for students of class six

2. Living things respond to sound,
light or touch. All living things
have ways of taking in the
substances that they need to
grow and survive. They respond
to sound, light, or touch. They
receive information about the
world around them in different
ways such as by hearing, seeing,
smelling, or sensing. All living
things reproduce; that is, they
make copies of themselves by a
process call Reproduction.

3. Cells All plants, animals, and other living things are made up of
cells. Cells are living things that feed, reproduce, and respond or react to
their surroundings. Some living things are made up of just one cell
(unicellular), but in the human body there are millions of cells,
(multicellular). Cells are the building blocks of all living things.

4. Cell Structure
Nearly all cells have the same basic structure. All calls have a round of
oval nucleus surrounded by a jelly-like substance called cytoplasm, both
of which are enclosed within a very thin skin known as cell-membrane.
All substances going into and coming out of the call pass through the call
membrane.

5. The cytoplasm contains a
large number of
important substances
such as oil droplets,
starch grains, water, salts,
and excretory matter. The
cytoplasm also contains
tiny living structures
called organelles, which
perform important
functions such as
respiration, excretion,
etc. for the cell.

6. Mitochondria are
round or elongated
organelles which help
in the process of
respiration. Golgi
bodies make special
secretions.
Chloroplasts in plant
cells trap the sunlight
energy needed for
photosynthesis.

7. A vacuole is a space filled with
fluid in the cytoplasm of a cell.
The nucleus of a cell contains rod-
shaped objects called
chromosomes, made up of a
nucleic acid called DNA. The
nucleus controls the whole
working of the cell. The
chromosomes take part in cell
division. The contain all the
information necessary for the
development of all the features as
organism inherits from its
parents.

8. A cell wall is absent
in the animal cell.
Cytoplasm is
present between
the nucleus and the
cell membrane.
Small vacuoles are
present in the
cytoplasm. The
nucleus is usually in
the centre.

9. Plant cellA hard cell wall made of
cellulose surrounds the cell.
A large vacuole containing
cell sap (a solution of salts
and sugars) is present in the
middle of the cell. A green
coloured substance called
chlorophyll is present in
structures called
chloroplasts. They help the
plant to produce food by
the process of
photosynthesis.

10. Root system in plants Root hold a plant firmly in the
soil. Some kinds of plants have one
large main root called a taproot,
with several smaller roots branching
off from it. Carrots, radishes, and
turnips all have tap roots. Other
kinds of plants such as wheat and
grass have many main roots about
the same size. These are called
fibrous roots. From the fibrous roots
many smaller roots branch off. A
thick root cap at the end protects
the sensitive growing point of the
root, the root tip.

11. Shoot system in plants
The stem and its
branches, along with
the leaf system make
up the shoot system.
If the stem remains
short with lots of
branches it is called a
shrub. Tall plants
with thick stems
(trunks) are called
trees.

12. Leaves are attached to the
stem at the nodes. Stems grow
from specialized growing-
structures called buds. Buds
many give rise to branches of
the stem or they may be
specialized to produce flowers.
The stem connects the roots to
leaves. It helps to transport
raw materials for
photosynthesis and the
products of photosynthesis to
all parts of the plant.

13. Tissues A group of similar
cells which are
specialized to
perform a particular
function is called a
tissue. Vascular
tissue, for example,
is used for
transporting food
and water in plants.
Muscle tissue is
used for movement
in animals.

14. Organs
Different types of tissues
grouped together form as
organ. An organ is specialized to
perform a particular function in
the body. For example, the
heart is an organ which pumps
blood to all parts of the body.
The leaf of a plant is an organ
for manufacturing food by
photosynthesis.

15. Organ systemsThe bodies of living organisms are made up of
a variety of systems. All these systems perform important functions
without which the body would not be able to survive. Systems are
made up of many organs which work together.

16. Transport system in plants
In multi-cellular plants, materials are
circulated in a system of tubes called the
vascular system. The vascular system of
plants is composed of specialized tissues
called xylem and phloem. Xylem is made up
of long, dead cells called vessels. Vessels
have thick walls. They carry water from the
roots through the stem to the veins in the
leaves. Phloem is made of long, thin-walled
tubes called sieve tubes. Sieve tubes are
made of living cells whose horizontal walls
have tiny holes. Food flows from the leaves
to other parts of the plant through the sieve
tubes.

17. Water enters plants through the
roots. The tiny parts of a root that
absorb water and minerals are
called root hairs. Barely covering
an inch or two, root hairs grow at
the tip of each root. Each root hair
is a hollow tube with thin walls. It
grows from a cell on the outside of
the root. Root hairs grow between
the soil particles where water is
held. As water enters the root cells,
pressure is built up. This root
pressure helps to push water a
short distance up the stem.

18. Plants lose water vapour through
evaporation into the atmosphere. The
water passes through tiny holes called
stomata which are found mainly on the
lower side of leaves. This process is called
transpiration. The movement of water
from the roots to the leaves is called the
transpiration stream. It appears that
water is pulled up by the xylem tubes as
water vapour is lost from the leaves
during transpiration. This transpiration
pull is the main way in which water is
transported in plants. Transpiration helps
a plant to keep cool in summer.

19. Photosynthesis in plants
Green plants make their own food in
their leaves, by a process called
photosynthesis. They use sunlight,
carbon dioxide absorbed from the air,
and water absorbed from the soil by
their roots to make simple sugars such as
glucose. Glucose is then use by the plant
or is change into insoluble substances
and stored in different parts such as the
stem, the root, the leaves, seeds, and
fruits to be used later.

20. Benefits of photosynthesis
Photosynthesis is
very important for
the continuation
of life on earth.

21. Photosynthesis
maintains the level of
oxygen in the
atmosphere which
supports life and
combustion.

22. Forests of the world
help to absorb the
huge amount of
carbon dioxide that
is produce by
modern industrial
societies.

23. Plants manufacture
all their body-
building and
energy-producing
substances from
simple raw
materials, using the
energy of sunlight.
Animals depend on
plants and plant-
eating animals for
their food and
energy supplies.

24. Cars aeroplane,
home-heating
systems and
industrial
complexes all make
use of natural
products like,
petroleum, gases,
etc. which were
made with sunlight
energy that was
absorbed by plants
millions of years
ago.

25. Respiration in plants

26. Respiratory system
Respiration is the process
by which food is oxidized in
the body cells to produce
energy. Oxygen is taken
into the body from the air
and carbon dioxide is given
out.
It is composed of the nose,
windpipe or trachea,
bronchi, bronchioles, and
air sacs or alveoli.

27. Air is taken in or inhaled by the nose. It passes
through the windpipe, bronchi, and bronchioles
and is delivered to the air sacs or alveoli. The
walls of the alveoli are thin and moist and are
surrounded by blood capillaries so that gaseous
exchange cam take place easily. Oxygen is
absorbed by the red blood cells in the capillaries
and is taken to the cells of the body. The food
present in the cells is oxidized and energy is
produced. This energy is used by the body for
performing various activities. As a result of
oxidation, carbon dioxide is produced in the cells.
This is absorbed by the blood and carried to the
lungs from where it is breathed out or exhaled.
Process of respiration

28. Gases Inhaled air Exhaled air
Oxygen 21% 16%
Carbon dioxide 0.04% 4%
Nitrogen 79% 79%
Water vapour Very little A lot

29. Circulatory System
Circulation of important materials
around the body takes place
through the circulatory system. The
parts of the circulatory system are
the heart, arteries, capillaries, and
veins.

30. Heart
The heart is a muscular organ found in the
center of the chest. It has four chambers.
The upper two chambers or atria are thin-
walled, while the lower two chambers or
ventricles are thick-walled. By the
pimping action of the heart, the
oxygenated blood is circulated to all parts
of the body, and the deoxygenated blood
from the cells is taken to the lungs for
removal of carbon dioxide and for getting
fresh oxygen.

31. Artery
An artery is a blood vessel which takes blood
away from the heart to an organ. For example,
the renal arteries take blood to the kidneys.
Vein
A vein is a blood vessel that takes blood from
an organ to the heart. For example, the renal
vein brings deoxygenated blood back to the
heart.
Capillary
A capillary is a very thin-walled blood vessel
which forms a connection between an artery
and a vein in an organ.

32. Digestive system
Digestive is the process by which insoluble
foods such as proteins, fats, and
carbohydrates are broken down by the
action of enzymes into simple, soluble
substances.
The parts of the digestive system are:
1.Mouth
2.Food pipe
3.Stomach
4.Small intestine
5.Large intestine

33. Mouth The mouth contains teeth, tongue,
and salvia. The teeth help to chew
food and break it into small pieces.
The tongue mixes the chewed food
with salvia. Salvia is a watery liquid
secreted into the mouth by glands,
providing lubrication for chewing and
swallowing. Saliva contains a chemical
substance or enzyme which starts the
digestion of starches by turning them
into simple sugars.

34. Food pipe or Esophagus
Food from the mouth passes into
the oesophagus from where it
enters the stomach.
Stomach
The stomach is a muscular bag
which stores food for some time.
Gastric juice, a colourless fluid
secreted by glands lining the inside
of the stomach, acts on protein and
changes it into digestible form.

35. Small intestine The partly-digested food passes
into the small intestine where bile
from the liver and pancreatic juice
from the pancreas mix with it and
digest it completely so that it can
be fully absorbed into the blood.
Digested food is absorbed by blood
capillaries in the finger-like
projections or villi found in the
small intestine. It is taken to the
liver from where it is sent further
to the cells and tissues. Excess food
is stored in the liver.

36. Large intestine
Food from the small
intestine passes into the
large intestine or colon,
where and salts are
absorbed. The undigested
food remains in the large
intestine for some time,
after which it is expelled
from the body through an
opening called the anus.

37. Excretory system
The process of removing harmful and
poisonous waste substances produced
by the body is called excretion. Lungs
and kidneys are the main excretory
organs of the body.
The parts of the excretory system are:
1.Kidneys
2.Ureters
3.Urinary bladder
4.Urethra

38. Process of excretion Blood containing waste substances
enters the kidneys through the renal
arteries. The blood is filtered by the
kidneys and the waste substances
are removed from it. It flows back
into the renal veins. Waste
substances along with excess water
pass down the ureters into the
urinary bladder, where it is stored for
some time in the form of urine.
When the bladder is full, urine is
passed out through the urethra.

39. The nervous system
control and
coordinates all parts
of the body. It is
made of specialized
cells called neurons
which have the ability
to carry messages
from one part of body
to another.

40. The brain The brain is part of the central
nervous system and is the main
control center of the whole body.
It is made up of nervous tissue
which is hollow. It is located in
the skull in a bony box called a
cranium. It receives messages
from the sense organs and sends
orders to the muscles to produce
suitable response.

41. The spinal cord
The spinal cord is also a part of the central nervous
system. It is a thick cord made of nervous tissue which
passes through the backbone or vertebral column. It is
connected to the brain at the top, and as it passes down
the vertebral column it gives off millions of branches
called nerves which carry messages between the body
and the central nervous system.
Nerves are actually bundles of neurons which are
covered by a tough covering or sheath. The nerves
which carry messages from the sense organs to the
central nervous system are called sensory nerves.

42. How the nervous system works
A sense organ for example, the eye receives
a sensation or stimulus (light). This message
is conveyed to the central nervous system
the brain or spinal cord by a sensory nerve
fiber. The central nervous system translators
this message and then sends a message to a
muscle or gland to produce a reaction or
response. The path by which the message is
received and a reaction is produce a reaction
is called a reflex arc.

43. Types of responses
Involuntary or reflex action
A reflex action is an involuntary
response, like sneezing, blinking, or
coughing, which takes place
without conscious thought.
Voluntary action
A voluntary action, like speaking,
walking, or running, takes place by
our own will.