T5-NCERT-X-Science

Chapter 1

Oxidation is the gain of oxygen or loss of hydrogen. Reduction is the loss of oxygen or gain of hydrogen. 

Chapter 2

Acidic nature of a substance is due to the formation of H+(aq) ions in solution. Formation of OH–(aq) ions in solution is responsible for the basic nature of a substance.

A neutral solution has a pH of exactly 7, while an acidic solution has a pH less than 7 and a basic solution a pH more than 7.

Living beings carry out their metabolic activities within an optimal pH range.

Mixing concentrated acids or bases with water is a highly exothermic process. 

Acids and bases neutralise each other to form corresponding salts and water.
Chapter 4

Carbon is a versatile element that forms the basis for all living organisms and many of the things we use.
Chapter 5

Elements in the Modern Periodic Table are arranged in 18 vertical columns called groups and 7 horizontal rows called periods. 

Chapter 6

Heterotrophic organisms include animals and fungi. 

Chapter 7

Movement Due to Growth 

Some plants like the pea plant climb up other plants or fences by means of tendrils. These tendrils are sensitive to touch. When they come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to circle around the object and thus cling to it. More commonly, plants respond to stimuli slowly by growing in a particular direction. Because this growth is directional, it appears as if the plant is moving. 

Adrenaline is secreted directly into the blood and carried to different parts of the body. The target organs or the specific tissues on which it acts include the heart. As a result, the heart beats faster, resulting in supply of more oxygen to our muscles. The blood to the digestive system and skin is reduced due to contraction of muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. The breathing rate also increases because of the contractions of the diaphragm and the rib muscles. All these responses together enable the animal body to be ready to deal with the situation. Such animal hormones are part of the endocrine system which constitutes a second way of control and coordination in our body. 

Iodine is necessary for the thyroid gland to make thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth. Iodine is essential for the synthesis of thyroxin. In case iodine is deficient in our diet, there is a possibility that we might suffer from goitre. One of the symptoms in this disease is a swollen neck. 

Do you know anyone in your family or friends who has been advised by the doctor to take less sugar in their diet because they are suffering from diabetes? As a treatment, they might be taking injections of insulin. This is a hormone which is produced by the pancreas and helps in regulating blood sugar levels. If it is not secreted in proper amounts, the sugar level in the blood rises causing many harmful effects. 

For example, if the sugar levels in blood rise, they are detected by the cells of the pancreas which respond by producing more insulin. As the blood sugar level falls, insulin secretion is reduced. 

A feedback mechanism regulates the action of the hormones.

Chapter 8

Reproduction, unlike other life processes, is not essential to maintain the life of an individual organism. 

Reproduction involves creation of a DNA copy and additional cellular apparatus by the cell involved in the process. 

In fission, many bacteria and protozoa simply divide into two or more daughter cells. 

Chapter 9

Charles Darwin, who came up with the idea of evolution of species by natural selection in the nineteenth century 

Origin of life on earth 

Darwin’s theory of evolution tells us how life evolved from simple to more complex forms and Mendel’s experiments give us the mechanism for the inheritance of traits from one generation to the next. But neither tells us anything about how life began on earth in the first place. 

J.B.S. Haldane, a British scientist (who became a citizen of India later), suggested in 1929 that life must have developed from the simple inorganic molecules which were present on earth soon after it was formed. He speculated that the conditions on earth at that time, which were far from the conditions we see today, could have given rise to more complex organic molecules that were necessary for life. The first primitive organisms would arise from further chemical synthesis. 

How did these organic molecules arise? An answer was suggested by the experiment conducted by Stanley L. Miller and Harold C. Urey in 1953. They assembled an atmosphere similar to that thought to exist on early earth (this had molecules like ammonia, methane and hydrogen sulphide, but no oxygen) over water. This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lightning. At the end of a week, 15% of the carbon (from methane) had been converted to simple compounds of carbon including amino acids which make up protein molecules. So, can life arise afresh on earth even now? 

The dinosaur skull fossil was found only a few years ago in the Narmada valley. 

The second way of dating fossils is by detecting the ratios of different isotopes of the same element in the fossil material. 

Tracing common ancestors back in time leads us to the idea that at some point of time, non-living material must have given rise to life.

Evolution cannot be said to ‘progress’ from ‘lower’ forms to ‘higher’ forms. Rather, evolution seems to have given rise to more complex body designs even while the simpler body designs continue to flourish.

Study of the evolution of human beings indicates that all of us belong to a single species that evolved in Africa and spread across the world in stages.

Chapter 11

A human being has a horizontal field of view of about 150° with one eye and of about 180° with two eyes. The ability to detect faint objects is, of course, enhanced with two detectors instead of one. 

About 35 million people in the developing world are blind and most of them can be cured. About 4.5 million people with corneal blindness can be cured through corneal transplantation of donated eyes. Out of these 4.5 million, 60% are children below the age of 12. So, if we have got the gift of vision, why not pass it on to somebody who does not have it? What do we have to keep in mind when eyes have to be donated? 

 Persons who were infected with or died because of AIDS, Hepatitis B or C, rabies, acute leukaemia, tetanus, cholera, meningitis or encephalitis cannot donate eyes.

One pair of eyes gives vision to TWO CORNEAL BLIND PEOPLE.

A rainbow is a natural spectrum appearing in the sky after a rain shower . It is caused by dispersion of sunlight by tiny water droplets, present in the atmosphere. A rainbow is always formed in a direction opposite to that of the Sun. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop . Due to the dispersion of light and internal reflection, different colours reach the observer’s eye. 

Twinkling of stars 

The twinkling of a star is due to atmospheric refraction of starlight. The starlight, on entering the earth’s atmosphere, undergoes refraction continuously before it reaches the earth. 

Why don’t the planets twinkle? The planets are much closer to the earth, and are thus seen as extended sources. If we consider a planet as a collection of a large number of point-sized sources of light, the total variation in the amount of light entering our eye from all the individual point-sized sources will average out to zero, thereby
nullifying the twinkling effect. 

Advance sunrise and delayed sunset 

The Sun is visible to us about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset because of atmospheric refraction. By actual sunrise, we mean the actual crossing of the horizon by the Sun. The time difference between actual sunset and the apparent sunset is about 2 minutes. The apparent flattening of the Sun’s disc at sunrise and sunset is also due to the same phenomenon. 

Tyndall Effect 

The earth’s atmosphere is a heterogeneous mixture of minute particles. These particles include smoke, tiny water droplets, suspended particles of dust and molecules of air. When a beam of light strikes such fine particles, the path of the beam becomes visible. The light reaches us, after being reflected diffusely by these particles. The phenomenon of scattering of light by the colloidal particles gives rise to Tyndall effect. 

The colour of the scattered light depends on the size of the scattering particles. Very fine particles scatter mainly blue light while particles of larger size scatter light of longer wavelengths. If the size of the scattering particles is large enough, then, the scattered light may even appear white. 

Why is the colour of the clear Sky Blue? 

The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. These are more effective in scattering light of shorter wavelengths at the blue end than light of longer wavelengths at the red end. The red light has a wavelength about 1.8 times greater than blue light. Thus, when sunlight passes through the atmosphere, the fine particles in air scatter the blue colour (shorter wavelengths) more strongly than red. The scattered blue light enters our eyes. If the earth had no atmosphere, there would not have been any scattering. Then, the sky would have looked dark. The sky appears dark to passengers flying at very high altitudes, as scattering is not prominent at such heights. 

You might have observed that ‘danger’ signal lights are red in colour. Do you know why? The red is least scattered by fog or smoke. Therefore, it can be seen in the same colour at a distance. 

cattering of light that helps you to understand the bluish colour of the sky and the reddish appearance of the Sun at the sunrise or the sunset. 

Light from the Sun near the horizon passes through thicker layers of air and larger distance in the earth’s atmosphere before reaching our eyes . 

However, light from the Sun overhead would
travel relatively shorter distance. At noon, the Sun
appears white as only a little of the blue and violet
colours are scattered. Near the horizon, most of
the blue light and shorter wavelengths are
scattered away by the particles. Therefore, the light that reaches our eyes is of longer wavelengths. This gives rise to the reddish appearance of the Sun. 

• The ability of the eye to focus both near and distant objects, by adjusting its focal length, is called the accommodation of the eye. 
•  The smallest distance, at which the eye can see objects clearly without strain, is called the near point of the eye or the least distance of distinct vision. For a young adult with normal vision, it is about 25 cm. 
•  The common refractive defects of vision include myopia, hypermetropia and presbyopia. Myopia (short-sightedness – the image of distant objects is focussed before the retina) is corrected by using a concave lens of suitable power. Hypermetropia (far-sightedness – the image of nearby objects is focussed beyond the retina) is corrected by using a convex lens of suitable power. The eye loses its power of accommodation at old age. 
•  The splitting of white light into its component colours is called dispersion. 
•  Scattering of light causes the blue colour of sky and the reddening of the Sun at
  sunrise and sunset.
  

Chapter 12

•  A stream of electrons moving through a conductor constitutes an electric current. Conventionally, the direction of current is taken opposite to the direction of flow of electrons. 
• The SI unit of electric current is ampere. 
• To set the electrons in motion in an electric circuit, we use a cell or a battery. A cell
  generates a potential difference across its terminals. It is measured in volts (V). 
•  Resistance is a property that resists the flow of electrons in a conductor. It controls
  the magnitude of the current. The SI unit of resistance is ohm (Ω). 
•  Ohm’s law: The potential difference across the ends of a resistor is directly
  proportional to the current through it, provided its temperature remains the same. 
• The resistance of a conductor depends directly on its length, inversely on its area of cross-section, and also on the material of the conductor. 
• The equivalent resistance of several resistors in series is equal to the sum of their individual resistances. 

The commercial unit of electrical energy is kilowatt hour (kWh). 1kWh=3,600,000J=3.6×106 J. 

Chapter 13

•  A generator converts mechanical energy into electrical energy. It works on the basis of electromagnetic induction. 
• In our houses we receive AC electric power of 220 V with a frequency of 50 Hz. One of the wires in this supply is with red insulation, called live wire. The other one is of black insulation, which is a neutral wire. The potential difference between the two is 220 V. The third is the earth wire that has green insulation and this is connected to a metallic body deep inside earth. It is used as a safety measure to ensure that any leakage of current to a metallic body does not give any severe shock to a user. 
• Fuse is the most important safety device, used for protecting the circuits due to short-circuiting or overloading of the circuits.

Chapter 14

Wind energy is an environment-friendly and efficient source of renewable energy. It requires no recurring expenses for the production of electricity. But there are many limitations in harnessing wind energy. Firstly, wind energy farms can be established only at those places where wind blows for the greater part of a year. The wind speed should also be higher than 15 km/h to maintain the required speed of the turbine. 

For a 1 MW generator, the farm needs about 2 hectares of land. The initial cost of establishment of the farm is quite high. Moreover, since the tower and blades are exposed to the vagaries of nature like rain, Sun, storm and cyclone, they need a high level of maintenance. 

It is estimated that nearly 45,000 MW of electrical power can be generated if India’s wind potential is fully exploited. The largest wind energy farm has been established near Kanyakumari in Tamil Nadu and it generates 380 MW of electricity. 

Solar cells that convert solar energy into electricity. A typical cell develops a voltage of 0.5–1 V and can produce about 0.7 W of electricity when exposed to the Sun. A large number of solar cells are, combined in an arrangement called solar cell panel (Fig. 14.7) that can deliver enough electricity for practical use. 

Silicon, which is used for making solar cells, is abundant in nature but availability of the special grade silicon for making solar cells is limited. 

Chapter 15

All organisms such as plants, animals, microorganisms and human beings as well as the physical surroundings interact with each other and maintain a balance in nature. All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem. Thus, an ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals. 

• The flow of energy between various components of the environment has been extensively studied and it has been found that – 
• The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves and convert it into food energy. 
• When green plants are eaten by primary consumers, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work and the rest goes towards growth and reproduction. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers. 
•  Therefore, 10% can be taken as the average value for the amount of organic matter that is present at each step and reaches the next level of consumers. 
•  Since so little energy is available for the next level of consumers, food chains generally consist of only three or four steps. The loss of energy at each step is so great that very little usable energy remains after four trophic levels. 
• There are generally a greater number of individuals at the lower trophic levels of an ecosystem, the greatest number is of the producers. 
• The length and complexity of food chains vary greatly. Each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms. So instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web
  
  From the energy flow diagram , two things become clear. Firstly, the flow of energy is unidirectional. The energy that is captured by the autotrophs does not revert back to the solar input and the energy which passes to the herbivores does not come back to autotrophs. As it moves progressively through the various trophic levels it is no longer available to the previous level.
  

Another interesting aspect of food chain is how unknowingly some harmful chemicals enter our bodies through the food chain. 

Chapter 16

Coliform is a group of bacteria, found in human intestines, whose presence in water indicates contamination by disease-causing microorganisms. 

Pollution of the Ganga 

The Ganga runs its course of over 2500 km from Gangotri in the Himalayas to Ganga Sagar in the Bay of Bengal. It is being turned into a drain by more than a hundred towns and cities in Uttar Pradesh, Bihar and West Bengal that pour their garbage and excreta into it. Largely untreated sewage is dumped into the Ganges every day. In addition, think of the pollution caused by other human activities like bathing, washing of clothes and immersion of ashes or unburnt corpses. And then, industries contribute chemical effluents to the Ganga’s pollution load and the toxicity kills fish in large sections of the river. 

You must have come across the three R’s to save the environment: Reduce, Recycle and Reuse. 

Forests are ‘biodiversity hot spots’. One measure of the biodiversity of an area is the number of species found there. 

The Government of India has recently instituted an ‘Amrita Devi Bishnoi National Award for Wildlife Conservation’ in the memory of Amrita Devi Bishnoi, who in 1731 sacrificed her life along with 363 others for the protection of ‘khejri’ trees in Khejrali village near Jodhpur in Rajasthan. 

An Example of People’s Participation in the Management of Forests 

In 1972, the West Bengal Forest Department recognised its failures in reviving the degraded Sal forests in the southwestern districts of the state. Traditional methods of surveillance and policing had led to a 

‘complete alienation of the people from the administration’, resulting in frequent clashes between forest officials and villagers. Forest and land related conflicts in the region were also a major factor in fuelling the militant peasant movements led by the Naxalites. 

Accordingly, the Department changed its strategy, making a beginning in the Arabari forest range of Midnapore district. Here, at the instance of a far-seeing forest officer, A.K. Banerjee, villagers were involved in the protection of 1,272 hectares of badly degraded sal forest. In return for help in protection, villagers were given employment in both silviculture and harvesting operations, 25 per cent of the final harvest, and allowed fuelwood and fodder collection on payment of a nominal fee. With the active and willing participation of the local community, the sal forests of Arabari underwent a remarkable recovery – by 1983, a previously worthless forest was valued Rs 12.5 crores.