SS Academy Rajapuram
Cell Structure and Functions
Cell
There is a large variety of
organism around us. They have different shapes and sizes. Their food habits and
habitats are also different. Inspite of great variation all the living organism
have a basic similarity among them :they are made up of tiny units called cells.
Cells are the structural and functional
units of life. Cork is a part of the bark of a tree. Cork is a dead plant
material.
In 1665,An English Scientist
named Robert Hook used a microscope to investigate the structure of a thin
slice of cork. He observed that cork had tiny compartment in it. Robert Hooke
thought of these compartments as small rooms and called them cells.
When better microscopes were
made, scientists investigated pieces of living plants and found that like cork,
they also had a cell structure. The living plant cell were found to contain a
number of tiny structures.
The cell theory states
that the basic unit of structure and function of all living organism is the
cell. All cells arises from pre-existing cells by cell division. The cells were
not studied or observed for thousands of years because most of them are
extremely small and cannot be seen with naked eyes.
Cells are the basic units of
life. All the living things are made up of cells. They are the building blocks
of plants and animals.
The simplest organism like
amoeba consist of only one cell but a complex organism like man is made up of
trillions of cells.
A cell is the smallest
unit of life which has a definite structure and performs a specific function.
Most of the cells are very, very small which cannot be seen with naked eyes.
They can be seen only with the help of microscope.
The cells are of 2 main
types: Animal cells and plant cells.
Nucleus
Nucleus is a large, spherical
organelle present in all the cells.
(1) In animal cells, nucleus
lies in the centre of the cell whereas in plant cells the nucleus may be on the
periphery of the cell.
(2) Nucleus is the largest
organelle in a cell.
(3) It can be stained and
seen easily with the help of a microscope.
(4) Nucleus is separated from
the cytoplasm by a membrane called nuclear
membrane.
(5) The transmission of
characteristics from the parents to the offsprings is called inheritance. Nucleus
contains thread like structures called chromosomes
(6) Chromosomes contain genes. The function of
chromosomes is to transfer the characteristics from the parents to the
offspring through the genes. The nucleus also contains a tiny round structure
called nucleolus.
(7) The nucleus containing
chromosomes and nucleolus is bound by a membrane called nuclear membrane. It
has tiny pores for the exchange of materials with cytoplasm. Red blood cells,
however, do not have a nucleus.
(8) Gene is a unit of
inheritance in living organism(which is transferred from a parent to offspring
during reproduction and determines some characteristics feature of the
offspring)
(9) Genes control the
transfer of heredity characteristics from parents to offspring. This means that
our parents pass on some of their characteristics features to us through their
genes.
(10) It is the genes on the
chromosomes which decide all sort of things, the colour of our eyes, the look
of our hair, the shape of our nose, our complexion, our appearance etc.
(11) The different
combinations of genes from both the parents results in different
characteristics in the offspring.
(12) All the living matter in
a cell is called protoplasm.
It is a liquid substance which is present inside the cell membrane. It includes
cytoplasm, nucleus and other organelles. Most of the protoplasm is made up of
compounds of only 4 elements :Carbon, hydrogen, oxygen. Some of the compounds
present in protoplasm are water, carbohydrates, proteins, fats, nucleic acid
and mineral salts.
Mitochondria
Mitochondria are the tiny rod
shaped organelles which are found in all cells.
They provide energy for all
activities of the cell. This energy is produced by the process of respiration
in which food is broken down by oxygen. Mitochondria use glucose and oxygen to
produce energy.
Cell wall
The plant cell wall is made
of a tough material called cellulose.
Cell wall gives shape and support to the plant cell.
The plant cells have a thick
cell wall around them. Cell wall give plants most of their strength. Plants
need protection against high wind speed, variations in temperature and
atmospheric moisture. The tough cell wall present in plant cells provide
protection to plants.
Cell wall is not there in
animal cell. The cell wall is a non-living part of the plant cell.
Chloroplasts
They are green coloured
organelles present in the cytoplasm of plant cells.
The process of food making by
plants known as photosynthesis
takes place in
chloroplasts. The green colour of chloroplast is due to the
presence of a green pigment called chlorophyll
in them. Chlorophyll can absorb sunlight energy.
In chloroplast, carbon
dioxide and water combine in the presence of sunlight energy to produce food
such as glucose. They are found only in those plant cells which carry out photosynthesis.
The organelles containing
pigments present in the cytoplasm of plant cells are called plastids.The plastids
containing green pigment(chlorophyll) are known as chloroplasts.
The green coloured plastids
present in the cells of leaves provide green colour to the leaves. The red
colour of tomatoes is due to the presence of plastids having red pigments in
the cytoplasm of its cells.The different colour of flowers are due to the
presence of plastids containing pigments of different colour.
Vacuole
It is a space in the
cytoplasm of a cell which is enclosed by a membrane and usually contains
substances dissolved in water.
All the plant cell have a
large vacuole. The vacuole is filled with a liquid called cell sap, which
contains dissolved sugar and salts.
(1) The pressure of liquid
pushes on the outer parts of the plant cell keeping the plant cell firm.
(2)The function of vacuole in
a cell is to store various substances including waste products of the cell.
(3) Most of the animal cells
do not have vacuole. Some of the animal cell have vacuole but they are much
smaller than those in plant cells.
Cell membrane and
cytoplasm
Cell membrane
Every cell is covered by a
thin sheet of skin which is called cell
membrane or plasma membrane.
1)The cytoplasm and nucleus
are enclosed within the cell membrane.It encloses the living part of the cell
called protoplasm.
2)Cell membrane protects the
cell and also gives shape to the cell.
3)The cell membrane has tiny
pores in it.The cell membrane controls the movement of substances into the cell
and out of the cell.
4)The dissolved substances
such as food and oxygen can enter into the cell whereas the waste products such
as carbon dioxide can go out from the cell whereas the waste products such as
carbon dioxide can go out from the cell membrane through the pores of the cell
membrane.
5)The cell membrane separates
the cells from one another and also from surrounding medium.
Cytoplasm
It is a transparent jelly
like material which fills the cell between nucleus and cell membrane.
1)New substances are built
from materials taken into the cell, and energy is released and stored.
2)It has many tiny structures
in it.The various structures present in the cytoplasm of a cell are called organelles.
3)Cytoplasm of all cells contain
other organelles such as mitochondria, golgi bodies , nucleus and ribosomes.
4)The cytoplasm and nucleus
taken together make up protoplasm.
Structure of Animal
cell
1)A cell consist of a jelly
like material enclosed in a thin membrane.The jelly like material which fills
the cell is called cytoplasm.The
function of cytoplasm is to carry out all the activities of the life processes.
2)The thin outer covering of
the cell is called cell
membrane.
3)There is a large floating
body usually in the centre of a cell which is called nucleus.The function
of nucleus is to control all the activities of the cell.
4)The nucleus contain a tiny
round structure called nucleolus
and a fibrous material called chromatin.It
also has a nuclear membrane on the outside.Chromatin form chromosomes during
cell division.These chromosomes transfer characteristics from the parents to
the next generation.
5)The cytoplasm and nucleus
taken together form the protoplasm
of the cell.It is the living material of a cell.
6)There are a number of small
bodies called
mitochondria in a cell.The function of mitochondria is to carry
out respiration for releasing energy from food.Since mitochondria produce
energy from food, they are kind of power house of the cell.
7)The tiny air spaces in the
cytoplasm of an animal cell are called vacuoles.
The function of a vacuole in an animal cell is to hold air , water and
particles of food.
8)The cell membrane is a
thin sheet of skin all around the cell.The main function of cell membrane is to
control the passage of materials which go into the cell or go out from the
cell.It also protects the cell and gives shape to the cell.
Structure of Plant
cell
1)A cell consist of a jelly
like material enclosed in a thin membrane.The jelly like material which fills the
cell is called cytoplasm.The
function of cytoplasm is to carry out all the activities of the life processes.
2)There is a large floating
nucleus in the cytoplasm.The nucleus contain a tiny round structure called nucleolus and a
fibrous material called chromatin.It
is surrounded by nuclear membrane.
3)There are a number of small
bodies called
mitochondria in a cell.The function of mitochondria is to carry
out respiration for releasing energy from food.
4)All plant cell have thick
cell wall all around the cell
membrane.This cell wall is made up of cellulose.The cell wall
protects the plant cell, gives it a fixed shape and makes it rigid.
5)The plant cell contain
green coloured plastids called chloroplasts.They
are green coloured bodies in the cytoplasm of the plant cell.They make food in
green plants by the process of photosynthesis.Plant cell may contain plastids
of different colours.
6)The plant cells have very
large vacuoles.These
vacuoles are filled with cell sap.It is a solution of sugars and mineral salts.
Staining of plant and animal specimen is done
to identify the different components of a cell easily through the microscope.
For Ex:Dilute iodine
solution, methylene blue, safranin.
Prokaryotic cells
The cell having nuclear
material without a nuclear membrane around it, are called prokaryotic cells.
The organism made of
prokaryotic cells are called prokaryotes.
1)The nucleus of prokaryotic
cell is not well organised.
2)There is no nuclear
membrane around the nuclear material in the prokaryotic cells.
3)The nuclear material is in
direct contact with the cytoplasm.
4)All the prokaryotes are
simple, unicellular organism.
5)They were probably the
first living things to evolve on the earth.
For Ex: Bacteria, blur green algae are
prokaryotes.
Eukaryotic Cells
The cells having nuclear
material enclosed by a nuclear membrane are called eukaryotic cells.
The organism whose cells
possess a nucleus bound by a nuclear membrane are called eukaryotes.
1)They have proper, well
organised nucleus.
2)The nuclear membrane in
eukaryotic cell is not in direct contact with cytoplasm, it is separated from
cytoplasm by the nuclear membrane.
For Ex: Amoeba, cheek cell, onion peel cell ,
plants, animals, protozoa, fungi etc.
The various organisms differ
in the number of cells which make up their body; they differ in the shapes of
cells in their body ; also they differ in the size of cells in their body.
Variety in number of
cell
Different organism have
different number of cells in their bodies.The number of cells varies from
organism to organism.Some are made up of just one cell while other are made up
of large number of cells.
The organism which are made
up of only one cell are called unicellular
organism or single-celled organism.
For Ex:Amoeba, paramecium, Euglena,
Chlamydomonas etc.
A unicellular organism
perform all necessary life functions with the help of just one cell.All basic
function such as taking of food, digestion, respiration, movement, response to
environment, excretion , reproduction etc are performed by single cell.
The organism which are made
up of only many cell are called multicellular
organism.
A multicellular organism is
made up of millions, billions, trillions of cell joined together.Most of the
plants and animals are multicellular.
In multi cellular organism
different cells perform different functions.
The number of cell being less
in small organism does not in any way affect the functioning of the small
organism.Even an organism made of million, billions or trillions of cells begin
its life as a single cell called fertilised
egg cell.The fertilised egg cell divides and multiplies due to
which the number of cell increases as the development of the organism proceeds.
Variety in shape of
cell
There are many types of cells
in the bodies of multicellular bodies.These cell differ in shapes.
The shape of a nerve cell
in nerve cell in animals is different from the shape of a muscle cell.
A nerve cell is long and
branched whereas a muscle cell is pointed at both ends and has a spindle
shape.The different shape of cells are related to their function which they
have to perform in the body of an animal or plant.
Nerve cell receives and transmit messages
between brain and other body parts whereas muscle cells bring about movement in
body parts.Nerve cells and muscle cells are actually specialised animal cells
because they perform functions in the bodies of animals.
Cells are different in shapes
and sizes so they can perform different functions.Each one of these cells are
adapted to perform some specific functions.
The human body is made up of
about 20 different types of cells and each type of cell perform different
function.
Some of the example of animal
cell are:Nerve cell or neuron, muscle cell, Epithelial cell, Red blood cell,
white blood cell, bone cell etc.
Nerve cell
The nerve cell are long and
have projections so that they can make contacts with many other nerve cells and
carry messages over long distances.Since nerve cells receive and transfer
messages they help to control and coordinate the working of different parts of
a body.
Muscle cell
They are specially adapted
for movement.The muscle cell can contract and relax.when the muscle are
contract, they shorten in length.So, the contraction of muscle cells moves the
body part.When these contracted muscle cell relax, they expand so that the body
part comes back to its original position.Muscle cell bring about movement of
body parts by contracting and relaxing.
Epithelial cell
They are rectangular in
shape.They form a thin layer over the body parts and protect the cells below
them from injury.
Red blood cells
They are spherical in
shape.RBC carry oxygen around the body.
White blood cells
They are irregular in
shape.They eat up or kill bacteria which enter the blood and save us from many
diseases.
Some of the plant cells
are:Epidermal cell , Xylem cells, phloem cells, photosynthetic cells
Epidermal cells form a layer
around the plant organs and protects the cell below from injury.
Xylem cells are the tube like plant having thick
and strong walls which carry water and mineral salts from the roots of the
plant to its leaves.
Phloem cells are also tube like plant cells having
thin walls which carry the food made by leaves to all parts of the plant.
The photosynthetic cells
of plant contain chlorophyll and prepare food by photosynthesis.
The mesophyll cells of
leaf are the photosynthetic plant cells.These cells in the leaf of a plant are
specially adapted for making food by photosynthesis.
Amoeba cell
The shape of an amoeba cell
is irregular.
1)The amoeba cell keeps on
changing its shape continuously.The shape of amoeba changes because amoeba can
make its cytoplasm flow in any direction it wants to.
2)The amoeba cell has finger
like projections of varying lengths protruding out of its body which are called
pseudopodia.
3)Amoeba can produce
pseudopodia on any side by pushing the cytoplasm in that side.The pseudopodia
appear and disappear when amoeba moves or feed.Amoeba moves very slowly with
the help of pseudopodia.
4)Amoeba also
uses pseudopodia to catch the food particles from the water in which it
lives.
Amoeba is a single cell which
can change its shape.
A white blood cell present in
human blood is a single cell which can also change its shape.The difference between amoeba cell and white blood
cell is that amoeba cell is a full fledged organism capable of
independence existence, white blood is merely a cell of human blood which
is not a full fledged organism and hence cannot exist independently.
Variety in size of
cell
The cells are of many
different sizes.The cells in living organism may be as small as a millionth of
a metre or it may be as large as a few centimetres.
Most of the cells are
extremely small in size and hence cannot be seen by naked eyes.Most of the
cells found in living organism have to be enlarged by using a microscope before
they can be seen by us.
The bacteria cells have a
length of 0.1 to 0.5 micrometer.Bacteria mycoplasma is the smallest cell having
the size of only 0.1 micrometer.
Even the long cells are so
thin that they can be seen only with a microscope.The muscle cell in animals
are a few centimetres long and the nerve cells are more than a metre long, but
they are are so thin that they can only be seen with the help a microscope.
Some of the cells are big and
can be seen easily with naked eyes.The bird’s egg are very large cells.Each egg
of the bird is a single cell.
The hen’s egg is a single cell.The
hen’s egg is quite big.We can see the single cell called hen’s egg with naked
eye.
The biggest cell is the
ostrich egg.The ostrich egg can be as much as 17 centimetres long.
In Human body, some blood
cells are the smallest and the nerve cells are the longest.The ostrich egg is
actually 17 cm * 13 cm.The size of cells has no relation with the size of the
body of an animal.
Cell
Cell is the smallest unit of
life which has a definite structure and perform a specific function.There are
many different shapes and sizes.Most of the cells are specialised to perform
different function.They are called specialised cells.
Muscle cells are specialised to contract and relax
so that they can bring about movement in body parts.
Photosynthetic cells are specialised to carry out
photosynthesis and make food.There are many types of specialised cells in
animals and plants which perform different functions.
Tissues
The group of similar cells
which work together to perform a particular function is called tissue.
A multicellular organism is
made up of millions of cells.The cells in multicellular organism do not work as
single cells, they work in groups of similar cells.
Muscle tissue is a group of muscle cells joined
together which is specialised to contract and relax so as to move body parts.
Photosynthetic tissue is a group of photosynthetic cells
joined together which is specialised to do photosynthesis and make food.There
are many types of tissue as there are cells.
Organs
An organ is a collection
of different tissues which can work together to perform a particular function
in the body of an organism.
The different tissue combine
together to form organs.These organs perform different tasks for the animals or
the plants.
The multicellular organism
are made up of many different organs which do different jobs for the organism.
Some of the organs which are
found in the bodies of animals are heart, stomach, lungs, brain, kidney, eyes,
mouth, hands etc.
The function of heart is to pump blood
around the body.
The function of stomach is to digest
food.
The function of brain is to control
all the parts of a body.
Lungs are the organs of breathing.The
function of lungs is to take in oxygen and give out carbon dioxide.
The various organs found in
the body of a plant are roots, stem, leaves, flower, fruits.
Roots absorb water and dissolved mineral
salts from the soil.
Stem carries water and mineral from the
roots to the leaves, and the prepared food from the leaves to other parts of
the plants.It holds branches and leaves.
The leaves prepare food
for the plant by the process of photosynthesis.
The flowers are the
reproductive organs which lead to the formation of fruits and seed.The fruit
protects the seeds.
Organ system
A group of interconnected
organs which work together to do a big job for the organism is called organ
system.
All the multicellular animals
and plants have many organ system in their bodies to carry out various life
processes.
For Ex:Digestive system,
circulatory system, muscular system, skeletal system, excretory system etc.
The function of digestive
system is to break down the food into simple substance which can be absorbed by
the body.The main organs of the digestive system are:Mouth, food pipe, stomach,
small intestine, large intestine, rectum, anus.Each organ of digestive system
perform a different function such as ingestion, digestion, absorption,
assimilation and egestion.
The plants have 2 main organ
system:Root system and shoot system.The root system consist of various types of
roots whereas shoot system is made up of organs like stem, leaves, flowers,
fruits.
Organism
An organism is an animal or
plant which can exist on its own.
An organism is made up of
many different organ system which work together to perform all the functions
necessary for maintaining .
For Ex:Human being is an
organism.It is made up of many different organ system.All the organ system work
together to make man a living organism.
A cat, dog, neem tree, mango
tree, rose plant are all organism which are made of many different organ
systems working together.
