Cellular Organizations This presentation covers everything you want to know about Cellular Organizations, especially class 8 science book Cellular Organizations chapter.

1. Cellular Organization

2. Some Facts about Cells
• The word cell is derived from the Latin word
“cellula” which means “a little room”
• It was the British botanist Robert Hooke
who, in 1665, while examining a slice of
bottle cork under a microscope, found its
structure resembling the box-like living
quarters of the monks in a monastery, and
coined the word “cells”

3. Some Facts about Cells
• The Dutch scientist A.V. Leeuwenhoek, in
1674, discovered the minute forms of life
such as bacteria and single celled animals in
a drop of water
• In 1831, Robert Brown discovered the
nucleus in the cell
• In the year 1838, Matthias Schleiden, a
German botanist, first proposed the idea
that all plants consist of cells

4. Some Facts about Cells
• In 1839, Theodor Schwann, another German
botanist, asserted that all plants and animals
are made up of cells
• J.E. Purkinje, in 1839, used the term
protoplasm to describe the juicy, slimy
gelatinous contents of the cell
• In 1885, Rudolf Virchow expressed that all
cells arise from pre-existing cells

5. Some Facts about Cells
• In 1940, two German Scientists, Ruska and
Knoll, invented the electron microscope
• Man is estimated to have about 100 trillion
(1014
) cells in number
• The cells that make up our body are so small
that you could fit over 200 of them on the
full stop at the end of this sentence.

6. Cells: An Introduction
• A cell is the structural and functional unit of all
life forms.
• All living organisms, whether plants or animals,
are made up of microscopic units called cells.
• The cell occupies the same central position in
biology as the atom in the physical sciences.
• Organisms may be broadly classified into two
kinds:
– Unicellular
– Multi-cellular

7. Cells: An Introduction
• All living beings, plants and animals, start their
life with a single cell.
• Some organisms exist as a single cell and carry
out the various metabolic life processes such as
assimilation, respiration, reproduction,
excretion, etc., that are essential for their
survival.
• These are known as unicellular organisms.
• Example: Yeast, bacteria, chlamydomonas,
amoeba

8. Some Unicellular Organisms
Amoeba Chlamydomona
Paramecium

9. Cells: An Introduction
• Some cells divide and give rise to organisms
with more than one cell, these organisms are
termed as multi-cellular.
• Example: animals, humans, most plants

10. Some Multi-cellular Organisms
Onion Peel Cells Cells from the cheek

11. Structure of a Cell
• Cells vary in shape and size. They may be oval,
spherical, rectangular, polygonal, spindle
shaped, star shaped, rod-shaped or totally
irregular like the nerve cell.
• The diversity in cells is in accordance with the
role or function it has to perform as part of the
tissue or organ system.
• In general, there is no typical shape for cells.

12. Various Cells from the Human Body

13. Structure of a Cell
• Each cell has got certain specific components
within it known as cell organelles, each of
which performs a special function
• A cell is able to live and perform all its
functions because of these organelles
• These organelles together constitute the basic
unit called the cell
• All cells have the same organelles, no matter
what their function is or what organism they
are found in

14. Structure of a Cell
• There are three features in almost every cell:
– Plasma Membrane
– Nucleus
– Cytoplasm
• All activities inside the cell and interactions
of the cell with its environment are possible
due to these features

15. Plasma Membrane or Cell Membrane
• Cell membrane is present in both plant and
animal cells.
• It is living, elastic and made of proteins and
lipids (fats).
• Its function is to provide a mechanical barrier
for the protection of the inner cell contents
and to regulate the movement of molecules in
and out of the cell.
• It is called a selectively permeable membrane

16. Cell Wall
• The cell wall is present only in plant cells and
lies outside the plasma membrane
• It is made up of a complex polysaccharide
(carbohydrate) called cellulose.
• Its function is to give strength and rigidity to
the cell. It is non-living.
• Cell walls permit the cells of plants, fungi and
bacteria to withstand hypotonic external media
without bursting

17. Nucleus
• This is a prominent, spherical or oval structure
found at the centre of the cell.
• It is the controlling centre of all cell activities
and has been described as the brain of the cell.
• It regulates all metabolic and hereditary
activities of the cell
• It also plays a central role in cellular
reproduction - the process by which a single
cell divides and forms two new cells

18. Nucleus
• The nucleus is composed of the following
structures:
– Nuclear Membrane
– Nucleoplasm
– Nucleolus
– Chromatin network
• Genes are present on the chromosomes

19. Nucleus: Electron Microscope View

20. Nucleus
• A gene is the functional unit of a chromosome.
• Genes are arranged in single linear order along
the chromosome.
• Genes are responsible for storing and
transmitting hereditary characteristics from one
generation to another.
• One gene may be responsible for a single
characteristic, or a single characteristic may be
transmitted by a set of genes.

21. Cytoplasm
• The part of the cell between the cell membrane
and the nuclear membrane is called the
cytoplasm.
• The cytoplasm consists of the matrix and the
organelles.
• The matrix is a transparent semi-fluid
substance.
• When active, it is always in a state of movement.

22. Cytoplasm
• The organelles are found embedded in the
cytoplasm.
• They have definite shape, structure and
function.
• All the metabolic activities of the cell such as
synthesis, secretion, digestion and energy
generation, are performed by the different cell
organelles.

23. Cell Organelles
• Large cells need a lot of chemical activities to
support their complicated structure and
function
• To keep these activities of different kinds
separate from each other, these cells use
membrane-bound little structures within
themselves
• These are called ‘organelles’ and are a key
feature of eukaryotic cells

24. Cell Organelles
• Following are the important Cell-organelles:
– Endoplasmic Reticulum (ER)
– Golgi Apparatus
– Lysosomes
– Ribosomes
– Centrosome
– Mitochondria
– Plastids

25. Cell Organelles
• The Endoplasmic Reticulum (ER) is a complex
network of tubes, the lumen of which is filled
with fluid.
• Two types of ER are seen. They are:
• Tubes with spherical bodies (Ribosomes)
attached are known as Rough Endoplasmic
Reticulum (RER).
• Ribosomes are the sites of protein
manufacture, which are sent to various places
in the cell (as per need) using the ER
Endoplasmic Reticulum

26. Cell Organelles
• Tubes with a smooth surface are called Smooth
Endoplasmic Reticulum (SER).
• They secrete lipids which are important for cell
function and some of these lipids help in
building the cell membrane
• In the liver cells of vertebrates, SER plays a
crucial role in detoxifying many poisons and
drugs
Endoplasmic Reticulum

27. Cell Organelles
• The functions of the endoplasmic reticulum
are:
– to form the skeletal framework of the cell
– to provide a pathway for the distribution of
nuclear material from one cell to the other
– to synthesize fats, steroids and cholesterol
with the help of enzymes secreted by the
cell.
Endoplasmic Reticulum

28. Cell Organelles
• They consist of tiny, elongated, membrane-
bound, flattened sacs (cisternae), which are
stacked parallel to one another along with some
vacuoles and clusters of vesicles.
• These membranes often have connections with
the membranes of the ER and constitute
another portion of a coplex cellular membrane
system
Golgi Apparatus

29. Cell Organelles
• The material synthesized near the ER is
packaged and despatched to various targets
inside and outside the cell through the Golgi
apparatus
• In some cases complex sugars may be made
from simple sugars in the Golgi apparatus
• They also secrete certain hormones and
enzymes, and is also involved in the formation
of lysosomes and peroxisomes.
Golgi Apparatus

30. Structure of Golgi Apparatus

31. Cell Organelles
• These are tiny, spherical, sac-like structures
scattered all over the cytoplasm.
• Their main function is digestion. They contain
powerful destructive enzymes capable of
digesting all organic material, and hence called
“digestive bags”.
• Lysosomes present in white blood cells are
capable of digesting bacteria and viruses.
Lysosomes

32. Cell Organelles
• During starvation, lysosomes digest proteins,
fats and glycogen in the cytoplasm, and supply
energy to the cell.
• They are also capable of digesting worn out
cell organelles, or even digesting the entire
damaged cell containing them.
• Hence, “suicide bag” is a sobriquet that is
often used for Lysosomes.
Lysosomes

33. Lysosome

34. Cell Organelles
• These are spherical, granular particles
which occur freely in the matrix or remain
attached to the rough endoplasmic
reticulum.
• Ribosomes contain RNA (ribonucleic acid)
and proteins.
• Their function is to provide the surface for
protein synthesis.
Ribosomes

35. Ribosomes

36. Cell Organelles
• The Centrosome is found in the cytoplasm
near the outer surface of the nucleus and
contains two cylinders called Centrioles.
• The centrosome is found only in the animal
cell.
• The centrosome and the centrioles play an
important role during cell division.
Centrosome and Centriole

37. Cell Organelles
• These may be cylindrical, rod-shaped or
spherical and distributed in the cytoplasm.
• Each mitochondrion is bound by a double
membrane.
• The outer membrane is very porous while the
inner membrane is folded into ridges called
cristae, which increase the surface area of the
membrane for ATP-generating chemical
reactions
Mitochondria

38. Cell Organelles
• It is in the mitochondria that the sugar is
finally burnt during cellular respiration.
• The energy thus released is stored as high-
energy chemicals called ATP (Adenosine
Tri-Phosphate).
• Hence, mitochondria are termed as the
“power house” or the “power plant” of the
cell.
Mitochondria

39. Cell Organelles
• The body cells use the energy stored in ATP
for synthesis of new chemical compounds,
the transport of these compounds and for
mechanical work.
• Mitochondria have their own DNA and
Ribosomes which enable them to make
some of their own proteins
Mitochondria

40. Structure of Mitochondria

41. Cell Organelles
• These organelles are found only in plant
cells.
• Plastids are of three types:
– Chloroplasts (plastids containing the
pigment chlorophyll)
– Chromoplasts (colored plastids)
– Leucoplasts (white or colorless plastids)
Plastids

42. Cell Organelles
• Plastids consist (internally) of numerous
membrane layers embedded in a material
called stroma
• Plastids are similar to mitochondria in their
external structure
• Like the mitochondria, they also have their
own DNA and Ribosomes
Plastids

43. Cell Organelles
• They are green and found in leaves. The green
colour is due to the presence of chlorophyll.
• The function of the chloroplast is to trap solar
energy for photosynthesis
Plastids - Chloroplasts

44. Cell Organelles
• They are yellow, orange and red, and found in
flowers and fruits.
• Chromoplasts impart colour to flowers to
attract insects for pollination
Plastids - Chromoplasts

45. Cell Organelles
• They are colorless and found in roots, seeds
and underground stems.
• Leucoplasts store food in the form of
carbohydrates, fats and proteins
Plastids - Leucoplasts

46. Cell Organelles
• Vacuoles are storage sacs for solid or liquid
contents; they are small in size in animal cells
whereas, plant cells have large vacuoles
• Central vacuoles of some plant cells may
occupy 50-90% of the cell volume
• Vacuoles in plant cells are full of cell sap and
provide turgidity and rigidity to the cell
• Amino acids, sugars, various organic acids and
some proteins are stored in vacuoles
Vacuoles

47. Cross-section of a Plant Cell

48. Cross-section of an Animal Cell

49. Plant Cell vs Animal Cell