difference between 70S and 80S
ribosomes?
PART: C LONG ANSWER TYPE QUESTION:
1. Explain the structure and functions of cilia and
flagella.
A86
Nucleus is a specialized double membrane’ bound
protoplasmic body which contains all the genetic information for controlling
cellular metabolism and transmission to the
posterity. A nucleus in non-dividing or metabolic
phase is call interphase nucleus. It directs and controls all the cellular
functions.
Discovery:
It was first described by Robert Brown (1831 A.D.) in the root cells of orchid
cells.
Occurrence:
A true nucleus is present in all the eukaryotes except mature
mammalian RBCs, sieve tube cells of phloem,
tracheids and vessels of xylem.
Position:
The nucleus is generally centric.
Number: Mostly the cells are monokaryotic but may be
anucleate,binucleate, multinucleate.
Shape:
It varies widely. Generally spherical, oval, discoidal, kidney shaped,
horse shoe shaped, bilobed, multilobed, long and
beaded moniliform and branched.
CHEMICAL COMPOSITION OF NUCLEUS
Proteins =80%
DNA =12%
RNA=5%
Lipids = 3%
Enzymes like polymerases are abundantly present and
help in synthesis of
DNA and RNA.Minerals in traces like Ca, Mg, Na and
K.A typical interphase nucleus is 5-25 ym in diameter. It has four components
1. Nuclear Envelope
2. Nucleoplasm
3. Nucleolus
4. Nuclear Chromatin
1. Nuclear Envelope:
It bounds the nucleus in the outside. The nuclear envelope separates the
nucleus from the cytoplasm. It is made up of two lipoprotein and trilaminar
membranes, each of which is 60-90A thick.The inner membrane is smooth. The
outer membrane may be smooth of its
cytoplasmic surface may bear ribosomes like the
rough endoplasmic reticulum. The two membranes of the nuclear envelope are
separates by an electron transparent perinuclear space. Nuclear envelope
contains a large number of pores (1000-10000)
Functions of Nuclear envelope:
1. It regulates the nucleo-cytoplasmic interactions.
2. It allows the passage of inorganic ions and small
organic molecules
3. It helps in pinocytosis and phagocytosis.
2. Nucleoplasm:
It is a transparent, semifluid and colloidal substance which
fills the nucleus. It contains nucleosides and a
number of enzymes which are required for the synthesis and functioning of DNA,
RNA, nucleoproteins, etc.Some of the proteins present in nucleoplasm are
essential for spindle formation.
3. Nucleolus:
It is a darkly stained granular naked organelle with no limiting
membrane. It is associated with nucleolar organizer
region of the chromosome. It is seat of biogenesis of r-RNA and also stores
r-RNA so it is called ribosome factory. It plays important role in spindle
formation during cell division.
4. Nuclear Chromatin:
It is a darkly stained network of long and fine
threads, called chromatin fibers. Chromatin fibers
are distributed throughout the nucleoplasm. They are differentiated into two
region-euchromatin and heterochromatin. Chromatin fibers contain DNA which
acts as a genetic material.
LET US SEE WHAT WE HAVE LEARNT! |
PART A: VERY SHORT ANSWER TYPE
QUESTIONS:
A. MULTIPLECHOICE QUESTIONS:
1) Nucleus is
discovered by :
a) Erclab
b) Robert Hook
c) Robert Brown
2) Nucleus is
absent in:
a) RBCs of mammals
b) Seive tube cells of phloem
c) Both a and b
3) Nucleolus is
found in:
a) Protoplasm
b) Nucleus
c) Cytoplasm
4) Nuclear
material without nuclear membrane is observed in:
a) Eukaryotes
b) Bacteria and cyanobacteria
c) Bacteria and green algae
5) Controlling
centre of cell is:
a) Ribosomes
b) Nucleus
c) Nucleolus
1) ......... is the principal site for the
development of r-RNA.
2) Incipient nucleus with no nuclear membrane is
called .........
1) Nuclear membrane regulates the nucleo-cytoplasmic
interactions.
2) Nucleoplasm possesses cyclosis.
3) A nucleolus is darkly stained granular naked
organelle with no limiting
membrane.
ANSWER KEY |
PART A: VERY SHORT ANSWER TYPE
QUESTIONS:
(A MULTIPLECHOICE QUESTIONS: _
1) c (Robert Brown) —
2) c (Both a and b ,RBCs of mammals and sieve tube
cells of phloem)
3) b (Nucleus)
4) b (Bacteria and cyanobacteria)
5) b (Nucleus) It controls the cellular metabolism
1) Nucleolus
2) Nucleoid
1) True
2) False (Nucleoplasm is a gel-like sticky material
covered by nuclear envelope and supports the chromosomes and nucleoli so do not
show cyclosis (streaming movement)).
3) True
PART-B: SHORT ANSWER TYPE QUESTIONS
1) Why nucleus is called director of the cell?
2) Name four components of nucleus.
3) List two functions of nuclear membrane.
PART-C: LONG ANSWER TYPE QUESTIONS
1) Draw the well labeled diagram of nucleus
2) Give the functions of components of nucleus.
A87
INTRODUCTION:CHROMOSOMES
are rod shaped or threadlike deeply stainable condensed chromatin fibres which
are hereditary vehicles as they store and transmit coded hereditary
information. Chromosomes appear only during karyokinesis. They are meant for
equitable distribution of genetic material.The number is fixed and is the same
in all the individuals of a species. There is a single set in gametophytic or
haploid forms and two sets in sporophytic
or diploid forms. Size and shape of individual chromosomes are quite distinct. The shape is more clearly is more clearly visibly in late prophase and metaphase (as well as anaphase) when primary constriction or centromere becomes distinct. During prophase and metaphase, theChromosomes are replicated. There are two chromosome halves or chromatids.
The two chromatids are attached to each other by a narrow area
called centromere or primary constriction. Anaphasic chromosomes do not have
chromatids. The two parts of chromosome or chromatid on either side of primary
construction are called arms. The two arms are equal in isobrachial chromosomes
and unequal’ in heterobrachial chromosomes. The ratio between the two arms of a
chromosome is called centromeric ratio.Based on the position of centromere,
chromosomes are of four types
(i) Telocentric: Centromere terminal in the area of
telomere.
(ii)Acrocentric: Centromere inner to telomere
(subterminal).
(iii) Submetacentric: Centromere submedian.
(iv) Metacentric: Centromere median.
Some chromosomes have additional non-staining sub
terminal constriction, called secondary constriction and such chromosomes are
called SAT-chromosomes. In human karyotype, there are five pairs of
SAT-chromosomes (13, 14, 15, 21 and 22).
Certain secondary constrictions are involved in the
formation of nucleoli and are called nucleolar organising regions (NORs) and
suchchromosomes are called nucleolar chromosomes.
NUCLEOSOME:Chromatin
fibre is formed of a chain of repeated units called nucleosomes. Each
nucleosome is formed of a core complex called nu body wrapped by DNA strand (of
166 to 200 base pairs). Core complex
is formed of HISTONE OCTOMER of four types of
histone molecules (2 molecules each) -H2A, H2B, H; and Hg.
SPECIAL TYPES OF CHROMOSOME
These are /argest-sized chromosome, so called giant chromosomes.For example:
lampbrush chromosomes of oocytic nuclei of
Salamandra are as long as 5900um (5.9mm). So these
are even visible with naked eye. Each chromosome is formed of a main
central axis and several pairs of lateral loops laying the appearance of a brush, so called lampbrush chromosome.
These are
second largest-sized chromosomes. These are about 200um or more in length
(normal chromosome is about 7.5um. So these are called giant chromosomes. These
are multi-stranded or polytenic chromosomes and may be formed as many as 512 to
1024
chromatids. It is due to a process called endomitosis.
Each chromosome is with a specific pattern of dark-coloured bands and
alternatively arranged light-coloured interbands.
One or more bands give rise to swelling called puffs or bulbs. Some
chromonemata give rise to a number of large-sized loops, called Balbiani rings.
CHROMOSOME FUNCTIONS
Chromosome contains genes. All the hereditary information is located in the
genes.They control cellular differentiation.Sat chromosomes produce nucleoli
for synthesis of ribosomes.
Their haploid or diploid number respectively brings
about gametophytic and sporphytic characteristics to the individual.Chromosomes
form a link between the offspring and the parents.
Some chromosomes called sex chromosomes (e.g., X and
Y or Xand 0) determine the sex of the individual.Through the process of
crossing over, chromosomes introduce
variations.
A. MULTIPLE CHOICE QUESTIONS:
1) Kinetochore is
present in:
a. Mitochondria
b. Chromosome
c. Lysosome
2) Ina cell that
is not dividing the chromosome are visible as a tangle
of thread called:
a. Chromatin
b. Microtubule
c. Microfilament
3) Chromosome are
always exist:
a. In pairs
b. Singly
c. In association with mitochondria
4) Chromosome
whose arms are equal are called:
a. Metacentric
b. Acrocentric
c. Acentric
5) Tips of chromosomes
are called:
a. Centromere
b. Chromomeric
c. Telomere
FILL UPS
1) Some chromonemata give rise to a number of large
sized loops
called...........
2) Chromosomes are observable during.......or.......
TRUE/FALSE
1) Lampbrush chromosomes are called giant
chromosomes.
2) Chromatin fibre is formed of a chain of repeated
unit called
nucleosomes.
3) Chromosome does not contain genes.
PART A: VERY SHORT ANSWER TYPE
QUESTIONS:
1) (b) Chromosome
2) (a) Chromatin
3) (a) In pairs
4) (a) Metacentric
5) (a) Telomere
FILL UPS °
1) Balbiani ring
2) M-phase or Nuclear division
TRUE/FALSE a
1) TRUE
2) TRUE
3) FALSE (Chromosome contain gene as all the
hereditary information is located in the genes)
PART B: SHORT ANSWER TYPE QUESTIONS:
1) What are SAT chromosomes?
2) Define nucleosomes.
3) Name two special types of chromosomes?
PART C: LONG ANSWER TYPE QUESTIONS:
1) What is centromere? How does the position of
centromere form
the basis of classification of chromosome? Support
your with
diagram.
2) List the functions of chromosomes.
A88
INTRODUCTION:The
cell is the structural and fundamental unit of life.Plant and animal cells are
eukaryotic, so they contain membrane bound organelles like the nucleus,
mitochondria etc. Plant Cell and Animal Cell do not look exactly the same.
All cells arise from pre-existing cells.
Animal cell:
Animal cells do not have a cell wall. Animal cell is composed of a
cell membrane, cells have cytoplasm in it, different
type of cellular activities
occurs in cytoplasm. Animal cells have different
oraganelles like mitochondria,
nuclueus, ribosome, golgi apparatus, endoplasmic
reticulum. Mitochondria are
the power house of cell.
Plant cell contains the rigid cell wall. Cell wall
provides the protection.
Plant cell contain large central vacuoles.
Chloroplasts present, help in food
synthesis.
MCQs:
1. Component of
plant cell absent in animal cell is:
[a] cytoplasm
[b] cell membrane
[c] cell wall
[d] nucleus
2. The main site
of different types of cellular activities is;
[a] mitopchondria
[b] nucleus
[c] cytoplasm
[d] plasma-membrane
3. Chloroplast is
found in:
[a] plant cell only
[b] Animal cell only
[c] both of these
[d]none of these
4. The functional
unit of Life is called:
[a] cell
[b] egg
[c] nucleus
[d] none of these
5. The power
house of cell is called:
[a] cell wall
[b] mitochondria
[c] ribosome
[d] nucleus
FILL IN THE BLANKS:
1. cell does not have a plastids.
2. All cells arise from cells.
TRUE/FALSE:
1. Cell is structural functional unit of an
organism.
2. Both animal and plant cells are eukaryotes.
MCQs:
1. c_ cell wall
2. c cytoplasm
3. a plant cell only
4. a cell
5. b mitochondria
FILL IN THE BLANKS:
1. Animal cell
2. Pre-existing
TRUE/FALSE:
1. True
2. True
1. Write down the function of cell wall.
2. What is cytoplasm?
3. Write function of chloroplast.
1. Differentiate between plant cell and animal cell.
A89
INTRODUCTION:Dear
students we have discussed the chapter; Cell: The Unit of Life.Now in this
assignment we will discuss about the NCERT exercise questions.
NCERT EXERCISE QUESTIONS
Q: 1 Which of the
following is not correct?
[a] Robert brown discovered the cell .
[b] Schleiden and scgwann formulated the cell theory
[c] Virchow explained that cells are formed from
pre-existing cells
[d] A uniceller organism carries out its
life actiivites within a single cell .
Q:2 New cells
generate from:
[a] bacterial fermentation
[b] regeneration of old cells
[c] pre-existing cells
[d] Abiotic material
Q: 3 Match the
following :
COLUMN [1] COLUMN [2]
[A] Cristae [1] Flat membranous sacs in stroma
[B] Cisternae [2] Infoldings in mitochondria
[C] Thylakoids [3] Disk shaked sacs in
Golgi-apparatus
ANS: A-1, B-3, C-2
Q: 4 Which of
following is correct?
[a] cells of all living organism have a nucleus
[b] Both animal and plant cells have a well-defined
cell wall
[c] In prokaryotes there are no membrane bound
organelles
[d] cells are formed de novo from abiotic material
Q: 5 what is a
mesosome in a prokaryotic cell? Mention the functions that it
perform.
ANS: Mesosome is a membranous structure in
prokaryotic cell which is formed by the
extensions of the plasma membrane into the cell in
the form of vesicles, tubules and
lamellae. Mesosome is equal to mitochondria in
eukaryotes as it performs aerobic
cellular respiration in prokaryotes. It helps in DNA
replication and distribution of genetic material to daughter cells. Mesosome
also helps in respiration by increasing the surface area of the plasma membrane
and enzymatic content. It helps in cell wall formation.
Q: 6 How do
neutral solutes more across the plasma membrane. Can the polar molecules also
move across it in the same way, If not then how are these transported across
the membrane?
ANS: Neutral solutes move across the membrane by the
process of simple diffusion
along the concentration gradient i.e, from higher
concentration to the lower
concentration. Polar molecules cannot pass through
the nonpolar lipid layer. They
require carrier protein of the membrane to
facilitate their transport across the
membrane. In facilitated diffusion, molecules are
transported along concentration gradient by the help of ion channels and
aquaporin. It does not involve energy expenditure.
Q: 7 Name two
cell organelles that are double membrane bound. What are the
characteristics
of these two organelles? State their function and draw labeled
diagram of both.
ANS: Mitochondria and Chloroplast are double
membrane bound organelles.
MITOCHONDRIA:
Mitochondria are cylindrical shaped cell organelles and contain two
membranes; outer and inner. The inner compartment is
called the matrix containing
DNA, RNA, ribosome etc. Outer membrane forms the
continuous limiting boundary of
the organelle. Inner membrane forms number of
infoldings, called the cristae which
increases the surface area. Oxysomes are present on
inner mitochondrial membrane.
Mitochondria are semi-autonomous organelles i.e,
have their own DNA and ribosomes.
FUNCTIONS OF MITOCHONDRIA:
1. Mitochondria are essential for aerobic
respiration.
2. Mitochondria provide intermediates for synthesis
of important biomolecules such
as chlorophyll cytochrome etc.
3. Mitochondria regulate the calcium ion
concentration in the cell.
4. Synthesis of many amino acids takes place here.
CHLOROPLAST:
They are green coloured plastids which are disc shaped. The
spaces limited by inner membrane of chloroplast is
called stroma. Stroma has
organized flattened membranous sacs called the
THALAKOID. Thalakoids are arranged in stacks called GRANA. Matrix of a
chloroplast contains DNA, RNA,riobosomes and enzymes.
FUNCTIONS OF CHLOROPLAST:
1. Photosynthesis is performed by chloroplast.
2. Chloroplast stores starch grains.
3. Maintains balance of CO: concentration in the
air.
4. Keeps oxygen balance constant in atmosphere by
liberating O2 into the
atmosphere used during respiration and combustion.
Q: 8 What are the
characteristics of prokaryotic cells?
ANS : The characteristics of prokaryotic cells are
as follows:The prokaryotes cell is essentially a single envelope system.
Prokaryotes lack membrane bound cell
organelles.Prokaryotes have 70s ribosomes.
e DNA is naked and lies coiled in cytroplasm. It is
not covered by nuclear
membrane and is turned as nucleaid.
e Nuclear components like nuclear envelope,
nucleolus, and nucleoplasm are absent. Cell wall is present in bacteria
and cyanobacteria but absent in
mycoplasma.
Multiplies by asexual reproduction.
Q: 9
Multicellular organisms have division of labor. Explain.
ANS: Division of labor is differentiation of certain
components or parts to perform
different functions for increased efficiency and
higher survival.Multicellular organisms
often possess millions of cells are grouped together to form specific tissue
organ system, with each specialized to perform particular function. Every cell
of a multicellular organism cannot obtain food from outsides.The organism
requires a system for obtaining food, its digestion and distribution.Therefore
a digestive system and system of transport are also required. Certain cells of
the body take over the function of reproduction. Other takes part in repair and
replacement of worn out portions for optimum functioning of cells. A
multicellular organism also requires an internal favorable environment. So a
multicellular organism comes to have division of labor.
Q: 10 Cell is the
basic unit of life. Discuss in brief.
ANS: Cell is fundamental, structural and functional
unit of life as no living
organism can have life without being cellular. All
life begins as a single cell. An organism single cell is capable of independent
existence and perform all essential functions of life, while in multicellular
organism each group of cells is specialized for specific function. Life passed
from one generation to the next in front of cells and new cells always arise
from division of pre-existing cells. Cells are totipotent i.e, single cell has
ability to form whole organism.The activities of an organism are sum total of
activities of its cells. Therefore cell is the basic unit of life.
Q: 11 What are
nuclear pores? State their function.
ANS: Nuclear envelope bounds the nucleus from
outside and separates it from
cytoplasm; it consists of two membranes, with outer
membrane continuous with
endoplasmic reticulum. The nuclear pores at a number
of places, which are produced by the fusion of its two membranes. These nuclear
pores are the passage through which movement of RNA and protein molecules takes
place in both directions between the nucleus and the cytoplasm.
Q: 12 Both
lysosomes and vacuoles are endomembrane structure, yet they
differ in terms
of their function, comment.
ANS: Organelles, of endomembrane system such as
lysosomes and vacuoles
function in close co-ordination with one another but
are specialized to perform
different functions. Lysosomes break down the ageing
and dead cells. They help
in digestion of food as they contain hydrolytic
digestive enzymes. They are
involved in cell division also. Vacuoles on other
hand help in excretion and
osmoregulation in Amoeba or provide buoyancy
mechanical strength in
prokaryotes. (Air- vacuoles)
Q: 13 Describe
the structure of following with the help of labeled diagrams:
(1) Nucleus (2)
Centrosome
ANS: NUCLEUS: Nucleus is
double membrane bound principal cell organelle,
which contains all genetic information for
controlling cellular metabolisim and
transmission of genetic information. Nucleus is
differentiated into following four parts :
[a] Nuclear envelope:
It is a double membrane envelope that surround the nucleus and separates the
latter from the cytoplasm.
[b] Nucleaplasm:
Its clear, non- staining fluid material present in the nucleus,which
contains raw materials (nucleotides ) enzymes
(DNA/RNA polymerase) and metal ions
for the synthesis of RNA’ s and DNA.
[c] Nucleolus:
It is a naked, round and slightly irregular structure which is attached to the
chromatin at a specific region.
[d] Chromatin:
It has the ability to get stained with certain basic dyes. It is known to be
hereditary DNA protein fiberilar complex.
CENTROSOME
It is an organelle usually containing two cylindrical structures called
centrioles. It is present near the nucleus. Centrioles are surrounded by
amorphous pericentriolar,centrosphere. The complex formed by centrosphere and
centrioles is called centrosome. In a centrosome, the two centrioles lie
perpendicular to each other. T.S. of
centriole gives a Cartwheel like appearance due to
presence of peripheral fibrils,
spokes and hub.
Q: 14 What is a
centromere? How does the position of centromere form the basis
of classification
of chromosome? Support your answer with a diagram, showing
the position of
centromere on different types of chromosome.
ANS: A chromosome consists of two identical halves,
the chromatids. The chromatids
held together at one point called the centromere.
The centromere is also called as primary constriction.Chromosome is classified
into four types according to position of centromere on chromosome:
1. Metacentric chromosome:
In this type centromere is in the middie and the two
arms of chromatids are almost equal in length.
2. Sub-metacentric chromosome:
The centromere is slightly away from middle
point, so one arm of chromatids is slightly shorter
than the other.
3. Acrocentric chromosome:
The centromere is near the end and one arm of the
chromatids is extremely short and other arm is
extremely long .
4. Telocentric chromosome:
The centromere is at the tip of chromatids. These
chromosomes are not present in humans.
A90
RECAPITULATION:All
cells arise from pre-existing cells.Animal cells plant cells both are eukaryotic
type cells.Cells have cell organelles in cytoplasm that is nucleus, nucleolus
Golgi apparatus, mitochondria, endoplasmic reticulum.
Plant cells have a cell wall outside the cell
membrane.Plasma membrane is selectively permeable and facilitates
transport of several molecules.
NUCLEUS:
It is main controlling center of the cell, nucleus contains nucleoli and
chromatin network .It controls activities of organelles.NUELEOLUS: tt is a
spherical structure present in nucleoplasm it is a
site for achive ribosomal RNA synthesis
ENDOPLASMIC RETICULUM:
It is network of tiny structure scattered inthe cytoplasm .It is of two type’s
smooth endoplasmic reticulum and rough endoplasmic reticulum.
They help in transport of substances.
Golgi apparatus: It is present near nucleus. It
consists of cisternal
tubules, vesicles. It is a membranous organelle.
Chloroplast: It is found in plant cells. They are
responsible for trapping
lignt energy essential for photo synthesis.
Chromatin: interphase nucleus has an indistinct work
of nucleoprotein
fibers called chromatin.
Chromosome: On the basis of position of centromere,
chromosome can be classified into following different types:
(1) Acrocentric:
In this type centromere is situated close to its end forming One short and one
long arm
(2) Telocentric:
In this type chromosome has terminal centromere .
(3) Metacentric:
It has middie centromere and forming two equal arms of
chromosome.
(4) Sub-metacentric:
It has centromere slightly away from the middle of the chromosome, so chromosome
has one shorter and one longer arm.
LET US KNOW WHAT WE HAVE LEARNT!
TEST YOUR KNOWLEDGE
MCQs: (1 Mark each)
1. Cell was first
observed and described by
a) Anton van leeuwenhoek
b) Robert brown
c) Robert Virchow
d) Schleiden and Schwann
2. Cell theory
was proposed by :
a) Robert brown
b) Robert Virchow
c) Schleiden and Schwann
d) Stanger and Nicolson
3. Which
organelle is the site of protein synthesis :
a) Mitochondria
b) Golgi bodies
c) Ribosomes
d) Chloroplast
4. Endoplasmic
reticulum is continuous with :
a) Mitochondria
b) Cell wall
c) Nucleus wall
d) Golgi bodies
5. Prokaryotic
cells do not have :
a) Nucleus
b) Membrane bound organelles
c) Centrioles
d) All of these
FILL IN THE BLANKS: (1 mark each)
6. The endoplasmic reticulum bearing ribosomes on
their outer surface
are Called 00... cee cee cee cee tte eee
7. Ribosomes are of two types 70S
and..............0......
8... IS the living matter of cell.
9. The cell is the basic structural and functional
unit of ............
10. Single celled organisms are
called...............
TRUE / FALSE: (1 Mark each)
11. Plasma membrane is selectively permeable.
12. Ribosomes are also known as protein factories of
the cell.
13. Presence of cell wall is characteristic feature
of animal cell.
14. There is a cell membrane around all cells.
15. Chromosomes are found in the cytoplasm.
SHORT ANSWER TYPE QUESTIONS: ee
16. Write about cell theory.
17. Define cell, unicellular and multicellular organisms.
LONG ANSWER TYPE QUESTION
18. Differentiate between prokaryotic cell and
eukaryotic cell.
