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Structure and Life Cycle of Bacteriophage

Write structure and life cycle of Bacteriophage?


The structure under an electron microscope looks like a tadpole and consists of a head and tail.

(1) Head:

(i) The head is elongated having:

      (a) Pyramidal (having two triangular structures with a common base).

      (b) Hexagonal or

      (c) Prism-shaped structure.

(ii) To it straight tail is attached.

(iii) Head contains double-stranded DNA.

(2) Tail:

The structure of the tail is more complex than the head.

(i) Tail has a core of protein which is surrounded by a sheath of another protein.

(ii) On one side of the sheath is the collar and on the other side is the end plate (Base plate).

(iii) Six tail fibers are attached to the end plate. These fibers are for attachment.

Volume of Phage:

It is about 1/1000 of the host.

Life Cycle of Bacteriophages:

The bacteriophage replicates only inside the bacterial cell. There are many steps in replication.

(1) Attachment (Adsorption) of Phage to the Host Cell:

(i) First of all the bacteriophage attaches to the bacterial cell at the receptor site. The receptor sites are present on the cell wall of the bacterium.

(ii) During attachment, weak chemical union occurs between virion and receptor site.

(2) Penetration:

In this step, the tail releases the enzyme lysozyme. This enzyme dissolves a portion of the bacterial cell wall.

The tail sheath contracts and the tail core is forced into the cell through the cell wall and cell membrane.

The virus injects its DNA into the cell (just as the syringe is used to inject the vaccine).

The protein coat, consisting of head and tail, remains outside the cell.

Many animal viruses enter the host cell as a whole.

A Phage Injecting its DNA in to host

After penetration one of the following cycles take place:

(1) Lytic cycle.

(2) Lysogenic cycle.

(1) Lytic Cycle:

During the lytic cycle following steps occur.

(i) Multiplication:

Soon after entering the bacterium, the viral DNA takes the control of the biosynthetic machinery of the host.

The host is forced to synthesize viral DNA and proteins. As a result, viruses begin to multiply.

Within 25 minutes about 200 new Bacteriophages are formed.

(ii) Lysis

After the formation of bacteriophages, the bacterial cell bursts (lysis occurs).

Newly formed bacteriophages are released to infect other bacteria. A new lytic cycle may start.

The phage that causes the lysis of the host cell is called lytic or virulent phage.

(2) Lysogenic Cycle:

In some cases instead of the lytic cycle, the lysogenic cycle takes place. It occurs as follows:

(i) Formation of Prophage:

The viral DNA does not take over the control of the host's machinery.

The DNA is incorporated into the bacterial chromosome. Phage at this stage is called prophage and this process is known as lysogeny.

The phage which causes lysogeny is called temperate (lysogenic) phage. 

Lysogenic bacteria are resistant to infection by the same or related phages.

(ii) Replication:

During lysogeny, the bacterium lives and reproduces normally.

Viral DNA is the part of a bacterial chromosome and passes to each daughter cell generation after generation.

(iii) Induction:

Some times the viral DNA detaches from the chromosomes of the host and the lytic cycle starts. This process is called induction is spontaneous or environmentally induced excision of the prophage from the bacterial chromosome. 

Structure and Life Cycle of Bacteriophage Structure and Life Cycle of Bacteriophage Reviewed by SaQLaiN HaShMi on 9:36 AM Rating: 5

First Law of Thermodynamics (ΔE = qv)

State first law of thermodynamics and prove ΔE = qv.

First Law of Thermodynamics

"This law is also called the law of conservation of energy. This law is stated as, "energy of the universe is constant".


"Energy can neither be created nor destroyed but can change from one form to another."

In other words, a system cannot destroy or create energy. However, it can exchange energy with its surrounding in the form of heat or work. Thus the energy change is the sum of both heat and work so that the total energy of the system and its surroundings remains constant.

Consider a gas enclosed in a cylinder having a piston. Suppose the internal energy of the system is E1. A quantity of heat q is given to the system and work W is done on the piston to keep it in its original position. During these operations, the internal energy of the system changes to E2, the change in internal ΔE is given by the following equation, which is the mathematical form of the first law of thermodynamics.

                    E2 - E =  ΔE = q + W

                    ΔE  = q + W

Sign of q will be positive when heat is supplied to the system and q is negative when heat flows out side across the boundary. W is negative when work is done by the system and W is positive when work is done in the system. Pressure volume work is given mathematically as:

                    Work = Force  x  Distance

An external pressure P exerted by a force F, spreads over the area A, as pressure is force per unit area.

                    P  =  F/A    or     F  =  P x A

The volume of the gas in the cylinder is equal to cross-section area A multiplied by the height of the column of the gas h.

                    V  =  A  x  h 

Now, let us assume that the gas expands and does work by pushing the piston against external pressure, "A" remains the same but "h" changes.

               ΔV  =  V2  -  V1

                    ΔV  =  Ahf  -  Ahi

                    ΔV  =  A (hf - hi)

                    ΔV  =  A  Δh

Work done by expansion of gas against constant pressure is given by

                    W  =  -F  x  Δh

                    W  =  -P  x  A  x  Δh

                    W  =  -P ΔV

The negative sign indicates that work is done by the system on the surrounding. So first law of thermodynamics can be written as:

                    ΔE  =  q  -  P ΔV

Energy changes at constant volume

If the volume of gas does not change, no work is done, (ΔV  =  0). By applying the first law of thermodynamics.

                    ΔE  =  qv  -  P ΔV

                    ΔE  =  qv  -  0      (ΔV = 0)

                    ΔE  =  qv

So the increase of heat at constant volume (qv) increases only the internal energy (ΔE) of the system and work done is zero.

First Law of Thermodynamics (ΔE = qv) First Law of Thermodynamics (ΔE = qv) Reviewed by SaQLaiN HaShMi on 6:03 AM Rating: 5

Hybridization, with Example of sp² hybridization

What is hybridization? Explain sp² hybridization with example.

"The process of mixing orbitals of different energy and shape to form set of new orbital of the same energy and same shape is called Hybridization and orbitals obtained are called hybrid orbitals".


The process of mixing one 's' and two 'p' orbitals to form three equivalent sp² hybrid orbitals is called sp2-Hybridization.

Each sp² orbital consists of 's' and 'p' in the ratio of 1 : 2 respectively.

sp²-hybrid orbitals lie at the angle of 120° in a plane. The geometry of the molecules is trigonal planar.

Formation of Ethylene or Ethane (C2H4) Molecule

Electron configuration of C (6) = 1s ⇵, 2s ⇵, 2px↑, 2py↑, 2pz

Excited state = 1s ⇵, 2s ↑, 2px ↑, 2py ↑, 2pz ↑

One s and two p orbitals intermix to form three hybrid (sp²) orbitals. The geometry of molecules depends upon the number of hybrid orbitals. Hybrid orbitals are trigonal planar and are oriented at the angle of 120°. Each atom is left with one half filled p-orbital perpendicular to the planar sp² hybrid orbitals. Each carbon atom undergeos sp² -s, overlaps with two hydrogen atoms and sp² -sp² overlap between themselves to form sigma bonds. These overlaps lead to the following shapes. The partially filled p-orvbitals undergo overlap sideways to form a pi-bond. So, a pi-bond is formed by the sideways overlap of two half filled co-planar p-orbital in such a way that the probability of finding the electron is maximum perpendicular to the line joining the two should be made clear that a π-bond is formed between two atoms only, when the with a sigma bond.

Hybridization, with Example of sp² hybridization Hybridization, with Example of sp² hybridization Reviewed by SaQLaiN HaShMi on 7:52 AM Rating: 5

London Forces & Factors Affecting It.

What are London forces? Explain various factors affecting it.

Induced Dipole - Induced Dipole Forces or (Instantaneous Dipole) or (London Dispersion Forces)

Neither dipole - dipole nor dipole induced dipole forces can explain the fact that helium becomes a liquid at temperature below 4.2K. Non-polar gases like noble gases (He, Ne, Ar, Kr, Xe), methane, chlorine etc, becomes liquid at low temperature and high pressure.

A German physicist Fritz London in 1930 offered a simple explanation for these weak attractive forces between non-polar molecules.

In helium gas, the electrons of one atom influence the moving electrons of the other atom. Electrons repel each other and they tend to stay as far apart as possible. When the electrons of one atom move nearer to the electron of other atom, they are pushed away from each other. In this way a temporary dipole is created in the atom as shown in the Figure.

The result is that, at any moment, the electron density of the atom is no more symmetrical. It has more negative charge on one side than one the other. At that particular instant, the atom becomes a dipole. This is called instantaneous dipole. This instantaneous dipole then disturbs the electronic could of other molecule and forms induced dipole.

"The momentary force of attraction created between instantaneous dipole and the induced dipole is called Instantaneous dipole or induced dipole - induced dipole interaction or London forces."

It is a very short-lived attraction because the electrons keep moving. The movement of electrons cause the dipoles to vanish as quickly as they are formed. Anyhow, a moment later, the dipoles will appear in different orientation and again weak attractions are developed.

London force are present in all types of molecules wheather polar non-polar but they are very significant for non-polar molecules like Cl2, H2 and noble gases.

"The distortion of electronic cloud of an atom or molecule is called polarizability."

Polarizability of atoms depend upon the size and atomic number. In a group of the periodic Table, size of atom increases and polarize ability increases. I2 has more polarizibility than Cl2 and Br2.

By increasing atomic number in a group, the polarizability increases.

Factors Affecting the London Dispersion Forces

(i) Boiling Points and Physical State of Noble Gases and Halogens 

London forces are weaker than dipole-dipole interactions. The strength of these forces depend upon the size of the electronic cloud of the atom or molecules. When the size of the atom or molecule is large then the dispersion becomes easy and these force become more prominent. The elements of the zero group in the periodic table are all mono-atomic gases. They don't make covalent bonds with other atoms because their outermost shells are complete. Their boiling points increase down in the group from helium to radon. The following graph shows the increase in their boiling points, Boiling points of noble gases are given in Table.

The atomic number increase down the group and the outermost electrons move away from the nuclei. The dispersion of the electronic clouds becomes more and more easy. So the polarize ability of these atoms go on increasing.

Polarizibiltyy is the quantitative measurement of the extent to which the electronic cloud can be polarized or distorted. This increased distortion of electrons creates stronger London forces and hence the boiling points are increases down the group.

Similarly, the boiling points of halogens in group VII-A also increase from fluorine to iodine. All the halogens are non-polardiatomic molecules, but there is a big difference in their physical states at room temperature. Fluorine is a gas and boils at -188.1°C. While iodine is solid at room temperature which boils at +184.4°C. The polarizability of iodine molecule is much greater than that of fluorine.


Boiling Points of Halogens and Noble Gases

Group VII A

B.P (°C)

Zero Group

B.P (°C)





















 (ii) Physical States and Boiling Points of Hydrocarbon Molecules

Another important factor that affects the strength of London forces is the number of atoms in a non-polar molecule. Greater the number of atoms in a molecule, greater is its polarizability. Let us discuss the boiling points of saturated hydrocarbons. These hydrocarbons have chain of C-atoms linked with hydrogen atoms. Compare the length of the chain for C2H6 and C6H14. They have the boling points -88.6°C and 68.7°C respectively. This means that the molecule with large chain length experiences stronger attractive forces. This reason is that longer molecules have more places along its length where they can be attracted to other molecules. It is very interesting to know that with the increasing molecular mass of these hydrocarbons, they change from gaseous to liquid and then finally become solids. The following Table gives the boiling points and the physical states of some hydrocarbons.

London Forces & Factors Affecting It. London Forces & Factors Affecting It. Reviewed by SaQLaiN HaShMi on 7:21 AM Rating: 5


Explain about Reptiles.


Reptiles are adapted for complete existence on land in contrast to amphibians that are still tied more or less to water or moist habitat this indicates that reptiles have certain adaptations not found in amphibians some of these advancements shown by reptiles are their:

Characteristics Features:

(i) Reptiles have developed some sort of copulatory organs (penis like) necessary for internal fertilization.

(ii) In amniotic eggs of reptiles the shell is leathery which can resists dryness and injury. They have large yolky eggs.

(iii) Reptiles have dry scaly skin which is adapted to land life.

(iv) Reptiles have protective embryonic membranes aminion, allantois, and chorion.

(v) In reptiles the ventricle of heart is in completely partitioned ensuring more oxygen supply through blood circulation to all parts of the body.

In crocodiles, ventricle is completely partitioned into two.

(vi) Most reptiles have better developed limbs well adapted for efficient locomotion.

(vii) Reptile like amphibians are cold blooded (Poikilotherm) and hibernate in winter.

The above characteristic are for terrestrial habitat in which the reptiles mostly live.

However it is determined fact that reptiles have evolved from amphibians by undergoing the above changes and have become fully terrestrial.

  • Reptiles flourished throughout Mesozoic period (225-65 million years).
  • The climate which had been suitable for reptiles in that period, became less favourable to them in tertiary period.
  • So most of them became extinct.
  • The existing reptiles belong to four, out of a dozen or more main lines that have existed.

(i) Lizards and Snakes:

The present day repltles are, the lizards and snklaes.

(ii) Tuatara:

Secondly the tuatara (sphenodon) of New Zealand, which have survived up to today with little change.

(iii) Crocodiles:

Thirdly the Crocodiles are an offshoot from the stock from which modern birds were derived.

The reptiles of today have been derived from dinosaurs of Jurassic (195-136 million years), and cretaceous period (136-65 million years).

The modern reptile for the most part live in the temperate and tropical zone, indeed they fourish only in the latter.

Reptiles Reptiles Reviewed by SaQLaiN HaShMi on 2:37 AM Rating: 5

Apicomplexans and Dinoflagellates

Write note on Apicomplexans and Dinoflagellates?

Apicomplexans :

(i) Habitat:

Apicomplexans are a large group of parasitic protozoans some of which cause serious diseases such as malaria in humans.

(ii) Locomotion:

Apicomplexans have no specific structures for locomotion but move by flexing.

(iii) Spore Formation:

At some stage in their lives, they develop a spore. It acts as a small infective agent which is transmitted to the next host.

(iv) More than One Host:

Many organisms of this group spend part of their life in one host and part in a different host species.

(v) Life Cycle of Plasmodium:

Plasmodium (that causes malaria), enters human blood through the bite of an infected female Anopheles mosquito.

Plasmodium first enters liver cells and then red blood cells, where it multiplies.

when each infected red blood cell bursts, many new parasites are released.

The released parasites infect new red blood cells. The process is repeated.

When millions of red blood cells burst simultaneously, the symptoms of malaria appear.

Chill, followed by high fever are the symptoms of malaria. These are due to toxic substances that are released and affect other organs of the body.

Dinoflagellates (Phyrrophyta):

These are the most unusual protists because of the following characters:

(i) Unicellular:

Most dinoflagellates are unicellular.

(ii) Shell:

Their cells are often covered with, the shells of interlocking cellulose plates impregnated with silicates.

(iii) Second Group Producers:

In the marine ecosystem they are second most important group of producers (first group is diatoms).

(iv) Photosynthetic Pigments:

They have chlorophyll a and c. They contain carotenes and fucoxanthin.

(v) Population Explosions or Blooms:

They have rarely population explosions or blooms. These blooms colour the water orange, red or brown and are called as red tides.


Gonyaulax, Ceratium.

Apicomplexans and Dinoflagellates Apicomplexans and Dinoflagellates Reviewed by SaQLaiN HaShMi on 5:49 AM Rating: 5

The Bacterial Cell Envelope



In bacteria the complex of layers external to the cell protoplasm is called as cell envelope. It includes capsule, slime and cell wall.

(i) Capsule:

Some bacteria produce capsule. It is tightly bound to the cell. Capsule is made up of of repeating polysaccharide units, or of protein, or of both.

(ii) Slime:

It is a loose, soluble cover of macromolecules called as slime capsule. It is present in some bacteria.

Slime provides greater pathogenicity to bacteria and protects them against phagocytosis.

(iii) Cell Wall:

Beneath the extracellular substances and (external to cytoplasmic membrane is cell wall).

It is rigid structure and determines the shape of bacterium.

Cell wall also protect the cells from osmotic lysis.

Cell wall is only absent in mycoplasmas.

Gram Stain Technique on the Basis of Differences in Cell Wall.

Christian Gram developed the technique of gram stain on the basis of differences in the cell wall.

On the basis of this technique bacteria can be divided into two groups.

(i) Gram Positive Bacteria:

These are the group of bacteria  that stained purple. They retain the primary dye due to the formation of CV-I complex in the cell wall.

(ii) Gram Negative Bacteria:

These bacteria are stained pink because they retain secondary dye in the cell wall.

Comparison of Gram Positive and Gram-Negative Cell Wall:

Difference in staining is due to difference in structure of cell walls of two groups. It is clear from the following table:


Gram Positive

Gram Negative

(i) Chemical make up.

(ii) Overall thickness

(iii) Outer membrane

(iv) Periplasmic space

(v) Permeability

(a) Peptidoglycan (50% of dry weight in some bacterial cells)

(b) Techoic acid

(c) Lipotechoic acid

(d) Lipids (1-4%)



Present in some

More permeable

(a) Lipopolysaccharides

(b) Lipoproteins

(c) Peptidoglycan 10% dry weight of some bacterial cells.

(d) Lipids (11-12%)



Present in all

Less permeable

Chemical Composition of Cell Wall:

(a) The cell walls of most bacteria have a macromolecules called peptidoglycan.
(b) Its amount varies in different types of bacteria.
(c) Peptidoglycan is composed of long glycan chains cross-linked with peptide fragments.
(d) The cell wall also contains sugar molecules, techoic acid, lipoproteins and lipopolysaccharides. These are linked to peptidoglycan.

Cell Walls of Archaeobacteria:
Cell walls of Archaeobacteria are different from Eubacteria. They do not contain peptidoglycan. Their cell walls are composed of proteins, glycoproteins and polysaccharides.

Cell Walls of Other Bacterial Groups:
Many bacterial group have no cell wall structure which is characteristics of gram positive or gram negative bacteria.

No Cell Wall in Some Bacteria:
Some bacteria have no cell wall (like Mycoplasmas).
The Bacterial Cell Envelope The Bacterial Cell Envelope Reviewed by SaQLaiN HaShMi on 8:45 AM Rating: 5

Nuclear War OR Ban on Nuclear Weapons

Nuclear War OR

 Ban on Nuclear Weapons


The developed countries like Russia, America, Japan and France have been making nuclear weapons for many years. America attacked the two cities of Japan, Nagasaki and Hiroshima in the Second World War with atomic bombs. It caused huge destruction in both the cities. Millions of people were wounded and killed in that bombing. Since then a serious thought has been given to the preparation of nuclear weapons. Every country considers it essential to equip itself with nuclear weapons for its security.

Nuclear energy is considered the basic armament of self-defence. In the mad race of preparing nuclear weapons, the underdeveloped countries like India, South Africa and Israel have also joined hands with the developed countries. India has already tested the capability of her nuclear weapons and has successfully exploded the atomic bomb.

 It seems that the nations of the world have forgotten the savagery of atom bombing by the Americans over the Japanese cities. The atom, despite its devastating powers, is still the favourite subject of study among scientists. They go on studying it with the sole object of killing mankind. Persistent nuclear explosions and tests in Siberia or Pacific are hailed as the greatest achievement of science.

The political rulers and statesmen of every country consider the collection of nuclear weapons as a safeguard of peace. They are mistaken in it. The piling up of nuclear weapons is an inevitable prelude to the whole destruction of mankind.

A nuclear war is an exercise is wholesale destruction. A single day's atomic bombing of the U.S.A is estimated to cause the death of about 50 million people and a serious injury to about half the number. Such a great destruction is expected to paralyse the whole steam of life. The influence of radiation will continue to haunt the world for many years. It may give rise to mysterious diseases and ailments. It may render the fertile land barren and wild.

Nobody can wish for such a gloomy and dark future. World peace can only be secured if all the countries decide to put a ban on the research, the production and preparation of nuclear weapons. No country, however powerful should be allowed to make nuclear explosion. Public opinion against the negative effects of nuclear energy should be launched by the people of world.  The existing stock of such destructive armaments must be destroyed.

A powerful organization should be set up in every country which should watch and control the production of nuclear weapons. It should mobilize the public opinion against the menace of atom bomb. People should be told that radio activity is an unchecked and uncontrollable monster. A world wide awareness against the use of nuclear weapons should be produced. The powerful and advanced countries should also be forced to stop producing the deadly weapons. This may seem to be an ideal plan to do away with nuclear weapons. But unless such drastic measure is taken, the future of mankind will continue to be dark. The statesmen, the rulers and politicians of all the countries should realize their responsibility regarding the bright future of mankind. If there is a total disarmament in all the countries, the world peace can be secured in a better way.

Nuclear War OR Ban on Nuclear Weapons Nuclear War OR Ban on Nuclear Weapons Reviewed by SaQLaiN HaShMi on 8:38 PM Rating: 5

Atom for Peace

12:03 AM
Atom for Peace

Atom is a Greek word which means a thing that cannot be cut or broken. It is the smallest particle of matter. It is no longer undivided and unbroken. The scientists have broken it into further smallest particles. They are called electrons, protons and neutrons. They release great power and energy. It was Albert Einstein who began to work on the theory of producing energy from atom in 1905. He explained many things. First, he showed that matter and energy are different forms of the same thing. In other words, matter can be converted into energy and vice versa. Second, a small amount of matter produces a great amount of energy. The discovery of atomic energy is one of the wonders of the modern science.

Atomic energy is a double-edged weapon. It can be utilized for destructive as well as peaceful purposes. The scientists, first of all, used it for destructive purposes. They prepared atomic bombs, hydrogen and cobalt bombs which could destroy cities and towns within the twinkling of an eye. It was in 1945, that a single atom bomb destroyed Hiroshima and Nagasaki. It killed thousands of men and women and destroyed vast areas of land. Now all the big powers possess much more atomic and dangerous hydrogen bombs. They can raze the world to ground if they are carelessly used.

Atomic energy can also be used for the welfare of mankind. The scientists in U.S.A, England, France, Canada and Germany are at work for peaceful use of energy. An atom for Peace conference was held at Geneva to think over the use of Nuclear Energy. The U.S.A has already started to use this energy to propel submarines and space rockets. The Russians have also harnessed it for space travel. At present, electricity is produced from the atomic energy in advanced countries like U.S.A, Russia and Britain. Our scientists are also trying to generate electricity from atomic energy. The scientists are also trying to find ways of using atomic power as fuel in ships, aeroplanes, motor cars etc. At present atomic reactors for boiling water exists in different countries.

Atomic energy is safely used to conquer many fatal diseases. Radium is used in the treatment of cancer. Radio-therapy is an important branch of medical science. It is used to destroy the overgrown cells of our body. The isotopes of sodium, potassium, bromine and iodine are used to known the origin of disease. The atomic energy is of immense help to alleviate human sufferings.

Nuclear energy has also brought a revolution in the field of industry. Petrol and coal are well known sources of energy and power. The supply of these two sources of power is coming to an end. The world is in search of another source of power. It is the nuclear energy. Electronic machines and computers are being used in our industry. They are used in the plastic, glass, paper, textile, rubber and cement industry.

Atomic energy is also of great help in agriculture. The barren lands can be tilled into smiling fields with the help of computerized tractors and machines. Crops can be ripened within a very short time. The yield of crops per acre can also be multiplied. In this way, the scientists are trying to solve the food problem. We can say that atomic energy can be used with full advantage for the welfare of mankind.

Atom for Peace Atom for Peace Reviewed by SaQLaiN HaShMi on 12:03 AM Rating: 5
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