● Biology is a natural science
concerned with the study of life and
living organisms, i.e., plants and
animals. It is classified into two part:
Botany and zoology.
● Study of plants is called Botany and
study of animals is called Zoology.
Zoology and Botany are collectively
called Biology. The term ‘Biology’
was coined by Lamarck and
● The scientist who gave his thought
for the first time about the life of
plants and animals was Aristotle.
That’s why he is known as the Father
of Biology. He is also known as the
Father of Zoology.
● Theophrastus is known as Father of
● They have cellular organisation and also
respire, i.e., take in O2
and evolve CO2
● Metabolism is one of the most important
characteristic feature of living organism. It
comprises two phases that are anabolism
(constructive phase) and catabolism
● They take nutrition for their growth.
● They have tendency to reproduce.
● They have the ability to respond to changes
in both internal and external environment
i.e., they have sensitivity. Their survival
chances are maximum.
● They move from place to place as animals or
some bacteria. Plants cannot move but
some movement can occur in plants.
● The Cell is the basic structural and
functional unit of all known living
organisms. It is the smallest unit of
life and is often called the building
block of life.
● The branch of biology which deals
with the study of cell, is called
● Robert Hooke coined the term cell
when he saw honey-comb like
structure in the section of cork.
However, he only discovered cell wall.
● The first living cell was discovered by
Types of Cells
These are of two types
1. Prokaryotic Cells
These are primitive cells, lacking a
well defined nucleus and most of
the other cell organelles, e.g.,
2. Eukaryotic Cells (Eu = true, karyos =
nucleus) These have a well defined
nucleus and membrane bound cell
organelles. These are present in
unicellular and multicellular plant and
Parts of Cell and their
A typical cell consists of cell wall and
Protoplasm of Cell
It is the living fluid matter present inside the
plasma membrane. The fluid present outside
the nuclear membrane is called cytoplasm and
the fluid present inside the nuclear membrane
is called nucleoplasm. Deutoplasm is the
non-living matter of the cell.
It is present in plant cells, bacteria, fungi, algae
and some archaea. It is composed of cellulose
in plants and chitin in fungi. It is non-living. Its
main function is to provide shape and rigidity to
The cell is enclosed by a thin membrane called
the cell membrane or plasmalemma. It is
composed of proteins and phospholipid
molecules. It is elastic, living and selectively
permeable, i.e., provide passage for various
● It was discovered by R Altman in
1880 and the term mitochondria
was coined by Carl Benda.
● It is bounded by a double memb-
rane. The inner membrane has
many folds, called the cristae. Fluid
(called matrix) is present on interior,
which contains many enzymes and
coenzymes. It is a semi- autonomous
(can form its own copies) organelle
and is called power house of the
cell because in it, stepwise oxidation
of fuel occurs which results in
release of chemical energy. This
energy is stored in the form of ATP.
● These are present only in plant cells
and are of three types– chloroplasts
(green), leucoplasts (white) and
chromoplasts (of various colours
except green). Chloroplast is the site
of photosynthesis as it contains
chlorophyll, while leucoplasts are
storage plastids. Chloroplast is called
the kitchen of the cell.
● The red colour of tomatoes is due to
the presence of lycopene pigment,
● The colour of carrot is due to
It was discovered by KR Porter. These
are hollow membranous system having
ribosomes (thus called Rough ER) or
no ribosomes (thus called Smooth
Rough endoplasmic reticulum is
the site of protein synthesis, while
smooth endoplasmic reticulum is the
site of synthesis of steroids and
It was discovered by Camillo Golgi. It
is made up of sac-like flattened
structures and play an important role
in secretion, transportation and
Ribosomes were discovered by GE Palade.
These are minute, non-membranous particles,
composed of RNA and protein. 70 S type of
ribosomes are found in prokaryotes, while 80 S
type in eukaryotes. These are the site of protein
● Lysosomes were discovered by de Duve.
These are polymorphic organelles having
hydrolytic enzymes. These enzymes function
at (acidic) pH ~ 5. These are sometimes
called suicidal bags of the cell.
● Lysosome helps in carcinogenesis, i.e.,
conversion of a normal cell into cancerous
It was discovered by T Boveri. It is composed of
two set of centrioles and participate in the
formation of mitotic spindle during cell division.
These are non-living reservior, bounded by
a membrane called tonoplast. Pigment
anthocyanin is present in the cell vacuole,
which provide colour to flowers. It stores toxic
metabolic waste and helps in osmoregulation.
It was discovered by Robert Brown. It contains
nucleoplasm, nucleolus and chromatin
material. Nucleolus is rich in protein and RNA.
All this material is covered up by a nuclear
membrane. Chromatin is the controlling
centre of cell as it form chromosomes.
Chromosome is thread-like structure,
found in the nucleus. Bead-like
structures found on chromosome are
called genes, which are made up of
DNA and are the carrier of genetic
information from generation to
generation. Chromosomes are units of
inheritance. In some viruses e.g.
retrovirus, RNA is the genetic
Plant Cell Animal Cell
It has cell wall. Cell wall is usually
Plastids are found. Plastids are usually
found in all cells.
A big vacuole is
Vacuole is absent
or very small in
These contain the genetic
instructions used in the development
and functioning of all known living
These are of two types : DNA and RNA.
● DNA was discovered by James
D Watson and Francis Crick, who
got Nobel Prize for this discovery.
● It is a long polymer made from
repeating units called nucleotides.
● Each nucleotide consists of a
nucleoside (i.e. nitrogenous base
and deoxyribose sugar) and a
phosphate group, joined together by
● It has four bases, i.e. adenine,
guanine, cytosine and thymine.
● Adenine and guanine are the
purine bases; cytosine and thymin
1 gm glucose provides about 17 kJ energy
or 4.2 kcal energy.
● Carbohydrates are better fuel as
compared to proteins and fats as they
readily decompose to give energy.
● Main sources of carbohydrates are wheat,
maize, rice, potato etc.
The carbohydrates are categorised into
following three types
● These are simple sugars, which cannot be
hydrolysed further, e.g., ribose, glucose,
fructose, galactose etc.
● In human beings, blood glucose level is
100-120 mg/mL. Extra glucose, if any, is
converted into glycogen in the liver by a
process called glycogenesis.
● D-fructose is the sweetest of all sugars
and is found in fruit juice, honey etc.
● They release 2-10 monosaccharides on
hydrolysis, like disaccharides, e.g.
sucrose, lactose maltose etc and
trisaccharides, like raffinose etc.
● Sucrose is also called invert sugar. It
gives glucose and fructose when
subjected to hydrolysis.
● They release more than ten
monosaccharides on hydrolysis. These
are non-sugars, i.e., do not have sweet
taste, e.g., cellulose, glycogen and starch.
● Cellulose is found in plant cell wall and is
digested by ruminants (like cow, goat,
buffalo, etc), but not by carnivorous or
omnivorous animals like human beings.
Thus, it acts as roughage in case of
Function of Carbohydrates
● Carbohydrates provide energy, that acts
as reserve food, help in the synthesis of
nucleic acid and form exoskeleton of
animals. Excessive intake of carbohydrate
results in digestive problems and obesity.
These are found in all living cells. These are
the compounds of carbon (C), hydrogen
(H), oxygen (O), nitrogen (N) and sulphur
(S). These form 15% part of human body.
Snake venom, ricin of castor and bacterial
toxins are proteinaceous in nature. Main
sources of protein are groundnuts,
soyabean, pulses, fish etc.
Function of Proteins
● These are important for the growth and
repair of the body (75% of our body is
protein only). However, in the
deficiency of carbohydrates, these acts
as the source of energy. Protein also
control the development of genetic
● Deficiency of protein causes
Kwashiorkor (a disease in which hands
and legs of children get slimmed and the
stomach comes out) and Marasmus (a
disease in which muscles of children are
loosened). Kwashiorkor occurs in
children between 1 to 5 years of age and
marasmus in children below 1 year.
● These are also the compounds of carbon
(C), hydrogen (H) and oxygen (O).
Chemically, these are the ester of
glycerol and fatty acids. These are
present in cytoplasm, cell wall etc.
● The main source of fats are ghee, butter,
almond, cheese, egg yolk, meat,
● Fats are digested by enzymes called
lipases in the small intestine. Generally,
at 20°C, these are in solid state but if
their state is liquid at this temperature,
these are termed as oils.
● Fatty acids are of two types- Saturated
and Unsaturated. Saturated fatty acids
are found in coconut oil and palm oil,
while unsaturated fatty acids are found
in fish oil and vegetable oil.
● Excess of saturated fats raises the level
of blood cholesterol and may cause
arteriosclerosis. This may lead to
Function of Lipids
The main functions of lipids are
● These provide twice the energy than
that from carbohydrates.
● These remain under the skin and
prevents the loss of heat from the body.
● Deficiency of fat results in dryskin and weight
● If fat is in excess, the body gets fatty and
result in several heart diseases and high
● The skin fat, in case of whales and seals,
forms a thick layer called the blubber. It acts
as reserve food and also maintains the body
● It was first discovered by FG Hopkin.
However, the term vitamin was coined by C
● Vitamin is an organic compound, which
cannot be synthesised in sufficient quantities
by an organism and must be obtained from
● They provide no calories, they only regulate
chemical reactions occurring in the
metabolism of the body.
These are divided into two groups
1. Fat soluble vitamin, viz. vitamin-
A, D, E and K.
2. Water soluble vitamin, viz.
vitamin-B and C.
● Vitamin-B12 contains cobalt.
Vitamin-D is synthesised in our skin
by the action of ultraviolet rays of
the sunlight. Vitamin-K is
synthesised in our colon by the
● Water soluble vitamins normally do
not show hypervitaminosis (this
disease occurs due to excess intake
of vitamins) as excess of these
vitamins is normally excreted
● In balanced diet, all the important
nutrients (like carbohydrate,
protein, fats, vitamins etc.) are
available in sufficient quantity.
Origin of Universe
● The universe is made up of matter and
energy. Scientists believe that it was
formed about 10 to 13 billion years ago
as a vast, dense, red-hot and rotating
gaseous cloud of cosmic dust called the
“primaeval matter or ‘ylem’.
● Two hypothesis i.e., Big -Bang
(universe formation through a very big
explosion) and Nebular (universe
formation by the condensation of
gaseous cloud) were given to explain
origin of Earth.
ORIGIN OF LIFE
● Life originated on Earth about 3.5
billion years ago. Some philosophical
theories like special creation,
spontaneous generation, Biogenesis,
panspermia (life originated in the form
of pansperms from some unknown
part of the universe) or cosmozoic and
catastrophism (life orginated suddenly
from inorganic matter) were given to
explain origin of life.
● The first scientific account of the
origin of life was given by Russian
scientist AI Oparin in his book ‘Origin
● The primitive atmosphere contained
hydrogen, methane, ammonia and
water vapour. In it, oxygen and ozone
were absent. Thus, it was believed that
life is originated from inorganic
substances by a series of complex
● Hydrogen atoms were most numerous
and most reactive in the primitive
atmosphere. First, these combined
with all available oxygen atoms,
forming water and leaving no free
oxygen atoms. Thus, the primitive
atmosphere was ‘reducing’ unlike the
present ‘oxidising’ atmosphere. This
was also supported by Miller and Urey
● In Miller-Urey experiment, a mixture
of water, hydrogen, methane and
ammonia was cycled through an
apparatus and the organic compound,
amino acids were obtained.
More and more creation of organism by
gradual changes from low category animal to
higher animal is called organic evolution.
There are several evidences regarding
Evidences from morphology
On the basis of morphology (outer
appearance) and anatomy (inner structure),
several evidences have been described as
● The organs which are similar in basic
structure and origin but dissimilar in
function are called homologous organs,
e.g., wings of bat, cat’s paw, front foot of
horse, human’s hand and wings of birds.
● These show divergent evolution.
● The organs which are similar in shape and
function but dissimilar in their origin and
development. e.g., wings of insects, birds
and bats, eyes of octopus and mammals.
● They show convergent evolution.
● These are degenerate, non-functional
organs which were functional earlier.
● Human body has been described to possess
about 90 vestigial organs. Some of these
are muscles of ear pinna, canine teeth and
third molar teeth, body hairs, vermiform
appendix, nictitating membrane of eye,
caudal vertebral (coccyx or tail bone) etc.
Atavism or Reversion
It is the sudden reappearance of some
ancestral features. Appearance of thick body
hair, large canines, monstral face, short
temporary tails, extra nipples etc are
examples of atavism.
Evidence from Connecting
Connecting link is one which exhibit
characteristics of more than one groups.
● These are unicellular animals, i.e., made
up of only one cell.
● In these, all the metabolic activity like
digestion, respiration, excretion and
reproduction takes place in unicellular
● Respiration and excretion take place
e.g., Amoeba, Plasmodium, Euglena etc.
● These are found in marine water and have
porous body. The pores are called ostia.
These are multicellular animals.
● Their skeleton is made up of minute
calcareous or siliceous spicules.
e.g., Sycon, Sponge etc.
● These are aquatic animals, have thread-like
structures called tentacles around the
mouth which help in holding the food.
● They have specialised cnidoblast cell to
help in catching the food.
● Phenomenon of polymorphism (many
forms) and metagenesis (alternation of
generation) are associated with
e.g., Hydra, Jelly fish, Sea Anemone etc.
● Hydra has a tendency of regeneration of
● Animals of this phylum have
alimentary canal with single opening,
anus is absent.
● Excretion takes place by flame cells.
● There is no skeletal system such as,
respiratory system, circulatory system
● These are hermaphrodite animals
(males are not separated from
e.g., Planaria, Liver fluke, Tape worm
● These are long, cylindrical,
● Their alimentary canal is complete in
which mouth and anus both are
● There is no circulatory and respiratory
system but nervous system is
developed. Excretion takes place
● They are unisexual.
● Most forms are parasitic but some are
free living in soil and water.
e.g., Ascaris, Threadworm, etc.
¡ Threadworm is found mainly in the
anus of child. Due to which children
feel itching and often vomits. Some
children urinate on the bed at night.
● Their body is long, thin, soft and
metamerically (truly) segmented.
● Alimentary canal is well-developed.
● These are the first to have proper organ
● Nervous system is normal and blood
(called haemolymph) is red (iron rich
● Their blood flows in closed vessels.
● Like in earthworm, there are five pairs of
blood vessels called as heart.
● They respire through skin, in some
animals respiration takes place through
● Excretion by nephridia.
● They move through setae made up of
e.g. Earthworm, Nereis, Leech etc.
● Arthropoda is the largest phylum
(contains maximum number of animals
and its existence is recorded for
maximum period over the Earth).
● Jointed leg is their main feature.
● Their body is divided into three
parts–head, thorax and abdomen.
● Circulatory system is open type.
Cockroach’s heart has 13 chambers.
● Trachea or book lungs, body surface are
e.g., Cockroach, Prawn, Crab, Bug, Fly,
Mosquito, Bees, etc.
¡ Insects generally have six feets and four
¡ Ant is a social animal which reflects
division of labour.
¡ Termite is also a social animal which
lives in colony.
● Their body is soft and divided into head
and muscular foot.
● Mantle is always present in it, which
secretes a hard calcareous shell.
● Their alimentary canal is well-
● Respiration takes place through gills or
ctenidia. Blood is colourless.
● Excretion takes place through kidneys.
e.g., Pila, Aplysia (Sea rabbit), Doris (Sea
lemon), Octopus (Devil-fish), Sepia
¡ Eyes of octopus are similar to chordate
● All the animals in this group are marine.
They have water vascular system.
Brain is not developed in nervous
● They have a special capacity of
● These are the only invertebrate animals
which contain proper bone like
e.g., Star fish, Sea urchin, Sea cucumber
● They have notochord. A dorsal hollow
tubular nerve cord and paired
pharyngeal gill slits at some stage of their
● In advanced forms, notochord changes
to vertebral column, nerve cord develops
to brain and spinal cord and pharyngeal
gill slits to structures of jaw attachment.
● This phylum is sub-divided into two
sub-phylum, i.e., Protochordata and
Some main classes of phylum– Chordata
are as follows
● These are aquatic animals (cold-blooded
animals). Their heart pumps only
impure blood and have two chambers.
● Respiration takes place through gills.
e.g., Trygon, Scoliodon, Torpedo etc.
Amphibia (First land
● These are found both on land and water.
All of them are cold-blooded.
● Respiration takes place through gills,
skin and lungs.
● They have three chambered heart.
e.g., Frog, Necturus, Toad, Icthyophis,
Reptilia (First true land
● These are crawling animals.
● These are cold-blooded and contains two
pair of limbs.
● The skeleton is completely flexible.
● Respiration takes place through lungs.
● They have 3
chambered heart (four
chambered in crocodile).
● Their eggs are covered with shell made up
of calcium carbonate.
e.g., Lizard, Snake, Tortoise, Crocodile,
Turtle, Sphenodon etc.
¡ Cobra is the only snake which makes
¡ Heloderma is the only poisonous lizard.
¡ Sea snake is also called Hydrophis
belcheri. It is the world’s most poisonous
Aves (Aerial Vertebrates
● The animals of this group are
warm-blooded tetrapod vertebrates with
● Their fore-feet are modified into wings to
● They respire through lungs.
● Birds have no teeth, beak helps in feeding.
● They have a single ovary and pneumatic
bones. e.g., Crow, Peacock, Parrot etc.
¡ Flightless birds are Kiwi and Emu.
¡ Largest bird is Ostrich.
¡ Smallest bird is Humming bird.
¡ Largest zoo in India is Alipur (Kolkata)
and the largest zoo of the world is Cruiser
National Park in South Africa.
● These are warm-blooded animals.
● Tooth comes twice in these animals
● There is no nucleus in their red blood cells
(except in camel and llama).
● Skin of mammals contains hair.
● External ear is present.
Mammalia is divided into three
● Prototheria It lays eggs, e.g.,
● Metatheria It bears the immature
child, e.g., Kangaroo.
● Eutheria It bears the well developed
child, e.g., Humans.
They give birth to young ones, but
Echidna and Platypus are the egg
The human skin (integumentary) is
composed of a minimum of three major
layers of tissue, the epidermis, dermis
The top layer of skin is made up of
epithelial cells and does not contain
● It gives elasticity to the integument,
allowing stretching and conferring
flexibility, while also resisting
distortions, wrinkling and sagging.
● Nails grow 1 mm per week on an
● Protein, keratin stiffens epidermal
tissue to form finger nails.
● It is made up of adipose tissue.
It performs several important functions
1. Protect against invasion by
2. Protect the body from dehydration.
3. Maintain homeostasis.
4. Act as a receptor for touch, pressure,
pain, heat and cold.
5. Protect the body against sunburns by
6. Generate vitamin-D through
exposure to ultraviolet light.
7. Store water, fat, glucose and
Animal Nutrition and
Animals are not able to synthesise their
own food, therefore they obtain it from
outside environment for their nutritional
● These are metals, non-metals and their
salts other than the four
elements—carbon, hydrogen, nitrogen
and oxygen and constitute about 4% of
total body weight.
● Milk, eggs, meat, fruit, food, vegetables
etc are the sources of minerals.
Minerals are of two types
1. Macronutrients These are required in
large amount, e.g., calcium (Ca),
phosphorus (P), potassium (K) etc.
2. Micronutrients These are required in
very small amount (less than 1 g), e.g.,
iodine (I), iron (Fe), zinc (Zn) etc.
About 70% of the human body consists of
water. Two-third of water exists inside
cells, the other one-third is outside the
cells in tissue fluid and blood plasma. It is
essential for digestion, transportation,
excretion and to regulate body
Many factors affects the health of human
body. One of them is adulteration.
Addition of undesirable, cheap and
harmful substances in the food is called
Indian Standards Institution (ISI) Mark
and Agmark (Agricultural marketing) are
given by the Bureau of Indian Standards
after testing the purity and quality of
material and food respectively.
Food Item/Stuff Adulterant
Milk, curd and
Water and urea
Sweets Saccharin, harmful colour
Ghee Vanaspati and animal
Cereals Stones, sand and grit
Dhania powder Powdered horse dung
Haldi powder Lead chromate
Pulses Metanil yellow
Edible oils Argemone oil
Black pepper Papaya seed
The human digestive system consists of
alimentary canal and digestive glands.
The alimentary canal consists of mouth,
(having teeth and tongue) oesophagus,
stomach, small intestine and large
● With the help of teeth the food is
chewed. Teeth are of four types
Incisors (for cutting)
Canines (for tearing)
Premolars (for chewing)
Molars (for chewing and grinding)
● The number of teeth are different in
different animals. These are represented
by dental formula as
I C Pm M – Upper half jaw
I C Pm M – Lower half jaw
Where, I − Incisors, C − Canines,
Pm − Premolars and M − Molars.
● Premolars and molars are called cheek
teeth. Milk teeth do not include molar
● In humans, first teeth come in between
6 and 8 months. By the age of 6, milk
teeth are gradually replaced by permanent
● Hardest part in the body is tooth enamel.
● In elephants, the tusks are the incisors of
● Maximum number of teeth are present in
horse and pig.
Man (child) 2102/2102 × 2 20
Man (adult) 2123/2123 × 2 32
Horse 3143/3143 × 2 44
Dog 3142/3143 × 2 42
0033/3133 × 2 32
Cat 3131/3121 × 2 30
Rabbit 2033/1023 × 2 28
Mouse 1003/1003 × 2 16
● Saliva, secreted by the salivary glands, is
mixed with the chewed food by the
● Tongue also contains taste buds due to
which we sense bitter, sour, salty or sweet
Digestion of Food
Digestion in Mouth
In mouth, salivary amylase acts on
Digestion in Stomach
● The food passes down through the
oesophagus into stomach.
● Now food is mixed with gastric juice
and hydrochloric acid which
disinfect the food and creates acidic
● Pepsin digests proteins and converts
them into peptones.
● Rennin convert milk into curd.
● Digested food now is called chyme.
Digestion in Duodenum
● Chyme moves to duodenum.
● Food is mixed with bile (liver) to breakdown
fats into smaller globules.
● Trypsin acts upon proteins and break them
into polypeptides. Amylase converts starch
into simple sugar.
● Lipase convert fats into fatty acids and
Digestion in Intestine
● Food passes into ileum and mixes with
intestinal juice, where
Maltase converts maltose into glucose
Lactase converts lactose into glucose
Sucrase converts sucrose into glucose and
Trypsin digests the peptides into amino
Absorption and Assimilation of
● Ileum’s internal surface has finger-like
folds called villi.
● It helps in absorption of food.
● Intestinal juice is alkaline in nature.
● pH of saliva, gastric juice, pancreatic
juice and intestinal juice is respectively
6.8, 2.0, 7.0 and 8.5.
Ejection of Unwanted Food
● Digested food passes into large intestine.
● Large intestine cannot absorb food, but
absorbs much of the water.
● The remaining semi solid waste is called
faeces and is passed into rectum.
● It is expelled out through anus.
● Roughage is another term for dietary
fibres e.g., Natural food, dalia etc.
● It does not provide energy but only helps
in retaining water in the body.
● It is the largest gland of the human body
and secretes bile juice, which is stored in
● It regulates the quantity of glucose in the
blood by converting extra glucose (if any)
into glycogen or glycogen (during
deficiency of glucose) is converted into
● It destroys dead RBC and regulates body
temperature. It converts excess of amino
acid into ammonia (which is converted
into urea by Ornithine cycle). Urea
comes out from the body through kidney.
● If there is any obstruction in bile duct,
liver cells stop taking bilirubin from the
blood, consequently it spreads
throughout the body which is called
● Liver is an important body organ in
investigation of a person’s death that has
been due to poison in food.
Human Respiratory System
● Overall passage of air in humans is as
Nostrils → Pharynx → Larynx → Trachea
→ Bronchi → Bronchioles → Alveoli →
● The human respiratory system is shown
in the following diagram.
Types of Respiration
● The respiration taking place in the
presence of oxygen is known as aerobic
● This respiratory oxygen oxidises the
substance into carbon dioxide, water
and energy, as follows
Glucose + O2 →Carbon dioxide
+ Water + Energy.
● In this process, each glucose molecule is
converted into two molecules of pyruvic
acid by the process, called glycolysis. It
takes place in the cytoplasm of the cell.
The pyruvic acid formed, releases energy
with the formation of carbon dioxide and
water (in Kreb’s cycle which occur in
● The respiration taking place in the
absence of oxygen is known as
● It is found in endoparasites like
roundworm. In this process, the
respiratory substances are incompletely
oxidised to carbon dioxide and alcohol.
Carbon dioxide +
muscles +Energy (in plants)
Glucose → Lactic acid
+ Energy (in animals)
PHASES OF AEROBIC
(Breathing or Ventilation of
● It involves inspiration and expiration of
● Inspiration is the process of intake of air.
During inspiration, muscles of the
diaphragm contract and diaphragm
● The lower ribs are raised upward and
outwards. The chest cavity enlarges, the
air pressure in the lungs gets decreased
and air rushes into the lungs.
● Expiration is breathing out of air. During
expiration, relaxation of muscles of the
ribs and diaphragm takes place.
● Diaphragm again become dome-shaped.
Chest cavity is reduced and air is
forced outwards through nose and
● Breathing rate in humans is 18 20 – times
● The exchange of gases, i.e., oxygen and
carbon dioxide takes place due to the
difference in their partial pressures.
(Oxidation of Food)
● It is a complex process in which food is
broken down to release energy.
● Transportation of oxygen takes place by
haemoglobin of blood. Whereas
transportation of only 10-20% carbon
dioxide takes place by haemoglobin of
● Approximately 400 ml water is lost
through breathing everyday.