Class 8 Science Chapter 15 Some Natural Phenomena

Lightning                                                                                                      Earthquake

 

 

Lightning is a natural phenomenon that has fascinated people for ages. Several people thought and researched about the cause of lightning and its process. Benjamin Franklin discovered that there is an electric discharge between clouds that produces a spark, and it is the electric spark between the clouds and the earth that appears as lightning. His famous kite experiment proved this fact.
The occurrence of lightning is as follows. The formation of clouds involves friction between water particles in the atmosphere. The friction charges the particles. Among the positive and negative charges, the negative charge accumulates at the bottom of the cloud and the positive charges in its top. As the accumulation of the charge increases, the cloud will create a positive charge on the ground nearby. As the amount of charge increases, the negative charge on the cloud tends to make a path towards the ground, and it results in a narrow streak of electrical discharge, which we call lightning.
An electroscope is a device that detects the type of charge on a body. Like charges repel and unlike charges attract each other.  This is used in an electroscope. An electroscope consists of a glass jar fitted with a cork lid and a metallic wire passing through it. There are two metallic strips at the bottom of the wire. The upper end of the wire is connected to a metal disc. A body that is positively charged is touched to the metal disc, so that the charge is transferred to the metal strips through the wire, and they diverge from each other on gaining a like charge. Now, if a negatively charged object is brought into contact with the disc, the strips converge towards each other, indicating the unlike charge on the body. Similarly, if a positively charged body is brought in contact with the metal disc, the divergence of the metal strips increases, indicating the like charge on the body. If the metal disc of the electroscope is touched with the hand, it loses its charge to the ground by transfer of charge through the human body. This is called earthing.

Protection from Lightning

Lightning and Safety

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Lightning is caused due to the heavy electric discharge from the clouds to the earth. If lightning is not controlled, it can cause heavy damage to life and property. Hence, protective measures are of utmost importance during lightning strikes. Interiors of buildings are safe places to protect ourselves from lightning strikes. Taking shelter in interiors and not staying in open areas is one of the best measures you can take. You should not take shelter under trees when in the open, or go to an open area if outside. If you are in a vehicle, you should not come out of it; you should also close the doors and windows of the vehicle.
Tall buildings are provided with lightning rods. A lightning rod a metal rod that is erected at the top of a building. It is connected to a thick metallic plate, made of a good conducting material like copper and buried under the earth, through a thick copper wire. If lightning is likely to strike the building, it is attracted by the lightning rod, and the electrical discharge is transferred through the wire to the ground. Thus, it keeps the building safe.

Earthquakes

Earthquakes

To view the complete lesson click the video below

A natural phenomenon that cannot be predicted is an earthquake. The earth consists of three major layers, called the crust, the mantle and the core. The core is further divided into the inner core and the outer core. The mantle consists of semi-solid material above which the crust floats. The crust consists of oceans and continents. The crust is divided into several parts, called tectonic plates. The regions where one tectonic plate slides against another are referred to as fault zones, and these are the regions where an earthquake is likely to occur. Hence, these zones are referred to as seismic zones.
The place in the interior of the earth where an earthquake occurs is the focus, and the region on the surface of the earth that is the closest to focus is likely to experience the largest damage. This region is called the epicentre of the earthquake.
The instrument that measures the severity of an earthquake is a seismograph. It basically consists of a drum that rolls and a pendulum with a stylus that traces the waves of an earthquake on a sheet like a graph paper. The severity of an earthquake is measured on the Richter scale. A major earthquake measures 7 or more on the Richter scale.

Some More Notes

Some Natural Phenomena

Lightning

We always see sparks on a electric pole when wires become loose. This phenomenon is quite common when a wind is blowing and shaking the wires. We also often see sparks when a plug is loose in its socket. Lightning is also an electric spark, but on a huge scale.

Lightning is an atmospheric discharge of electricity usually accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms. Lightning is caused when two clouds collide or slide against one another. This involves same process which happens when you rub a comb on your dry hair and the hair gets an electric charge.

As amount of charge generated during collision of clouds is huge so we witness it as flashing lights in the sky. This flashing light is called lightning. Once a cloud gets electrically charged it releases the charge to earth. In other words the earth receives the charge and neutralizing the cloud in the process.

Lightning Safety:

During lightning and thunderstorm no open place is safe.

• Hearing thunder is an alert to rush to a safer place.

• After hearing the last thunder, wait for some time before coming out of the safe place.

Do’s and Don’ts during a Thunderstorm:

Outside: Open vehicles, like motorbikes, tractors, construction machinery, open cars are not safe. Open fields, tall trees, shelters in parks, elevated places do not protect us from lightning strokes. Carrying umbrella is not a good idea at all during thunderstorms. If in a forest, we should take shelter under shorter trees. If no shelter is available and we are in an open field, stay far away from all trees. We should stay away from poles or other metal objects. We should not lie on the ground. Instead, we should squat low on the ground.

Inside the House: Lightning can strike telephone cords, electrical wires and metal pipes. During a thunderstorm contact with these should be avoided. It is safer to use mobile phones and cordless phones. Bathing should be avoided during thunderstorms to avoid contact with running water. Electrical appliances like computers, TVs, etc., should be unplugged. Electrical lights can remain on. They do not cause any harm.

Lightning Conductors: Lightning Conductor is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed in the walls of the building during its construction. One end of the rod is kept out in the air and the other is buried deep in the ground. The rod provides easy route for the transfer of electric charge to the ground. The metal columns used during construction, electrical wires and water pipes in the buildings also protect us to an extent. But do not touch them during a thunderstorm.

You can notice trident shaped iron rod on top of temples, TV towers and cell phone towers. These are lightning conductors.

Earthquake

An earthquake is a sudden shaking or trembling of the earth lasting for a very short time. It is caused by a disturbance deep inside the earth’s crust. Earthquakes occur all the time, all over the earth. They are not even noticed. Major earthquakes are much less frequent. They can cause immense damage to buildings, bridges, dams and people. There can be a great loss to life and property. The earthquakes can cause floods, landslides and tsunamis.

Causes of Earthquake

The outermost layer of the earth is not in one piece. It is fragmented. Each fragment is called a tectonic plate. These plates are in continual motion. When they brush past one another, or a plate goes under another due to collision, they cause disturbance in the earth’s crust. It is this disturbance that shows up as an earthquake on the surface of the earth.

Tremors on the earth can also be caused when a volcano erupts, or a meteor hits the earth, or an underground nuclear explosion is carried out. However, most earthquakes are caused by the movement of earth’s plates.

Since earthquakes are caused by the movement of plates, the boundaries of the plates are the weak zones where earthquakes are more likely to occur. The weak zones are also known as seismic or fault zones. In India, the areas most threatened are Kashmir, Western and Central Himalayas, the whole of North East, Rann of Kutch, Rajasthan and the Indo – Gangetic Plane. Some areas of South India also fall in the danger zone

Power of Earthquakes: The power of an earthquake is expressed in terms of a magnitude on a scale called Richter scale. Really destructive earthquakes have magnitudes higher than 7 on the Richter scale. Both Bhuj and Kashmir earthquakes had magnitudes greater than 7.5.

Protection against Earthquakes

It is, important that we take necessary precautions to protect ourselves all the time. People living in seismic zones, where the earthquakes are more likely to occur, have to be specially prepared. First of all, the buildings in these zones should be designed so that they can withstand major tremors. Modern building technology can make it possible. It is advisable to make the structure simple so that it is ‘Quake Safe’.

• Consult qualified architects and structural engineers. In highly seismic areas, the use of mud or timber is better than the heavy construction material. Keep roofs as light as possible. In case the structure falls, the damage will not be heavy.

• It is better if the cupboards and shelves are fixed to the walls, so that they do not fall easily.

• Be careful where you hang wall clocks, photo-frames, water heaters etc., so that in the event of an earthquake, they do not fall on people.

• Since some buildings may catch fire due to an earthquake, it is necessary that all buildings, especially tall buildings, have fire fighting equipment in working order.

Summary

• Some objects can be charged by rubbing with other objects.

• There are two kinds of charges — positive charge and negative charge

• Like charges repel and unlike charges attract each other.

• The electrical charges produced by rubbing are called static charges.

• When charges move, they constitute an electric current.

• An electroscope may be used to detect whether a body is charged or not.

• The process of transfer of charge from a charged object to the earth is called earthing.

• The process of electric discharge between clouds and the earth or between different clouds causes lightning.

• Lightning strike can destroy life and property.

• Lightning conductors can protect buildings from the effects of lightning.

• An earthquake is a sudden shaking or trembling of the earth.

• Earthquake is caused by a disturbance deep inside the earth’s crust.

• It is not possible to predict the occurrence of an earthquake.

• Earthquakes tend to occur at the boundaries of earth’s plates. These boundaries are known as fault zones.

• Destructive energy of an earthquake is measured on the Richter scale. The earthquake measuring 7 or more on Richter scale can cause severe damage to life and property.

• We should take necessary precautions to protect ourselves from earthquakes.

Question 1:

Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth

Answer :

(b) A copper rod
Only non-conducting materials can be easily charged by friction. Copper is a highly conducting materials. Therefore, a copper rod cannot be charged easily by friction.

Question 2:

When a glass rod is rubbed with a piece of silk cloth the rod
(a) and the cloth both acquire positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire negative charge.
(d) becomes negatively charged while the cloth has a positive charge.

Answer :

(b) The rod becomes positively charged, while the cloth has a negative charge.
When an object is charged by rubbing it against another object, the two objects get oppositely charged. By convention, it is considered that the charged acquired by the glass rod is positive and charged acquired by the cloth is negative. Therefore, the rod becomes positively charged and the cloth becomes negatively charged.

Question 3:

Write T against true and F against false in the following statements.
(a) Like charges attract each other. (T / F)
(b) A charged glass rod attracts a charged plastic straw. (T / F)
(c) Lightning conductor cannot protect a building from lightning. (T/F)
(d) Earthquakes can be predicted in advance. (T / F)

Answer :

(a) False
Like charges repel each other. It is the unlike charges that attract each other.
(b) True
A charged glass rod has positive charges on its surface while a charged plastic straw has negative charges on its surface. Since unlike charges attract each other, a charged glass rod attracts a charged plastic straw.
(c) False
During a lightning, the lightning conductor conducts all the atmospheric charges to the Earth directly, leaving the building safe. Hence, lightning conductors protect a building from lightning.
(d) False
Although the causes of earthquakes is known, but no instrument could be invented to detect it till now. Hence, earthquakes cannot be predicted in advance.

Question 4:

Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.

Answer :

When a sweater is taken off, the woollen sweater gets charged because of the friction between the sweater and the body. Hence, one can hear a crackling sound during the given process.

Question 5:

Explain why a charged body loses its charge if we touch it with our hand.

Answer :

When we touch a charged object, our body conducts its charges to the earth. That is why a charged body loses its charge, if we touch it with our hand. This phenomenon is known as electric discharge.

Question 6:

Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?

Answer :

The destructive energy of an earthquake is measured by the Richter scale. This scale has the readings from 1 to 10.
The reading of magnitude 3 on the Richter scale would be recorded by a seismograph.
If the Richter scale gives a reading of magnitude 3, then the earthquake is not likely to cause much damage. Generally, earthquake of magnitudes higher than 5 is considered destructive in nature.

Question 7:

Suggest three measures to protect ourselves from lightning.

Answer :

Protective measures against lightning are as follows:
(i) Stay in a completely closed place. If you are moving in a car, then remain there until the lightning is over. Close the windows of the car immediately.
(ii) Do not touch any electrical wires, telephone cables, metal pipes, etc.
(iii) Do not bath in running water. This may cause an electric shock.

Question 8:

Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

Answer :

The nature of charges present on the surface of charged balloons are similar. Since like charges repel each other, two charged balloons repel each other. When a charged body is brought near an uncharged body, the uncharged body acquires charges on its surface caused by the induction of charges. The charges are of opposite nature in relation to the charged body. Since unlike charges attract each other, a charged body always attracts an uncharged body. Hence, an uncharged balloon is attracted by another charged balloon.

Question 9:

Describe with the help of a diagram an instrument which can be used to detect a charged body.

Answer :

An electroscope can be used to detect whether a body is charged or not. The following figure shows a simple electroscope.

It consists of a metal rod. At one end of the rod, two leaves of aluminium foil are fixed and at the other end, there is a metal disc. The leaves of aluminium foil are placed inside a conical flask and the flask is corked to isolate the leaves from air.
When the metal disc is touched with a charged body, the aluminium strips move away from each other. This happens because some of the charges of the body are transferred to the strips through the metal rod. This method of charging a body is called charging by conduction. The nature of charges on both the leaves and the charged body are the similar. Hence, both the leaves of the aluminium foil will move away from each other. If the body was not charged, then the leaves of the foil would remain as they were before. They would not repel each other.

Question 10:

List three states in India where earthquakes are more likely to strike.

Answer :

The three states in India where earthquakes are more likely to strike are Jammu and Kashmir, Gujrat, and Assam.

Question 11:

Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?

Answer :

Some of the precautions are as follows:
(i) Try to find an open field away from tall buildings, installations, tall trees, and electric wires and poles.
(ii) If travelling in a bus or a car, then do not come out when an earthquake strikes. Ask the driver to drive in an open field.

uestion 12:
The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.

Answer :

No. We should not carry an umbrella in a thunderstorm. During thunderstorms, which are accompanied with lightning, electric discharge from the clouds can travel through the metallic rod of the umbrella. This may give an electric shock to the person who is carrying it. Hence, it is not safe to carry an umbrella during lightning.

Class 9 SST Civics CHAPTER 2 Meaning of Democracy

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Meaning of Democracy

Democracy: Democracy is a form of government in which the rulers are elected by people.

Features of Democracy:

• The final decision making power rests with those who are elected by people.
• A democracy must be based on a free and fair election. The ruling party must have a fair chance of losing that election.
• In a democracy, each adult citizen must have one vote and each vote should have equal value.
• A democratic government rules within the limits which are set by constitutional laws and citizens’ rights.

Arguments against Democracy:

• Change in leadership may lead to instability.
• Democracy involves political competition and power play. This leaves no scope for morality.
• The decision making is often delayed because a large number of people need to be consulted.
• Elected leaders may not aware about the best decisions for people. More often, bad decisions are made in a democracy.
• Involvement of electoral competition in a democracy gives rise to corruption.
• Ordinary people may not understand the meaning of collective good and hence they should not be made a part of the decision making process.

Arguments for Democracy:

• Democratic government is more accountable to people and hence is a better form of government; compared to other forms of government.
• Since a large number of people are consulted in the decision making process, so democracy enhances the quality of decision making.
• Democracy provides a method to deal with conflicts and differences. In a diverse country; like India; there can be very sharp social differences and conflicts. Such differences can be resolved through democracy in a better and amicable way.
• Democracy provides the fundamental rights to its citizens and thus enhances the dignity of the people.
• Democracy allows to correct its own mistakes and hence is a better form of governance. 
•  

• Meaning of Democracy

  NCERT Solution

  Question – 1 - Here is some information about four countries. Based on this information, how would you classify each of these countries. Write ‘democratic’, ‘undemocratic’ or ‘not sure’ against each of these.
  (a) Country A: People who do not accept the country’s official religion do not have a right to vote
  
  Answer: Undemocratic
  (b)Country B: The same party has been winning elections for the last twenty years
  
  Answer: Not sure
  (c) Country C: Ruling party has lost in the last three elections
  
  Answer: Democratic
  (d) Country D: There is no independent election commission
  
  Answer: Undemocratic
  Question – 2 - Here is some information about four countries. Based on this information, how would you classify each of these countries. Write ‘democratic’, ‘undemocratic’ or ‘not sure’ against each of these.
  (a) Country P: The parliament cannot pass a law about the army without the consent of the Chief of Army
  
  Answer: Undemocratic
  (b) Country Q: The parliament cannot pass a law reducing the powers of the judiciary
  
  Answer: Undemocratic
  (c) Country R: The country’s leaders cannot sign any treaty with another country without taking permission from its neighbouring country.
  
  Answer: Not sure
  (d) Country S: All the major economic decisions about the country are taken by officials of the central bank which the ministers cannot change.
  
  Answer: Not sure
  Question – 3 - Which of these is not a good argument in favour of democracy? Why?
  
• People feel free and equal in a democracy
• Democracies resolve conflict in a better way than others
• Democratic government is more accountable to the people
• Democracies are more prosperous than others

Answer: Economic prosperity depends on many factors; like availability of natural resources, quality of human resources, finance, geopolitical scenario, etc. A particular form of government is some role to play, so it cannot be seen as a good argument in favour of democracy.

Question – 4 - Each of these statements contains a democratic and an undemocratic element. Write out the two separately for each statement.
(a) A minister said that some laws have to be passed by the parliament in order to conform to the regulations decided by the World Trade Organisation.

Answer: The fact that the laws need to be passed by the parliament is democratic, while conformation to the WTO regulations is undemocratic.

(b) The Election Commission ordered re-polling in a constituency where large scale rigging was reported.

Answer: Re-polling is democratic, while rigging is undemocratic.

(c) Women’s representation in the parliament has never reached 10 per cent. This led women’s organisations to demand one-third seats for women.

Answer: Poor level of women’s representation is undemocratic, while the demand for one-third seats is democratic.

Question – 5 - Which of these is not a valid reason for arguing that there is a lesser possibility of famine in a democratic country?

1. Opposition parties can draw attention to hunger and starvation.
2. Free press can report suffering from famine in different parts of the country.
3. Government fears its defeat in the next elections.
4. People are free to believe in and practise any religion.

Answer: (d) People are free to believe in and practise any religion.

Question – 6 - There are 40 villages in a district where the government has made no provision for drinking water. These villagers met and considered many methods of forcing the government to respond to their need. Which of these is not a democratic method?

1. Filing a case in the courts claiming that water is part of right to life.
2. Boycotting the next elections to give a message to all parties.
3. Organising public meetings against government’s policies.
4. Paying money to government officials to get water.

Answer: (d) Paying money to government officials to get water.

Question – 7 - Write a response to the following arguments against democracy:
(a) Army is the most disciplined and corruption-free organisation in the country. Therefore army should rule the country.

Answer: Army officers are not elected by people and hence an army rule would be undemocratic.

(b) Rule of the majority means the rule of ignorant people. What we need is the rule of the wise, even if they are in small numbers.

Answer: Democracy is based on the idea of universal adult franchise. Restricting the rulers from a small section comprising of ‘wise’ people would defeat the purpose of representational democracy.

(c) If we want religious leaders to guide us in spiritual matters, why not invite them to guide us in politics as well. The country should be ruled by religious leaders.

Answer: Religious leaders are not elected by people and hence a country should not be ruled by religious leaders.

Question – 8 - Are the following statements in keeping with democracy as a value? Why?
(a) Father to daughter: I don’t want to hear your opinion about your marriage. In our family children marry where the parents tell them to.

Answer: In this case, the daughter does not have the freedom of choice, hence this is undemocratic.

(b) Teacher to student: Don’t disturb my concentration by asking me questions in the classroom.

Answer: The teacher may be involved in thinking about an important topic and hence is asking the student not to disturb her. It cannot be said with surety whether the teacher’s request is democratic or not.

(c) Employee to the officer: Our working hours must be reduced according to the law.

Answer: The employee is asking for a fundamental right and hence it is democratic.

Question – 9 - Consider the following facts about a country and decide if you would call it a democracy. Give reasons to support your decision.
(a) All the citizens of the country have right to vote. Elections are held regularly.

Answer: Regular elections and universal adult franchise are two important features of a democracy and hence this is a democratic situation.

(b) The country took loan from international agencies. One of the conditions for giving loan was that the government would reduce its expenses on education and health.

Answer: An international agency should not interfere in the internal matters of a country. Hence this is undemocratic.

(c) People speak more than seven languages but education is available only in one language, the language spoken by 52 percent people of that country.

Answer: This is an example where majority view is being imposed and hence is undemocratic.

(d) Several organisations have given a call for peaceful demonstrations and nation wide strikes in the country to oppose these policies. Government has arrested these leaders.

Answer: Democratic government should provide the right to protest. The government is denying such right to its citizens and hence is undemocratic.

(e) The government owns the radio and television in the country. All the newspapers have to get permission from the government to publish any news about government’s policies and protests.
Answer: Freedom of media is very important for a democracy. This is an undemocratic exampl

•  

Class 9 SST Civics CHAPTER 1 Democracy in the Contemporary World

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Democracy in The Contemporary World

 

Democracy: The classic definition of democracy says that it is government for the people, of the people and by the people. In other words, democracy is a form of government in which people are allowed to choose their rulers. Following are the two important features of democracy:
(a) Only elected leaders by people rule the country.
(b) People have freedom to express views, freedom to organize and freedom to protest.

The Changing Map of Democracy

Note: These maps are taken from NCERT Text Book
The world map given here shows democratic governments from 1900 to 1950. The countries which are shaded in red had already become democracies before 1900. The countries shaded in yellow became democracies between 1900 and 1970.
This world map shows democratic countries in 1975. Compared to the earlier map, the number of democratic countries has increased in this map. This was mainly because of freedom of many countries from colonialism. The end of colonialism resulted in the birth of many new nations during this period and many of them preferred for democratic rule.
This world map shows democratic countries in 2000. It can be said that most of the countries became democratic by this period. Collapse of the Soviet Union in the 1990s and subsequent collapse of communist regimes in Eastern Europe and many other parts of the world led to rise of democracies around the world. This map also shows that a major portion of Africa is yet to embrace democracy. Additionally, China and some central Asian countries are the regions where democracy has not taken roots.

Phases in the Expansion of Democracy

The process of democratization began with the French Revolution in 1789. It took about 100 years of struggle for France and many other European countries to develop into proper democracies.
The process of democratization of Britain began much earlier than in France. It was a comparatively peaceful process.
The British colonies in the North America declared their independence in 1776 and established democratic regime. Hence, USA is known as the oldest democracy in the world. The USA adopted its democratic constitution in 1787.
Many changes took place during Europe’s struggle for democracy. It took many years of constant struggle to secure universal adult franchise. New Zealand was the first country to grant voting rights to women. Early democracies were established in North America, Europe and Latin America.

End of Colonialism

The colonialism was beginning to end after the end of the Second World War. Many colonies became independent within a short period after the Second World War. India was one of them.
While India continues to be a thriving democracy, many former colonies experience various ups and downs. Military coups became the norm in many former colonies and democratic regimes were overthrown by dictatorial regimes, e.g. Ghana, Pakistan, Myanmar, etc.
The next big push for democracy came with revival of democracy in many Latin American countries; like Chile.
The collapse of the Soviet Union further accelerated this process. Communist regimes in many countries came to an end and paved the way for democratic regimes. At present, more than 140 countries have multi-party democracies.

Democracy at the Global Level

There are certain issues which do not come under the purview of a country or even under a small group of countries. These issues are discussed and resolved at various international forums.
United Nations is a world organization which makes convention on international law, security, global cooperation and social equality. The UN Secretary General is its chief administrative officer.
Important issues on international security are discussed and resolved by the UN Security Council.
The International Monetary Fund (IMF) and the World Bank lends money to governments as per the situation.
These organizations are association of different countries. Initially, they came into origin because of initiative of the developed and powerful countries. The power equation in these organizations depends on the relative amount of fund received by a particular country. Since USA is the largest contributor of funds, hence it enjoys the maximum power. There are times when a decision made by the world bodies may not be democratic at all.
The UN Security Council has 5 permanent members and 10 temporary members. The 10 temporary members are elected by the General Assembly for two year term. The permanent members enjoy veto power in the Security Council. There are many examples of misuse of veto power by the permanent members.
The International Monetary Fund presents the same situation. More than 52% of its votes is contributed by 10 member countries, viz. US, Japan, Germany, France, UK, China, Italy, Saudi Arabia, Canada and Russia. The World Bank has a similar system of voting. The President of the World Bank has always been a US citizen and is nominated by the Treasury Secretary of the US government.

Promotion of Democracy

Many democratic regimes in the world believe in promoting democracy so that remaining non-democratic regimes should change. While the idea of promotion is very good, some countries have tried to enforce democracy in some other countries. The case of Iraq is a good example. It was ruled by the dictator Saddam Hussein. Although he earned bad repute because of annihilation of his political opponents, we should not forget that he gave liberties to women and pupil during his rule. USA attacked Iraq on the pretext of finding the weapons of mass destruction and for establishing a democratic regime. Saddam Hussein was finally captured and tried for several offences. An interim government of US’ choice was installed in Iraq after that.

Democracy in The Contemporary World

NCERT Solution

Question – 1-Which of the following does not lead to the spread of democracy?

1. Struggle by the people
2. Invasion by foreign countries
3. End of colonialism
4. People’s desire for freedom

Answer: (b) Invasion by foreign countries

Question – 2 - Which of the following statement is true about today’s world?

1. Monarchy as a form of government has vanished .
2. The relationship between different countries has become more democratic than ever before.
3. In more and more countries rulers are being elected by the people.
4. There are no more military dictators in the world.

Answer: (c) In more and more countries rulers are being elected by the people

Question – 3 - Use one of the following statements to complete the sentence: Democracy in the international organisations requires that …

1. The rich countries should have a greater say.
2. Countries should have a say according to their military power.
3. Countries should be treated with respect in proportion to their population.
4. All countries in the world should be treated equally.

Answer: (d) All countries in the world should be treated equally

Question – 4 - Based on the information given in this chapter, match the following countries and the path democracy has taken in that country.
Question – 5 - What are the difficulties people face in a non-democratic country?

Answer: People face following difficulties in a non-democratic country:

1. People cannot choose their rulers.
2. People do not have the freedom to express their views, to organize and to protest.

Question – 6 - Which freedoms are usually taken away when a democracy is overthrown by the military?

Answer: When a democracy is overthrown by the military then most of the basic freedoms are taken away. People no longer have a say in the choice of ruler. They do not enjoy the freedom of expression and personal liberty.

Question – 7 - Which of the following positions can contribute to democracy at the global level? Give reasons for your answer in each case.

1. My country gives more money to international institutions. Therefore, I want to be treated with more respect and exercise more power.
2. My country may be small or poor. But my voice must be heard with equal respect, because these decisions will affect my country.
3. Wealthy nations will have a greater say in international affairs. They cannot let their interests suffer just because they are outnumbered by poor nations.
4. Big countries like India must have a greater say in international organisations.

Answer: (b) My country may be small or poor. But my voice must be heard with equal respect, because these decisions will affect my country. 

Answer :

The positions voiced by alternatives ‘b’ and ‘c’ can contribute to democracy at the global level. While ‘b’ provides weaker nations an opportunity to be recognised in the decision making process, ‘c’ (if exercised properly) would protect the wealthy nations from being reduced to a minority.

Question 8:

Here are three opinions heard in a television debate on the struggle for democracy in Nepal. Which of these do you agree with and why?
Guest 1: India is a democracy. Therefore, the Indian government must support the people of Nepal who are struggling against monarchy and for democracy.
Guest 2: That is a dangerous argument. We would be in the same position as the US was in Iraq. Remember, no outside force can promote democracy.
Guest 3: But why should we bother about the internal affairs of another country? We should be worried about our business interests there, not about democracy.

Answer :

The opinion of Guest 3 can be easily agreed with. This is because it is a diplomatic approach towards a sensitive international situation, while at the same time it upholds the fact that only the people of a nation can establish democracy in their own country.

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Class 9 Science Chapter 5 Cell: Fundamental Unit of Life

AMEND EDUCATION ACADEMY 9999908238
B6 97 SECTOR 8 Rohini

Cell: Fundamental Unit of Life

 

Solution of NCERT Exercise

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1. Who discovered cells and how?

Answer: It was Robert Hooke who discovered cells. He observed the cells in thin slices of cork. They appeared like small compartments when viewed through the microscope.

2. Why is the cell called structural and functional unit of life?

Answer: A cell is capable of carrying out all the life functions; such as nutrition, excretion, respiration, etc. Hence a cell is called the functional unit of life. Additionally, the cell is the smallest unit of life and all the living beings are made up of cells. Hence a cell is called the structural unit of life.

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1. How do substances like CO₂ and water move in and out of the cell? Discuss.

Answer: Substances move in and out of the cell because of diffusion. Diffusion is the random movement of particles in order to attain concentration equilibrium. The movement of water through a semi-permeable membrane is called osmosis. It is important to note that plasma membrane is a semi-permeable membrane. Water always moves from high water concentration to low water concentration.

2. Why is the plasma membrane called a selectively permeable membrane?

Answer: Plasma membrane allows passage to some selected substances. Hence it is called a selectively permeable or semi-permeable membrane.

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1. Can you name the two organelles we have studied that contain their own genetic material?

Answer: Mitochondria and Chloroplast contain their own genetic material.

2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Answer: Various parts of a cell are responsible for various functions. They work in tandem to continue life in the cell. In case, the organization of a cell is destroyed due to some physical or chemical influence, the cell will die.

3. Why are lysosomes known as suicide bags?

Answer: Lysosomes contain digestive enzymes. In case of a rupture in lysosome, the enzymes are released in the cytoplasm and end up digesting the contents of the cell. This results in cell death. Due to this, lysosome is also known as suicide bags of cells.

4. Where are proteins synthesized inside the cell?

Answer: Proteins are synthesized in ribosome.

Exercise Questions

1. Make a comparison and write down ways in which plant cells are different from animal cells.

Answer:

2. How is a prokaryotic cell different from a eukaryotic cell?

Answer:

3. What would happen if the plasma membrane ruptures or breaks down?

Answer: Plasma membrane provides a container for the cell organelles and cytoplasm. Moreover, plasma membrane also protects the contents of a cell from external environment. In case the plasma membrane ruptures or breaks down, the cell contents would be exposed to the external environment. This would prove lethal for the cell and the cell would cease to exist.

4. What would happen to the life of a cell if there was no Golgi apparatus?

Answer: Golgi apparatus plays the important role of packaging various substances for further use or for storage. If there was no Golgi apparatus, various substances would not be in a position to be transformed in proper forms for further use. Certain substances; like protein and lipid are important for the formation of plasma membrane and hence absence of Golgi apparatus will hamper the formation of new cells during cell division.

5. Which organelle is known as the powerhouse of the cell? Why?

Answer: Mitochondrion is known as the powerhouse of the cell. The reason for this is the fact that cellular respiration takes place in mitochondria and the energy released after that gets stored in mitochondria; in the form of ATP. These ATP molecules are utilized on an SOS basis.

6. Where do the lipids and proteins constituting the cell membrane get synthesised?

Answer: Lipids are synthesized in the endoplasmic reticulum. Protein is synthesized in ribosomes which are usually present on the rough ER.

7. How does an Amoeba obtain its food?

Answer: Amoeba obtains its food through a process called phagocytosis. The cell membrane of amoeba is projected into numerous finger-like outgrowths; called pseudopodia. Amoeba surrounds a food particle by pseudopodia and makes a food vacuole; after engulfing the food.

8. What is osmosis?

Answer: The movement of water from high concentration to low concentration through a semi-permeable membrane is called osmosis.

Cell Summary and notes

CELL: THE FUNDAMENTAL UNIT OF LIFE

Cell: Cell is called the fundamental unit of life.

A cell is capable of independent existence and can carry out all the functions which are necessary for a living being. A cell carries out nutrition, respiration, excretion, transportation and reproduction; the way an individual organism does. Unicellular organisms are capable of independent existence which shows a cell’s capability to exist independently. Due to this, a cell is called the fundamental and structural unit of life. All living beings are composed of the basic unit of life, i.e. cell.

CELL THEORY (Schleiden, Schwann and Virchow):

• All living organisms are composed of one or more cells.

• The cell is the basic unit of structure, function, and organization in all organisms.

• All cells come from preexisting, living cells.

STRUCTURE OF CELL

Shape and Size of Cells:- Cells come in all shapes and sizes. While most of the cells are spherical in shape, cells of various other shapes are also found. Most of the cells are microscopic in size, i.e. it is impossible to see them with naked eyes. Some cells are fairly large, e.g. a neuron in human body can be as long as 1 meter. The egg of an ostrich is the largest known cell of a living animal and an average egg is 15 cm long and 13 cm wide.

A cell is enclosed in a membranous casing and is filled with a liquid substance which is called the cytoplasm. There are many cell organelles in a typical cell. Some of the main structures of a cell are as follows:

Cell wall: Cell wall is made of cellulose. It is somewhat hard but permeable to most of the substances. Cell wall is available in plant cells and in cells of bacteria and fungi.

Plasma membrane: Plasma membrane is a semi-permeable membrane. It is composed of bilayer of lipid and protein.

Functions of Plasma Membrane: Plasma membrane provides a container to the cytoplasm. It facilitates passage of various substances in and out of the cell.

Nucleus: Nucleus is covered by double membrane; called nuclear membrane. The fluid which is inside the nucleus is called nucleoplasm. Nucleus contains chromosomes which are important for the functioning of a cell. Chromosomes contain genes which are the carriers of genetic information. Nucleus plays an important role during cell division. Nucleus controls all the functions of the cell.

Prokaryotes and Eukaryotes:- Based on the level of organization of nuclear material, a cell can be categorized as prokaryote or eukaryote. In some organisms, the true nucleus is absent. This means that the DNA and RNA are not bound by a membrane. Bacteria are examples of prokaryotes. When genetic materials are bound by a membrane, it is termed as true nucleus. In this case, the cell is called eukaryotic. Organisms other than bacteria are eukaryotes. Eukaryotes are considered as more advanced than prokaryotes.

Mitochondria: Mitochondrion is a capsule-like structure. It is a double membrane structure. Its inner membrane is projected into numerous finger-like structures; called cristae. Mitochondria are the sites of cellular respiration. After cellular respiration, energy is stored in the form of ATP (Adenosine triphosphate); in mitochondria. Mitochondria have their own DNA and ribosomes and hence mitochondria can produce their own protein.

Functions of Mitochondria:- Cellular respiration; due to this, mitochondria are also known as the ‘powerhouse of the cell’.

Endoplasmic Reticulum: Endoplasmic reticulum is a mesh-like structure which is composed of numerous tubes. It extends from the plasma membrane to the nuclear membrane. There are two kinds of endoplasmic reticulum, viz. smooth ER and rough ER. Rough ER has ribosomes on its surface which give it the rough appearance.

Function of ER: It serves as the transport channel in the cell. Substances are transported from cell membrane to cytoplasm and to nucleus and vice-versa. ER also serves the role of packaging many substances in the cell.

Golgi Complex: Golgi Complex was discovered by Camillo Golgi. It is composed of many sac-like structures which are stacked one above another.

Functions of Golgi Complex: Golgi complex is responsible for packaging of various substances in the cell.

Lysosome: Lysosome are small sac-like structures and they are derived from Golgi complex. Lysosome contains digestive enzymes.

Functions of lysosome: The enzymes in the lysosome digest foreign particles and thus destroy them. Sometimes, the lysosome may burst open and its content ends up digesting the contents of the cell. The cell gets killed in the process. Due to this, lysosome is also called the ‘suicide bag of the cell’.

Ribosome: These are tiny dot like structures interspersed in the cytoplasm and also on the surface of Rough ER. Ribosome is responsible for protein synthesis.

Plastids: These are somewhat similar to mitochondria; in appearance. Plastids are found in plant cells. They are of two types, chromoplast and leucoplast. Colourful plastids are called chromomplast and colourless plastids are called leucoplast. Chloroplast is green in colour and is found in green parts of plants. Plastids too have their own DNA and ribosome.

Functions of Plastids: Leucoplasts are responsible for storing food; such as carbohydrates, protein and lipid. Chromoplasts impart various colours to the plant parts. A leaf of a plant is green in colour because of chloroplast. Chloroplast is the site of photosynthesis.

Vacuoles: These are fluid filled chambers and are often seen in many cells. Vacuoles are very large in plant cells. A plant cell usually has single but large vacuole. Such a vacuole fills almost the entire space inside the cell. Vacuoles are much smaller and very few in animal cells.

Plant Cell Vs Animal Cell

HISTORY OF DISCOVERY OF CELLS

• Robert Hooke was the first to discover cell (1665).

• Leeuwenhoek was the first to discover free living cells in pond water (1674).

• Robert Brown discovered the nucleus (1831).

• Purkinje coined the term ‘protoplasm (1839).

• Schleiden (1838) and Schwann (1839) proposed the Cell Theory. Virchow (1855) made further addition to the cell theory.

• The discovery of electron microscope (1940) made it possible to study the structures of cell organelles