Notes Guide Book

Describe the early computing machines and their inventors in the dark age.

noreply@blogger.com (Anonymous) — Mon, 09 Feb 2015 08:34:00 +0000

DEVICES USED IN DARK AGE

1. Abacus

About 5,000 years ago 'abacus' was invented in China. It is considered as the first computer. It is a rectangular frame with vertical wires containing a number of beads for representing units, tens, hundreds, thousands and so on. Calculations were done by moving the beads along with the wires. The structure of abacus is divided into two parts, the upper part is called the 'HEAVEN' and lower part the 'EARTH'.

2. Napier's Rods

In 1612, John Napier made the first printed use of the decimal point and invented logarithms and he designed a device called Napier's rods or bones. This device consisted of a set of eleven rods or bones with number marked on them. By placing these rods side by side products and quotients of large numbers could be obtained very easily.

3. Oughtred's Slide rule

In 1622, Oughtred developed a slide rule based on Napier's logarithms that was uses! by engineers as primary calculator. It was consisted of two movable rulers placed side by side. Each ruler is marked in such a way that the actual distances from the beginning of the ruler are proportional to the logarithm of the numbers printed on the ruler. By sliding the rulers multiplication and division could be done quickly.

4. Pascaline (Pascal's Calculator)

In 1640a French mathematician, Blaise Pascal started developing a device to add sums of money. In 1642 he invented the first operating model a numerical wheel calculator. This brass rectangular box,also called a Pascaline, used 8 movable dials to add numbers upto eight figures long. Pascal's device used a base of ten to accomplish this. It could perform addition and subtraction only, while multiplication and divisions were implemented by performing a series of addition and subtractions. In fact this device could really only add, because subtractions were performed using complement techniques. Modern computers use similar complement techniques for subtraction.

5. G.W. Leibniz's

Calculator Leibniz improved on Pascal's calculator in 1694 by creating a machine, that could also multiply. Leibniz's mechanical multiplier worked by a system of gears and dials.

6. Jacquard's Loom

In ( 820 French Weaver Joseph Marie Jacquard invented the first punch card to control the patterns to be woven. Jacquard's Loom is considered the first significant use of binary automation.

7. Arithometer

Charles Xavier Thomas de Colmar, a Frenchman invented a machine in 1820 that could perform the four basic arithmetic operations. Colmar's mechanical calculator, the Arithometer, presented a more practical approach to computing

HISTORY AND DEVELOPMENT OF COMPUTER

noreply@blogger.com (Anonymous) — Mon, 09 Feb 2015 08:29:00 +0000

Into how many ages is the computer era divided

AGES OF THE COMPUTER ERA

The computer era is divided into three ages:
1. The Dark Age (5000 B.C. to 1890 A.D.)
2. The Middle Age ( 1890 A.D. to 1944 A.D.)

What are the limitations of the computers

noreply@blogger.com (Anonymous) — Mon, 09 Feb 2015 08:27:00 +0000

LIMITATIONS OF THE COMPUTERS

1. No ability to generate Information

A computer cannot generate information on its own.

2. No ability to correct

A computer cannot correct wrong instructions.

3. No decision at its own

A computer cannot come up with an original decision.

What are the Capabilities of computer

noreply@blogger.com (Anonymous) — Mon, 09 Feb 2015 08:25:00 +0000

CAPABILITIES OF COMPUTER

1. Speed

A Computer can process data faster than any other machine designed to perform a similar task.

2. Repetitions

A computer can tirelessly perform the same operations millions of times in exactly the same way without getting bored and tired as a human clerk would.

3. Accuracy

A computer's high-speed processing is accompanied by high-accuracy results. No other system can have as much accuracy as a computer system.

4. Logical operations

The computer can make decision based on some conditions and take alternative course of action accordingly.

5. Store and recall information

The computer is like human brain as it can store facts, instructions and information and recall them when needed.

6. Self-checking

The computer verifies the accuracy of its own work by means of a parity check.

7. Self-operating

Once the data and program are fed into the computer memory, the computer is capable of executing the instructions on its own, without human intervention.

Describe some of the characteristics of computers.

noreply@blogger.com (Anonymous) — Mon, 09 Feb 2015 08:21:00 +0000

CHARACTERISTICS OF COMPUTER

1. Machine:

It is a machine. It is an inanimate object. It needs outside intervention for it to run. It can only do things for which it is designed.

2. Electronic:

It is Electronic because it is made up of electronic circuits. It runs on electrical energy.

3. Automatic:

It is automatic. Once started it continues to run without outside intervention.

4. Data Manipulator:

It can manipulate data, following specific rules. It can perform arithmetic functions such as addition, subtraction, multiplication, and division. It can compare data.

5. Memory:

It has memory. It has the capacity to remember what it has done. It can store instructions in its memory and follow these through unaided.

Write a note on Software.

noreply@blogger.com (Anonymous) — Sat, 07 Feb 2015 16:18:00 +0000

SOFTWARE DEFINITION

Software refers to the programs that instruct the computer what to do. Software makes the computer useful. Software is the set of all the programs (instructions) and data necessary to make the computer usable.

Examples Windows

Visual Basic, Norton antivirus, Microsoft Word, Microsoft Excel etc.

TYPES OF SOFTWARE

Software are of two types.
• System Software
• Application Software

Write a note on Hardware.

noreply@blogger.com (Anonymous) — Sat, 07 Feb 2015 13:04:00 +0000

HARDWARE DEFINITION

The physical or tangible components forming a computer are called Hardware. When people talk about a computer, they usually mean the hardware.

The physical components of computer and other attached input ad output devices are called hardware.

COMPONENTS OF HARDWARE

Hardware is a collective term. All hardware components may be connected mechanically electrically or electronically with each other. It includes the cables, connecters, power supply units and peripheral devices such as.

• Keyboard
• Mouse
• Audio speakers
• Printers

Define Computer

noreply@blogger.com (Anonymous) — Wed, 04 Feb 2015 17:46:00 +0000

DEFINITIONS OF COMPUTER

Computer is an electronic device that accepts data and instructions (in form of programs) as input, processes that data according to the given instructions and produces information as output.

Computer is a machine that can accept input data, processes it and gives output.

A computer is an electronic device that can interpret and execute programmed commands for input, output, computation and logic operations.

A computer is an automatic electronic calculating device which can process given data and gives results.

A computer is a device capable of accepting data and gives desired result by processing.

A computer is a device which processes the given data with the help of a stored program at high speed.

My Aim In Life

noreply@blogger.com (Anonymous) — Tue, 03 Feb 2015 17:47:00 +0000

Everyone in the world, however great or small, has some aim in Life. A prince may have an aim to be a king and a king may have an aim to be an emperor. A professor aims at being a principal and a peon aims at being a head-peon. Someone's aim for fame, someone's aim for power, someone's for money; while some aim at acquiring knowledge.

I have also a high aim of life though I do not know how far I would be able to realise it. I do not want to run after money, nor after cheap popularity. I have resolved to be a doctor and spend my life in the service of others. I believes it is a good selection. I would not charge high fees and shall never exploit the needy and the poor at the most critical moments of their life.

If were a good a doctor, I would, of course, get fame and popularity. Being a good doctor; having connections with several families, I would naturally acquire power and influence. This profession gives better greater opportunities to serve mankind in their moments of urgent need, when they are involved in a struggle of life and death.

My aim does not end there I shall devote a part of my time in doing free work in charitable dispensaries. I shall follow the principles of truth and justice. Whether I achieve anything substantial in my life is another matter, but I shall always strive to keep my aim pure, honest and honourable.

Patriotism Essay

noreply@blogger.com (Anonymous) — Mon, 02 Feb 2015 10:56:00 +0000

Patriotism means love for one's country. This love is not created by any artificial methods, but it is already deeply rooted in our heart. Patriotism is an instinct which comes to us from the moment we are born. There are some, who think that patriotism is a narrow-minded sentiment, and a sign of a semi civilized state of mind.

A man loves the whole universe and considers all people of the world as his brethren. This idea of universal brotherhood makes every man a citizen of the world and not of his narrow world, known as his country. We should not be narrow-minded patriots. Love of one's country should not and does not mean hatred of the rest of the world. It is a false patriotism which makes us hate other countries.

True patriotism is based on unselfish love for our country and our respect for its history and culture. It makes us great and teaches us to love mankind as one family, created by one God and governed by the laws of one universe.

A true patriot, therefore, will never like to say such things about other countries as he would not tolerate about his own country. True patriotism demands sacrifices of ones life, family, property and everything. Those who lay down their lives for the sake of the mother-country are martyrs.

STATES OF EQUILIBRIUM

noreply@blogger.com (Anonymous) — Mon, 02 Feb 2015 05:06:00 +0000

STATES OF EQUILIBRIUM

There are three states of equilibrium.
They are the following.

STABLE EQUILIBRIUM

Definition
A body is said to be in stable equilibrium if it returns to its original position when tilted a little.
OR
The centre of gravity of a body rises with a jerk is called stable equilibrium.
Examples
• Book on a table.
• Chair on flat ground.
• Table on a floor.
• A standing car on a smooth road.

UNSTABLE EQUILIBRIUM

Definition
A body is said to be in unstable equilibrium if it moves further away from its original position when tilted a little.
OR
The C.G of a body lowered with a slight move the equilibrium of that body is called unstable equilibrium.
Examples
• A stick standing vertically on the tip of a figure.
• A standing pencil on the table.
• An acrobat walking on a rope.

NEUTRAL EQUILIBRIUM

Definition

A body is said to be in neutral equilibrium if it neither returns to its former position nor moves further away when tilted a little.

The equilibrium of that body is called neutral equilibrium whose C.G is neither raised nor lowered on disturbing.

Examples

• Horizontally lying cylinder and funnel.

• Lying a ball on the floor.

CENTRE OF GRAVITY

Definition

It is the point at which the entire weight of the body is said to be situated.

The point on a body at which the whole weight of the body appears to act. It may be on the body or out side the body in case of a hollow object.

TORQUE OR MOMENT OF A FORCE

noreply@blogger.com (Anonymous) — Mon, 02 Feb 2015 04:57:00 +0000

Definition

It is the turning effect of a force about the axis of rotation.
Formula
Torque = force x moment arm
t =f x d
Unit
Its unit is N-m.

TYPES OF TORQUE

Torque or moment may rotate a body in clock wise or anti clock wise direction.

NEGATIVE TORQUE

The clock wise torque is called negative torque.

POSITIVE TORQUE

The anti clock wise torque is called positive torque.
Notation It is denoted by the Greek letter t (tau)
Formula
Torque = Force x moment arm.
t= F x d
Unit The unit of torque is (N-m)
Nature
It is a vector quantity.

MOMENT ARM

Definition
The perpendicular distance between the line of the force and the axis of rotation is called the moment arm.
Notation
It is denoted by d.

FACTORS ON WHICH TORQUE DEPENDS

Torque depends upon two factors.
1. Magnitude of the applied force.
2. The moment arm Torque increases with the increase of force. Torque is directly proportional to the applied force. Torque is directly proportional to the moment arm.

PRINCIPLE OF MOMENT

Statement

According to the principle of Moment -If a system is in equilibrium under influence of some Torques then the sum of clock wise torques is equal to the sum of anti clock wise torques i.e.

Mathematically

In Equilibrium position.

Clock wise torque = Anti clock wise torque.

EQUILIBRIUM

noreply@blogger.com (Anonymous) — Mon, 02 Feb 2015 04:47:00 +0000

Definition

When the resultant of all the forces acting on a body comes to zero, the body is said to be in the state of equilibrium.
OR
In other words the body is said to be in the state of equilibrium if left-ward forces are equal to the rightward forces and upward forces are equal to the downward forces.
Example
• A book lying on the table.
• A train moving in a straight line with a constant velocity.
• A body hanging at rest from the ceiling by a vertical string.
• A Paratrooper moving down with uniform velocity after opening his parachute.

TYPES OF EQUILIBRIUM

There are two types of equilibrium.
1. Static equilibrium
2. Dynamic equilibrium

STATIC EQUILIBRIUM

Definition
If some forces are acting on a body vertically or horizontally and the body maintains its state of rest, Then it is called static equilibrium.
Example
• A book lying on the table.
• A body hanging at rest from the ceiling by a vertical string.

DYNAMIC EQUILIBRIUM

Definition
If some forces are acting on a body vertically or horizontally and the body maintains its state of motion, then it is called dynamic equilibrium.
Example
• Train moving with uniform velocity.
• Paratrooper falling down with uniform velocity.

CONDITIONS OF EQUILIBRIUM

FIRST CONDITION OF EQUILIBRIUM

Statement
The body is said to be in the state of equilibrium if the resultant of all forces acting on a body is equal to zero i.e.

In other words the algebraic sum of all the forces acting along X-axis should be zero i.e.

And the algebraic sum of all the forces acting along Y-axis should be zero i.e.

When first condition of equilibrium is satisfied. the body is in translational equilibrium and there is no linear acceleration.

SECOND CONDITION OF EQUILIBRIUM

Statement The body is said to be in the state of equilibrium if the sum of all the torques or moments acting on the body must be zero i.e.

RESULTANT OF TWO FORCES

noreply@blogger.com (Anonymous) — Mon, 02 Feb 2015 04:33:00 +0000

Definition

The net effect of the forces is a single force which is called the resultant of the forces.
OR
A single that gives combined effect of forces is called resultant force.

If two forces F1 and F2 are acting on a body at a straight line but in opposite direction and body remains at rest or in equilibrium. Then we say that F1 and F2 are equal in magnitude but opposite in direction.

If two forces F1 and F2 are acting on a body at a straight line but in opposite direction and body moves in the direction of any one of them which is greater than the other. Net force is calculated as:

F2-F1 net force
or F1-F2 net force
Body will move in the direction of greater force.

RESULTANT OF TWO FORCES ACTING AT AN ANGLE

If two forces are acting on an object making a certain angle. In this case the force can be represented in magnitude and direction by two adjacent sides of a parallelogram (I In). The resultant force FR is a vector represented by the diagonal from the point of intersection. This is called the parallelogram of forces.

As PR is diagonal of I Im PQRs so the resultant is diagonal. And the I Im is called I Im of force F1 and F2.

By head to tail rule, we can draw force F- from the terminal point of force F2. To get the resultant FR we draw a vector from the initial point of force F2 to the terminal point of the force Fr. This is the same force as obtained from the I l 1 of force as shown in the figure.

FACTORS ON WHICH THE FRICTION DEPENDS

noreply@blogger.com (Anonymous) — Fri, 30 Jan 2015 14:15:00 +0000

Friction depends upon the following two factors.

1. Normal Reaction
2. Nature, of Surfaces

NORMAL REACTION

Force of friction is directly proportional to the normal reaction R which acts in upward' direction against the weight of the body sliding on a surface i.e.

NATURE OF SURFACES

Force of friction also depends upon the nature of two surfaces in contact with each other, it is constant for various pairs of surfaces in contact and this value is called co-efficient of friction.

SELF ADJUSTING FORCE

The force of friction' has the ability to increase its value with the increase of applied force till it reaches a maximum value..,Due to this strange nature of frictional forces we call them as the self adjusting force. It is denoted by Fs.

LIMITING FRICTION

Definition

The maximum force of friction which just stops the body from moving is called limiting friction

COEFFICIENT OF FRICTION

Definition

Coefficient of friction is the ratio between force of friction and perpendicular reaction.

p is coefficient of friction. R is perpendicular reaction. F is force of friction.

ROLLING FRICTION

Definition :

Then a body rolls over a surface it experiences an opposing force that is called rolling friction. polling friction between two bodies is much less than the sliding friction because in rolling the contact S-Irface is much less than that in sliding.

ADVANTAGES OF FRICTION

• Frictional forces help us to move forward.

• Nut and bolt can hold a body due to friction.

• A nail stays in the wood because of friction.

• We can not hold any thing without friction.

• We can tie a knot because of friction.

DISADVANTAGES OF FRICTION

There are so many disadvantages of friction but some are as follows.

In a car engine oil under pressure is supplied continuously to ball bearing surface. Failure of the oil supply will allow metal to metal contact and the resulting friction, often raises the temperature and due to this ball bearings and piston are sized up.

MOMENTUM

noreply@blogger.com (Anonymous) — Fri, 30 Jan 2015 14:05:00 +0000

Definition

Momentum of a body is the product of its mass and velocity.
OR
The quantity of motion of a body is called its momentum.

Mathematically

If "m" is the mass and "v" is the velocity of a body then Momentum P is given by:
P = mv

Unit

In M.K.S. system the unit of Momentum is kg-m/s or N-s

Nature

It is a vector quantity. Its direction is same as that of velocity,

LAW OF CONSERVATION OF MOMENTUM

Statement

The total momentum of a system remains constant provided no external forces act on it.
OR
The Momentum of an isolated system always remains constant.

PROOF

Consider a system consisting of two balls A and B of masses m₁ and m2 moving in a straight line, with velocities U1 and U₂. On colliding with each other they move with velocities V1 and V₂ respectively as shown in the figure.
The total Momentum of the system before collision= m₁U1 + m₂U₂
The total Momentum of the system after collision = m_1V1 + m_2V₂
According to the law of conservation of Momentum Initial momentum = Final momentum
m₁U1 + m₂U₂ = m1V1+ m₂V₂

Hence the Momentum of a system remains constant.

FRICTION

Definition

When two bodies are in contact with each other and the force is applied to the upper body to make it move over the lower body, an opposing force is developed in the plane of contact which resists the motion. This force is called friction.

When one bod / slides over the surface of another body, an opposing force is set up to resist the motion. The force which opposes the motion is called friction.

CAUSES OF FRICTION

There is no ideal smooth surface present in universe. Each surface has elevations and depressions which causes to friction.

When two surfaces are brought into physical contact. the elevations of one impacts into the depressions of first or vice versa which causes an inter locking with two surfaces. This interlocking opposes the relative motion of one surface on the other.

Compulsory Military Training

noreply@blogger.com (Anonymous) — Tue, 27 Jan 2015 16:06:00 +0000

There is a proverb that, "If you want to have peace, prepare for war." The best preparation for war is to keep man-power and munitions ready. Before the beginning of the Second World War, England and France were not prepared for war, while Germany and Japan were prepared for it. England and France wanted peace at any cost, but they forgot the above proverb.

Wars have become a necessary evil in modern times, and the only way to fight out this evil is through a preparation for war at the national level. In every country there are schools and colleges for military training. There are three branches of the army: ground force, naval force and air force. Military training is voluntary in almost all countries.

But in ancient Greece there was compulsory training. Germany and Japan had made military training compulsory till the end of the Second World War. Now there is compulsory military training in Russia, France, China, Italy and Germany and so many other have introduced compulsory military training.

In Pakistan, we are still dependent of our defence upon a professional army. It is with this objective in view that the Commission on National Education has recommended the introduction of compulsory military training in all the schools and colleges of our country. A few years ago a sort of military training called the N.C.C. force was introduced in some of the colleges. But now, after the recent Indo-Pak war, the importance of compulsory military training has been realised anew.

There are many advantages of military training. It develops the sense of orderliness and discipline in a nation. It makes people strong and courageous. The concept of new citizenship is incomplete without military training, it makes soldiers patriotic. It narrows the gap between civil life and military life. No other training can create in our young men the habit of self-obedience, team spirit and co-operation in a better than military training does. A compulsory military training is the only way to make our people smart and active.

Write a note on the excretory system of frog with the help of a diagram.

noreply@blogger.com (Anonymous) — Mon, 26 Jan 2015 16:09:00 +0000

EXCRETORY SYSTEM OF FROG:
In frogs, waste materials are excreted out in many ways e.g. skin, lungs, liver. digestive system. etc. It is the set of organs involved in the process of excretion--that is, the removal of metabolic waste- matters from the body. Besides these organs. nitrogenous waste materials are excreted through two kidneys, which are attached to the dorsal wall of the body cavity These are elongated in shape and composed of urinary tubules. Urinary tubules combine to form collecting ducts, which open into ureter. The urine collected by the kidneys comes into ureters. Each ureter starts from the edge of each kidney of its side and opens into cloaca. From here, the urine is excreted or stored in urinary bladder which is passed out of the body from the cloacal aperture. Carbon dioxide and water are excreted through skin and lungs while undigested food and some waste materials are excreted through liver and digestive system.

Write a note on electron microscope.

noreply@blogger.com (Anonymous) — Mon, 26 Jan 2015 16:06:00 +0000

ELECTRON MICROSCOPE:

Electron microscope was invented in 1935. It has a resolving power 250 times or more than that of. a compound microscope. It uses a beam of electron as a source of illumination. The electron beam increases its resolving power. Modern electron microscope can achieve a resolution of .about 0.2 nm, a thousand times improvement over light microscope. The electron microscope uses electromagnet as lenses instead of glass lenses. Its image cannot be focused in human eye, therefore screen or photographic plates are used to review and focus these images. Electron microscope has a capacity to magnify an object up to 250,000 times of its original size.

Electron microscopes reveal many organelles that are impossible to resolve with the light microscope.

In electron microscopy, chemical and physical methods are used to prepare samples which not only kill cells but also may introduce artifacts. A light microscope has many advantages especially for the study of live cells.

Write down the structure of an animal cell.

noreply@blogger.com (Anonymous) — Mon, 26 Jan 2015 15:52:00 +0000

STRUCTURE OF AN ANIMAL CELL:

Cell Membrane: This is the outermost boundary of an animal cell. It is also called the plasma membrane. In fact, a cell membrane surrounds the cytoplasm and nucleus in all types of cells. However, in plants and bacteria, cell membrane itself is surrounded by a cell wall. Cell membranes are composed of lipids and proteins (lipoproteins). A cell membrane is selectively or semi-permeable.

Fluid Mosaic Model of Cell Membrane:

Singer and Nicholson proposed a model of plasma membrane in 1972 According to this model:
(1) Lipids are in the form of a fluid bilayer.
(ii) Lipids are either phospholipids or glycolipids suspended in water.
(iii)• Protein molecules float like icebergs in the sea in the lipid bilayer.
(iv) Proteins are completely or partially embedded in the lipid bilayer forming a mosaic arrangement

Functions:

(1) Cell membrane regulates selective movement of molecules into and out of the cell. It allows certain molecules to pass through it while others can not pass through it.

(2) Cell membrane takes in material by infolding in the form of vacuoles. It is called endocytosis.

Cytoplasm:

It is a viscous opaque (translucent) fluid portion of the cell which is present between the cell membrane and nuclear membrane. It consists of an aqueous ground substance called cytosol and granular portion called cytoplasmic organelles Its chemical analysis shows that it is composed of organic compounds such as proteins. carbohydrates, lipids (fats), enzymes and some inorganic compounds, e.g. water and salts. Some important cytoplasmic organelles found in eukaryotic cells are as under:
1. endoplasmic reliculum.
2. Golgi complex.
3. mitochondria.
4. plastids (in case of plant cells).
5. ceritrioles.
6. ribosomes.
7 vacuoles.

Functions:

(1) It serves as a storehouse of vital chemicals.
(2) It is a site of metabolic reactions like protein synthesis, glycolysis, etc.
(3) Many reactions can occur at the same time in different regions of the cytoplasm.

Mitochondria (singular mitochondrion):

They are an important organelle of a eukaryotic cell because they provide energy to the cell and are called the powerhouse of the cell.

They are generally rod like or bean shaped bounded by double membrane. Their outer membrane is smooth while the inner membrane is folded. These infoldings are called cristae while the fluid present inside is called matrix. The number of mitochondria in a cells relates to its activities. In different animal cells, number of mitochondria differ. The cells which are more active e.g. liver cells have more than one thousand mitochondria while ear lobes have very small numbers only 50.

Function:

(1) Mitochondria play an important role in respiration.
(2) They contain enzymes which break down the food for the production of energy.

Endoplasmic Reticulum:

It is a network of channels extending throughout cytoplasm from plasma membrane to nuclear membrane. They are tube like. They are of two types.
(1) smooth endoplasmic reticulum (SER): It is nongranular because ribosomes are not attached to it.
(2) rough endoplasmic reticulum (RER): It is granular as ribosomes in the form of small granules are attached to it.

Function:

(1) Endoplasmic reticulum plays an important role in the transport of material from one part of the cell to the other.
(2) It is involved in the synthesis of proteins.
(3) It provides mechanical support to the cell so that its shape is maintained.
(4) It detoxifies the harmful drugs.

Nucleus (Karyon):

It was discovered by Robert Brown in 1831. It may be spherical or irregular in shape. In animal cells, it is usually present in the centre but in plant cells due to the presence of a large vacuole, it is pushed towards the cell membrane. Nucleus is surrounded by a double membrane called the nuclear membrane. This membrane has a large number of pores. Nucleus is filled with a gel like substance called nucleoplasm. The nucleoplasm contains nucleoli and a network of thread like structures called chromatin network. The threads of chromatin become prominent during cell division. Each thread is called chromosome. Chromosomes are made up of deoxyribonucleic acid (DNA) and proteins. DNA plays an important role in the inheritance of characters as well as in controlling and regulating the activities of cells. The number of chromosomes in the cells of a particular species always remains constant. It is the characteristic of that species.

Function:

Nucleus controls all the activities of cells.

GOIgi Complex:

They were discovered by Camillo Golgi and thus called Golgi complex or Golgi bodies or Golgi apparatus. They are a set of smooth membranes that are stacked into flattened, fluid filled sacs or vesicles containing carbohydrates, glyco-proteins and enzymes. They are especially prominent in glandular cells. In animal cells, usually a Golgi apparatus is found in each cell. In plant cells, there may be more.

Function:

(1) They are mainly concerned with cell secretions.
(2) In plants they synthesize cell walls.

Centrioles or Centrosome:

A rounded structure, the centrosome is present in the cytoplasm near the nucleus in animals cells. A centrosome contains two centrioles. Higher plants lack centrioles. Each centriole consists of a cylindrical. array of nine rows of microtubules. Both the centrioles lie perpendicular to one another.

Function:

They form fibrous protein spindles, which help in movement of chromosomes towards poles during animal cell division.

Ribosomes:

They are granules, which are rich in ribonucleic acid (RNA). They are found either freely suspended in the cytoplasm or attached to the surface of rough endoplasmic reticulum. They are the only organelle found in prokaryotic cells. They are the only organelle, which are not bound by a membrane.

Function:

They serve as sites for protein synthesis and hence called the protein factories of the cell.

Nucleolus:

It is found inside the nucleus. It has got no membrane. There may be one or more nucleoli in the nucleus. It disappears during the cell division and reappears later.

Functions:

1. The ribosomal RNA is synthesized and stored in the nucleolus.
2. It is the nucleolus where ribosomes are assembled and exported to cytoplasm via nuclear pores.

Vacuoles:

They are liquid filled cavities in the cytoplasm. They are surrounded by a membrane called tonoplast. In plant cells, there is usually one large permanent vacuole. In animal cells, there may be many small temporary vacuoles.

FUNCTIONS:

(1). They are connected with the storage of cell sap.

(2) .In small organisms , water and waste materials are excreted through special vacoules called contractile vacoules and food is digested in food vacoules.

Essay On An Accident

noreply@blogger.com (Anonymous) — Sun, 25 Jan 2015 21:47:00 +0000

Accidents are quite common in Karachi. The drivers are so ignorant of traffic law, and so careless about it, that they never like to look round while driving even on the main roads, or while taking sudden turns. Many a time I have noticed them stopping in the middle of the road, without looking back or sideways and without giving any signal.

It is rather unfortunate that public interest is easily ignored by the drivers. They drive very speedily and carelessly. The buses are often founded over-crowded. Even the traffic police are found helpless because they have failed to control the traffic. Although there are hundreds of buses on the roads, yet they are not sufficient for this huge population. Complaints of the public fall on deaf ears. The middle class travels by rickshaws and taxies. They are also tar more troublesome. They often charge double fare, hence cannot be availed by the poor. The taxi-drivers do not go to short distances. Public is continuously harassed by the all drivers because most of them are illiterate.

One day 1 was going to college with my friend, Amir, we were near the College. We heard a collision between a bus and a truck. The engine and the body of the bus were completely wrecked. The bus was overloaded. Some people were also hanging on the foot-board and some were on the roof of the bus.

The two drivers and six passengers were on the bus were killed instantly. Several of the passengers including a large number of women and children were seriously injured.

The Medical aid was rushed from AbdulSattar Edhi Welfare Centre. The Superintendent of the police and other officials of the Police Department also visited the scene of the accident. The seriously injured were taken to the Civil Hospital Karachi.

What is the significance of meiosis.

noreply@blogger.com (Anonymous) — Sat, 24 Jan 2015 10:13:00 +0000

SIGNIFICANCE/IMPORTANCE OF MEIOSIS:

The most significant features of meiosis are the halving of the chromosome number and the occurrence of chiasmata during the prophase of the first division. In the reproductive organs, certain cells give rise to gametes (e.g. sperms or ova) by a special kind of cell division which results in the gametes containing only half the number of chromosomes as compared to other cells of the organism. When the gametes fuse together during fertilization, the 2n chromosome number or diploid number is restored. There is a fixed number of chromosomes for each species, e.g. for man it is 46.

The formation of chiasmata brings about a new combination of genes in the gametes. At each chiasma, an exchange of genetic material takes place between the maternal and paternal members of a homologous pair of chromosomes, the phenomenon is called crossing over.

During fertilization, the male and female gametes unite. The offspring that results from this union will inherit a mixture of characters from both the parents.

Thus meiosis keeps the chromosome number constant generation after generation and it provides a chance for genetic reshuffling so that a better species can result to suit the environment.

Write the external features of the Frog.

noreply@blogger.com (Anonymous) — Sat, 24 Jan 2015 09:28:00 +0000

EXTERNAL FEATURES OF THE FROG:

A frog has greenish spots and dark lines on its skin which is kept moist and slimy due to the secretion of glands. Its ventral side is yellowish white in colour. The body of frog consists of head, trunk and limbs Neck and tail are absent Head directly joins with the trunk and therefore it can not move its head. The conical head has two large bulging eyes. .Behind each eye is a circular area called tympanic membrane. These membranes help in hearing At the tip of the snout, it has two openings called external nostrils through which the frog breathes. There is a membranous skin between its toes, which help in swimming. There are five toes in each foot but the hand has only four fingers because the thumb is rudimentary. In male frog, the first finger is thicker than the others. The eyes of frogs have two eyelids. An upper eyelid which is immovable and a lower eyelid which is slightly movable. A transparent membrane, the nictitating membrane is attached under the lower eyelid. This membrane can be drawn upwards over the surface of the eye to clean and moisten it when the frog is on land and to protect it when the frog is in water Frogs lay eggs in winter season in water. They hibernate (go to winter sleep) by burying themselves in the mud for the whole winter.

Write a note on different parts of brassica flower.

noreply@blogger.com (Anonymous) — Sat, 24 Jan 2015 09:19:00 +0000

PARTS OF BRASSICA FLOWER:

A flower is a reproductive part of the plant. With the maturation of age, the plant bears small yellowish flowers. Flowers grow on young branches in a special way. This branch is called pedicel and the arrangement is called inflorescence. The tip of the pedicel bears thalamus. The floral leaves are arranged in four whorls on the thalamus. They are as under:

(1) Calyx:

This is the outermost whorl and consists of four free sepals. The sepals are light greenish in young flowers. but as the flowers mature, their colour also becomes yellowish like that of the petals. In young flowers, sepals cover the inner parts of the flower. The basic function of calyx is to protect the inner parts of the flower.

(2) Corolla:

Corolla is the second whorl of floral leaves. It consists of four free yellow petals. Its yellow colour is conspicuous and can attracts insects, honey bees and butterflies which helps in pollination (transfer of pollen grains from another to stigma).

(3) Androecium:

The androecium lies inside the petals. It makes the third whorl of the floral leaves. Its parts are not leaf like. The androecium consists of six free stamens, which are the male reproductive organs of the flower. In brassica flower, the stamens are arranged in two circles. The outer circle has two small stamens. The inner circle has four long stamens. Each stamen has two parts: a lower delicate stalk called the filament and an upper swollen part called the anther. Each anther contains numerous pollen grains. When the anther matures, a longitudinal slit appears in its walls from which pollen grains escape. At the base of the filament, four nectaries are present. When insects are attracted towards the flowers to collect this nectar, pollen grains get attached to their bodies and are transferred from one flower to another and pollination results.

(4) Gynoecium:

This is the inner most and the fourth whorl occupying a central position in the flower. Each part of the gynoecium is called carpel. Gynoecium makes the female reproductive organs of the plant. In Brassica, gynoecium is formed by the union of two carpels. Each carpel is divisible into three main parts. The lower swollen part is the ovary. Above the ovary, camel extends into a thin stalk, the style. The style has swollen tip which is called stigma. In the ovary, many ovules are present which become seeds. The ovary becomes a fruit. The fruit of brassica is a dry capsule.

Write a note on the structure of amoeba.

noreply@blogger.com (Anonymous) — Sat, 24 Jan 2015 08:58:00 +0000

STRUCTURE OF AMOEBA:

Amoeba is a unicellular organism found in muddy water .at the bottom of ponds and ditches. It measures about 0.25 mm in size. It does not have a fixed shape. It keeps on changing its shape all the times.

1. Cell Membrane:

It is a thin membrane. It is also called plasmalemma. It is protective in function.

2. Cytoplasm:

It is differentiated into two parts:
(i) Ectoplasm: The outer portion of cytoplasm is clear and transparent.
(ii) Endoplasm:The inner, viscous, translucent and granular part of cytoplasm is called endoplasm. The endoplasm appears granular and darker in colour due to the presence of reserve food materials.

3. Food Vacuoles:

The endoplasm contains food vacuoles of all sizes. There are many of them inside the endoplasm. Food vacuoles contain food particles. 4. Contractile Vacuole:
There is also a large contractile vacuole inside the endoplasm. The contractile vacuole functions to remove excess water from the body. When it reaches its maximum size, it bursts and starts forming again.

5. Nucleus:

There is an oval shaped nucleus in the centre which controls all the metabolic activities of the organism.

6. Pseudopodia (singular pseudopodium):

Amoeba moves by producing finger like projections called pseudopodia. The pseudopodia are also used to capture food particles, which are then placed inside the food vacuole. Amoeba respires by exchanging gases with the surrounding water through its surface by diffusion.