The Cell Theory
In this presentation you will:
 explore the cell theory
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Introduction
All living things are
made up of cells.
They are the building
blocks of life.
Without living cells, an
organism is not alive.
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Introduction
Some organisms, like
bacteria and yeast, are
made up of only one cell.
Unicellular
These are called
unicellular organisms.
Others, like most plants and
animals (including humans)
are made up of many cells.
These are called
multicellular organisms.
Multicellular
Multicellular
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Discovery of the Cell
In the mid-17th century
an English scientist
named Robert Hooke
used a microscope to
look at a section of cork.
He noticed that cork was
made up of microscopic
box-like units.
He called them cells.
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Discovery of the Cell
Hooke was the first
person to observe and
define the cell.
After Hooke’s initial
discovery, more
scientists became
involved in
understanding cells.
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Discovery of the Cell
Modern microscopes look
quite different from the
one Hooke used.
Eyepiece
They work in the same
way, but can use:
 either one or two
eyepieces
Objective lens
 either one or two
objective lenses
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Discovery of the Cell
A microscope that uses
one eyepiece and one
objective lens is called a
monocular microscope.
One that uses two eyepieces
and one objective lens is
binocular.
Monocular
Binocular
Stereoscope
The stereoscope uses two eye
pieces and two objective lenses.
This makes the specimen appear in 3D to the user.
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Cell Theory
The investigation of the cell
led to these accepted facts
about cells:
 cells are the basic unit of life
 all living organisms are
made up of at least one cell
 all cells come from other cells
This is known as the Cell Theory.
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What Cells Do
All living organisms must be able to carry out the
seven life processes to survive.
These processes are:
 movement
 respiration
 sensitivity
 growth
 reproduction
 excretion
 nutrition
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Life Processes
To be ‘alive’ an organism must be able to carry out
all these life processes.
Cells can carry out these
processes independently.
They are the smallest
living thing that can.
They are alive.
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Life Processes
There are many
different types of cells
with many different
jobs to do.
However, every cell
carries out all of the
life processes.
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Life Processes
Cells carry out the
same functions, and
have the same needs,
as a whole organism.
In fact, the function
and survival of an
organism depends on
the ability of individual
cells to carry out these
processes.
oxygen, water
and glucose in
carbon dioxide
and water out
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Life Processes
For example, you need
food and water
because your cells
need food and water.
You grow because your
cells grow and divide.
oxygen, water
and glucose in
carbon dioxide
and water out
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Movement
Organisms need to
be able to move to
find food, shelter and
avoid danger.
Animals can walk, swim
or fly…
…plants can turn to face
the light or close their
leaves.
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Movement
Cells, and
parts of cells,
also move.
For example,
chemicals and
molecules move
to other parts
of the cell that
need them.
If you were to examine a live cell using a
microscope, you would see things moving about
inside.
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Respiration
Living things need to
take in oxygen and
food to make energy.
carbon dioxide
oxygen
The process that
releases energy from
these things is called
respiration.
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Respiration
Cells carry out respiration. It is called cellular
respiration.
They use oxygen and glucose to produce energy in
the form of a molecule called ATP.
oxygen + glucose → carbon dioxide + water + energy (ATP)
ATP is used by the cell to carry out the activities
necessary for life.
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Sensitivity
Organisms need to be
sensitive to their
environment.
They need to respond to
danger, or to a change
in light or temperature.
Cells also need this
ability to sense their
environment.
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Sensitivity
For example, when a
plant is placed in bright
light, the cells on the
darker side of the stem
get longer.
bright side
of stem
shaded side
of stem
light
The cells on the lighter
side stay the same.
longer
cells
This causes the whole
stem to bend towards
the light.
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Reproduction
Cells are able to grow and reproduce.
Each cell originated from a
previous living cell.
Mitosis
Once mature, a cell can
divide in half to produce
two new identical cells.
This process is called mitosis.
All cells eventually die.
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Reproduction
The ability of cells to
grow and reproduce in
this way, allows
organisms to grow and
repair themselves.
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Nutrition
Cells need nutrients like
oxygen, water and
glucose (sugar).
These nutrients are
used to provide it
with energy to live
and grow.
oxygen, water
and glucose in
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Nutrition
All cells have a skin,
called a cell membrane.
This separates and
protects the cell from
its surroundings.
The cell membrane
regulates the
movement of water,
nutrients and waste
products into and out
of the cell.
oxygen, water
and glucose in
cell membrane
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Excretion
Organisms must excrete
(get rid of) waste
products to stay healthy.
This is the same
for cells.
oxygen, water
and glucose in
carbon dioxide
and water out
If waste materials are
not excreted from a
cell, they will poison
the cell and possibly kill it.
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Excretion
During cellular respiration,
carbon dioxide and excess
water are produced as waste
products.
These must pass out
of the cell through the
cell membrane.
waste
carbon
dioxide
andproducts
water out
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Question 1
All cells of an organism must carry out each life
process so that the organism can survive.
Is this statement true or false?
Answer True or False.
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Question 1
All cells of an organism must carry out each life
process so that the organism can survive.
Is this statement true or false?
Answer True or False.
True
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Question 2
According to the cell theory, cells carry out similar
functions in order to sustain life. Which of the
following can cells do?
A) Use nutrients to make energy
B) Get rid of waste materials
C) Grow and reproduce
D) All of the above
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Question 2
According to the cell theory, cells carry out similar
functions in order to sustain life. Which of the
following can cells do?
A) Use nutrients to make energy
B) Get rid of waste materials
C) Grow and reproduce
D) All of the above
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Question 3
Which of the following statements is NOT accepted
in the Cell Theory?
A) All living organisms are made up of many cells
B) Cells are the basic unit of life
C) Organisms and cells carry out similar functions in
order to sustain life.
D) All cells come from other cells
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Question 3
Which of the following statements is NOT accepted
in the Cell Theory?
A) All living organisms are made up of many cells
B) Cells are the basic unit of life
C) Organisms and cells carry out similar functions in
order to sustain life.
D) All cells come from other cells
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Summary
In this presentation you have seen:
 the Cell Theory
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