Monthly Archives: October 2022

Introduction

→ Actions like picking, opening, shutting, kicking, hitting, lifting, flicking, pushing, pulling are often used to describe certain tasks.

→ Each of these actions usually results in some kind of change in the motion of an object.

Force

→ A push or pull on an object is called a force.

• Push: When an object is moving away from the applier of force.

• Pull: When an object is moving towards the applier of force.

→ Force is a push or a pull which changes or tends to change the state of rest or of uniform motion, or direction of motion or the shape or size of a body.

→ Force is any action that has the tendency to change the position, shape, or size of an object.

→ Interaction of one object with another object results in a force between the two objects.

→ The effect of force depends on the magnitude and direction of the force.

→ Force applied in the same direction added to one another.

→ Force applied in the opposite direction, the net force is given by the difference of two forces.

→ Force can move a body initially at rest.

→ Force can bring a moving body to rest.

→ Force can change the direction of a moving body.

→ Force can change the speed of a moving body.

→Force can change the shape of a body.

→ Force can change the size of a body.

Muscular force

→ It involves the action of muscles.

→ Animals make use of muscular force to carry out their physical activities and other tasks.

Friction

→ It is an opposing force that acts between surfaces in contact moving with respect to each other.

→ The direction of force of friction is always opposite to the direction of motion.

→ Frictional force always acts between two moving objects, which are in contact with one another.

→ Frictional force always acts opposite to the direction of motion.

→ Frictional force depends on the nature of the surface in contact.

→ Non-contact force come into play even when the bodies are not in contact.

Magnetic force

→ Force acting between two magnets or a magnet and a magnetic material.
Example: iron, steel, nickel, cobalt etc.).

→ It can be attractive and repulsive.

Electrostatic force

→ Force due to electric charges.

→ It can be attractive and repulsive.

Gravitational force

→ It is a kind of attractive force that comes into play because of the mass of a body.
Example: earth’s gravitational attraction.

Pressure

→ The force acting per unit area of surface is called pressure.

• Pressure = Force/Area on which it acts

→ The unit of pressure is Newton per square meter (N/m²), which is also known as Pascal.

→ Smaller the area larger the pressure for the same force.

→ Liquids exerts pressure on the walls of the container.

→ Pressure exerted by liquids increases with depth.

→ Liquids exert equal pressure at the same depth.

→ The pressure at which water comes out of the holes is directly proportional to its depth.

Fluid

→ Substance which can flow and has no fixed shape

• Pressure due to a liquid column of height h (p) = hrg

where, h = Height of column
r = Density of fluid
g = Acceleration due to gravity

→ Pressure inside a fluid increases with increase in depth and density of the fluid.

→  Water and gas exert pressure on the walls of their container.

→ Atmosphere exerts pressure on the surface of the Earth.

• Atmospheric pressure = Weight of the atmosphere per unit area.

Pressure inside our body is equal to the atmospheric pressure and cancels the pressure from out side.

Air surrounding the Earth: atmosphere

Air exerts pressure on its surroundings: thrust on unit area is called atmospheric pressure

Adolescence

→ The time period when the body undergoes changes to reach reproductive maturity is known as
adolescence.

→ It begins around the age of 11 and lasts till about 18 or 19 years of age.

→ Adolescence in girls can begin one or two years earlier than boys.

Puberty

→ The various changes that occur in the body during adolescence marks the onset of puberty.

→ Puberty ends when teenagers attain sexual maturity.

→ Changes that take place during puberty

Increase in height

→ It is caused by the growth in long bones of the arms and legs.

→ Girls grow faster than boys initially but both reach their maximum height by the age of 18
years.

Change in body shape

→ Boys develop broader shoulders, wider chests, and prominent muscles.
→ In girls the region below the waist becomes wider.

Change in the voice pattern

→ Voice box or larynx starts growing during puberty.

→ It protrudes in males in the neck region and is called Adam’s apple.

→ Boys develop deep low-pitched voice.

→ Girls develop high-pitched voice.

Change in activity of sweat and sebaceous glands

→ The activity of sweat glands increases during puberty, resulting in production of more sweat.

→ The oily secretions from sebaceous glands increase. The accumulation of oil and bacterial action leads to acne problems in teenagers.

Changes in sex organs

→ Testes and penis develop completely in boys.

→ Testes start producing sperms.

→ Ovaries develop completely and start producing eggs in girls.

Change in intellectual level

→ The learning capacity of brain increases.

→ Intellectual development takes place during adolescence.

→ Development of secondary sexual characteristics.

Secondary sexual characteristics in boys

→ Appearance of moustaches and beard.

→ Appearance of hair on chest.

→ Growth of hair in genital area and other parts.

Secondary sexual characteristics in girls

→ Increase in breast size

→ Growth of hair in the pubic region.

Hormones

→ Hormones are chemical secretions that bring about various changes in the body.

→ They are produced by endocrine glands.

→ These glands release hormones into blood to reach specific target site.

→ Production of hormones is under the control of hormones produced from pituitary gland.

Characteristics of hormones

→ Hormones act as chemical messengers.

→ They are secreted by living cells/tissues or organs called glands.

→ They are secreted in very small quantities by glands.

→ They act upon specific cells, tissues, or organs called the target sites.

→ They are generally slow in action, but have long lasting effects.

→ They either accelerate or inhibit a reaction.

Endocrine glands

→ Hormones are secreted by endocrine glands such as the pituitary gland, thyroid gland, adrenal gland, pancreas etc.

• Major endocrine glands in humans are

(i) Pituitary
(ii) Hypothalamus
(iii) Pineal
(iv) Thyroid
(v) Parathyroid
(vi) Thymus
(vii) Pancreas
(viii) Adrenal
(ix) Testis in men /ovary in women

→ A feedback mechanism (positive and negative) regulates the action of the hormones.

Pituitary gland

→ It is a pea sized gland situated at the base of the brain. It secretes a growth hormone (GH).

→ It is required for proper body growth.

→ The hyposecretion of growth hormone causes a condition called dwarfism.

→ The hypersecretion causes gigantism in children and acromegaly in adults.

Thyroid gland

→ It is located close to trachea in the neck. It produces a hormone called thyroxine.

→ It is required for regulating metabolism in the body.

→ The hyposecretion of thyroxine causes hypothyroidism.

→ This condition causes abnormalities like simple goitre, myxoedema and cretinism.

→ Lack of iodine leads to deficiency of thyroxine, which results in a disease called goitre.

→ The excess secretion of thyroxine causes hyperthyroidism. It results in high metabolism, protrusion of the eye balls, high BP, nervous tension, etc.

Parathyroid Gland

→ There are four parathyroid glands present on back side of thyroid glands that secrete parathyroid hormone or parathormone (PTH).

→ This hormone regulates the level of calcium ions in the bloodstream.

→ Excess of parathyroid hormone removes calcium from bones and makes them soft.

Pancreas

→ It produces two hormones- Insulin and Glucagon.

→ These hormones maintain blood sugar level.

→ Deficiency of insulin results in diabetes.

Adrenal Gland

→ There are two adrenal glands located one on upper part of each kidney.

→ It has two parts- cortex and medulla.

→ Cortex secretes the hormones like cortisol that regulates the rate of metabolism.

→ The medulla secretes a hormone like adrenaline that prepares the body to face various stressful situations.

Gonads

→ It includes testes in males and ovaries in females.

→ Male sex hormone is testosterone. It is produced by the testes on the onset of puberty.

→ Female sex hormones produced by ovaries are estrogen and progesterone.

→ Deficiency of estrogen causes infertility.

→ Process of Hormonal Action

→ Endocrine glands release their secretions (hormones) into the bloodstream.

→ Hormones, on reaching their target site, bring about necessary changes to maintain proper functioning of the body.

Historical background and Discovery of HIV

→ The first cases of AIDS were recognized in U.S.A in the year 1981.

→ The AIDS virus was first discovered by the team of French scientists lead by Luc Montagnier in1983.

→ In 1984, the American virologist named Robert Charles Gallo gave the first report on the virus causing AIDS.

→ The name HIV was suggested by the International committee on the nomenclature of viruses.

→ In India the firsts AIDS patient was identified in Chennai in the year 1987.

→ AIDS or Acquired Immune deficiency syndrome is a viral disease, caused by the deadly virus (HIV).

Structure of HIV

→ Human Immunodeficiency virus (HIV) is spherical in shape and contains RNA as its genetic material.

→ Externally, the virus is covered by the double layered membrane made up of fatty substances.

→ Inside the fatty membrane a core of proteins is found that surrounds the viral RNA along with the enzyme reverse transcriptase.

Transmission of HIV

→ Sharing of syringes during drug abuse.

→ Unsafe sexual contact.

→ Transfusion of infected blood

→ From infected mother to her infant through milk.

Prevention of HIV

→ Avoid sexual contact with infected persons

→ Ensure use of disposable syringes

→ Screening blood from blood banks

Tests for detection of HIV

→ PCR (Polymerase Chain Reaction)

→ ELISA (Enzyme linked Immuno Sorbent Assay)

→ Western Blot

Personal health and hygiene in adolescents

→ Adolescents should have a balanced diet with right proportions of various nutrients.

→ Adolescents should maintain cleanliness to prevent bacterial infections.

→ They should indulge in some physical exercises to keep their bodies fit.

→ They should avoid the consumption of drugs and alcohol.

Sex determination in humans

• Autosomes: First 22 pairs of chromosomes that do not determine the sex of an individual.

• Sex chromosomes: Last pair of chromosomes, represented as X and Y.

→ Females have two X chromosomes,so can be represented as 44+XX.

→ Males have one X and one Y chromosome, so can be represented as 44+XY.

→ Each gamete receives half of the chromosomes i.e. 22+X or 22+Y.

→ Male gametes have 22 autosomes and either X or Y sex chromosome.

→ Male gametes can be of two types, 22+X or 22+Y.

→ Female gametes can be of only one type, 22+X.

→ Sex of a baby is determined by the type of the male gamete (X or Y) that fuses with the female gamete.

Male Reproductive System

→ It consists of testis, sperm duct and penis.

→ Testes are involved in the production of male gametes called sperms.

→ Millions of sperms are produced by the testes.

→ Each sperm consists of three parts: Head, middle piece and tail.

Female reproductive system

→ It consists of ovaries, oviduct and uterus.

→ Ovaries produce ova or eggs.

→ A single matured egg is released from ovary into oviduct every month.

→ Baby develops in the uterus.

→ Egg is also single celled like sperm.

Fertilization

→ The process of fusion of male and female gametes (egg and sperm) to form zygote is known as fertilization.

→ It is of two types:
(i) Internal fertilization
(ii) External fertilization

Internal fertilization

→ In this, the fusion of sperm and egg takes place inside the female’s body.

→ It occurs in cows, dogs and humans.

External fertilization

→ In this, the fusion of sperm and egg takes place outside the female’s body in a surrounding medium, generally water.

→ It occurs in frogs, fishes, starfish, etc.

Test tube baby

→ A baby conceived by fertilization that occurs outside the mother’s body is called test tube baby.

→ Development of the embryo

→ The zygote repeatedly divides to form a ball of cells.

→ The ball of cells then starts differentiating into tissues and organs. At this stage, it is called embryo.

→ Embryo gets attached to the wall of the uterus and develops various body parts such as hands and legs.

→ Foetus is a stage of embryo that shows main recognizable feature of mature organism.

→ Foetus develops for nine months inside the mother’s womb and is finally delivered.

Fertilization in Humans

→  Fusion of the nucleus of the sperm with the ovum to form a zygote. It occurs in the fallopian tube of females.

→ Zygote divides to form an embryo.

→ Embryo is implanted in the uterus.

→ Foetus develops inside the mother’s body for nine months (gestation period).

Asexual reproduction

→ The type of reproduction which involves only a single parent and the new individuals are formed without the fusion of gametes is known as asexual reproduction.

• Three common methods of asexual reproduction are:
(i) Budding
(ii) Fission
(iii) Cloning

Budding

→ It involves the formation of new individual from the bulging of the parent body.

→ This phenomenon is very common in plants, fungi and animals such as Hydra and yeast.

Fission

→ Binary fission is the type of asexual reproduction that occurs in Amoeba.

→ It is a type of asexual reproduction in which a single cell divides into two halves.

Cloning

→ Cloning is the process used to create an exact copy of a cell, tissue or an organism.

→ Dolly, a sheep was the first mammal to be cloned. It was cloned by Ian Wilmut and his colleagues in 1996.

Oviparous animals

→ The animals that lay eggs are called oviparous animals.

→ The examples include all kinds of birds, lizards, snakes, and frogs.

Viviparous animals

→ The animals that give birth to young ones are called viviparous animals.

→ The examples include cows, dogs, and humans.

Metamorphosis

→ The biological process of transformation of larva into an adult is known as metamorphosis.

• The life cycle of frog consists of the following stages:
Egg → Tadpole (larva) → Adult

→ Hormones controlling metamorphosis in frogs

→ Thyroxin (produced by the thyroid gland) initiates the process of a tadpole’s metamorphosis into an adult frog.

→ In the absence of thyroxin, the tadpole does not transform into an adult and remains in the tadpole stage.

Life cycle of silkworm

→ Silkworm grows on mulberry trees and feeds on its leaves.

→ During a stage in its life cycle, silkworm spins a cocoon around itself.

→ Silk is obtained from this cocoon.

Hormone responsible for metamorphosis in insects

→ In insects, metamorphosis is controlled by the insect hormones. Some of the insect hormones are:
(i) Prothoracicotropic Hormone (PTTH)
(ii) Ecdysone
(iii) Juvenile Hormone (JH)

Cell

Discovery of the Cell
→ Cells are the basic structural units and the building blocks of all living organisms.
→ Cell was discovered by Robert Hooke in 1665 after observing a piece of cork under a magnifying device.

→ Robert Hooke coined the term “cell”.

Cell Theory

→ Schleiden and Schwann proposed the cell theory. 

→ According to cell theory: Cells are the basic structural and functional units of life. 

→ All living organisms are made up of one or more cells.

→ New cells arise from pre-existing cells.

Types of Organisms on the basis of cell

(i) Unicellular Organisms
(ii) Multicellular Organisms

Unicellular organisms

• Number of Cells Organisms made of only a single cell are called unicellular organisms.
For example: Amoeba and Paramecium

→ All the basic functions such as digestion, respiration, excretion, etc. in these organisms performed by a single cell.

Multicellular organisms

• Organisms made up of more than one cells are called multicellular organisms.
For example: Humans, cow, rose, etc.

→ In these organisms, the cells show division of labour as particular set of cells are involved in performing a specific body function. 

Shape of the Cells

→ Most of the cells have a definite shape.

→ Some cells such as that in Amoeba have no definite shape.

→ The human red blood cell (RBC) is spherical-shaped.

→ The muscle cells in humans are spindle-shaped. 

→ The human nerve cells have elongated branched structure. 

→ In plants and bacteria, the cell is enclosed in a protective covering called cell wall, which gives shape and rigidity to the cells.

Size of the Cells

→ The smallest cell is 0.1 to 0.5 micrometre in bacteria.

→ The largest cell is of size 170 mm x 130 mm, which is the egg of an ostrich.

→ Size of a cell has no relation with the size of an organism. 

Cell Structure and Functions

→ In multicellular organisms, each organ system is made up of several organs.

→ Organs are further made up of tissues.

→ Tissues are groups of similar cells performing a specific function.

→ Number of cells Organisms made up of only a single cell are called unicellular organisms.
For example: Amoeba and Paramecium

→ Single cell in unicellular organisms performs all the basic functions such as digestion, respiration, and excretion.

→ Organisms made up of more than one cells are called multicellular organisms.
For example: Humans, cow, etc.

→ In multicellular organisms, the cells show division of labour as a particular set of cells are involved in performing a specific body function. 

Types of cell

There are two types of cells.

(i) Prokaryotic cells
(ii) Eukaryotic cells

• Prokaryotic cells

Cells which do not have a well defined nuclear membrane and the nuclear material lies freely in the cytoplasm of the cell.
For example: bacteria, blue green algae.

• Eukaryotic cells

Cells having nucleus with well defined nuclear membrane.
For example: plant and animal cells

Components of the cell

Cell membrane

→ It is the protective layer that surrounds the cell.

→ Cell membrane selectively allows the entry of only some substances and prevents the movement of other materials. 

→ Hence, it checks the transport of substances in and out of the cell. 

Cell wall

→ In plants, an extra protective covering of a polysaccharide, cellulose is present. 

→ It is called cell wall that protects plant cells from environmental variations. 

Cytoplasm

→ It is a jelly-like substance present between cell membrane and nucleus. 

→ It contains various cell organelles such as mitochondria, Golgi bodies, lysosomes etc.

Nucleus

→ It is a dense spherical body located at the centre of the cell.

→ It is surrounded by porous nuclear membrane.

→ It contains spherical body called nucleolus.

→ It also contains thread-like structures called chromosomes. 

Chromosomes

→ These are the structures that carry genes and play an important role in inheritance. 

→ Genes are the structural and functional unit of inheritance.

→ The entire living substance in a cell is known as protoplast.

Vacuoles

→ Vacuoles are fluid-filled membrane-bound structures in the cell.

→ In plant cells, a single large vacuole is present.

→ In animal cells, numerous small vacuoles are present.

→ The membrane of the vacuole is called tonoplast.


→ This membrane encloses a fluid called cell sap. 

Plastids

→ They are present only in plant cells.

→ Plastids that contain green colour pigment chlorophyll are known as chloroplasts.

→ It is the chlorophyll that gives green colour to the leaves.

→ Chloroplast traps solar energy and utilizes this energy to manufacture food for the plant. 

• Plastids are of two types:
(i) Leucoplasts 
(ii) Chromoplasts 

→ Leucoplasts are colourless and are used to store food while chromoplasts are plastids containing pigments.

→ Chloroplasts are a type of chromoplasts. 

• Chloroplasts consist of two regions:
(i) grana (stacks of sac like membrane bound structures that contain pigment chlorophyll)
(ii) stroma (ground substance containing enzymes and starch grains)

Endoplasmic Reticulum (ER)

(i) Rough Endoplasmic Reticulum (RER): It is important for the synthesis and packaging of proteins.

(ii) Smooth Endoplasmic Reticulum (SER): It acts as storage organelle. It also helps in lipid (fat) synthesis. 

Golgi Apparatus

→ It is made up of parallel arranged membrane-bound vesicles called cisternae. 

→ It helps in storage, modification, and packaging of products in vesicles. 

→ It helps in formation of glycoproteins and glycolipids.

Lysosomes

→ It is a membrane-bound structure that holds variety of enzymes. 

→ Rich in all types of hydrolytic enzymes, which are active at acidic pH. 

→ It is involved in the digestion of carbohydrates, proteins, lipids, and nucleic acids.

Mitochondria

→ It is a double membrane-bound structure. 

→ The inner membrane of mitochondria is deeply folded to form cristae. 

→ Cristae increase the surface area in the organelle.

→ It is the site of cellular respiration and hence known as ‘power house of cell’. 

→ They have their own circular DNA.

→ They divide by fission.

Differences between plant and animal cells

Plant Cells	Animal Cells
Cell wall is present.	Cell wall is absent.
Nucleus is located in the periphery of the cell.	Nucleus is located in the centre of the cell.
Plastids are present.	Plastids are absent.
A large single vacuole is present in the centre of the cytoplasm.	Numerous small vacuoles are present in the cytoplasm.

Diagram of Plant Cells and Animal Cells

Deforestation

→ Deforestation is the process of clearing of forests in order to use the land for industrial, agricultural, and other purposes.

Causes of Deforestation

→ Natural causes
→ Forest fire
→ Severe droughts
→ Man-made causes
→ Using land for agricultural purposes
→ Rapid urbanization
→ Procurement of wood for fuel and furniture

Consequences of Deforestation

→ Increase in the level of carbon dioxide in atmosphere, which leads to global warming

→ Lowering of ground water levels

→ Increase in pollution level and temperature

→ Decrease in fertility of soil and amount of rainfall

→ Increase in frequency of droughts and floods

→ Desertification- conversion of fertile lands into deserts.

Biodiversity

→ Biodiversity is the species richness of the biosphere. It is defined as the number and variety of life forms such as plants, animals and microorganisms in an area.

→ It supports all the essential living resources such as wild life, fisheries and forests.

→ Forests help in maintaining the delicate balance of nature.

→ Animals living in forests are called wild animals.

→ The plants found in a particular area are known as flora of that area.

→ The animals found in a particular area constitute fauna of that area.

→ Those species of plants and animals, which are found only in a particular area, are called endemic species.

→ Species is a group of organisms in population which are capable of interbreeding.

→ The animals, whose numbers are diminishing to a level that they might face extinction, are called endangered animals.
For example: tiger, lion, and elephants

→ Project tiger was launched by the government of India to protect endangered tigers in their natural habitat.

→ The flora and fauna of a particular habitat can be protected through special protected areas.

Protected areas

A protected area is a clearly defined geographical space which is recognised and managed by government to achieve the long term conservation of nature, culture and preserve ecosystem.

Wildlife sanctuary

→ It is the place where wild animals are protected from hunting and are provided with suitable living conditions.
For example: Madhumalai wildlife sanctuary in Tamil Nadu, Chilika bird sanctuary in Orissa, etc.

National parks

→ These are the areas reserved for wildlife. They are maintained and preserved by the government for the public to visit.
For example: Ranthambore National Park in Rajasthan, Kanha National Park in Madhya Pradesh, etc.

→ Satpura National Park is the first reserve forest of India.

Biosphere Reserves

→ It is a large protected land for conservation of wild life, plant and animals resources, and the traditional life of the tribal groups living in the area.
For example: Pachmarhi Biosphere Reserve and Nilgiri Biosphere Reserve in India.

Red Data Book

→ It is the source book maintained by IUCN (International Union for Conservation of Nature and Natural resources).

→ It keeps a track record of various endangered species of plants and animals.

Migration

→ It is the movement of birds and animals from their original habitat to other places at a particular time.

→ Migratory birds fly to distant areas every year during a particular time because of climatic changes their original habitat becomes very cold and inhospitable lack of food availability

→ Numerous migratory birds including ducks, geese, flamingos, and cranes fly to India every year.

Recycling of paper

→ One ton of paper is made from about seventeen fully-grown trees.

→ Papers should be recycled and reused to conserve forest.

→ Each paper can be recycled three to seven times.

→ Recycling of paper saves trees, energy and water.

→ It prevents the release of harmful chemicals emitted during paper manufacturing in nature.

Reforestation

→ Restoring of destroyed forests by planting new trees is called reforestation.

→ It helps in checking environmental degradation.

What is Combustion?

Combustion is a chemical process in which a substance reacts with oxygen and generates heat in the process.

Combustible substances are those substances that undergo combustion. It means that these substances give off heat and sometimes light (as a flame or glow) when they react with oxygen.

Inflammable substances are substances which have low ignition temperature and catch fire easily. They burn with a flame. For example, petrol, LPG etc.

Why do we say that food is fuel for our body?

When we eat food, it gets broken down in simpler substances which react with oxygen and generate energy (or heat). Hence, food is referred to as ‘fuel’ for our body.

Conditions necessary for the Combustion to take place are:

1. Combustion requires fuel.

Combustion only takes place when there is a fuel which produces heat and light when it catches fire. For example, petrol and diesel.

1. Combustion requires air.

We can prove it with the help of the following experiment:

A candle keeps burning in open air. However, when we cover it with a glass or a jar, it only burns until the oxygen inside it is consumed. Once the oxygen is exhausted, the flame of the candle flickers off.

1. Combustion requires heat.

The substance must reach its ignition temperature to catch fire.

Ignition temperature is the lowest temperature at which a substance catches fire or starts burning.

Types of Combustion

• Rapid Combustion: Combustion in which a gas burns quickly producing heat and light in the process. E.g. LPG
• Spontaneous Combustion: Combustion in which a material bursts into flames suddenly without applying heat. E.g. Phosphorus which burns at room temperature.Spontaneous combustion of coal dust often causes accidental fires in coal mines. Heat from the sun or lighting may also cause spontaneous forest fires.
• Explosion: When a material bursts suddenly to produce heat, light and sound on the application of heat or pressure, it is called an explosion. E.g. Crackers and fireworks which release a large amount of gas too.

How do We Control Fire?

We can control the fire by one or more of the following:

• Removing the fuel
• Cutting off the air supply (or oxygen supply)
• Cutting off heat or lowering the temperature of the fuel

How do fire extinguishers work?

Fire extinguishers are devices used to put out fires. They either cut off the air supply to fire or cool off the fuel (below the ignition temperature) or both. The three main types of fire extinguishers are:

1. ‘Dry Powder’ Fire Extinguisher: This type of fire extinguishers contain a mixture of baking soda (sodium bicarbonate) and sand. When you throw it over the fire, the baking soda decomposes by its heat to produce carbon dioxide. Since CO₂ is heavier than air, it descends to envelop the burning flame and cuts off its contact with air (and the oxygen supply).

2NaHCO₃  → Na₂CO₃ + H₂O + CO₂

1. ‘Soda-acid’ Fire Extinguisher: This fire extinguisher is a metallic cylinder which contains the sodium bicarbonate (NaHCO₃) solution. At the bottom of the cylinder, the concentrated sulphuric acid (H₂SO₄) is placed in a thin sealed glass tube. A fixed wire gauze surrounds this tube.

Below the tube, a plunger is placed with its sharp end touching the thin glass tube.

On the top of the cylinder, there is a nozzle which is sealed with wax.

When the plunger hits against the floor, its sharp end breaks the thin glass tube and the acid inside it reacts with sodium bicarbonate to produce carbon dioxide. CO₂ forces the wax seal open and rushes out of the nozzle to put out the fire in the direction where the nozzle is pointed.

1. ‘Foam-type’ Fire Extinguisher: Like the soda-acid fire extinguisher, it uses sodium bicarbonate solution. However, in this case, a substance called Saporin or Turkey Red Oil is added to the solution to produce foam along with the gas from the nozzle. Since this foam is lighter than oil, it floats on the surface of the oil and cuts off its air supply. Hence, it is very effective in putting out oil fires.

When should we use (or not use) water to extinguish the fire?

When wood, paper and clothes are on fire, we can use water to extinguish them. Water lowers the temperature of burning material below ignition temperature and thus, the fire stops burning.

We should not use water when electrical equipment is on fire as water may conduct electricity and give a shock to people dousing the fire. Also, it should not be used when oil or petrol catches fire as water is lighter than oil and petrol and sinks down. Oil and petrol keep floating on the top and keep burning.

What should we do when electrical equipment or inflammable materials (like petrol) catch fire?

Carbon Dioxide is the best fire extinguisher in such cases. CO₂ is heavier than oxygen and hence, covers the burning material like a blanket and cuts off its oxygen supply. Also, it does not harm the electrical equipment.

CO₂ can be stored as a liquid in cylinders at high pressure. When it is released, it immediately expands, cools down, and envelopes the fire – bringing down the temperature of the fuel. One can also pour dry chemicals like sodium bicarbonate (or baking soda) or potassium carbonate on the fire as they release CO₂ near a fire.

Flame

Flame is a hot glowing body of ignited gas which is produced when something is on fire.

Some materials burn with a flame and some do not. Here is a table based on a general observation:

Materials forming Flame on Burning

Material	Forms flame	Does not form a flame
Candle	Forms flame
Magnesium		Does not form a flame
Camphor	Forms flame
Kerosene Stove	Forms flame
Charcoal	Forms flame

Structure of a Flame

A flame has three zones:

1. Outermost zone is blue in colour and is the hottest part of the flame. This is also the zone where complete combustion takes place.
2. Middle zone is yellow in colour and is moderately hot. In this zone, partial combustion takes place.
3. Innermost zone is black in colour and least hot. Here, we can find the unburned wax vapours of a candle.

Note: Kerosene oil and molten wax vapourise during burning but charcoal does not produce flame or vapourise when it burns.

Why do goldsmiths blow at the outermost zone of a flame for melting gold and silver?

The outermost zone of a flame is its hottest part. Gold and silver have high melting points and hence, goldsmiths blow at the outermost zone of the flame to melt gold and silver quickly.

What is a Fuel?

Fuels are substances that give us heat which we use for domestic and industrial purposes, such as wood, kerosene, and petrol.

What will an ideal fuel or good fuel look like?

Ideally, a good fuel is one which:

• has proper ignition temperature (neither too high nor too low),
• does not produce undesirable or poisonous substances and cause pollution,
• does not leave behind much ash,
• is cheap,
• is readily available,
• produces a large amount of heat or have high calorific value,
• has a moderate rate of consumption,
• is easily controllable (can be started or stopped as needed),
• is easy to handle and transport, and
• has low moisture content (so that it burns easily).

Note: Some fuels are cheaper than others.

Fuel Efficiency

Fuel efficiency of a fuel depends on its calorific value.

The calorific value of a fuel depends on the amount of heat produced by complete combustion of 1 kg of the fuel. The unit used to measure the calorific value of a fuel is kilojoule per kg (kJ/kg).

Calorific Value of Common Fuels We Use

If we look at the table, we will see that hydrogen seems to be the most efficient fuel followed by LPG. CNG and Methane come next, closely followed by Kerosene, Diesel and Methane. Cow dung cake seems to be the least efficient fuel here.

Uses of Fuels

Some of the ways in which common fuels are used are:

1. Gasoline is used in cars, scooters and other vehicles we use every day.
2. Natural gas is used in heating systems, water heaters, dryers, and stovetops in our homes.
3. Oil and natural gas are used in making several things that we use every day. Hydrocarbons, for example, are used in making plastics, pharmaceuticals and several other items we use daily.
4. Coal is the primary fossil fuel used in many thermal power plants to produce electricity.

Types of Fuels

Fuels can mainly be divided into three groups:

• Liquid Fuels: Petroleum (which is a fossil fuel), crude oil (from which we get petrol or gasoline), diesel, kerosene oil etc.
• Solid Fuels: Firewood, charcoal, coal (fossil fuel which is mined as steam coke or soft coke), dung cakes, tallow (animal fat), straw and other agricultural wastes, paraffin wax, camphor etc.
• Gaseous Fuels: Most commonly used gas is LPG (Liquid Petroleum Gas) which we use as cooking gas at home. Some of the other commonly used gaseous fuels are:
  • We get CNG (Compressed Natural Gas) from natural oil wells.
  • Natural gas (or methane) gets released from the putrefying organic matter.
  • Butane gas is obtained from natural gas.
  • In the villages, animal dung and farm waste are used to produce biogas. Biogas is also collected from sewage plants.
  • When hard coke is heated and converted into coke, coal gas is produced.
  • Water gas is produced by passing steam over red-hot coke.
  • Acetylene used a gas produced by adding calcium carbide to water. Its smell is a bit unpleasant but the flame it produces is so hot that it is used for cutting metals and welding purposes.

Harmful Effects of Burning Fuels

1. Carbon fuels like wood, coal and petroleum release ash and fine unburnt carbon particles in the air which can cause respiratory diseases like asthma. These fine particles are referred to as Suspended Particulate Matter (SPM).
2. Incomplete combustion of fuels (such as coal, gasoline and other fossil fuels) releases carbon monoxide gas which is very poisonous and can kill people sleeping in the room where coal is burning. CO combines with haemoglobin in our blood to form carboxyhemoglobin and renders it incapable of transporting oxygen. These fuels also release unburnt hydrocarbons, many of which are carcinogenic (cause cancer) and pose serious health hazards.
3. Carbon dioxide released by most fuels during combustion is causing an imbalance in the atmosphere. Deforestation is also leading to a situation where there are fewer trees to absorb the carbon dioxide. This is leading to global warming.
4. Burning of coal and diesel releases sulphur dioxide gas which is corrosive in nature and causes irritation in nose, throat and airways. It also causes shortness of breath, wheezing, and a feeling of tightness around the chest. Petrol engines release gaseous oxides of nitrogen. These sulphur and nitrogen oxides dissolve in rainwater to form acids and cause acid rain.

Global warming is the rising temperature of the Earth’s atmosphere which is causing the melting down of glaciers making the sea levels rise and causing floods in coastal areas. It is caused due to the elevated levels of carbon dioxide in the atmosphere as CO2 absorbs infrared radiation emitted by the Earth and radiate it back to the atmosphere and raise its temperature. This is also known as the ‘greenhouse effect’.Acid Rain refers to the rain of acids that is very harmful to crops, soil, animals, and buildings. These acids are formed when sulphur and nitrogen oxides dissolve in rainwater. Acid rains also damage trees at high elevation (such as red spruce that grows 2,000 ft above sea level), causes acidification of lake or stream water, and damage forest soils. Irreplaceable buildings, statues and sculptures which are part of a nation’s cultural heritage can get destroyed due to acid rain.

Why do we not burn wood anymore?

Wood is a low-cost fuel and is easily available but burning it releases a lot of smoke which causes respiratory problems. Moreover, cutting of trees for wood (as fuel) also leads to deforestation. Hence, people now prefer to use coal or LPG as fuel instead.

Why should we use CNG as automobile fuels?

CNG is a cleaner fuel and causes much less pollution than petrol and diesel. Hence, we should use CNG-powered vehicles now.

How to Conserve Fuels?

To conserve fuels, we should:

• Collect all material required while cooking at one place before switching on the gas,
• Check the pressure of tyres regularly,
• Choose walking over using cars or motorbikes for short distances, and
• Use public transportation for travelling instead of private vehicles.

Introduction

→ There are two types of resources:
(i) Inexhaustible Natural Resources (Renewable sources of energy)
(ii) Exhaustible Natural Resources (Non-renewable sources of energy)

Inexhaustible Natural Resources

→ They are renewable sources of energy that are replenished at a rate faster than that at which they are consumed.

→ These resources are present in unlimited quantity in nature and are not likely to be exhausted by human activities.

Examples:

→ Tidal energy, wave energy, ocean thermal energy.

→ Solar energy: Solar cooker, solar water heater (very efficient for small scale electricity production)

→ Geothermal energy: Heat energy inside the earth

→ Nuclear energy: Not dependent on solar energy, never-ending source, very efficient source, more environment friendly.

Exhaustible Natural Resources

They are non-renewable sources of energy are those that are consumed at a rate faster than that at
which they are replenished. The amount of these resources in nature is limited which can be exhausted by human activities.

Examples:

→ Forests, wildlife, minerals, coal, petroleum, natural gas etc.

→ Fossil fuels: Coal, petroleum and natural gas
Advantages of using fossils fuels:
Easy availability
Generate heat that is easily converted into electricity.

→ Coal, petroleum, and natural gas were formed from the dead remains of living organisms. Hence, they are known as fossil fuels

→ Resources such as coal and petroleum are limited. Burning of such fuels is the major cause of air pollution. Therefore, these fuels should be used only when necessary.

→ Burning of fossil fuels releases gases like carbon dioxide which cause greenhouse effect.

Coal

→ It is a fossil fuels which is hard solid and black in colour.

• Story of Coal

→ Due to natural processes, the dense forests got buried under the soil.

→ Under high temperature and high pressure, dead plants got slowly converted to coal.

→ The slow process of conversion of dead vegetation into coal is called carbonisation.

• Uses of Coal

→ It is used as fuel to cook food. Earlier, it was used in railway engines to produce steam.

→ It is used in thermal power stations to generate electricity.

→ Coke, coal tar, and coal gas are the products of coal.

Products from coal

Coke

→ It is a tough, porous and black substance.

→ It is the pure form of carbon and is used in the extraction of steel and many other metals.

Coal tar

→ It is black, thick liquid with unpleasant smell.

→ It is the mixture of about 200 substances.

→ The products obtained from coal tar are used as starting materials for dyes, drugs, paints, perfumes, etc.

Coal gas

→ It is obtained during the processing of coal to obtain coke.

→ It is used as a fuel in many industries situated near the coal processing plants.

Petroleum

→ Petroleum was formed from the dead organisms present in the sea.

→ Petrol, diesel, kerosene, paraffin wax, lubricating oil, and petroleum gas are the products of petroleum.

→ The process of separating various constituents of petroleum is known as refining.

→ Refining of petroleum is done in fractionating column.

→ Components with higher boiling points are collected at the bottom of the fractionating column.

→ Components with lower boiling points are collected at the top of the column.

Petroleum and its uses

Constituents of Petroleum	Uses
Petroleum Gas in Liquid form (LPG)	Fuel for home and industry.
Petrol	Motor fuel, aviation fuel, solvent for dry cleaning
Paraffin wax	Candle, Vaseline, Ointments etc.
Diesel	Fuel for heavy motor vehicles, electric generators
Kerosene	Fuel for stoves, lamps.
Lubricating oil	Lubrication.
Bitumen	Paints, road surfacing

→ Complete combustion of hydrocarbons lead to formation of carbon dioxide and water, while incomplete combustion of hydrocarbons yield carbon monoxide and water.

→ Carbon dioxide as well as carbon monoxide are responsible for pollution in our environment.

→ The test used to determine the amount of carbon monoxide in vehicle’s exhaust gases is known as emission test.

→ Gas analyzer is used in detection of carbon monoxide in exhaust gases.

→ Petroleum is a natural resource

→ The formation of petroleum takes place over a period of millions of years.

→ Petroleum reserves are limited i.e. they are found only in a few places on the Earth.

→ The ever increasing population has further increased the demand for petroleum and its products.

→ In India, the Petroleum Conservation Research Association (PCRA) advises people on the various methods that can be adopted to conserve petrol/diesel.

Cracking

→ Heating higher alkanes to sufficiently high temperatures in absence of oxygen, in order to obtain lower hydrocarbons is known as cracking or pyrolysis.

Natural Gas

→ Natural gas is formed from dead organisms which decompose in the absence of air under conditions of high pressure and temperature.

→ It is stored under high pressure as compressed natural gas (CNG). It is used as a fuel for vehicles because it is a cleaner fuel (less polluting).

Introduction

→ Materials are classified in two types i.e. metals and non-metals.

→ Metals can be distinguished from non-metals on the basis of their physical and chemical properties.

Metals

Physical properties of metals

→ They have shining surface in their pure state. It is also called metallic lustre.

→ They are generally hard. The hardness varies from metal to metal.

→ Metals are malleable. This means it can be made thin sheets by beating.

→ Ductile which means it can be drawn into thin wires. As an example, Gold is highly ductile metal.

→  The are good conductors of heat and have high melting point.

→ The conduct electricity.

→ Most of metals are sonorous which means it can produce sound.

Chemical Properties of metals

→ Metals combine with oxygen to form metal oxides.
2Cu + O₂ → 2CuO
4Al + 3O₂ → 2Al₂O₃

→ Most metal oxides are insoluble in water.
If metal oxides are soluble, they form alkali.
Na₂O + H₂O → 2NaOH
K₂O + H₂O → 2KOH

→ Sodium, potassium react very easily with O₂. So, they are kept immersed in kerosene.

→ Mg, Al, Zn, Pb form thin layers of oxides when kept in open.

Reaction of metals with water

→ Metals produce metal oxide + H₂ on reaction with water.
If oxide is soluble, then metal hydroxide is formed.

→ Magnesium doesn’t react with cold water.

→ Al, Zn, Fe do not react with H₂O, but react with steam.
2Al + 3H₂O → Al₂O₃ + 3H₂
3Fe + 4H₂O → Fe₃O₄ + 4H₂

Non-metals

Physical properties of non-metals

→ Non-metals are found in all the three states i.e. solid, liquid and gas, at room temperature.

→ Iodine (non-metal) has lustre.

→ Carbon has allotropes which means it exists in different forms.

→ Diamond is hard and Graphite conducts electricity.

Difference between Metals and Non-metals

Metals	Non-metals
Generally, these are hard and lustrous.	These are soft and have no lustre.
These are malleable and ductile.	These are non-malleable and non-ductile
These are sonorous (produce ringing sound when struck).	These are not sonorous.
These are good conductors of heat and electricity.	These are poor conductors of heat and electricity.
These react with oxygen to produce metal oxides, which are basic in nature.	These react with oxygen to form non-metallic oxides, which are acidic in nature.
These react with acids to produce metal salts and hydrogen gas.	These do not react with acids.
Some metals react with bases to produce hydrogen gas.	Reactions of non-metals with bases are complex.

Reaction with Acids

→ Metal + Dilute acid → Metal salt + H₂

→ H₂ doesn’t evolve in the case of HNO₃ as it is a strong oxidising agent. It oxidises H₂.

→ Cu does not react with acids like dilute H₂SO₄ and dilute HCl.

• Aqua regia

→ Freshly-prepared concentrated HCl and concentrated HNO₃ in 3:1 ratio

→ It can dissolve even gold and platinum.

Reaction with Bases

→ Metals react with bases to produce hydrogen gas.

→ Reactions of non-metals with bases are complex.

Uses of metals

→ In making machinery, automobiles, jewellery, trains, aeroplanes, cooking utensils, etc.

→ Gold is used for making jewellery, wires, and coins and in dentistry.

→ Silver is used for making coins, ornaments, very thin wires, table cutlery and in photographic films.

→ Copper is used for making wires, utensils, statues, alloys and coins.

→ Iron is used for construction of ships, buildings, automobiles and railway bridges etc.

→ Tin is used for tinning food cans, and making alloys.

→ Lead is used for making batteries, and alloys.

→ Zinc is used in prevention of rusting, making brass and bronze and in dry cells.

→ Aluminium is used in making wires, foils, and alloys.

→ Mercury is used for making amalgams and in thermometers.
→ Magnesium is used for making fire works, and alloys.

Uses of non-metals

→ They are used in fertilizers, in water purification process, crackers, etc. Oxygen, a non-metal, is essential for our life as all living beings inhale it during breathing.

→ Nitrogen dilutes the activity of oxygen in air. It is used by plants to manufacture proteins.

→ Oxygen is essential for respiration and combustion of fuels.

→ Chlorine is used for bleaching fabrics, sterilization of drinking water, and in manufacturing insecticides and pesticides.

→ Iodine is essential for proper functioning of human body, and in photographic films.

→ Graphite is used as pencil lead, dry lubricant, in electrolytic cells and nuclear reactors.

→ Helium is a noble gas which is used in weather observation balloons.

→ Argon is a noble gas which is used for filling electric bulbs.

Types of Reactions

• Displacement reactions

In this reactions, a more reactive metal displaces a less reactive metal from their compounds in aqueous solutions. (However, a less reactive metal cannot displace a more reactive metal.)
Example:
CuSO₄ (Blue) + Zn → ZnSO₄ (Colourless) + Cu (Red)
(Copper Sulphate + Zinc → Zinc Sulphate + Copper)

Pb + CuCl₂ → PbCl₂ + Cu

• Double displacement reaction

In this reaction, exchange of ions occurs between two compounds.

Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Alloys

→ Alloys are homogeneous mixtures of two or more metals (or metal and non-metal). Alloying is done to enhance the properties of metals.

→ Alloys of aluminium are also useful as they are both light and strong. Some of its alloys are duralumin, magnelium, etc.

→ Some alloys of iron are steel, stainless steel, etc. Steel is an alloy of iron and carbon.

→ Some alloys of zinc are brass, bronze, and German silver.

→ On the basis of composition, alloys are of two types: Substitutional alloys in which atoms of one element randomly replace the atoms of another metal. And interstitial alloys in which small atoms like hydrogen, boron, carbon and nitrogen occupy the holes in the crystal structure of the metal.

• On the basis of constituent elements, alloys are of two types:
→ Ferrous alloys: They contain iron as base metal. Example: steel, alnico etc.
→ Non ferrous alloys: They do not contain iron as base metal. Example: brass, bronze, duralumin etc.

Fabrics are made by weaving fibres (or threads) obtained from natural or artificial sources. They can be of two types:

What are Synthetic Fibres?

What is a synthetic fibre made up of?

A synthetic fibre, as well as plastic, is made up of a chain of small units (called Monomers) which combine to form polymers.

Monomers: A monomer is a single molecule that can bond with other identical molecules to form polymers through a process called Polymerization.

Polymers: Polymer is a Greek word in which ‘poly’ means ‘many’ and ‘mer’ means units. Hence, polymers are large molecule made up of several molecules (or monomers) linked together.

Example of Polymers:

• All synthetic fibres, such as Rayon and Nylon, are polymers.
• Polymers are also found in Nature. ‘Cotton’ is a polymer called ‘Cellulose’. ‘Cellulose’ is made up of a number of single units (or monomers) called ‘Glucose’.

Polymerization Reaction: The process of linking small monomers together to form polymers is called Polymerization.

Types of Synthetic Fibres 

Rayon

Rayon is a versatile fibre and can imitate the feel and texture of silk, wool, cotton and linen with drape and slipperiness akin to nylon.

Why Rayon is called artificial silk?

Rayon resembles silk in appearance, texture and shine. Hence, it is also known as Artificial Silk.

Silk fibre was discovered in China and made from silkworms. It had a beautiful texture and was very costly. By the end of the 19^th century, scientists managed to make an artificial silk-like fibre made by treating wood pulp chemically.

Uses of Rayon

This man-made fibre uses natural material (wood pulp) and can be woven like silk fibre. It is cheaper than silk and can be dyed in a variety of colours. It can be:

• Make apparels like suits, slacks, jackets etc.
• Make automobile tyre cords (because of its strength)
• Mixed with cotton to make bedsheets and bedspreads
• Mixed with wool to make carpets and blankets
• Used to make other home furnishings, such as curtains and tablecloths

Nylon

Nylon is the first synthetic fibre to be prepared without using any natural raw materials (materials produced by plants and animals).

Which properties make Nylon suitable for:

Making Ropes used for Rock Climbing: Strong fibre, Lightweight, Weather Resistant

Making Fishing Nets: Strong, Elastic, Water Resistant

Making Tents: Strong, Light, Does Not Absorb Much Water, Dries Quickly

Uses of Nylon

Developed in 1931, this thermoplastic silky material is strong, elastic, light, lustrous and easy to wash. A nylon thread is, in fact, stronger than a steel wire. Hence, it is used to:

• Make clothes (including socks)
• Make parachutes as well as ropes for rock climbing
• Make ropes, toothbrushes, and car seat belts etc.
• Make tents, curtains, and sleeping bags

Polyester

Polyester fibre does not get wrinkled easily. Hence, a fabric made from this fibre is easy to wash and does not need to be ironed – which makes it suitable for dress material.

Polyester is made up of two words – ‘poly’ which means many, and ‘ester’ which is a chemical.

Esters are chemicals which give fruits their smell.

Name some types of Polyester fibres.

Some popular polyester fibres are:

• Terylene (often known by brand name Dacron) which can be drawn into a very fine fibre and can be woven like any other yarn.
• Polyethylene terephthalate (P.E.T.) is used for making wires, films, bottles, utensils and other products.

What are blended fibres? Give some examples.

Blended fibres are formed by mixing natural and synthetic fibres. Polyester is often used in blended fibres. For Example,

• Polywool is made by mixing polyester and wool.
• Polycot is made my mixing polyester and cotton.
• Terrycot is made by mixing Terylene and cotton.

Uses of Polyester

Since polyester is strong, wrinkle-resistant and water-resistant, it has several uses. It can be used to:

• Make a variety of textiles (including sarees, curtains, dress materials etc.) and can be blended with natural fibres (like cotton and wool)
• Make films, magnetic recording tapes, etc (as Mylar)
• Make sails of sailboats
• Make water hoses for firefighting purposes

Acrylic

Acrylic is a strong, lightweight and warm synthetic fibre that resembles wool. It is available in a number of colours and is more durable and affordable than natural wool.

Acrylic fibre, fabric, plastic or paint are all made from acrylic acid. The word ‘acrylic‘ means ‘containing acryl (or acrolein)‘ Acrolein is the sharp and bitter liquid in onions and has its roots in two Latin words – ‘acer’ which means ‘sharp’, and ‘olere’ which means ‘to smell’.

Why storage of acrylic clothes is easier than woollen clothes?

Woollen clothes need naphthalene balls to protect them from attack by insects. Acrylic is synthetic wool and is hence, resistant to the action of moths and insects.

Uses of Acrylic Fibre

Acrylic can mimic wool as well as cotton at times and is hypoallergenic in nature. It means that people who have sensitive skin can wear it easily. Some acrylic fibres are very resilient – more than other natural or synthetic fibres. It can be used to:

• Make woollen clothes like hats, scarves, gloves, sweaters, blankets, and other home-furnishing fabrics.
• Make fake fur used for making toys and fur accessories.
• Make garments for babies (as the fabric is machine-washable).

Characteristics of Synthetic Fibres

What are synthetic fibres made up of?

All the synthetic fibres are manufactured by processing raw materials of petroleum origin in a number of ways. The raw materials of petroleum origin are called Petrochemicals.

Why should we not wear synthetic clothes in the kitchen?

Synthetic fibres melt on heating. If the clothes catch fire, the fabric made up of synthetic fibres will melt and stick to one’s body. Hence, it is recommended that one should not wear synthetic clothes while working in the kitchen or laboratory.

Plastics

Plastic is a polymer (like the synthetic fibre) which can be moulded into different shapes. The word ‘plastic’ originates from the Greek word ‘plastikos’ which means ‘that can be moulded or shaped’. Plastic polymers can have different types of arrangement of monomers:

Plastic can be recycled and used. It can also be melted, rolled into sheets, made into wires, and coloured.

Some popular types of plastics are:

Plastics as Materials of Choice

Advantages of Plastic
Lightweight	Lower price	Good strength	Easy handling	Not-reactive(does not rust like iron when exposed to water and air, and doesnot corrode easily)	Poor conductor of heat and electricity

Give Reasons Why:

Buckets are made of plastic these days.

Plastic buckets are strong, lightweight, and do not rust.

Bakelite plastic is used to make electrical switches.

Bakelite is a poor conductor of heat and electricity. Hence, they would not give anyone an electric shock when someone touches the switch.

Melamine is used to make crockery.

Melamine is unbreakable, fire resistant, and tolerates heat better than plastics. Hence, it can be used to make crockery that can hold hot liquids or dishes served in it.

Plastics are used in cars, aircraft and spacecraft.

Plastics are strong, durable, lightweight, and corrosion-resistant.

Chemicals are stored in plastic bottles.

Plastic bottles are lightweight, unbreakable, corrosion-resistant, and are resistant to the action of chemicals. Hence, they are suitable for storing chemicals.

Which plastic is used to make:

Non-stick coating on Cookware: Teflon

Insulation covering on Wires: PVC

Polythene Bags: Polythene

Flame-resistant Uniforms: Melamine

Special uses of Plastic

Besides being used in packaging for food and non-food items and several daily-used items (such as furniture, electrical switches, slippers etc.), plastic also has special uses such as:

• Used in the healthcare industry for packaging of tablets, syringes, doctor’s gloves, a number of medical instruments, and threads for stitching wounds.
• Used to make cookware used in microwave ovens
• Used as a non-stick coating on cookware (made of a special plastic called Teflon is used on which oil and water do not stick)
• Used to make the fire-resistant uniform for firefighters (made of Melamine)

Plastics and the Environment

Plastic is a threat to the environment as it is non-biodegradable. Its disposal is a big problem.

Biodegradable: Material which gets decomposed through natural processes (such as bacterial action) is called Biodegradable.

Non-biodegradable: Material which cannot be easily decomposed by natural processes is called Non-biodegradable.

How do plastics cause environmental pollution?

Plastics cause pollution as they:

• are non-biodegradable, and
• release toxic fumes when burnt (and hence, cause air pollution).

5 Rs to Minimize the Environmental Damage caused by Plastic

Refuse: Do not buy things we do not need.

Reduce: Minimize the use of plastics in our daily lives.

Reuse: Reuse the items we already instead of throwing them away.

Repurpose: If we are not using something, alter or change to use it in a different way.

Recycle: Some plastic waste can be sorted and made into other things in recycling factories. This helps us to reduce our carbon footprint.

How can we minimize pollution caused by plastics at home?

We should use jute, cotton, or paper bags instead of plastics. We also need to minimize the use of plastic in our daily lives (such as using a steel lunch box instead of a plastic one). Also, we should not throw plastics on the road or in the water bodies.

What are Microbes? Microbes or microorganisms are tiny organisms which are so small that we cannot see them with an unaided eye. Some microorganisms can be seen with the help of a magnifying glass (such as fungus that grows on bread) while some can only be seen when you use a microscope (such as bacteria and protozoa). Microorganism were first observed by Anton Van Leeuwenhoek. Viral, Bacterial, and Protozoan Diseases
Causes	Diseases
Viruses	Common Ailments: Cold, Cough, and Influenza (or Flu) Serious Diseases: Polio, Chicken Pox, Measles etc
Bacteria	Typhoid and Tuberculosis (TB) etc
Protozoans	Dysentery and Malaria etc
Table 1: Microbial Diseases

Microorganisms

There are four major types of microorganisms:

Fig 1: Types of Microorganisms

• Bacteria: These are single-celled organisms with a rigid cell wall. They can only be seen under a microscope which enlarges images from 100 to 1000 times.

Fig 2: Ultrastructure of a Bacterial Cell

Types of Bacteria (based on their Shapes) and their Examples

Shape of Bacteria	Example	Image
Comma-shaped Bacteria	Fig 3: Vibrio Cholera	Vibrio Cholerae
Spherical-shaped Bacteria (Cocci)	Fig 3: Streptococcus	Staphylococcus and Streptococcus
Rod-shaped Bacteria (Bacilli)	Fig 4: Salmonella	E.coli and Salmonella
Spiral-shaped Bacteria (Spirilla)	Fig 5: Borrelia	Treponema and Borrelia

Table 2: Shapes of Bacteria (with Examples)

• Fungi: These are non-green plants and hence, cannot make their own food. They either live as parasites (deriving nutrition from host organisms, for example, Puccinia which causes wheat leaf rust) or grow on the organic matter (such as bread mould). 

Fig 7: Puccinia triticina

Fig 8: Bread Mould

Fungi, like mushrooms, moulds, mildews, and years, are eukaryotic. It means that they have a true nucleus.

The  main components of fungi are:

i. Hyphae: They are thread-like filaments which penetrate into substrates, secrete enzymes to break down nutrients into smaller molecules, and absorb them.

ii. Spores are a unit of sexual or asexual reproduction. They can adapt for dispersal and survival for extended periods of time in unfavourable conditions.

• Algae : These are simple plant- like organisms which are usually aquatic in nature. They contain a cell wall and chlorophyll and can make their own food by photosynthesis.Algae can be unicellular or multicellular. Some of the common examples are diatoms, Chlamydomonas, and seaweed.
• Protozoa: Protozoa are unicellular are organisms. Some of them live independently while others live as parasites. Many of the parasitic protozoans cause diseases in plants, domestic animals, and human beings. Example of some protozoans are  Amoeba, Plasmodium and Paramecium

​

Fig 9: Paramecium

How are Viruses different from other microbes?

Viruses are microscopic organisms but they are different from other microbes because they reproduce only inside the cells of the host organism (which can be a plant, animal, or a bacterium).

Fig 10: Types of Viruses

Viruses are much smaller than bacteria and come in a wide variety of shapes and sizes. A complete virus particle is known as Virion.
Virion consists of a nucleic acid surrounded by ‘capsid’. Capsid is a protective coat made of protein. The subunits of this protein called ‘Capsomeres‘. Viruses can be seen only by an electron microscope as they are ultramicroscopic in size.

Outside the body of a living organism, they do not show any reaction and hence, can be crystallized and stored like non-living things.

Where do Microorganisms Live?

Microbes can survive in all kinds of environments – from icy cold climates to hot springs (any kind of temperature); and deserts to marshy lands (any humidity level). Some live independently while others live as parasites – inside the bodies of other organisms (including animals and human beings).

Microorganisms and Us

Some microorganisms are beneficial to us while others are harmful and cause diseases.

How are bacteria useful to us?

Bacteria are helpful because:

• It decomposes organic wastes (such as vegetable peels, animal remains, and faeces etc.).
• It is used in the preparation of medicines.
• It increases soil fertility by fixing nitrogen.
• It is used in the setting of curd and making cheese, pickles, and other food items.

How is yeast useful to us?

Yeast is used in the baking industry (to make bread, pastries, and cakes) because it helps in fermentation. It reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the carbon-dioxide gas it produces fill the spaces in the dough and increases its volume.

It is also used in the commercial production of alcohol and wine which is done by growing yeast on natural sugars present in fruit juices and grains like rice, wheat, and barley.

Antibiotics

What are Antibiotics? What are their uses?

Antibiotics are medicines that can kill or stop the growth of disease-causing microorganisms. For Example, Penicillin.

Antibiotics are used to:

• Cure a variety of diseases (such as streptomycin, erythromycin, and tetracycline that are made from bacteria and fungi),
• Cure microbial infection in animals (by mixing antibiotics with the feed of livestock and poultry), and
• Control several plant diseases.

What precautions should be followed while taking antibiotics and why?

Antibiotics should be taken only on the advice of the doctor, and one must complete the course the doctor prescribes.

Antibiotics taken in wrong doses may make the body resistant to the drug and it may not be effective in the future. Moreover, antibiotics may also kill the beneficial bacteria in the body.

Please Note: Antibiotics cannot cure cold and flu caused by viruses.

Vaccines

Some Definitions to Remember:Pathogens: Disease-causing microbes are called Pathogens. Antibodies: Antibodies are substances our body produces to fight disease-causing microbes. Vaccines: Vaccines are weakened or dead disease-causing microbes that are injected in our body to trigger the production of antibodies. These antibodies remain in the body for a long time to protect it against any attack of disease-causing microbes. Vaccination: The process of protecting the body from pathogens with the help of vaccines is called Vaccination.

Name some of the diseases which can be prevented by vaccines

Some of the diseases that can be prevented by vaccination are:

• Cholera,
• Hepatitis,
• Smallpox, and
• Tuberculosis.

One can get necessary vaccines from nearby hospitals.

How do microbes clean up the environment?

Microbes or microorganisms decompose organic waste and dead remains of plants and animals and convert them into simpler substances (which can again be used by other plants and animals) by the process of biodegradation. Thus, they help us in getting rid of harmful and smelly substances and clean up the environment.

Harmful Microorganisms

Some Definitions to Remember:Communicable Diseases: These are microbial diseases (diseases caused by microbes) that spread from one infected person to a healthy person through air, water, food or physical contact,  such as cholera, chicken pox, common cold and tuberculosis. Carriers: Insects and animals that carry disease-causing microbes and transfer them from one place to other are called carriers or vectors, such as house flies and mosquitoes.

How do houseflies transfer pathogens?

A housefly may sit on the garbage and animal excreta and the pathogens stick to their body. When they sit on uncovered food, these pathogens get transferred to the food. When someone eats this contaminated food, he or she may fall sick.

To avoid this, we must keep the food covered.

Name the carriers of:

Malaria

Female Anopheles mosquito (carries the parasite of malaria called Plasmodium)

Dengue

Female Aedes mosquito (carries the dengue virus called Flavivirus)

Common Diseases and their Modes of Transmission

How to prevent diseases that spread through air or contact?

To prevent diseases that spread through the air, keep the patient in complete isolation and keep his or her personal belongings away from others. Vaccination at the suitable age can prevent the onset of tuberculosis, chicken pox, polio, and measles.

How to prevent diseases that spread through water or food?

To prevent the spread of polio, cholera, typhoid and hepatitis A, vaccination is effective. One should also maintain personal hygiene and good sanitary habits and drink boiled drinking water.

One should also eat properly cooked food to avoid diseases like cholera.

How to prevent diseases that spread through mosquitoes?

We can stop the spreading of diseases caused by mosquitoes (such as malaria and dengue) by not allowing the mosquitoes to breed. We should keep our surroundings clean and dry, and not let water collect anywhere – in coolers, tyres, and flower pots etc.

We should also spray insecticides and use mosquito repellents and mosquito nets to protect ourselves from mosquito bites.

Common Diseases and the Microorganisms that cause them

Diseases Caused by Microorganisms in Animals

Anthrax: A dangerous disease that affects human and cattle is caused by a bacterium called Bacillus Anthracis.

Foot and mouth disease in Cattle: It is caused by a virus called Foot-and-mouth-disease Virus (FMDV) or Picornavirus.

Diseases Caused by Microorganisms in Plants

Microorganisms can cause diseases in plants and reduce crop yield. Some of the plants in which they cause diseases are:

The plants can be protected by using chemicals that kill these microbes.

Common Diseases in Plants caused by Microbes

Citrus Canker is caused by Bacteria and spreads through Air.

Rust of Wheat is caused by Fungi and spreads through Air or Seeds.

Yellow Vein Mosaic of Okra (Bhindi) is caused by Virus and spreads through Insects.

Food Preservation

Why do we need to preserve food?

We need to preserve food because microorganisms that grow on food can sometimes produce toxic substances which are poisonous to us. If we consume this spoilt food, we can become seriously ill or die. Hence, we need to preserve food from being spoilt.

Common Methods of preserving food are:

Nitrogen Fixation

Nitrogen constitutes 78% of our atmosphere.

In living organisms, it is found in:

• Proteins,
• Nucleic Acids,
• Chlorophyll, and
• Vitamins.

Atmospheric nitrogen cannot be used directly by the plants and animals. It gets fixed by either lightning or natural nitrogen fixers.

Nitrogen Cycle

A step-by-step explanation of Nitrogen Cycle

• Nitrogen Fixation: Atmospheric nitrogen is converted by lightning or certain bacteria like Rhizobium, Azotobacter and blue-green algae (present in soil) into compounds usable by plants.
• Nitrification: Ammonia conversion into nitrites by Nitrosomonas and further conversion of nitrites into nitrates by Nitrobacter. Plants take up nitrogen in form of ammonia or nitrates.
• Assimilation: Roots of plants absorb these nitrogenous compounds from soils and plants use them to synthesize proteins and other compounds.
• Animals feeding on plants get these proteins and nitrogen compounds.
• Ammonification: When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into compounds that can be used by plants again.
• Denitrification:Nitrates can be converted  into nitrogen gas which is released back in the atmosphere by certain bacteria. Eg. Pseudomonas