PSEB Notes

This PSEB 8th Class Science Notes Chapter 11 Force and Pressure will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 11 Force and Pressure

→ Force is a push or a pull that produces or tends to produce a change in the state of a body.

→ The effect of force depends not only on the magnitude of force but also depends on the area on which it is applied.

→ Force can change the speed, the direction of motion, and the shape of an object,

→ There are various types of forces such as muscular, magnetic, electrostatic, gravitational, and frictional.

→ Force acting per unit area is called pressure.

→ Liquids and gases apply pressure on the surfaces of the container.

→ The atmosphere also exerts pressure, called atmospheric pressure.

→ The pressure exerted by liquids at a given depth is equal in all directions.

→ The pressure of a column of liquid depends on its depth. The more the depth of the liquid column, the more is the pressure.

→ Gases exert pressure in all directions.

→ Force: It is defined as an external cause that changes or tends to change the state of rest or of uniform motion of an object. It is a vector quantity.

→ Resultant Force: When two or more forces act on a body simultaneously, then a single force that produces the same effect as the combined effect of all the forces together, is called resultant force.

→ The force of Friction: The force which opposes the motion of one body over another body in contact with it, is called the force of friction or simply friction.

→ Gravitation: Gravitation is the attraction between any two bodies (particles) in the universe.

→ Weight: The weight of a body is the force with which the body is attracted towards the centre of the earth.

→ Pressure: Force acting per unit area is called pressure.

→ Atmospheric Pressure: Pressure exerted by the atmosphere on all the objects lying on the earth is called atmospheric pressure.

This PSEB 8th Class Science Notes Chapter 10 Reaching the Age of Adolescence will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 10 Reaching the Age of Adolescence

→ It is after growing up to a certain age that human beings and other animals become capable of reproduction.

→ On crossing the age of 10 or 11 in human beings there is a sudden spurt in growth.

→ Growth is a natural process.

→ The period of life when the body undergoes changes, leading to reproduction maturity is called adolescence.

→ Adolescence begins at the age of 11 and lasts upto 18 or 19 years of age.

→ Adolescents are also called teenagers.

→ The human body undergoes severe changes during adolescence which marks the onset of puberty.

→ The most conspicuous change during puberty is height.

→ The rate of growth in height varies in different individuals.

→ All the body parts do not grow at the same rate.

→ Height also depends on the genes inherited from parents.

→ At puberty, the voice box begins to grow. Generally, girls have a high-pitched voice, whereas the voice in boys is deep.

→ During puberty, the secretion of sweat glands and sebaceous glands also increases.

→ Endocrine glands release hormones directly into the bloodstream.

→ Adolescence is also a period of change in a person’s way of thinking.

→ The appearance of secondary sexual characters helps in distinguishing males from females.

→ Changes occurring in adolescence are controlled by hormones which are the chemical substances secreted by endocrine glands.

→ Hormones are secreted by endocrine or ductless glands.

→ The endocrine glands are the pituitary, adrenal, thyroid, and gonads.

→ The pancreas is an exocrine as well as an endocrine gland.

→ Pheromones are the hormones present in insects.

→ An endocrine gland does not have a duct and is, therefore, also called a ductless gland.

→ A ductless or endocrine gland pours its secretion into the circulatory system of the body for sending to the target cells.

→ Secretions of endocrine glands are called hormones.

→ Testes or male gonads are mixed organs that produce sperms as well as male sex hormones or androgens (e.g., testosterone, androsterone).

→ Ovary secretes estrogen and progesterone hormones.

→ The cyclic changes that occur every 28 days (lunar month) in the reproductive tract of human females from the period of puberty to the age of menopause are called the menstrual cycle.

→ At the age of 45-50 women stop menstruation. It is called menopause.

→ There are 23 pairs of chromosomes in humans.

→ There are 22 pairs of autosomes and 1 pair of sex chromosomes in human beings.

→ The change from larva to adult is called metamorphosis. These changes are also controlled by hormones.

→ The physical and mental well-being of an individual is regarded as an individual’s health.

→ Diet for an adolescent has to be carefully planned as it is a stage of rapid growth and development.

→ Personal hygiene is more necessary for teenagers because the increased activity of sweat glands makes the body smelly.

→ All adolescents should take walks, do exercise and play other games.

→ Adolescence: Children between the ages of 10 or 11 years to 18 or 19 years are called adolescents. This period of the age is called adolescence.

→ Puberty: It is a period (11 to 18 years) when the reproductive organs start functioning.

→ Voice Box: It is a box consisting of cartilages present in the throat of human beings causing voice.

→ Adam’s Apple: In boys, the growing voice box is seen as a protruding part of the throat called Adam’s apple.

→ Secondary Sexual Characters: In boys and girls some characters are present which helps to distinguish them. These are called secondary sexual characters.

→ Endocrine Glands: The ductless glands present in animals which secrete hormones and pour them directly into the bloodstream are called endocrine glands.

→ Hormones: These are the chemical secretions secreted by endocrine glands to control the activities of the human body.

→ Target Site: It is a particular body part where hormones released by the endocrine glands through the bloodstream reach.

→ Pituitary Gland: It is a master gland present in the brain.

→ Testosterone: It is a male hormone secreted by the testes at the onset of puberty.

→ Estrogen: It is a female hormone released by the ovaries at the onset of puberty which makes the breasts develop.

→ Sex Chromosomes: Human beings have 23 pairs of chromosomes. One pair out of them (23rd pair) is called a sex chromosome.

→ Thyroxine: It is a hormone secreted by the thyroid gland situated in the neck.

→ Insulin: It is a hormone secreted by the pancreas which controls sugar levels in the blood.

→ Adrenalin: It is a hormone secreted by the adrenal gland which maintains the salt balance in the blood.

→ Balanced Diet: A diet that contains the various components of food (carbohydrates, fats, proteins, minerals, vitamins, water) in the right proportion.

→ Health: The physical and mental well-being of an individual is regarded as an individual’s health.

This PSEB 8th Class Science Notes Chapter 9 Reproduction in Animals will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 9 Reproduction in Animals

→ Reproduction ensures the continuation of similar kinds of individuals, generation after generation.

→ All living organisms reproduce to create more of their own kind. This process is called reproduction.

→ There are two main methods of reproduction.

• Asexual reproduction
• Sexual reproduction

→ In asexual reproduction, a new individual is formed from a single parent.

→ Living organisms reproduce asexually by the following five methods:

• Binary fission
• Budding
• Spore formation.
• Vegetative reproduction
• Regeneration

→ In sexual reproduction, two parents are needed to produce new individuals.

→ The male parent produces male gametes and the female parent produces female gametes.

→ The union of male and female gametes is known as fertilization.

→ There are some organisms in which both the gametes exist in the same individual. Such organisms are called hermaphrodites.

→ The fertilization in some animals is internal and in others external.

→ The process of forming specific shapes and patterns and increasing in size is called development and growth.

→ The growth of parts involves changes in shape, size, and number of constituents.

→ In plants the growth is indefinite but in animals it is definite.

→ The process of formation of the individual from seed, zygote, or body part is called development.

→ There are different ways for the development of individuals.

→ Sexual reproduction is highly evolved.

→ Male Reproductive System consists of a pair of testes, two epididymis, two vasa differentia, accessory glands, two ejaculatory ducts, urethra, and a copulatory organ or penis. Except for testes, all others are secondary male sex organs.

→ The female Reproductive System is made up of a pair of ovaries, a pair of oviducts, uterus, vagina, external genitalia, accessory genital glands, and mammary glands. Except for the first, all others are secondary female sex organs.

→ Semen is a milky fluid produced by the male reproductive system and ejaculated during orgasm.

→ It contains spermatozoa and secretions of glands (seminal vesicles, prostate gland, and Cowper’s glands).

→ The penis is the male copulatory organ that also takes part in the conduction of urine from the body.

→ Spermatazoan (Sperm) is a motile, microscopic male gamete.

→ A typical spermatozoan consists of 4 parts – head, neck, middle piece, and tail.

→ Cloning is the production of an identical cell, carries another living part of a complete organism.

→ The cloned animals are found to be born with severe abnormalities.

→ Sexual Reproduction: A kind of reproduction in which the union of two opposite sexes (male and female) accomplishes fertilization is called sexual reproduction.

→ Asexual Reproduction: A kind of reproduction in which new ones are produced from a single parent is called asexual reproduction.

→ Egg: It is a female gamete produced by the ovary of a female.

→ Sperms: These are male gametes that are produced by the testes of males.

→ Fertilization: The union of male gamete (sperm) and female gamete (egg or ovum) is called fertilization.

→ Zygote: A single-celled structure formed by the union of sperm and egg is called a zygote.

→ Internal Fertilization: Fertilization that takes place inside the body of a female body is known as internal fertilization.

→ External Fertilization: Fertilization that takes place outside the body of females is called external fertilization.

→ Embryo: The zygote divides repeatedly into a structure called an embryo.

→ Foetus: The stage of development of an embryo in which all the body parts are identifiable is called foetus.

→ Viviparous Animals: The animals which produce young ones are known as viviparous animals.

→ Oviparous Animals: The egg-laying animals are known as oviparous animals.

→ Metamorphosis: The drastic change which transforms a larva into an adult is called metamorphosis.

→ Budding: The kind of asexual reproduction in which a new individual develops from the buds is called budding.

→ Binary Fission: A kind of asexual reproduction in which two individuals are produced simply by dividing itself is called binary fission.

→ Cloning: Cloning is the production of an exact copy of a cell or a complete organism.

This PSEB 8th Class Science Notes Chapter 8 Cell Structure and Functions will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 8 Cell Structure and Functions

→ All living things carry out certain basic functions.

→ Roots, stems, leaves, and flowers are the organs of plants.

→ Animals have also parts such as hands, feet, legs, etc.

→ You cannot observe small pores in your skin without the help of a magnifying lens.

→ All living organisms take and digest food, respire, and excrete waste products.

→ Each organism represents an individual of its own kind.

→ Cells in living organisms are complex structures unlike bricks in a building.

→ Cells found in living organisms show a variety of numbers, shapes, and sizes.

→ Single-celled organisms like Amoeba, Paramecium, and Bacteria are called unicellular organisms.

→ Cells in multicellular plants and animals have a variety of shapes. Cells are generally round or spherical in shape.

→ The yellow part of the hen’s egg is called yolk and it is surrounded by white albumen, yellow yolk represents a single cell.

→ All cells are bounded by a membrane called plasma membrane or cell membrane.

→ Plasma membrane encloses a liquid substance known as protoplasm.

→ The cell wall is present in plant cells which are made up of cellulose.

→ Both the plasma membrane and cell wall give shape to the cell.

→ Ostrich egg represents the largest cell visible to the unaided eye.

→ Each cell has smaller components called cell organelles.

→ Cell multiplies and organisms become multicellular and grow in size.

→ Cells in the living organism are basic structural units.

→ Different groups of cells perform a variety of functions.

→ The number of cells being less in smaller organisms does not affect the functioning of the organisms.

→ WBC in human blood is also single-celled.

→ A group of cells performing a definite function is called a tissue.

→ Each organ is made up of a number of tissues.

→ Organ: These are the smaller parts of all living organisms. Each organ is made up of a number of tissues.

→ Tissue: A group of cells performing a definite function is called a tissue.

→ Cell: It is the basic structural and functional unit of all living organisms.

→ Unicellular: Some living organisms are made up of only a single cell that performs all the metabolic functions. Such organisms are called unicellular.

→ Multicellular: Some organisms are made up of a number of cells. Such organisms are called multicellular. In these organisms, different cells perform different functions.

→ Pseudopodia: These are finger-like false feet of amoeba.

→ White Blood Cell (WBC): These are some of the components of blood cells that engulf harmful foreign materials. These are single-celled.

→ Cell Membrane or Plasma Membrane: It is a thin covering present outside the cell which gives shape to it.

→ Cytoplasm: It is a liquid portion present between the cell membrane and nucleus of a cell.

→ Organelles: These are the living components of cells present in their cytoplasm.

→ Cell Wall: It is an extra covering present around the cell membrane of only plant cells. It gives shape and rigidity to the cell.

→ Nucleus: It is the round part of the cell which is called the controlling centre of the cell.

→ Nucleolus: It is a component of the nucleus which is dense and has a spherical body.

→ Nuclear Membrane: The nucleus is separated from the cytoplasm by a membrane called the nuclear membrane.

→ Prokaryotes: The organisms whose cells are without a well-organized nucleus i.e. lacking nuclear membrane are called prokaryotes.

→ Eukaryotes: The organisms whose cells have a distinct and clear nucleus bounded by the nuclear membrane are called eukaryotes.

→ Vacuole: The fluid-filled organelles present in a cell are called vacuoles.

→ Plastids: Small coloured bodies present in plant cells only are called plastids.

→ Chloroplasts: Green plastids present in plant cells are called chloroplasts.

→ Gene: Genes are dot-like structures present on chromosomes that help in the inheritance of characters from parents to the next generation.

→ Chromosome: These are thread-like structures present in the nucleus of a cell.

This PSEB 8th Class Science Notes Chapter 7 Conservation of Plants and Animals will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 7 Conservation of Plants and Animals

→ These days the forests are being cut down and that land is used for other purposes.

→ Some natural causes of deforestation have been forest fires and severe drought.

→ Deforestation increases the temperature and pollution on the earth. It disturbs the balance in nature.

→ Deforestation also leads to global warming, change in soil properties, results in soil erosion, leads to a decrease in water holding capacity of the soil.

→ The government has framed rules, methods, and policies to protect and conserve plants and animals in forests.

→ The biosphere is that part of the earth where organisms live or which supports life.

→ Biodiversity can be defined for a specified geographical region, or for the entire biosphere.

→ Biosphere reserves are the areas meant for the conservation of biodiversity.

→ The plants and animals found in a particular area are known as flora and fauna respectively of that area.

→ A species is a group of populations that are capable of interbreeding with each other.

→ The areas where wild animals are protected and preserved area known as wildlife sanctuaries.

→ It provides protection and suitable living conditions to wild animals.

→ Sometimes the protected forests are not safe because the people living in the neighbourhood encroach upon them and destroy them.

→ National parks preserve flora, fauna, landscape, and historical objects of an area.

→ The forest teak of India is found in Satpura National Park.

→ Project Tiger was launched on 1st April 1973 by our government to protect the tigers of our country.

→ Endangered animals are those which are facing extinction.

→ The ecosystem consists of plants, animals, and micro-organisms in an area alongwith non-living components.

→ Red Data Book is a book that keeps a record of all the endangered animals and plants.

→ Migratory birds fly too far away from specific areas every year during a particular time because of climatic changes.

→ Paper is one of the important products we get from forests. So we should save paper.

→ Reforestation is the restocking of the destroyed forests by planting new trees.

→ Biodiversity: It refers to the variety in life existing on earth, their interrelationships, and their relationships with the environment.

→ Deforestation: Cutting and clearing trees on a large scale is called deforestation.

→ Desertification: The conversion of fertile land into the desert is called desertification.

→ Ecosystem: The relationship between a living community and its non-living environment is known as an ecosystem.

→ Reforestation: It is the restocking of the destroyed forests by planting new trees.

→ Endangered Species: The species which are facing the danger of extinction are called endangered species. e.g. Leopard, Wild dog, etc.

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

→ Red Data Book: A book that contains a record of all the endangered species is called a red data book.

→ Endemic Species: These are exclusively found in a particular area only which may be any geographical unit.

→ Flora: The plants found in a particular area constitute the flora of that area.

→ Extinct: It means the disappearance of the species from the earth.

→ Migration: Going far away from the original habitat of some species during a particular period of the year is called migration.

→ Sanctuaries: These are the places where killing or capturing any animal is strictly prohibited.

→ National Parks: These are the reserves or places which preserve flora, fauna, landscape, and historical objects of an area.

→ Biosphere Reserves: It is a specified area in which multiple uses of land is permitted by dividing it into certain zones and each zone is specified for a particular activity.

This PSEB 8th Class Science Notes Chapter 6 Combustion and Flame will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 6 Combustion and Flame

→ Fuels of different varieties are used for various purposes.

→ Fuels are used in homes, industries, automobiles.

→ Cowdung, wood, coal, charcoal, petrol, diesel, natural gas. L.P.G. etc. is various fuels.

→ Some fuels burn with flame and some do not give a flame on burning.

→ Combustion is a chemical process in which a substance reacts with oxygen to give off heat and light.

→ Fuel is a substance that gives off heat and light on burning.

→ Food is fuel to one’s body.

→ Fuels can be classified into solid, liquid, or gas fuels.

→ The substance which can burn to give light and heat are called combustible substances.

→ The non-combustible substance cannot react with oxygen on burning and cannot give light or heat.

→ Wood, Paper, Kerosene oil, Straw, Charcoal, Match sticks are combustible substances.

→ Iron nails, stone pieces, glass, etc. are non-combustible substances.

→ The lowest temperature at which a substance catches fire is called its ignition temperature.

→ The burning of various combustible materials requires different temperatures.

→ Inflammable substances are those substances that have very low ignition temperature and they easily catch fire with a flame.

→ Petrol, Diesel, LPG, alcohol are a few examples of inflammable substances.

→ Forest fire is very harmful.

→ Oxygen is necessary for combustion.

→ Three requirements for producing fire are:

• Presence of oxygen
• Presence of combustible substance
• Minimum ignition temperature of the substance

→ To control fire, one of the requirements for combustion is to be removed.

→ Water is mainly used to control fire as it lowers the ignition temperature.

→ Oil or petrol fire cannot be controlled by water as water is heavier than oil, it gets settle down below the oil and oil continues to burn.

→ Being a good conductor of electricity water is also not used in case of fires produced by short-circuiting.

→ Sand/soil is used to control fires caused by the burning of liquid fuels or electricity.

→ Fires can be controlled either by cutting off the supply of air or bringing down the ignition temperature or removing the combustible substance.

→ Different types of fire extinguishers are used to control fire.

→ Combustion is of many types such as Rapid combustion, Spontaneous combustion, Explosion.

→ Flame is formed by the burning of vapours or combustible substances.

→ The Blue non-luminous zone of the flame is the hottest part of the flame.

→ A luminous zone of flame usually contains unburnt particles of carbon.

→ The calorific value of a fuel is energy produced by the complete combustion of kg of the fuel.

→ The unit of calorific value in kilojoules per Kg (KJ/Kg).

→ No fuel is an ideal fuel.

→ The burning of fuels is caused by air pollution, health hazards, global warming, acid rains, etc.

→ Global warming is a slow rise in the temperature of the environment of the earth.

→ Nitrogen and Sulphur oxides produced by the burning of fossil fuels, dissolve in water to produce acid rains.

→ Acid rain is harmful to crops, buildings, and soil.

→ CNG is a clean fuel as it causes no air pollution.

→ Combustion: It is a chemical process in which a substance reacts with oxygen to give off heat and light.

→ Combustible Substance: The substance which on burning produces light and heat, is called a combustible substance.

→ Non-Combustible Substance: The substance which cannot produce light and heat and cannot react with oxygen on burning is called a non-combustible substance.

→ Ignition Temperature: The lowest temperature at which a substance catches fire, is called its ignition temperature.

→ Inflammable Substance: The substance which has low ignition temperature and catches fire easily.

→ Fire Extinguisher: A device used to control fire.

→ Combustion: The process of burning fuel to give light and heat.

→ Calorific Value: The energy produced by the complete burning of 1 kg of fuel.

→ Global Warming: The slow rise in temperature of the environment of the earth.

This PSEB 8th Class Science Notes Chapter 5 Coal and Petroleum will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 5 Coal and Petroleum

→ Various materials are necessary for basic needs.

→ Materials needed can be classified into

• Natural materials
• Man-made materials

→ Materials obtained from nature are called natural resources.

→ Natural resources are soil, water, minerals, plants, and forests.

→ On the basis of the availability of various resources in nature, they are classified as Exhaustible and In-exhaustible natural resources.

→ The resources which are unlimited in nature and cannot be finished or exhausted by human activities are called Inexhaustible Natural Resources.

→ The resources which are limited in nature and can be exhausted by human activities are called Exhaustible Natural Resources.

→ Coal, Petroleum, and Natural gas are Exhaustible Natural Resources.

→ Fossil fuels are formed from the dead remains of living organisms and include coal, petroleum, and natural gas.

→ Coal is hard, black in colour, and is used as a fuel.

→ On burning, coal produces carbon dioxide gas.

→ Destructive distillation of coal produces coke, coal tar, and coal gas.

→ Coke is a tough, porous black substance and is a pure form of carbon.

→ Coal tar is a mixture of about 200 substances. It is a black thick liquid with an unpleasant smell.

→ Coal tar is starting material for synthetic dyes, drugs, explosives, plastics, perfumes, paints, photographic chemicals, roofing material, Naptha balls, etc.

→ Petroleum is a dark oily liquid with an unpleasant odour. It is a mixture of many constituents.

→ Constituents of petroleum include LPG, Petrol, Diesel, Kerosene, Lubricating oil, Paraffin wax, and Bitumen.

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

→ Coal and Petroleum are limited in nature. So they should be used judiciously.

→ LPG is Petroleum gas in liquid form.

→ Fuels: The substances which are burnt to produce heat energy.

→ Fossil Fuels: The combustible substances that were formed from the remains of the plants and animals which got buried under the surface of the earth over millions of years.

→ Carbonisation: The slow process of conversion of plants and animals buried inside the earth under high temperature and pressure to produce coal.

→ Destructive Distillation of Coal: The process of heating coal to high temperatures (above 1000°C) in the absence of air.

→ Refining: The process of separating petroleum into useful fractions and removal of undesirable impurities.

→ Exhaustible Natural Resources: Those resources which are being finished by the Various activities of human beings are called exhaustible resources or limited natural resources. Examples: coal, petroleum and natural gas, etc.

→ In-exhaustible Natural Resources: Those resources which can not finish or exhaust by human activities are called in-exhaustible or unlimited natural resources. Examples: air, water, and solar light, etc.

This PSEB 8th Class Science Notes Chapter 4 Materials: Metals and Non-Metals will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 4 Materials: Metals and Non-Metals

→ Materials can either be metals or non-metals.

→ Metals differ from non-metals in physical and chemical properties.

→ All metals share certain physical and chemical properties.

→ Metals are usually shiny, hard, sonorous, malleable, and ductile.

→ They conduct heat and electricity.

→ They are solids at room temperature with the exception of mercury which is liquid.

→ They have high melting points.

→ Non-metals exhibit a dull luster.

→ They are poor conductors of heat and electricity, non-sonorus, and are brittle.

→ They exist as solids, liquids, or gases at room temperature.

→ They have low melting points.

→ Metals usually combine with oxygen to form basic oxides.

→ Non-metals usually combine with oxygen to form acidic oxides.

→ Rust is formed by the action of water and air on iron.

→ Some metals react with water. Sodium reacts vigorously even with cold water forming sodium hydroxide and hydrogen. Gold does not react even with steam.

→ Sodium is stored in kerosene oil.

→ Phosphorus is kept in water as it reacts vigorously with air.

→ Non-metals do not react with water.

→ Some metals react with acids (hydrochloric acid) and replace hydrogen atoms in their molecules.

→ Gold, copper, and silver are unaffected by hydrochloric acid.

→ Metals in their increasing order of reactivity with oxygen, water, and acid are Gold, Silver, Copper, Iron, Zinc, Aluminium, Magnesium, and Sodium.

→ More reactive metals replace less reactive metals from their compounds.

→ Hydrogen gas burns with a pop sound.

→ Metals have wide use in industry, kitchen, household items transport, etc.

→ Non-metals are also widely used.

→ Oxygen is essential for life sustenance.

→ Nitrogen is used in fertilizer and crackers.

→ Iron, Magnesium, Sodium, etc. are needed by the human body.

→ Malleability: The property by which metals can be hammered/beaten into sheets.

→ Ductility: The property by which metals can be drawn into wires.

→ Sonorus: The property of metals to give a ringing (tinkling) sound when struck.

→ Lustre: The property of materials having a shining appearance.

→ Conductance: The property by which heat or electricity can be transferred from one end of a metal to another end.

→ Acidic Oxides: The oxides of non-metals are acidic oxides as they dissolve in water to give acids.

→ Basic Oxides: The oxides of metal the basic in nature as they form bases on the addition of water.

This PSEB 8th Class Science Notes Chapter 3 Synthetic Fibres and Plastics will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 3 Synthetic Fibres and Plastics

→ Clothes are made of fabrics.

→ Fabrics are made by using fibres.

→ Fibers can be obtained from natural or artificial sources.

→ Synthetic fibres are also known as man-made or artificial fibres.

→ Synthetic or natural fibres are chains of small units joined together. Long chains are called polymers.

→ Cellulose is a natural polymer.

→ Rayon, Nylon, Polyester, or Acrylic are man-made fibres.

→ The Source of natural fabric (cotton, silk, etc.) is plants or animals.

→ The Source of artificial fabric is either plants (wood) or fossil fuels (coal etc).

→ Nylon was the first fully synthetic fibre.

→ Different fabrics have different strengths, water holding capacities, cost, durability, availability, and maintenance requirements.

→ Plastics are also polymers having different types of arrangement of units.

→ Plastics are of two types:

• Thermoplastics
• Thermosetting plastics

→ Polythene is a type of plastic.

→ Plastic is a light, strong, durable, non-corrosive, poor conductor of electricity and heat.

→ Plastic waste is not environmentally friendly. It is non-biodegradable.

→ On burning, it produces harmful gases and a bad odour.

→ Dumping in the soil makes the soil barren because it does not decompose quickly.

→ 4R principle (Reduce, Reuse. Recycle and Recover) must be used for the disposal of synthetic waste.

→ Man-made Fibres: The fibres made by human beings are called man-made fibres.

→ Polymer: A large unit made up of a chain of smaller units of chemical substances or a large unit made up of many repeating units.

→ Rayon: A synthetic fibre having properties of silk and is also known as artificial silk.

→ PET: A familiar form of polyester used for making bottles, films, ropes, and utensils, etc.

→ Thermoplastic: A type of plastic that gets deformed on heating and can be bent easily is known as thermoplastic.

→ Thermosetting Plastic: A plastic that does not get deformed on heating is called thermosetting plastic. It can be moulded only once.

This PSEB 8th Class Science Notes Chapter 2 Microorganisms: Friend and Foe will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 2 Microorganisms: Friend and Foe

→ Micro-organisms are very small organisms that can be seen with the help of a microscope.

→ Micro-organisms can survive in almost all kinds of environments like hot springs, ice-cold water, saline water, desert soil or even in marshy land.

→ Micro-organisms are classified as bacteria, fungi, protozoa, algae, and viruses.

→ Micro-organisms exist in all types of habitats.

→ Generally, they are single-celled (unicellular) sometimes occur in a chain or group of cells.

→ Micro-organisms play an important role in our life.

→ Bacteria are present almost everywhere and are smaller in size.

→ The average size of bacteria is 1.25 times one-thousandth of a millimeter in diameter.

→ Bacteria are divided into three types

• Bacillus or rod-shaped
• Coccus or round-shaped
• Spirillum or spiral

→ Bacteria are autotrophic as well as heterotrophic in nutrition.

→ Bacteria reproduce by cell division or binary fission.

→ There are many similarities between algae and bacteria.

→ They are called cyanobacteria. They are helpful in fixing atmospheric nitrogen and in increasing soil fertility.

→ Diatoms are microscopic algae that occur in springs, estuaries, sediments, and the ocean.

→ Fungi are saprophytic or parasitic in their mode of nutrition.

→ Some fungi damage and spoil food products, leather, paper, and textile whereas others are pathogenic to crops and animals.

→ Yeasts are unicellular and saprophytic fungi used in fermentation to produce beer, wine, and other beverages.

→ Viruses are the smallest parasitic organisms that have the ability to replicate inside the living cells.

→ Protozoans are unicellular organisms that cause serious diseases like dysentery and malaria.

→ Food poisoning is due to the consumption of food spoilt by some microorganisms.

→ Micro-organisms that grow on our food produce toxic substances.

→ The common methods used to preserve our food are chemical methods, salting, sugar, oil, and vinegar, by heat and cold treatments.

→ Protozoa: These are single-celled microorganisms, which may cause some serious diseases like dysentery and malaria.

→ Fungi: Fungi are non-green plants (micro-organisms) that spoil most of the food items.

→ Virus: These are micro-organisms that are present on the borderline between living and non-living. They reproduce only inside the host organism.

→ Bacteria: Bacteria are microorganisms that are present almost everywhere ant) are smaller in size. They are autotrophic as well as heterotrophic in nutrition.

→ Yeast: Yeast is fungi that are unicellular used in fermentation to produce beer, wine, and other beverages.

→ Rhizobium: It is a bacteria that helps in the fixation of nitrogen. It is present in root nodules of leguminous plants.

→ Soil Fertility: It means enriching the soil with nutrients especially nitrogen. It is done by some bacteria and blue-green algae.

→ Micro-organisms: These are very small organisms that cannot be seen with the naked eye. They can only be seen under a microscope. They exist in all types of habitats.

→ Microbes: The other name of micro-organisms is a microbe.

→ Lactobacillus: The bacteria present in curd is called lactobacillus which promotes the formation of curd.

→ Carriers: Carriers are insects and other animals which carry the disease-carrying micro-organisms.

→ Antibodies: When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader.

→ Antibiotics: These are the chemicals that are produced by micro-organisms and are used to kill harmful micro-organisms.

→ Vaccine: It is a dead or weakened microbe which is introduced into a healthy body.

→ Pathogen: The disease-causing micro-organism is called a pathogen.

→ Fermentation: The conversion of sugar into alcohol with the help of micro-organisms is called fermentation.

→ Nitrogen Fixation: The process of conversion of atmospheric nitrogen into nitrites and nitrates with the help of Rhizobium bacteria is called nitrogen fixation.

→ Nitrogen Cycle: When atmospheric nitrogen after going through various phenomenon like nitrogen fixation, nitrification, denitrification again enters the atmosphere, it is called the nitrogen cycle.