Synopsis – Grade 9 Science Term II

Chapter 1: Atoms and Molecules Law of conservation of mass: Mass can neither be created nor can it be destroyed in a

chemical reaction.

Law of constant proportion: A chemical substance always contains the same elements in a

fixed proportion by mass, irrespective of the source of compound.

Atom: The smallest particle which is the building block of matter.

The symbol of the element is made from one or two letters of the English or the Latin name

of the element.

Atomic mass: The sum of the protons and neutrons in an element gives its atomic mass. The

atomic mass of an atom of an element is also known as its relative atomic mass, since it is

determined relative to the mass of C-12 isotope.

Molecule: It is formed when two or more atoms of the same element or different elements

get combined chemically.

Atomicity: The number of atoms that combine to form a molecule is called the atomicity of

the molecule.

Ion: A charged species in which an atom or a group of atoms possess a net electric charge

(positive or negative).

Cations → Positively charged ion

Anion → Negatively charged ion

Chemical formula: Representation of the composition of a molecule in terms of the

symbols of elements present in that molecule.

Molecular mass: It is the sum of the atomic masses of all the atoms present in a molecule of

that substance.

Formula unit mass: It is the sum of the atomic masses of all the atoms present in a formula

unit of that substance.

Mole: The mole is a unit of measurement for the amount of substance. One mole of a

substance is the quantity of the substance containing 6.022 1023

numbers of particles

(atoms, molecules, or ions).

Chapter 2: Structure of the Atom

Atoms are not indivisible and are composed of three fundamental particles. These particles

are electrons, protons, and neutrons.

Electrons: These are the negatively charged particle and were discovered by J. J. Thomson,

by cathode ray experiment.

Canal rays are positively charged radiations consisting of protons.

Protons: These are the positively-charged particles and were discovered by E. Goldstein.

Neutron: These are electrically-neutral particle and were discovered by J. Chadwick.

Various atomic models:

Thomson's atomic model: Thomson thought that an atom is a sphere of positive charge

in which electrons are embedded. An atom as a whole is electrically neutral because the

negative and positive charges are equal in magnitude.

Rutherford's atomic model: All the positive charges (i.e., protons) were present at the

centre of the atom, inside the nucleus, and the electrons were present in circular orbits

around the nucleus. The electrons are not at rest and keep moving continuously in these

circular orbits. The size of the nucleus is very small as compared to that of the atom.

Bohr’s atomic model: The electrons present around the nucleus revolve in specific orbits

called energy levels. He also stated that the electrons do not release energy while

revolving. The shells in which the electrons are present are known as K, L, M, N, and so

on (or 1, 2, 3, 4, and so on), as proposed by Bohr and Bury. Each shell contains a specific

number of electrons, which can be calculated using the formula 2n2.

Atomic Models

Dalton’s atomic model Thomson’s atomic model

Rutherford’s atomic model Bohr’s atomic model

Valency: It is defined as the combining capacity of the atom of an element. It depends upon

the number of electrons present in the outermost shell of its atom.

Atomic number of an element is equal to the number of protons present in the atom and

atomic mass is equal to the sum of the number of protons and neutrons present in it.

Isotopes: These are the atoms having the same atomic number and different atomic masses.

Isobars: These are the atoms having the same atomic mass and different atomic numbers.

Chapter 3: Diversity in Living Organisms

Diversity: It refers to the variety and variability among living organisms from all sources

including land, water, and other ecosystems.

Classification: It refers to the identification, naming, and grouping of organisms into a

formal system based on similarities in internal and external structures or evolutionary history

Characteristic: A feature that helps identify or describe a person or a thing.

Principles of classification

Nature of cell (Fundamental characteristic): prokaryotes and eukaryotes

Cellularity: unicellular and multicellular

Mode of nutrition: autotrophs and heterotrophs

Classification and evolution

Primitive organism or lower organism has a simple body structure and ancient body

design

Advanced organism or higher organism has a complex body structure and organisation

Evolution: The process of gradual and continuous change in primitive or simple

organisms to give rise to advanced organisms

Biodiversity: The variety of life forms present in various ecosystems

Hierarchy of classification: Kingdom Phylum (for animals)/ Division (for plants)

Class Order Family Genus Species.

Mnemonic to learn this hierarchy: Kids Prefer Cheese Over Fried Green Spinach

Species is the basic unit of classification

Carolus Linnaeus developed the hierarchy of classification. Linnaeus also developed the

concept of binomial nomenclature

Binomial nomenclature In this system, the name of a species is made up of two words:

the genus name and the species name. E.g. Rosa indica

R.H. Whittaker (in 1969) proposed a five-kingdom classification of living organisms

The five kingdoms proposed by Whittaker along with their features are

Kingdom Special feature Example of organisms

Kingdom Monera Prokaryotic and unicellular

organisms.

bacteria, blue-green algae, or

cyanobacteria

Kingdom Protista Unicellular, eukaryotic organism Amoeba, Paramecium, diatoms etc

Kingdom Fungi Multicellular eukaryotic

heterotrophic (saprophytic)

organisms with citinious cell wall

Yeast, mushroom, Penicillium,

Aspergillus, etc

Kingdom Plantae

Multicellular eukaryotic

autotrophic organisms with

cellulosic cell wall

All plants

Kingdom Animalia

Multicellular eukaryotic

heterotrophic organisms with no

cell wall

All animals

Kingdom Plantae: It includes five divisions:

Division Thallophyta: Includes Spirogyra, Cladophora, Ulva

Plant body is not differentiated into true root, stem, and leaves

Division Bryophyta (also called amphibians of plant kingdom):

o Includes mosses, Riccia, Marchantia,

o Specialised vascular tissues (such as xylem) for the conduction of water are absent

o Body is differentiated into stem and leaf like structures

o Naked embryo i.e. spores are present.

Division Pteridophyta: o Includes ferns, Marsilea, Equisetum

o Specialised vascular tissues for the conduction of water are absent

o Naked embryo i.e. spores are present

Cryptogams: Plants that do not have well differentiated reproductive organs and produce

naked embryo (spores) are called cryptogams. Thallophyta, Bryophyta and Pteridophyta all

possess naked embryo.

Phanerogams: Plants that have well developed reproductive organs that finally make seeds

are called Phanerogams. Gymnosperms and angiosperms belong to Phanerogams.

Division Gymnospermae:

o Includes Pinus, cedar, fir, Juniper, Cycas, etc:

o Seed bearing, non-flowering plants.

o Bear naked seeds, not enclosed inside fruits.

Division Angiospermae: Includes all flowering plants:

Flowering plants in which seeds are enclosed inside fruits.

Seeds develop inside the ovary, which develops into a fruit

o Monocotyledons: Seeds that have one cotyledon. E.g. maize, wheat etc

o Dicotyledons: Seeds that have two cotyledons. E.g. Sunflower, gram etc

Kingdom Animalia

Kingdom Animalia can be divided into two major groups on the basis of the presence or

absence of notochord: non-chordata and chordata

Non-chordata can be further divided into the following phyla:

Phylum Porifera: Includes sponges such as Spongilla, Euplectella, etc:

o Cellular level of organisation

o Mainly found in marine habitats

o Posses canal system for circulating water.

Phylum Coelenterata: Includes sponges such as Spongilla, Euplectella, etc

o Tissue level of organisation

o Body cavity (coelom) is absent

o Diploblastic i.e body is made of two layers of cells.

Phylum Platyhelminthes: Includes flatworms, liver flukes and planarians

o Bilateral symmetry

o Triploblastic i.e. three layers of cells are present

o Body cavity is absent

Phylum Nematoda (Aschelminthes): Includes roundworms - Ascaris

o Bilaterally symmetrical

o Triploblastic

o Pseudocoelom (false coelom) is present

Phylum Annelida: Includes segmented worms such as earthworms and leeches

o Bilaterally symmetrical

o Triploblastic

o Body is segmented

Phylum Arthropoda: Includes crabs, prawns, insects, spiders, scorpions, etc

o Largest group of the animal kingdom.

o Bilaterally symmetrical and segmented

o Coelomic cavity is blood-filled

o Presence of Jointed legs

Phylum Mollusca: Includes snails, octopus, Pila, etc

o Bilaterally symmetrical, little segmentation

o Coelomic cavity is reduced

o Open circulatory system and kidney like organ for excretion is present.

Phylum Echinodermata: Includes marine animals such as starfishes, sea urchins, etc

o Spiny skinned organisms

o Free living marine organisms

o Triploblastic and coelomate

o Skeleton is made of calcium carbonate

Chordata can be further divided into sub-phyla Protochordata and Vertebrata

Protochordata: Includes Herdmania and Amphioxus

o Triploblastic, and have a coelom cavity

o Bilaterally symmetrical

o Notochord at some stages of life is present.

o Notochord is a flexible rod like structure that forms the supporting axis of the body in

the chordates.

Vertebrata: The sub-phylum Vertebrata is further divided into five classes:

Class Pisces: Includes all fishes

o Exclusively aquatic animals

o Body is streamlined and covered with scales

o They are cold blooded animals

o Heart is two chambered

o Skeleton is bony or cartilaginous

o Oviparous. They lay eggs in water.

Class Amphibia: Includes frogs, toads, and salamanders

o Scales are absent

o Cold blooded animals

o Heart is three chambered

o Oviparous. They lay eggs in water

o Have a dual mode of life (in water and land); respire through gills, skin and lungs

Class Reptilia: Includes reptiles such as lizard, snake, turtle, etc

o Cold blooded animals

o Most of them have three chambered heart (Crocodiles have four chambered heart)

o Skin is covered with scales

o These animals are completely terrestrial. They breath through lungs

o Lay eggs on land (oviparous)

Class Aves: Includes all birds

o Warm-blooded animals with four chambered heart

o They breathe through lungs

o Have feathers and forelimbs modified for flight

o Exclusively egg-laying animals

Class Mammalia: Includes kangaroo, rat, dolphin, elephant, horse, human, tiger, etc

o Warm-blooded animals with four chambered heart

o Most of them are viviparous except for platypus and echidna. They both are

oviparous

o These animals have milk-producing glands (mammary glands) to nourish their young

ones

Chapter 4: Work and Energy

Scientifically, work is done when:

There is a displacement.

Displacement is in any direction except the direction normal to the direction of force.

No work is done when

Net displacement is zero. [No work is done in circular path]

Displacement occurs perpendicularly to the applied force

Work = Force Displacement [along force direction]

W = F s [Unit – Joule, 1 J = 1 N.m]

Unit of energy: Joule

Commercial unit of Energy: kWh 6

1 kWh 3.6 10 J

The energy possessed by a body by virtue of its motion is called kinetic energy.

Kinetic energy of a body = 21

2mv , where m is mass and v is speed of the body.

Proof:

2 2

2 2

2 2

2 2 2

2

2

2

1 10

2 2

v u as

v us

a

v uW ma

a

m v u mv u

when

Energy possessed by a body by virtue of its position or its shape is called potential energy.

Gravitational potential energy = mgh where, m is mass, g acceleration due to gravity, and h is

the height above surface of Earth.

Law of conservation of energy: Energy can neither be created nor destroyed, it is only

converted from one form to other.

Total energy is constant: 21

2m h mv g Constant

Power is the rate of work done. Work done 1 J

P = Unit Watt, 1 W =1 s

Time taken

Chapter 5: Sound

Sound is a mechanical wave and requires a medium to propagate.

It cannot pass through vacuum.

Sound waves are longitudinal waves and propagate by continuous compressions and

rarefactions of the medium.

Longitudinal wave:

Individual particles of the medium move in the direction parallel to the direction of wave

propagation

Transverse wave:

Particle movement is perpendicular to the wave propagation

Characteristics of sound waves

Amplitude – Magnitude of maximum displacement from mean position

Wavelength (λ) – Distance between two consecutive compressions or two consecutive

rarefactions.

Frequency – Number of oscillations per unit time (Unit - Hertz, Hz)

Time period – Time taken by two consecutive compressions or rarefactions to cross a fixed

point

1

Frequency =Time period

Pitch – Higher the frequency, higher the pitch

Loudness – Determined by amplitude

Tone – Sound of single frequency

Speed of sound depends on temperature, pressure, humidity and nature of the material

medium.

Speed increases with increasing temp.

Speed in solid > Speed in liquid > Speed in gas

In air, speed 344 m s–1

at 22 C

Supersonic – More speed than sound

Sonic boom loud noise produced by supersonic object is sonic boom

Echo- Reflection of sound

Sensation of sound persists 1

= 0.1 s10

in the human brain

Minimum distance to hear echo = 344×0.1

=17.2 m2

Reverberation – Persistence of sound by repeated reflection

Uses – Loud speaker, stethoscope, curved ceiling of a concert hall, sound board in a big

hall

Range of hearing for humans: 20 – 20000 Hz

But, rhinoceroses use infrasound

Application of ultrasound : Cleaning, detecting defects in metals, echocardiography,

ultrasonography, to break small kidney stone

SONAR is Sound navigation and Ranging.

Human ear: Pinna collects sound; eardrum vibrates in response to sound

Vibrations are amplified by the three ear bones [hammer, anvil, stirrup (smallest human

bone)]

Chapter 6: Why Do We Fall Ill

Health: A state of physical, mental, and social well-being, which includes a unity and

harmony within the mind, body, and soul of an organism

Disease: Any condition that can lead to discomfort, distress, health problems, and even death

of the affected person

Symptoms: Indications of disease, such as headache, stomach pain, nausea, etc that can only

be felt by the patient

Signs of a disease include fever, vomiting, diarrhoea, etc that can be observed by a physician

Incubation period: The time interval between infection and appearance of symptoms

Causes of diseases

On the basis of its duration - Acute and Chronic

o Acute: Lasts for a short period of time, E.g. Cold, cough, influenza, etc.

o Chronic: Lasts for long periods of time, E.g. Diabetes, kidney stones, etc.

On the basis of causative agents - Infectious and Non-infectious

o Infectious: Diseases such as influenza, cold, etc., which are caused due to infectious

agents

o Non-infectious; Diseases such as high blood pressure, cancer, etc., which are caused

by some internal causes such as excessive weight, genetic defects, etc.

Infectious agents: disease-causing microorganisms which belong to different categories

such as:

Viruses: These are tiny organisms that grow, multiply, or reproduce only inside the host

cells. Diseases caused by viruses include Influenza, cold (Rhinovirus), dengue, AIDS,

SARS etc.

Bacteria: These are unicellular organisms; larger than viruses. Diseases caused by

bacteria include whooping cough, typhoid, cholera, anthrax, etc.

Fungi: These are plant-like organisms; heterotrophic. Diseases caused by Fungi include

Athlete’s foot, candidiasis, ringworms, etc.

Protozoa: These are simple, primitive unicellular organisms which are often found in

water. Diseases caused by Protozoa include amoebiasis, kala azar (Leishmania), malaria,

African sleeping sickness (Trypanosoma), etc.

Multicellular animals like worms - These are parasites that infect the intestines of

human beings and other animals. Diseases caused by worms include diarrhoea, liver rot,

etc.

Communicable diseases: An infectious disease is classified as communicable disease when

it can be transferred from an infected person to a healthy person

Means of disease spread

Air-borne diseases: Transmitted when disease-causing microorganisms are expelled into

the air by coughing, sneezing, talking, etc. E.g. common cold, chicken pox, small pox,

pneumonia, influenza, tuberculosis, etc.

Water-borne diseases: Spreads when the excretions (from an infected person)

containing causal microorganisms get mixed with drinking water and this contaminated

water is consumed. E.g. cholera, typhoid, hepatitis A, etc.

Physical contact: Includes sexually-transmitted diseases. E.g. syphilis, gonorrhoea,

AIDS, etc.

Blood to blood contact: Such contact is established during blood transfusion or

pregnancy (between the mother and her baby). E.g. AIDS can spread through blood

contact

Animals: Animals which transfer disease-causing microorganisms from an infected

person to others are called vectors. E.g. female mosquitoes can transfer the malaria-

causing Plasmodium

Effects of diseases

Local effects: Includes swelling, pain, joint stiffness, etc., occur only at the site of

infection

General effects: Includes fever chills, headaches, fatigue, loss of appetite, etc., occur all

over the body

Inflammation: The process by which the body’s immune system shows response to

protect the body from infection

Prevention of diseases

Antigens: Foreign substances that invade our body

Immunisation: The protection of the body from communicable diseases by

administration of some agent that mimics the microbe.

Vaccine: The suspension of killed microbes that mimics the disease causing microbes.

Vaccines are available against tetanus, polio, measles, hepatitis B, etc.

Chapter 7: Natural Resources

Role of the atmosphere → Atmosphere acts as a heat protector and it plays an important

role in the generation of wind.

Soil: It is a mixture of small rock particles and decayed living organisms.

Humus: A constituent of soil which makes it fertile

Factors that influence soil formation:

Sun: Heats up the rock during the day

Rocks cool during night time

Formation of creaksbreaking of rocks

Water – water in cracks freeze breaks rocks

Water carries rocks friction breaks rocks

Wind – Particles in air erode the rocks

Greenhouse effect: The trapping up of reflected solar radiations by the earth’s atmosphere

and gradual heating up is known as greenhouse effect.

Biogeochemical cycles

Water Cycle

Nitrogen cycle

Carbon cycle

Oxygen cycle

Ozone layer: It is a very important layer of the atmosphere which absorbs the harmful

ultraviolet rays. A hole in the ozone layer has been caused by CFCs which results from

human activities.