Solutions of NCERT Problems

Classification Based on Physical State of Dispersed Phase and Dispersion Medium

2011-12-04T08:25:00.000-08:00

Depending upon whether the dispersed phase and the dispersion medium are solids, liquids or gases, eight types of colloidal systems are possible. A gas mixed with another gas forms a homogeneous mixture and hence is not a colloidal system.

Many familiar commercial products and natural objects are colloids. For example, whipped cream is a foam, which is a gas dispersed in a liquid. Firefighting foams, used at emergency airplane landings are also colloidal systems. Most biological fluids are aqueous sols (solids dispersed in water). Within a typical cell, proteins and nucleic acids are colloidal-sized particles dispersed in an aqueous solution of ions and small molecules.

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CBSE(NCERT) Class 12th English Book Chapter 1 - THE THIRD LEVEL

2011-08-10T12:13:00.000-07:00

The chapter “The Third Level” deals with the imagination and fantasy in which a young man name charley use to feel that there were three level at grand central station each having a definite feature as Ist level was related to that kind of a platform from which one can board the trains for far off places and IInd level was related that halt from which the trains of sub-urban areas could be board up and the last but not the least that only charley use to feel that there was really a third level. Charley was a young man of 31 years who use to feel that third level really existed because he uses to get escaped from the insecurity, fear, selfishness, misunderstandings, bloods heel etc. being prevalent in the modern world. So, he wanted to go such a place where he could be able to get peace and friendly people. So, he always use to feel that the place of his Grand Father, Galesburg in the Era of 1894 was the best place to live in as he had heard from his Grand Father that in his time things were pretty nice and the people were very amiable (Friendly) and social. Charley therefore wanted to get settled there with his wife Louisa every time, Charley use to wonder (to walk) in such of third level. Generally in his lunch time. A part from looking for the third level. Charley also use to collect stamps, it was his past time hobby. Dr. Sam who was a psychiatrist and the friend of Charley. He diagnosed him and came to the conclusion refuge from the realty. He hoped that getting engaged in such a habit of collecting stamp would be very better for him to get relief from his ailment of working dream wish fulfillment. Dr. Sam also got very worried when the wife of Charley informed him that her husband had withdrawn 300 dollars from the bank in order to pay the fare of the tickets because according to her husband, he had actually got into the third level at grand central station which he use to feel was growing like a tree spreading all its branches and roots in all the direction. Dr. Sam thought that to treat Charley, then he himself had to feel the third level so he made a plan that he would not meet Charley for several days and his wife provided Dr. Sam, the first day cover that was issued on 18th july 1894. In the provided first day cover, Dr. Sam mentioned that he was very happy to be on the IIIrd level invented Charley with his wife on the IIIrd level to live peacefully as expected to be there at Galesburg, In the Era of 1894.

First Day Cover:-

“First day cover refers to the affixment of the new stamp on an envelope and self address on the day of the issue of the stamp.”

PART II - WE TOO ARE HUMAN BEINGS BY BAMA

In the second part of the story “Memories of Childhood” the author Bama has also recounted her experience in the form of a story named “we too are human beings”. In this story, Bama has recounted her childhood experience about the system of untouchability when she was in class-3. She use to take 30 min or 1 complete hour to go back home from the school after the departure time. She used to enjoy all fun and the shops of the market once it so happen when she could not control herself from a great laughter. She saw an elder man from her street was holding that the packet was meant for the landlord and when the elderly man went up to him, with great sense of respect, that man gave the packet to the landlord taking care not to touch the packing except its string.

When Bama narrated the whole event to her elder brother Anand in just a very comical and a hilarious way. When Anand heard all this, he explained Bama that it was not a hilarious at the elderly man had hold up the packet only by its string because the elderly man was belonged to the lower cast while the landlord was belonged to the higher cast. The lower cast people were not permitted to touch the belongings of the high cast people and the lower cast people were bound to face all humiliations and all the indignities. Here Anand also narrated his experience when he was asked about his cast through his address. Here, the small girl, Bama felt very sat and angry also. She wanted to break all these borders of the caste system. At this, her brother explained her that in order to get the equal status with the dignity, she had to work very hard. The words of her brother put a very deep impression in her mind and she really worked very hard and stood first in her class and stood first in her class and achieved al dignity and the equal status.

Ques-1 Give two reasons why Zitkala-Sa misses her mother?

Ans. When zitkala-Sa was sent to the Christian school she was really missing her another very much because she was not able to take up all the restrictions with all the rules and regulations and also she remembered her mother very much when she came to know that her long hair was going to be cut off.

Ques-2 Why did Zitkala-Sa sneak away the dining hall? Where did she go away from there?

Ans. When Zitkala-Sa came to know that her long hair was going to be cut off then she decided that she would not kneel down in front of the authorities so she sneaked away the dining hall to dark room.

Ques-3 How did Zitkala-Sa try to save her hair?

Ans. Zitkala-Sa tried a lot to save her hair by hiding herself into a dark room under the bed.

Ques-4 How did way side’s scene and activities afflict Bama’s going back from school?

Ans. While going back from school, Bama use to take 30 min or just one complete hour to enjoy all the activities and the marked scenes going on at that time.

Ques-5 How did the elder belonging to Bama’s community behave before his master why?

Ans. The elder was holding the packet of the food stuffs just by its string before his master. The elder was holding the packet in this strange manner because he was belonged to the lower cast and was just an untouchable.

Ques-6 What was Bama’s chief worry on seeing an elder carrying the foodstuffs? What was she ignorant about?

Ans. When Bama’s saw the elder carrying the food stuff in such a strange manner, Bama got worried that the food stuff will fall down. Bama was completely ignorant about the cast system and the system of untouhchability prevalent at that point of time.

CBSE Chapter wise Notes Class 12 | Chemistry | THE SOLID STATE

2011-08-05T09:00:00.000-07:00

The vast majority of solid substances like high temperature superconductor’s biocompatible plastics, silicon chips etc. are destined to play an ever expanding role in future development of science.

Liquids and gases are called fluids because of their ability to flow. The fluidity in both of these states is due to the fact that the molecules are free to move about. On the contrary, the constituent are free to move about. On the contrary, the constituent particles in solids have fixed positions and can only oscillate about their mean positions. This explains the rigidity in solids. In crystalline solids, the constituent particles are arranged in regular patterns.

General characteristics of Solid State

Matter can exist in three state namely solid, liquid and gas, under a given set of condition of temperature and pressure, which of these would be the most sable state of a given substance depends upon the net effect of two opposing factors. Intermolecular forces tend to keep the molecules closer, whereas thermal energy tends to keep them apart by making them move faster. At sufficiently low temperature, the thermal energy is low and intermolecular forces bring them so close that they cling to one another and occupy fixed positions. These can still oscillate about their mean positions and substance exists in solid state. The following are the characteristics properties of the solid state:

Properties of the solid state

The have definite mass, volume and shape.
Intermolecular distances are short.
Intermolecular forces are strong.
Their constituent particles have fixed positions and can only oscillate about their mean positions.
They are incompressible and rigid.

Amorphous and crystalline Solids

Solid can be classified as crystalline or amorphous on the basis of the nature of order present in the arrangement of their constituent particles. A crystalline solid usually consists of a large number of small crystals, each of them having a definite characteristics geometrical shape. In a crystal, the arrangement of constituent particles is ordered. It has long range order which means that there is a regular pattern of arrangement of particles which repast itself periodically over the entire crystal. Sodium chloride and quartz are typical example of crystalline solids. An amorphous solid consists of particles of irregular shape. The arrangement of constituent particles in such a solid has only short range order. In such an arrangement, a regular and periodically repeating pattern is observed over short distances only. Such portions are scattered and in between the arrangement is disordered.

While the two structures are almost identical, yet in the case of amorphous quartz glass there is no long range order. The structure of amorphous solid is similar to that of liquids. Glass, rubber and plastics are typical example of amorphous solids. Due to the differences in the arrangement of the constituent particles, the tow types of solids differ in their properties.

Crystalline solids have a sharp melting point. In the other hand, amorphous solids soften over a range of temperature and can be molded and blown into various shapes. On heating they become crystalline at some temperature. Some glass objects from ancient civilizations are found to become milky in appearance because of some crystallization.

Crystalline solids are in nature, that is, some of their physical properties like electrical resistance or refractive index show different values when measured along different directions in the same crystals. This arises from different arrangement f particles in different directions.

Since the arrangement of particles is different along different directions, the value of same physical property is found to be different along each direction.

Amorphous solids on the other hand are isotropic in nature. It is because there is no long range order in them and arrangement is irregular along all the directions. Therefore, value of any physical property would be same along any directions.

CHAPTER 13 | WHY DO WE FALL ILL | Class 9th | NCERT | Notes

2011-07-17T11:13:00.000-07:00

Health and disease in human communities are very complex issuers, with many interconnected causes. We also realize that the ideas of what health and disease mean are themselves very complicated.

We have seen that cells are the basic units of living beings. Cells are made of a variety of chemical substances proteins, carbohydrates, and fats of lipids. Some thing of the other is always happening. Cells move from place. Something or the other is always happening. Cells move from place to place. Even in cells that do move, there is repair going on. New cells are being made, in our organs or tissues, there are various specialized activities going on the heart is beating, the lungs are breathing the kidney is filtering urine, the brain is thinking.

Personal and community issues both matter for health

If health means a state of physical, mental and social well-being, it cannot be something our own. The health of all organisms will depend on their surroundings or their environment. The environment includes the physical environment. So for example, health is at risk in a cyclone in many ways.

Distinctions between healthy and disease-free

If this is what we mean by health what do we mean by disease? The word is actually self-explanatory- we can think of it as disease – disturbed ease. Disease in words literally means being uncomfortable. However, the word is used in a more limited meaning, We talk of disease when we can find a specific and particular cause for discomfort. This does not mean that we have to know threw absolute final cause: we can say that someone is suffering from diarrhea without knowing exactly what has caused the loose motions.

What does disease look like?

When there is a disease. Either the functioning or the appearance of one or more systems of the body will change for the worse. These changes give rise to symptoms and signs of disease. Symptoms of disease are the things we feel as being wrong. So we have a headache, we have cough, we have loose motions, we have cough, we have loose motions, we have wound with pew: these are all symptoms. These indicate that there may be disease, but they don’t indicate what the disease is for example a headache may mean just examination stress or, very lately. It may mean meningitis, or any one of a dozen different diseases. Acute and chronic diseases

The manifestations of disease will be different depending on a number of factors, one of the most obvious factors that determine how we perceive the disease is its duration. Some diseases last for only very short periods of all know from experience that the common cold lasts only a few days, other ailments can last for a long time, even as much as a life time and for a long time even as much as lifetime, and are called chronic diseases. An example is the infection causing elephantiasis which is very common in some parts of India.

Chronic diseases and poor health

As we can imagine, acute and chronic disease have different effects on out health. Any disease that causes poor functioning of some part of the body will affect out general health as well. This is because all functions but an acute disease, which is over very soon, will not have time to cause major effects on general health, while a chronic disease will do so.

Causes of diseases

What causes disease? When we think about causes of diseases, we must remember that there ate many levels of such causes. Let us look at an example. If there is baby suffering from loose motions, we can say that the cause of the lose motions is an infection with a virus. So the immediate cause of the disease is a virus.

One reason might be that this baby is not health. As a result it might be more likely to have disease when exposed to risk whereas healthier babies would not. Why is the baby not healthy? Perhaps because it is not well nourished and does not get enough food. So, lack of good nourishment becomes a second level cause of the disease the baby is suffering from, perhaps because it is from a household which is poor.

Infectious and non infectious causes

As we have seen. It is important to keep public health and community health factors in mind when we think about causes of disease. We can take that approach a little further, it is useful to think of the immediate causes of disease as belonging to two distinct types, one group of causes is the infectious agents, mostly microbes or micro organisms. Diseases whr3e microbes are the immediate causes are called infectious diseases. This is because the microbes can spread in the community, and the disease they cause will spread with them.

On the other hand, there are also diseases that are not caused by infectious agents. Their causes vary, but they are not external causes like microbes that can spread in the community. Instead, these are mostly internal, non infectious causes,

For example, some cancers are caused by genetic abnormalities; high blood pressure can be caused by excessive weight and lack of exercise. You can think of many other diseases where the immediate causes will not be infectious.

Infections diseases

We have seen that the entire diversity seen in the living world can be classified into a few groups. This classification is based on common characteristics between different organisms. Organisms that can cause disease are found in a wide range of such categories of classification. Some of them are viruses, some are bacteria, some are fungi, and some are single celled animals or protozoan. Some diseases are also caused by multicellular organisms, such as worms of different kinds.

Common example of disease caused by viruses are the common cold, influenza, dengue fever AIDS. Disease like typhoid fever, cholera, tuberculosis and anthrax are caused by bacteria. Many common skin infections are caused by different kinds of fungi. Protozoan microbes cause many familiar diseases, such as malaria and Kalahari. All of us have also come across intestinal worm infections, as well as diseases like elephantiasis caused by different species of worm.

All viruses and all bacteria are closely related to each other than to viruses and vices versa. This means that many important life processes are similar in the bacteria group result, drugs that block one of these life processes in one member of the group is likely of the group. But the same drug will not work against a microbe belonging to a different group.

Activity

Find out how many of you in yours class had cold/cough/fever recently.

How many of you took antibiotics ask your parents if you had antibiotics?

How long were those who took antibiotics ill?

How long were those who didn’t take antibiotics ill?

Means of spread

Many microbial agents can commonly move from an affect person to someone else in a variety of ways. In other words, they can be communicated, and so are also called communicable disease.

Such disease causing microbes can spread through the air. This occurs through the little droplets thrown out by an infected person who sneezes or coughs. Someone standing close by can breathe in these droplets, and the microbes get a chance to start a new infection. Examples of such dis3eases spread through the air are the common cold, pneumonia and tuberculosis

Diseases can also be spread through water. This occurs if the excreta from some on suffering from an in factious gut disease, such as cholera, get mixed with the drinking water used by people living nearby. The cholera causing microbes will enter new hosts through the water they drink and cause disease in them. Such diseases are much more likely to spread in the absence of safe supplies of drinking water.

The sexual act is one of the closest physical contacts two people can have with each other. Not surprisingly, there are microbial diseases such as syphilis or AIDS that are transmitted by sexual contact from one partner to the other. However, such sexually transmitted disease is not spread by casual physical contact. Casual physical contacts include handshakes or hugs or sports, like wrestling, or by any of the other ways in which we touch each other socially. Other than the sexual contact, the AIDS virus can also spread through blood to blood contact with infected people or from an infected mother her baby during pregnancy or through breasts feeding.

Organ – Specific and tissue Specific Manifestations

The disease causing microbes enter the body though these different means. The body is very large when compared to the microbes. So there are many possible places, organs or tissues, where they could go.

Different spices of microbes seem to have evolved to home in on different parts of the body. In part, this selection is connected to their point of entry. If they enter from the air via the nose, they are likely to go to the lungs.

The signs and symptoms of a disease will thus depend on the tissue or organ which the microbe targets. If the lungs are the targets, then symptoms will be cough and breathlessness. If the liver is targeted, there will be jaundice. If the brain is the target, we will observe headaches, vomiting, fits or unconsciousness. We can imagine what the symptoms and signs of an infection will be if we know what the target tissue or organ is, and the function that are carried out by this tissue or organ.

In some cases, the tissue specifies of the infection leads to very general seeming effects. For example, in HIV infection, the virus goes to the immune system and damages its function. Thus, many of the effects of HIV-AIDS are because the body can no longer fight off the many minor infections that we face everyday. Instead, every small cold can become pneumonia. Similarly, a manor gut infection can produce major diarrhea with blood loss. Ultimately, it is these other infection that kill people suffering from HIV-AIDS.

PRINCIPLES OF TREATMENT

Based on what we have learnt so far, it would appear that there are two ways to treat an infectious disease. One would be to reduce the effects of the disease and the other to kill the cause of the disease. For the first, we can provide treatment that will reduce the symptoms. The symptoms are usually because of inflammation. For example, we can take medicines that bring down fever, reduce pain or loose motions. We can take bed rest so that we can conserve our energy. This will enables to focus on healing.

But this kind of symptom directed treatment by it self will not make the infecting microbe go away and the disease will not be cured. For that, we need to be able to kill off the microbes.

Principles of prevention

All of what we have talked about so far deals with how to get rid of an infection in some one who has the disease. But there are three limitations of this approach to dealing with infectious disease. The first is that once someone has a disease, their body functions are damage and may never recover completely. The second is that treatment will take time, which means that someone suffering from a disease is likely to be bedridden for some time even if we can give proper treatment. The third is that person suffering from an infectious disease can serve as the source from where the infection may spread to other people. This leads to the multiplication of the above difficulties. It is because of such reasons that prevention of disease is better than their cure.

These are the general ways of preventing infections. They relate to a peculiar property of the immune syst4em that usually fights off microbial infections. Let us cite an example to try and understand this property.

These days, there is no small pox any where in the world. But as recently as a hundred years ago, small pox epidemics were not at all uncommon. In such an epidemic, people used to be very afraid of coming near someone suffering from the disease since they were afraid of catching the disease.

Important Point

Health is a state of physical, mental and social well being.
Diseases are classified as acute or chronic, depending on their duration.
Infectious agents belong to different categories of organisms and may be unicellular and microscopic or multicellular.
Infectious diseases can be prevented by public health hygiene measures that reduce exposure to infectious agents.

CHAPTER 12 | Class 9th | CBSE | NCERT | SOUNDS

2011-07-17T11:12:00.000-07:00

Sound is a form of energy which produces a sensation of hearing in our ears. There are also other forms of energy like mechanical energy, heat energy, light energy etc.

Propagation of Sound

Sound is produced by vibrating objects. The matter or substance through which sound is transmitted is called a medium. It can be solid, liquid or gas. Sound moves through a medium from the point of generation to the listener. When an object vibrates, it sets the particles of the medium around it vibrating.

Air is the most common medium through which sound travels. When a vibrating object moves forward, it pushes and compresses the air in front of it creating a region of high pressure. This region is called a compression. This compression starts to move away from the vibrating object. When the vibrating objects moves back words, it creates a region of low pressure called rarefaction. As the object moves back and forth rapidly, a series of compressions and rarefaction is created in the air.

Sound needs a medium to Travel

Sound is a mechanical wave and needs a material medium like air, water, steel etc. for its propagation. It cannot travel through vacuum.

Characteristics of a Sound Wave

We can describe a sound wave by its

· Frequency

· Amplitude and

· Speed

The density as well as the pressure of the medium at a given time varies with distance, above and below the average value of density and pressure.

The distance between two consecutive compressions or two consecutive rarefactions is called the wavelength is usually represented by l (lambda). Its SI unit is metre (m).

The time taken by two consecutive compressions or rarefactions to cross a fixed point pint is called the time period of the wave. In other words, we can say that the time taken for one complete oscillation in the density of the medium is called the time period of the sound wave. It is represented by the symbol T. its SI unit is second (s). Frequency and time period are related as follows: v = 1 / T.

The speed of sound is defined as the distance which a point on a wave, such as a compression or a rarefaction, travels per unit time.

We know,

Speed, v = distance / time

= l / t

Here l is the wave length of the sound wave. It is the distance traveled by the sound wave in one time period (T) of the wave. Thus,

v = l v (1 / T = v)

v = l v

This is, speed = wavelength x frequency.

The amount of sound energy passing each second through until area is called the intensity of sound. We sometimes use the terms “loudness” and “intensity” interchangeably, but they are not the same. Loudness is a measure of the response of the ear to the sound. Even when two sounds are of equal intensity, we may hear one as louder than the other simply because our ear detects in better.

Speed of Sound in different media

State	Substance	Speed in m/s
Solids	Aluminium Nickel Steel Iron Brass Glass (Flint)	6420 6040 5960 5950 4700 3980
Liquids	Water (Sea) Water (distilled) Ethanol Methanol	1531 1498 1207 1103
Gases	Hydrogen Helium Air Oxygen Sulphur dioxide	1284 965 346 316 213

Sound propagates through a medium at a finite speed. The sound of a thunder is heard a little later than the flash of light is seen. So we can make out that sound travels with a speed which is much less than the speed of light. The speed of sound depends on the properties of the medium through which it travels. The speed of sound in a medium depends on temperature the speed of sound increases. For example the speed of sound in air is 331 m s^-1 at 0⁰ C and 344 ms^-1 at 22⁰ C. the speeds of sound at a particular temperature in various media are listed in table.

Reflection of Sound

Sound bounces off a solid or a liquid like a rubber ball bounces off a wall. Like light, sound gets reflected at the surface of solid or liquid and follows the same laws of reflection. The directions in which the sound is incident and is reflected make equal angels with normal to the reflecting surface at the point of incidence, and the three are in the same plane. An obstacle of large size which may be polished or rough is needed for the reflection of sound waves.

Echo

If we shout or clap near a suitable reflecting object such as tall building or a mountain, we will hear the same sound again a little later. This sound which we hear is called an echo. The sensation of sound persists in our brain for about 0.1 s. to hear a distinct echo the time interval between the original sound and reflected one must be at least 0.1 se. If we take the speed of sound to be 344 m/s at a given temperature, say at 22⁰ C in air, the sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1s.

Reverberation

A sound created in a big hall will persist by repeated reflection from the walls until it is reduced to a value where it is no longer audible. The repeated reflection that results in this persistence of sound is called reverberation. In an auditorium or big hall excessive reverberation is highly undesirable. To reduce reverberation, the roof and walls of the auditorium are generally covered with sound absorbent material like compressed fiberboard, rough plaster or draperies. The seat materials are also selected on the basis of their sound absorbing properties.

Range of Hearing

The audible range of sound for human beings extends from about 20 Hz to 20000 Hz. Children under the age of five and some animal, such as dogs can hear up to 25 kHz (1 kHz = 1000 Hz). As people grow older their ears become less sensitive to higher frequencies. Sounds of frequencies below 20 Hz are called infrasonic sound or infrasound. If we could hear infrasound we would hear the vibrations of a pendulum just as we hear the vibration of the wings of a bee. Rhinoceroses communicate using infrasound of frequency as low as 5 Hz.

Applications of Ultrasound

Ultrasounds are high frequency waves. Ultrasounds are able to travel along well defined paths even in the presence of obstacles. Ultrasounds are used extensively in industries and for medical purpose.

Sonar

The acronym SONAR stands for sound navigation and ranging. Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.

Sonar consists of a transmitter and a detector and is installed in a boat or a ship. The transmitter produces and transmits ultrasonic waves. These waves travel through water and after striking the object on the seabed, get reflected back and are sensed by the detector. The detector converts the ultrasonic waves into electrical signal which are appropriately interpreted. The distance of the object that reflected the sound wave can be calculated by knowing the speed of sound in water and time interval between transmission and reception of the ultrasound. Let the time interval between transmission and reception of ultrasound signal be t and the speed of sound through seawater be v. the total distance, 2d traveled by the ultrasound is then, 2d = v x t.

Structure of Human Ear

We are able to hear with the help of an extremely sensitive device called ear. It allows us to convert pressure variations in air with audible frequencies into electric signal that travel to the brain via the auditory nerve. The auditory aspect of human ear is discussed below.

The outer ear is called ‘pinna’. It collects the sound from the surroundings. The collected sound passes through the auditory canal. At the end of the auditory canal there is a thin membrane called the ear drum or tympanic membrane. When a compression of the medium reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward. Similarly, the eardrum moves out ward when a rare faction reaches it. In this way the eardrum vibrates. The vibrations are amplified several times by three bones in the middle ear. The middle ear transmits the amplified pressure variations received from the sound wave to the inner ear. In the inner ear, the pressure variations are turned into electrical signals by the cochlea. These electrical signals are sent to the brain via the auditory nerve, and the brain interprets them as sound.

Important Point

Sound is produced due to vibration of different objects.
Sound travels as a longitudinal wave through a material medium.
Sound cannot travel in vacuum.
The number of complete oscillations power unit time is called frequency (v), v = 1/T.
The speed v, frequency v, and wavelength l, of sound are related by the equation, v = lv
The speed of sound depends primarily on the nature and the temperature of the transmitting medium.
The persistence of sound in an auditorium is the result of repeated reflection of sound and is called reverberation.
The amount of sound energy passing each second through unit area is called the intensity of sound.
The audible range of hearing for average human beings is in the frequency range of 20 Hz – 20 kHz.
Ultrasound has many medical and industrial applications.

CHAPTER 10 | GRAVITATION | NCERT | NOTES | Class 9th

2011-07-17T11:09:00.000-07:00

CHAPTER 10 GRAVITATION

Gravitation

An object when thrown upwards reaches a certain height and then falls downwards. It is due to gravitational force.

Universal law of gravitation

Every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance between them. The force is along the line joining the centers of two objects.

Let two objects A and B of masses M and m lay at a distance d from each other. Let the force of attraction between two objects be F. According to the universal law of gravitation, the force between two objects is directly proportional to the product of their masses. That is,

F µ M x m

And the force between two objects is inversely proportional to the square of the distance between them, that is, F µ 1 / d²

Combining eqs we get. F µ (M x m) / d²

Or F = G (M x m) / d²

Where G is the constant of proportionality and is called the universal gravitational constant. By multiplying crosswise, Eqs gives

F x d² = G M x m

Or G = F d² / M x m

The SI unit of G can be obtained by substituting the units of force, distance and mass in eqs. As N m² kg^-2

The accepted value of G is 6.673 X 10^-11 N m² kg^-2

Important of the universal Law of Gravitation

The universal law of gravitation successfully explained several phenomena which were believed to be unconnected:

v The force that binds us to the earth;

v The motion of the moon around the earth;

v The motion of planets around the sun;

v The tides due to the moon and the sun;

Free Fall

The earth attracts objects towards it. This is due to the gravitational force. Whenever objects fall towards it the earth under this force alone, we say that the objects are in free fall.

From the second law of motion that force is the product of mass and acceleration.

There is acceleration involved in falling objects due to the gravitational force and is denoted by g. therefore the magnitude of the gravitational force F will be equal to the product of mass and acceleration due to the gravitational force, that is,

F = m g

From Eqs. We have

mg = G (M x m) / d²

Or g = G M / d²

Where M is the mass of the earth, and d is the distance between the object and the earth.

Let an object be on or near the surface of the earth. The distance d will be equal to R, the radius of the earth. Thus, for object on or near the surface of the earth,

mg = G (M x m) / d²

g = G M / R²

To calculate the value of g

To calculate the value of g, we should put the values of G, M and R in eqs namely, universal gravitational constant,

G = 6.7 x 10^-11 N m² kg^-2, mass of the earth

M = 6 x 10²⁴ kg, and radius of the earth,

R = 6.4 x 10⁶ m.

g = G M / R²

= 6.7 x 10^-11 N m² kg^-2 x 6 x 10²⁴ kg / (6.4 x 10⁶m)²

Thus, the value of acceleration due to gravity of the earth, g = 9.8 ms^-2

Mass

The mass of an object is the measure of its inertia. We have also learnt that greater the mass, the greater is the inertia. It remains the same whether the object is on the earth, the moon or even in outer space. Thus, the mass of an object is constant and does not change from place to place.

Weight

The earth attracts every object with a certain force and this force depends on the mass (m) of the object and the acceleration due to the gravity (g). the weight of an object is the force with which it is attracted towards the earth,

We know that F = m x a,

That is F = m x g.

The force of attraction of the earth on an object is known as the weight of the object. It is denoted by W. Substituting the same in Eqs, we have W = m x g.

Weight of an object on the Moon

The weight of an object on the earth is the force with which the earth attracts the object. In the same way, the weight of an object on the moon is the force with which the moon attracts that object. The mass of the moon is less than that of the earth. due to this the moon exerts lesser force of attraction on objects.

Let the mass of an object be m. let its weight on the moon be W m. let the mass of the moon be Mm and its radius be Rm. By applying the universal law of gravitation, the weight of the object on the moon will be

Wm = G Mm x m / R²m

Let the weight of the same object on the earth be W e. the mass of the earth is M and its radius is R.

Celestial Body	Mass (kg)	Radius (m)
Earth Moon	5.98 x 10²⁴ 7.36 x 10²²	6.37 x 10⁶ 1.74 x 10⁶

From the eqs we have

We = G M x m / R²

Substituting the values from table in eqs, we get.

Wm = G 7.36 x 10²² kg x m / (1.74 x 10⁶m)²

Wm = 2.431 x 10¹⁰ G x m

And We = 1.474 x 10¹¹ G x m

Dividing eqs:

Wm/ We = 2.431 x 10¹⁰/ 1.474 x 10¹¹

Or Wm/ We = 0.165 = 1 / 6

Weight of the object on the moon / weight of the object on the earth = 1 / 6

Weight of the object on the moon = (1 / 6) x its weighty on the earth.

Thrust and Pressure

When we stand on loose sand, the force that is the weight of our body is acting on area equal to area of our feet. When we lie down, the same force acts on an area equal to the contact area of our whole body. This is larger than the area of our feet. Thus, the effects of forces of the same magnitude on different areas are different. In the above cases, thrust is the same. But effects are different. Therefore the effect of thrust depends on the area on which it acts.

The effect of thrust on sand is larger while standing than while lying. The thrust on unit area is called pressure. Thus,

Pressure = Thrust / area

Substituting the SI unit of thrust and area in eqs. We get the SI unit of pressure as N / m² or N m^-2

Pressure in Fluids

All liquids and gases are fluids. A solid exerts pressure on a surface due to its weight. Similarly, fluids have weight, and they also exert pressure on the base and walls of the container in which they are enclosed. Pressure exerted in any confined mass of fluid is transmitted undiminished in all directions.

Why objects float or sink when placed on the surface of the water?

Activity

· Take a beaker filled with water.

· Take an iron nail and placed it on the surface of the water.

· Observe what happens

The nail sinks. The force due to the gravitational attraction of the earth on the iron nail pulls it downwards. There is an up thrust of water on the nail, which pushes it upwards. But the downward force acting on the nail is greater than the up thrust of water on the nail. So it sinks.

Archimedes’ Principle

Activity

· Take a Piece of stone and tie it to one end of a rubber string or a spring balance.

· Suspend the stone by holding the balance or the string.

· None the elongation of the string or the reading on the spring balance due to the weight of the stone.

· Now, slowly dip the stone in the water in a container.

· Observe what happens to elongation of the string or the reading on the balance.

We find that the elongation of the string or the reading of the balance decreases as the stone is gradually lowered inn the water. However, no further change is observed once the stone get fully immersed in the water.

Relative Density

The density of a substance is defined as mass of a unit volume. The unit of density is kilogram per meter cube the density of a given substance, under specified conditions, remains the same. Therefore the density of a substance is one of its characteristic properties. It is different for different substances. For example, the density of gold is 19300 kg m^-3 while that of water is 1000 kg m^-3. The density of a given sample of a substance can help us to determine its purity.

It is often convenient to express density of a substance in comparison with that of water. The relative density of a substance is the ratio of its density to that of water:

Relative density = density of a substance / density of water.

Since the relative density is a ratio of similar quantities, it has no unit.

Important Point

The law of gravitation states that the force of attraction between any two objects is proportional to the product of their masses and inversely proportional to the square of the distance between them. The law applies to objects any where in the universe. Such a law is said to be universal.
Gravitation is a weak force unless large masses are involved.
Force of gravitation due to the earth is called gravity.
The weight of a body is the force with which the earth attracts it.
The weight is equal to the product of mass and acceleration due to gravity.
The weight may vary from place to place but the mass stays constant.
All objects experience as force of buoyancy when they are immersed in a fluid.

CHAPTER 11 WORK AND ENERGY

Scientific Conception of Work

If we push a pebble lying on a surface, the pebble moves through a distance. We exerted a force on the pebble and the pebble got displaced. In this situation work is done.

Work don by a Constant Force

Let a constant force, F act on an object. Let the object be displaced through a distance, s in the direction of the force. Let W be the work done. We define work to be equal to the product of the force and displacement.

Work done = force x displacement

W = Fs

Thus, work done by force acting on an object is equal to the magnitude and no direction.

In eqs, if F = 1 N and s = 1 m then the work done by the force will be 1 N m. Here the unit of work is Newton meter (N m) or joule (J). Thus 1 J is the amount of work done an object when a force of 1 N displaces it by 1 m along the line of action of the force.

Energy

When a balloon is filled with air and we press it we notice a change in its shape. As long as we press it gently, it can come back to its original shape when the force is withdrawn. However, if we press the balloon hard, it can even explode producing a blasting sound. In all these examples, the objects acquire, through different means, the capability of doing work. An object having a capability to do work is said to possess energy. The object which does the work loses energy and the object on which the work is done gains energy.

The energy possessed by an object is thus measured in terms of its capacity of doing work. The unit of energy is, therefore, the same as that of work, that is, joule (J). 1 J is the energy requires doing 1 Joule of work. Some times a larger unit of energy called kilo joule (k J) is used. 1 kJ equals 1000 J.

Forms of Energy

The various forms include mechanical energy (potential energy + kinetic energy), heat energy, chemical energy, electrical energy and light energy.

The relation connection the initial velocity (u) and final velocity (v) of an object moving with a uniform acceleration a, and the displacement, s is

v²- u² = 2 a s

This gives s = (v²- u²)/2 a

We know F = m a. thus, we can write the work done by the force,

F as W = m a x { (v²- u²) / 2a}

Or W = ½ m (v²- u²)

If the object is starting form its stationary position, that is, u = 0, then

W = ½ m v²

Thus, the kinetic energy possessed by an object of ass, m and moving with a uniform velocity, v is Ek = ½ m v²

Potential Energy

The energy gets stored due to the work done on the object. The energy transferred to an object is stored as potential energy if it is not used to cause a change in the velocity or speed of the object.

We transfer energy when we stretch a rubber band. The energy transferred to the band is its potential energy. We do work while winding the key of a toy car. The energy transferred to the spring inside is stored as potential energy. The potential energy possessed by the object is the energy present in it by virtue of its position or configuration.

Potential energy of an object at height

Consider an object of mass, m. let it be raised through a height, h from the ground. A force is required to do this. The minimum force required to raise the object is equal to the weight of the object, mg. the object gains energy equal to the work done on it. Let the work done on the object against gravity be W. that is

Work done, W = force x displacement

= mg x h

= mgh

Since work done on the object is equal to mgh, energy equal to mgh units is gained by the object. This is potential energy (Ep) of the object.

Ep = mgh

Law of Conservation of Energy

Let an object of mass, m be made to fall freely form a height, h. at the start, the potential energy is mgh and kinetic energy is zero. It is zero because its velocity is zero. The total energy of the object is thus mgh. As it falls, its potential energy will change into kinetic. If v is the velocity of the object at a given instant, the kinetic energy would be ½ m v². As the fall of the object continues, the potential energy would decrease while the kinetic energy would increase. When the object is about to reach the ground, h = 0 and v will be the highest. Therefore the kinetic energy would be the largest and potential energy the least. However, the sum of the potential energy and kinetic energy of the object would be the same at all points, that is,

Potential energy + kinetic energy = constant or mgh + ½ mv²= constant.

Rate of doing Work

A stronger person may do certain work in relatively less time. A more powerful vehicle would complete a journey in a shorter time than a less powerful one. We talk of the power of machines like motorbikes and motor cars. The speed with which these vehicles change energy or do work is a basis for their classification. Power measures the speed of work done, that is, how fast or slow work is done. Power is defined as the rate of doing work or the rate of transfer of energy. If an agent does a work W in time t, then power is given by:

Power = work / time or p = W / t

The unit of power is watt having the symbol W. 1 watt is the power of an agent, which does work at the rate of 1 joule per second. We can also say that power is 1 W when the rate of consumption of energy is 1 J s^-1.

1 watt = 1 joule / second or 1 W = 1 J s^-1

We express larger rates of energy transfer in kilowatts (kW)

1 kilowatt = 1000 watts

1 k W = 1000 W

1 k W = 1000 J s^-1

The power of an agent may vary with time.

Commercial unit of Energy

The unit joule is too small and hence is inconvenient to express large quantities of energy. We use a bigger unit of energy called kilowatt hour (k W h).

Let us say we have a machine that uses 1000 J of energy every second. If this machine is used continuously for one hour, it will consume 1 kW h of energy. Thus 1 kW h is the energy used in one hour at the rate of 1000 J s^-1 (or 1 kW).

1 k W h = 1kW x 1 h

= 1000 W x 3600 s

= 3600000 J

1 k W h = 3.6 x 10⁶ J.

Important Point

Work done on an object is defined as the magnitude of the force multiplied by the distance moved by the object in the direction of the applied force. The unit of work is joule: 1 joule = 1 Newton x 1 meter
Work done an object by a force would be zero if the displacement of the object is zero.
An object having capability to do work is said to possess energy. Energy has the same unit as that of work.
An object in motion possesses what is known as the kinetic energy of the object. An object of mass, m moving with velocity v has a kinetic energy of ½ mv².
Power is defined as the rate of doing work. The SI unit of power is watt. 1 W = J/s.

CHAPTER 9 | FORCE AND LAWS OF MOTION | CBSE | Class 9th | NOTES

2011-07-17T11:08:00.000-07:00

Some effort is required to put stationary object into motion to stop a moving object. We ordinarily experience this as a muscular effort and say that we must push or hit or pull on an object to change its state of motion. The concept of force is based on this push hit or pull.

Balanced and Unbalanced Forces

If we put wooden block on a horizontal table, two opposite faces of the block as shown. If we apply a force by pulling the string X, the block begins to move to the right. Similarly, if we pull the string Y, the block moves to the left. But, if the block is pulled from both the sides with equal forces, the block will not move, such forces are called balanced forces and do not change the state of rest or of motion of an object.

Let us consider a situation in which two opposite forces of different magnitudes pull the block. In this case, the block would begin to move in the direction of the greater force. Thus the two forces are not balanced and the unbalanced force acts in the direction the block moves. This suggests that an unbalance force acting on an object bring it in motion.

Newton’s Law of Motion

First Law of Motion: The first law of motion is stated as:

An object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force.

In other words, all objects resist a change in their state of motion. In a qualitative way the tendency of undisturbed object to stay at rest or to keep moving with the same velocity is called inertia. This is why, the first law of motion is also known as the law of inertia.

Second Law of Motion: The first law of motion indicates that when an unbalanced external force facts on an object, its velocity changes, that is the object gets acceleration.

The second law of motion states that the rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of force.

Formula of second Law of Motion

Suppose an object of mass, m is moving along a straight line with an initial velocity, u. it is uniformly accelerated to velocity, v in time t by the application of a constant force, F throughout the time, t. The initial and final momentum of he object will be, p1 = mu and p2 = mv respectively

The change in momentum µ p2 – p1

µ mv – mu

µ m x (v – u)

The rate of change of momentum µ m x (v – u) / t

Or the applied force, F µ m x (v – u) / t

F = km x (v – u) / t

= k m a

Here a [= (v – u) / t] is the acceleration. The quantity, k is a constant of proportionality. One unit of force is defined as the amount that produces an acceleration of 1 m s-² in an object of 1 kg mass that is,

1 unit of force = k x (1 kg) x (1 m s-²).

Thus, the value of k becomes 1. From eqs. F = ma.

The unit of force is kg m s-² or Newton, which has the symbol N.

The second law of motion gives us a method to measure the force acting on an object as a product of its mass and acceleration.

Third Law of Motion

The third law of motion states that when one object exerts a force on another object, the second object instantaneously exerts a force back on the first. These two forces are always equals in magnitude but opposite in direction. These forces act on different objects and never on the same object.

Important Point

· First law of motion: an object continues to be in a state of rest or of uniform motion along a straight line unless acted upon by an unbalanced force.

· The natural tendency of objects to resist a change in their state of rest or of uniform motion is called inertia.

· The mass of an object is a measure of its inertia. Its SI unit is kilogram.

· Second law of motion: the rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force.

· Third law of motion: to every action. There is an equal and opposite reaction and they act on two different bodies.

CHAPTER 8 | MOTION | NCERT | NOTES | CLASS 9th

2011-07-17T11:06:00.000-07:00

Describing Motion

We describe the location of an object by specifying a reference point. Let us understand this by an example. Let us assume that a school in a village is 2 km north of the railway station. We have specified the position of the school with respect to the railway station. In this example, the railway station is the reference point. We could have also chosen other reference point. We could have also chosen other reference points according to our convenience. Therefore, to describe the position of an object we need to specify a reference point called origin.

Uniform Motion and Non-Uniform Motion

Consider an object moving along a straight line. Let it travel 5m the first second, 5 m more in the next second, and 5 m in the third second and 5 m in fourth second. In this case, the object covers 5 m in each second. As the object covers equal distances in equal intervals of time, it is said to be in uniform motion.

The time interval in this motion should be small. In our day-to-day life, we come across motion where objects cover unequal distances in equal intervals of time, for example, when a car is moving on a crowded street or a person is jogging in a park. These are some instances of non-uniform motion.

Example: An object travels 16 m in 4 s and then another 16 m in 2 s. what is the average speed of the object?

Solution: Total distance traveled by the object = 16m + 16m = 32m

Total time taken = 4s + 2s =6s

Average speed = total distance traveled / total time taken

= 32m / 6s = 5.33 ms^-1

Speed with Direction

The rate of motion of an object can be more comprehensive if we specify its direction of motion along with its speed. The quantity that specifies both these aspects is called velocity. Velocity is the speed of an object moving in definite direction. The velocity of an object can be uniform or variable. It can be changed by changing the object’s speed, direction of motion or both.

In case the velocity of the object is changing at a uniform rate, then average velocity is given by the arithmetic mean of initial velocity and final velocity or a given period of time, that is

Average velocity = (initial velocity +final velocity) / 2

Mathematically, vav = (u + v) / 2

Where vav is the average velocity, u is the initial velocity and v is the final velocity of the object.

Speed and velocity have the same units, that is ms^-1or m/s.

Rage of change of Velocity

During uniform motion of an object along a straight line, the velocity remains constant with time; in this case, the change in velocity of the object for any time interval is zero. However, in non-uniform motion, velocity varies with time. It has different values at different instants and at different points of the path. Thus, the change in velocity of the object during any time interval is not zero.

Another physical quantity called acceleration, which is a measure of the change in the velocity of an object per unit time. That is,

Acceleration = change in velocity / time taken

If the velocity of an object changes from an initial value u to the final value v in time t, the acceleration a is,

A = (v - u) / t

This kind of motion is known as accelerated motion. The acceleration is taken to be positive if it is in the direction of velocity and negative when it is opposite to the direction of velocity. The SI unit of acceleration is ms^-2.

Equations of Motion by Graphical Method

When an object moves along a straight line with uniform acceleration, it is possible to relate its velocity, acceleration during motion and the distance covered by it in a certain time interval by a set of equations known as the equations of motion. There are three such equations.

These are:

V = u + at

S = u + ¹/2 at²

2 a s = v² - u²

Where u is the initial velocity of the object which moves with uniform acceleration a for time t, v is the final velocity, and s is the distance traveled by the object in time t.

Equation for Velocity – Time relation

Consider the velocity-time graph of an object that moves under uniform acceleration. From the graph, we can see that initial velocity of the object is u and then it increases to v in time t the velocity changes at a uniform rate a. the perpendicular lines BC and the velocity axes respectively, so that the initial velocity is represented by OA, the final velocity is represented by BC and the time interval t is represented by OC. BD = BC-CD, represents the change in velocity in the time interval t.

Let us draw AD parallel to OC, from the graph, we observe that

BC = BD + DC = BD + OA

Substituting BC = v and OA = u,

We get v = BD + u

Or BD = v - u

From the velocity time graph the acceleration of the object is given by

a = change in velocity / time taken

= BD/AD = BD/OC

Substituting OC = t, we get

a = BD/t

Or BD = at

And we get v = u + at

Equation for position time Relation

Let us consider that the object has traveled a distance s in time t under uniform acceleration a. the distance traveled by the object is obtained by the area enclosed within OABC under the velocity time graph AB.

Thus, the distance s traveled by the object is given by

s = area OABC (which is a trapezium)

= area of the rectangle OADC + area of the triangle ABD

= OA x OC + ½ (AD x BD)

Substituting OA = u, OC = AD = t and BD = at, we get

s = u x t + ½ (t x at)

Or s = u t + ½ a t²

Equation for Position-Velocity Relation

From the velocity-time graph, the distance s traveled by the object in time t, moving under uniform acceleration a is given by the area enclosed within the trapezium OABC under the graph. That is,

s = area of the trapezium OABC

= {(OA + BC) x OC} / 2

Substituting OA = u, BC = v and OC = t,

We get s = (u + v) t /2

From the velocity time relation we get

t = (v – u) / a

Using eqs and we have s= {(v + u) x (v - u)} / 2a

Or = 2 a s = v²- u²

Uniform Circular Motion

When the velocity of an object changes, we say that the object is accelerating. The change in the velocity could be due to change in its magnitude or the direction of the motion or both.

Important points

Ø Motion is a change of position; it can be described in terms of the distance moved or the displacement.

Ø The motion of an object could be uniform or non uniform depending on whether its velocity is constant or changing.

Ø The acceleration of an object is the change in velocity per unit time.

Ø Uniform and non uniform motion of objects can be shown through graphs.

Ø The motion of an object moving at uniform acceleration can be described with the help of three equation s, namely

v = u + at

u t + ½ a t²

2 a s = v²- u²

Where u is initial velocity of the object, which moves with uniform acceleration a for time t, v is its final velocity and s is the distance it traveled in time t.

Ø If an object moves in a circular path with uniform speed, its motion is called uniform circular motion.

DIVERSITY IN LIVING ORGANISMS | CHAPTER 7 | Class 9th | NCERT | CBSE | Notes

2011-07-17T11:03:00.000-07:00

Classification and Evolution

All living things are identified and categorized on the basis of their body design in form and function. Some characteristics are likely to make more wide ranging changes in body design than others. There is a role of time in this as well. So, once a certain body design comes into existence, it will shape the effects of all other subsequent design changes, simply because it already exists. In other words, characteristics that came into existence earlier are likely to be come basic than characteristics that have come into existence earlier are likely to be more basic than characteristics that have come into existence later.

Monera

These organisms do not have a defined nucleus or organelles, nor do any of them show multi-cellular body designs. On the other hand, they show diversity based on many other characteristics. Some of them have cell walls while some do not.

Protista

This group includes many kinds of unicellular eukaryotic organisms. Some of these organisms use appendages, such as hair-like cilia or whip-like flagella for moving around. Their mode of nutrition can be autotrophic or heterotrophic. Examples are unicellular algae, diatoms and protozoan.

Fungi

These are heterotrophic eukaryotic organisms. They used decaying organic material as food and are therefore called saprophytes. Many of them have the capacity to become multicellular organisms at certain stages in their lives. They have cell-wall made of a tough complex sugar called chitin. Examples are yeast and mushrooms.

Plantae

The first level of classification among plants depends on whether the plant body has well differentiated, distinct components. The next level of classification is based on whether the differentiated plant body has special tissues for the transport of water and other substances within it.

Thallophyta

Plants that do not have well differentiated body design fall in this group are commonly called algae. These plants are predominantly aquatic. Examples are spirogyra, ulothrix, cladophora, and chara.

Pteridophyta

The plant body is differentiated into roots, stem and leaves and has specialized tissue for the conduction of water and other substances from one part of the plant body to another. Some examples are marsilea, ferns and horse-tails.

The thallophytes, the bryophytes and the pteridophytes have naked embryos that are called spores. The reproductive organs of plants in all these three groups are very inconspicuous, and they are therefore called ‘cryptogamae’, or ‘those with hidden reproductive organs’.

Gymnosperms

This term is made from two Greek words: gymno- means naked seeds and is usually perennial, evergreen and woody. Examples are pines and deodar.

Angiosperms

The seeds develop inside an organ which is modified to become a fruit. These are also called flowering plants. Plant embryos in seeds have structures called cotyledons. Cotyledons are called ‘seed leaves’ because in many instances they emerge and become green when the seed germinates. Thus, cotyledons represent a bit of pre-designed plant in the seed. The angiosperms are divided into two groups on the basis on the basis of the number of cotyledons present in the seed. Plants with seeds having a single cotyledon are called monocotyledonous or monocots. Pants with seeds having two cotyledons are called dicots.

Animalia

These are organisms which are eukaryotic, multicellular and heterotrophic. Their cells do not have cell-walls. Most animal are mobile.

They are further classified based on the extent and type of the body design differentiation found.

Porifera

The word Porifera means organisms with holes. These are non-matile animals attached to some solid support. There are holes or ‘pores’, all over the body. These lead to a canal system that helps in circulating’ water throughout the body to bring in food and oxygen. These animals are covered with a hard outside layer or skeleton. The body design involves very minimal differentiation and division into tissues. They are commonly called sponges, and are mainly found in marine habitats.

Platyhelminthes

The body of animal in this group is far more complexly designed than in the two other groups we have considered so far. The body is bilaterally symmetrical, meaning that the left and right halves of the body have the same design.

This allows out side and inside body linings as well as some organs to be made. There is thus some degree of tissue formation. There is no true internal body cavity or coelom, in which well developed organs can be accommodated.

They are either freeing living or parasitic. Some examples are free living animals like planarians, or parasitic animal like liver flukes.

Nematode

The nematode body is also bilaterally symmetrical and triploblastic. There are tissues, but no real organs, although a sort of body cavity or a pseudocoelom is present. These are very familiar as parasitic worms causing diseases, such as the worms causing elephantiasis.

Annelida

Annelida animal are also bilaterally symmetrical and triploblastic, but in addition they have a true body cavity. This allows true organs to be packaged in the body structure. There is, thus, extensive organ differentiation. This differentiation occurs in a segmental fashion, with the segments lined up one after the other from head to tail. These animals are found in a variety of habitats-fresh water marine water as well as land. Earth worms and leeches are familiar example.

Arthropoda

This is probably the largest group of animals. These animals are bilaterally symmetrical and segmented. There is an open circulatory system, and so the blood does not flow in well defined blood vessels. The coelomic cavity is blood-filled. They have jointed legs. Some familiar examples are prawns, butterflies, houseflies.

Echinodermata

In greed, echinos mean hedgehog, and derma means skin. Thus, these are spiny skinned organisms. These are exclusively free-living marine animals. They have hard calcium carbonate structures that they use a skeleton. Examples are starfish and sea urchins.

Protochordata

These animals are bilaterally symmetrical, triploblastic and have a coelom. In addition, they show a new feature of body design, namely a notochord, at least at some stages during their lives. The notochord is a long rod like support structure that runs along the back of the animal separating the nervous tissue from the gut. It provides a place for muscle to attach for ease of movement.

Vertebrata

These animals have a true vertebral column and internal skeleton, allowing a completely different distribution of muscle attachment points to be used for movement.

All chordates possess the following features:

Ø Have a notochord

Ø Have a dorsal nerve cord

Ø Are triploblastic

Ø Have paired gill pouches

Ø Are coelomate.

Pisces

These are fish. They are exclusively aquatic animals. Their skin is covered with scales/plates. They obtain oxygen dissolved in water by using gills. The body is streamlined, and a muscular tail is used for movement, they are cold-blooded and their hearts have only two chambers, unlike the four that humans have. They lay eggs.

Amphibia

These animals differ from the fish in the lack of scales, in having mucus glands in the skin, and a three- chambered heart. Respiration is through either gills or lungs. They lay eggs. These animals are found both in water and on land. Frogs, toads and salamanders are some examples.

Reptilia

These animals are cold blooded, have scales and breathe through lungs. While most of them have a three-chambered heart, crocodiles have four hear chambers. They lay eggs with tough coverings and do not need to lay their eggs in water, unlike amphibians. Snakes, turtles, lizards and crocodiles fallen this category.

Aves

These are warm-blooded animal and have four chambered heart. They lay eggs. There is an outside covering of feathers, and two forelimbs are modified for flight. They breathe through lungs. All birds fall in this category.

Mammalian

Mammals are warm-blooded animals with four chambered hearts. They have mammary glands for the production of milk to nourish their young. Their skin has hairs as well as seat and oil glands. Most mammals familiar to us produce live young ones. However, a few of the, like the platypus and the echidna lay eggs, and some, like kangaroos give birth to very poorly developed young ones.

Important points

Ø Classification helps us in exploring the diversity of life forms.

Ø All living organisms are divided on the above bases into five kingdoms, namely Monera, Protista, fungi, Plantae and Animalia.

Ø The classification of life forms is related to their evolution.

Ø Animal are divided into ten groups: Porifera, coelenterate, plathelminthes, nematode, Annelida, Arthropoda, mollusca, Echinodermata, Protochordata and vertebrata.

Ø The binomial nomenclature is made up of two words- a generic name and specific name.

TISSUES | Chapter 6 | NCERT | Notes | CBSE Class 9th

2011-07-17T11:01:00.000-07:00

Are plants and animals made of same types of tissues?

There are noticeable differences between the two. Plants are stationary or fixed- they don’t move. Most of the tissues they have are supportive, which provides them with structural strength most of these tissues are dead, since dead cells can provide mechanical strength as easily as life ones and need less maintenance.

Animals on the other hand move around in search of food, mates and shelter. They consume more energy as compared to plants most of the tissues they contain are living. Another difference between animals and plants is in the pattern of growth. The growth in plants is limited to certain regions, while this is not so in animals.

Cell growth in animals is more uniformed. So, there is no such demarcation of dividing and non dividing regions in animals.

The structural organization of organs and organ systems is far more specialized and localized in complex animals than even in very complex plants.

Plant Tissues

The growth of plants occurs only in certain specific regions. This is because the dividing tissue, also known as meristematic tissue is located only at these points.

Permanent Tissue

What happens to the cells formed by meristematic tissue? They take up a specific role and lose the ability to divide. As a result, they form a permanent tissue. This process of taking up a permanent shape, size and a function is called differentiation. Cells of meristematic tissue differentiation to form different types of permanent tissue.

Simple permanent tissue

A few layers of cells form the basic packing tissue. This tissue is parenchyma a type of permanent tissue. It consists of relatively unspecialized cells with thin cell walls. They are live cells. They are usually loosely packed, so that large spaces between cells are found this tissue. This tissue provides support to plants and also store food. In some situations, it contains chlorophyll and performs photosynthesis, and then it is called chlorenchyma.

Complex permanent tissue

The different types of tissues we have discussed until now are all made of one type of cells, which look like each other. Such tissues are called simple permanent tissue. Yet another type of permanent tissue is complex tissue. Complex tissues are made of more than one type of cells. All these cells coordinate to perform a common function. Xylem and phloem are example of such complex tissues. They are both conducting tissues and constitute a vascular bundle. Vascular or conductive tissue is a distinctive feature of the complex plants, one that has made possible their survival in the terrestrial environment.

Epithelial Tissue

The covering or protective tissues in the animal body are epithelial tissues. Epithelium covers most organs and cavities within the body. It also forms a barrier to keep different body systems separate. The skin, the lining of the mouth, the lining of blood vessels, lung alveoli and kidney tubules are all made of epithelial tissue.

Epithelial tissue cell are tightly packed and form a continuous sheet. They have only a small amount of cementing material between them and almost no intercellular tissue.

Connective tissue

Blood is a type of connective tissue. The cells of connective tissue are loosely spaced and embedded in an intercellular matrix. The matrix may be jelly like, fluid, dense or rigid. The nature of matrix differs in concordance with the function of the particular connective tissue.

Bone is another example of a connective tissue. It forms the framework that supports the body. It also anchors the muscles and supports the main organs of the body. It is a strong and nonflexible tissue.

Muscular tissue

Muscular tissue consists of elongated cells, also called muscle fibers. This tissue is responsible for movement in our body. Muscles contain special proteins called contractile proteins, which contract and relax to cause movement.

Nervous Tissue

Cells of the nervous tissue are highly specialized for being stimulated and then transmitting the stimulus very rapidly from one place to another within the body. The brain, spinal cord and nerves are all composed of the nervous tissue. The cells of this tissue are called nerve cells or neurons.

Important Points

· Tissue is a group of cells similar in structure and function.

· Plant tissues are of two main types – meristematic and permanent.

· Permanent tissues are derived from meristematic tissue once they lose the ability to divide. They are classified as simple and complex tissues.

· Parenchyma, collenchymas and chlorenchyma are three types of simple tissues. Xylem and phloem are types of complex tissues.

· Nervous tissue is made of neurons that receive and conduct impulses.

CHAPTER 5 | THE FUNDAMENTAL UNIT OF LIFE | CBSE | NCERT | Notes

2011-07-17T10:56:00.000-07:00

CHAPTER 5 THE FUNDAMENTAL UNIT OF LIFE

What are Living Organisms made up of?

Activity

Let us take a small piece from an onion bulb. With the help of a pair of forceps, we can peel off the skin (called epidermis) from the concave side (inner layer) of the onion. This layer can be put immediately in a watch-glass containing water. This will prevent the peel from getting folded or getting dry.

What is a cell made up of? What is the structural organization of cell?

If we study a cell under a microscope, we would come across three feature in almost every cell; plasma membrane, nucleus and cytoplasm. All activities inside the cell and interaction of the cell with its environment are possible due to this feature.

Plasma membrane or Cell Membrane

This is the outermost covering of the cell that separates the contents of the cell from its external environment. The plasma membrane allows or permits the entry and exit of some materials in and out of the cell. It also prevents movements of some other materials. The cell membrane, therefore, is called a selectively permeable membrane.

Cell Wall

Plant cells, in addition to the plasma membrane, have another rigid outer covering called the cell wall. The cell wall lies outside the plasma membrane. The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance and provides structural strength to plants.

Nucleus

According to their chemical composition different regions of cell get coloured differentially. Some regions appear darker than other regions. Apart from iodine solution we could also use safranin solution or methylene blue solution to stain the cells.

The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell is about divide. Chromosomes contain information for inheritance of features from parents to next generation in the form of DNA (Deoxyribo Nucleic Acid) molecules. Chromosomes are composed of DNA and protein. DNA molecule contain the information necessary for constructing and organising cells. Functional segments of DNA are called genes. In a cell which is not dividing, this DNA is present as part of chromatin material. Chromatin material is visible as entangled mass of thread like structure. Whenever the cell is about to divide, the chromatin material gets organized into chromosomes.

In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the absence of a nuclear membrane; such an undefined nuclear region containing only nucleic acids is called a nucleoid. Such organisms, whose cells lack a nuclear membrane, are called prokaryotes (Pro= primitive or primary; karyote = karyon = nucleus)

Cytoplasm

When we look at the temporary mounts of onion peel as well as human cheek cell, we can see a large region of each cell enclosed by the cell membrane. This region takes up very little stain. It is called the cytoplasm. The cytoplasm is the fluid contains many specialized cell organelles. Each of these organelles performs a specific function for the cell.

Cell Organelles

Every cell has a membrane around it to keep its own contents separate from the external environment. Large and complex cells, including cells from multi cellular organisms, need a lot of chemical activities to support their complicated structure and function. To keep these activities of different kinds separate from each other, these cells use membrane-bound little structures within themselves. This is one of the features of the eukaryotic cell that distinguish them from prokaryotic cells. Some of these organelles are visible only with an electron microscope.

Endoplasmic reticulum (ER)

The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets. It looks like long tubules or round or oblong bags. The ER membrane is similar in structure to the plasma membrane. There are two types of ER-rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). RER looks rough under a microscope because it has particles called ribosomes attached to its surface. The ribosomes, which are present in all active cells, are the sites of protein manufacture. The manufactured proteins are then sent to various places in the cell depending on need, using the ER. The SER helps in the manufacture of fat molecules, or lipids, important for cell function. Some of these proteins and lipids help in building the cell membrane. This process is known as membrane biogenesis. Some other proteins and lipids function as enzymes and hormones. Although the ER varies greatly in appearance in different cells, it always forms a network system.

Golgi apparatus

The Golgi apparatus, first described by camillo Golgi, consists of a system of membrane bound vesicles arranged approximately parallel to each other in stacks called cisterns. These membranes often have connection with the membranes of ER and therefore constitute another portion of a complex cellular membrane system.

Lysosomes

Lysosomes are a kind of waste disposal system of the cell. Lysosomes help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles. Foreign materials entering the cell, such as bacteria or food, as well as old organelles end up in the lylosomes, which break them up into small pieces. Lysosomes are able to do this because they contain powerful digestive enzymes capable of breaking down all organic material. During the disturbance in cellular metabolism, for example, when the cell gets damaged, Lysosomes may burst and the enzymes digest their own cell. Therefore, Lysosomes are also known as the ‘suicide bags’ of a cell. Structurally, Lysosomes are membrane bound sacs filled with digestive enzymes. These enzymes are made by RER.

Mitochondria

Mitochondria are known as the powerhouses of the cell. The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP molecules, ATP is known as the energy currency of the cell. The body uses energy stored in ATP for making new chemical compounds and for mechanical work. Mitochondria have two membrane coverings instead of just one. The outer membrane is very porous while the inner membrane is deeply folded. These folds create a large surface area for ATP-generating chemical reactions.

Mitochondria are strange organelles in the sense that they have their own DNA and ribosome. Therefore, mitochondria are able to make some of their own proteins.

Plastids

Plastids are present only in plant cells. There are two types of plastids- chromoplasts and leucoplasts. Plastids containing the pigment chlorophyll are known as chloroplasts. Chloroplasts also contain various yellow or orange pigments in addition to chlorophyll. Leucoplasts are primarily organelles in which materials such as starch, oils and protein granules are stored.

Vacuoles

Vacuoles are storage sacs for solid or liquid contents. Vacuoles are small sized in animal cells while plant cell have very large vacuoles. The central vacuole of some plant cell may occupy 50-90% of the cell volume.

Important points

· The fundamental organisational unit of life is the cell.

· Cells are enclosed by a plasma membrane composed of lipids and proteins.

· In plant cell a cell wall composed mainly of cellulose is located outside the cell membrane.

· The presence of the cell wall enables the cells of plants, fungi and bacteria to exist in hypotonic media without bursting.

· The ER function both as a passageway for intracellular transport and as a manufacturing surface.

· The primary function of leucoplasts is storage.

STRUCTURE OF THE ATOM | Chapter 4 | NCERT | CBSE | Class 9th

2011-07-17T10:55:00.001-07:00

The Structure of an Atom

The discovery of two fundamental particles (electrons and protons) inside the atom, led to the failure of this aspect of Dalton’s atomic theory. It was then considered necessary to know how electrons and protons are arranged within an atom. For explaining this, many scientists proposed various atomic models. J.J. Thomson was the first one to propose a model for the structure of an atom.

Thomson’s Model of an Atom

Thomson proposed the model of an atom to be similar to that of a Christmas pudding. The electrons, in a sphere of positive charge, were like currants (dry fruits) in a spherical Christmas pudding. We can also think of a watermelon, the positive charge in the atom is spread all over like the red edible part of the watermelon, while the electrons are studded in the positively charged sphere.

Positive sphere

Electron

Thomson proposed that:

I. An atom consists of a positively charged sphere and the electrons are embedded in it.

II. The negative and positive charge are equal in magnitude. So, the atom as a whole is electrically neutral.

Rutherford’s Model of an Atom

Rutherford designed an experiment for this. In this experiment, fast moving alpha (a

)-particles were made to fall on a thin gold foil.

· He selected a gold foil because he wanted as thin a layer as possible. This gold foil was about 1000 atoms thick.

· a-particles are doubly-charged helium ions. Since they have a mass of 4u, the fast-moving a-particles have a considerable amount of energy.

· It was expected that a-particles would be deflected by the sub-atomic particles in the gold atoms. Since the a-particles were much heavier than the protons, he did not expect to see large deflections. But the a-particles scattering experiment gave totally unexpected results. The following observations were made:

I. Most of the fast moving a-particles passed straight through the gold foil.

II. Some of the a-particles were deflected by the foil by small angles.

III. Surprisingly one out of every 12000 particles appeared to rebound.

In the words of Rutherford, “this result was almost as incredible as if you fire a 15-inch shell at a piece of tissue paper and it comes back and hits you”.

Rutherford concluded from the a-particles scattering experiment that-

· Most of the space inside the atoms is empty because most of a-particles passed through the gold foil without getting deflected.

· Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.

· A very small fraction of a-particles were deflected by 180⁰ indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.

From the data he also calculated that the radius of the nucleus is about 10⁵ times less than the radius of the atom.

Rutherford put forward the nuclear model of an atom, which had the following feature:

· There is a positively charged centre in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus.

· The electrons revolve around the nucleus in well-defined orbits.

· The size of the nucleus is very small as compared to the size of the atom.

Drawbacks of Rutherford’s model of the atom

The revolution of the electron in a circular orbit is not expected to be stable. Any particle in a circular orbit would undergo acceleration. During acceleration, charged particles would radiate energy. Thus, the revolving electron would lose energy and finally fall into the nucleus. If this were so, the atom should be highly unstable and hence matter would not exist in the form that we know. We know that atoms are quite stable.

Bohr’s Model of Atom

Neils Bohr put forward the following postulates about the model of an atom:

· Only certain special orbits known as discrete orbits of electrons are allowed inside the atom.

· While revolving in discrete orbits the electrons do not radiate energy.

These orbits or shell are called energy levels energy levels in an atom are shown here.

N shell (n=4)

M shell (n=3)

L shell (n=2)

K shell (n=1)

Nucleus

The orbits or shells are represented by the letters K, L, M, N, .or the numbers, n=1, 2, 3, 4,

Neutrons

In 1932, J Chadwick discovered another subatomic particle which had no charge and a mass nearly equal to that of a proton. It was eventually named as neutron. Neutrons are present in the nucleus of all atoms, except hydrogen. In general, a neutron is represented as ‘n’. The mass of an atom is therefore given by the sum of the masses of protons and neutrons present in the nucleus.

How are Electrons distributed in Different Orbits (Shells)?

The distribution of electrons into different orbits of an atom was suggested by Bohr and Bury.

The number of electrons in different energy levels or shells:

· The maximum number of electrons present in a shell is given by the formula 2n² , where ‘n’ is the orbit number or energy level index, 1,2,3,…. Hence the maximum number of electrons in different shells:

· The maximum number of electrons that can be accommodated in the outermost orbit is 8.

· Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in a step-wise manner.

Valency

The electrons in an atom are arranged in different shell/orbits. The electrons present in the outer most shell of an atom are known as the valence electrons.

The outermost shell of an atom can accommodate a maximum of 8 electrons. It was observed that the atoms of elements, having a completely filled outer most shell show little chemical activity. In other words, their combining capacity or valency is zero, of these inert elements, the helium atom has two electrons in its outermost shell and all other elements have atoms with eight electrons in the outer most shell.

The combining capacity of the atoms of other elements, that is, their tendency to react and form molecules with atoms of the same or different elements was thus explained as an attempt to attain a fully-filled outer most shell. An outermost-shell, which had eight electrons, was said to possess an octet. Atoms would thus react, so as to achieve an octet in the outer most shell. This was done by sharing, gaining or losing electrons. The number of electrons gained, lost or shared so as to make the octet of electrons in the outermost shell, gives us directly the combining capacity of the element, that is, the valency discussed in the previous chapter. For example, hydrogen/lithium/sodium atoms contain one electron each in their outermost shell; therefore each one of them can lose one electron. So they are said to have valency of one. The valency of magnesium and Aluminium is two and three, respectively, because magnesium has two electrons in its outer most shell.

If the number of electrons in the outermost shell of an atom is close to its full capacity, then valency is determined in a different way. For example, the fluorine atom has 7 electrons in the outermost shell, and its valency could be 7. But it is easier for fluorine to gain one electron instead of losing seven electrons. Hence, its valency is determined by subtracting seven electrons from the octet and this gives us a valency of one for fluorine. Valency can be calculated in a similar manner for oxygen.

Atomic Number

Protons are present in nucleus of an atom. It is the number of protons of an atom, which determines its atomic number.

Mass Number

Mass of an atom is practically due to protons and neutrons alone. These are present in the nucleus of an atom. Hence protons and neutrons are also called nucleons. Therefore, the mass of an atom resides in its nucleus. For example, mass of carbon is 12u because it has 6 protons and 6 neutrons, 6u + 6u = 12 u (13 protons + 14 neutrons).

The atomic number, mass number and symbol of the element are to be written as:

Mass number

Symbol of

Element

Atomic number

Isotopes

A number of atoms of some elements have been identified, which have the same atomic number but different mass numbers. For example, take the case of hydrogen atom, it has three atomic species. Namely protium (1(1)H), deuterium (1(2)H or D) and tritium (1(3)H or T). The atomic number of each one is 1, but the mass number is 1, 2 and 3, respectively.

Many elements consist of a mixture of isotopes. Each isotope of an element is a pure substance. The chemical properties of isotopes are similar but their physical properties are different.

The mass of an atom of any natural element is taken as the average mass of all the naturally occurring atoms of that element. If an element has no isotopes, then the mass of its atom would be the same as the sum of protons and neutrons in it. But if an element occurs in isotopic forms, then we have to know the percentage of each isotopic form and the average mass is calculated.

Isobars

Let us consider two elements – calcium, atomic number 20, and argon, atomic number 18. The number of electrons in these atoms is different, but the mass number of both these elements is 40. That is the total number of nucleons is the same in the atoms of this pair of elements, atoms of different elements with different atomic numbers, which have the same mass number, are known as isobars.

Important points:

· Credit for the discovery of electron and proton goes to J.J. Thomson and E. Goldstein, respectively.

· J.J. Thomson proposed that electrons are embedded in a positive sphere.

· Rutherford’s alpha-particle scattering experiment led to the discovery of the atomic nucleus.

· Rutherford’s model of the atom proposed that a very tiny nucleus is present inside the atom and electrons revolve around this nucleus. The stability of the atom could not be explained by this model.

· Neils Bohr’s model of the atom, in which he proposed that electrons are distributed in different shell with discrete energy around the nucleus. If the atomic shells are complete, then the atom will be stable and less reactive.

· Shells of an atom are designated as K, L, M, N,

· Valency is the combining capacity of an atom.

· The atomic number of an element is the same as the number of nucleons in its nucleus.

· Isotopes are atoms of the same element, which have different mass numbers.

· Isobars are atoms having the same mass number but different atomic number.

· Element are defined by the number of protons they posses.