CBSE Class 10 Science Revision Notes Ch-16 Management of Natural Resources

CBSE Class 10 Science
Revision Notes
Ch-16 Management of Natural Resources

Management of Natural Resources – CBSE Notes for Class 10 Science

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

2. In 1985, our government started a multi-crore project named as ‘Ganga Action Plan’. The main aim of this project is to improve the water quality of Our holy river Ganga.

3. The water of river Ganga gets polluted because of the following reasons :
(a) Dumping of untreated sewage.
(b) Human activities like bathing or washing of clothes.
(c) Immersion of ashes or unburnt corpses.
(d) Chemical effluents from industries.
This all pollutes water, increasing the toxicity level which kills fish in large sections of the river.

4. One should keep in mind the three R’s to save the environment:
Reduce : Using less and less of natural resources.
One can help by switching off unnecessary lights and fans, repairing leaky taps, preventing wastage of food. Recycling: It minimises the faster depletion of natural resources.
Reuse: It is better than recycling because the process of recycling uses some energy.

5. Economic development is linked to environmental conservation.

6. The concept of sustainable development encourages forms of growth that meet current basic human needs, while preserving the resources for the needs of future generation.

7. The sustainable development : It implies a change in all aspects of life. It depends upon the willingness of the people to change their perceptions of the socioeconomic and environmental conditions around them and the readiness of each individual to alter their present use of natural resources.

8. Sustainable natural resource management demands the following:

Using resources carefully because these are not unlimited.
A long term perspective so that these resources will last for the generations to come and will not merely be exploited for short-term gains.
Equitable distribution of resources so that all and not just a handful of rich and powerful people, benefit from the development of these resources.
Checking the damage caused to the environment while these resources are either extracted or used,
Planning for the safe disposal of the waste which is generated when natural resources are either extracted or used.

9. Forests are ‘biodiversity hot spots’. One measure of the biodiversity of.an area is the number of different species found there. However, the range of different life forms (such as bacteria, fungi, ferns, flowering plants, nematodes, insects, birds, reptiles and so on) is also important.

10. One of the main aim of conservation is to try and preserve the biodiversity that we have inherited.

11. A loss of diversity may lead to a loss of ecological stability.

12. Forest resources ought to be used in a manner that is both environmentally and developmentally sound.

13. The destruction of forests not only affects the availability of forest products, but also the quality of soil and the sources of water.

14. Despite nature’s monsoon bounty, failure to sustain water availability underground has resulted largely from the loss of vegetation cover, diversion for high water demanding crops and pollution from industrial effluents and urban wastes.

15. Dams are built to ensure the storage of adequate water not only for irrigation but also for generating electricity. However, building of large dams cause social, economic and environmental problem.

16. Watershed Management: Watershed management emphasises scientific soil and water conservation in order to increase the biomass production. The aim is to develop primary resources of land and water, to produce secondary resources of plants and animals for use in a manner which will not cause ecological imbalance. Watershed management not only increase the production and income of the watershed
: community, but also mitigates droughts and floods and increases the life of the downstream dam and reservoirs.

17. The Chipko Andolan (‘Hug the Trees Movement’) :
It started in a remote village called Reni in Garhwal in early 1970s. In this movement, women of the village used to clasp the tree trunks thus preventing the felling of trees.
Role of Chipko Andolan :

It helped in conservation and preservation of forests, one of the most important natural resources.
It allowed the village communities to utilise the forest produce and allowing the resource to replenish over time.
It taught people that, the destruction of forests not only affects the availability of forest products but also the quality of soil and the sources of water.
It forced government to rethink the priorities of the local people (to whom the forests belong) in the use of forest produce.
It encouraged the participation of the local people in the efficient management of forests.

18. Stakeholders of forest:

People living in or around forest: They depend on forest produce for their living.
The forest Department of the Government : Which owns the land and controls the resources from forests.
The industrialists : Who use various forest produce as raw material, but are not dependent on the forest in any orie area.
The wildlife and nature enthusiasts: Who want to conserve nature in its pristine form.

19. Water harvesting : It is an age-old concept in India which involves capturing rainwater in the large structures which can hold this water round the year. The main purpose is not only to hold the surface water but also to recharge the groundwater beneath.
Advantages of water harvesting :

The water does not evaporate, but spreads out to recharge wells and provides moisture for vegetation over a wide area.
It does not provide breeding grounds for mosquitoes like stagnant water collected in ponds or artificial lakes.
The groundwater is also relatively protected . from contamination by human and animal
wastes.
It raises the groundwater level.

CBSE Class 10 Science Revision Notes Ch-15 Our Environment

CBSE Class 10 Science
Revision Notes
Ch-15 Our Environment

Our Environment – CBSE Notes for Class 10 Science

1. Environment : The physical, chemical and ‘ biological conditions of the region in which an organism lives is called its Environment. It includes air, light, soil, temperature, water and the presence or absence of other organisms, i.e., the conditions for development or growth.
Environment has three main components, viz :
(a) Physical surroundings [soil, air and water bodies]
(b) Living organisms [plants, animals, decomposers (bacteria and fungi)]
(c) Meteorological factors (or climatic factors) . [sunlight, temperature, rainfall, humidity, pressure and wind speed].

2. Physical environment: It is also called as abiotic or non-living environment. It includes :

Soil, water bodies and air on the surface of the earth.
Meteorological factors.

Physical environment is essential for :
(a) Supply of nutrient elements to the living beings.
(b) Providing space to the organisms for living.
(c) Controlling weather of a place.

3. Biotic (or biological) environment : It includes :

Plants.
Animals (including human beings).
Decomposers (bacteria and.fungi).

Other important constituent of biotic environment includes : Kites and vultures as they feed on dead organisms and act as scavengers (cleansing agents) of the environment.

4. Ecosystem : A community of organisms, interacting with each other, plus the environment in which they
live and with which they also interact. The examples of ecosystem are : a pond ; a desert; a forest; a lake ; a river ; a mountain ; the sea.
All the above ecosystems are made-up of two main components.

5. Autotrophs (Producers) and Heterotrophs (consumers):

6. Food chain: The sequence of living organisms in a . community in which one organism.e^ts other and is
itself eaten by another organism to transfer energy is called a food chain. It is also defined as, “chain of organisms, existing in any natural community, through which energy is transferred”.

7. Ozone layer : Ozone (O₃) is a molecule formed by three atoms of oxygen unlike oxygen which is required for respiration by aerobic forms, ozone is a deadly poison. However, at the higher levels of the atmosphere,
ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.
Ozone at the higher levels of the atmosphere is a product of UV radiation, acting on oxygen (O2) molecule. The higher energy UV radiations split apart some molecular
oxygen (02) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown:

Depletion of ozone layer: Ozone layer gets depleted – due to the use of chemicals called aerosol, spray propellants like chlorofluorocarbons. Depletion of ‘ ozone layer would cause skin cancer in men and animals and severe damage to the plants.

8. Biological magnification : It means accumulation of non-biodegradable chemicals (like pesticides) in the living organisms (like plants, animals, including man) in a food chain. “The increase in concentration of harmful chemicals in the body of living organisms at each trophic level of a food chain is called biological magnification”.

9. Biodegradable wastes and Non-biodegradable wastes:

10. A generalised food chain:

11. Food web: A food web is a network of food chains which establish a network of relationships between various species. Food web showing 8 interlinked food chains.

13. The flow of energy between various components of the environment:

Green plants capture about 1 % of the energy and convert it into food energy.
About f % of the food eaten is turned into the body of an organism and made available for the next level of consumers.
About 10% of organic matter 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.

CBSE Class 10 Science Revision Notes Ch-15 Our Environment

CBSE Class 10 Science
Revision Notes
Ch-15 Our Environment

Our Environment – CBSE Notes for Class 10 Science

1. Environment : The physical, chemical and ‘ biological conditions of the region in which an organism lives is called its Environment. It includes air, light, soil, temperature, water and the presence or absence of other organisms, i.e., the conditions for development or growth.
Environment has three main components, viz :
(a) Physical surroundings [soil, air and water bodies]
(b) Living organisms [plants, animals, decomposers (bacteria and fungi)]
(c) Meteorological factors (or climatic factors) . [sunlight, temperature, rainfall, humidity, pressure and wind speed].

2. Physical environment: It is also called as abiotic or non-living environment. It includes :

Soil, water bodies and air on the surface of the earth.
Meteorological factors.

Physical environment is essential for :
(a) Supply of nutrient elements to the living beings.
(b) Providing space to the organisms for living.
(c) Controlling weather of a place.

3. Biotic (or biological) environment : It includes :

Plants.
Animals (including human beings).
Decomposers (bacteria and.fungi).

Other important constituent of biotic environment includes : Kites and vultures as they feed on dead organisms and act as scavengers (cleansing agents) of the environment.

4. Ecosystem : A community of organisms, interacting with each other, plus the environment in which they
live and with which they also interact. The examples of ecosystem are : a pond ; a desert; a forest; a lake ; a river ; a mountain ; the sea.
All the above ecosystems are made-up of two main components.

5. Autotrophs (Producers) and Heterotrophs (consumers):

6. Food chain: The sequence of living organisms in a . community in which one organism.e^ts other and is
itself eaten by another organism to transfer energy is called a food chain. It is also defined as, “chain of organisms, existing in any natural community, through which energy is transferred”.

7. Ozone layer : Ozone (O₃) is a molecule formed by three atoms of oxygen unlike oxygen which is required for respiration by aerobic forms, ozone is a deadly poison. However, at the higher levels of the atmosphere,
ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.
Ozone at the higher levels of the atmosphere is a product of UV radiation, acting on oxygen (O2) molecule. The higher energy UV radiations split apart some molecular
oxygen (02) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown:

Depletion of ozone layer: Ozone layer gets depleted – due to the use of chemicals called aerosol, spray propellants like chlorofluorocarbons. Depletion of ‘ ozone layer would cause skin cancer in men and animals and severe damage to the plants.

8. Biological magnification : It means accumulation of non-biodegradable chemicals (like pesticides) in the living organisms (like plants, animals, including man) in a food chain. “The increase in concentration of harmful chemicals in the body of living organisms at each trophic level of a food chain is called biological magnification”.

9. Biodegradable wastes and Non-biodegradable wastes:

10. A generalised food chain:

11. Food web: A food web is a network of food chains which establish a network of relationships between various species. Food web showing 8 interlinked food chains.

13. The flow of energy between various components of the environment:

Green plants capture about 1 % of the energy and convert it into food energy.
About f % of the food eaten is turned into the body of an organism and made available for the next level of consumers.
About 10% of organic matter 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.

CBSE Class 10 Science Revision Notes Ch-11 Human Eye and Colourful World

CBSE Class 10 Science
Revision Notes
Ch-11 Human Eye and Colourful World

Human Eye and Colourful World – CBSE Notes for Class 10 Science

1. The human eye is one of the most valuable and sensitive sense organs. It enables us to see the wonderful world and the colours around us.

2. The eyeball is approximately spherical in shape with a diameter of about 2.3 cm.

3. Most of the refraction for the light rays entering the eye occurs at the outer surface of the cornea. The crystalline lens merely provides the finer adjustment of focal length required to focus.

4. The human eye has the following parts :

Cornea : The transparent spherical membrane covering the front of the eye.
Iris: The coloured diaphragm between the cornea and lens.
Pupil: The small hole in the iris.
Eye lens : It is a transparent lens made of jelly like material.
Ciliary muscles: These muscles hold the lens in position.
Retina: The back surface of the eye.
Blind spot: The point at which the optic nerve leaves the eye. An image formed at this point is not sent to the brain.
Aqueous humour: A clear liquid region between the cornea and the lens.
Vitreous humour: The space between eye lens and retina is filled with another liquid called vitreous humour.

5. In the eye, the image is formed on the retina by successive refractions at the cornea, the aqueous humour, the lens and the vitreous humour. Electrical signals then travel along the optic nerve to the brain to be interpreted. In good light, the yellow spot is most sensitive to detail and the image is automatically formed there.

6. Accommodation: The ability of the eye to focus both near and distant objects, by adjusting its focal length, is called the accommodation of the eye or the ability of the ciliary muscles to change the focal length of the eye lens is called accommodation.

7. Defects of the Eye : Although the eye is one of the most remarkable organs in the body, it may have several abnormalities, which can often be corrected with eyeglasses, contact lenses, or surgery. The various defects from which an eye can suffer are (i) Hypermetropia or long sightedness, (ii) Myopia or shortsightedness and (iii) Astigmatism, (iv) Presbyopia.

8. Hypermetropia, hyperopia, or long sightedness : A person suffering from this defect can see distant objects I clearly but cannot see nearby objects clearly. In this defect, the near point lies farther away than 25 cm. 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.

9. Hypermetropia is due to the following reasons :

Either the hyperopic eyeball is too short or
The ciliary muscle is unable to change the shape
of the lens enough to properly focus the image i.e. the focal length of the eye lens increases.

10. Myopia or short sightedness or near sightedness: A person suffering frommyopia or short sightedness can see nearby objects clearly but cannot see the far away objects clearly. Myopia (short sightedness — the image of distant objects is focussed before the retina) is corrected by using a concave lens of suitable power.

11. This defect is due to the following reasons :

Either the eyeball is longer than normal or
The maximum focal length (due to excessive curvature of the cornea) of the lens is insufficient to produce a clearly formed image on the retina.

12. A person may also have an eye defect known as astigmatism, in which light from a point-source produces a line image on the retina. A person suffering from this defect cannot see in all directions equally well i.e., he cannot see the vertical and horizontal lines simultaneously. This condition arises either when the cornea or the crystalline lens or both are not perfectly spherical. Astigmatism can be corrected with lenses having different curvatures in two mutually perpendicular directions i.e., cylindrical lens.

13. When a person suffers from both, the myopia as well as Hypermetropia, his spectacles for correction have bifocal lenses. The upper half is a concave lens for distant vision and lower half is a convex lens for reading.

14. Presbyopia is that defect of human eye, due to which an old person cannot read and write comfortably. That is why Presbyopia is also called old sight.

15. To correct Presbyopia, an old person has to use spectacles with a convex lens of suitable focal length, or power as explained already.

16. The cause of Hypermetropia is decrease in length of eyeball or increase In focal length of eye lens. But the cause of Presbyopia is only increase in focal length of eye lens. The eyeball, in Presbyopia, has normal length.
the vision of the eye decreases, leading sometimes to total loss of vision. The problem is overcome by cataract surgery i.e., removal of the eye lens, and its replacement by a lens of suitable focal length.

18. We need two eyes because a human being has a horizontal field of view of about 150° with one eye and of about 180° with two eyes. Thus, two eyes provide us wider horizontal field of view.
With one eye, the world looks flat, i.e., two dimensional only. With two eyes, the view is three dimensional, i.e., dimension of depth is added to our view.

19. As our two eyes are separated by a few centimetres, each eye observes a slightly different image. Our brain combines the two views into one and we get to know how close or far away the things seen are.

20. By donating our eyes after we die, one pair of our eyes can give vision to two corneal blind people. Eye donors may belong to any sex or any age group. People suffering from diabetes, hypertension, asthma or any other non- communicable diseases can donate eyes. People who have been using spectacles or those operated for cataract can also donate eyes.

21. 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.

22. Persistence of vision of the eye: The image of an object persists on the retina for 1/16 second, even after the removal of the object. The sequence of still pictures taken by a movie camera is projected on a screen at a rate of about 24 images or more per second. The successive impressions of images on the screen appear to merge smoothly into one another to give us the feeling of moving images.

23. The large numbers of light sensitive cells contained in the retina of the eye are of two types: rod shaped cells which respond to brightness or intensity of light and cone shaped cells, which respond to colour of light. Thus/cone shaped cells enable us to distinguish between different colours.

24. When a person cannot distinguish between different colours, he is said to be colour blind though his vision may otherwise be normal. Colour blindness is a genetic disorder which occurs by inheritance. So far, there is no cure for colour blindness.

25. Farpoint: The farthest point upto which a short sighted eye can see clearly is called the far point of the eye. For a normal eye, the far point is infinity.

26. Near point : The nearest point upto which a long sighted eye can see clearly is called the near point of the eye. For a normal human eye, of an adult, the near point is about 25 cm from the eye.

27. Least cfistance of distinct vision: The minimum distance upto which an eye can see clearly is called the legist distance of distinct vision ; it is normally denoted by D. The least distance of distinct vision is equal to the distance between the eye and its near point. For a normal human eye, this distance is around 25 cm.

28. The distance between far point and near point of the eye is called range of vision of the eye.

29. When white light passes through a prism, the violet light bends most and the red light bends the least. Dispersion of light is the phenomenon of splitting of white light into its constituent seven colours on passing through a glass prism. The band of seven colours so obtained is called visible spectrum.

30. The seven colours of white light are violet, indigo, blue, green, yellow, orange and red. It is remembered by the acronym VIBGYOR.

31. Isaac Newton was the first to use a prism to obtain a spectrum of sunlight.

32. Spectrum is the band of distinct colours we obtain when white light is split by a prism.

33. Cause of dispersion : Every colour has its own characteristic wavelength/frequency. Different colours move with same speed in air/vacuum. But their speeds in refracting media like glass are different. Therefore, refractive index of the medium for different colours is different. As a result, different colours undergo different deviations on passing through the prism. Hence, different colours emerge from the prism along different directions.

34. The speed of light in vacuum is same for all wavelengths, but the speed in a material substance is different for different wavelengths.

35. In any medium other than air/vacuum red light travels the fastest and violet light travels the slowest.

36. The most familiar form of electromagnetic radiation may be defined as that part of the spectrum that the human eye can detect. Light is produced by the rearrangement of electrons in atoms and molecules. The various wavelengths of visible light are classified with colours ranging from violet (λ = 4 x 10^-7 m) to red (λ = 7 x 10^-7 m). The eye’s sensitivity is a function of wavelength, the sensitivity being a maximum at a wavelength of about λ = 5.6 x 10^-7 m (yellow-green).

37. When we pass white light through two ideptical prisms held side by side with their refracting edges in opposite directions; the first prism disperses white light into seven colours and the second prism recombines the seven colours into white light. Thus, light emerging from 2nd prism is white.

38. A rainbow is formed due to dispersion of light by tiny droplets of water which act as prisms.

39. Atmospheric refraction is the cause of twinkling of stars, advance sunrise and delayed sunset.

40. Scattering of light causes the blue colour of sky and the reddening of the Sun at sunrise and sunset.

CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction

CBSE Class 10 Science
Revision Notes
Ch-10 Light Reflection and Refraction

Light Reflection and Refraction – CBSE Notes for Class 10 Science

1. Light travels in a straight line.

2. Light gets reflected when it falls on polished surfaces; like mirrors.

3. Light suffers refraction when it travels from one medium to another.

4. There is a change in the wavelengths!light when it moves from one medium into another.

5. The bouncing back of light when it strikes a smooth or polished surface is called reflection of light. Reflection is of two types; Specular or regular and Diffuse or irregular reflection.

6. The angle of incidence is equal to the angle of reflection. Mathematically, we have ∠i = ∠r.

7. The image is as far behind the mirror as the object is in front.

8. The image is unmagnified, virtual and erect.

9. The image has right-left reversal.

10. Focal length of a plane mirror is infinity.

11. Power of a plane mirror is zero.

12. If a plane mirror is turned by an angle, the reflected ray turns by 2θ.

13. The least size of a plane mirror to view an object is equal to half the size of the object.

14. Pole (Vertex): The central point of a mirror is called its pole.

15. Centre of curvature : The centre of the sphere of which the mirror is a part is called the centre of curvature. It is denoted by C.

16. Radius of curvature : The radius of the sphere of which the mirror is a part is called the radius of curvature. It is denoted by R.

17. Principal axis : The straight line passing through the pole and the centre of curvature of the mirror is called the principal axis.

18. Principal focus : It is a point on the principal axis at which the rays parallel to the principal axis meet after reflection or seem to come from. For a concave mirror, the focus lies in front of the mirror and for a convex mirror, it lies behind the mirror. In short, a concave mirror has a real focus while aconvex mirror has a virtual focus.

19. Focal plane : A plane, drawn perpendicular to the principal axis and passing through the principal focus.

20. Focal length : The distance between the pole and the focus is called the focal length. It is represented by f. The focal length is half the radius of curvature.

21. Aperture: The size of the mirror is called its aperture. It is also defined as the effective diameter of the light reflecting area of the mirror.

22. Real image : When the rays of light, after reflection from a mirror, actually meet at a point, then the image formed by these rays is said to be real. Real images can be obtained on a screen.

23. Virtual image: When the rays of light, after reflection from a mirror, appear to meet at a point, then the image formed by these rays is said to be virtual. Virtual images can’t be obtained on a screen.

24. The following rays are used while drawing ray diagrams to find the position of an image :

A ray of light parallel to the principal axis after reflection passes through the focus. (1)
A ray of light passing through the focus after reflection becomes parallel to the principal axis. (2)
A ray of light incident on the centre of curvature retraces its path after reflection form the mirror.
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$

25. For mirrors, the following results hold :
u is – ve, if the object is in front of the mirror.
(Real object)
u is + ve, if the object is behind the mirror.
(Virtual object)
v is – ve, if the image is in front of the mirror.
(Real image)
vis +ve, if the image is behind the mirror.
(Virtual image)
Focal length of a concave mirror is taken as – ve. Focal length of a convex mirror is taken as +ve.

26. When the image formed by a spherical mirror is real, it is also inverted and is on the same side of the mirror as the object. Since both v and u are negative, the magnification is negative.

27. When the image formed by a spherical mirror is virtual, it is also erect and is on the other side of the mirror as the object. In this case, u is – ve and v is + ve , therefore, m is positive.

28. The expression for the mirror formula is 1/u+1/v = 1/f

29. Linear magnification is given by the expression
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$

30. If m is positive, the image is erect w.r.t the object and if m is negative, the image is inverted w.r.t. the object.

31.The position of the image for various positions of the object for a concave mirror is as shown in the table below. The table also shows the use of the mirror for different positions of the object.
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$
The position of the image for various positions of the object for a convex mirror is as shown in the table below. The table also shows the use of the mirror for different positions of the object.
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$

32. The bending of light when it travels from one medium into another is called refraction of light

33.
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$

34. As light travels from ,one medium to another, the frequency of light does not change.

35. Light refracts because it has different speeds in different media.

36. The refraction of light obeys the following two laws :

The incident ray, the refracted ray and the normal at the point of incidence all lie in the same plane.
The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.This
constant is called the index of refraction or refractive index.
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$

37. If _wn_g is the refractive index of glass w.r.t. water, _an_g be the refractive index of glass w.r.t. air and _an_w be the refractive index of water w.r.t. air ,then
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$

38. The most familiar and widely used optical device is the lens. A lens is an optical system with two refracting surfaces. The simplest lens has two spherical surfaces close enough together that we can neglect the distance between them. Such a lens is called a thin lens. The two common types of lenses are Converging lens or Convex lens, Diverging lens or Concave lens.

39. It should be noted that, if the above lenses are surrounded by .a material with a refractive index greater than that of the lens, the convex lens gets converted into a concave lens and vice-versa.

40. Any lens that is thicker at its centre than at its edges is a converging lens with positive f, and any lens that is thicker at its edges than at the centre is a diverging lens with negative f.

41. Optical centre : The central point C in the lens is called the optical centre. If a ray is incident towards the optical centre, it passes undeviated .through the lens.
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$

42.Principal axis: Since the lens contains two spherical surfaces, therefore, it has two centres of curvatures.
The line joining these centres and passing through the optical centre is called principal axis.

43. Aperture: The effective width of a lens through which refraction takes place is called the aperture.

44. Focus and Focal Length : If a beam of light moving parallel to the principal axis of a convex lens is incident on it, the rays converge or meet at a point on the principal axis. This point F is called the focus. The distance CF is called the focal length. If a beam of light moving parallel to the principal axis is incident on a concave lens, the beam of light diverges. If these diverged rays are produced backward, they meet at a point F on the principal . axis. The transmitted rays appear to come from this point. This point F is called the focus and distance CF is called the focal length.

45. For drawing the ray diagrams, we note the following :
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$

All rays parallel to the principal axis after refraction pass through the principal focus or seem to come from it.
A ray of light passing through the focus after refraction becomes parallel to the principal axis.
A ray of light passing through the optical centre of the lens after refraction passes undeviated.

46. A convex and a concave lens can be supposed to be made-up of prisms.

47. Image formation by a concave lens.
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$

48. Image formation by a convex lens.
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$

49. New Cartesian sign conventions :

All distances, object distance (u), image distance (v) and focal length f are measured from the optical centre.
The distances measured in the direction of incident ray are taken as positive and distances measured against the direction of incident ray are taken as negative.
All distances (heights) of objects and images above principal axis are taken as positive and those below the principal axis are taken as negative.

50. For the two lenses, the sign conventions take the form

u is- ve, if the object is in front of the lens. (Real object)
u is +ve, if the object is virtual.
v is – ve, if the image is on the same side as that of the object. (Virtual image )
v is +ve, if the image is real.
Focal length of a concave lens is taken as – ve.
Focal length of a convex lens is taken as +ve.

51. Lens formula for convex lens 1/v-1/u = 1/f

52. The linear magnification produced by a lens is defined as the ratio of the size of the image (h’) to the size of the object (h). It is represented by m i.e.,
$CBSE Class 10 Science Revision Notes Ch-10 Light Reflection and Refraction$

53. If the magnification of a lens is negative, then the image formed is inverted and real.

54. If the magnification of a lens is positive, then the image formed is erect and virtual.

55. Power is defined as the reciprocal of the focal length. Power is measured in dioptre.

CBSE Class 10 Science Revision Notes Ch-9 Heredity and Evolution

CBSE Class 10 Science
Revision Notes
Ch-9 Heredity and Evolution

Heredity and Evolution – CBSE Notes for Class 10 Science

1. Heredity : It refers to the transmission of characters or traits from the parents to their offspring. Heredity is the continuity of features from one generation to another which are present in fertilised egg or zygote. The zygote develops into an organism of a particular type only.

2. Genetics : It is the branch of biology which deals with heredity and variation. Genetics is to help our understanding of heredity by knowing how offspring inherit characteristics from their parents.

3. Variation : It means the differences in the characters or traits among the individuals of a species. Variations occur during reproduction both because of error in DNA copying and as a result of sexual reproduction. Variations contribute to evolution.
Causes of variations:

Different combinations of genetic material.
Some positive gene mutations.
Interaction of genes with environmental changes (adaptations).

Importance of variations:

It forms, the. basis of heredity.
It causes adaptations due to which organism can easily adjust to its changing environment.
Accumulation of variations forms the basis of evolution.

Remember!
Variations are produced both in sexual and asexual reproduction but amount of variations produced in asexual reproduction are subtle (so little) that they are hardly noticeable as compared to variations caused due to sexual reproduction.

4. Genotype : The genetic constitution of an organism e.g., Genotype of human male is 44 + XY and
genotype of human female is 44 + XX

5. Phenotype : The appearance of the organism, i.e., the way in which genotype is expressed. Phenotype is the result of interaction of genes with the environment.
e.g., Red colour may be controlled by a pair of genes RR. Now if genotype is RR phenotype will be red only but if genotype is Rr then also phenotype will be red since R is a dominant gene.

6. Gene : It is the basic unit of inheritance by which characters are transferred from parents to their offspring. Gene consists of a specific length of DNA on a chromosome. A specific Segment of DNA that provides the information for one protein is called gene for that protein.
According to Mendel, both parents must contribute equally to the DNA of the progeny during sexual reproduction. As both parents determine the trait in the progeny, so both parents must be contributing a copy of the same gene.

7. Chromosomes : These are the long threads present in the nucleus of every cell. Chromosomes are made- up of DNA and protein. Each chromosome contains very long molecule of DNA.
Remember!
Each gene set is present as separate independent pieces each called a chromosome. Each cell have two copies of each chromosome, one each from male and female parents. Every germ cell will take one chromosome from each pair and these may be of either maternal or paternal origin. When two germ cells combine, they will restore the normal number of chromosomes in the progeny, ensuring the stability of the DNA of the species. Such mechanism of inheritance is used by all sexually and asexually reproducing organisms.

8. Allele : It is a alternative form of a gene occupying the same position on a chromosome and affecting the same characteristic but in two alternative ways, e.g., the free and attached ear lobe are the alleles of ear lobe character.
Expressing allele of a gene :

Homozygous dominant in capital letters, e.g., tallness(TT)
Homozygous recessive in smalMetters, e.g., shortness or dwarfness (tt)
Heterozygous (Tt)-lt will be called hybrid tall.

9. Dominant allele: An allele that affects the phenotype of an organism both in heterozygous and homozygous condition. It is denoted by a capital letter, e.g., tallness in pea plant is denoted by ‘T.

10. Recessive allele: An allele that affects the phenotype of the organism in absence of a dominant allele, i.e., in homozygous recessive individuals. It is denoted by a small alphabet, e.g., dwarfness in pea plant is denoted by’t’.

11. Homozygous: When both alleles of a particular gene are the same, e.g., TT

12. Heterozygous : When both alleles of a particular gene are different, e.g., Tt

13. Diploid : Cells or organism containing two sets of genes, e.g., human body cells. Diploid cells have genetic constitution of 2n.

14. Haploid : Cells or organism containing one set of genes, e.g., human reproductive cells (sperms and ova). Haploid cells have genetic constitution of n.

15. Monohybrid cross : A cross between two parents taking the alternative traits of one single character, e.g., A cross between tall and dwarf pea plants.
Monohybrid Ratio :

In F₁ generation : 100% hybrid
In F₂ generation : phenotypic ratio is 3 : 1 and genotypic ratio is 1 : 2 : 1

16. Dihybrid cross: A cross between two parents taking into consideration alternative traits of two different characters, e.g., A cross between two pea plants one having round, green seeds and the other having wrinkled, yellow seeds.
Dihybrid Ratio :

F₁ ratio is 100% Hybrid type.
F₂ ratio : Phenotypic is 9 : 3 : 3 : 1 and Genotypic . ratio is very complex.

17. Human Blood Groups: There are four types of blood groups A, B, AB or O. These are controlled by a gene which is denoted by symbols I^A, I^B and I^O (sometimes also denoted as i). The genes I^A and I^B show no dominance over each other (they are codominant, i.e., both expresses themselves independently). But these both genes are dominant over the gene I^O. Therefore, blood group of a person depends on the type of genes present, e.g., (i) Blood group A has the following gene types :

18. Determining sex of a newborn individual genetically:
(a) In human beings the sex of the individual is ” determined genetically.
(b) There are 23 pairs of chromosomes of which 22 are similar in male and female and are known as autosomes.
(c) The remaining one is sex chromosome which is XY in males and XX in females.
(d) Males produce two types of sperms X and Y, while female produces one type of egg X.
(e) If a X type of sperm fertilizers the egg then the sex of baby will be female (XX).
(f) If Y type of sperm fertilizers the egg then the sex of the baby will be male (XY).

19. Mendel’s experiment to show that traits may be dominant or recessive:
(a) Mendel conducted breeding experiments in garden pea.
(b) selected pure plant of a tall/short plant.
(c) produced first generation plants by crossing them.
(d) found that all plants were tall.
(e) produced second generation by self fertilization of hybrids.
(f) found that three quarter of the plants were tall and one quarter was short.

20. Homologous chromosomes: A pair of corresponding chromosomes of the same shape and size, one from each parent.

21. Autosomes and Sex chromosomes : The identical » chromosome pairs are called autosomes. The
chromosome pair which is different are called sex chromosomes. Humans have 23 pairs of chromosomes. 1-22 pairs are autosomes while 23rd pair (XX in females and XY in males) which are designated as X and Y are sex chromosomes.

22. Molecular Phylogeny: It is the study of evolutionary relationships by comparing DNA of different species.

23. Natural selection : Natural selection is one of the basic mechanisms of evolution, along with mutation, migration and genetic drift. Natural selection means the environmental conditions prevailing around an organism against which organism adapts itself, grows – and reproduces further. This leads to a change in the composition of genes within a population further causing evolution. Thus, it can be said that,
Natural selection results in adaptation in population to fit their environment better. Thus, natural selection direct evolution in the population of a particular species.

24. Fossils of the information which they provide regarding evolution: Fossils are the remains of ancient life forms, which got preserved somehow in the layers of earth, snow or oil.
Information given by fossils:

They reveal that the life forms which existed earlier do not exist today
which indicate that the living forms are ever changing (evolving).
They are used to guess the time when a particular organism existed on earth. It is done through carbon dating.

25. Genetic drift: The change in the frequency of some genes in a population which provides diversity without any survival advantage is called genetic drift.

26. The various ways in which individuals with a particular trait may increase in a population : Differences in population are responsible for the diversity such as, colour of eyes, hair, shape of ear lobes. This occurs due to : (i) Sexual reproduction (ii) Inaccuracies during DNA replication (iii) Due to environmental changes. This diversity will increase with time as these variations can be passed on only through DNA/genes during reproduction through reproductive tissue (germ cells or gametes).
(i) If these variations give survival advantage, then such traits are selected in nature and such traits increase in a population.
(ii) Due to genetic drift. This occurs due to geographical or reproductive isolation. It results in the change in gene frequency in a particular : population.
(iii) Migration which leads to gene flow in and out of the population.
(v) Mutation caused due to particular type of environment. ,
(v) Acquired traits due to particular type of environment.

27.Evidence of evolution : Errors in DNA copying (mutation) and sexual reproduction lead to variations which form the basis of evolution. Characteristics that
are common in different kinds of living organisms provide evidence in favour of evolution.

28.Evolution : Evolution can be defined as a naturally occurring slow, continuous and irreversible process of change. The gradual change of living organisms from pre-existing organisms since the beginning of life is called organic evolution. Whereas, gradual change in elements from one form to another with time is termed as inorganic evolution, i.

29.Inherited traits : are those traits which are passed from one generation to another through specific genes. Any change in DNA of the germ cells will be passed.
30. Acquired traits : are those traits which are acquired by the organism in its lifetime, e.g., removal of tail cannot change the genes of the germ cells of the mice thus cannot be passed to next generation.

31. Speciation : It means the origin of new species from the existing ones. It happens when different populations of the same species evolve along different lines.
How speciation occurs ?

It occurs when two populations are isolated (both geographically and reproductively) leading to almost no gene flow between the two populations.
Over generations, genetic drift will accumulate different changes in each sub-population.
Natural selection may also operate differently in these different locations.
Together natural selection and genetic drift will cause such changes (severe changes in the DNA) that these two groups will not be able to reproduce with each other even if they happen to meet.
When DNA changes occur to larger extent, it may lead to change in the number of chromosomes or gene expression, eventually the germ cells of the two groups cannot fuse with each other. This leads to emergence of new species.

32. Estimating Age of Fossil: There are 2 methods :

Relative method : On digging, the fossils which are closer to the surface are more recent than the fossils found in deeper layers.
Dating fossils (carbon dating method): It is done by detecting the ratios of different isotopes of the same element (i.e., isotope of C-14 which is radioactive) in the fossil material.

33. Evolution by stages :

Complex organs like eye has evolved from rudimentary organs, (e.g., rudimentary eye in flatworm might be useful enough to give only a fitness advantage and the structure of eye in different organisms is different indicating them to have different evolutionary origins) not by a single DNA change but created bit-by-bit over generations.
A change that is useful for one property to start with can become useful later for quite a different
function (e.g., Feathers might start as providing insulation in cold weather. But later, they might be useful for flight. Some heavy birds and reptiles also have feathers but they do not fly.
Some very dissimilar looking structures evolve from a common ancestral design, e.g., wild cabbage was cultivated as a food plant and many different vegetables were generated by selection over last two thousand years, (a) Selection of very small distances between the leaves gave rise to cabbage we eat. (b) Selection for arrested flower development gave rise to broccoli, (c) Selection for sterile flowers gave rise to cauliflower (d) Selection for swollen parts gave rise to kohlrabi.(e) Selection for larger leaves gave rise to leafy vegetable kale. It suggests that, if these selections were not done then there would have been only wild cabbage.

34. Homologous organs are organs having same origin and basic structure but they appear different and perform different functions in various organisms, e.g., (a) Fore limbs of horse and arms of man.
(b) Wings of birds and flippers of whale.
Similarities in basic structure of (homologous) organs in different organisms, indifferent groups indicate common ancestry.

35. Analogous organs are organs, which look similar because they perform same function, but they do not have same origin and basic structure.
e.g.,(a) Wings of birds and wings of insects. (b) Fins of fish and flippers of whale.

CBSE Class 10 Science Revision Notes Ch-8 How do Organisms Reproduce?

CBSE Class 10 Science
Revision Notes
Ch-8 How do Organisms Reproduce?

How do Organisms Reproduce? – CBSE Notes for Class 10 Science

1. Reproduction is the process by which a living organism is able to produce new individuals of its own kind. Unlike other life processes such as nutrition, respiration, etc., it is not essential to, maintain the life of an individual organism. But it is important for the existence and continuity of the species.

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

3. The process of DNA copying leads to variations. This inbuilt tendency for variations during reproduction is the basis for evolution.

4. Living organisms’ reproduce mainly through :
(i) Asexual reproduction
(ii) Sexual reproduction

5. ASEXUAL REPRODUCTION
(a) Single ceiled organisms reproduce through following ways:

(ii) Budding (also by multicellular organisms)
(iii) Spore formation (also by multicellular organisms)
(b) Asexual reproduction by multicellular organisms:
(i) Fragmentation and Regeneration

6. Fission: In unicellular organisms when cell becomes fully mature, it splits into two or more parts. It is called the fission. In organisms such as Amoeba, splitting can take place in any plane. But in organisms like Leishmania, having whip like structure at one end of the cell, binary fission occurs in a definite orientation in relation to these structures.

7. Regeneration : It is the ability to give rise to new organism. When the individual is cut or broken up into many pieces. It can be seen in Hydra and Planaria and is known as regeneration.
Regeneration is carried out by specialised cells. These cells proliferate and rqgkeJarge numbers of cells. From this mass of cells, different cells undergo changes to become various cell types and tissues. These changes take place in an organised sequence referred to as ” development. However, regeneration is not the same as reproduction, since most organisms would not normally depend on being cut up to be able to reproduce.

8. Budding: Organisms such as Hydra use regenerative cells for reproduction in the process of budding. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals.

9. Spore Formation (Sporulation): Some bacteria and lower organisms make spores. During spore formation, knob like structure called sporangium develops from the fungal hypha. Sporangia contain spores that eventually develop into new individual. The spores are covered by thick walls that protect them until they come in contact with moist surface or substratum and can begin to grow.

10. Fragmentation : It can be seen in Spirogyra. During this process filament of spirogyra simply breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals. This process occurs under favourable conditions of moisture, temperature, light and nutrient availability.

11. Vegetative propagation: It is the simplest method of reproduction in some higher plants in which new plant is produced from any vegetative part of the plant such as root, stem, leaf, etc.
Advantages of vegetative propagation : Vegetative propagation is useful for plants those have lost the capacity to produce seeds, e.g. banana, rose, jasmine. Moreover, all plants produced are genetically similar to the parent plant.
Natural Vegetative Propagation: In some plants like guava, sweet potato, dahlia, roots sprout and grow into new plants during favourable conditions. In some other,stems grow horizontally and develop root below and leaves above the ground. Many other common examples of vegetatively propagating plants are onion, banana, garlic, ginger, turmeric, bryophyllum and water hyacinth.

12. Vegetative propagation in Bryophyllum: Bryophyllum reproduces by the vegetative propagation method. During this method, buds produced in the notches along the leaf margin of bryophyllum fall on the soil and develop into new plants.

13. SEXUAL REPRODUCTION :
Sexual reproduction involves two individuals for producing a new individual. Sexual reproduction begins with fertilization, which is defined as the union of two different gametes. The motile germ-cell fptrUeh or sperm) is called the male gamete and germ-cell containing stored food (egg or ovum) is called the female gamete. The process of fusion of two gametes is called fertilization. After fertilization, a zygote is formed , which develops into a new organism.

14. Sexual reproduction in Plants : The flowering plants or angiosperms bear special reproductive parts located in the flower. Various parts of flower are; sepals, petals, stamens and carpels.
Most flowers have both male and female reproductive organs. The flower may be unisexual (papaya, watermelon) when it contains either stamen or carpel or bisexual (Hibiscus, Mustard) when it contains both stamens and carpels. It has male reproductive part cal led stamen and a female reproductive part called carpel. Carpel is made of three parts. The swollen bottom part is the ovary, middle elongated part is the style and the terminal part which may be sticky is the stigma. The ovary contains ovules and each ovule has an egg cell. Each stamen consists of stalk called filament, and a flattened fertile top called anther. The anthers produce the pollen grains. The pollen grains produce male gametes which fuse with (egg cel I) female gamete present in the ovule. This fusion of the germ-cells or fertilization gives zygote which grows into a new plant. Pollination: It is the process of transfer of pollen grains from the anther to the stigma of flower. If this transfer of pollen occurs in the same flower, it is referred to as self-pollination, whereas if the pollen is transferred from one flower to another, it is known as cross-pollination. This transfer is carried out by different agencies like wind, water, insects or animals.
Fertilization : A tube grows out of pollen grain and travels through the style to reach the female germ-cells present in ovule in the ovary. Out of two male gametes present in pollen tube one fuses with egg to form zygote. This fusion is called fertilization. After fertilization, the zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and gradually turns into a seed. The ovary grows rapidly and ripens to form a fruit. Meanwhile the petals, sepals, stamens, style and stigma may shrivel and fall off.

15. Reproduction in human beings : The reproductive organs of human beings are called gonads. These are testes in male and ovaries in female. The male gonad produces sperms and female gonad produces ova (eggs) at the age of puberty (after attainment of sexual maturity). Various changes occur in girls and boys at this age.

16. Male Reproductive System consists of the following organs:
Testes: A pair of testes are situated in scrotum that lie outside the abdominal cavity and behind the penis. Testes produce sperms and hormone, Testosterone hormone. Testosterone brings about changes in appearance of boys at the time of puberty.

VAS deferens: From each testis, a duct arises which is known as vas deferens which unites with a tube coming from urinary bladder. It brings sperms from testis.
Urethra: Vas deferens tube opens into a common tube called urethra. It runs through a muscular organ called Penis. Penis is male copulatory organ.
Accessory Glands: Glands like prostate and seminal vesicles and Cowper’s gland add their secretions which make transport of sperms easier and this fluid also provides nutrition.

17. Female Reproductive System : It consists of the following organs:

Ovaries: Paired ovaries are located in the abdominal cavity near the kidney. Ovaries produce female gamete (ovum or egg) and secrete female hormones (estrogen and progesterone). One egg is produced every month alternately by one of the ovaries.
Fallopian Tube: The egg is carried from the ovary to womb/uterus through a thin oviduct or fallopian tube.
Uterus: The two oviducts unite into an elastic bag like structure known as the uterus.
Vagina : Uterus opens into vagina. It is female copulatory organ.

18. Sexual Cycle in female: After puberty, only one egg is produced alternately from one ovary after a period of 28 days. Egg in fallopian tube encounter sperms which enter through the vaginal passage during sexual intercourse. This fertilized egg (zygote) gets implanted in the lining of uterus which later forms embryo. Embryo gets nutrition from the mother’s blood with the help of special tissue called placenta.
If the egg is not fertilized, if lives for about one day since the ovary releases one egg every month, the uterus prepares itself every month to receive the fertilized egg. Thus, its lining becomes thick and spongy. If it does not get zygote, the developed lining slowly breaks down and comes out through vagina as blood and mucus. This cycle takes place roughly every month and is known as menstruation. It usually lasts for about 2-5 days.

19. Reproductive Flealth: Reproductive organs need a lot of care and hygiene. Otherwise they are susceptible to many infections or diseases. The diseases which spread through sexual routes are known as sexually transmitted diseases e.g., bacterial infections like syphilis, gonorrhoea and viral infections such as warts and HIV- AIDS. Condom helps to prevent transmission of many of these infections to some extent.
Frequent pregnancy causes many health problems and also adds to an already exploding population. Many ways have been devised to avoid pregnancy. Contraception can be achieved by:
• Mechanical barrier method (use of condoms).
• Chemical methods (use of pills).
• Use of contraceptive devices (copper-T).
• Surgical methods (vasectomy in males and tubectomy in females)

CBSE Class 10 Science Revision Notes Ch-5 Periodic Classification of Elements

CBSE Class 10 Science
Revision Notes
Ch-5 Periodic Classification of Elements

Periodic Classification of Elements – CBSE Notes for Class 10 Science

1. Need for classification of elements:
Increase in discovery of different elements, made it difficult to organise all that was known about the elements. To study the large number of elements with ease, various attempts were made. The attempts resulted in classification of elements into metals and non-metals.

2. Dobereiner’s triads: –
Johann Wolfgang Dobereiner, a German chemist, classified the known elements in groups of three elements on the basis of similarities in their properties. These groups were called triads.
(i) Characteristics of Triads:
(a) Properties of elements in each triad were similar.
(b) Atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.
(ii) Examples of Triads:

(iii) Limitations: Dobereiner could identify only three triads. He was not able to prepare triads of all the known elements.

3. Newlands’ Law of Octaves:
John Newlands’, an English scientist, arranged the known elements in the order of increasing atomic masses and called it the ‘Law of Octaves’. It is known as ‘Newlands’ Law of Octaves’.
(i) Characteristics of Newlands’ Law of Octaves:
(a) It contained the elements from hydrogen to thorium.
(b) Properties of every eighth element was similar to that of the first element.
(ii) Table showing Newlands’ Octaves:

(iii) Limitations of Newlands’ law of Octaves:
(a) The law was applicable to elements up to calcium (Ca).
(b) It contained only 56 elements.
(c) In order to fit elements into the table, Newlands’ adjusted two elements like cobalt and nickel in die same slot and also put some unlike elements under same note.

4. Mendeleev’s Periodic Table : Dmitri Ivanovich – 5 ’ Mendeleev, a Russian demist, was the most important contributor to the early development of a periodic table of elements wherein the elements were arranged on the basis of their atomic mass and chemical properties.
(i) Characteristics of Mendeleev’s Periodic Table:
(a) Mendeleev arranged all the 63 known elements in an increasing order of their atomic masses.
(b) The table contained vertical columns called ‘groups’ and horizontal rows called ‘periods’.
(c) The elements with similar physical and chemical properties came under same groups.
(ii) Mendeleev’s Periodic Law : The properties of elements are the periodic function of their atomic masses.
(iii) Achievements of Mendeleev’s Periodic Table:
(a) Through this table, it was very easy to study the physical and chemical properties of various elements.
(b) Mendeleev adjusted few elements with a slightly greater atomic mass before the elements with slightly lower atomic mass, so that elements with similar properties could be grouped together. For example, aluminium appeared before silicon, cobalt appeared before nickel.
(c) Mendeleev left some gaps in his periodic table.
He predicted the existence of some elements that had not been discovered at that time. His predictions were quite true as elements like scandium, gallium and germanium were discovered later.
(d) The gases like helium, neon and argon, which were discovered later, were placed in a new group without disturbing the existing order.
(iv) Limitations:
(a) No fixed positions was given to hydrogen in the Mendeleev’s periodic table.
(b) Positions of Isotopes of all elements was not certain according to Mendeleev’s periodic table.
(c) Atomic masses did not increase in a regular manner in going from one element to the next.

5. Modem Periodic Table: Henry Moseley, gave a new ! property of elements, ‘atomic number’ and this was I adopted as the basis of Modem Periodic Table.
(i) Modem Periodic Law: Properties of elements are a periodic function of i their atomic number.
(ii) Position of elements in Modem Periodic Table:
(a) The modem periodic table consists of 18 groups and 7 periods.
(b) Elements present in any one group have the same number of valence electrons. Also, the number of shells increases as we go down the group.
(c) Elements present in any one period, contain the same number of shells. Also, with increase in atomic number by one unit on moving from left to right, the valence shell electrons increases by one unit.
(d) Each period marks a new electronic shell getting filled.
(iii) Table showing Electronic Configuration of First 20 Elements:

Trends in the Modern Periodic Table:
(i) Valency: Valency of an element is determined by the number of valence electrons present in the outermost shell of its atom.
• Valency of elements in a particular group is same.
• Valency of elements in a period first increases from one to four and then decreases to zero.
(ii) Atomic Size: Atomic size refers to the radius of an atom.
In a period, atomic size and radii decreases from left to right.
In a group, atomic size and radii increases from top to bottom.
(iii) Metallic and Non-metallic Properties:
(a) The tendency to lose electrons from the outermost shell of an atom, is called metallic character of an element.
(b) The tendency to gain electrons from the outermost shell of an atom, is called non-metallic character of an element.

CBSE Class 10 Science Revision Notes Ch-4 Carbon and its Compounds

CBSE Class 10 Science
Revision Notes
Ch-4 Carbon and its Compounds

Carbon and its Compounds – CBSE Notes for Class 10 Science

1. The earth’s crust, has only 0.02% carbon in the form of minerals (like carbonates^bicarbonates, coal, and petroleum).

2. The atmosphere has 0.03% of carbon dioxide.

3. Inspite of its small amount available in nature carbon is a versatile element as it forms the basis for all living organisms and many things which we use.

4. Bonding in carbon :
(a) Atomic number of carbon = 6
(b) Electronic configuration has 2 electrons in K shell and 4 electrons in L shell.
(c) In order to attain the noble gas configuration, carbon should either gain 4 electrons or lose 4 electrons or can share it’s 4 electrons with some other element.
(d) Gain of 4 electrons (to form octet, i.e., 8 electrons in C^4- anion) is difficult because then a nucleus with 6 protons will have to hold extra four electrons.
(e) Loss of 4 electrons (to attain duplet, i.e., 2 electrons like He atom in C⁴⁺ cation) is difficult as it requires large amount of energy to remove four electrons.
(f) Carbon, hence, overcomes this difficulty by sharing it’s four valence electrons with other atoms of carbon or with atoms of other elements. These electrons contributed by the atoms for mutual sharing in order to acquire the stable noble gas configuration is called covalency of that atom. Hence, carbon shows TETRACOVALENCY.
(g) The simplest molecule formed by sharing of electrons (i.e., covalent bonds), can be represented by electron dot structure.

5. Allotropes of carbon: The phenomenon by means of which an element can exist in two or more forms, with similar chemical properties but different physical properties is called allotropy and the different forms are called allotropes. Carbon shows three allotropic forms :

Note:
» Diamond is the hardest substance whereas graphite is very soft.
» Diamond is used for grinding and polishing of ‘ hard materials and gnaphite is used as a lubricant.
» Diamond has three dimensional rigid structure but graphite has hexagonal sheet layer structure.
» Diamond is a bad conductor of electricity but graphite is very good conductor of electricity.

6. Fullerenes : A new category of carbon allotrope, fullerenes are spherical in shape or a soccer ball like. The first fullerene identified was C-60 with 60 carbon atoms arranged like the godesic dome designed by US architect, Buckminster Fuller, hence these are also known as Buckminster Fullerenes or Bucky Ball structures.

7. Cause of versatile nature of carbon : Four main reasons for versatile nature of carbon are:
(a) Catenation : It is the unique property of self linkage of carbon atoms by means of covalent bonds to form straight chains, or branched chains, or the rings of different sizes (as shown below):

(b) Tetracovalency: Due to small size, and presence of four valence electrons, carbon can form strong bonds with other carbon atoms, hydrogen, oxygen, nitrogen, or sulphur, etc. For example, compounds of carbon with hydrogen are called hydrocarbons.
(c) Multiple Bond Formation : Small size of carbon also enables it to form multiple bonds, (i.e., double bonds or triple bonds) with other elements as well as with its own atoms. This increases the number of carbon compounds.
Note:
» Compounds of carbon with double bonds and triple bonds are called as unsaturated compounds while those with carbon-carbon single bonds are called saturated compounds.
» Alkenes (with —C = C —) and Alkynes (with —C = C—) are hence unsaturated, whereas Alkanes (with — C — C—) are saturated compounds.
(d) Isomerism: The phenomenon by means of which the carbon compounds with same molecular formula show different structures, and properties, e.g., A chain of 4 carbon atoms can be written in two ways :

Hence, number of carbon compounds increases to a huge number.

8. Hydrocarbons : Large number of hydrocarbons can be classified as:

Note: In open chain, the name of parent chain is derived from the root word and suffix ane, ene or yne is added depending on the type of bond present in a chain :

Important: No alkene or alkyne is possible with single carbon atom because double or triple bond is not possible between carbon and hydrogen atom. It is only between two carbon atoms.

9. Functional Group:
» An atom or a group of atoms which when present in a compound gives specific properties to it, is called a functional group.
» A single line shown along with a functional group is called as its free valency by which it gets attached to a compound by replacing one hydrogen atom or atoms, e.g., -Cl.
» Functional group, replacing the hydrogen is also called as heteroatom because it is different from carbon, and can be nitrogen, sulphur, or halogen, etc.
» Important: Replacement of hydrogen atom by a functional group is always in such a manner that valency of carbon remains satisfied.

Note : Cl is named as prefix Chloro; Br as Bromo; NH₂ as Amino and N0₂ as Nitro.
Important Note: Symbol ‘R’ in a formula represents an Alkyl Group which is formed by the removal of one hydrogen atom from an alkane.

10. Homologous series: A series of organic compounds in which every succeeding member differs from the previous one by -CH₂ group or 14 a.m.u.
Note : As the molecular mass increases in a series, : so physical properties of the compounds
show a variation, but chemical properties which are determined solely by a functional group, remains same within a series.

11. Nomenclature of Organic Compounds
(I) Trivial or common names : These names were given after the source from which the organic compounds were first isolated, e.g., If a compound has one carbon atom, then its common name will have root word form and so on (see table).

(II) IUPAC name : International Union of Pure and Applied Chemistry gave following rules for naming various compounds :
(i) Identify the number of carbon atoms and write the word root corresponding to it. e.g., If number of carbon atoms are three, then word root is prop.
(ii) Presence of a functional group is indicated by prefix or suffix as given in table 2, and table 3.
(iii) If the name of functional group is to be given as a suffix, the last letter ‘e’ in the name of compound is deleted and suffix is added. e.g., ketone with three carbon atoms is named as :
Propane – e = Propan + ‘one’ = Propanone. Alcohol with three carbons is propanol. Carboxylic acid with three carbons is propanoic acid.
(iv) Halogens, in IUPAC, are written as Prefixes, e.g., Compound With two carbons and one chloro group is named as : chloroethane (CH₃CH₂CI).

12. Chemical properties of carbon compounds :
Main properties of carbon compounds are :
(a) Combustion Reaction
(b) Oxidation Reaction
(c) Addition Reaction .
(d) Substitution Reaction
(a) Combustion Reaction : A chemical reaction in which a substance burns in the presence of air or oxygen is called combustion reaction.
Note: Combustion is always a EXOTHERMIC reaction, e.g.,

Remember:
» Saturated hydrocarbons generally give clean flame whereas unsaturated hydrocarbons give sooty flame (because carbon content is more than hydrogen content in these, and hence carbon shows incomplete combustion, and appears as soot).
» Saturated hydrocarbons can give sooty flame in limited supply of oxygen.
(b) Oxidation Reaction : The addition of oxygen in a compound upon combustion is called oxidation.
In addition to combustion, oxidation can also be : brought about by some substances which are
capable of giving oxygen to others, i.e., Oxidising agents, e.g., Acidified K₂Cr₂0₇ (Potassium dichromate) and alkaline KMn0₄ (Potassium permanganate).
Note:

(c) Addition Reaction : Addition of a molecule in unsaturated compounds in the presence of a catalyst, to give saturated compound is called an addition reaction, e.g.,
Hydrogenation of vegetable oils as shown in the reaction below :

(d) Substitution Reaction : The reactions which involve the replacement of an atom or group of atoms from a molecule by another atom without any change in structure in the remaining part of the molecule.

13. Ethanol: (or alcohol)
Colourless liquid, soluble in water, and has a distinct smell and burning taste. Its consumption in small quantities causes drunkenness and can be lethal.

14. Ethanoic Acid : CH₃COOH
Common Name : Acetic Acid.
5-8% solution of acetic acid in water is called Vinegar. And 100% pure acetic acid is called Glacial acetic acid because it has m.pt. 290 K and freezes forming glacier like crystals.
Reactions of ethanoic acid :

Saponification : Esters in the presence of acid or base react to give back alcohol and carboxylic acid is called saponification.

15. Soaps and Detergents :
Soaps and Synthetic Detergents : Soaps and detergents are substances used for cleaning.
Soap : Soaps are sodium or potassium salts of higher fatty acids, such as Oleic acid (C₁₇H₃₃COOH), Stearic acid (C₁₇H₃₅COOH), Palmitic acid (C₁₅H₃₁COOH), etc. These acids are present in the form of their esters along with glycerol (an alcohol containing three hydroxyl groups). These esters, called ‘glycerides’ are present in fats and oils of animal and vegetable origin.
Preparation of Soap: When an oil or a fat (glyceride) is treated with sodium hydroxide solution, it gets converted to sodium salt of the acid (soap) and glycerol. The reaction is known as saponification.

Detergents : Chemically, detergents are sodium salts of sulphonic acids, i.e., detergents contain a sulphonic acid group (—S0₃H), instead^of a carboxylic acid group (—COOH), on one end of the hydrocarbon.

The cleansing action of a detergent is considered to be more effective than a soap.
Cleansing Action of Soaps and Detergents : The cleansing action of soaps and detergents follows the same principle.

When a soap or detergent is dissolved in water, the molecules gather together as clusters, called micelles. The tails stick inwards and the heads outwards.
In cleansing, the hydrocarbon tail attaches.itself to oily dirt. When water is agitated, the oily dirt tends to lift off from the dirty surface and dissociates into fragments. This gives an opportunity to other tails to stick to oil. The solution now contains small globules of oil surrounded by detergent molecules. The negatively charged heads present in water prevent the small globules from coming together and form aggregates. Thus, the oily dirt is removed from the object.

16. Scum : The insoluble precipitates formed by soap molecule when they react with calcium and magnesium ions present in hard water. Due to this, lot of soap gets wasted and cleansing action gets reduced to a larger extent.

CBSE Class 10 Economics NCERT Solutions Ch-5 Consumer Rights

CBSE Class 10 Economics
NCERT Solutions
Ch-5 Consumer Rights

NCERT Solutions for Class 10th Social Science Consumer Rights

Page 87
Question 1: Why are rules and regulations required in the marketplace? Illustrate with a few examples.
Answer: Rules and regulations are required in the marketplace to protect consumers. Sellers often abdicate responsibility for a low-quality product, cheat in weighing out goods, add extra charges over the retail price, and sell adulterated/ defective goods. Hence, rules and regulations are needed to protect the scattered buyers from powerful and fewer producers who monopolise markets. For example, a grocery shop owner might sell expired products, and then blame the customer for not checking the date of expiry before buying the items.

Question 2: What factors gave birth to the consumer movement in India? Trace its evolution?
Answer: The factors that gave birth to the consumer movement in India are manifold. It started as a “social force” with the need to protect and promote consumer interests against unfair and unethical trade practices. Extreme food shortages, hoarding, black marketing and adulteration of food led to the consumer movement becoming an organised arena in the 1960s. Till the 1970s, consumer organisations were mostly busy writing articles and holding exhibitions. More recently, there has been an upsurge in the number of consumer groups who have shown concern towards ration shop malpractices and overcrowding of public transport vehicles. In 1986, the Indian government enacted the Consumer Protection Act, also known as COPRA. This was a major step in the consumer movement in India.

Question 3: Explain the need for consumer consciousness by giving two examples.
Answer: There is a need for consumer consciousness so that the buyers themselves can take action against cheating traders. The ISI and Agmark logos are certifications of good quality. Consumers must look for such certifications while buying goods and services. Secondly, to be able to discriminate and make informed choices, a consumer needs to have an adequate knowledge of the goods or services purchased by him/her.

Question 4: Mention a few factors which cause exploitation of consumers.
Answer: Exploitation of consumers is caused by a variety of factors. Producers are always looking for easy ways to increase profits. Adulterated or low-quality goods have less production costs, and if the consumer is unaware or illiterate, it is easy to cheat him/her. Also, shopkeepers brush off their responsibility by claiming that the manufacturer is to blame. Consumers feel helpless in this situation. Often, when the consumers are known not to check the retail price of a commodity on its packing, sellers add extra charges to the same. In places where there is no awareness of consumer rights and the COPRA, consumer exploitation is rampant.

Question 5:What is the rationale behind the enactment of Consumer Protection Act 1986?
Answer: The rationale behind the enactment of Consumer Protection Act of 1986 is to protect the consumer against unethical and unfair trade practices. Also, it recognises the consumer’s right to be informed, right to choose, right to seek redressal and right to represent himself/herself in consumer courts.

Question 6: Describe some of your duties as consumers if you visit a shopping complex in your locality.
Answer: Some of my duties as a consumer if I visit a shopping complex include checking expiry dates of the products I wish to purchase, paying only the maximum retail price printed on the goods, preventing shopkeepers from duping me with defective products, and registering a complaint with a consumer forum or court in case a seller refuses to take responsibility for an adulterated or flawed product.

Question 7: Suppose you buy a bottle of honey and a biscuit packet. Which logo or mark you will have to look for and why?
Answer: While buying a bottle of honey or a biscuit packet, the logo or mark one will have to look for is ISI or Agmark. These are logos certifying the quality of goods in the market. Only those producers are allowed to use these marks who follow certain quality standards set by the organisations issuing these certifications. Thus, if a bottle of honey or a biscuit packet has one of these logos on it, then it implies that the product is of good quality.

Question 8: What legal measures were taken by the government to empower the consumers in India?
Answer: Legal measures taken by the government to empower consumers in India are plenty. First and foremost being the COPRA in 1986. Then, in October 2005, the Right to Information Act was passed, ensuring citizens all information about the functioning of government departments. Also, under COPRA, a consumer can appeal in state and national courts, even if his case has been dismissed at the district level. Thus, consumers even have the right to represent themselves in consumer courts now.

Question 9: Mention some of the rights of consumers and write a few sentences on each?
Answer: Some of the rights of consumers include the right to be informed, the right to choose, the right to seek redressal and the right to representation in consumer courts. Under the RTI Act of 2005, consumers can now even get information regarding the working of government departments. The right to choose allows a consumer to choose if he wishes to continue or discontinue the use of a service he purchased. The right to seek redressal permits a consumer to complain against unfair trade practices and exploitation.

Question 10: By what means can the consumers express their solidarity?
Answer: Consumers can express their solidarity by forming consumer groups that write articles or hold exhibitions against traders’ exploitation. These groups guide individuals on how to approach a consumer court, and they even fight cases for consumers. Such groups receive financial aid from the government to create public awareness. Participation of one and all will further strengthen consumer solidarity.

Question 11: Critically examine the progress of consumer movement in India?
Answer: The consumer movement in India has evolved vastly since it began. There has been a significant change in consumer awareness in the country. Till the enactment of COPRA in 1986, the consumer movement did not bear much force, but ever since its inception, the movement has been empowered substantially. The setting up of consumer courts and consumer groups has been a progressive move. However, in contemporary India, the consumer redressal process is quite complicated, expensive and time-consuming. Filing cases, attending court proceedings, hiring lawyers, and other procedures make it cumbersome. In India, there are over 700 consumer groups of which, unfortunately, only about 20-25 are well-organised and functioning smoothly.

Question 13: Say True or False.
(i) COPRA applies only to goods.
(ii) India is one of the many countries in the world which has exclusive courts for consumer redressal.
(iii) When a consumer feels that he has been exploited, he must file a case in the District Consumer Court.
(iv) It is worthwhile to move to consumer courts only if the damages incurred are of high value.
(v) Hallmark is the certification maintained for standardisation of jewellry.
(vi) The consumer redressal process is very simple and quick.
(vii) A consumer has the right to get compensation depending on the degree of the damage.
Answer:
(i) False
(ii) True
(iii) True
(iv) True
(v) True
(vi) False
(vii) True

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CBSE Class 10 Science Revision Notes Ch-16 Management of Natural Resources