Yearly Archives: 2022

Introduction: It is common knowledge that water is important on our Earth and without water, life as we know it would cease to exist. While Earth has an abundant reservoir of water, covering three-fourths of its surface, Freshwater is a mere 2.6% of the total water. Water is said to be a renewable resource but the rate at which humans and animals are using water, fresh water might be a scarce resource in the recent future. Our body is also made up of 70% water and we use water for a number of reasons from cooking to cleaning and of course drinking it. A lot of experts predict that the next World War will be fought over water!

Figure 1 Two-thirds of Earth’s surface covered with water

Where does water come from?

People living in different regions have different sources of the water that they use. While some draw it from wells, ponds and lakes directly, others like many of us receive water through taps via a network of pipes connected to these lakes, ponds and rivers.

Water Cycle

To know how these rivers get their water from we need to study a little about the water cycle and the processes of evaporation and condensation.

Evaporation: The process of conversion of water into its gaseous state i.e. vapours is known as evaporation.

Condensation: The process of conversion of vapours into water is referred to as condensation.

Water cycle can be defined as the process through which water gets evaporated from open surfaces like oceans and seas, gets condensed as it rises in the cool atmosphere and ultimately pours down as rain (precipitation) back into oceans, lakes, rivers and ponds.

Figure 2 Water cycle

Transpiration: The process of evaporation of water from the surface of the leaves into the atmosphere is defined as the process of transpiration. In this manner, plants also contribute to the water cycle.

It is through the process of water cycle that we are able to make use of the ocean water. Ocean water is saline in nature and hence cannot be used directly. When it gets evaporated, it leaves behind the salts and forms clouds.

As the warm air from these surfaces rises into the cold air of the atmosphere, saturation and condensation occur to form tiny droplets of water which result in cloud formation.

These clouds then lead to rainfall and snow which deposit in lakes, wells and ponds is then used by us to satisfy our needs. Apart of this rainwater gets absorbed by the soil, some of it gets evaporated while the rest seeps in the ground and becomes another source of water for us in the form of groundwater. Handpumps, wells and even lakes draw water from groundwater. The water cycle is a continuous process.

Excess v/s deficient rainfall

Intensity and duration of rain vary in different regions across the country. While rainfall is very important for irrigation and the continuous availability of water, excess rainfall can pose a number of problems. Due to excess rainfall, the water level of rivers and oceans rises which can potentially spread and submerge nearby cities and villages which poses a grave danger to both life and property. These are known as floods.

Figure 3 Floods posing danger to property and life

Similarly, deficient rainfall can also prove to be life-threatening. A lot of farmers in India continue to depend on rainfall to irrigate their fields. In case of deficient rain, soil and wells still continue to lose water through transpiration and evaporation and if it doesn’t rain for a prolonged period, fields can dry up because even the groundwater does not get replenished. These are known as droughts.

Figure 4 Dried fields as a result of droughts

Conservation of water

There are a number of reasons why water conservation needs to be a priority for everyone. Here are some of them:

• Mostly all water is in the oceans in saline form and can’t be used directly
• While the total water on Earth does not change, but the water available for us to use diminishes with overuse
• When the groundwater goes below drastically, it cannot be accessed anymore
• Water is required in industries and for production of food
• The population growth is exponential but the water sources are only depleting

Figure 5 A few tips to help save water

Rainwater Harvesting

Rainwater does not always fall on soil or water sources; in fact, much of it falls on rooftops of houses and concrete roads and thus does not become a part of groundwater. Hence, a very important method has been devised to harvest rainwater so that it can be stored for future use:

Rooftop Rainwater Harvesting – In this method, rainwater that falls on rooftops is allowed to pass in a storage tank through pipes. This water might be dirty and hence not fit for direct use; hence it can be allowed to seep directly into the ground with the help of pipes.

Figure 6 Rainwater harvesting

What are Magnets?

Magnets are pieces of iron or other materials which exhibit the properties of magnetism i.e. the ability to attract other objects that contain iron. Compass needles, fridge magnets and MRI scanners are some common examples of magnets.

It is said that magnets were discovered after a shepherd named Magnes accidentally got his iron stick stuck to a rock. It was later discovered that the said rock had magnetic properties and was called Magnetite, named so after the shepherd.

These days magnets come in different shapes and forms such as: horseshoe magnet, bar magnet, cylindrical or a ball-ended magnet, needle magnet etc.

Magnetic and Non-Magnetic Materials

Magnetic Materials: Materials like nickel, cobalt and iron are called magnetic materials. These materials are attracted to magnets.

Non-Magnetic Materials: Materials like rubber, plastic, cloth, glasses etc. which are not attracted to magnets are referred to as non-magnetic materials.

Poles of Magnet

We can observe a very interesting property about magnets which is that when we try to attract iron filings or any other magnetic objects to a magnet, they always accumulate at the ends of the magnet.

This is because near the poles the magnetic field of the magnet is very strong.

A Magnetic field is defined as the region around a magnet within which the magnetic force acts. Being strongest at the poles, this is why magnetic objects get attracted to the ends of the magnet.

Magnetic fields around a bar magnet

Finding Directions

Another great property of a magnet is that it can prove extremely helpful in navigating directions. This is because a freely suspended magnet always points in the North-South direction.

This property of magnet is used to make a compass. A magnetic needle is placed inside a box with directions marked on it. It is allowed to rotate freely so that when the compass is kept at the position of rest, the needle points towards the north and south direction.

Steps to make own Magnet

• Take a rectangular piece of iron. Place it on the table.
• Take a bar magnet and place one of its poles near one edge of the bar of iron. Without lifting the bar magnet, move it along the length of the iron bar till it reaches the other end.
• Lift the magnet and bring the pole (the same pole we started with) to the same point of the iron bar from which we began. Move the magnet again along the iron bar in the same direction as we did before.
• Repeat this process about 30-40 times. The iron piece has become bar magnet.

Attraction and Repulsion among Magnets

• Opposite or unlike poles i.e. North and the South Pole attract each and vice versa.
• Similar or like poles like north and north poles of two magnets repel each other. Same is the case with South poles of two magnets.

Attraction between opposite poles and repulsion between similar poles

Notes of caution

• When heated, hammered or dropped from a height, magnets tend to lose their properties.
• They become weak if they are not stored properly and hence:
  • Bar magnets should be stored in pairs separated by a small block of wood and their unlike poles facing the same side with a soft iron across their ends.
  • A piece of iron should be kept across the poles in case of a horseshoe magnet.
• Magnets should be kept away from computers, mobiles, televisions etc.

 Magnets should be handled with care and they should be stored properly

Introduction to Electricity and Circuits

Electricity has become so common that sometimes we forget its immense applications.

Advantages of Electricity:

• Light in our houses, offices, roads etc. even past sunset
• To operate pumps which in turn have a lot of applications
• Electrical appliances like refrigerator, fans etc.
• Building houses, installing equipment etc.

Fig 1: Refrigerator {Electric Appliance}

Electric Cell and Electric Bulb

Features of an Electric Cell:

• It is a small cylindrical structure which helps in operating the devices.
• A small metal cap is placed on one side and a metal disc is present on the other side.
• All cells have two terminals: Positive and Negative.
• The metal cap and metal disc are positive (+) and negative (-) terminals of the electric cell respectively.
• Chemical energy is converted into electrical energy inside a cell. When the chemicals are exhausted, the cell stops working.

Fig 2: Electric Cell

Features of an Electric Bulb:

• The outer covering is glass and the base is metallic.
• The part of the bulb which glows is called Filament and is made up of tungsten.
• The filament is attached to two wires. One of the wires is connected to the metal case at the base and the other wire is connected to the metal wire at the centre of the base.
• Base of the bulb and metal tip are the terminals of the bulb and they do not touch each other.

Fig 3: Electric Bulb

An Electric Circuit

Consider an electric cell and a bulb. The terminals of the cell are connected to the terminals of the bulb by the means of electric wires. Such an arrangement of cell and bulb is called an Electric Circuit. The circuit is said to be complete in this case because of which electricity will flow and the bulb will glow.

• One should be careful while setting up an electric circuit. It should be done under supervision.

Electric Switch

Switch is an integral part of an electric circuit. It is a simple device which breaks or completes a circuit. When the switch is ‘on’, the circuit is complete. When the switch is ‘off’, current does not flow in the circuit. So an electric appliance will only work if the switch is ‘on’.

Fig 4: Switch on and off respectively

Electric Conductors and Insulators:

Conductors – Materials that allow electricity to flow through them easily.

Insulators – Materials that do not allow electricity to pass through them.

• Human body is a conductor, so touch a current carrying wire is detrimental and so insulating it prevents from an electric shock.
• Some examples of conductors are: Metals like copper, Iron
• Some examples of insulators are: Rubber, Plastic

Fig 5: Danger Sign

This sign is used in areas which are near electric junctions as a warning.

Topics in the chapter

• Light
• Luminous objects
• Non-Luminous objects
• Transparent, Opaque and Translucent Objects
• Characteristics of light
• Shadow and its properties 
• Pinhole camera
• Mirror and types of mirror

Light

→ It is a form of energy which is responsible for seeing objects.

→ When light falls on an object, some light get reflected, this reflected light come to our eyes and we are able to see an object.

→ Example: sun, torch, candle, fireflies and glow worm etc.

Sources of light

(i) Luminous object: The objects which emit their own light is called luminous object.

→ Example: sun, torch bulb, star

(ii) Non-luminous object: The objects which do not emit their own light is called non-luminous object.

→ Example: Moon, shoe, trees.

Types of materials transmit light

→ There are three types of materials which transmit light:

(i) Transparent
(ii) Translucent
(iii) Opaque

(i) Transparent

→ These objects allow light to pass through them in straight line completely.

→  We can see through these objects clearly.

→  Examples: air, water, etc.

(ii) Translucent

→ These objects allow light to pass through them partially.

→ The object is not clearly seen in translucent object.

→ Examples: Tissue paper, frosted glass, butter paper, etc.

(iii) Opaque

→ These objects do not allow light to pass through them.

→ We can’t see the object through this.

→ Examples: wall, door, trees etc.

Characteristics of light

→ Light travels in straight line

→ Light can be reflected

→ Light can be bent

→ The speed of light is 3 × 108 m/sec

→ Light can be polarized

Shadow

→ When an opaque object blocked the path of light it forms a dark portion on the opposite side of the object this dark portion is known as shadow.

Properties of shadow

→ The object must be opaque or translucent

→ Transparent object do not make shadow

→ It is dark in color

→ It is formed opposite to the source of light

→ It gives the information about the shape of object

→ Size of shadow can be increase or decrees by change in distance between object and screen are changed.

Pin hole camera

→ It is a toy device use to study light travels in straight line

Properties of image formed by a Pin Hole Camera

(i) Image formed by a pin hole camera is coloured.

(ii) Image formed by a pin hole camera is inverted.

(iii) Image formed by a pin hole camera is smaller in size.

Rectilinear propagation of light

→ Light travels in a straight line are called rectilinear propagation of light.

Important terms regard rectilinear propagation of light

(i) Ray of light: It is a path along which light travels in the given direction.

(ii) Beam of light: Bunch of ray of light travel in the given direction.

Mirror

→ A mirror is a polished surface which can make the image of an object.

Types of Mirror

(i) Plane mirror: Image formed is of the same size

(ii) Concave mirror: Reflecting surface is bent–in.

(iii) Convex Mirror: Reflecting surface is bulged-out.

Reflection

→ When light falls on a mirror, light wave may change their direction upon the striking surface this phenomena is called reflection.

• Objects that do not produce their own light but are visible when reflect light falling on them are called Non-Luminous Objects. Example – Table, planets. Non-luminous objects can be classified as-

Shadows are dark regions formed when an opaque object blocks the path of light. This formation is possible only because light only travels in a straight line.

How to make a Pinhole Camera?

Step 1: Take two cardboard boxes one larger than the other such that one box slides into the other without any gap.

Step 2: Cut out open one side of each box. On the opposite side of the larger box cut a small hole in the centre.

Step 3: On the opposite side of the smaller box cut a square of about 5 cm and cover this open area with a tracing paper.

Step 4: Slide the smaller box inside the larger one such that the side with the tracing paper is on the inside.

Step 5: Cover the camera and your head with a black cloth and then get ready to observe the distant objects.

Fig: A Pinhole Cameria

It is a simple camera with a small aperture and forms an inverted image of the object.

Mirrors and Reflections

All of us are used to seeing a mirror every day. The image that we see in a mirror is called Reflection. The mirror deflects the direction of the light that falls upon it.

Fig: A Mirror Changing the direction of light as it falls on it

With the changing times, transport also has gone through various modifications i.e. from animals to the invention of wheels. The evolution of transport is evident when we observe the fast cars, bullet trains etc. Even today new modes of transport are being researched upon.

Fig 1: Shows the advancement in transport

• Distance: How far an object travels constitutes distance!! The GPS system introduced these days accurately measures the distance from one place to another.
• Arbitrary ways to measure the length or width:
  • Measuring using handspan and measurement by a string were used in ancient times but these methods are not so reliable and hence some standard units of measurement have been introduced.

Fig 2: The Handspan Method

Standard Units of Measurement

Earlier the ‘cubit’ was accepted as a standard unit in Egypt. A cubit meant the length between fingertips and elbow. Owing to the differences in the length of body parts of each person these arbitrary systems became obsolete. Other units used earlier were ‘foot’, end of outstretched arm and chin, fist, etc.

Nowadays, the International System of units or the SI units have been accepted all over the world as a standard unit of measurement.

1 m = 100 cm

1 kg = 1000 g

1s = 1/60 min

The MKS system i.e. the metre-kilogram-second system is called the SI System.

Correct Way to Use a Mater Scale

Step 1: Keep the scale in contact with the object to be measured.

Step 2: Start measuring from the 0 mark of the scale.

Step 3: To avoid taking incorrect measurements the eye position should be correct. Consider the following figure:

The eye position in the centre is correct to get an accurate measurement, while the ones in the left and right direction will give some error in measurement.

Measurement Along Curved Line

Is it possible to measure a curved line with a metre scale? Well, it is not so. Hence to measure a curved line the following steps can be taken into account:

• Take a thread and tie a knot at one end.
• From this end measure a small portion of the curved line which is somewhat straight and put the thumb.
• Now again start from the thumb marked position and measure another small portion of the line.
• Repeat this process until you reach the end of the line. Tie a knot on the thread on reaching the end. Now measure the two knots using a metre scale.

Fig 4: Measuring A Curved Line

Types of Motion

• Rectilinear Motion: When an object moves along a straight line, it is said to be undergoing rectilinear motion. For Example, A train moving along a railway track.
• Circular Motion: Have you seen the hands of a clock? The motion exhibited by the hands of a clock is called Circular Motion.
• Periodic Motion: When an object repeats its motion after a fixed interval of time it is said to be undergoing periodic motion. For Example, Pendulum
• Rotational Motion: This motion can be easily understood by imagining Earth’s rotation. When the Earth spins on its own axis it is said to be undergoing rotational motion.
• Motion is defined as the change in position of an object.

Fig 5: Shows the examples of types of motion

Introduction: Different regions in the world have various types of living creatures called organisms. Even the openings of volcanoes have tiny living organisms. Even our homes are not devoid of these tiny organisms. List some of the tiny organisms which you have encountered at home!

Environment: Everything that we see surrounding us; living, non-living, physical, chemical etc. is called as environment

Biotic Components: These are the living components of the ecosystem. e.g. flora and fauna

Abiotic Components: The non-living components of the ecosystem like soil, water ,air etc. are called abiotic components.

Organisms and the surroundings where they live

The table shows some common organisms and their place to live

ORGANISM	WHERE THEY LIVE
CAMELS	DESERTS
YAK	MOUNTAINS
CRABS	SEA
ANTS	VARIOUS LOCATIONS

Habitat and Adaptation

The region or place where an organism lives is termed as its habitat.Habitat provides an organism everything it needs to survive like food, shelter, proper weather conditions such as rainfall, heat etc to breed and flourish.

Camel:

It has long legs which provide protection from the heat of sand

Excrete small quantity of urine

They do not sweat and their dung is dry

Can live without water for many days as their bodies lose little water.

Figure 1 Camel

Fish:

Their streamline shape helps to move easily in water

Presence of slippery scales

Gills help in utilizing dissolved oxygen

Flat fins and tail help in changing direction in the water

Figure 2 Aquatic Organisms

Both the organisms discussed above have specific features or characteristics that enable them to survive in their habitat. These features are termed as adaptations.

TERRESTRIAL HABITAT:Plants and Animals that thrive on land said to live in terrestrial habitat.E.g.: forests, deserts, mountain regions

AQUATIC HABITAT:Plants and Animals that thrive in water said to live in aquatic habitat.E.g.: rivers, lakes

Journey through different habitats

Terrestrial Habitat:

a) Deserts:

The following adaptations of various organisms are enlisted below:

• Snakes and rats dig burrows to escape intense heat as they dont have long legs such as a camel. These animals come out only during the night, when it is cooler
• In desert plants leaves are reduced to spines and lose little water through transpiration
• The stems of desert plants have a waxy coating on them and in most of them photosynthesis is carried out by the stem
• Their roots go deep into the soil so as to absorb water.
• The leaves in desert plants are absent to prevent loss of water due to transpiration.
• Some of the animals are camels, kangaroo rats etc

b) Mountain Regions:

• The trees are cone shaped with slope like branches, also needle-like leaves are present so that rain and snow slide off them easily.
• Animals have thick fur which provides protection from cold. e.g. Snow Leopard
• Presence of strong hooves help the mountain goat to run on the rocky slopes.
• Eg are Pines, mountain goats, yaks, sheep etc. Yaks have long hair to keep them warm.

Figure 3 A tree found in mountain region

c) Grasslands:

• The light brown colour of the lion helps it to hide in dry grasslands and the presence of long claws help to capture the prey.
• Deer has strong teeth to eat plant stems also its long ears help to listen to predator movement. They have eyes on its sides of the head which help them to look in all directions to lookout for danger.
• Some of the animals living in these habitats are elephants, giraffes, lions .

d) Rainforest:

• This habitat receives a lot of rain and hence its rich in animal life.
• Mammals, Amphibians, Reptiles all sorts of animals are found here.
• The climate is hot and humid and animals have to learn to adapt to survive.

e) Polar Habitat:

• These habitats are very cold and windy.
• The animals are mostly carnivores and have thick fur to survive in cold.
• Some blend in ice and some may hibernate in the coldest months.
• Examples of animals are polar bears, reindeers, penguins etc.

Aquatic Habitats

Figure 4 An aquatic plant

Marine Habitat

1. Marine Habitat comprises of oceans and seas, and both have saltwater.
2. They are home to a wide variety of creatures like the most part of fish population is found here.
3. Marine creatures are found in Estuaries – where rivers and oceans meet and the water is salty.
4. Marine Mammals like whales migrate to long distances in order to cope up with the temperature changes.

Oceans

• Most organisms have streamlined bodies and gills
• Octopuses do not have streamlined bodies so they stay deep in ocean, but when moving they make a streamline motion.
• Whales have blowholes instead of gills This enables them to breathe easily when they swim near the surface of water.

Figure 5 An Octopus

Freshwater Habitat:

1. Rivers, lakes, ponds etc comprise the freshwater habitats.
2. Three percent of world’s water is accounted as freshwater but still a wide variety of species are found here.
3. Snails, worms, mollusks etc are found in this habitat

Ponds and Lakes:

• Plants: Water plants can be completely submerged in water (like Hydrilla) or floating on the surface of water(like Water Lily, Lotus, Water Hyacinth). Roots are much reduced in size, since their main function is to hold the plant in place. Stems of aquatic plants are long, hollow and light so that these can bend in along with water movement. e.g Water Lily. The stems grow up to surface of water, while the leaves and flowers float on surface of water.
• Totally submerged plants have narrow and ribbon like leaves (e.g tape grass). These can bend in flowing water.
• Stems have air spaces to enable the plant to float. Floating plants are large and flat. They have waxy upper surfaces that makes them waterproof. They have stomata on the upper surfaces which are exposed to air.
• Frogs are adapted to live both on land and water, they have strong back and legs and webbed feet which allows them to swim in water.

Coastal Habitat:

1. Habitats where the land meets the sea.
2. Beaches, special type of trees called mangroves are found in this habitat
3. Coastal plants like seaweed attach to the rocks firmly so that they are not swayed by the waves,

Acclimatisation: Due to certain changes in the surroundings, organisms adapt through them by making small changes in the body over short periods of time.

For e.g: The changes which take place in the body when we travel from plains to mountains. The adjustment which the body makes is called Acclimatisation

Characteristics of Living Organisms

Living

They require food to grow and carry out life processes

They grow in size

All living organisms breathe and respire(process of generating energy)

They Respond to stimuli(changes in environment)

They carry out reproduction(producing next generation) and excretion(elimination of waste from body)

Movement is shown by living organisms

Human Body And Its Movements

The human skeleton is the internal framework which is responsible for giving support, shape and protection to our bodies. It contains 206 bones, each playing a distinct yet important task. The skeleton can be classified into two parts called as the axial and the appendicular. The axial skeleton comprises of the central part of the skull, spine, and ribs and the appendicular skeleton consists of the arms and legs.

Terms –

Limbs: The arms or legs of an animal.

Bones: These are the hard white structures below our skin that protect our internal organs. Bones are incapable of bending.

Joints: These are defined as the points at which two bones are fitted together. These are the points at which we can rotate and bend our bodies.

Figure 1: Body Movements

Types of Joints and their Location in Human Body

• A Pivot joint is a joint that rotates.. Examples of pivot joints in the body in the neck that allows the head to rotate and the ones between the radius and ulna that allow forearm rotation.
• When bones can move along one axis, it indicates the presence of Hinge joint. e.g. Elbows and Knees.
• In the Ball and Socket joint, a partial spherical structure is present inside a socket allowing movement in all directions. e.g. hips and arms
• As the name suggests Fixed joint allows no movement to occur. e.g Skull

Figure 2: Types of Joints

Important Points to remember in a Human Skeleton:

• Bones provide support, protection, movement and perform several other functions.
• The bones in the skull (Cranium, Mandible, Maxilla) give protection to the brain.
• The long bones such as humerus, radius, ulna, tibia, fibula support the weight of body
• The carpals are located in wrist and tarsals are located in ankles. They are examples of short bones.
• The bones protecting the spine are called as the vertebral column. Cervical area (top 7 vertebrae), Thoracic (next 12), Lumbar (bottom 5 vertebrae), Sacrum (5 fused or stuck together bones) and Coccyx (the tiny bit at the bottom of the spine).
• The sternum and rib cage constitute the chest bones.

Figure 3: Human Skeleton

Some More Points to Remember

Gait of Animals

1. Earthworm:

• Does not have bones
• Earthworm body is made up of rings
• A slimy substances secreted by its body aids movement (NSO)

Figure 4: Detailed Movement in Earthworm

2. Snail:

• It has a slimy body, which does not have bones.
• The shell of the snail does not help in movement. It has to be carried along.
• The foot of the snail is a thick structure and is made up of strong muscles.
• A muscular organ called ‘Foot’ helps in locomotion.

Figure 5: A Snail

Cockroach	Belongs to Phylum ArthropodaIts Exoskeleton is hard and stiff.3 pairs of legs help in walking and 4 wings help to flyThe body muscles move the wings when it flies
Fish	Presence of scales on the fish skin reduce  frictional dragIt possess a streamlined shape which enhances locomotionCoordination between muscles and tail help the fish to move.Fins aid the movement in the water
Birds	Their forelimbs are modified into wings Presence of hollow and light bones, which reduces weight.Hind limbs help in walking and perchingThey have strong shoulder bones
Snakes	Presence of long backbone and thin muscles.Loops made by its body help in moving forward.Moves fast but not in a straight lineThey cannot move on frictionless surface.

As we all know, Earth is the only planet in our solar system that has the viable conditions for life to exist. While the presence of water and oxygen is the main reason, we must also recognize that life would not have been possible if it weren’t for the oxygen-emitting plants, life would not have been able to take shape on Earth. These plants are not only our source of oxygen but also the major source of the food that we eat.

Herbs, Shrubs and Trees

We can classify plants on the basis of the thickness of their stems and the place of origin of their branches, into three broad categories:

Herb: These are plants that have green and frail stems. Usually, these are small plants with not many branches.

Some common examples of herbs are Basil, Coriander, Mint, Oregano, Thyme, Parsley, Rosemary etc.

Herbs: Small plants with tender stems

Common herb examples

Shrubs: These are plants with hard but not exactly thick stems. Their branches generally originate from the base of their stems. These are much taller than herbs but usually shorter than trees.

Some common examples of shrubs are Aloe Vera, Rose plant, Jasmine plant, Blackberry plant etc.

Common shrub examples

Trees: These are plants which are very tall and have a thick and hard stem. The branches originate from the upper part of the tree and are very high above the ground.

Some common examples of trees are neem, peepal, coconut tree, mango tree etc.

Some common examples of trees

There are two other kinds of plants which are:

Creepers: These are plants which have soft, weak and green stems and hence cannot stand straight and instead spread on the ground.

Some common examples are sweet potato, watermelon, pumpkin etc.

Some common examples of creepers

Climbers: These are also plants with soft and weak stems but instead of spreading on the ground they take support with a nearby object to climb up.

Some common examples of creepers are cucumber, bean, grapevine, money-plant etc.

Some common examples of climbers

Let us observe and study each part of a plant step by step:

Stem

Growth cycle of a common stem

The Stem is the part of a plant which is responsible for supplying water to all parts of the plant. It is the stem which bears branches, flowers, leaves, fruits and buds. The root sucks the water and minerals from the soil and it is the stem’s function to push this water upward to other parts of the plant.

We can observe this by soaking the stem of a plant in a glass with water. On adding coloured ink to the water, we observe that after a while the stem and leaves of the plant start to turn the colour of the ink, which is proof that the stem carries the water to the different parts of the plant.

The experiment helps demonstrate how stems are responsible for carrying water to different plant parts

Leaf

The leaves of plants are majorly responsible for performing two essential functions for the plant’s survival and growth. These two functions are called transpiration and photosynthesis.

Transpiration: Transpiration is the process through which plants release the excess amount of water in the air. When the water travels via the stem to the leaves, some of it gets used up to prepare food, while the excess water is converted to water vapour due to the presence of the sun. Transpiration is important for the plants as it helps the plants to cool down. In the absence of transpiration, the temperature of the leaf becomes unregulated which may lead to the eventual death of the plant.

We can observe transpiration by enclosing a leafy part of a plant in a closed polythene bag and keeping it in the sun. After a while, we see tiny droplets of water on the inside of polythene bags, which are proof that the leaves have performed transpiration.

The process of transpiration

Photosynthesis: Photosynthesis is defined as the process that helps leaves prepare food for the plant with the help of carbon dioxide and water. Photosynthesis occurs in the presence of sun and is aided by the presence of a green pigment in leaves called chlorophyll. Plants also release oxygen in the process. The food prepared is stored in various parts of the plant. In absence of photosynthesis, the plant is unable to utilise the water and minerals to prepare food for its nourishment and gradually dies.

In order to see if leaves really do perform photosynthesis, we take a leaf and immerse it in a test tube filled with spirit. Placing this test tube in a beaker filled with water, we heat the beaker. After the leaf loses its color, we wash it and pour iodine solution on it, as can be seen below, which shows the presence of starch thus disproving our doubts.

Parts of a Leaf

Petiole: This is the stalk via which the leaf is joined to the plant.

Lamina: This is the expanded part or the green portion of any leaf which is responsible for photosynthesis.

Veins: The many lines that run through the surface of the leaf are called veins and the design made by them is called leaf venation. They transport water and minerals.

Midrib: This is the central, prominent thick structure right in the middle of the leaf that helps support the leaf and prevent it from breaking.

A labelled diagram of a leaf

We distinguish between two major types of leaf venation.

Reticulate venation is said to exist when the veins form a net-like shape on either side of the midrib. This type of venation is seen to exist in dicots like guava and mango.

Parallel venation is said to exist when the veins run parallel to one another. This type of venation is seen to exist in monocots like banana, wheat, coconut etc.

Parallel and reticulate venation

Root

The root is a very important component of the plant system, as, without the presence of roots the plant ceases to exist. This is because the roots perform three major functions essential to the growth and survival of the plant which are:

• Roots are responsible for absorbing minerals and water from the soil and transferring them to the stem. It’s only after root has transported water and minerals to stem that the stem becomes capable of transporting these to all parts of the plant.
• Another important function of roots is to firmly anchor the plant in the ground. This is essential to support the upright position of the plants.
• Roots also perform the function of storing important nutrients and food for growth.

There are two major types of roots that exist in plants and these are:

Tap Roots	Fibrous Roots
1. In this type of root system, there is one prominent and long root and a bunch of smaller roots that grow from this main root called lateral roots.	1. In this type of root system, a group of similar sized roots emerge from the base of the plant. They do not have a main root.
2. It is hard to pull out plants with tap roots as these go deep within the soil.	2. These plants are relatively easier to pull out as the roots don’t go very deep in the soil.
3. This root system is seen to exist in plants with leaves displaying reticulate venation.	3. This root system is seen to exist in plants with leaves displaying parallel venation
4. Examples of plants with tap roots: carrots, turnip, gram, gram, China rose etc.	4. Examples of plants with fibrous roots: banana, wheat, maize, onion, bamboo etc.

Flower

The flowers are the colourful, seed-bearing parts of the plant that grows at the end of the stem. A typical flower exhibits the following structure:

Petals: These are bright, colourful and broad parts of the flower. Taken together, the petals of the flower form what is called a Corolla.

Sepal: This is the green, leaf-like structure of the flower that encloses the petals and is responsible for protecting the flower when it is in its bud form and supporting it when it is in its bloom stage.

Stamen: These are the long and slender parts of the flower that become visible upon removing the petals and sepal of a flower. Typically, a stamen consists of an anther i.e. the head of the stamen and a filament i.e. the long cream-colored stick. The stamen is also known as the male reproductive part of the plant.

Pistil: This is the innermost part of the flower, typically consisting of a stigma i.e. the head of the pistil, a style, which is the long sticky part that attaches the stigma to the ovary i.e. the small and swollen sphere at the base of the pistil. Pistil is the female reproductive part of any flower. The ovary contains small bead-like structures which are called ovules.

The structure of a flower

Stamen	Pistil	Ovary

Important Definitions

Stomata: These are the small microscopic pores present on the leaf through which exchange of gases and transpiration takes place.

Annuals: These are plants like wheat and maize that complete their life cycle in one season and then die. They are usually herbs.

Biennials: These are plants like carrots and radishes that complete their life cycle in two seasons.

Perennials: These are plants guava and palm that continue their life cycle for more than two seasons, i.e. they manage to re-grow every spring.

Aerial roots: These are roots of plants and trees that grow above the ground instead of under the ground as shown in the image below.

Aerial Roots

Everything around us is undergoing a process of change. Our hair and nails keep growing. Leaves die and new leaves take their place. While some changes in our environment are temporary and can change back to their original positions, other changes are relatively permanent.

On this basis, changes around us can be classified into two broad categories:

1. Reversible changes
2. Irreversible changes

Reversible changes can be described as changes that can be reversed by reversing the action or changing the conditions. Example: freezing of water, rolling of a chapati from dough etc.

Irreversible changes can be described as changes that cannot be reversed even after bringing about changes in the conditions. Example: rusting of iron, cooking of vegetables etc.

Figure 1 Closing and opening of mimosa leaves represent a reversible change

Figure 2 Cooking of an egg into an omelette represents an irreversible change

Substances and materials usually undergo two major types of changes:

• Physical change: This represents a change not in the chemical identity but the physical form of a substance. When substances undergo a physical change, there is no formation of a new substance and more or less these changes can be reversed. Example: boiling of water and melting of ice represent reversible physical changes while growing of height is an irreversible physical change.

Figure 3 Physical Change

• Chemical change: This represents a change in the chemical identity of a substance. These are irreversible changes because the original substance gets converted into a new substance and cannot be brought back. Example: cooking of rice, burning of matchstick etc.

Figure 4 Chemical Change

Difference between physical and chemical changes:

Physical Change	Chemical Change
A change in matter which occurs without causing any change in the composition of the matter is known as physical change	While a chemical change is defined as the change in the chemical composition of matter
Usually, physical changes are reversible in nature	While chemical changes are often irreversible
No new products are formed when an object undergoes physical change	Chemical changes often lead to formation of new products
These changes have no impact on the molecular composition of the substance	Chemical changes have a direct impact on the chemical bonds and molecular composition of a substance
A few changes occur when cooling or heating is done	These changes involve absorption or release of energy

There are other ways to bring about changes in substances:

• Mixing two substances together: A small amount of curd is added to warm milk which leads to conversion of that milk into curd. This is an irreversible change.

When we add a salt to water it becomes salty but this is a reversible change.

• Expansion and Contraction: In order to make tools like an axe, the ring of its iron blade is heated which allows it to expand i.e. become larger in size and then is allowed to cool down which makes it contract again i.e. become smaller in size leading to a tight fit of the handle.

Figure 5 Curd is added to milk to allow it to set into curd

On a day-to-day basis, we are faced with various instances when we are required to separate substances from one another. Whether it is picking out chillies from our paranthas/poha or separating tea leaves from tea while serving it, the need for separation of substances is something we encounter on a daily basis. It is usually because of one or all three of the following reasons:

• To separate two dissimilar but useful elements like in the case of butter and milk. Milk is churned in order to obtain butter.
• To segregate useless elements from the useful ones like in the case of separating tea leaves from tea.
• To remove and discard impurities or potentially harmful substances like picking out small pieces of stones and other impurities from rice and wheat.

Figure 1 Separating tea leaves from tea

Problems arise when the materials to be separated are really small in size or differ in their composition. It is nearly impossible to separate grains of salt from grains of sand by hand or trying to separate oil from water. We might need to use methods other than simple handpicking even though for a lot of separation processes, even handpicking might be enough.

Methods of Separation

Figure 2 Methods of Separation

• Handpicking: The simple process of separating slightly bigger sized harmful substances or other useful substances or impurities like small pieces of stones, husk and dirt from grains of wheat, pulses and rice is called handpicking. In situations when the quantity of such impurities is not very large, handpicking turns out to be a time-saving and convenient procedure of separating substances.

Figure 3 A group of individuals separating two types of grains

• Threshing: After the crop is harvested, stalks are left to dry under the sun. A single stalk has some 100 pieces of grain seeds joined to it. It is manually impossible to pluck each grain seed which is very small in size from the stalk and hence handpicking as a method of separation does not work here. That is why we use a method called threshing to separate these grain seeds.
  • Thus, Threshing can be defined as the process of separating the edible part i.e. grain seeds from the stalk by either with the help of machines, bullocks or sometimes by beating them.

Figure 4 a) Threshing by hand b) Threshing by machine

• Winnowing: Even when threshing is done, husk or chaff is still attached to the grain seed and since the size of the two is quite similar, handpicking does not work and neither does threshing. Hence, a method called winnowing can be used.
  • Winnowing can be defined as the method of separating lighter husk particles and heavier grain seed components by blowing a current of air through them. The lighter husk particles are carried away by the wind and the grain seeds get separated. This husk can be further used as fodder for the cattle.

Figure 5 Process of winnowing

• Sieving: Sometimes even after the grain seeds have passed through the stages of threshing and winnowing, husk may still be attached to the grain or it may have collected stones and dirt in the earlier stages which need to be removed and this separation is usually done with the help of a sieve.
  • Sieving is a very simple, convenient and time-saving process through which particles of varying sizes can be separated from each other with the help of a sieve. A sieve is nothing but a simple device with small pores in it which allow finer materials like flour to pass through leaving behind any impurities it might contain.

Figure 6 Sieving

• Sedimentation, Decantation and Filtration
  1. Sedimentation: Sedimentation can be defined as the process through which dirt and other heavier particles in a mixture settle at the bottom of the vessel when water is added to it. When the dust and dirt particles have settled, the clear water which forms the upper layer is moved to a different container and the dirt and dust is done away with. This technique can also be used to separate two liquids which do not mix with each other (also called immiscible liquids) and is called decantation.
  2. Decantation: Decantation can be defined as a technique through which immiscible liquids or a liquid and a solid substance are separated. For example, take the case of oil and water. These are two examples of immiscible liquids. Once we pour oil in water, oil forms the upper layer of water and can be easily separated by gently pouring the mixture in another container till all the oil has been removed. Sometimes smaller dirt particles get carried along with the water in the process of decantation which needs to be further removed. This can be achieved through the process of filtration.
  3. Filtration: Filtration is the process through which smaller particles like dirt etc. are separated from a solution by making the solution pass through a medium (often a filter paper). This medium is such that only liquids are able to pass through it because of the presence of very tiny pores in it. The filter paper is molded to form a cone and this cone-like structure is then affixed to a funnel through which the dirty solution is allowed to pass. Sometimes, filtration can also be applied to separate pulp and seeds from the juice. It can also be used to separate cottage cheese or paneer from milk.

Figure 7 Sedimentation, Decantation and Filtration

• Evaporation: Evaporation is the process of converting liquid into gas or vapour by increasing the temperature or pressure of the liquid. This process is often used to separate salt from salt water or salty sea water. Sea water has a number of salts present in it. Shallow pits called evaporation ponds are constructed and salt water is allowed to stand in these. After some time, the water gets evaporated, leaving behind the salts. Common salt is separated from this mixture upon further purification.

Figure 8 Salt Evaporation Ponds

Use of more than one method of separation

Often, we are faced with mixtures and solutions that cannot be separated by use of a single separation technique. A number of such techniques need to be applied simultaneously to achieve the desired result.

Take for example the case of a salt and sand mixture. We know handpicking will not work and considering both of them weigh just about the same, neither will winnowing.

And hence we try to separate the two with the help of filtration or decantation.

We take a beaker and add water to the said mixture of salt and sand. While the salt dissolves in water, the sand deposits at the bottom of the beaker and can be separated from the salt solution with the help of a filter paper or by gently pouring the salt solution in another container. We now have to separate the salt from water, for which we will simultaneously use the methods of evaporation and condensation. While heating the solution in a kettle, we observe that vapour or steam starts to rise from the spout of the kettle. What we then do is allow this steam to come in contact with a metal plate which has some ice on it. When this happens, the steam gets converted to small drops of water which we transfer to another container and thus successfully manage to separate salt which gets left behind in the kettle and the water which we collect in a separate container.

Condensation is the defined as the simple process of converting gas or vapour to its liquid form by decreasing the temperature or pressure exerted on it. This is what we did when we allowed the steam to come in contact with the cold metal plate

Figure 9 Use of more than one method of separation

Can Water Dissolve Any Amount of a Substance?

Even though water can dissolve a number of substances and solutions in it, it has a limit to how much it can dissolve. After a certain point, it stops dissolving any more of that substance and the substance collects at the bottom of the vessel. We say that the solution has become saturated.

A saturated solution is one that contains the maximum possible concentration of a particular solute. For example, if we continue to add increasing amounts of salt to a small quantity of water, there will come a point that the salt will not get mixed with the water and instead deposit at the bottom. At this point, we say that the solution has become saturated i.e. it is now incapable of dissolving any more of the given solute which is in this case, salt.

A salute is defined as a very small element in a solution that is dissolved in a solution.

One way of ensuring that the given amount of water takes more salt even after it has reached its saturation point is by heating the said water. This is because heating the solution helps to increase the solubility of salt or any solute and hence more amount of the same solute can now be dissolved in the same amount of water.

Some Important Definitions

Churning: The process of shaking milk or cream in order to allow lighter particles to come to the surface in order to make butter is called churning.

Pure Substance: This can be defined as a substance composed of only a single type of particle.

Impure Substance: A substance composed of more than one type of particles.

Sublimation: When a solid directly gets converted into vapour, this process is known as sublimation.

Magnetic Separation: This is another method of separation which allows metals (and other articles which are attracted to a magnet) to be separated from a mixture with the help of a magnetic or by applying a magnetic force to it. For example, a mixture of salt and iron filings can be separated with the help of a magnet.