Revision Notes on Water: A Precious Resource

Quick Facts

• 22 March is celebrated as World Water Day to bring awareness among the people about the conservation of water.
• 2003 was called as the International year of freshwater to bring awareness among the people about the importance of water as a resource and why it is depleting at such a fast rate.

How much water is available on the earth?

Figure 1: Distribution of Water on Earth

• 71% of the Earth is covered with water. However, all of that cannot be consumed by the living organisms.
• The figure given above represents that 97% of the earth’s water is saline that is present in the oceans and 3% of the earth’s water is fresh that is present in ice caps, glaciers and underground. This fresh water can be obtained from underground, rivers and lakes. Even then, just 1 percent of our freshwater is easily accessible, with much of it trapped in glaciers and snowfields.

Different forms of Water

• Solid State – Water exists in the solid form as ice and snow on the earth.
• Liquid State – Water exist in the liquid state in rivers lakes, oceans and under the ground.
• Gaseous State – Water exists as water vapour in the atmosphere.

The Water Cycle

Figure 2: The Water Cycle

The water cycle is a natural process that continuously happens on earth. The water cycle maintains the amount of water on the earth. It can be divided into four phases:

• Evaporation – It is a process when the water from the earth’s surface gets converted into water vapour due to the heat of the sun. The water vapour then gets into the air.
• Condensation – The water vapour rises up in the atmosphere and get accumulated above, condenses and form water droplets. These droplets collect together and form clouds.
• Precipitation – When the volume of droplets increases in the atmosphere, it falls on the earth as rainfall also called as Precipitation. Sometimes it also occurs as snowfall in some areas.
• Collection of Water – As the water falls back on the earth, it travels along the surface and gets accumulated at different places like lakes, rivers, sea, oceans and under the ground. That’s how the amount of water is regulated on the earth.

Groundwater

Figure 3: Groundwater

• The water that falls on the earth’s surface slips inside the earth and gets accumulated in the cracks and gaps of the rocks present inside the earth. 
• The water table is called the upper limit of the layer of water present beneath the earth. The water table can vary from one place to another.
• The water that is present beneath the water table of a place is called Groundwater. This water gets accumulated inside the earth because of different sources:
  • Rainwater that falls on the earth slips inside the ground
  • Water in the rivers, lakes and Ponds often slips into the earth and get accumulated as groundwater
• Infiltration – The process by which water accumulates into the ground by travelling through the soil pores is called Infiltration.

Figure 4: Infiltration

• Aquifer – The underground layer of rocks that contain water present between their cracks and empty spaces is called Aquifer.

Figure 5: Aquifer and Groundwater

How underground water can be obtained?

Groundwater is generally obtained by digging Wells, using hand pumps and electric pumps.

Uses of Groundwater

Groundwater is fresh water and therefore can be used for various purposes such as:

• consumption or drinking water
• domestic chores
• irrigation of crops
• water services in public buildings and offices
• firefighting
• industrial purposes

Water Table Depletion

Figure 6: How Water table gets affected in different seasons

The water table of a place may decrease if we keep on taking out more water than what is getting replenished due to rainfall. There are several factors that can cause water table depletion:

1. Increasing Population

• As the population of a region increases the demand of freshwater also rises sharply. This means more water is being required.
• Also, increasing population demands more space which leads to the construction of more houses, shops, industries, buildings and roads.
• The number of places like parks, grounds or forests decreases.
• All this reduces the possibility of rainwater getting into the soil particles because the concrete floors and roads to not allow seepage of water.
• This means that an increased demand and usage of groundwater as compared to the replenishment of water tables.
• This results in depletion of the water table of that region.

2. Increasing Industries

Every industry requires water in its production process. As a number of industries increases, more water is drawn from the ground. All of this result in depletion of the water table.

3. Agricultural Activities

In case of no or low rainfall, farmers use groundwater to irrigate their land for agriculture. This depletes the water table over the years. 

4. Deforestation

We know that plants and trees keep the soil bounded together and allow absorption of water in the soil. Uprooting them exposes the first layer of the soil which can get washed away easily. This affects the water table of that region.

5. Low Rainfall

In places where there is low or scanty rainfall the underground water table is generally low.

Distribution of Water

• The distribution of water across the earth is not even due to different factors such as rainfall and climatic conditions.
• Some places have a high amount of water while others face scarcity of water.
• For Example, in India, places like Rajasthan get very low rainfall and hence have less water. On the other hand, places like Meghalaya receive high rainfall and have a high amount of water. Hence, there can be times when one part of India faces floods while other is suffering from a drought -like condition.

Figure 7: Rainfall in India

Water Management

• No matter whether a place receives a high rainfall or low rainfall, water management is necessary to ensure that everyone gets access to an adequate amount of water.
• Generally, the Civic authorities of a region are responsible for the adequate supply of water in that area.
• They generally use a well-structured pipeline system to deliver water to every house and building of the locality.
• Not only this it is also a responsibility of the civic authorities to prevent wastage of water and check if their supply system is adequate or not.
• Along with these authorities, every individual is also responsible for saving water and preventing it from getting wasted. Hence, we should always keep a check on how we use water in our daily lives.

Water Harvesting or Rainwater Harvesting

Figure 8: Water harvesting or Rainwater harvesting

• The rainwater that falls on the earth is generally allowed to flow away.
• However, it can be saved and used to replenish the groundwater levels of the Earth. This process of preventing rainwater from flowing away and storing it for different purposes such as replenishing groundwater levels, household chores or industrial purposes is called rainwater harvesting.

Bawris

An ancient practice of storing water involved construction of Bawris. In old times rainwater was collected in Bawris. However, with time their usage declined. Now due to scanty rainfall people are again using them to solve the problem of water storage.

Drip Irrigation

• It is an allocation technique used by farmers to water their fields.
• In this, water is allowed to slowly drip into the plants so that their water directly gets into the roots of the plants.
• This minimizes evaporation, saves water and allows the nutrients to reach the plants easily.
• Narrow tubes are used to make water reach the roots of the plants in drip irrigation.

Figure 9: Drip irrigation

How can we save water?

We can adopt different ways to minimize the wastage of water:

• Always keep the taps closed while brushing or washing the face to prevent water from flowing away unnecessarily. One should use it only when needed.
• Fix any water taps that are leaking, immediately.
• Instead of taking a shower use a bucket to take bath.
• Use water left from washing clothes for mopping the floor and washing cars instead of running water.
• Water your plans in the morning or evening times so that the water does not immediately get evaporated.
• Do not waste food as it takes a lot of water to irrigate the fruits and vegetables.
• Do not throw away water unnecessarily. Use water in a judicious amount

Figure 10: Outdoor Water Conservation Tips

Figure 11: Indoor Water Conservation Tips

How scarcity of water affects the plants?

• The plants get dried up as they get no water and hence they can die.
• There is no water to conduct photosynthesis and hence they are not able to produce any food.
• They will not be able to grow upright because of scarce water.
• They will no longer be able to get enough nutrients from the soil because of less or water.
• As a result, there will be no food, no oxygen and hence no life without the plants.

What is light?

Light is a radiation or a form of energy that our eyes can detect. Light enables us to view our surroundings. Light travels from one place to another in a straight line.

Figure 1: Light always travels in straight line

For instance, if you look at the flame of a candle with a straight pipe we can easily view the candle. However, if we bend the pipe we cannot view the candle and the light coming through it because it is blocked.

Reflection of Light

• Whenever light hits an object it is either absorbed or reflected back.
• Reflection of light can be defined as the phenomenon of an object throws back the light that falls on it. Hence, the reflection of light changes its path.
• A mirror is generally any shiny surface that can reflect back light.
• A mirror that has a plane surface is called a Plane Mirror.
• A mirror that is curved, it either bulges in or out, is called a Curved Mirror.

Figure 2: Reflection of light by plane mirror

What is an image?

Figure 3: Image of Candle Formed by a Mirror

• As a mirror reflects light, an image of the object that is in front of the mirror is formed on it.
• The image of an object can be defined as the impression of the object created by the light on the mirror.
• The distance between the image and the mirror, and the object and the mirror always remain the same.
• If we increase or decrease the distance between the object and the mirror, the distance between the image and the mirror also increases or decreases, respectively.
• However, the size of the image formed on the mirror can vary with respect to the distance between the object and the mirror.
• If the distance between the object and the mirror increases, the size of the image decreases and vice-versa.
• An image is said to be erect if the image is formed the same side up as that of the object.
• The image will be called Inverted if it is formed upside-down compared to the object.

Figure 4: Inverted Image of a Candle

Left-right inversion of the image

Figure 5: Left-right inversion of the image

The image formed by the mirror is always left-right inverted. This means that the right side of the object appears as the left side of the image, and the left side of the object appears at the right side of the image.

Why the word ‘AMBULANCE’ is painted on an ambulance left-right inverted?

Figure 6: Ambulance

This is because of the left-right inversion of the image on a mirror. The word ambulance written as left-right inverted would, therefore, be read easily by the driver of the vehicle ahead of the ambulance in its rearview mirror. The rear view mirror will again invert the word left-right wise.

The Laws of Reflection of Light

• Incident Ray – The light ray that falls on the reflecting surface is called an Incident Ray.
• Reflected Ray –Tthe light ray that gets reflected back from a reflecting surface is called a Reflected Ray.
• Normal – It is a line that is perpendicular to the reflected plane at the point of incidence of Incident Ray.

Figure 7: Incident Ray, Reflected Ray and Normal

Figure 8: The Two Laws of Reflection

Types of Reflection

Depending upon the surface of the reflecting object, the reflection of light can vary.

• Diffused Reflection or Irregular Reflection: In this type of reflection, the light rays that fall on the surface are reflected back in different directions irregularly. This generally happens in the case of an irregular or roughly surfaced object.
• Regular Reflection: In this type of reflection, the light rays that fall on the surface of the reflecting object reflect back in a particular direction. The reflected rays are always parallel to each other. This generally happens in case of a smooth and shiny surface.

Figure 9: Types of Reflection

Spherical Mirrors

Spherical mirror, as the name suggests, has a sphere-like shape. It appears as if it is a part of a sphere. There are two types of spherical mirrors:

• Concave Mirror – It is a spherical mirror whose reflecting surface is curved inwards.
• Convex Mirror – It is a spherical mirror whose reflecting surface is curved outwards.

Figure 10: Concave and Convex Mirror

The Image formed by a Concave and Convex Mirror

An image can be of two types:

Real Image	Virtual Image
The real image is formed when the light rays reflect and meet at the same point.	A virtual image is formed when light rays reflect and diverge from the same point.
It can be viewed on a screen.	It cannot be viewed on the screen.
It is always inverted.	It is always erect.
Formed by Concave mirror	Formed by Convex, Concave and Plane Mirrors

Figure 11: Formation of Real Image by Concave Mirror

Figure 12: Virtual Image by Plane Mirror

The image formed by a concave mirror has the following properties:

• It can either be real or virtual.
• It can either be inverted or erect.
• It can have the same size as that of the object, a larger size that of the object or smaller size than that of the object.

The image formed by a convex mirror has the following properties:

• It is always virtual.
• It is always upright (erect).
• It is smaller in size as that of the object

Applications of Concave Mirrors:

• Satellite dishes use a concave mirror to gather all the signals and reflect them on a certain point.
• Dentists use a concave mirror to reflect light on a particular tooth.
• Shaving Mirrors are concave in shape.
• Headlights of a car have a concave mirror so that we can reflect back light straight on the path.
• Torches also use concave Mirrors.

Figure 13: Concave Mirror Used in Torch

Applications of Convex Mirrors

• The rear view mirrors are convex mirrors as they provide a wider view of the road behind.
• Security mirrors near an ATM are convex so that the user can detect easily if anyone else is watching from behind or not.

Figure 14: Convex Mirror used in a Rearview Mirror

Lenses

A lens is a part of a reflecting material like glass or plastic but curved from both sides. Lenses are unlike mirrors that have a reflecting surface only on one side. Depending upon its shape a lens can be categorized as:

• Convex Lens – A Convex Lens is curved outwards. It is thicker in the centre and narrows down at the edges. It merges the light rays passing through it at a certain point. Therefore, it is also called a Converging Lens.
• Concave Lens – A Concave Lens is curved inwards. It has wider edges and a thinner centre. It reflects back the light that travels through it in different directions. Therefore, it is also called a Diverging Lens.

Figure 15: Convex Lens and Concave Lens

Images formed by Convex and Concave Lenses

A Convex lens forms an image that is:

• real
• inverted
• the image is large and appears close to the lens

A Concave lens forms an image that is:

• virtual
• erect
• small and appears far away

Figure 16: Image formed by Convex and Concave Lense

Sunlight

What is a Rainbow?

Figure 17: Formation of Rainbow

• A rainbow is a natural phenomenon in which the light rays of the sun are reflected and refracted by the water droplets present in the atmosphere.
• A rainbow appears as an arc on the sky that contains a band of seven colours – Red, orange, yellow, green, blue, indigo and violet.
• This also means that the white light of the sun contains seven coloured lights in it that separate out due to refraction (called a Spectrum of Lights). This spectrum of white light can be seen in the following:
  • Rainbows
  • Soap bubbles
  • Surface of a CD
  • Prisms

Figure 18: Spectrum of White Light through a Prism

Newton’s Disc

Figure 19: Newton’s Disc

• The Newton’s disc can be obtained by dividing a disk into 7 partitions and painting each of them with the seven colours of the rainbow.
• When the disc is rotated at a fast pace in daylight all the colours tend to mix together and the disc appears whitish in colour.

What is light?

Light is a radiation or a form of energy that our eyes can detect. Light enables us to view our surroundings. Light travels from one place to another in a straight line.

Figure 1: Light always travels in straight line

For instance, if you look at the flame of a candle with a straight pipe we can easily view the candle. However, if we bend the pipe we cannot view the candle and the light coming through it because it is blocked.

Reflection of Light

• Whenever light hits an object it is either absorbed or reflected back.
• Reflection of light can be defined as the phenomenon of an object throws back the light that falls on it. Hence, the reflection of light changes its path.
• A mirror is generally any shiny surface that can reflect back light.
• A mirror that has a plane surface is called a Plane Mirror.
• A mirror that is curved, it either bulges in or out, is called a Curved Mirror.

Figure 2: Reflection of light by plane mirror

What is an image?

Figure 3: Image of Candle Formed by a Mirror

• As a mirror reflects light, an image of the object that is in front of the mirror is formed on it.
• The image of an object can be defined as the impression of the object created by the light on the mirror.
• The distance between the image and the mirror, and the object and the mirror always remain the same.
• If we increase or decrease the distance between the object and the mirror, the distance between the image and the mirror also increases or decreases, respectively.
• However, the size of the image formed on the mirror can vary with respect to the distance between the object and the mirror.
• If the distance between the object and the mirror increases, the size of the image decreases and vice-versa.
• An image is said to be erect if the image is formed the same side up as that of the object.
• The image will be called Inverted if it is formed upside-down compared to the object.

Figure 4: Inverted Image of a Candle

Left-right inversion of the image

Figure 5: Left-right inversion of the image

The image formed by the mirror is always left-right inverted. This means that the right side of the object appears as the left side of the image, and the left side of the object appears at the right side of the image.

Why the word ‘AMBULANCE’ is painted on an ambulance left-right inverted?

Figure 6: Ambulance

This is because of the left-right inversion of the image on a mirror. The word ambulance written as left-right inverted would, therefore, be read easily by the driver of the vehicle ahead of the ambulance in its rearview mirror. The rear view mirror will again invert the word left-right wise.

The Laws of Reflection of Light

• Incident Ray – The light ray that falls on the reflecting surface is called an Incident Ray.
• Reflected Ray –Tthe light ray that gets reflected back from a reflecting surface is called a Reflected Ray.
• Normal – It is a line that is perpendicular to the reflected plane at the point of incidence of Incident Ray.

Figure 7: Incident Ray, Reflected Ray and Normal

Figure 8: The Two Laws of Reflection

Types of Reflection

Depending upon the surface of the reflecting object, the reflection of light can vary.

• Diffused Reflection or Irregular Reflection: In this type of reflection, the light rays that fall on the surface are reflected back in different directions irregularly. This generally happens in the case of an irregular or roughly surfaced object.
• Regular Reflection: In this type of reflection, the light rays that fall on the surface of the reflecting object reflect back in a particular direction. The reflected rays are always parallel to each other. This generally happens in case of a smooth and shiny surface.

Figure 9: Types of Reflection

Spherical Mirrors

Spherical mirror, as the name suggests, has a sphere-like shape. It appears as if it is a part of a sphere. There are two types of spherical mirrors:

• Concave Mirror – It is a spherical mirror whose reflecting surface is curved inwards.
• Convex Mirror – It is a spherical mirror whose reflecting surface is curved outwards.

Figure 10: Concave and Convex Mirror

The Image formed by a Concave and Convex Mirror

An image can be of two types:

Real Image	Virtual Image
The real image is formed when the light rays reflect and meet at the same point.	A virtual image is formed when light rays reflect and diverge from the same point.
It can be viewed on a screen.	It cannot be viewed on the screen.
It is always inverted.	It is always erect.
Formed by Concave mirror	Formed by Convex, Concave and Plane Mirrors

Figure 11: Formation of Real Image by Concave Mirror

Figure 12: Virtual Image by Plane Mirror

The image formed by a concave mirror has the following properties:

• It can either be real or virtual.
• It can either be inverted or erect.
• It can have the same size as that of the object, a larger size that of the object or smaller size than that of the object.

The image formed by a convex mirror has the following properties:

• It is always virtual.
• It is always upright (erect).
• It is smaller in size as that of the object

Applications of Concave Mirrors:

• Satellite dishes use a concave mirror to gather all the signals and reflect them on a certain point.
• Dentists use a concave mirror to reflect light on a particular tooth.
• Shaving Mirrors are concave in shape.
• Headlights of a car have a concave mirror so that we can reflect back light straight on the path.
• Torches also use concave Mirrors.

Figure 13: Concave Mirror Used in Torch

Applications of Convex Mirrors

• The rear view mirrors are convex mirrors as they provide a wider view of the road behind.
• Security mirrors near an ATM are convex so that the user can detect easily if anyone else is watching from behind or not.

Figure 14: Convex Mirror used in a Rearview Mirror

Lenses

A lens is a part of a reflecting material like glass or plastic but curved from both sides. Lenses are unlike mirrors that have a reflecting surface only on one side. Depending upon its shape a lens can be categorized as:

• Convex Lens – A Convex Lens is curved outwards. It is thicker in the centre and narrows down at the edges. It merges the light rays passing through it at a certain point. Therefore, it is also called a Converging Lens.
• Concave Lens – A Concave Lens is curved inwards. It has wider edges and a thinner centre. It reflects back the light that travels through it in different directions. Therefore, it is also called a Diverging Lens.

Figure 15: Convex Lens and Concave Lens

Images formed by Convex and Concave Lenses

A Convex lens forms an image that is:

• real
• inverted
• the image is large and appears close to the lens

A Concave lens forms an image that is:

• virtual
• erect
• small and appears far away

Figure 16: Image formed by Convex and Concave Lense

Sunlight

What is a Rainbow?

Figure 17: Formation of Rainbow

• A rainbow is a natural phenomenon in which the light rays of the sun are reflected and refracted by the water droplets present in the atmosphere.
• A rainbow appears as an arc on the sky that contains a band of seven colours – Red, orange, yellow, green, blue, indigo and violet.
• This also means that the white light of the sun contains seven coloured lights in it that separate out due to refraction (called a Spectrum of Lights). This spectrum of white light can be seen in the following:
  • Rainbows
  • Soap bubbles
  • Surface of a CD
  • Prisms

Figure 18: Spectrum of White Light through a Prism

Newton’s Disc

Figure 19: Newton’s Disc

• The Newton’s disc can be obtained by dividing a disk into 7 partitions and painting each of them with the seven colours of the rainbow.
• When the disc is rotated at a fast pace in daylight all the colours tend to mix together and the disc appears whitish in colour.

Revision Notes on Light

What is light?

Light is a radiation or a form of energy that our eyes can detect. Light enables us to view our surroundings. Light travels from one place to another in a straight line.

Figure 1: Light always travels in straight line

For instance, if you look at the flame of a candle with a straight pipe we can easily view the candle. However, if we bend the pipe we cannot view the candle and the light coming through it because it is blocked.

Reflection of Light

• Whenever light hits an object it is either absorbed or reflected back.
• Reflection of light can be defined as the phenomenon of an object throws back the light that falls on it. Hence, the reflection of light changes its path.
• A mirror is generally any shiny surface that can reflect back light.
• A mirror that has a plane surface is called a Plane Mirror.
• A mirror that is curved, it either bulges in or out, is called a Curved Mirror.

Figure 2: Reflection of light by plane mirror

What is an image?

Figure 3: Image of Candle Formed by a Mirror

• As a mirror reflects light, an image of the object that is in front of the mirror is formed on it.
• The image of an object can be defined as the impression of the object created by the light on the mirror.
• The distance between the image and the mirror, and the object and the mirror always remain the same.
• If we increase or decrease the distance between the object and the mirror, the distance between the image and the mirror also increases or decreases, respectively.
• However, the size of the image formed on the mirror can vary with respect to the distance between the object and the mirror.
• If the distance between the object and the mirror increases, the size of the image decreases and vice-versa.
• An image is said to be erect if the image is formed the same side up as that of the object.
• The image will be called Inverted if it is formed upside-down compared to the object.

Figure 4: Inverted Image of a Candle

Left-right inversion of the image

Figure 5: Left-right inversion of the image

The image formed by the mirror is always left-right inverted. This means that the right side of the object appears as the left side of the image, and the left side of the object appears at the right side of the image.

Why the word ‘AMBULANCE’ is painted on an ambulance left-right inverted?

Figure 6: Ambulance

This is because of the left-right inversion of the image on a mirror. The word ambulance written as left-right inverted would, therefore, be read easily by the driver of the vehicle ahead of the ambulance in its rearview mirror. The rear view mirror will again invert the word left-right wise.

The Laws of Reflection of Light

• Incident Ray – The light ray that falls on the reflecting surface is called an Incident Ray.
• Reflected Ray –Tthe light ray that gets reflected back from a reflecting surface is called a Reflected Ray.
• Normal – It is a line that is perpendicular to the reflected plane at the point of incidence of Incident Ray.

Figure 7: Incident Ray, Reflected Ray and Normal

Figure 8: The Two Laws of Reflection

Types of Reflection

Depending upon the surface of the reflecting object, the reflection of light can vary.

• Diffused Reflection or Irregular Reflection: In this type of reflection, the light rays that fall on the surface are reflected back in different directions irregularly. This generally happens in the case of an irregular or roughly surfaced object.
• Regular Reflection: In this type of reflection, the light rays that fall on the surface of the reflecting object reflect back in a particular direction. The reflected rays are always parallel to each other. This generally happens in case of a smooth and shiny surface.

Figure 9: Types of Reflection

Spherical Mirrors

Spherical mirror, as the name suggests, has a sphere-like shape. It appears as if it is a part of a sphere. There are two types of spherical mirrors:

• Concave Mirror – It is a spherical mirror whose reflecting surface is curved inwards.
• Convex Mirror – It is a spherical mirror whose reflecting surface is curved outwards.

Figure 10: Concave and Convex Mirror

The Image formed by a Concave and Convex Mirror

An image can be of two types:

Real Image	Virtual Image
The real image is formed when the light rays reflect and meet at the same point.	A virtual image is formed when light rays reflect and diverge from the same point.
It can be viewed on a screen.	It cannot be viewed on the screen.
It is always inverted.	It is always erect.
Formed by Concave mirror	Formed by Convex, Concave and Plane Mirrors

Figure 11: Formation of Real Image by Concave Mirror

Figure 12: Virtual Image by Plane Mirror

The image formed by a concave mirror has the following properties:

• It can either be real or virtual.
• It can either be inverted or erect.
• It can have the same size as that of the object, a larger size that of the object or smaller size than that of the object.

The image formed by a convex mirror has the following properties:

• It is always virtual.
• It is always upright (erect).
• It is smaller in size as that of the object

Applications of Concave Mirrors:

• Satellite dishes use a concave mirror to gather all the signals and reflect them on a certain point.
• Dentists use a concave mirror to reflect light on a particular tooth.
• Shaving Mirrors are concave in shape.
• Headlights of a car have a concave mirror so that we can reflect back light straight on the path.
• Torches also use concave Mirrors.

Figure 13: Concave Mirror Used in Torch

Applications of Convex Mirrors

• The rear view mirrors are convex mirrors as they provide a wider view of the road behind.
• Security mirrors near an ATM are convex so that the user can detect easily if anyone else is watching from behind or not.

Figure 14: Convex Mirror used in a Rearview Mirror

Lenses

A lens is a part of a reflecting material like glass or plastic but curved from both sides. Lenses are unlike mirrors that have a reflecting surface only on one side. Depending upon its shape a lens can be categorized as:

• Convex Lens – A Convex Lens is curved outwards. It is thicker in the centre and narrows down at the edges. It merges the light rays passing through it at a certain point. Therefore, it is also called a Converging Lens.
• Concave Lens – A Concave Lens is curved inwards. It has wider edges and a thinner centre. It reflects back the light that travels through it in different directions. Therefore, it is also called a Diverging Lens.

Figure 15: Convex Lens and Concave Lens

Images formed by Convex and Concave Lenses

A Convex lens forms an image that is:

• real
• inverted
• the image is large and appears close to the lens

A Concave lens forms an image that is:

• virtual
• erect
• small and appears far away

Figure 16: Image formed by Convex and Concave Lense

Sunlight

What is a Rainbow?

Figure 17: Formation of Rainbow

• A rainbow is a natural phenomenon in which the light rays of the sun are reflected and refracted by the water droplets present in the atmosphere.
• A rainbow appears as an arc on the sky that contains a band of seven colours – Red, orange, yellow, green, blue, indigo and violet.
• This also means that the white light of the sun contains seven coloured lights in it that separate out due to refraction (called a Spectrum of Lights). This spectrum of white light can be seen in the following:
  • Rainbows
  • Soap bubbles
  • Surface of a CD
  • Prisms

Figure 18: Spectrum of White Light through a Prism

Newton’s Disc

Figure 19: Newton’s Disc

• The Newton’s disc can be obtained by dividing a disk into 7 partitions and painting each of them with the seven colours of the rainbow.
• When the disc is rotated at a fast pace in daylight all the colours tend to mix together and the disc appears whitish in colour.

Electric Circuits
A continuous conducting path (consisting of wires, bulb, switch, etc.) between the two terminals of a cell or battery along with an electric current flows, is known as an electric circuit.
e.g. take a cell having a positive terminal (+) and a negative terminal (-). Now try to connect the positive terminal of the cell to one end of the switch with a piece of copper wire and other ends of the switch to one end of bulb holder with another piece of copper wire.
The negative terminal of the cell is connected directly to the other end of the bulb holder with a wire (as shown in the figure), so this kind of setup is known as an electric circuit.

Circuit Diagram
A circuit diagram tells us how the various components in an electric circuit have been connected by using the electrical symbols of the components.
(i) When the bulb glows In an electric circuit when the switch is closed, then the switch is said to be in the ON position. And when the switch in a circuit is open, then the switch is said to be in the OFF position. So, in an electric circuit, a bulb lights up only when the switch is in the ON position and at that time, we can say that the electric circuit is complete because the current flows throughout the circuit instantly (as shown in the figure) electric circuit

(ii) When the bulb does not glow While checking the circuit notice that sometimes the bulb does not glow even when the switch is in the ON position. This condition can occur only if the bulb gets fused, i.e. its filament breaks. It is a difficult and time-consuming job to draw the electric circuit by making the actual drawings of cell, battery, switch, bulb, etc.

So, the scientists have devised a very easy way to represent the component of an electric circuit (cell, battery, switch, bulb, etc.) with the help of symbols, which are easy to draw.

Some of the commonly used symbols for electric components are shown here:

Electric Cell and Battery
The common source of electricity to run the number of devices, e.g. torches, radio, electric clocks and watches, toys, etc., is an electric cell, but sometimes a single cell is not sufficient to run many devices as they require high voltage to run all these appliances. The cell provides much less electricity as compared to that provided by the electric supply line, e.g. in the case, a single electric cell which provides only 1.5 V of electricity, whereas electricity from the power station is supplied to our home at very high voltage of 220 V.

Combination of Electric Cells
Since the higher voltage can be obtained by combining a number of cells in series. So, when the positive terminal of one cell is joined with the negative terminal of the other cell, then the cells are said to be joined in series (as shown in figure given below). So, a battery can be defined as the group of cells joined together in the series, e.g. in a torch, the cells are placed one after the other. But in many devices, cells are not placed one after the other, e.g. in a TV remote control, the two cells are placed side by side (or parallel to each other) instead of single one. So, two or more cells connected in side by side manner are said to be joined in parallel. This combination is also known as battery.

If we combine two cells by keeping the positive terminal of one cell in contact with the positive terminal of the other cell or negative terminal of one cell in contact with the negative terminal of the other cell, then the battery obtained will not work.

The batteries which are used in cars, buses, trucks, inverters, etc., are also made of cells. There is a special feature of car battery is that its cells can be recharged. Ordinary cells, however, cannot be recharged.

Connection of Cells/Battery
‘+’ and ‘-‘ symbols are printed in the battery in order to have an exact placement of the cells in their respective battery compartment.

• The switch or key can be placed anywhere in the circuit.
• The circuit is complete and it is said to be closed only when the switch is ON.
• The circuit is incomplete and it is said to be open, only when the switch is OFF.

There is a thin wire in the bulb, called filament which glows when an electric current passes through it. So, if the bulb gets fused, then its filament gets broken.
Note: Never touch a lighted electric bulb connected to the mains as it may be very hot and can damage your hands.

Heating Effect of Electric Current
Production of heat in an electric device due to the flow of electric current is called the heating effect of electric current. We have seen an electric heater used for cooking, an electric bulb or room heater. So, when these appliances are switched ON after connecting to the electric supply, then their elements become red hot and release the heat. This happens due to the heating effect of electric current.

The degree to which a material opposes the passage of current through itself is known as its resistance. Actually, when an electric current passes through a high resistance wire, the electric energy gets converted into heat energy and this heat energy heats up the wire.

Element
All electrical heating devices consist of a coil of wire called an element. When these appliances are switched ON after connecting to the electric supply, then their elements become red hot and release the heat. There are some electric appliances such as immersion heaters, hotplates, irons, geysers, electric kettles, hair dryers, etc., which have elements inside them.

Factors on Which the Heating Effect of Current Depends
There are two factors on which the heating effect of current depends:
(i) Resistance of wire: Greater the resistance of a wire, greater will be the heat produced in it by a given
current, e.g. if we choose two wires, one of copper and other is nichrome of equal length and equal thickness and pass them the equal amount of current through them for the same duration, then we will notice that nichrome wire will become hotter in comparison to the copper wire. It is due to the reason that the resistance of nichrome wire is more than that of the copper wire.
That is why the nichrome wire is used to make heating elements of electric heating appliances such as electric room heater, electric iron, etc. The resistance of a wire depends on the material of the wire, length of wire and thickness of the wire.

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Applications of the Heating Effect of Current
Some of the important applications of heating effect of electric current are

• For the production of light, the heating effect of electric current is utilised in the electric bulbs.
• For the working of electrical heating appliances such as water heater, electric room heater, electric iron, etc., the heating effect of electric current is utilised.
• The heating effect of electric current is utilised in a safety device called ‘electric fuse’.
  

Compact Fluorescent Lamps (CFLs)
An electric bulb is basically used for producing light but it also releases the heat which is not desirable because a major part of the electricity consumed by the filament of a bulb is converted into heat and results in the wastage of electricity. So, this wastage can be decreased by using fluorescent tube light or CFLs (as shown in the figure) in place of the bulbs.
However, before purchasing bulbs, tubes orCFL’s we should look for the ISI marl? (ISI- Bureau of Indian standard). It is because the ISI mark ensures that the appliance is safe and wastage of energy is minimum.

Electric Fuse
A safety device which works on the heating effect of current and prevents electric fires or damage to electrical appliances due to excessive flow of current is known as the fuse. This safety device consists of a short length of a thin wire of tin plated copper having a low melting point and this wire has a much greater resistance than the rest of the electric wiring in the house.

So, due to this, if the current in the electric wiring suddenly increases too much, then the fuse wire gets heated, then it melts and breaks the circuit which means that the current flowing in the household circuit will stop. This prevents fire in the house and also the damage of various electrical appliances like refrigerator, fans, tube lights, TV, etc. When a fuse gets blown (breaks), a new fuse has to be fitted in its place in order to restore the electricity supply in the household circuit.

Note: We should not use a thick wire as a fuse wire because it will have low resistance and thus it will not get heated to its melting point ‘ when a large current passes through it.

Cause of Large Current Flow in Household Electric Wiring
An extremely large current can flow in the household electric wiring circuits under two circumstances overloading and short circuit. We might have read reports in the newspaper about fires caused by short circuits and overloading. Now, let’s study these two terms.

Overloading
It is a situation when too many electrical appliances are connected to a single socket, they draw an extremely large amount of current from the household circuit. The flow of large current due to overloading may heat the copper wires of household wiring to a very high temperature and fire may be started.

Short Circuit
Electric current is supplied by household through two insulated wires which run together and reach each and every electrical appliances. One insulated wire is called live wire and the other insulated wire is called neutral wire and both these wires are necessary for the working of an electrical appliance (say an electric iron).

So, if in case the plastic insulation of the live wire and the neutral wire gets worn due to wear and tear, then the two naked wires touch each other. So, this touching of live wire and neutral wire directly is known as a short circuit. Due to which a large current flows through the household wiring and this large’ current may heat the wires to a dangerously high temperature and a fire may be started.
Note: Always use proper fuses which have been specified for particular applications carrying ISI mark Never use just any wire or strip of metal in place of a fuse.

Miniature Circuit Breakers (MCBs)
This ore increasingly being used these days in place of fuses. MCB does not work on the heating effect of current as it works on the magnetic effect of current. These switches outomaticoUy turn OFF when the current in a circuit exceeds the safe limit. We turn them ON and the circuit ¡s once again completed.

Magnetic Effect of Electric Current
If the electric current passes through a wire, then the current carrying wire behaves like a magnet. This phenomenon is known as the magnetic effect of current. It was discovered by a scientist Hans Christian Oersted who found that when an electric current is passed in a wire, then the compass needle placed near it got deflected from its usual North-South position.

A straight wire carrying an electric current produces a magnetic effect. The magnetic effect is increased only if we use a long coil of wire instead of a straight wire. Even further the magnetic effect is increased if the coil of wire is wound around an iron rod and then current is passed through it.

Electromagnets
It is a magnet made by using electric current. An electromagnet works on the magnetic effect of current. An electromagnet consists of a coil of insulated wire wrapped around a piece of iron which is magnetised only when an electric current is passed through the coil.

This magnet consists of a long coil of insulated copper wire wound around an iron rod and when the two ends of the coil get connected to a cell, then a current passes through the coil and produces a magnetic effect. The magnetic effect magnetises the iron rod. In this way, the iron rod becomes an electromagnet. The magnetism of an electromagnet remains as long as the current is flowing in its coil. So, if we switch OFF the current in the coil, then all the magnetism of the iron rod disappear and it will no longer behave like a magnet.
There are two factors through which an electromagnet can be made stronger, i.e.

• By increasing the amount of current used in the coil.
• By increasing the number of turns forming the coil.

Uses of Electromagnets

• These magnets are used in electrical appliances such as an electric bell, electric fan, electric motor.
• These magnets have their utilisation in electric generators where the very strong magnetic field is required.
• For deflecting electron beam of the picture tube of TV electromagnets are used.
• For the magnetic separation of iron ores from the earthly substances, electromagnets are used.
• For preparing strong permanent magnets, electromagnets are used.

Advantages of Electromagnets over Permanent Magnets
An electromagnet is a temporary form of the magnet because its magnetism is only for the duration of current flowing in its coil. Actually, an electromagnet is better than a permanent magnet in many respects. There are some of the advantages of the electromagnets over the permanent magnets which are stated as follows:

• The magnetism of an electromagnet can be switched ON or switched OFF as desired. While it is not possible with a permanent magnet.
• By increasing the number of turns in the coil and by increasing the current passing through the coil an electromagnet can be made very strong. On the other hand, a permanent magnet cannot be made so strong.

Electric Bell
An electric bell works on the magnetic effect of current. It has an electromagnet in it. Let us study its construction and working as well.

Construction of Electric Bell
The electric bell has a U-shaped electromagnet. There is a small iron bar called armature which is h^d in front of the poles of the electromagnet. The lower end of the iron bar is attached to a flat spring and the flat spring is itself fixed to a metal bracket. The upper end of the iron bar has a clapper attach to it. A metal gong is fixed near the clapper.

Working of Electric Bell
In order to ring the bell, first of all, we press the push button switch in order to ring the bell. So, when we press the switch, then the electric circuit of the bell is completed and a current passes through the coil of the electromagnet and it gets magnetised. The electromagnet attracts the iron armature towards itself.

So, as the armature moves towards the poles of the electromagnet, the clapper attached to it strikes the gong and produces a ringing sound. It implies that the bell rings.

When the armature moves towards the magnet, its contact with the contact screw is broken. Due to this, the electric circuit breaks and no current flows in the electromagnet coil. The electromagnet loses its magnetism for a moment and the armature is no longer attracted by it. The flat spring brings back the iron armature to its original position and the clapper also moves away from the gong.

As soon as the armature comes back and touches the contact screw the circuit is completed and current starts flowing in the electromagnet coil again. The electromagnet attracts the iron armature once again and the clapper strikes the gong again producing a ringing sound.

So, this process of ‘make and break’ of the electric circuit continues as long as we are pressing the switch. Due to this, the armature vibrates forwards and backwards rapidly each time making the clapper strike the gong. Thus, the clapper strikes the gong rapidly producing an almost continuous sound.

We hope the given CBSE Class 7 Science Notes Chapter 14 Electric Current and Its Effects Pdf free download will help you. If you have any query regarding NCERT Class 7 Science Notes Chapter 14 Electric Current and Its Effects, drop a comment below and we will get back to you at the earliest.

All the living organisms including plants and animals have the capability to produce new individuals during their lifespan. This process of producing a new organism from the existing organism (or the parent) of the same species is called reproduction. The new individuals produced, are the copies of their parents. The process of reproduction is one of the important life processes and is essential for the continuity of the species.

Thus, reproduction makes the life continuous which is not only essential for the survival of an organism but it is also very necessary for the perpetuation and preservation of the species because it increases the number of members of a species.

Modes of Reproduction
The various parts of a plant such as roots stem and leaves each with a specific function is called vegetative parts. After a certain period of growth, plants bear flowers. These flowers develop into fruits and seeds.

The parts of a plant that participate in the process of sexual reproduction are called reproductive parts or organs. In plants, the reproductive parts are a flower which may have the male or female part or both the parts on the same flower.
Different organisms reproduce in a different way. In plants, there are two different methods of reproduction:

1. Asexual reproduction
2. Sexual reproduction

The term ‘sexual’ means involving the fusion of sex cells or gametes while ‘asexual’ means without involving the fusion of gametes.

Asexual Reproduction
The process in which only one parent is involved in the production of new individuals of the same kind is called asexual reproduction. In plants, asexual reproduction results in the formation of offsprings or new plants without seeds or spores.
Asexual reproduction in plants occurs through the following methods:

1. Vegetative propagation
2. Budding
3. Fragmentation
4. Spore formation

1. Vegetative Propagation
It is the formation of new plants from vegetative units of bud, stem, etc. These vegetative units are called propagules. Vegetative reproduction may take place using various plant parts as given below:

(i) Vegetative Reproduction by Stem
The stems or branches of the plant normally bear buds in the axils. The buds that are present in the axil (i.e. the point of attachment of leaf at the node) develops into the shoot. These are called vegetative buds.3

(ii) Another method of vegetative reproduction in stem is by layering. In this method, a mature branch of parent plant is bent down and covered with soil. The tip of the plant is kept above the ground. The root develops from the branches and grows into a new plant. Layering method is usually done in the plants that have long and slender branches, e.g. jasmine.

(iii) Grafting is also a method of vegetative reproduction in stems, where new plants of desired qualities is developed from two different plants. The part that has shoot part is called scion and part having root is called stock. Scion is attached to the stock which provides support and basic requirement for the development of plant, e.g. apple, mango, rose, etc.

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(ii) Vegetative Reproduction by Leaves
When the leaf of some plants are hurried into the moist soil, the cut edges or margins of leaves develop a new plants that resemble to the parent, e.g. Bryopbyllum or sprout leaf plant.

(iii) Vegetative Reproduction by Roots and Bulbs
In some plants like sweet potato, dahlia, etc, a new plant develops through their roots and bulbs.

Note: Plants like cacti produces new plants when their parts get detached from the main plant body. Each detached part can grow into a new plant.

Advantages of Vegetative Propagation

• Plants produced with vegetative reproduction takes less time to grow and bear flower and fruits earlier than those produced from seeds.
• The new plants are the exact copies of parent plant because they are produced from a single parent.

2. Budding
In this process, a daughter individual is formed from a small projection on parent body called a bud. Most of the fungi-like, yeast reproduce by budding.
Yeast grow and multiply in every few hours, if provided with sufficient nutrients and favourable condition.

3. Fragmentation
Some algae (Spirogyra) that are present in waterbodies reproduce by fragmentation. In this- method, the body of the parent breaks into small pieces called fragments and each fragment grows up to become a new plant. Fragmentation of parent body occurs when they are matured.

If water and nutrient are available, the algae will grow and multiply rapidly by fragmentation. If this process continues, it will cover a large area in a very short period of time.

4. Spore Formation
Some fungus like bread mould reproduces asexually by spore formation. Spores (present in the air) are the small spherical bodies, having a thick protective wall that protects them from unfavourable conditions. When favourable conditions arrive the spores burst and germinate to develop into new plants.

Spores are very light asexually reproducing bodies which can be carried over a long distance by air or wind. Some other plants like mosses and ferns also reproduce by spore formation in the underside of their leaves.

Sexual Reproduction
Flowers are the reproductive part of a plant. They help the plants in sexual reproduction and producing fruits and seeds. In sexual reproduction, a male cell is produced by the male part of a flower which fuses with a female cell produced by the female part of the flower. These cells are called gametes, which when combined form a zygote by the process called fertilisation.

Parts of a Flower
The main parts of a flower are
(i) Sepals These are the green leaf-like outermost circle of the flower. All the sepals are together referred to as calyx. The function of the calyx is to protect the flower when it is in bud form.

(ii) Petals These are the colourful and most attractive part of the flower. These lie inside the sepals. All the petals are together referred to as corolla. These are scented and attract insects for pollination.

(iii) Stamen It is a male reproductive organ of a plant. These are the little stalks with swollen top and lies inside the ring of petals. The stamen is made up of two parts, i.e. filament and another. The stalk of stamen is called filament and the swollen top of stamen is called anther.

The anther contains the pollen grain which have male gamete in it. Pollen grains are exposed when the anther ripens and splits. These appear as the yellow powder like substance which is sticky in nature. Flowers usually have a number of stamens in it.

(iv) Pistil It is the female reproductive part of a flower that lies in the centre of a flower. These are a flask-shaped structure which is made up of three parts, i.e. stigma, style and ovary.

The top part of the pistil is called stigma. It receives the pollen grains from the anther during pollination. The middle part of the pistil is tube-like structure called style which connects stigma to the ovary.

The swollen bottom part at the base of pistil is called ovary. The ovary makes ovules and stores them. These ovules contain the female sex cells also called an egg cell. It is the female gamete of flower. Pistil is also called as carpel. The pistil is surrounded by several stamens.
The base of the flower on which all the parts of the flower are attached is called receptacle.

Types of Flower
On the basis of the type of reproductive organs present in a flower, the flowers are of following types:
(i) Unisexual flower: The flower which contains only one reproductive organ (i.e. either male or female) are called unisexual flowers. These are also called as an incomplete flower, e.g. papaya, watermelon, corn, cucumber, etc.

(ii) Bisexual flower: The flower that contains both reproductive parts (i.e. male and female) in a single flower are called a bisexual flower. These are also termed as hermaphrodites or complete flower, e.g. rose, mustard, Hibiscus, etc.

Function of a Flower
The function of a flower is to make male and female gametes and also to ensure that fertilisation would take place for the seed formation. During sexual reproduction male and female gametes fuse to form the zygote.

Pollination
The transfer of pollen grains from the anther of a stamen to the stigma of a pistil is called pollination. Pollination takes place in two different ways:
(i) Self-pollination: When the pollen grain from the anther of one flower reaches to the stigma of the same ‘ flower, it is called self-pollination. Self-pollination generally occurs in a bisexual flower.

(ii) Cross-pollination: When the pollen grains from the anther of a flower or of a plant are transferred to the stigma of a flower of the same plant or that of a different plant of the same kind the process is called cross-pollination. This transfer to another plant is mediated by insects, wind, water, animals, birds, etc.

Agents of Pollination
The process of pollination is carried out by some external agencies like wind, water, insects, birds, etc. These are called agents of pollination.

Fertilisation
The process in which the male gamete fuses with the female gamete to form a new cell (called zygote) is called fertilisation.

When the pollens are deposited on the stigma of the pistol, it begins to germinate. After some time, a long pollen tube is developed from the pollen grain which passes through the style towards the female gametes in the ovary. The male gametes move down the pollen tube and the tube enters the ovule present inside the ovary.

The tip of pollen tube bursts and the male gamete comes out of the pollen tube. Inside the ovary, the male gametes fuse with the female gametes present in the ovule to form a fertilised egg cell which is called zygote.
The zygote develops into an embryo which is a part of a seed that develops into a new plant.

Fruit and Seed Formation
After the fertilisation, the ovary grows into the fruit and the ovule develops into the seeds. The outer parts of the flower, i.e. petals, sepals and stamen become dry and fall off. Stigma and style also fall off leaving ovary on the receptacle. The zygote inside the ovary gets its food from the ovule and grows by cell division to form an embryo. Parts of the ovule develop into the seed covering or seed coat.

Fruits are the ripened ovary of a flower. Which protect the seed. Some fruits are fleshy and juicy, e.g. mango, apple and orange, while some are hard like almonds and walnuts.

Seed Dispersal
Seeds are developed from the ovule. Seeds contain an embryo enclosed in a protective seed coat. Plants produce a large number of seeds. When these seeds fall down, they start growing. If a large number of seeds falls on the same place, they will not get enough space for water and light, and will not develop into a healthy plant. Thus, the seeds are moved away by some external agencies to far off places.

The process by which the seeds are scattered to different places (far and wide from their parents) is called dispersal. The seeds and fruits are dispersed away through various agencies like wind, water, birds and some animals. Sometime seed dispersal takes place naturally by the explosion or bursting of fruits.

Seed Dispersing Agents
Wind, water, animals, birds and humans are the dispersing agents of seeds. These are described below:

Dispersal by Wind or Air
The seeds that are very light and have wing or hair-like structure on them, are easily carried away by the blowing wind, e.g. seeds of maple, drumstick have wings, seeds of Madar or oak have hairs on them, cottonseed also possess hairs on them, while seeds of grasses, orchids, begonia are very small and light. These seeds can be easily carried away by the wind and dispersed away from their natural habitat.

Dispersal by Water
The seeds of some plants that have an outer fibrous or spongy covering are dispersed through water. They have the ability to float in the water and drift along with its flow, e.g. seeds of water lily, lotus, chestnut (singhara) and coconut are dispersed through water. The coconut fruits have a fibrous outer coat which enables them to float in water and carried away by flowing water to far off places.

Dispersal by Birds
The birds eat fruits along with the seeds. These seeds have hard outer covering. The seeds are dispersed to some other place through the bird’s faeces. The digestive enzymes present in the digestive system of birds helps in dissolving the hard seed coat and when they are released or excreted along with the faeces, they germinate, e.g. neem seeds are dispersed by the bird’s faeces.

Dispersal by Animals
Some seeds have hooks or spines which get attached to the fur or body of the grazing animals. When these animals move to a distant place, the seeds get dispersed (while animal rub their body surface), e.g. fruit of Xantbium and Urena plants are covered by numerous hooks which attach to the animal’s fur and are dispersed with them. Along with the fruits, the seeds also get dispersed.

Dispersal by Explosion or Bursting of Fruits
Sometimes fruits mature and a strain is produced in their walls. This produces a sudden jerk causing fruits to break open, thus allowing the seeds to scatter far away from their parent plants. Due to the explosion of fruit, the seeds are thrown away from the plant with a great force in all direction, e.g. castor plant burst suddenly with a jerk and scatter the seeds far away from the parent plant. Similarly, fruit of balsam is also dispersed through the explosion mechanism.

Benefits of Seed Dispersals

• Seed dispersal avoids overcrowding of young plants around their parent plants.
• It helps in preventing competition between the plants and its own seedlings for sunlight, water and minerals.
• One of the benefits of seed dispersal is that it enables the plant to grow into new habitats for wider distribution and provides them with a better chance of survival.

Germination of Seed
A seed contains a plant embryo in a resting state which begin to grow only under favourable conditions. The process by which seeds begin to grow is called seed germination. It is the growth of a plant from its seed. When the seed germinates, the seed coat splits and a tiny root called radicle grows downward and shoot called plumule starts growing upwards. This produces seedling of the plant.

The seedling grows faster and ultimately forms a new plant

In unicellular organisms, the intake of food, water, oxygen and removal of waste material occur across the cell surface by the process of diffusion. Plants and animals are multicellular. They have a specific organ to perform specific functions. To perform these functions, every cell in the plant and animal body require useful substances such as nutrients, oxygen and water. Plants and animals have a transport system to carry useful substance to every cell of the body and for the removal of waste material produced by the body.
In animals, the transportation system is called the circulatory system and in plants, the transportation takes place through pipeline connection called vascular bundles.

Transportation of substances in humans:

Diffusion in higher multicellular organisms like humans is too slow to transport substances to all the cells. Hence, a fluid medium called blood always circulates throughout the body within a narrow tube channel called blood vessels. The heart, blood and blood vessels together make up the circulatory system in humans.

Blood

Blood is red-coloured fluid that transport respiratory gases, nutrients, secretions as well as waste material from one part of our body to another.
Blood consists of a pale yellow liquid called Plasma in which red blood cells (RBCs), white blood cells (WBCs) and blood platelets float.

Functions of Blood:
Blood perform several functions:

• It transport digested food from the small intestine to the other parts of the body.
• It carries oxygen from the lungs to the cells and carbon dioxide from the cells to the lungs.
• It protects the body against infection by destroying disease causing germs.
• It clot blood when there is an injury or cut, preventing excess loss of blood.
• It also carries waste products from the cell to the kidney for removal from the body.

Blood Vessels

The blood in our body moves through tube-like structures called blood vessels. Blood vessels are of three types: artery veins and capillaries.

The heart

• The heart is a fist-sized muscular organ found in the chest cavity towards the left lungs. It pumps blood to all parts of the body. It beats 60-80 times a minute throughout our life.
• The heart is made up of four chambers. The Upper two chambers are called right atrium and left atrium. The two lower chambers are called right ventricle and left ventricle.
• A muscular wall called septum separates the right and left side of the heart, preventing the mixing of oxygenated blood with the deoxygenated blood and have valves. Valves allow the blood to flow in only one direction.
• The blood rich in carbon dioxide flows through the right side of the heart, while the blood rich in oxygen flows through the left side of the heart.

The arteries and veins in the heart connect to other parts of the body. The blood vessels that enter or leave the heart are:
Vena cava:  It is a large vein that collect blood rich in carbon dioxide from all parts of the body through smaller veins and empties the blood from the right atrium.
Pulmonary artery: It carries blood rich in carbon dioxide from the right ventricle of the heart to the lungs.
Pulmonary vein: It brings oxygenated blood from the lungs to the left atrium of the heart.
Aorta: It is the largest artery which receives blood rich in oxygen from the left ventricle. The oxygenated blood is then circulated to different parts of the body.

Working of  heart:

• The heart functions as a double pump. Impure (deoxygenated) blood from the veins flows into the right Atrium of the heart.
• From here, the blood enters the right ventricle through an opening.
• The impure blood is transported from the right ventricle to the lungs by the Pulmonary artery.
• Gaseous exchange takes place in the lungs.
• The blood gives off carbon dioxide and takes in oxygen.
• Oxygen-rich blood is carried to the left Atrium by the Pulmonary vein.
• From here, the blood flows through an opening into the left ventricle.
• The left ventricle pumps oxygen rich blood to every part of the body through the aorta.
• The oxygen is then used by the cells and the cell produces carbon dioxide.
• The blood takes in carbon dioxide and returns to the right ventricle of the heart.

Heartbeat and pulse:
The heart works by contracting and relaxing its muscles. The contraction and relaxation follows a rhythm called heartbeat.
Pulse is the throbbing sensation of an artery at each beat of the heart. A Doctor uses an instrument called the Stethoscope to listen to your heartbeat. The number of beats per minute is called the pulse rate.

Lymphatic system of the human body

• The lymphatic system is made up of lymph vessels and lymph nodes.
• As the blood flows through the capillary some of the plasma oozes out of the walls. Most of the fluid enters the lymph vessels and is drained back into the blood vessels.
• Before this blood is returned to the circulatory system, it is filtered through lymph nodes. lymph nodes contain special types of cells called Lymphocytes which protect the human body from disease causing organisms and harmful substances.

Transportation of substances in plants

Transportation of water

Like animals, plants also need to transport water minerals and nutrients to all their parts.

• Once the water and minerals are absorbed from the soil by the roots through root hair, they move up the stem and leaves through tube-like tissues called the xylem.
• Absorption and transportation of water is a continuous process  which occurs with the help of transpiration.
• Transpiration is the process in which plants lose  water through the stomata in the form of water vapour. This results in water loss in the cells of the leaves and creates pressure. The pressure helps to pull the water from the roots through the xylem of the stem to reach all the way to the leaves.
• The upward movement of sap is called the ascent of sap.

Transportation of food

The food manufactured in the leaves during photosynthesis reaches all parts of the plant through another tube- like tissues called the phloem. This process is called translocation.

Excretory system

Besides carbon dioxide gas, the human body produces several other kinds of waste materials which mix into the blood. Waste  products are often toxic and need to be removed from the body. The process by which metabolic waste products are removed from the body is called excretion.

Excretion in animals:

In unicellular organisms like Amoeba, Paramecium and lower animals like Hydra and sponges, waste products are excreted by the process of diffusion through their body surface. Large animals have special organs for excretion.

Human excretory system:

The human excretory system is made up of Kidneys, ureter, urinary bladder and urethra.

• A Human being has two Kidneys, located in the abdominal cavity.
• Each kidney consists of a large number of coiled tubes called nephrons. The nephrons filter out waste products from the blood. The end product of this process is urine. Urine contains wastes such as urea, ammonia and uric acid.
• The urine flows through two long tubes called ureters and collects in the urinary bladder.
• Urinary bladder is the storage sac for the urine. The urine ultimately is drained out of the body through the urethra.

Sometimes due to infection, genetic conditions or injury, the kidneys may stop functioning which results in the accumulation of waste substances within the body. In such cases, blood is passed through an artificial kidney machine to remove waste products from the body. This process is known as dialysis. Kidney transplant is another option to treat a failed kidney.

Excretion in plants:

Plants excrete waste products from their body. They get rid of their waste product in the following ways:

• Oxygen and Carbon dioxide are given out during the process of photosynthesis and respiration.
• The excess water is lost by the plants through transpiration.
• Some plants excrete their waste product in the form of gums, resins and latex. The substances are of great use as adhesive, paints, varnishes and rubber.

Revision Notes on Respiration in Organisms

Why do we respire?

• All the living organisms are made up of small microscopic units called the cells.
• These cells have different functions to perform in these organisms such as digestion, respiration, transportation and excretion.
• The cells can perform this function only if they get the energy to do so.
• Hence, all living organisms need food which gives them the required energy.
• The energy present in the food gets released when the organisms respire or breathe.

How food helps us in gaining energy?

• As we breathe, we take in the air that contains oxygen in it and breathe out air which contains carbon dioxide. This oxygen when transported to our cells helps in breaking down the food and we get energy.

What is cellular respiration?

• Cellular respiration can be defined as the process in which the food that we eat is broken down inside the cells which results in the release of energy. All the cells in living organisms undergo cellular respiration.
• The cellular respiration takes place in a cell organelle called mitochondria.
• The oxygen that an organism breathes in reacts with the carbohydrates (glucose) present in the food and results in the release of carbon dioxide, water and energy.

Figure 1 Cellular Respiration

Types of respiration

Aerobic Respiration	Anaerobic Respiration
1. This kind of respiration takes place in the presence of oxygen.	1. This type of respiration happens in the cells in the absence of oxygen.
2. It leads to release of a high amount of energy in living organisms.	2. It results in a low amount of energy.
3. Human beings and many other animals undergo aerobic respiration.	3. Yeast and sometimes human beings undergo anaerobic respiration.
4. Carbon dioxide and water are also released in aerobic respiration.	4. Animal muscle cells release lactic acid and Yeasts release ethanol and carbon dioxide in anaerobic respiration.

Figure 2 Aerobic Respiration in Animals

Figure 3 Anaerobic Respiration in Yeast

Anaerobes:

• Organisms that can exist in the absence of air are called anaerobes.
• They undergo anaerobic respiration hence can get energy even without oxygen.
• For example, Yeasts. These are unicellular organisms that exist in the absence of oxygen as well.
• As a byproduct, they release ethanol and carbon dioxide. That is why they are used to make wine and beer.  This is called as alcohol fermentation.

Anaerobic respiration in human beings

• Sometimes muscles of human beings can respire without oxygen.
• This generally happens when we undergo a heavy exercise such as running, weightlifting, cycling or walking for a longer duration.
• In such situations, the muscles require more energy and the supply of oxygen is not enough.
• Hence anaerobic respiration takes place in the muscles.
• As a result of muscles also produce lactic acid along with energy.
• This lactic acid accumulates in the muscles and causes cramps.
• That is why we often feel cramps while we do heavy exercises.
• In order to get relief from cramps, we can take a hot water bath or massage our muscles.
• This is so because hot water bath or massage improves the blood circulation in the muscles.
• As a result, the oxygen reaches the cells easily which breaks on the lactic acid into carbon dioxide and water.

Figure 4 Anaerobic Respiration in Muscles Releases Lactic Acid

Breathing:

• Breathing can be defined as a process in which organisms, with the help of their respiratory organs, take in the oxygen-rich air present in the surroundings and release out air that contains high amount of carbon dioxide in it. Breathing occurs continuously in the organisms.
• Inhalation is the process of taking the air that contains oxygen inside the body.
• Exhalation is a process of releasing out air that contains carbon dioxide out of the body. Inhalation and exhalation take place alternatively in the breathing process.
• Breathing rate can be defined as the number of times a person breathes in a minute.
• A breath can be defined as an inhalation followed by an exhalation.
• The breathing rate is not always constant in human beings. We generally breathe faster when our body needs more energy for example while exercising.
• This is so because the body needs more oxygen that can break down the food and produce more energy.
• An average adult human being breeds 15 to 18 times in a minute. While exercising, this rate can change up to 25 times a minute.

Figure 5 Relation between Breathing and Cellular Respiration

Why do we feel hungry after doing a physical activity like walking or running?

When we do a physical activity the food that is present in our body is converted into energy. Since all the food gets consumed in generating the energy we start feeling hungry. Hence in order to gain more energy we need to eat more food.

The mechanism of breathing in human beings

Figure 6 The Respiratory System in Humans

• We take in the air present in the environment through our nostrils which travels through the nasal cavity.
• Then it moves through the windpipe and reaches the lungs.
• The lungs are located in the chest cavity which is surrounded by the ribs.
• On the floor of the chest cavity lays a muscle sheet called diaphragm.
• During the breathing process, the movement of the ribs and diaphragm takes place. This is so because the lungs expand and contract during breathing.
• As we take in the air it fills up the lungs. This moves the diaphragm downwards and the ribs outwards.
• The lungs when releasing out air from the body which brings back the diaphragm and the ribs to their original positions.

Figure 7 Breathing

Why do we sneeze?

• As we inhale the air present in the surroundings sometimes various unwanted elements such as smoke and dust are also included in it.
• However, they get stuck in the hair in our nostrils but some of them can get through the nasal cavity.
• They thus cause irritation in the nasal cavity which makes us sneeze.
• This helps in getting rid of the unwanted particles out of the nasal cavity.

What do we breathe out?

Figure 8 What do we Inhale and Exhale

Breathing in other organisms

• Many animals have just cavities in their bodies just like human beings for example lions, elephants, goats, cows, snakes and birds.
• Breathing in cockroach:

• Many insects like Cockroaches have small openings called spiracles present on the sides of the bodies.
• Also, they have an air tube-like structure called the trachea that allows the exchange of gases in these insects.
• The air enters the body through the spiracles and diffuses in the cells via the trachea.
• Similarly, the air from the cells enters the trachea and moves out of the body through spiracles.

Figure 9 Respiratory system of Cockroach

• Breathing in earthworms:
  • Earthworms have a soft, slimming and moist skin.
  • Hence the gases can easily pass in and out of the earthworm through its skin.
  • Similarly, frogs also have a slippery and moist skin that can help in breathing. However, frogs contain lungs too.

Figure 10 Respiration in Earthworms

• Breathing underwater
  • Animals that live underwater have special respiratory organs called gills.
  • They are a comb-like structure present on the skin of these animals.
  • Gills allow the exchange of gases between animals and the water easily.
  • Some animals called the amphibians can breathe on land by lungs and through moist skin under water. For example frogs and toads.

Figure 11 Respiration through Gills in Fishes

Respiration in plants

Figure 12 Respiration in plants

1. We know that plants also respire. They take in the carbon dioxide present in the atmosphere and use it in the process of photosynthesis to produce food. As a result of photosynthesis in plants, they release out oxygen in the environment.

2. All the parts of the plants can independently respire that is they can take in the carbon dioxide and release oxygen on their own.

3. The leaves of the plants have stomata present upon them which are small pore-like structures. The allow gases exchange in leaves.

4. The woody stems of the plants also respire. This is because of the presence of special tissue called Lenticels. The cells of this tissue have large intercellular spaces. They exist as dead cells on woody plants and roots and allow the exchange of gases. The bark of trees although is impermeable to gases hence these tissues serve an important purpose of respiration in the stems.  As the name suggests, lenticels have a lens-like shape.

Lenticels in plants

5. The roots of the plants have hair-like structures on them. Hence they can absorb the air present in the soil.

Figure 13 Respiration in Leaves through Stomata

Why plants can die if overwatered?

• We know that the roots get oxygen from the soil.
• We also understand that the air in the soil is present between the soil particles.
• Along with the air, soil also contains some water or moisture.
• If we over-water the plants the spaces between the soil particles get clogged.
• As a result, the roots will not be able to get enough air and the plant can die.

Figure 14 Roots can absorb air from the soil

Importance of Soil

• Soil allows the growth of plants. It supplies water and nutrients that are required in the growth of plants.
• The soil is the main part of agriculture. Different types of soils support different kinds of crops. Without agriculture, food, shelter and clothing are not possible.
• Many microorganisms live in the soil.
• Underground water is used for various purposes.

Figure 1: Importance of Soil

What pollutes the soil?

• Dumping non-biodegradable substances such as plastic bags and polythene causes soil pollution.
• Waste products from industries which contain chemicals can affect the soil adversely.
• Excess use of fertilizers and pesticides pollute the soil and decrease its fertility.

Therefore, before dumping anything waste into the soil it must be treated properly. Pesticides and fertilizers should be used in minimum quantity. Lastly, materials like plastic should be banned as we pollute the soil and affect the living organisms as well.

Figure 2: What Causes Soil Pollution?

Soil Profile

The soil consists of distinct layers which are also called Horizons of the Soil.

The Soil Profile is a vertical section of the soil which depicts all the layers of the soil. The layers of the soil can be seen if we dig deep through it like while creating a well or while laying the foundation of a building.

• Humus – The decaying matter in the soil is called Humus.
• Weathering – Soil is formed when rocks break down. This process is also called Weathering. The weathering of rocks takes place because of rains, flowing water, winds, temperature and climatic conditions of a place.
• Parent Rock – The nature of the soil that is its texture and availability of minerals depends upon the rock from which it is formed. This rock is often called as the Parent Rock.

Figure 3: Soil Profile

Layers of the Soil

Horizon A

• This layer is also called the topsoil. It is visible to us.
• It contains large amounts of humus and minerals which makes it dark in colour.
• The soil is rich in nutrients because of the presence of humus.
• The topsoil has a soft texture and can retain water easily. That is why plants roots grow in the topsoil region.
• The topsoil is a home to many living organisms as well like insects, worms, beetles, rodents and moles.

Horizon B or the Middle Layer

• It is the next layer of the soil which does not contain much humus.
• The minerals are found in large quantities in this layer.
• This layer has a hard texture, light colour and is more compact than the topsoil.

Horizon C or Third Layer

• The third layer of the soil consists of small rocks with cracks in them. These rocks are partly weathered.

Bedrock

• The last layer of the soil is called the Bedrock.
• It contains large pieces of rocks that are not weathered or exposed to any winds or water.
• Bedrock cannot be dug with the help of a spade. It is very hard in texture.

How is Soil Formed?

We know that soil is formed from weathering of the parent rock and the texture of the soil depends upon the parent rocks only. This process takes time, maybe a hundred years, and then the fine soil is formed.

• In the first stage of soil formation, the soil is generally non-porous in nature. Then it slowly turns into soil having air and water in the pores.
• We can define soil as a mixture of rock particles and humus. Based on the size of the particles and the textures of the soil it can be divided into various types.

Figure 4: Formation of Soil

Types of Soil

Figure 5: Types of Soil

Sandy Soil

• Sandy soil has big particles that have large spaces between them.
• The spaces between these particles are filled with air. Hence, sandy soils are called well-aerated soils.
• Because of large spaces, water can easily penetrate through the particles of sand. Sandy soils, however, cannot hold water.
• Hence, sandy soils are light aerated and dry in nature.
• Sandy soils lack much nutrients hence do not support the diverse growth of plants.

Clayey Soil

• It consists of fine particles which have less space between them.
• Since there is not much space between the particles clayey soils are not well-aerated like sandy soils.
• The tiny gaps between the particles although allow absorption of water in the clayey soils easily
• They are able to hold water hence are suitable for the growth of different kinds of plants.

Loamy Soils

• Loamy soil contains a similar amount of large and small particles in them.
• They are combination of sandy, clayey and silty soil.
• They also contain humus.
• They can hold water in appropriate amounts and therefore support the growth of plants.
• They are also called Agricultural Soils because of their fertility and appropriate texture.
• They contain good amounts of calcium and have a high pH level.

Silt Soil

• The silt soil particles are smaller than that of sandy soils but larger than clayey soils.
• Silt soil can hold water to some extent because of its fine quality.
• They are generally found near the water bodies like river banks and lakes.
• They are rich in nutrients, highly fertile and hence are suitable for agriculture.
• They are often mixed with other soils to improve the fertility of the soil. 

Figure 6: Particle Size in Sand, Silt and Clay

Properties of Soils

1. Percolation of water through the Soil

Percolation can be defined as the property of the soil by which it allows the flow of water through it. The rate at which water percolates or moves through soils may vary in different kind of soils. Some soils absorb water while others allow it to flow through them. The rate of percolation can be calculated by:

Figure 7: Percolation of Water

2. Moisture

Moisture is the amount of water that is present in the soil. Even a dry soil has some amount of moisture in the air. However, the clayey soil has the highest content of moisture.

Why air above farmland appears shimmering during the daytime?

We know that soil contains water. Due to sunlight, the water from the soil begins to evaporate and turns into water vapour. This water vapour when reflects the sunlight appears as if it is shining and hence the air above the soil makes the land look shimmery.

3. Absorption

Every soil has a water absorption capacity which depends upon how porous the soil is. Clayey and loamy soils are most porous hence can retain water in large quantities. That is why crops can grow over these soils. Sandy soils, on the other hand, do not absorb water and hence do not support much vegetation.

4. Texture

The texture is the size of particles of the soil. Different kinds of soils have a different texture.

5. Colour

Different soils have different colours as well. This is because of the minerals and nutrients present in the soil. For instance, some soils are black in colour because of the presence of humus and minerals while some soils are red in colour because they have iron in large quantities in them.

Figure 8: Soils have different Colors

6. pH of Soil

Soils can have different pH depending upon their acidic, basic or neutral nature. Based upon the pH different types of crops grow in the soil.

7. Air Content

Since soil is made up of particles of different sizes these particles can be loosely bound or tightly bound. The air often occupies the space in between these particles. This allows life to sustain in the soil such as microorganisms.

Figure 9: Different Properties of Soils

Soil and Crops

Different kinds of soils are found in different regions because of the following factors that decide the soil structure of that place:

• temperature
• humidity
• rainfall
• sunlight
• winds

The type of crops that will grow in the soil depends upon these factors as well as the properties of a soil.

Type of Soil	Crops Grown
Sandy	Potato, Lettuce, Corn, Peppers
Clayey	Sprouts, Broccoli, Kale, Beans, Cabbage
Loamy	Apples, Carrots, Tomatoes, Cucumber

What is soil erosion?

• When the top layer of soil gets removed it is called soil erosion.
• The soil erosion mainly occurs when the soil is left loose without vegetation or when deforestation occurs.
• In such a situation, strong winds and flowing water or rainwater takes away the topsoil and therefore decrease its quality.
• Also, this kills the organisms living inside the soil.
• The roots of the plants and trees keep the soil together and allow several microorganisms to grow and survive there. Therefore, it is always advised to plant more trees and avoid deforestation.

Winds – When the air moves in a flow in a particular direction it is called wind.

Air Exerts Pressure

Why a tin can with hot water when cooled down with freshwater distorts its shape?

Figure 1 Air Exerts Pressure

As fresh water is poured over the hot can the steam in the can condensers and converts into the water. This results in reducing the amount of air that is present in water. The pressure of the air outside the can becomes more than the pressure of the air inside the can. This results in compressing of the can. Therefore, it is proved that air exerts pressure.

Flow of Air

When the speed of the wind increases it lowers down the air pressure. Therefore, we can say that air flows from a region of high pressure to low pressure.

The speed of Air/ Winds

The speed of air or wind depends upon the difference between the pressures of the two regions. If the difference between the pressures increases, the speed of the air also increases.

Hot Air and Cold Air

When the air is heated it expands. As a result, it occupies more space and becomes lighter in weight. Therefore, we can say that warm air is light in weight and cold air is heavy.

Why does smoke move in upward direction?

Smoke is hot air. Hot air is lighter hence it moves in an upward direction.

How Convection in air occurs?

When the hot air in a region rises up, the pressure becomes low in that region. As a result, the colder air fills its place. This is how convection in air occurs.

Figure 2 Convection in Air

Generation of Wind currents due to uneven heating of the earth

There are two situations where winds on earth generate:

1. Uneven heating between the equator and poles causes the north-south winds

• We know that the Earth is divided into circular lines called latitudes that specify the north-south position of a place on the globe.
• Also, the equator is latitude that is perpendicular to the axis of the earth’s rotation.
• The regions that are close to the equator receive maximum sunlight on the earth.
• Hence the air in these regions is generally warm. The warm air, therefore, rises above and the cold air from the latitude around the equator moves in that place.
• Similarly, cold winds from North and South poles move towards the equator and the neighbouring latitude and the circulation of winds take place on the earth.

Figure 3 Flow of Winds on Earth

You might observe in the figure given above the direction of the wind is not exactly from north to south or from South to North. This diversion in the direction of winds occurs because of the earth’s rotation.

2. Uneven heating of land and water causes monsoon winds on earth which bring rainfall

• In the summer season, the land near the equator gets warmer and its temperature generally remains higher than the oceans.
• As a result, what are above the land rises and the cold air from the oceans moves towards the land. These winds are called monsoon winds.
• Since these winds come from the ocean they carry water with them. In a similar way, the winds in the winter season move from the land towards the oceans.

Figure 4 Direction of Monsoon Winds in India

Thunderstorms and Cyclones

Although monsoon winds are important for agricultural purposes and in regulating the temperature conditions of a place sometimes excess of rainfalls and strong winds can lead to natural disasters such as thunderstorms and cyclones.

Thunderstorms

• An event in the environment in which strong winds blow accompanied by heavy rainfall, thunder and lightning are called thunderstorm.
• Thunderstorms occur in hot and humid tropical regions mainly. These regions generally have higher temperatures which cause winds.
• These hot winds when move upwards also have water vapour within them which freezes and falls on the earth as rain.
• The rainfall and rising air create lightning in the air accompanied by sound and as a result, a thunderstorm occurs.

Figure 5 Formation of Thunderstorms

Precautions that one should take during a thunderstorm

• One should not take shelter under an isolated tree during storm and lightning. Instead, one can take shelter under a small tree if near a forest area.
• One should not lie on the ground.
• One should not use or carry an umbrella which has a metallic rod.
• One should stay away from windows and doors at that time.
• One should not take shelter in an open garage, metal shed or storage sheds.
• It is advisable to take a shelter in a car for a bus.
• One should not stay in the water. People should try to move inside a building as soon as possible.

Figure 6 Protect yourself during Thunderstorm

Cyclones

• Clouds are formed due to water vapour in the air.
• As the water turns into vapour, it takes up the heat from the atmosphere.
• When the water vapour turns into clouds and falls back as raindrops the same heat is released back into the atmosphere.
• This heat warms up the air around the raindrops and the warm air starts rising.
• This leads to decreasing their pressure in the region.
• So, the air from the surroundings takes the place of the warm air. This cycle continues until the rain falls.
• As a result, a very low-pressure region is created and strong winds start revolving in that low-pressure region. This is the condition of a cyclone.
• The formation of a cyclone that depends upon different factors:

• the temperature of the place
• the wind speed
• the direction of the winds
• the humidity of the place

Figure 7 Formation and Structure of A Cyclone

Structure of a Cyclone

• Cyclone is a rotation of air in the atmosphere at a height of around 10 to 15 km.
• The centre of the cyclone(also called the eye of the storm) is a clean area where there are no clouds but only light winds.
• This area ranges from 10 to 30 km in diameter.
• The cloud region lies around this eye and has a diameter of around 150 km.
• The cloud region has high-speed winds blowing at 150 to 250 km per hour accompanied by heavy rainfall.
• The first indication of a cyclone can be observed when strong winds start flowing and pushing away the water from the shores.

The destruction caused by a cyclone

• Cyclone can result in extremely high waves in the sea or ocean because of the low pressure. These waves can be 3 to 12m high.
• When these high waves hit the shore it results in the destruction of life and property to a great extent.
• The soil of the area also loses its fertility after a cyclone.
• Floods can appear if rainfall continues for a longer duration.
• High-speed winds in the cyclone affect the telephonic communication lines, uproot trees, damage houses and cause loss of life.

Other names of a cyclone

• Hurricane – American continent
• Typhoon – Japan and the Philippines

Figure 8 Different types of Cyclones

Tornado

• A tornado is a weather condition when a cloud having a dark funnel-shape reaches the ground.
• The diameter of a tornado can range from one meter to several kilometres.
• The tornadoes can be formed within cyclones as well.
• In a tornado, winds blow at high speed of 300 km per hour.
• The funnel-like shape of a tornado sucks everything that comes near it at the base because of the low pressure exerted by the winds.
• It then throws the things upwards. Hence, tornados can be devastating.

Figure 9 Formation of Tornado

Protecting yourself from a tornado

• To protect oneself in a tornado one should take shelter in an underground room with no windows.
• If in a room with windows, one should close them and hide under a table or a workbench.
• One should bow down on the knees protecting their neck and head using their arms.

Figure 10 Protecting yourself from a tornado

Safety measures for cyclones

• There should be a cyclone forecasting service that can want the people of a particular area that can be hit by a cyclone.
• The speed of winds plays a major role in predicting any calamity like cyclones hence the speed of wind in coastal areas should be measured regularly. Anemometer is a device that can measure the speed of the Wind.

Figure 11 Anemometer

• The warnings should be communicated rapidly to the citizens, ships that are sailing in the sea, government agencies and fisherman as well.
• Along with this, cyclone shelters should be built in coastal areas and agencies should be appointed who can help the people at the time of calamity.

How individuals can protect themselves from cyclones

• One should not ignore the warnings given by the weather forecasting team. If you can, you must move to safe places and carry all your important belongings with you.
• One should not drive on roads that have standing water as they might be damaged.
• One should keep all the emergency numbers with themselves so that they can seek help when required.

Figure 12 Protecting yourself during a cyclone

What to do if you are living in a cyclone hit area

• The water in such region can be contaminated. Hence one should make sure if the water is safe and only then drink it.
• One should stay away from power lines for electrical switches of any kind.
• One should stay at home or at the shelters and should not move out unnecessarily.
• One should not put unnecessary demands to the rescue team and should co-operate with them.
• One should help each other in such a situation.

Role of Technology in predicting and protecting from the cyclone

• The satellites and radars have made it possible to predict cyclones ahead of time so that appropriate precautionary measures can be taken accordingly.
• There are now several National and international organizations that monitor cyclone-related issues.
• Generally, a cyclone watch or a cyclone and alert is issued every 48 hours in advance if a storm is expected in an area.
• Then a cyclone warning is issued before 24 hours. This warning is then broadcasted in the area after intervals of half an hour or 1 hour.

The weather of a place can be defined as the measure of its daily atmospheric conditions such as humidity, temperature, lightning events, rainfall Storms, snow and so on.

Different elements of weather are:

• Rainfall
• Temperature
• Humidity
• Snowfall
• Storms
• Winds etc.

Figure 1: Different types of Weather

A weather report generally contains the information about the weather of the day.

The government has a special department called the Meteorological Department that predict the weather of a place and prepare the weather report.

The weather report is generally published in newspapers, radio and television.

The weather forecast is important for people because many of our day-to-day activities are based on weather conditions. For Example, we can check the possibility of rainfall on a particular day and carry an umbrella with us accordingly.

Figure 2: Weather Forecast

The weather of a place is never constant. It can alter every day or even every hour. For instance, the weather might be sunny in the morning in an area but really in the evening.

The weather report of a place always includes the minimum and maximum temperatures of the day which are measured using a minimum-maximum thermometer. The minimum temperature can be experienced in the morning time while the maximum temperature is experienced in the afternoon.

To measure the rainfall of a place an instrument called the Rain Gauge is used. The rain gauge collects the rainwater of origin and has a measuring scale which determines the quantity of rainfall of that place.

Figure 3: Rain Gauge

How do changes in weather occur?

Any change in the weather of a place on the earth is because of the Sun which radiates large amounts of heat and light energy on the earth. The formation of winds, the phenomena of rainfall and the change in seasons, all occur because of the Sun.

Why days are shorter in the winter season?

• We know that the Earth spins on an axis around the sun.
• Hence, the amount of sunlight a place receives various throughout the year as its position with respect to the sun changes because of the rotation of the Earth.
• This also leads to change in the seasons of a place.
• In the summer season, the position of the place is closer to the sun and hence it receives sunlight for longer hours while in the winter season the position of a place is farther to the sun and hence, it receives sunlight for shorter hours.

Figure 4: Change in Seasons

Climate

• The climate of a place can be defined as the prevailing weather conditions of the place for a long period of time, for example, 25 years.
• For Example, the temperature of Rajasthan is generally high throughout the year and it does not receive much rainfall so we can say that Rajasthan is a hot and dry place.

Figure 5: Different Climates on Earth

Climate and Adaptation

• The climate of a place can affect the living organisms of that area.
• The animals living in a particular region adapt themselves so that they can survive the weather conditions of that place.
• The features and habits of the animals start to change as per the climate of the place.

Polar Region

Figure 6: The polar region on the earth

• The area of the earth that surrounds the North Pole and the South Pole is called the Polar Region.
• The climate of the polar region is extremely cold throughout the year and receives heavy snow.
• The sun does not rise for 6 months of the year in the polar region and then It stays up for the next 6 months.
• The temperature in the polar region can be as low as – 37^°C.
• Most common animals found in these regions are polar bears and penguins. Other animals that can be found in polar areas are fishes, birds, oxen, musk, reindeers, fox, whales and seals.
• They have adapted themselves so that they can survive easily in these places. 

Figure 7: Animals in Polar Region

The Polar Bear

• The white fur of the polar bear makes it easier for them to hide in the snow and therefore save them from predators.
• In the same way, it makes it easier for them to catch their prey.
• The polar bears have two layers of thick fur on them so that they can survive extremely cold conditions.
• The polar bears move slowly and rest a lot so that they do not get overheated because of their thick fur.
• The polar bears often swim on warm days to keep themselves cool.
• The paws of the polar bear are large and wide so that it can swim as well as walk easily in the snow.
• The polar bear can swim underwater as well because it can keep its nostrils closed for a long time.
• The strong sense of smell of polar bears makes it possible to locate its prey during such harsh weathers.

Figure 8: Adaptation of Polar Bear

The Penguins

• The penguins are also white in colour so that they can hide in the snow.
• They have thick skin with large fat content in their body so that they can survive the cold weather easily.
• The Penguins generally live in a crowd or nest closely so that they can stay warm.
• The Penguins have webbed feet which allow them to swim.

Figure 9: Adaptation of Penguin

Migratory Birds in the Polar Region

• The birds in order to protect themselves from cold weather of the winters in the polar region often migrate from these areas to warmer places.
• They then return back after the winter season.
• For example, The Siberian crane migrates to India in Rajasthan, Haryana and some North East regions during the winter season in Siberia.
• These birds that migrate to different places during a change in weather are often called migratory birds.
• They can travel used instances of 15000 km to protect themselves from the extremely cold environment.
• Such birds migrate to the same places every year.
• The migratory birds fly very high so that the heat generated by the flight wings can be disposed of in the cold conditions.
• The migratory birds have a sense of direction so that they can travel to the same place every time.
• The migratory birds also use landmarks or follow the direction of the sun and stars to migrate.
• Some birds also use the magnetic field of the earth and find direction.
• Apart from birds, fishes, insects and mammals also migrate.

Figure 10: The Siberian Crane

Tropical Rainforests

Figure 11: The tropical region on earth

• The tropical regions on the earth are the regions which are close to the equator and hence receive more amount of sunlight during the year.
• Because of this, these areas have a hot climate.
• The temperature in tropical regions can be as high as 40^o C and can drop until 15 ^o C only.
• The length of the day and night are almost equal in these regions.
• However, there is a lot of rainfall and so the tropical rainforests are found in this region.
• The Tropical rainforests are home to a wide variety of vegetation and animals.
• Due to large habitation, the animals often compete for food in these regions.
• Many animals have adapted themselves so that they can live on the trees and find their food easily. The skin colour of these animals is generally similar to that of the surroundings so that they can catch their prey easily and protect themselves from the predators. Also, many of these animals have a good eyesight and better sense of hearing.