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Chapter – 1 - Molecules and their Interaction Relevant to Biology
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Chart
S. N. TOPIC
LIFE SCIENCE
PAGE
NO.
A. Structure of atoms, molecules and chemical bonds 002-030
B.
J.
Composition, structure and function of biomolecules
(carbohydrates, lipids, proteins, nucleic acids and
vitamins).
Metabolism of carbohydrates, lipids, amino acids
nucleotides and vitamins.
031-230
C. Stablizing interactions (Van der Waals, electrostatic,
hydrogen bonding, hydrophobic interaction, etc.).
231-258
D. Principles of biophysical chemistry (pH, buffer, reaction
kinetics, thermodynamics, colligative properties).
259-291
E. Bioenergetics, glycolysis, oxidative phosphorylation,
coupled reaction, group transfer, biological energy
transducers
292-336
F. Principles of catalysis, enzymes and enzyme kinetics,
enzyme regulation, mechanism of enzyme catalysis,
isozymes
337-355
G. Conformation of proteins (Ramachandran plot,
secondary structure, domains, motif and folds).
356-367
H. Conformation of nucleic acids (helix (A, B, Z), t-RNA,
micro-RNA).
368-392
I. Stability of proteins and nucleic acids. 393-409

A. Structure of atoms, molecules and chemical bonds.
Structure of atoms
An atom is the smallest unit of matter that retains all of the chemical properties
of an element. Atoms combine to form molecules, which then interact to form
solids, gases, or liquids. For example, water is composed of hydrogen and oxygen
atoms that have combined to form water molecules. Many biological processes
are devoted to breaking down molecules into their component atoms so they can
be reassembled into a more useful molecule.
Atomic structure refers to the structure of atom comprising a nucleus (center) in
which the protons (positively charged) and neutrons (neutral) are present. The
negatively charged particles called electrons revolve around the center of the
nucleus.
The history of atomic structure and quantum mechanics dates back to the times
of Democritus, the man who first proposed that matter is composed of atoms.
The study about the structure of atom gives a great insight into the entire class of
chemical reactions, bonds and their physical properties. The first scientific theory
of atomic structure was proposed by John Dalton in 1800s.

The advances in atomic structure and quantum mechanics have led to the
discovery of other fundamental particles. The discovery of subatomic
particles has been the base for many other discoveries and inventions.
What is Atomic Structure?
The atomic structure of an element refers to the constitution of its nucleus and
the arrangement of the electrons around it. Primarily, the atomic structure of
matter is made up of protons, electrons and neutrons.
The protons and neutrons make up the nucleus of the atom, which is surrounded
by the electrons belonging to the atom. The atomic number of an element
describes the total number of protons in its nucleus.
Neutral atoms have equal numbers of protons and electrons. However, atoms
may gain or lose electrons in order to increase their stability and the resulting
charged entity is called an ion.
Atoms of different elements have different atomic structures because they
contain different numbers of protons and electrons. This is the reason for the
unique characteristics of different elements.
Atomic Particles
Atoms consist of three basic particles: protons, electrons, and neutrons. The
nucleus (center) of the atom contains the protons (positively charged) and the
neutrons (no charge). The outermost regions of the atom are called electron
shells and contain the electrons (negatively charged). Atoms have different
properties based on the arrangement and number of their basic particles.
The hydrogen atom (H) contains only one proton, one electron, and no neutrons.
This can be determined using the atomic number and the mass number of the
element.

Structure of an atom: Elements, such as helium, depicted here, are made up of atoms. Atoms
are made up of protons and neutrons located within the nucleus, with electrons in orbitals
surrounding the nucleus.
Atomic Mass
Protons and neutrons have approximately the same mass, about 1.67 × 10-
24 grams. Scientists define this amount of mass as one atomic mass unit (amu) or
one Dalton. Although similar in mass, protons are positively charged, while
neutrons have no charge. Therefore, the number of neutrons in an atom
contributes significantly to its mass, but not to its charge.
Electrons are much smaller in mass than protons, weighing only 9.11 × 10-
28
grams, or about 1/1800 of an atomic mass unit. Therefore, they do not
contribute much to an element’s overall atomic mass. When considering atomic
mass, it is customary to ignore the mass of any electrons and calculate the atom’s
mass based on the number of protons and neutrons alone.
Electrons contribute greatly to the atom’s charge, as each electron has a negative
charge equal to the positive charge of a proton. Scientists define these charges as
“+1” and “-1. ” In an uncharged, neutral atom, the number of electrons orbiting
the nucleus is equal to the number of protons inside the nucleus. In these atoms,
the positive and negative charges cancel each other out, leading to an atom with
no net charge.

Protons, neutrons, and electrons: Both protons and neutrons have a mass of 1 amu and are found in
the nucleus. However, protons have a charge of +1, and neutrons are uncharged. Electrons have a mass
of approximately 0 amu, orbit the nucleus, and have a charge of -1.
Volume of Atoms
Accounting for the sizes of protons, neutrons, and electrons, most of the volume
of an atom—greater than 99 percent—is, in fact, empty space. Despite all this
empty space, solid objects do not just pass through one another. The electrons
that surround all atoms are negatively charged and cause atoms to repel one
another, preventing atoms from occupying the same space.
Atomic Number and Mass Number
The atomic number is the number of protons in an element, while the mass
number is the number of protons plus the number of neutrons.
Atomic Number
Neutral atoms of an element contain an equal number of protons and electrons.
The number of protons determines an element’s atomic number (Z) and
distinguishes one element from another. For example, carbon’s atomic number
(Z) is 6 because it has 6 protons. The number of neutrons can vary to produce
isotopes, which are atoms of the same element that have different numbers of
neutrons. The number of electrons can also be different in atoms of the same
element, thus producing ions (charged atoms). For instance, iron, Fe, can exist in
its neutral state, or in the +2 and +3 ionic states.
Mass Number

An element’s mass number (A) is the sum of the number of protons and the
number of neutrons. The small contribution of mass from electrons is disregarded
in calculating the mass number. This approximation of mass can be used to easily
calculate how many neutrons an element has by simply subtracting the number of
protons from the mass number. Protons and neutrons both weigh about one
atomic mass unit or amu. Isotopes of the same element will have the same atomic
number but different mass numbers.
Atomic number, chemical symbol, and mass number: Carbon has an atomic number of six, and two
stable isotopes with mass numbers of twelve and thirteen, respectively. Its average atomic mass is
12.11.
Scientists determine the atomic mass by calculating the mean of the mass
numbers for its naturally-occurring isotopes. Often, the resulting number contains
a decimal. For example, the atomic mass of chlorine (Cl) is 35.45 amu because
chlorine is composed of several isotopes, some (the majority) with an atomic
mass of 35 amu (17 protons and 18 neutrons) and some with an atomic mass of
37 amu (17 protons and 20 neutrons).
Given an atomic number (Z) and mass number (A), you can find the number of
protons, neutrons, and electrons in a neutral atom. For example, a lithium atom
(Z=3, A=7 amu) contains three protons (found from Z), three electrons (as the
number of protons is equal to the number of electrons in an atom), and four
neutrons (7 – 3 = 4).
Atomic Models

In the 18th and 19th centuries, many scientists attempted to explain the structure
of the atom with the help of atomic models. Each of these models had their own
merits and demerits and were pivotal to the development of the modern atomic
model. The most notable contributions to the field were by the scientists John
Dalton, J.J. Thomson, Ernest Rutherford and Niels Bohr. Their ideas on the
structure of the atom are discussed in this subsection.
Dalton’s Atomic Theory
The English chemist John Dalton suggested that all matter is made up of atoms,
which were indivisible and indestructible. He also stated that all the atoms of an
element were exactly the same, but the atoms of different elements differ in size
and mass.
Chemical reactions, according to Dalton’s atomic theory, involve a rearrangement
of atoms to form products. According to the postulates proposed by Dalton, the
atomic structure comprised atoms, the smallest particle responsible for
the chemical reactions to occur.
The following are the postulates of his theory:
 Every matter is made up of atoms.
 Atoms are indivisible.
 Specific elements have only one type of atoms in them.
 Each atom has its own constant mass that varies from element to
element.
 Atoms undergo rearrangement during a chemical reaction.
 Atoms can neither be created nor be destroyed but can be transformed
from one form to another.
Dalton’s atomic theory successfully explained the Laws of chemical reactions,
namely, the Law of conservation of mass, Law of constant properties, Law of
multiple proportions and Law of reciprocal proportions.
Demerits of Dalton’s Atomic Theory

Chapter – 1 - Molecules and their Interaction Relevant to Biology MCQs

1. Why has nuclear energy become
an inevitable option for the
development of the country?
a) Because less pollution caused by
nuclear plant
b) High efficiency of nuclear energy
c) Due to acute shortage of other
sources of energy
d) High cost of energy production of
other sources
Answer: c
Explanation: With the acute shortage
of other sources of energy viz. fossil
based fuels and hydel sources the use
of nuclear energy has become an
inevitable option for the both
developed and developing country.
2. How much amount of nuclear
energy burnt is equivalent to the
energy produced by 3000 tonnes of
coal?
a) 1kg
b) 5kg
c) 15kg
d) 20kg
Answer: a
Explanation: The amount of heat
generated by burning one kg of
nuclear fuel is equivalent to the
energy generated by burning 3000
tonnes of coal or 1600 tonnes of oil.
The production of Nuclear energy is
carried out by two methods which
are nuclear fission and nuclear fusion.
3. What is the most attractive part of
nuclear energy?
a) Supports countries development
b) Causes no pollution
c) Has high efficiency of energy
production
d) Is available in abundance
Answer: b
Explanation: Most attractive part of
nuclear energy is that it has no
combustion products and under safe
working conditions contributes no
pollutant to air. Site selection is
completely independent of
geographical area.
4. Nucleus consists of two sub-
particles known as?
a) Nucleotides
b) Nucleons
c) Neutrons
d) Nucleosides
Answer: b
Explanation: Atom consists of a
relatively heavy, positively charged
nucleus and a number of much
lighter negatively charged electrons.
Electrons exist in various orbits
around the nucleus. The nucleus

consists of two sub-particles known
as nucleons.
5. The atom as a whole is electrically
charged.
a) True
b) False
Answer: b
Explanation: The atom as a whole is
not electrically charged it is actually
electrically neutral in its state. The
electric charge on the proton is equal
in magnitude but opposite in sign to
that of electron, the number of
protons is equal to the number of
electrons in the orbit.
6. On which law is the nuclear energy
explained?
a) Einstein’s law
b) Newton’s law
c) Rutherford law
d) Mendeleev law
Answer: a
Explanation: The nuclear energy is
explained the basis of Einstein’s law,
one atom may be transformed into
another by losing or acquiring some
of the above sub-particles. This
results in mass change Δm and
enormous amount of energy is
released (or absorbed). According to
Einstein’s law,
ΔE = Δmc2
Where, c=light of speed.
7. Electrons that orbit outermost
shell of an atom are called?
a) Valence electrons
b) Electrons
c) Electron Coefficients
d) Neutrons
Answer: a
Explanation: Electrons that orbit
outermost shell of an atom are called
Valence electrons. The outermost
shell is called valence shell. The
presence of valence electron can
determine the element’s chemical
properties.
8. A covalent bond is also called as
____________
a) Atomic bond
b) Metal bond
c) Molecular bond
d) Metal bond
Answer: c
Explanation: A covalent bond is also
called as molecular bond, which
involves sharing of electron pairs
between atoms. These electron pairs
are known as shared pairs or bonding
pairs, when these share an electron
than it is called as covalent bonding.

9. What is the solubility of lipids in
water?
a) Soluble
b) Partially soluble
c) Insoluble
d) Partially insoluble
Answer: c
Explanation: In general, lipids are
hydrophobic in nature due to the
presence of hydrocarbon chains in
their structure. These are poorly
soluble in water but highly soluble in
a nonpolar solvent like ether,
chloroform, or benzene.
10. Fatty acids are amphipathic by
nature.
a) True
b) False
Answer: a
Explanation: Fatty acids are long-
chain hydrocarbons and are the
simplest form of lipids. Fatty acids are
said to be amphipathic by nature as
they have both polar and nonpolar
ends.
11. Find the INCORRECT statement
about the biological functions of
lipids.
a) Storage form of metabolic fuel
b) Have a protective function in
bacteria, plant, and insects
c) The structural component of
membranes
d) Exhibit increased catalytic activity
Answer: d
Explanation: Exhibit increased
catalytic activity is incorrect as all
other options are correct. Lipids take
part in a structural component of the
membrane of animals, plants, or
bacteria where it has protective
functions. Lipid is also considered as
the metabolic fuel of the body.
12. Which of the following is an
example of unsaturated fatty acids?
a) Lauric or Dodecanoic
b) Linoleic or octadecatrienoic
c) Palmitic or hexadecanoic
d) Myristic or tetradecanoic
Answer: b
Explanation: The name of fatty acids
is given by the number of carbons,
and presence of a double bond, with
the suffix -anoic in saturated fatty
acid and -enoic in unsaturated fatty
acids.
13. Name the two essential fatty
acids?
a) Linoleate and linolenate
b) Oleic and linoleic
c) Lauric and myristic
d) Arachidonic and oleic

Chapter – 1 - Molecules and their Interaction Relevant to Biology MCQs for Part C

1. Identify the element by its Atomic
structure.
a) Helium
b) Hydrogen
c) Carbon
d) Oxygen
Answer: b
Explanation:
Most of the mass of the atom is in
nucleus. The red dot is a proton it has
positive charge of 1 unit, and black
one is an electron, which has a
negative charge of -1. There is only
one orbital for hydrogen.
2. Identify the element by its atomic
structure?
a) Hydrogen
b) Helium
c) Carbon
d) Oxygen
Answer: b
Explanation:
The masses of three atomic sub-
particles are,
Neutron mass, mn = 1.008665 amu
Proton mass, mp = 1.007277 amu
Electron mass, me = 0.0005486 amu.
3. Number of protons in the nucleus
is called ___________
a) Atomic number
b) Mass number
c) Electric charge
d) Periodic number
Answer: a
Explanation: Number of protons in
the nucleus is called atomic number
Z. it is unique for each chemical
element, and represents both the
number of positive charges on the
central massive nucleus of the atom
and the number of electrons in orbits
around the nucleus.
4. The total number of nucleons in
the nucleus is called _________
a) Atomic number
b) Mass number
c) Electric charge
d) Periodic number

Answer: b
Explanation: The total number of
nucleons in the nucleus is called the
mass number A. Nuclear symbols are
written as zXA
Where X is chemical
symbol. The masses of atoms are
compared on a scale in which an
isotope of 6C12
has a mass of exactly
12.
5. To disrupt a nucleus and separate
in into its component nucleons,
energy must be supplied from
outside and this energy is called?
a) Bonding energy
b) Kinetic energy
c) Binding energy
d) Nuclear energy
Answer: c
Explanation: To disrupt a nucleus and
separate in into its component
nucleons, energy must be supplied
from outside and this energy is called
Binding energy. The nuclear force
acts only when the nucleons are very
close to each other and binds them
into compact stable structure.
6. The net neutrons produced per
initial neutron accounting for all
possible losses is called?
a) Bombardment
b) Half life
c) Multiplication factors
d) Covalent bond
Answer: c
Explanation: The net neutrons
produced per initial neutron
accounting for all possible losses is
called multiplication factor (K). If: K <
1 = system is subcritical.
K = 1 = System is critical.
K > 1 = system is super critical.
7. What is the time during which one
half of a number of radioactive
species decays or one half of their
activity ceases?
a) Half Life
b) Super critical state
c) Semi life
d) Critical life
Answer: a
Explanation: Half life is the time
during which one half of a number of
radioactive species decays or one half
of their activity ceases. It is also used
to characterize any type of
exponential and Non-exponential
decay.
8. Which of the following statement
is correct regarding pH Scale?
(i) It is the negative logarithm of H+
ion concentration of a given solution.

(ii) It is the positive logarithm of H+
(iii) It is a 14 point scale.
(iv) pH is an example of an extrinsic
property.
Correct Options are:
A. (i) and (iii)
B. (ii) and (iii)
C. (i), (iii) and (iv)
D. Only (ii)
Answer: C
is correct regarding pH Scale?
(i) It is the negative logarithm of H+
(ii) It is the positive logarithm of H+
(iii) It is a 14 point scale.
(iv) pH is an example of an extrinsic
property.
Correct Options are:
A. (i) and (iii)
B. (ii) and (iii)
C. (i), (iii) and (iv)
D. Only (ii)
Answer: C
10. The tetra-peptide KDEL is well
known as retrieval signal for several
newly synthesized proteins. This
process is mediated through specific
receptor – KDEL interaction. Any
single amino acid change in this tetra-
peptide is not allowed in terms of its
binding with its receptors and its
subsequent retention in specific
organelle whereas; secretory proteins
are devoid of such tetra-peptide.
From this observation indicate the
localization of the receptor of this
tetra-peptide:
(a) Plasma membrane
(b) Golgi
(c) Endoplasmic reticulum
(d) Mitochondria
Answer: c
11. The following statements are
made on DNA replication:
(A) Replication form is a branched
point in a replication ‘eye’ or
‘bubble’.
(B) A replication bubble contains two
replication forks
(C) DNA replication is continuous
according to the interpretation make
by Okazaki
(D) Multiple priming events are
required for both leading and lagging
strands to initiate DNA synthesis.

Chapter – 2 - Cellular Organization

Chart
S. N. TOPIC
LIFE SCIENCE
PAGE
NO.
A. Membrane structure and function
(Structure of model membrane, lipid bilayer and
membrane protein diffusion, osmosis, ion channels, active
transport, membrane pumps, mechanism of sorting and
regulation of intracellular transport,electrical properties of
membranes).
3-73
B. Structural organization and function of intracellular
organelles
(Cell wall, nucleus, mitochondria, Golgi bodies, lysosomes,
endoplasmic reticulum, peroxisomes, plastids, vacuoles,
chloroplast, structure & function of cytoskeleton and its
role in motility).
74-257
C. Organization of genes and chromosomes
(Operon, unique and repetitive DNA, interrupted genes,
gene families, structure of chromatin and chromosomes,
heterochromatin, euchromatin, transposons).
258-327
D. Cell division and cell cycle (Mitosis and meiosis, their
regulation, steps in cell cycle, regulation and control of cell
cycle).
328-352
E. Microbial Physiology
(Growth yield and characteristics, strategies of cell
division, stress response)
353-364

(A) Membrane structure and function
(Structure of model membrane, lipid bilayer and membrane protein diffusion,
osmosis, ion channels, active transport, membrane pumps, mechanism of
sorting and regulation of intracellular transport,electrical properties of
membranes).
Membrane, in biology, the thin layer that forms the outer boundary of a
living cell or of an internal cell compartment. The outer boundary is the plasma
membrane, and the compartments enclosed by internal membranes are
called organelles. 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.
Molecular view of the cell 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 a 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 bind to specific molecules on one
side of a membrane 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.
Plasma Membrane
Plasma membrane or plasma-lemma is a bio membrane that occurs on the
outside of the cytoplasm in both prokaryotes and eukaryotic cells.
It separates the cellular protoplasm from its external environment. Prokaryotic
cells do not have internal membranous partitions. The latter occur in eukaryotic
cells as covering of several cell organelles like nucleus, mitochondria, plastids,
lysosomes, Golgi bodies, peroxisomes, etc.
Bio membranes line the endoplasmic reticulum. They also occur on thylakoids
inside plastids or cristae inside the mitochondria. Vacuoles are separatzd from
cytoplasm by a membrane called tonoplast. All bio membranes are dynamic in
nature, continually showing changes in their form, size, structure and function.
Plasma membrane was discovered by Schwann (1838). It was named as cell
membrane by Nageli and Cramer (1855). The membrane was given the name of
plasma lemma by Plowe (1931).
Chemical Nature of Membranes
Chemically a bio membrane consists of lipids (20—40%), proteins (59—75%) and
carbohydrates (1—5%). The important lipids of the membrane are phospholipids
(some 100 types), sterols (e.g., cholesterol), glycolipids, sphingolipids (e.g.,
sphingomyelin, cerebrosides).
Carbohydrates present in the membrane are branched or un-branched
oligosaccharides, e.g., hexose, fucose, hexoamine, sialic acid, etc. Proteins can be
fibrous or globular, structural, carrier, receptor or enzymatic. About 30 kinds of
enzymes have been recorded in different bio membranes, e.g. phosphatases,
ATP-ase esterases, nucleases, etc.

The lipid molecules are amphiatic or amphipathic, that is, they possess both polar
hydrophilic (water loving) and nonpolar hydrophobic (water repelling) ends. The
hydrophilic region is in the form of a head while the hydrophobic part contains
two tails of fatty acids.
Hydrophobic tails usually occur towards the centre of the membrane. Protein
molecules also possess both polar and nonpolar side chains. Usually their polar
hydrophilic linkages are towards the outer side. The nonpolar or hydrophobic
linkages are either kept folded inside or used to establish connections with
hydrophobic part of the lipids.
Molecular Structure of Plasma Membrane!
All biological membranes, including the plasma membrane and the internal
membranes of eukaryotic cells, have a common overall structure: they are
assemblies of lipid and protein molecules held together by non-covalent
interactions.
The lipid molecules are arranged as a continuous double layer 4 to 5 nm thick.
This lipid bilayer provides the basic structure of the membrane and serves as a
relatively impermeable barrier to the flow of most water-soluble molecules.
The protein molecules are “dissolved” in the lipid bilayer and mediate the various
functions of the membrane; some serve to transport specific molecules into or
obit of the cell; others are enzymes that catalyze membrane associated reactions;
and still others serve as structural links between the cell’s cytoskeleton and the
extracellular matrix, or as receptors for receiving and transuding chemical signals
from the cell’s environment.
All cell membranes are dynamic, fluid structures: most of their lipid and protein
molecules are able to move about rapidly in the plane of the membrane.
Membranes are also asymmetrical structures: the lipid and protein compositions
of the two faces differ from one another in ways that reflect the different
functions performed at the two surfaces.

Although the specific lipid and protein components vary greatly from one type of
membrane to another, most of the basic structural and functional concepts are
applicable to intracellular membranes as well as to plasma membranes.
After considering the structure and organization of the main constituents of
biological membranes- the lipids, proteins and carbohydrates-we will discuss the
mechanisms cell employ to transport small molecules across their plasma
membranes and the very different mechanisms they use to transfer
macromolecules and larger particles across this membrane.
The Lipid Bilayer
The first indication that the lipid molecules in biological membranes are organized
in a bilayer came from an experiment performed in 1925. Lipids from red blood
cell membranes were extracted with acetone and floated on the surface of water.
The area they occupied was then decreased by means of a movable barrier until a
monomolecular film (a monolayer) was formed.
This monolayer occupied a final area about twice the surface area of the original
red blood cells, because the only membrane in a red blood cell is the plasma
membrane. The experimenters concluded that the lipid molecules in this
membrane must be arranged as a continuous bilayer.
The conclusion was right but it turned out to be based on two wrong assumptions
that fortuitously compensated for each other. On the one hand, the acetone did
not extract the entire lipid. On the other hand, the surface area calculated for the
red blood cells was based on dried preparations and was substantially less than
the true value seen in wet preparations.
Therefore, the conclusions drawn from this experiment had a profound influence
on cell biology; as a result, the lipid bilayer became an accepted part of most
models of membrane structure, long before its existence was actually established.

Several types of models have been put forward to explain the structure of a
biomembrane. The more important are Lamellar and Mosaic.
Lamellar Models (= Sandwich Models)
They are the early molecular models of bio membranes. According to these
models, bio membranes are believed to have a stable layered structure.
Danielli and Davson Model: The first lamellar model was proposed by James
Danielli and Hugh Davson in 1935 on the basis of their physiological studies.
According to Danielli and Davson, a biomembrane contains four molecular layers,
two of phospholipids and two of proteins. Phospholipids form a double layer.
The phospholipids bilayer is covered on either side by a layer of hydrated globular
or a-protein molecules. The hydrophilic polar heads of the phospholipid
molecules are directed towards the proteins. The two are held together by
electrostatic forces. The hydrophobic nonpolar tails of the two lipid layers are
directed towards the centre where they are held together by hydrophobic bonds
and van der Waals forces.

Features of the Davson–Danielli Model
 Danielli and Davson, proposed a model, called sandwich model, for
membrane structure in which a lipid bilayer was coated on its either side
with hydrated proteins (globular proteins).
 Hence, the plasma membrane might be composed of two lipid-protein
bilayers—one facing the interior of the cell and the other facing the
external milieu.
 In this arrangement, the association between the surface proteins and
bimolecular lipid leaflet would be maintained primarily by electrostatic
interactions between the polar ends of each lipid molecule and charged
amino acid side chains of the polypeptide layers.
 Either electrostatic or van der Waals bonds could bind other groups to
the outer protein surface.
 Danielli and Davson proposed that such a membrane would exhibit
selective permeability, being capable of distinguishing between
molecules of different size and solubility properties and also between
ions of different charge.
 From the speed at which various molecules penetrate the membrane,
they predicted the lipid bilayer to be about 6.0 nm in thickness, and

Chapter – 2 - Cellular Organization MCQs

1. What is the basic functional and
structural unit of organisms?
a) Nucleus
b) DNA
c) Cell
d) Gene
Answer: c
Explanation: Cell is the basic
structural and functional unit of life.
It is a compartment filled with an
aqueous solution along with several
organelles which perform the
essential function of life and is
surrounded by the cell membrane.
2. Who was the first person to
describe various forms of bacteria?
a) Robert Hooke
b) Schwann and Schleiden
c) Antonie van Leeuwenhoek
d) Peter
Answer: c
Explanation: Antonie Van
Leeuwenhoek from the Netherlands
sold buttons and clothes to earn a
living, in his spare time grinded
glasses and constructed simple
microscopes. He observed various
forms of bacteria under the
microscope which came from water
in which pepper was soaked and
scrapping of his teeth.
3. Name the Scientists who first
discovered the cell in the piece of
cork?
a) Louis Pasteur
b) Anton van Leeuwenhoek
c) Robert Hooke
d) Rudolf Virchow
Answer: c
Explanation: Robert Hooke was the
first scientist who discovered the cells
in the piece of cork and also given the
term of the cell. He published his
work in his famous book,
Micrographia.
4. What is the permeability of the
plasma membrane?
a) Selectively permeable
b) Impermeable
c) Single phase flow
d) Highly permeable
Answer: a
Explanation: Plasma membrane is
selectively permeable as it does not
allow every solute to pass through it.
Hydrophobic molecules and small
molecules can easily traverse the
plasma membrane while large
molecules and ions cannot cross the
membrane without the help of
transporters.

5. Which of the following is described
by the fluid mosaic model?
a) Nucleus
b) Plasma membrane
c) Endoplasmic reticulum
d) Ribosome
Answer: b
Explanation: Jonathan Singer and
Garth Nicolson in 1972, proposed a
fluid mosaic model for the structure
and composition of the plasma
membrane. This model is now
accepted worldwide for the plasma
membrane study.
6. Mark the component which is not
the part of lipid bilayer?
a) Glycerol or Sphingosine
b) Fatty acids
c) Tryptophan and methionine
d) Phosphate
Answer: c
Explanation: Phospholipids are
composed of two types of
components one is hydrophobic and
other is hydrophilic. The fatty acid
component is only hydrophobic while
rest of the molecules is hydrophilic
i.e. glycerol, phosphate, and alcohol
attached to phosphate.
7. What is the name of the hollow
sphere formed by lipid bilayer?
a) Cholesterol
b) Lipid raft
c) Micelle
d) Liposome
Answer: d
Explanation: Liposomes are closed,
solvent filled and self-sealing vesicle
which is bound only by a single
bilayer and forms a hollow sphere.
8. Which of the following is ABC
transport protein that transport lipid
in opposite direction?
a) ATPase
b) Scramblase
c) Floppases
d) Flippase
Answer: c
Explanation: Floppases is ATP
dependent ABC transporter protein
which transports lipids in an opposite
direction while flippase is P-type
ATPase which transports
glycerophospholipid from outer layer
to inner membrane.
9. Out of the following, which is not
an ATP dependent transporter of
lipid?
a) V-type ATPase
b) Scramblase
c) Flippase
d) Floppases

Answer: b
Explanation: Scramblase does not
require ATP but it is activated by
calcium. It moves phospholipids along
its concentration gradient, non-
specifically in either direction and
ensures the monolayer to be equally
populated with phospholipids.
10. Name the technique which is
used to visualize the lateral
movement of lipids?
a) FRAP
b) Microscopy
c) Electrophoresis
d) Spectrometry
Answer: a
Explanation: FRAP is a technique of
fluorescence microscopy which is
used to visualize the rapid lateral
movement of lipids in the bilayer. The
fluidity of lipid bilayer is dependent
upon the amount of lipid content and
temperature.
11. Spectrin and ankyrin are the
example of ___________
a) Polytopic
b) Monotopic
c) Peripheral protein
d) Integral protein
Answer: c
Explanation: Spectrin and ankyrin are
the peripheral proteins present in the
membrane of RBC. Peripheral
proteins are extrinsic proteins bound
to membranes by electrostatic and
hydrogen bond interactions.
12. Glycophorin is a major multi-pass
transmembrane protein of RBC.
a) True
b) False
Answer: b
Explanation: Glycophorin is a single
pass transmembrane protein of RBC.
It was the first transmembrane
protein whose complete amino acid
sequence was determined. These are
present in abundance on the plasma
membrane of RBC.
13. Name the technique which is
used to visualize the distribution of
the protein in the membrane?
a) Patch clamp technique
b) FRAP
c) Freeze-etching
d) Freeze-fracture technique
Answer: d
Explanation: Freeze-fracture
technique is used to visualize the
protein distribution in the membrane
by quickly frozen the specimen at -
196°C and then split with a cold knife

Chapter – 2 - Cellular Organization MCQs For Part C

1. Which of the following is not the
part of modern cell theory?
a) All living things are made up of one
or more cells
b) The cell is a functional and
structural unit of life
c) Energy flow takes place within the
cell
d) All cells do not have the same
chemical composition
Answer: d
Explanation: According to modern
cell theory all cells are basically the
same in chemical composition. The
modern theory also states that the
hereditary information passed from
cell to cell.
is defines polysomes?
a) Lysosomal aggregation
b) Multiple units of ribosomes
c) Attachment of many ribosomes to
common mRNA
d) Attachment of many mRNA to
ribosomes
Answer: c
Explanation: Polysome is also known
as polyribosome, it is a structure
where a single mRNA holds a number
of ribosomes translocating in 5’ to 3’
direction.
3. Arrange the following sequences of
tumor development in the correct
order?
1) Metastasis
2) Progression
3) Promotion
4) Initiation
a) 2, 3, 4, 1
b) 4, 3, 2, 1
c) 1, 2, 3, 4
d) 1, 3, 4, 2
Answer: b
Explanation: Tumor initiation starts
with the change of normal cell to the
cancerous cell then these cancerous
cells travel to other cell and invade
them, it comes under promotion and
progression and then finally tumor is
established.
4. Mark the INCORRECT statement
about nuclear lamina.
a) Filaments present in the inner
membrane of the nucleus
b) Made up of lamin proteins
c) Provide mechanical support to the
nucleus
d) It has bounded with the ribosomes
Answer: d
Explanation: Bounded with the
ribosomes is incorrect for nuclear
lamina as ribosomes present on the

outer membrane of nucleus while
nuclear lamina is a network of an
intermediate filament which is
present on the nuclear side of the
inner membrane of the nucleus.
5. Which of the following is not true
for chromatin?
a) Organized structure of DNA and
protein
b) These are highly condensed DNA
c) It is found in the nucleus
d) It contains a single dsDNA
Answer: a
Explanation: Organized structure of
DNA and protein is incorrect as
chromatin is less condensed and
extended DNA while highly
condensed DNA is of chromosomes.
6. Which of the following is
INCORRECT evidence to support the
endosymbiotic theory?
a) Mitochondria are self-repeating
bodies like microscopic organisms
b) Mitochondria have their own
particular DNA
c) Mitochondrial ribosomes, and
enzymes are similar to the bacteria
d) Mitochondria and bacteria differ in
size
Answer: d
Explanation: Endosymbiotic theory
had supported the fact that
mitochondria have evolved in
eukaryotes by the symbiotic
association of bacteria. Mitochondria
and bacteria differ in size is incorrect
as the size of mitochondria and
bacteria is approximately same.
7. Which of the following is not true
about secondary protein structure?
a) The hydrophilic/hydrophobic
character of amino acid residues is
important to secondary structure
b) The ability of peptide bonds to
form intramolecular hydrogen bonds
is important to secondary structure
c) The alpha helix, beta pleated sheet
and beta turns are examples of
protein secondary structure
d) The steric influence of amino acid
residues is important to secondary
structure
Answer: a
Explanation: The
hydrophilic/hydrophobic character of
amino acid residues is important to
protein tertiary structure rather than
to secondary structure. In secondary
structure, it is the steric size of the
residues that are important and
residues are positioned to minimize
interactions between each other and
the peptide chain.

8. Which of the following feature is
the same in cilia and flagella?
a) Help in locomotion
b) Wave-like motion
c) Occurring all over the surface of
the cell
d) Very small in size
Answer: a
Explanation: Cilia and flagella differ
from each other as cilia are smaller in
size and many in numbers while
flagella are larger in size and very less
in numbers. Only the function of
them is same as they both help in
locomotion.
9. Which of the following serves as a
bactericidal agent?
a) Ribonuclease
b) Lysozyme
c) Cytochrome c
d) Myoglobin
Answer: b
Explanation: Lysozyme can lyse, or
degrade, bacterial cell walls, so it
serves as a bactericidal agent.
is false?
a) Lysozyme has S-S linkage
b) Ribonuclease has S-S linkage
c) Heme group in cytochrome c is
covalently linked to the protein on
two sides
d) Ribonuclease has SH-SH linkage
Answer: d
Explanation: Lysozyme and
ribonuclease have disulfide linkages.
11. Arrange the following sequence
of extracellular signaling in the
correct order?
1) Transport of signal to a target
2) Start of signal transduction
pathways
3) Signaling cell synthesize and
release signaling molecules
4) Binding of the signal to the specific
receptor
a) 2, 3, 4, 1
b) 3, 1, 4, 2
c) 1, 2, 3, 4
d) 1, 3, 4, 2
Answer: b
Explanation: Specific extracellular
signaling molecules are defined for
each cell. Extracellular signaling
involves the synthesis and release of
signal molecules, which bind to the
specific receptor and initiate signal
transduction pathway.
12. Which of the following signaling
pathway is followed by T-
lymphocytes in response to antigenic
stimulation?

Chapter – 3 - Fundamental Processes

Chart
S. N. TOPIC
LIFE SCIENCE
PAGE
NO.
A. DNA replication, repair and recombination
(Unit of replication, enzymes involved, replication origin and
replication fork, fidelity of replication, extrachromosomal
replicons, DNA damage and repair mechanisms, homologous
and site-specific recombination).
3-67
B. RNA synthesis and processing
(transcription factors and machinery, formation of initiation
complex, transcription activator and repressor, RNA
polymerases, capping, elongation, and termination, RNA
processing, RNA editing, splicing, and polyadenylation,
structure and function of different types of RNA, RNA
transport).
68-142
C. Protein synthesis and processing
(Ribosome, formation of initiation complex, initiation factors
and their regulation, elongation and elongation factors,
termination, genetic code, aminoacylation of tRNA, tRNA-
identity, aminoacyl tRNA synthetase, and translational proof-
reading, translational inhibitors, Post- translational
modification of proteins).
143-215
D. Control of gene expression at transcription and translation
level
(regulating the expression of phages, viruses, prokaryotic and
eukaryotic genes, role of chromatin in gene expression and
gene silencing).
216-291

(A) DNA replication, repair and recombination
(Unit of replication, enzymes involved, replication origin and replication fork,
fidelity of replication, extrachromosomal replicons, DNA damage and repair
mechanisms, homologous and site-specific recombination).
DNA Replication
Meaning of DNA Replication
One of the most important
properties of DNA functioning as
the genetic material is that it can
make exact copies of itself
(autocatalytic function) forming
the basis for transmission of
hereditary characters it controls.
This process is called replication.
Replication of a DNA molecule
gives rise to two identical
daughter molecules, fulfilling the
criterion of autocatalytic function.
Measurements of DNA content
during the divisional cycle of cells
shows that DNA replication takes
place at a specific portion of
interphase—the ‘S’ phase.
Every time a cell divides—just
prior to cell division, the DNA of
the cell must duplicate so that
each of the two newly forming
cells receives exactly the same
complement of DNA and

therefore the same set of genes—both quantitatively and qualitatively—as was
contained in the parent.
Replication of a DNA leads to the duplication of the entire chromosome once for
every cell division cycle. As a result each chromosome exists as a pair of
chromatids joined together by a centromere and they are separated equally
during anaphase into newly forming daughter cells. Hence both chemical nature
and the total amount of DNA in similar kind of cells remain constant every
generation.
The mechanism of DNA replication is implicit in the Watson-Crick model of DNA.
The two chains of a DNA are united by hydrogen bonds. When the hydrogen
bonds break the two chains part and unwind. It starts from one end of DNA to the
other end of DNA.
One by one each purine base separates from its partner pyrimidine base in each
base pair, but the sugar-phosphate backbones do not break. It looks much like a
zipper opening up. Each parental chain of the DNA then serves as template or
mould for the synthesis of its complementary new chain on itself and forms two
daughter identical DNA double helices (Fig. 20.1).
Modes of DNA Replication:
There are three possible modes of DNA replication:
(i) Semiconservative;
(ii) Conservative; and
(iii) Dispersive.
i. Semiconservative:
The semiconservative mode of DNA replication was suggested (1953) by Watson
and Crick along with the double-helix model of DNA. Here the replication of DNA
involves the progressive separation of the two strands of DNA molecules by
breaking up of hydrogen bonds between base pairs.

Each strand, acting as template, synthesizes their complementary new strand on
itself taking raw materials from the nuclear sap. Thus two daughter DNA helices
are formed. Each daughter DNA helix has one old or parental and one new strand.
It indicates that in each daughter DNA helix, one parental strand is retained and
conserved while its complementary strand is new. Hence, according to this mode
of DNA replication, the parental DNA is partially conserved in each new daughter
DNA molecule. So this mode of DNA replication is called semiconservative
replication [Fig. 20.2(a)].

Experimental Evidences for Semiconservative Replication:
Although three possible modes of DNA replication were proposed, the
semiconservative mode of DNA replication has been widely accepted. For this
acceptance, experimental proof or evidence is needed to establish that DNA, in
fact, duplicates in that manner.
At the same time it is necessary to rule out several other possibilities. Several
experimental evidences has been presented to explain the mode of DNA repli-
cation but the results of all experiments have proved conclusively that DNA
replication is semiconservative.
The experimental evidences are:
(a) Meselson-Stahl Experiment;
(b) Cairns’ autoradiography experiment, and
(c) Taylor’s Experiment.
a. Meselson-Stahl Experiment:
The experimental evidence for semiconservative replication of DNA was first
demonstrated by Mathew Meselson and Franklin Stahl in 1958. They grew cells of
the bacterium Escherichia coli on a medium that contained 15
N (a heavy isotope
of 14N) in the form of ammonium chloride (NH4C1).
The cells of E. coli were grown for 14 cell generation so that the cells used the 15
N
to synthesise bases which were then incorporated into DNA. DNA having 15N has a
detectable higher density (1.724 gm/cm2) than that having 14N (1.710 gm/cm2).
Therefore, they are called heavy and light DNA, respectively. Heavy and light DNA
can be separated readily through equilibrium density gradient centrifugation
where they form distinct band in the centrifuge tube (Fig. 20.3).

The cells of E. coli were then sub-cultured and grown to a medium containing
normal 14 N. The transfer of cell to medium containing normal 14 N was followed
by extraction of DNA from cells after zero, one, two, three etc. cell generations
(one cell generation represents the time during which all the cells undergo one
cell division).
The extracted DNAs in each cell generation were analysed in cesium chloride
(CsCl) density gradient.

DNA that containing 15
N in both strand (heavy DNA) forms a band in the CsCl
density gradient at a higher density position than that contains 14
N in both strand
(light DNA). After one generation of growth in 14
N medium, the DNA bands at an
intermediate (hybrid DNA) density.
Such hybrid DNA contains 15N in one strand and 14N in the other strand. After two
generations of growth in 14N medium, half of the DNA bands are seen at the
hybrid density and half band at light density.
It may be pointed out that according to the conservative mode of replication, no
intermediate band will appear after one generation. Only heavy and light bands
would be formed. Similarly, the dispersive mode of replication would make only
one band having identical density. No light or intermediate bands would be
formed.
Therefore, the result of Meselson and Stahl’s experiment clearly explains the
semiconservative mode of DNA replication, while the expectation of other mode
of replication (conservative, dispersive) are not fulfilled.
Messelson and Stahl (1958) cultured bacteria E. coli in a cultural medium
containing 15
N isotopes 15
NH4 Cl (15
N is heavy isotope of nitrogen) of nitrogen.
After the replication of DNA of E. coli for many generations in 15
N medium, it was
found that both strands of DNA contained 15
N as constituent of purines and
pyrimidines.
This heavy DNA molecule could be distinguished from the normal DNA by
centrifugation in a cesium chloride (CsCl) density gradient. Being 15N not a
radioisotopic isotope, it can be separated from 14
N only based on densities.

Chapter – 3 - Fundamental Processes MCQs

1. Control of gene expression in
eukaryotic cells occurs at which
level(s)?
a) only the transcriptional level
b) epigenetic and transcriptional
levels
c) epigenetic, transcriptional, and
translational levels
d) epigenetic, transcriptional,
post-transcriptional,
translational, and post-
translational levels
Answer: d
Explanation: Control of gene
expression in eukaryotic cells occurs
at epigenetic, transcriptional, post-
transcriptional, translational, and
post-translational levels.
2. Post-translational control refers to
the:
a) regulation of gene
expression after
transcription
b) regulation of gene
expression after translation
c) control of epigenetic
activation
d) period between
transcription and
translation
Answer: b
Explanation: Post-translational
control refers to the regulation of
gene expression after translation
3. What is DNA replication?
a) Conservative
b) Non-conservative
c) Semi-conservative
d) None of the mentioned
Answer: c
Explanation: Each DNA strand serves
as a template for the synthesis of a
new strand, producing two new DNA
molecules, each with one new strand
and one old strand.
4. Semi-conservative DNA replication
was first demonstrated in
____________
a) Drosophila melanogaster
b) Escherichia coli
c) Streptococcus pneumonae
d) Drosophila melanogaster
Answer: a
Explanation: Semi-conservative DNA
replication was first demonstrated in
E. coli.
5. Eukaryotes differ from prokaryote
in mechanism of DNA replication due
to ____________
a) Use of DNA primer rather than

RNA primer
b) Different enzyme for synthesis of
lagging and leading strand
c) Discontinuous rather than semi-
discontinuous replication
d) Unidirectional rather than semi-
discontinuous replication
Answer: c
Explanation: In eukaryotes one strand
of DNA is synthesized continuously
but the other one is made of Okazaki
fragments.
6. Which of the following enzymes
remove supercoiling in replicating
DNA ahead of the replication fork?
a) DNA polymerases
b) Helicases
c) Primases
d) Topoisomerases
Answer: d
Explanation: Strand separation
creates topological stress in the
helical DNA structure which is
relieved by the action of
topoisomerases.
7. DNA unwinding is done by
____________
a) Ligase
b) Helicase
c) Topoisomerase
d) Hexonuclease
Answer: b
Explanation: These enzymes move
along the DNA and separate the
strands using chemical energy from
ATP.
8. Which of the following enzymes is
the principal replication enzyme in E.
coli?
a) DNA polymerase I
b) DNA polymerase II
c) DNA polymerase III
d) None of the mentioned
Answer: c
Explanation: Only DNA pol III is the
principal replication enzyme in E. coli.
9. Which enzyme used to join bits of
DNA?
a) DNA polymerase
b) DNA ligase
c) Endonuclease
d) Primase
Answer: b
Explanation: DNA ligase can be used
to join the nicked sites.
10. Double-helix structure of DNA is
discovered by___________
a) Gobind Khurana
b) Nirenberg
c) Watson and Crick
d) Darwin

Answer: c
Explanation: In 1953, Watson and
Crick worked out on the double –
helix structure of DNA and find out
the complementary nature of two
strands.
11. Base sequence of each parental
strand considered to synthesis new
complementary strand.
a) True
b) False
Answer: a
Explanation: The two strands of DNA
are separated without breakage of a
covalent bond and its base sequence
act as the template strand to
synthesize a new complementary
strand.
12. What is a mode of replication in
E.coli?
a) Intermediate
b) Dispersive
c) Conservative
d) Semiconservative
Answer: d
Explanation: Meselson and Stahl in
1958 conducted an experiment and
demonstrated the semiconservative
replication of DNA in E.coli.
13. What is the origin of replication?
a) Particular site at which DNA
replication starts
b) Site which prevents initiation
c) Random location on the DNA
d) Site at which replication
terminated
Answer: a
Explanation: Origin of replication is
particular sites on DNA as replication
does not start at random sites.
Replication starts from a particular
site and proceeds bidirectionally or
unidirectionally till the terminus site.
14. How many numbers of replicon is
found in E.coli?
a) Five replicon
b) Two replicon
c) Single replicon
d) Multiple replicon
Answer: c
Explanation: E.coli is monorepliconic
and have single replicon while
eukaryotic cells contain many
replication origins on a single
chromosome and called
multirepliconic.
15. Which of the following protein
does not involve in the initiation of
replication?
a) DnaA

Chapter – 3 - Fundamental Processes MCQs For Part C

1. You grow a bacterial culture in a
media containing N15 and transfer it
to a media with N14
. After two rounds
of replication you perform a CsCl
density gradient centrifugation of the
DNA. How many bands will you
observe what will be their intensity?
a) One, very intense
b) Two, equally intense
c) Three with middle one more
intense than upper and lower
d) Three equally intense
Answer: b
Explanation: In semi conservative
replication initially the DNA was N15
-
N15
. After 1st round of replication
both strands were N14
-N15
, making
only a single band as they have same
density. In the next round we will get
N14
N14
, and N14
-N15
making two bands
which are equally intense for having
1:1 concentration.
2. Which of the following is true
about DNA polymerase?
a) It can synthesize DNA in the 5’ to 3’
direction
b) It can synthesize DNA in the 3’ to
5’ direction
c) It can synthesize mRNA in the 3’ to
5’ direction
d) It can synthesize mRNA in the 5’ to
3’ direction
Answer: a
Explanation: DNA pol can synthesize
only a new DNA strand not m-RNA. It
can do this in the 5’ to 3’ direction.
3. What is the reaction in DNA
replication catalyzed by DNA ligase?
a) Addition of new nucleotides to the
leading strand
b) Addition of new nucleotide to the
lagging strand
c) Formation of a phosphodiester
bond between the 3’-OH of one
Okazaki fragment and the 5’-
phosphate of the next on the lagging
strand
d) Base pairing of the template and
the newly formed DNA strand
Answer: c
Explanation: DNA ligase catalyzes the
formation of a phosphodiester bond
between 3’-OH of one Okazaki
fragment and 5’-phosphate of the
next.
4. In an experiment you take a DNA in
vitro and attempt to replicate it.
Which combination will you add to
your DNA to get the maximum
replication product?

a) Dna a, Dna b, HU, SSB,
topoisomerase I, polymerase I
b) Dna a, Dna b, HU, SSB, polymerase
III
c) Dna a, Dna b, Dna c, HU ,SSB
polymerase I
d) Dna a, Dna b, Dna c, HU, SSB,
polymerase III
Answer: c
Explanation: DNA pol I has primase
activity which is mandatory for
starting DNA replication. As pol III
lacks primase activity it will not be
able to initiate replication. Also in
vitro(specially in open DNA strand)
topoisomerase doesn’t have much
role to play but Dna c is a must for
replication as it loads the helicase.
5. In an experiment you use DNA pol I
– Klenow fragment. When all other
requisites for replication are added,
then what will be the effect on the
newly replicated DNA? Consider
leading strand only.
a) No difference from intact DNA pol I
replication
b) Replication will be slower
c) Replication will be error prone
d) DNA produced will be shorter
Answer: d
Explanation: Klenow fragment
provides the 5’ -> 3’ exonuclease
activity used to remove the primer. In
its absence the primer remains and
hence DNA produced is shorter (i.e.
original length-length of primer).
6. If the events in post transcriptional
modification are listed as-
i) Polyadenylation
ii) capping
iii) splicing
What would be the correct
sequence?
a) i->ii->iii
b) iii->ii->i
c) i->iii->ii
d)ii->i->iii
Answer: d
Explanation: Post transcriptional
modification is very strictly
synchronized process and no next
step takes place unless the preceding
one is complete. The sequence is
1st
adding cap, then Polyadenylation
and then splicing.
7. If we mutate the DNA ligase and
observe the length of the replicated
strands in different time slots after
replication initiation, what will we
observe?

a) The DNA will gradually increase in
length till it is fully replicated
b) Small fragments of DNA will be
obtained increasing in number with
time
c) Mixture of small and long
Fragments of definite length from the
start whose concentration simply
increases with time
d) At first small fragment, then two
separate bands showing long
fragment with increasing length and
short fragments of definite length.
Answer: d
Explanation: The small fragments are
the Okazaki fragments of lagging
strand while the longer is the leading
stand DNA. While leading strand
grows in length the Okazaki
fragments in absence of ligation to
each other results in small fragments
of definite length.
8. Acyclovir is a drug used to treat
viral infection by impairing its
replication. Why will it not effect
bacterial replication as well?
a) Bacteria under viral attack don’t
replicate
b) Viral polymerase binds to it and
thus can’t perform its function
c) Virus uses it in a polymerization
d) Cellular mechanism deactivates it
Answer: c
Explanation: Acyclovir is a GMP
analogue that cellular mechanism
activates to GTP analogue, which the
virus uses as a substrate while
polymerizing. However, as it lacks 3’-
OH it terminates the replication
process. Thus, cellular processes
activate this drug, yet its specificity to
viral polymerase protects the cell.
9. DNA replication in the two strands
proceed in opposite direction as they
are aligned oppositely with respect to
3’ and 5’ ends
( 5’——————————-3’
3’——————————-5’).
In this context which of the following
is true.
a) The two arms of the DNA Pol are
exactly same with same orientation
b) The two arms of the DNA Pol are
exactly same with opposite
orientation
c) The two arms of the DNA Pol have
different catalytic mechanism i.e. one
polymerizes 3’ -> 5’ other 5’ -> 3’
d) The two arms are isomers i.e. they
have different arrangement of the
subunits.

Chapter – 4 - Cell communication and cell signaling

Chart
S. N. TOPIC
LIFE SCIENCE
PAGE
NO.
A. Host parasite interaction
Recognition and entry processes of different pathogens like
bacteria, viruses into animal and plant host cells, alteration
of host cell behavior by pathogens, virus-induced cell
transformation, pathogen-induced diseases in animals and
plants, cell-cell fusion in both normal and abnormal cells.
4-40
B. Cell signaling
Hormones and their receptors, cell surface receptor,
signaling through G-protein coupled receptors, signal
transduction pathways, second messengers, regulation of
signaling pathways, bacterial and plant twocomponent
systems, light signaling in plants, bacterial chemotaxis and
quorum sensing.
41-80
C. Cellular communication
Regulation of hematopoiesis, general principles of cell
communication, cell adhesion and roles of different
adhesion molecules, gap junctions, extracellular matrix,
integrins, neurotransmission and its regulation.
81-153
D. Cancer
Genetic rearrangements in progenitor cells, oncogenes,
tumor suppressor genes, cancer and the cell cycle, virus-
induced cancer, metastasis, interaction of cancer cells with
normal cells, apoptosis, therapeutic interventions of
uncontrolled cell growth.
154-220

E. Innate and adaptive immune system
Cells and molecules involved in innate and adaptive
immunity, antigens, antigenicity and immunogenicity. B and
T cell epitopes, structure and function of antibody
molecules. generation of antibody diversity, monoclonal
antibodies, antibody engineering, antigen-antibody
interactions, MHC molecules, antigen processing and
presentation, activation and differentiation of B and T cells,
B and T cell receptors, humoral and cellmediated immune
responses, primary and secondary immune modulation, the
complement system, Toll-like receptors, cell-mediated
effector functions, inflammation, hypersensitivity and
autoimmunity, immune response during bacterial
(tuberculosis), parasitic (malaria) and viral (HIV) infections,
congenital and acquired immunodeficiencies, vaccines
221-383

HOST PARASITE INTERACTION
• Parasitism is a type of symbiotic relationship between two organisms: a
parasite, usually the smaller of the two, and a host, upon which the
parasite is physiologically dependent.
• The host in a host-parasite interaction is the animal that maintains the
parasite.
Types of Parasites
There are two major types of parasites, endoparasites, and ectoparasites,
according to location.
• Endoparasites live within the body of the host at sites such as the
alimentary tract, liver, lungs, and urinary bladder.
• Ectoparasites are attached to the outer surface of the host or are
superficially embedded in the body surface.
Types of Hosts
The host may be classified as:

• A definitive host, if the parasite attains sexual maturity therein;
• An intermediate host, if it serves as a temporary, but essential,
environment for the development of the parasite and/or its
metamorphosis short of sexual maturity; and
• A transfer or paratenic host, if it is not necessary for the completion of
the parasite’s life cycle but is utilized as a temporary refuge and a
vehicle for reaching an obligatory, usually the definitive, host in the
cycle.
The Host-Parasite Interaction
• The host and parasite are in dynamic interaction, the outcome of which
depends upon the properties of the parasite and of the host.
• The parasite has its determinants of virulence that allow it to invade
and damage the host and to resist the defenses of the host.
• The host has various degrees of resistance to the parasite in the form of
the host defenses.
The Host Defense
• A healthy animal can defend itself against pathogens at different stages
in the infectious disease process.
• The host defenses may be of such a degree that infection can be
prevented entirely.
• Or, if an infection does occur, the defenses may stop the process before
the disease is apparent.
• At other times, the defenses that are necessary to defeat a pathogen
may not be effective until an infectious disease is well into progress.
Defense Mechanisms
• Immune defense against pathogenic organisms is tailored to meet the
broad range of their extracellular and intracellular lifecycles within the
host environment.
• Defense against bacterial agents primarily utilizes antibodies, antibodies
and complement, and direct cytotoxic mechanisms to control infection.

• Defense against mycobacteria requires T-cell–mediated DTH responses
that result in granuloma formation. Antifungal defenses also use similar
mechanisms to control organisms.
• Defense against viral agents requires antibody neutralization upon
initial infection, and cytotoxic mechanisms regulated by NK cells and
CTLs when expanding within cellular compartments.
• Defense against protozoal agents incorporates DTH and antibody to
limit growth.
• Defense against helminths and larger multicellular organisms utilizes
atopic and ADCC-dependent reactions, as well as granulomatous
responses, to sequester and destroy deposited eggs.
• Organisms have evolved multiple mechanisms to evade host responses,
ranging from antigenic modulation of surface proteins to direct
immunosuppressive action on specific cellular subsets.
The Parasite Interaction
Releasing the determinants of virulence
• Parasites are able to produce disease because they possess
certain structural or biochemical or genetic traits that render them
pathogenic or virulent.
• The sum of the characteristics that allow a given bacterium to produce
disease are the pathogen’s determinants of virulence.
• Some pathogens may rely on a single determinant of virulence, such as
toxin production while others maintain a large repertoire of virulence
determinants and consequently are able to produce a more complete
range of diseases that affect different tissues in their host.
Avoiding Host Defences
• In the ongoing evolution of host-parasite relationships between humans
and their infections, infectious organisms have developed ingenious ways
to avoid immune defense mechanisms.

• Virtually all classes of infectious agents have devised ways to avoid host
defenses.
• Organisms may locate in niches (privileged sites) not accessible to immune
effector mechanisms (protective niche) or hide by acquiring host molecules
(masking). They may change their surface antigens (antigenic modulation),
hide within cells, and produce factors that inhibit the immune response
(immunosuppression) or fool the immune system into responding with an
ineffective effector mechanism (immune deviation).
• Also, bacteria have evolved to evade different aspects of phagocyte-
mediated killing.
For example, they may
• Secrete toxins to inhibit chemotaxis
• Contain outer capsules that block attachment
• Block intracellular fusion with lysosomal compartments, and
• Escape from the phagosome to multiply in the cytoplasm.
• Viral entities also subvert immune responses, usually through the presence
of virally encoded proteins.
• Some of these proteins block effector functions of antibody binding, block
complement-mediated pathways, inhibit activation of infected cells, and
can downregulate major histocompatibility complex class I antigens to
escape CTL killing.
The Result of Interaction
• In case the host defenses are of an effective degree, it can overcome
the parasite and that the infection can be prevented entirely.
• Or, if an infection does occur, the defenses may well stop the process
before the disease is apparent.
• At other times, the defenses that are necessary to defeat a pathogen
may not be effective until an infectious disease is well into progress.
• However, the ultimate endpoint of coevolution of the human host and
its infectious organisms results in an eventual mutual coexistence with
most environmental organisms.

• No better evidence is the loss of this coexistence when the immune
mechanisms do not function properly. Then, organisms that do not
normally cause the disease to become virulent.
• In a fully evolved, mature relationship, host and infectious agent initially
coexist with limited detrimental effects.
• Thus, the ultimate evolution of the host-parasite relationship is not
“cure” of infection by complete elimination of the parasite, but at least
mutual coexistence without deleterious effects of the parasite on the
host.
• In fact, in many human infections, the infectious agent is never fully
destroyed and the disease enters a latent state, only to be reactivated
when immune surveillance wanes.
Mechanism of Pathogenesis (in plants)
Pathogenesis is the process of infection or the actual way in which the disease
develops in plant body. Infection is the establishment of a pathogenic
microorganism within the host, following entrance.
It signifies the sum of biological processes which takes place in the host body after
penetration of the pathogen, independent of the fact whether the pathogen
causes a disease or not. As the result of infection visible or latent diseases are
produced in the host plants. The potential capacity of infection of any pathogen is
called its pathogenicity.
The pathogenicity of every pathogen is its specific feature. This characteristic
depends upon the capacity of parasitic adaptation and struggle for existence of
the pathogen. The phenomenon of pathogenesis can be understood easily by
studying the three phases of penetration of the pathogen, viz., pre-penetration,
during penetration and post-penetration phases. These three phases of
penetration are briefly discussed below.
(I) Pre-penetration Changes: The pre-penetration phase includes the growth of
the pathogen before actual entry or penetration into the host. Spores of various

Chapter – 4 - Cell communication and cell signaling MCQs

1. Degree of pathogenicity is referred
to as _________________
a) infection
b) virulence
c) avirulent
d) attenuated
Answer: b
Explanation: Various strains of
pathogenic species differ with regard
to their degree of pathogenicity, i.e.,
with regard to their virulence.
2. Which type of strains are used in
vaccines?
a) virulent
b) avirulent
c) attenuated
d) non-pathogenic
Answer: c
Explanation: Attenuated strains are
widely used as vaccines to elicit
immunity to various diseases.
3. The LD50 dose can be determined
more precisely than LD100 dose.
a) True
b) False
Answer: a
Explanation: The LD50 dose can be
determined more precisely than
LD100 dose because the rate of
change in mortality versus change in
dose is greatest around the point of
50 percent mortality.
4. Microbial adherence is selective in
nature.
a) True
b) False
Answer: a
Explanation: Microbial adherence or
attachment of the pathogen to some
surface of the host is selective:
various pathogens attach only to
certain tissues.
5. When the infection occurs
suddenly and with severe intensity it
is known as ______________
a) chronic
b) fulminating
c) acute
d) localized
Answer: b
Explanation: Fulminating type of
infection occurs suddenly and with
severe intensity. An example is
cerebrospinal meningitis caused by
Neisseria meningitidis.
6. Tuberculosis is which type of
infection?
a) acute
b) chronic

c) primary
d) secondary
Answer: b
Explanation: Chronic infections are
those diseases which has a long
duration like tuberculosis disease.
7. Where does Streptococcus
pyogenes infects in the body to cause
infection?
a) cervix
b) small intestine
c) urethra
d) throat
Answer: d
Explanation: Streptococcus pyogenes,
the causative agent of streptococcal
sore throat, attaches specifically to
the epithelial cells of the throat by
means of cell wall proteins.
8. Vibrio cholerae adheres to the
epithelial cells of the small intestine
by means of ______________
a) pili
b) proteins
c) hemagglutinin
d) hydrogen bonds
Answer: c
Explanation: Vibrio cholerae adheres
to the epithelial cells of the small
intestine of humans by means of
hemagglutinin.
9. Poliovirus attaches to central
nervous system by means of
______________
a) pili
b) proteins
c) hemagglutinin
d) hydrogen bonds
Answer: b
Explanation: There is a protein on the
surface of poliovirus which seems to
be critical for attachment of the virus
to lipid- and glycoprotein- containing
receptors on the host cells; the
attachment is specific for cells of the
intestinal tract and central nervous
system.
10. From which of the following
animal was the material isolated
which was used for the vaccination
for the first time?
a) cat
b) cow
c) pig
d) goat
Answer: b
Explanation: Jenner used the material
isolated from cows to be used as
vaccination and it provided

protection against natural smallpox
infection.
11. Vaccination was invented by
____________
a) Jenner
b) Pasteur
c) Watson
d) Crick
Answer: a
Explanation: In 1796 Jenner first
vaccinated an 8-year old boy with
material removed from cow and it
gave protection against the smallpox
virus.
12. Causative agent of tobacco
mosaic disease was filterable.
a) True
b) False
Answer: a
Explanation: In 1892, Dmitrii
Ivanowski discovered that the
causative agent of tobacco mosaic
disease was filterable. Viruses that
can pass through porcelain filters are
known as filterable viruses.
13. Yellow fever virus can be
attenuated by serial passage on
cultures of ______________
a) embryonated eggs
b) tissue
c) chick embryo tissue
d) pig embryo tissue
Answer: c
Explanation: Max Theiler found in
1937 that virulent yellow fever virus
can be attenuated by serial passage
on cultures of chick embryo tissue.
14. Effective poliomyelitis vaccines
were developed by culturing the virus
of poliomyelitis on the kidney cells of
which animal?
a) cow
b) monkey
c) giraffe
d) pig
Answer: b
Explanation: Enders, Robbins, and
Weller laid the foundation for the
development of effective
poliomyelitis vaccines by culturing
the virus of poliomyelitis on monkey
kidney cells in 1949.
15. For which viral disease, vaccine
has been recently developed through
the use of tissue culture?
a) Measles
b) Mumps
c) Rabies
d) S mallpox

Chapter – 4 - Cell communication and cell signaling MCQs For Part C

1. Match the correct columns.
1 - Adelphous A - Anther of
different stamen is infused state
2 - Syngansious B - Filament of
different stamen is fused
3 - Synandrous C - Stamen is
attached to the petals
4 - Epipelalous D - Anther and
filament both are fused
a) 1-B, 2-A, 3-D, 4-C
b) 1-D, 2-C, 3-A, 4-B
c) 1-C, 2-A, 3-B, 4-D
d) 1-A, 2-D, 3-B, 4-C
Answer: a
Explanation: Sometimes a flower’s
part is fused or attached to each
other and this condition is known as
coalescence of parts. It involves
sepal, petal, stamen, and carpel.
2. Arrange in the correct order.
1) Class
2) Kingdom
3) Phylum
4) Order
5) Genus
6) Family
7) Species
a) 6, 2, 4, 1, 5, 7, 3
b) 7, 1, 3, 4, 5, 6, 1
c) 1, 2, 3, 4, 5, 6, 7
d) 2, 3, 1, 4, 6, 5, 7
Answer: d
Explanation: Classification is the
arrangement of steps represents a
category terms rank or taxonomic
category. Each organism is classified
according to the seven taxonomic
ranks.
3. The a, b, and c respectively in the
following image are
_________________________
a) autocrine, paracrine, endocrine
b) autocrine, endocrine, paracrine
c) endocrine, paracrine, autocrine
d) endocrine, autocrine, paracrine
Answer: a
Explanation: The signaling pathways
in the figure shown are autocrine,
paracrine and endocrine signaling

pathways respectively. All the three
are stimulation pathways in which
messenger molecules reach cell
surface receptors.
4. The two important compounds of
serum that are necessary for cell
culture are __________________
a) insulin, epidermal growth factor
b) insulin, phosphatidylserine
c) tumor necrosis factor, epidermal
growth factor
d) epidermal growth factor,
phosphatidylserine
Answer: a
Explanation: The two important
compounds those are required for
the culture of normal mammalian
cells, are insulin and epidermal
growth factor, present as
components of the serum’s fluid
fraction. However, these are not
required for the culturing of cancer
cells.
5. Arrange the following sequence of
extracellular signaling in the correct
order?
1) Transport of signal to a target
2) Start of signal transduction
pathways
3) Signaling cell synthesize and
release signaling molecules
4) Binding of the signal to the specific
receptor
a) 2, 3, 4, 1
b) 3, 1, 4, 2
c) 1, 2, 3, 4
d) 1, 3, 4, 2
Answer: b
Explanation: Specific extracellular
signaling molecules are defined for
each cell. Extracellular signaling
involves the synthesis and release of
signal molecules, which bind to the
specific receptor and initiate signal
transduction pathway.
6. Arrange the following sequences of
tumor development in the correct
order?
1) Metastasis
2) Progression
3) Promotion
4) Initiation
a) 2, 3, 4, 1
b) 4, 3, 2, 1
c) 1, 2, 3, 4
d) 1, 3, 4, 2
Answer: b
Explanation: Tumor initiation starts
with the change of normal cell to the
cancerous cell then these cancerous
cells travel to other cell and invade
them, it comes under promotion and

progression and then finally tumor is
established.
7. In which of the following situations
will the logarithmic plot of survivors
be constant?
a) physiological conditions are
different
b) cells of microbial population vary
in size
c) age and physiological conditions
are uniform
d) temperature conditions are
different
Answer: c
Explanation: Logarithmic plot reveals
that the death rate is constant when
all conditions are strictly uniform,
including the age and the
physiological condition of all the
microorganisms in the population.
8. Vaccines are used in which form?
a) Live-attenuated vaccines
b) Inactivated vaccines
c) Subunit, recombinant,
polysaccharide, and conjugate
vaccines
d) Attenuated, inactivated, portions
of protein, polysaccharides
Answer: d
Explanation: There are 3 main types
of vaccine: live-attenuated vaccines;
inactivated vaccines; and subunit,
recombinant, polysaccharide, and
conjugate vaccines. The vaccine is
something which will activate the
immune system up to the memory
level. So that memory cells are
produced in the body to protect from
any further infection.
9. Which of the following is a true
statement?
a) IgG is involved in primary immune
response
b) IgM is involved in primary immune
response
c) IgG is involved only in secondary
immune response
d) IgG and IgM both are involved in
primary immune response
Answer: d
Explanation: IgG and IgM are involved
in primary immune response.
10. Which of the following is not the
function of helper T cells is
____________
a) Produce soluble signaling proteins
called cytokines, which include the
interleukins
b) They help activate cytotoxic T cells
to kill infected target cells
c) They help activate B cells to
secrete antibodies and macrophages

Chapter – 5 - Developmental Biology

Chart
S. N. TOPIC
LIFE SCIENCE
PAGE
NO.
A. Basic concepts of development:
Potency, commitment, specification, induction, competence,
determination and differentiation; morphogenetic
gradients; cell fate and cell lineages; stem cells; genomic
equivalence and the cytoplasmic determinants; imprinting;
mutants and transgenics in analysis of development
4-89
B. Gametogenesis, fertilization and early development:
Production of gametes, cell surface molecules in sperm-egg
recognition in animals; embryo sac development and double
fertilization in plants; zygote formation, cleavage, blastula
formation, embryonic fields, gastrulation and formation of
germ layers in animals; embryogenesis, establishment of
symmetry in plants; seed formation and germination.
90-170
C. Morphogenesis and organogenesis in animals:
Cell aggregation and differentiation in Dictyostelium; axes
and pattern formation in Drosophila, amphibia and chick;
organogenesis – vulva formation in Caenorhabditis elegans,
eye lens induction, limb development and regeneration in
vertebrates; differentiation of neurons, post embryonic
development- larval formation, metamorphosis;
environmental regulation of normal development; sex
determination.
171-288
D. Morphogenesis and organogenesis in plants:
Organization of shoot and root apical meristem; shoot and
root development; leaf development and phyllotaxy;
transition to flowering, floral meristems and floral
development in Arabidopsis and Antirrhinum
289-331

E. Programmed cell death, aging and senescence 332-384
(A) Basic concepts of development:
Potency, commitment, specification, induction, competence, determination and
differentiation; morphogenetic gradients; cell fate and cell lineages; stem cells;
genomic equivalence and the cytoplasmic determinants; imprinting; mutants
and transgenics in analysis of development
Developmental biology is the field of biology that studies the processes by which
multicellular organisms grow and develop, controlled by their genes. Knowledge
of normal developmental processes can aid in the understanding of
developmental abnormalities and other conditions such as cancer.
Developmental biology is the science that investigates how a variety of interacting
processes generate an organism’s heterogeneous shapes, size, and structural
features that arise on the trajectory from embryo to adult, or more generally
throughout a life cycle. It represents an exemplary area of contemporary
experimental biology that focuses on phenomena that have puzzled natural
philosophers and scientists for more than two millennia. Philosophers of biology
have shown interest in developmental biology due to the potential relevance of
development for understanding evolution, the theme of reductionism in genetic
explanations, and via increased attention to the details of particular research
programs, such as stem cell biology. Developmental biology displays a rich array
of material and conceptual practices that can be analyzed to better understand
the scientific reasoning exhibited in experimental life science. This entry briefly
reviews some central phenomena of ontogeny and then explores four domains
that represent some of the import and promise of conceptual reflection on the
epistemology of developmental biology.
From the history of development, developmental biology is an old and young
discipline. It was developed on the basis of embryology. It originated in the 1950s

and formally formed an independent discipline in the 1970s. A new discipline
gradually formed in the process of learning molecular embryology which is also
the comprehensive and further development of this discipline. Since the 1980s,
due to the development of disciplines such as genetics, cell biology, and
molecular biology, a large number of new research methods have been applied,
and developmental biology has made great progress. The research content of this
subject includes the occurrence and formation of gametes, fertilization
process, cell differentiation and morphogenesis, including how different cell
groups in the development process are reconfigured and specialized, the
emergence of various cell types, the appearance of the final organ phenotypic
characteristics and the establishment of special functions, the expression, control
and regulation of genes at different developmental stages, the causal relationship
between genotype and phenotypic expression, the relationship between nucleus
and cytoplasm during development, interrelationships between cells, and the
effects of external factors on embryonic development. Among them, cell
differentiation is a core problem in developmental biology.
The research status of developmental biology
Developmental biology is one of the important basic branches of biological
sciences. The research content is infiltrated with many other disciplines,
especially with genetics, cell biology and molecular biology. It uses modern
science and technology to study and analyze the processes and mechanisms of
organisms from spermatogenesis and egg development, fertilization, growth,
aging and death from the molecular level, submicroscopic level and cellular level.
Although there are many species of animals, the development of embryos still has
a similar process, which can be divided into stages of fertilization, cleavage,
morula, blastocyst, gastrula and organ formation. In addition, during the
embryonic development of vertebrates, the characteristics common to various
animals will appear first (such as the skin), and then specialized structures (such
as fish scales) will be developed. In general, the ectoderm forms the epidermis
and nerve tissue. The endoderm forms the intestinal epithelium and the digestive
gland epithelium, which forms bone, muscle, blood, lymph and other connective
tissues. Others are derived from the mesoderm. But there are exceptions: the

sphincter of the eye iridescence does not come from the mesoderm, nor from the
mesenchyme, but from a part of the retina, that is, from the ectoderm. The
smooth muscle of the sweat gland is not from the mesoderm, but from the
ectoderm; the mesenchyme itself is unclear, as it may come from the ectoderm,
or from the mesoderm, or even from the endoderm. Research on developmental
biology needs further advancement, which will help to understand the
developmental mechanisms of organisms.
Development
The process by which a multicellular organism arises from a single cell is known as
development. It is involves a gradual developmental strategy known as epigenesis
whereby the simple embryo, comprising of few cell types organised crudely is
gradually refined to produce a complex organism with many cell types showing
highly detailed organization. Development involves five major process which are
in interlinked: growth, cell division, differentiation, pattern formation and
morphogenesis.
Animal and Plant Development
Animals show great diversity, but early development in majority of the animals
involves a common series of events. Development usually begins with fertilization
after the formation of gametes (gametogenesis). The diploid zygote formed by
fertilization then undergoes cleavage to form blastula.
The next stage of development is gastrulation, which involves a complex series of
cell movements that reorganizes the embryo into three fundamental cell layers,
called the germ layers (ectoderm, mesoderm and endoderm). Gastrulation is
followed by neurulation and organogenesis respectively.
Development in flowering plants begins with double fertilization which produce
the zygote and the endosperm tissue that nourishes the embryo. Fertilization is
followed by a series of stereotyped cell divisions to produce group of cells called
as pre-embryo, attached to the ovule by a suspensor.

There is absence of gastrulation-like stage in plants because relative cell
movement is prevented by the rigid cell walls. Further growth and cell division
produces an embryo organized radially into three fundamental cell layers and
organized radially into a series of organ forming regions corresponding to the
shoot, root and cotyledons of the seedling. After germination, all parts of the
mature plant are produced from two small groups of proliferative cells
established in the embryo, the shoot and root meristems.
A. Growth and Cell Division
Development involves both growth and cell division which can occur
independently. Cell division leads to increase in cell number which is necessary to
allow cells to specialize, organize into patterns and carry-out different functions.
In the earliest stages of animal development, the cell number increases in the
absence of growth.
During the cleavage divisions, there is an increase in cell number without growth,
so that the egg is divided into a series of progressively smaller cells. Later in
development, growth can take place in the absence of cell division, as growth can
be achieved not only by increasing cell numbers, but also by growth of
extracellular structures generated by materials secreted from cells as in the case
of bone and cartilage.
B. Cellular Differentiation
Cellular differentiation, or simply cell differentiation, is the process through which
a cell undergoes changes in gene expression to become a more specific type of
cell. The process of cell differentiation allows multi-cellular organisms to create
uniquely functional cell types and body plans. The process of cell differentiation is
driven by genetics, and their interaction with the environment.
All organisms begin from a single cell. This single cell carries the DNA coding for all
the proteins the adult organism will use. However, if this cell expressed all of
these proteins at once it would not be functional. This cell must divide repeatedly,
and the cells must begin the process of cell differentiation as they divide. The cell

lines begin to emerge, and the cells get more and more specific. Eventually, an
entire organism is formed with hundreds of different cell types from this process
of cell differentiation.
The original mass of cells, which have not undergone differentiation, are known
as stem cells. Unlike normal cell division, which creates two identical daughter
cells, the division of stem cells is asymmetric cell division. In this case, one of the
cells remains identical to the parent stem cell. In the other cell, chemical triggers
activate the process of cell differentiation, and the cell will start to express the
DNA of a specific cell type. Stem cells which can differentiate into entire
organisms are known as embryonic stem cells and are said to be totipotent.
By contrast, the body also has many cells which are only pluripotent. These cells
have already undergone some cell differentiation. These stem cells can only
divide into a narrow range of cell types. Bone marrow, for instance,
contains somatic stem cells which can only become red blood cells. These cells are
necessary for the constant replenishment of blood cells, which are mostly inactive
besides their oxygen-carrying ability.
The fully-developed organism consists of a number of different kinds of cells.
Cellular differentiation is the full sequence of changes involved in the progressive
diversification of cell structure and functions that is the hallmark of development.
Differentiation occurs simultaneously with growth and the two processes cannot
be separated. Normally the differentiation process is irreversible. Almost every
cell of developing embryo multiplies and become different from the original
conditions as well as from one another.
Cell differentiation may simply be described as the process through which a
young and immature cell evolves in to a specialized cell, reaching its mature form
and function. For such unicellular organisms like bacteria, various life functions
occur within a single cell.
That is, such processes as the transport of molecules, metabolism and
reproduction all take place within a single cell given that they are single celled.

However, multicellular organisms require different types of cells for these
processes to be possible.
Here, different types of cells play a specific function given that they have varied
structures. For instance, whereas the nerve cells play a crucial role in the
transmission of signals to different parts of the body, blood cells play an
important role carrying oxygen to different parts of the body.
The differences in structure and functions between the cells mean that they are
specialized cells. To be able to perform different functions, cells have to become
specialized. This becomes possible through the process referred to as cell
specialization.
Differentiation and Development Process in Plants
Plants are different and special living organisms belong to the kingdom Plantae.
They display many distinctive characters from animals. They have different cell
structure and organelles which make them self-sufficient. They are also unique in
their life cycle and development processes which are discussed below.
Plants: Differentiation and Development Process
Differentiation process in Plants

Chapter – 5 - DEVELOPMENTAL BIOLOGY MCQs

1. Drosophila follows which of these
modes of sex determination?
a) XX /XY
b) XX/ XO
c) ZZ/ ZW
d) MM/NN
Answer: a
Explanation: Drosophila follows the
XY system of sex determination while
other modes are seen in other
animals. MM/NN or MN is a system
of blood group and not a system of
sex determination.
2. Which of these genes is
responsible for the development of
sex of Drosophila?
a) Xce
b) Xist
c) XIC
d) Sxl
Answer: d
Explanation: Sxl or sex lethal gene is
responsible for the development of
male or female characters in
Drosophila. Other genes mentioned
work in human beings.
3. The Sxl gene is turned
____________ by a ratio of
_____________for X:A.
a) OFF, 1
b) OFF, 0.5
c) ON, 0.5
d) ON, 0.75
Answer: b
Explanation: The Sxl gene is turned
ON only when the ratio of X:A is 1,
other times it is OFF. An OFF state
produces a male while on state
produces a female.
4. Sxl directly affects _____________
a) SR
b) Dsx
c) Tra
d) Xce
Answer: c
Explanation: Sxl directly affects the
splicing of tra pre-mRNA and
produces a functional gene when Sxl
is turned on. Downstream of this the
female characters are produced. Xce
is present in human and not in
Drosophila.
5. Which of the following is a default
pathway in Drosophila?
a) Development of male characters
b) Repression of male characters
c) Development of female characters
d) All pathways are induced
Answer: a
Explanation: Development of male
characters is like a default pathway in

Drosophila which is turned off by
female specific genes.
6. Which of the following will give a
normal female Drosophila?
a) AAA + XX
b) AA + XXY
c) AA + XY
d) AA + XX
Answer: b
Explanation: In the following case the
X: A ratio is 1 which is required for
developing female characters. In all
the other cases viable female is not
produced.
7. Hormone inhibin is secreted by
______
a) Theca cells
b) Zona pellucida
c) Granulosa cells
d) Corpus luteum
Answer: d
Explanation: Hormone inhibin is
secreted by Corpus luteum. It inhibits
the production of FSG by pituitary
gland.
8. The follicle that ruptures at the
time of ovulation promptly fills with
blood forming is _______
a) Corpus albicans
b) Corpus luteum
c) Corpus haemorrhagium
d) Corpus callosum
Answer: c
Explanation: Corpus haemorrhagium
is a temporary structure formed by
immediately after ovulation from the
ovarian follicle as it collapses and is
filled with blood that quickly clots.
9. Cessation of menstrual cycle is
called __________
a) Ovulation
b) Menopause
c) Parturition
d) Menarche
Answer: b
Explanation: Menopause is the
natural decline in reproductive
hormones when a woman reaches
40s or 50s. It is absence of a
menstrual cycle. It is a gradual
process.
10. Graafian follicle is maintained by
____________
a) FSH
b) Prolactin
c) Estrogen
d) Androgens
Answer: a
Explanation: FSH stands for follicle
stimulating hormone. It is

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