1. Synopsis – Grade 8 Science
Chapter 1: Crop Production And Management
Crop: Same kinds of plants cultivated on a large scale
Types
Kharif
crops
Rabi crops
Season
Sown in rainy season (June to
September).
grown during winter season
(October to March)
Examples
soyabean, paddy, maize
wheat, gram, pea
Basic crop production practices
Practices
Preparation
of soil
Sowing
Process
Loosening and upturning of the
soil. This process is known as
tilling or ploughing.
Placing of seeds of a crop in the
soil is called sowing.
Adding
Adding nutrients to the soil
manure and
fertilizers
Irrigation
Supplying of water to plants at
various intervals is called
irrigation.
Tools
Plough
Hoe
Cultivator
Funnel shaped traditional
tool driven by animals
Seed Drills
Manures - Prepared from
decomposed animals and plant
waste.
Fertilizers
Commercially
available
inorganic salts rich in plant
nutrients
Moat (pulley system)
Chain pump
Dhekli
Rahat (chain system)
Sprinkler system
Drip system
Manually by hands
Seed drills
Khurpi
Weedicides like 2,4-D
Sickle
Combine
Protection
Removal of unwanted plants
from weeds from the field that compete with
(weeding)
crops for space, water and
nutrients
Harvesting The process of cutting of mature
crops from the field is called
harvesting
Threshing
The process of removing grains Combine
2. Storage
from chaff is called threshing.
The process of keeping seeds Jute bags and metallic bins
safe from spoilage due to
for small scale storage
moisture, insects, rats, and Silos and granaries for large
microorganisms for a long time
scale storage
is called storage
Sources of irrigation: Wells, tube wells, ponds, lakes, canal, river, dams etc.
The process of separating grains from the husk in the mixture of threshed chaff is
called winnowing.
Small scale storage of grains: It is usually done in jute bags and metallic bins.
Large scale storage of grains: It is done in.
Food from animals - Milk from cow, buffalo, goat, and camel; Meat from
chicken, goat, and sheep; Eggs from chicken and ducks.
Animal husbandry - The rearing of animals, which includes feeding, breeding,
and disease control on a large scale, is called animal husbandry.
Chapter 2: Microorganisms
Microorganisms: The living organisms that cannot be seen with unaided eye are
called microorganisms.
Classification of microorganisms: There are five major groups of
microorganisms.
Microorganisms
Discripion
Bacteria
Single-celled organisms
Found in wide range of habitats ranging from glaciers to
deserts and hot springs
Example – curd bacteria (Lactobacillus)
Fungi
Multicellular, heterotrophic organisms
Lack chlorophyll and are generally found in colonies
Example – Penicillium, Aspergillus
Protozoa
Unicellular or multicellular microorganisms
Usually found in water
Example – Amoeba and Paramecium
Algae
Unicellular or multicellular autotrophic organisms
Contain chlorophyll pigment and carry out photosynthesis
Example – Chlamydomonas and Spirogyra
Viruses
Ultramicroscopic organisms
Require cells of host organisms to reproduce
Example – Influenza virus, polio virus
3. Importance of microorganisms
In food industry
o Lactobacillus bacteria promote the conversion of milk into curd.
o Yeast is used in preparation of breads, pastries, and cakes.
In beverage industry
o Yeast acts on sugar and converts into alcohol by the process of
fermentation.
o Louis Pasteur discovered fermentation.
o Yeast is used for commercial production of alcohol, wine and vinegar
(acetic acid).
In medicine production
o Medicines produced by certain microorganisms to kill or stop the growth
of other disease-causing microorganisms are called antibiotics.
o Antibiotics are obtained from bacteria and fungi.
o Commonly used antibiotics are streptomycin, tetracycline, and
erythromycin.
o First antibiotic i.e. penicillin was prepared by Alexander Fleming
In vaccine production
o Protection of the body from the attack of various disease-causing
microorganisms through vaccines is known as vaccination.
o Vaccine includes dead or weakened microbes that trigger the production
of antibodies in the body.
o These antibodies help in preventing attack from disease-causing
microorganisms.
o Vaccination helps in controlling diseases such as cholera, polio, small
pox, hepatitis, etc.
o Vaccine for small pox was discovered by Edward Jenner
In increasing soil fertility
o Blue green algae and Rhizobium bacteria are called biological nitrogen
fixers.
o They fix atmospheric free nitrogen to enhance soil fertility.
In cleaning the environment
o Microorganisms (decomposers) help in converting dead waste of plants
and animals into simple substances by the process of decomposition.
Harmful microorganisms – Disease-causing microorganisms are called
pathogens.
Diseases in humans caused by microorganisms
o Diseases caused by microorganisms that spread from an infected person
to a healthy person through air, water, or food are called communicable
diseases.
o The example includes cholera, chicken pox, and tuberculosis
o The organisms that transmit diseases from one place to the other are
called carriers.
4. o Example of carriers:
Carrier
Housefly
Female Anopheles
Female Aedes
Disease spread
Cholera, dysentery and
typhoid.
Malaria
Dengue
Examples of communicable diseases
Disease
Causative agent
Tuberculosis
Bacteria
Chicken pox
Virus
Hepatitis-B
Virus
Malaria
Protozoa
Cholera
Bacteria
Measles
Virus
Typhoid
Bacteria
Polio
Virus
Diseases in animals caused by microorganisms
o Anthrax is caused by bacteria
o Foot and mouth disease in cattle is caused by virus
Diseases in plants caused by microorganisms
o Citrus canker disease is caused by bacteria
o Rust of wheat is caused by fungi
o Yellow mosaic of Bhindi is caused by virus
Food preservation
Microorganisms act on food items and spoil them.
Process of preventing the spoilage of food items by the action of microbes is
called food preservation.
Methods of food preservation
Chemical methods
o The chemical that controls the growth of microorganisms on food are
called preservatives. For example, sodium benzoate and sodium meta
bisulphate
o Common salt is used as preservative in pickles. It is also used to preserve
meat and fish.
o Sugar is used as preservative in jams and jellies.
o Oil and vinegar are used as preservatives in pickles and vegetables.
Heat and cold treatments
o Boiling the milk helps in killing microorganisms that are present in food.
o Pasteurization is a technique of preserving milk in which it is boiled to
about 70C for 15 to 30 seconds and then suddenly chilled and stored.
5.
Storage and packing: Dry fruits and vegetables are sealed in air tight
packets to prevent microbe attack.
Nitrogen cycle: It involves the circulation of nitrogen through living and nonliving components of nature.
Nitrogen gas comprises 78% of the atmosphere.
First process of nitrogen cycle is fixation of nitrogen gas into nitrogenous
compounds caused by Rhizobium bacteria and lightning.
Nitrogen compounds in soil are taken up by plants through roots and used up
in synthesis of plant proteins. Animals obtain nitrogen by feeding on plants.
Waste of plants and animals are converted to nitrogenous compounds by the
action of bacteria and fungi in the soil.
Some bacteria convert nitrogenous compounds back to nitrogen to maintain
atmospheric levels of nitrogen.
Chapter 3: Synthetic Fibres And Plastics
Synthetic fibres (or man-made fibres) : Chains of small units joined together
(each small unit is a chemical substance).
Types of Synthetic fibres:
Rayon (or artificial silk): Mixed with cotton to make bed sheets or mixed
with wool to make carpets.
Nylon: Strong, elastic, light and used for making clothes, parachutes and
ropes for rock climbing.
Polyester: Remains crisp and is easy to wash. Terylene (used for making
dress materials) and PET (used for making utensils, films, wires and bottles)
are two well known polyesters.
Acrylic: Used for making sweaters, shawls and blankets.
Characteristics of synthetic fibres :
Dry up quickly
Durable
Less expensive
Readily available
Easy to maintain
Plastics : Polymer like synthetic materials where the arrangement of small units
is linear or cross-linked
6. Plastics can be recycled, reused, coloured, melted, rolled into sheets, or made
into wires.
Types of plastics :
Thermoplastics: Get deformed easily on heating and can be bent easily.
Examples: polythene and PVC
Thermosetting plastics: If moulded once, cannot be softened by heating.
Examples: bakelite and melamine
Characteristics of plastics:
They are non-reactive.
They are light, strong, and durable.
They are poor conductors of heat and electricity.
Harmful effects of plastics:
They cause environment pollution. To minimise the hazard, 4R principle
(Reduce, Reuse, Recycle, and Recover) is used.
Biodegradable substances: Get decomposed through natural processes such as
by the action of bacteria. Examples: paper, peels of vegetables, wood and fruits,
etc.
Non-biodegradable substances: Do not get decomposed easily by natural
processes. Examples: plastic bags, metals, etc.
Chapter 4: Materials - Metals And Non-Metals
Differences in physical properties of metals and non-metals:
Metals
Generally, found in solid states
(Exception: Mercury is a liquid metal)
Generally, these are hard and lustrous
(Exception: Sodium and potassium are
soft and can be cut with knife).
Non-metals
Generally, found in liquid and gaseous
states.
These are soft and have no lustre.
7. These are malleable and ductile.
These are sonorous (produce ringing
sound when struck).
These are good conductors of heat and
electricity.
These do not show such properties.
These are not sonorous.
These are poor conductors of heat and
electricity.
Differences in chemical properties of metals and non-metals:
Metals
These react with oxygen to produce
metal oxides, which are basic in nature.
Some metals react with water to produce
metal hydroxides and hydrogen.
These react with acids to produce metal
salts and hydrogen gas.
Some metals react with bases to produce
hydrogen gas.
Non-metals
These react with oxygen to form nonmetallic oxides, which are acidic in
nature.
These do not react with water.
These do not react with acids.
Reactions of non-metals with bases are
complex.
Displacement reactions → A more reactive metal can displace a less reactive
metal from their compounds in aqueous solutions.
Example:
Copper Sulphate(CuSO4 ) + Zinc(Zn) Zinc Sulphate (ZnSO4 ) + Copper(Cu)
(Blue)
(Colourless)
(R e d)
Uses of metals: In making machinery, automobiles, jewellery, trains, aeroplanes,
cooking utensils, etc.
Uses of non-metals: 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.
Chapter 5: Coal And Petroleum
In the light of availability of natural resources in nature, they can be broadly
classified into exhaustible and inexhaustible natural resources.
Inexhaustible natural resources: They are present in unlimited quantity in
nature. Examples: sunlight, air
Exhaustible natural resources: The amount of these resources in nature is
limited. Examples: coal, petroleum, natural gas, etc.
Fossil fuels : These are formed from the dead remains of living organisms.
Examples: coal, petroleum, and natural gas
8. Coal: A fossil fuel used to cook food, in railway engines to produce steam, in
thermal power stations to generate electricity.
Products of coal: Coke, coal tar, and coal gas
Coke: It is the pure form of carbon and is used in the extraction of steel and
many other metals.
Coal tar: 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.
Petroleum: A fossil fuel formed from the dead organisms present in the sea. The
process of separating various constituents of petroleum is known as refining.
Products of petroleum: Petrol, diesel, kerosene, paraffin wax, lubricating
oil, and petroleum gas
Constituents of Petroleum
LPG
Petrol
Paraffin wax
Diesel
Kerosene
Uses
As fuel for home and industry
As motor fuel, aviation fuel
Candle, vaseline, etc.
As fuel for heavy motor vehicles
As fuel for stoves, lamps
Natural gas: It is stored under high pressure as compressed natural gas (CNG).
It is used as a fuel for transport vehicles because it is a cleaner fuel (less
polluting).
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.
Chapter 6: Combustion And Flame
Combustion: It is a chemical process in which a substance reacts with oxygen to
give off heat and light.
Oxygen (in air) is essential for combustion.
Substances that burn in air are called combustible substances (also called fuels)
and those that do not burn in air are non-combustible substances.
Ignition temperature: It is the lowest temperature at which a substance catches
fire.
Control of fire:
Water is commonly used to extinguish fire. It is not suitable for fires
involving oil, petrol, and electrical equipments.
For fires involving oil, petrol, and electrical equipments, carbon dioxide is
the best extinguisher.
9. Inflammable substances → They have very low ignition temperature and can
easily catch fire with flame.
Types of combustion: Rapid combustion, spontaneous combustion, and
explosion
Zones of candle flame:
Zone
Outermost
(Luminous)
Middle
Innermost (Nonluminous)
Temperature
Colour
Combustion
Maximum
Blue
Complete
Moderate
Yellow
Minimum
Black
Partial
Unburnt carbon
particles
A good fuel is one which
is cheap
is readily available
burns easily in air at a moderate rate
produces large amount of heat
does not leave behind any undesirable substances
Fuel efficiency: It is expressed in terms of calorific value. The unit is kilojoule
per kg.
Calorific value: It is the amount of heat energy produced by complete
combustion of 1 kg of a fuel.
Harmful effects of burning of fuels:
Burning of fuels releases unburnt fine carbon particles, which cause
respiratory diseases such as asthma.
Incomplete combustion of fuels produces carbon monoxide gas (poisonous
gas).
Increased percentage of carbon dioxide in the atmosphere causes global
warming.
Oxides of sulphur and nitrogen produced by burning of fuels (coal, diesel,
petrol, etc.) cause acid rain, which is harmful for crops, buildings, and soil.
Chapter 7: Conservation Of Plants And Animals
10. Deforestation: Deforestation is the process of removal of forests for industrial,
agricultural, and other purposes.
Causes of deforestation
Natural causes
o Forest fire
o Severe droughts
Man-made causes
o Using land for agricultural purposes
o Rapid urbanization
o 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 levels and temperature
Decrease in fertility of soil and amount of rainfall
Increase in frequency of droughts and floods
Conversion of fertile land into deserts (desertification)
Conservation of forests and wildlife
Biodiversity: It is the number and variety of life forms such as plants,
animals and microorganisms in an area.
Forests help in maintaining the delicate balance of nature.
Animals living in forests are called wild animals.
Flora: The plants found in a particular area.
Fauna: The animals found in a particular area.
Endemic species: Species of plants and animals that are found only in a
particular area, are called endemic species.
Species: It is a group of population which are capable of interbreeding.
Endangered animals: The animals, whose numbers are diminishing to a
level that they might face extinction. For example: tiger, lion, and elephants
Project tiger was launched 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
Wildlife sanctuary: It is the place where wild animals are protected from
hunting and damage to their habitat. For example: Mudumalai wildlife
sanctuary in Tamil Nadu, Chilika bird sanctuary in Orissa, etc.
National parks: These are the areas reserved for wildlife where they can
freely use the habitats and natural resources. For example: Ranthambore
national park in Rajasthan, Kanha national park in Madhya Pradesh, etc.
11.
Satpura national park is the first reserve forest of India. The finest Indian teak
is found in this forest.
Biosphere reserves: It is a large protected land for conservation of wild life,
plant and animals resources, and the traditional life of the tribals 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 every year.
Numerous migratory birds including ducks, geese, sandpipers, and cranes fly
to India every year.
Migration by birds every year occurs due to
o change in climatic conditions in their original habitat
o lack of food availability in their original habitats during winters
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 energy and water.
It prevents the release of harmful chemicals (used during paper
manufacturing) in nature.
Reforestation
Restocking of destroyed forests by planting new trees is called reforestation.
It helps in checking environmental degradation.
Ecosystem: An ecosystem is a natural unit consisting of all plants, animals and
micro-organisms in an area functioning together with all of the non-living
physical factors of the environment
Chapter 8: Cell - Structure And Function
Cell: Cells are the basic structural units and the building blocks of living
organisms.
Discovery of the cell
Cell was first discovered by Robert Hooke in 1665 after observing a piece of
cork under a magnifying device.
Hooke coined the term “cell”.
12. Number of cells
Organisms made of only a single cell are called unicellular organisms; for
example: Amoeba and Paramecium
Single cell in these 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 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
Some cells such as 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 μm in bacteria.
The largest cell is the egg of an ostrich which is about 170 mm 130 mm in
size.
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
Components of the cell
Cell membrane
o It is the protective layer that surrounds the cell.
o 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
o An extra protective covering of a polysaccharide, cellulose is present In
plants.
Cytoplasm
o A jelly-like substance present between cell membrane and nucleus.
o It contains various cell organelles such as mitochondria, golgi bodies,
lysosomes etc.
Nucleus
o It is surrounded by porous nuclear membrane.
o It contains spherical body called nucleolus.
o It also contains thread-like structures called chromosomes.
13. o Chromosomes are the structures that carry genes and play an important
role in inheritance.
o Genes are the structural and functional unit of inheritance.
o The entire living substance in a cell is known as protoplast.
Vacuoles
o Vacuoles are fluid-filled membrane-bound structures in the cell.
o In plant cells, a single large vacuole is present.
o In animal cells, numerous small vacuoles are present.
Plastids
o They are present only in plant cells.
o Plastid that contains green colour pigment called chlorophyll is known as
chloroplasts. It is the chlorophyll that gives green colour to the leaves.
o Chloroplast traps solar energy and utilizes this energy to manufacture
food for the plant.
Types of cell
Prokaryotic cells - Cells having nuclear material without well defined
nuclear membrane. For example - bacteria, blue green algae
Eukaryotic cells - Cells having nucleus with well defined nuclear
membrane. For example - plant and animal cells
Differences between plant and animal cells
Cell organelle
Cell Wall
Cell Membrane
Nucleus
Nuclear Membrane
Plastids
Cytoplasm
Vacuoles
Plant cell
Plant Cell
Present
Present
Present
Present
Present
Present
Present
Animal Cell
Absent
Present
Present
Present
Absent
Present
Present
14.
Animal cells
Chapter 9: Reproduction in Animals
Reproduction: It is a biological process through which living organisms produce
offsprings similar to themselves.
Modes of reproduction: Sexual and asexual reproduction.
Sexual reproduction
Involves the fusion of male and female gametes.
Male gametes are called sperms and female gametes are called ova.
Male reproductive system: Consists of testis, sperm duct and penis.
o Testis is involved in sperm production.
o Sperm contains three parts: Head, middle piece and tail.
Female reproductive system: Consists of ovaries, oviduct and uterus.
o Ovaries produce ova or eggs.
o A single matured egg is released from ovum into oviduct every month.
Fertilization
The process of fusion of male and female gametes (egg and sperm) to form
zygote is known as fertilization. There are two types of fertilisation;
o Internal fertilization: In this, the fusion of sperm and egg takes place
inside the female body. For example, cows, dogs and humans.
o External fertilization: In this, the fusion of sperm and eggs takes place
outside the female 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 mother’s
body is called test tube baby.
Development of 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.
15.
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.
Viviparous animals: The animals that give birth to live young ones. Example:
cows, dogs, and humans.
Oviparous animals: The animals that lay eggs outside the body. Example: birds,
lizards, snakes, and frogs.
Metamorphosis
The biological process of transformation of larva into adult is known as
metamorphosis.
The life cycle of frog consists of the following stages.
Egg Tadpole (larva) Adult
The life cycle of a silk worm consists of the following stages.
Egg Larva Pupa Adult
Asexual reproduction: Involves only a single parent and the new individuals
are formed without fusion of gametes.
Two common methods of asexual reproduction
Budding
o Budding involves the formation of new individual from the bulging of
parent body.
o This phenomenon is very common in plants, fungi and animals such as
Hydra and yeast.
Fission
o Binary fission is the type of asexual reproduction that occurs in Amoeba.
o It is a type of asexual reproduction in which a single cell divides into two
halves.
o
Cloning: 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 by Ian Wilmut and
his colleagues in 1996.
Chapter 10: Reaching the Age Of Adolescence
16. Adolescence: The time period when the body undergoes changes to reach
reproductive maturity is known as adolescence. It begins at the age of 10 or 11
and lasts till about 18 or 19 years of age.
Puberty: The various changes that occur in the body during adolescence marks
the onset of puberty.
Changes that take place during puberty
Sudden increase in height
o Girls grow faster than boys initially but both reach their maximum height
by the age of 18 years.
Change in body shape
o Boys develop broader shoulders, wider chests and prominent muscles.
o In girls the region below the waist becomes wider
Change in the voice pattern
o Voice box or larynx starts growing during puberty.
o It protrudes in males in the neck region and is called Adam’s apple.
o Boys develop deep low-pitched voice while girls develop high-pitched
voice.
Change in activity of sweat and sebaceous glands
o Production of more sweat.
o The oily secretions from sebaceous glands increase. The accumulation of
oil and bacterial action leads to acne problems in teenagers.
Changes in sex organs
o Testes and penis develop completely in boys. Testes start producing
sperms.
o Ovaries develop completely and start producing eggs in girls.
Change in intellectual level
o The learning capacity of brain increases.
o Intellectual development takes place during adolescence.
Development of secondary sexual characters
In boys
In girls
o Appearance of moustaches o Increase in breast size
and beard
o Growth of hair in the pubic
o Appearance of hair on chest
regions
o Growth of hair in genital
area and other parts of skin
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.
Sex hormones
17. o Male sex hormone is testosterone. It is produced by the testes on the
onset of puberty.
o Female sex hormone is called Oestrogen. It is produced by ovaries.
Non-sex hormones
Thyroxine
o It is produced by thyroid glands.
o It is required for regulating metabolism in the body.
o Lack of iodine leads to deficiency of thyroxine, which results in a disease
called goitre.
Insulin
o It is produced by the pancreas.
o It maintains blood sugar level.
o Deficiency of insulin results in diabetes.
Adrenalin
o It is secreted by adrenal glands.
o It helps the body to adjust various stress conditions.
Growth hormone
o It is secreted from pituitary glands.
o It is required for proper body growth.
Role of hormones in other animals
Insect hormone: Ecdysone is an insect hormone that causes metamorphosis
in insects.
Thyroxine: Thyroxine produced by thyroid glands play an important role in
the metamorphosis of tadpoles into adults.
Reproductive phase in humans
In males, the production of sperm continues throughout the life.
In females, the reproductive phase starts from 10-12 years and continues till
45-50 years.
The female reproductive tract undergoes series of cyclic changes, called
menstrual cycle, which is of 28 to 30 days.
One ovum is produced during one cycle.
The wall of uterus becomes thick to receive fertilized egg.
If pregnancy does not occur, the unfertilized egg and uterus lining are shed
off, which results in bleeding, called menstruation.
First menstrual flow in a female is called menarche.
Stoppage of menstruation in females is called menopause.
Sex determination in babies
In humans, two chromosomes, called sex chromosomes, are present along
with other pairs of chromosomes (autosomes).
Sex chromosomes are of two types, X and Y.
Females have two X chromosomes (XX) while males have one X and one Y
chromosomes (XY).
Sex chromosome of the male parent decides the sex of the child.
18.
When a sperm with X chromosome fuses with an egg containing X
chromosome, it leads to the development of a female child.
When a sperm with Y chromosome fuses with X chromosome of an egg, it
leads to the development of a male child.
Reproductive health
Adolescents should have a balanced diet with right proportions of various
body nutrients.
They should maintain cleanliness to prevent bacterial infections.
They should avoid usage of drugs and alcohols.
Sharing of syringes during drug abuse leads to spread of HIV virus causes
AIDS.
AIDS is also caused by unsafe sexual contact and from infected mother to
her infant through milk.
Chapter 11: Force and Pressure
Force is a physical quantity which can change speed, direction or shape of a
body.
Push When an object is moving away from the applier of force
Pull When an object is moving towards the applier of force
Resultant of more than one force acting on a body:
Forces are applied in the same direction Addition, direction same as the
forces
Force applied in the opposite direction Subtraction, direction same as of
the greater force
Effects of force
Force can change the state of motion.
Force can change the shape or size of an object.
Contact forces: when the applier is in contact with the body.
Muscular force – It involves the action of muscles.
Friction – The force which always opposes the relative motion of two bodies
in contact.
None-contact forces
Magnetic force – Force active between two magnets or one magnet and one
non-magnet
Electrostatic force – Force of attraction/repulsion between electric charges
Gravitational force – Force of attraction between any two bodies in the
universe
Pressure Force per unit area
Force
Pressure =
Area on which it acts
19. Water and gas exert pressure on the walls of their container, which varies with
depth (or height)
At a given depth, pressure is always the same irrespective of the shape/size of the
vessel.
Atmospheric pressure = Weight of the atmosphere per unit area
Chapter 12: Friction
The force which always opposes relative motion of the two surfaces which are in
contact.
Cause of friction the irregularities on the two surfaces in contact lock into one
another.
Factors affecting friction
Nature of surfaces – Smooth surfaces less friction
Rough surfaces greater friction
How hard an object is pressed – Greater pressing force Greater friction
Mass of object – Greater mass Greater friction
Sliding friction < Static friction
Rolling friction < Sliding friction
Reducing friction
Lubrication – Powder on carom board, oil in machine
Wheel – Wheels reduce friction (because rolling friction < sliding friction).
In many machines, friction is reduced by using ball-bearing.
Shoe soles and tires are threaded to increase friction for a better grip.
The friction between layers of fluid or between a solid object and fluid is called
fluid friction.
Fluid friction between an object and fluid depends upon:
Speed of the object relative to the fluid
Shape and size of the object
Nature of fluid
Fluid friction is minimised by giving suitable shapes to vehicles moving through
fluids.
Fluid friction is also called drag
Chapter 13: Sound
Sound is a form of energy which produces sensation of hearing.
Vibrating body produces sound.
Vibration – to-and-fro or back-and-forth or up-and-down motion of a body
Musical instruments and their vibrating parts
20. Musical instrument
Veena
Tabla
Flute
Vibrating part producing sound
Stretched string
Stretched membrane
Air column
Sound requires a medium to propagate (solid, liquid, or gas).
Sound cannot travel through vacuum.
In humans, sound is produced by larynx (voice-box).
In human ear, the eardrum vibrates and passes vibration to the inner ear
Frequency – Number of oscillations per unit time. [Unithertz = (Hz)]
Pitch or shrillness depends on frequency.
Higher frequency higher pitch
Loudness of sound:
It is measured in decibel (dB).
It depends on amplitude.
Higher amplitude louder sound
Audible sound – Human ear can hear sounds having frequency in the range of
20-20,000 Hz.
Noise pollution – Presence of unwanted and excessive sound in the
environment.
It can be reduced by plantation on roadside.
Chapter 14: Chemical Effects of Electric Current
Some liquids are good conductor while some are bad conductors.
Conductivity can be tested by using given set-ups.
The bulb will glow or the magnetic needle will show deflection if the liquid
in the beaker is a good conductor of electricity.
Greater the deflection of needle or brighter the light, better is the
conductivity of the liquid.
Classification of some liquids on the basis of their conductivity.
Good conductor
Lemon juice
Poor conductor
Milk
21. Vinegar
Acid solutions
Basic solutions
Salty water
(tap water, sea water)
Distilled water
Honey
Vegetable oil
Kerosene
The electric current passing through a conducting liquid causes chemical
reactions. The resulting effects are called chemical effects of electric current.
The process of depositing a desired metal or material, by means of electricity is
called electroplating.
Chapter 15: Some Natural Phenomena
Objects get charged when rubbed with another material.
Objects that get charged
Refill
Balloon
Eraser
Steel spoon
Ebonite comb
Glass rod
Material used for rubbing
Polythene, woollen cloth
Polythene, woollen cloth, dry hair
Wool
Polythene, woollen cloth
Dry hair, silk cloth
Woollen cloth, silk cloth
There are two kinds of charges, positive and negative.
Like charges repel each other.
Opposite charges attract each other.
Charge generated by rubbing is static.
When charges move they constitute an electric current.
Electroscope is used to detect whether an object is charged or not. It cannot
detect the nature of charge.
The process of transfer of charge from a charged object to Earth is called
earthing.
The sudden flow of charge (discharge) from cloud to objects on Earth is called
lightening.
Lightening safety
Safe placesinside building, inside car/bus, any fully covered place
Unsafe placesopen spaces, beneath tall trees, any elevated place
Using an umbrella is not safe during lightning.
During lightning, one should avoid using electrical appliances (should be
unplugged) and running water.
Lightning conductor is the pointed metal rod on top of tall buildings.
It transfers charge from lightening to Earth via conducting wire.
22. Earthquake is the sudden shaking or trembling of the earth’s surface because of
disturbance deep inside the earth’s crust. Earthquakes cannot be predicted.
Causes of Earthquake:
The uppermost layer of the earth (crust) is fragmented and each fragment is
called plate.
Movements of earth’s plates cause Earthquake. Plate boundaries are called
seismic zones or fault zones.
Earthquake may also occur because of volcanic eruption.
Power of earthquake is measured on Richter scale.
Chapter 16: Light
Reflection of light is the change in the path of a light ray upon collision with an
interface of two medium.
Laws of reflection:
i (angle of incidence) = r (angle of reflection)
Rays AO, OM and OB lie in the same plane.
Image formation by a plane mirror
Image formed is virtual and of same size as that of object.
The image is laterally inverted.
Regular and irregular reflection
23. Regular reflection
Irregular reflection
Kaleidoscope works on the theory of multiple reflections which forms beautiful
patterns.
Sunlight consists of several colours.
Splitting of white light is called dispersion.
Human eye
The image forms on retina.
Iris controls the size of pupil.
Pupil controls the amount of light.
Optic nerves sense the image and send it to the brain.
The junction of optic nerve and the retina is called blind spot.
1
Impression of an image persists for seconds in our brain.
6
Vitamin A (raw carrots, broccoli, green vegetables, cod-liver oil, etc.) is
necessary for good vision.
Braille system is helpful for visually challenged persons for reading.
CHAPTER 17: Stars and the Solar System
All natural objects in the sky are celestial objects.
New Moon day: when moon is not visible
Full Moon day: when full moon is visible
Gap between consecutive new moon day and full moon day is of 15 days.
Rotational period and revolution period of moon are the same (almost 29 days).
Moon’s surface: Because of lack of atmosphere, one cannot hear any sound on
moon.
All stars emit their own light. In day time, stars are not visible because of bright
sunlight.
The biggest star that can be seen is the sun.
Stars appear to move from east to west because of earth’s rotation from west to
east.
Constellations: Groups of stars of particular shapes
24. Planets revolve around the sun along definite paths, called orbits.
Time taken by a planet to complete one revolution of its orbit is called
revolution period.
Time taken by a planet to rotate about its axis is called period of rotation.
Inner planets
Outer planets
Mercury
Nearest planet to the sun
It is seen just before sunrise and just
after sunset near horizon. It has no
satellite.
Venus
Brightest planet planet and nearest to
the earth
Also known as morning or evening
star
Has no satellite and rotates from east
to west (sun rises in the west of
Venus)
Earth
From space, it appears blue because
of 75% water content.
Mars
It appears reddish and therefore, is
known as red planet
Jupiter
Largest planet in the solar system
Rotates very fast about its axis and
has large numbers of satellites
Saturn
Has prominent ring system and large
numbers of satellites
Its density is less than water and is
the least among the planets
Uranus and Neptune
Both have ring system.
Uranus has a tilted rotational axis
and appears to roll on its side.
Uranus rotates from east to west
similar to Venus.
Asteroids
25. Small rocky objects found in large numbers between Mars and Jupiter
Comets
Highly elliptical objects
Have a bright head and long gaseous tail which always directed away from
sun
Halley’s comet appears after every 76 years.
Meteors & Meteorites
Objects that enter the earth’s atmosphere and burn because of friction with
the atmosphere
Large meteors that reach earth’s surface are called meteorites.
Artificial satellite
Revolves around the earth
Used for weather forecasting, remote sensing, communication system, etc.
Chapter 18: Pollution Of Air And Water
Atmosphere: The layer of air present around the earth. It is composed of 78% of
nitrogen, 21% of oxygen, and 1% percent other gases such as carbon dioxide,
ozone, water vapour, methane, etc.
Air pollution: The phenomenon of contamination of air with unwanted
substances so that it becomes harmful for living organisms and non-living
substances.
Air pollutants: Substances which cause air pollution.
Sources of air pollution are
o Power plants
o Factories
o Automobiles
o Burning of firewood
Types of air pollutants
o Carbon monoxide: A colourless poisonous gas produced from
incomplete burning of fossil fuels. It reduces oxygen carrying capacity of
the blood.
o Sulphur dioxide: Produced from combustion of fuels and causes
respiratory problems including permanent lungs damage. It causes
formation of acid rain.
o Nitrogen dioxide: Produced from incomplete burning of fuels and causes
respiratory problems. It causes formation of acid rain.
o Chlorofluorocarbons (CFCs): These are released from refrigerators, air
conditioners, and aerosol spray and cause damage to the ozone layer
resulting in the formation of ozone hole.
26.
o Suspended particulate matter: These are produced during burning of
fossil power plants, mining, steelmaking, and other industrial processes
and comprises of tiny particles, which remain suspended in air for a long
time.
Acid rain: It is formed when sulphur dioxide and nitrogen dioxide present in air
react with water droplets to form nitric and sulphuric acid. It has caused
corrosion of the marble of Taj Mahal.
Green house effect: The trapping up of reflected solar radiations by the earth’s
atmosphere and gradual heating up is known as greenhouse effect.
Greenhouse gases: These are the gases, which trap the solar radiations, and
prevent them from escaping into the atmosphere. Example: carbon dioxide,
methane, nitrous oxide, and water vapours.
Global warming: The gradual warming up of the earth’s atmosphere by the
increased carbon dioxide level. The CO2 level in atmosphere is increasing due to
various human activities such as deforestation and burning of fossil fuels.
Prevention of air pollution:
Use of clear fuels such as CNG, LPG, and unleaded petrol in public and
private transport
Use of renewable sources of energy such as solar, wind, and hydel energy
Planting more and more trees to prevent pollution
Prevent burning of dry leaves and use them in composting
Water pollution: Mixing of harmful substances in water such as sewage and
toxic chemicals so that its physical and chemical properties get altered and it
becomes toxic for living organisms.
Water pollutants: Substances that pollute water
Sources of water pollution in Ganga river:
Untreated discharges from textile, paper and sugar mills, and oil refineries
Disposal of agricultural discharge from near-by fields, which are rich in
pesticides and weedicides, into the river
Flow of untreated domestic sewage into the river
Cremation of dead bodies into the river
Immersion of idols of gods and goddesses, flowers, garbage, and polythene
bags into the river
Types of water pollutants
Domestic sewage.
Industrial waste.
Agricultural waste: Rich in agricultural pesticides and weedicides which
causes ground water pollution and an increase in the population of algae in
water resulting in eutrophication.
Potable water: Water that is fit for drinking is called potable water.
Methods of obtaining potable water
Physical methods
o Boiling of water
27. o Use of domestic filters such as candle type filter
Chemical methods
o Use of chlorine tablets
Prevention of water pollution
Proper treatment of industrial waste and domestic waste before its disposal
into rivers
Strict implementation of environmental laws in industrial units
Reusing water
Preventing wastage of water
