The document provides an overview of cells and their structures. It discusses that cells were first discovered by Robert Hooke in 1665 using a microscope. He observed compartments in cork and honeycomb that he termed "cells". The document then explains that the cell is the basic structural and functional unit of life. It describes various cellular structures like the cell membrane, nucleus, cytoplasm, and organelles and their functions. It compares plant and animal cells and summarizes cellular processes like diffusion, osmosis, and endocytosis.

1. A TOUR OF THE CELL
the fundamental unit of life
PRESENTATION BY: SAMANTHA BARRETO

2. CELLS WERE FIRST DISCOVERED BY
HIM IN 1665
ROBERT HOOKE

3. ROBERT HOOKE’S MICROSCOPE

4. ROBERT OBSERVED :
CORK COMES FROM THE BARK
OF THE TREE
HONEY COMB

5. ROBERT CALLED
 THESE LITTLE COMPARTMENTS AS
CELLS.
 CELL IS A LATIN WORD FOR ‘ A LITTLE
ROOM’.

6. COMPOUND MICROSCOPE

7. ONION PEEL
1)THESE STRUCTURES LOOK
SIMILAR TO EACH OTHER.
2) TOGETHER THEY FORM A BIG
STRUCTURE LIKE AN ONION
BULB.
3) THE CELLS OF AN ONION
PEEL WILL ALL LOOK
SAME,REGARDLESS OF THE
SIZE OF THE ONION.
4) THESE SMALL STRUCTURES
ARE THE BASIC BUILDING
UNITS OF THE ONION BULB AND
ARE CALLED CELLS.

8. UNICELLULAR ORGANISMS
 ORGANISMS THAT HAVE A SINGLE
CELL.
AMOEBA
PARAMOECIUM
CHLAMYDOMONAS

9. MULTICELLULAR ORGANISMS
 ORGANISMS HAVING MORE THAN
ONE CELL TO PERFORM VARIOUS
FUNCTIONS.
ANIMALS
PLANTS
FUNGI

10. DIFFERENT CELLS
BONE CELL
OVUM
SPERM BLOOD CELL
NERVE CELL FAT CELL

11. CELL
 A cell is the smallest unit that is capable of
performing life functions.

12. CELL
 THE SHAPE AND SIZE OF CELLS ARE RELATED TO THE
SPECIFIC FUNCTION THEY PERFORM.
 EACH LIVING CEL LHAS THE CAPACITY TO PERFORM
CERTAIN BASIC FUNCTIONS.
 CELL CONTAINS A SPECIFIC COMPONENT CALLED
ORGANELLES.
 EACH KIND OF CELL ORGANELLE PERFORMS A
SPECIAL FUNCTION.
 ALL CELLS ARE FOUND TO HAVE THE SAME
ORGANELLES,IRRESPECTIVE OF THEIR FUNCTION AND
WHICH ORGANISM THEY ARE FOUND IN.

13. Why are cells of different shapes and sizes
found in the human body?
> The shape and size of the cells depend upon
the function they perform. In a human body,
each organ performs a specific function,
hence the cells of different organs have
different shapes and sizes.

14. Who discovered cells, and how?
> Cells were first discovered by Robert Hooke,
in1665. He observed a thin slice of cork
under his self designed microscope.This
slice of cork resembled the structure of the
honeycomb consisting of small
compartments. He named these small
compartments as cells.

15. Why is the cell called the structural
and functional unit of life?
> Cell is called the structural and functional unit
of life because
a) It gives structure to the living organism.
b) It helps the living organism to perform
various life functions.

16. Cell membrane or Plasma membrane
 It is the outermost covering of the
cell that separates the contents of
the cell from the external
environment.
 Allows the entry and exit of
materials in and out of the cell.It
also prevents the movement of
some other material and is
therefore called a selectively
permeable membrane.
 The plasma membrane is flexible
and is made up of organic
molecules like proteins and lipids.

17. DIFFUSION
 GASEOUS EXCHANGE TAKES PLACE FROM A
REGION OF HIGHER CONCENTRATION TO A
REGION OF LOW CONCENTRATION.

18. OSMOSIS
The movement of water from a region of high
water concentration through a semi- permeable
membrane to a region of low water
concentration.

19. How do substances like CO2 and water move
in and out the cell? Discuss.
As the cell functions the concentration of CO2 in
the cell increases whereas the concentration of
CO2 in the external environment is low. CO2
moves out of the cell from a region of higher
concentration to the external environment which
is the region of lower concentration.
Water moves in and out the cell from a region of
higher concentration through a semi- permeable
membrane to a region of lower concentration by
the process of osmosis.

20. Difference between
Diffusion Osmosis
1)It can occur in any
medium.
2)It does not require
a semi-permeable
membrane.
1)It occurs only in a
liquid medium.
2)It requires a semi-
permeable membrane.

21. What is a hypotonic solution?
Hypotonic solution is the solution
surrounding the cell which has higher water
concentration than that in the cell.
Water molecules are free to pass across the
cell membrane in both directions, but more
water will come into the cell than will leave.
The net result is that the water enters the
cell and the cell is likely to swell up.

22. HYPOTONIC SOLUTION

23. When is a solution said to be isotonic?
When the medium surrounding a cell has
the same concentration of water as that in
the cell it is said to be isotonic.
Water crosses the cell membrane in both
the directions, but the amount going in is
the same as the amount going out, so
there is no overall movement of water.
The cell will stay the same size.

24. ISOTONIC SOLUTION

25. What is a hypertonic solution?
When the medium surrounding a cell has
lower concentration of water than that in
the cell it is said to be hypertonic.
Water crosses the membrane in both the
directions, but this time more water
leaves the cell than enters it. Therefore
the cell will shrink.

26. HYPERTONIC SOLUTION

28. What is Plasmolysis?
Plasmolysis is the phenomenon by which
a plant cell shrinks away from the cell wall
when it loses water by osmosis.

29. PLASMOLYSIS

30. What is endocytosis?
Endocytosis is the process by which a cell
is able to engulf food and other material
from its external environment due to the
flexibility of the plasma membrane.
Example : Amoeba acquires its food
through such processes.

31. ENDOCTYOSIS

32. Plasma membrane is called a selectively
permeable membrane. Why?
> Plasma membrane is called a selectively
permeable membrane because it allows
some materials to enter and leave the cell.

33. Cell wall
>Hard outer covering of the cell.
>Present outside the cell
membrane.
>Cell wall is composed of
cellulose.
>Cellulose is a complex
substance and provides structural
strength to plants.
>Cell wall is present in the plant
cell and helps the plant to
withstand the environmental
changes.

34. Nucleus
>Has a double layered covering called
nuclear membrane.
 Nuclear membrane has pores which
allow the transfer of material from inside
the nucleus to its outside (cytoplasm).
 Contains chromosomes which are
visible as rod-shaped structures only
when the cell is about to divide.
Chromosomes contain information for
inheritance of features from parents to
the next generation in the form of DNA
molecules. (Deoxyribo Nucleic Acid).

35. Nucleus
 DNA molecules contain information necessary for constructing
and organising cells.
 Functional segments of DNA are called genes.
 When the cell is not dividing, DNA is present as a part of the
chromatin material. Chromatin material is visible as entangled
mass of thread like structures. Whenever the cell is about to
divide , the chromatin material gets organised into
chromosomes.
 Plays an important role in cellular reproduction.
 It helps in determining the way the cell will develop and what
form it will exhibit on maturity by directing the chemical activites
of the cell.

38. Significance of membranes
 Example : Viruses
 Viruses lack any membranes and hence
do not show any characteristics of life
until they enter a living body and use its
cell machinery to multiply.

39. Cytoplasm
• It is the fluid content inside the plasma
membrane.
• Contains specialised cell organelles.

40. Cell organelles
1) Endoplasmic reticulum
2) Golgi apparatus
3) Lysosomes
4) Mitochondria
5) Plastids
6) Vacuoles

41. Endoplasmic Reticulum
 ER is a large network of membrane bound tubes and
sheets.
 Extends throughout cytoplasm
 Two types - Rough Endoplasmic Reticulum (RER)
Smooth Endoplasmic Reticulum (SER)
 Serves as channels for the transport of materials
between various regions of the cytoplasm or between
the cytoplasm and the nucleus.
 Functions as a cytoplasmic framework providing a
surface for biochemical activities.

42. RER
 Arranged into flattened sacs
 Ribosomes on surface give it a rough
appearance
 Ribosomes are the sites of protein synthesis.
 Cells that specialize in secreting proteins
have lots of rough ER

43. SER
 A series of
interconnected tubules .
 No ribosomes on surface.
 Helps in the manufacture
of fat molecules or lipids.
 In liver cells of
vertebrates, SER
detoxifies many poisons
and drugs.

44. Membrane Biogenesis
 It is the process of formation of the cell
membrane from proteins and lipids.

45. GOLGI APPARATUS
First discovered by Camillo Golgi.
 It consist of a system of membrane-
bound vesicles arranged parallel to each
other in stacks called cisterns.
 The material synthesised near the ER is
packaged and dispatched to various
targets inside and outside the cell through
the Golgi apparatus.
 Its functions include storage ,
modification and packaging of products in
vesicles.
Involved in the formation of the lysosome.

47. LYSOSOMES
>Waste disposal system of the
cell.
Keep the cell clean by digesting
any foreign material as well as
worn out cell organelles.
 Contain powerful digestive
enzymes capable of breaking
down all organic material.
When the cell gets damaged,
lysosomes may break open and
the enzymes digest their own cell.
Thus known as suicide bags of a
cell.

48. Mitochondria
Known as the powerhouse of the cell.
 The energy required for various chemical activities is
released by the mitochondria in the form of ATP
molecules.( Adenosine triphosphate).
ATP is known as the energy currency of the cell.
 Mitochondria have two membrane coverings.
 Outer membrane is very porous.
Inner membrane is deeply folded.
Mitochondria are able to make their own proteins as
they have their own DNA and ribosomes .

49. Plastids
 Present in plant cells.
 Two types- 1) Chromoplasts (coloured)
2) Leucoplasts (colourless)
> Plastids containing green pigment chlorophyll are called
Chloroplasts.
 Leucoplasts store materials as starch, oils and protein
granules.
 Plastids contain membrane layers embedded in a material
called stroma.
 Has a similar structure like the mitochondria.
 Have their own DNA and ribosomes.

50. CHLOROPLASTS

51. Vacuoles
 Storage sac for solid or liquid contents.
 Small size vacuoles are present in animals.
 Large in plants.
 In plant cells, vacuoles are full of cell sap and provide
turgidity and rigidity to the cell.
 Vacuoles store amino acids, sugars, various organic acids
and some proteins.
 In Amoeba, the food vacuole contains the food items that
the Amoeba has consumed.
 Vacuoles play an important role in expelling excess water
and some wastes from the cell.

53. Overview of a plant cell

54. Overview of an animal cell

55. Can you name the two organelles
we have studied that contain their
own genetic material?
Ans : Mitochondria and plastids are the two
organelles that contain their own genetic
material. Both these organelles have their
own DNA and ribosomes.

56. Make a comparison and write
down ways in which plant cells are
different from animal cells.
Animal cell Plant cell
Animal cells are generally small
in size.
Plants cells are usually larger
than animal cells.
Cell wall is absent. Cell wall is present.
Except the protozoan Euglena,
no animal cell possesses
plastids.
Plastids (chromoplasts and
leucoplasts) are present.
Vacuoles are smaller in size. Vacuoles are larger in size.

57. What would happen to the life of a
cell if there was no Golgi
apparatus?
 (i) Membranes of the Golgi apparatus are often connected
to ER membranes. It collects simpler molecules and
combines them to make more complex molecules. These
are then packaged in small vesicles and are either stored
in the cell or sent out as per the requirement. Thus, if the
Golgi apparatus is absent in the cell, then the above
process of storage, modification, and packaging of
products will not be possible.
 (ii) The formation of complex sugars from simple sugars
will not be possible as this takes place with the help of
enzymes present in Golgi bodies.
 (iii) The Golgi apparatus is involved in the formation of
lysosomes. Thus, if the Golgi body is absent in a cell, the
synthesis of lysosomes will not be possible in the cell.

58. Which organelle is known as the
powerhouse of the cell? Why?
 Mitochondria are known as the powerhouse of cells.
Mitochondria create energy for the cell, and this
process of creating energy for the cell is known as
cellular respiration. Most chemical reactions involved
in cellular respiration occur in the mitochondria. The
energy required for various chemical activities
needed for life is released by the mitochondria in the
form of ATP (Adenosine triphosphate) molecules. For
this reason, mitochondria are known as the
powerhouse of cells.

59. Where do the lipids and proteins
constituting the cell membrane get
synthesized?
Lipids and proteins constituting the cell
membrane are synthesized in the
endoplasmic reticulum.
1)SER (Smooth endoplasmic reticulum)
helps in the manufacturing of lipids.
2)RER (Rough endoplasmic reticulum) has
particles attached to its surface, called
ribosomes. These ribosomes are the site
for protein synthesis.

60. How does an Amoeba obtain its
food?
 Amoeba obtains its food through the process
of endocytosis. The flexibility of the cell
membrane enables the cell to engulf the solid
particles of food and other materials from its
external environment.

61. What is osmosis?
 The movement of water molecules from a
region of high concentration to a region of
low concentration through a selectively
permeable membrane is called osmosis.