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Essential idea: The evolution
of multicellular organisms
allowed cell specialization and
cell replacement.
Topic 1: Cell Biology
1.1 Introduction to cells
Nature of Science
Looking for trends and discrepancies—
although most organisms conform to
cell theory, there are exceptions. (3.1)
Ethical implications of research—
research involving stem cells is growing
in importance and raises ethical issues.
(4.5)
Understandings
 According to the cell theory, living organisms are composed of
cells.
 Organisms consisting of only one cell carry out all functions of
life in that cell.
 Surface area to volume ratio is important in the limitation of cell
size.
 Multicellular organisms have properties that emerge from the
interaction of their cellular components.
 •Specialized tissues can develop by cell differentiation in
multicellular organisms.
 Differentiation involves the expression of some genes and not
others in a cell’s genome.
 The capacity of stem cells to divide and differentiate along
different pathways is necessary in embryonic development and
also makes stem cells suitable for therapeutic uses.
Topic 1.1 Introduction to Cells
1: Outline the cell theory
Outline:
Means to give a brief account or
summary.
http://www.cellsalive.com/howbig.htm
What Does the Cell Theory State?
All living things are made of
cells.
Cells are the smallest unit of
life.
Existing cells have come from
other cells.
Starter:
 You have 5 minutes to read the introductory note on cell
theory:
 In the middle of the 17th century, one of the pioneers of
microscopy, Robert Hooke(1635-1703), decided to examine a
piece of cork tissue with his home made microscope. He saw
numerous box shaped structures that he thought resembled
‘monks cells’ (rooms), so he called them ‘cells’. As microscopes
became more sophisticated, other scientists observed cells
and found that that they occur in every living organism. No
organism has yet been discovered that does not have at least
one cell. Living things may vary in size and shape, but
scientists agree that they are all composed of cells.
 The study of cells has enabled us to learn more about how
whole organisms function.
You have 5 minutes to answer the
following questions on the passage you
have just read:
1.
Name a pioneer of microscopy.
2.
Why did he call the structures he saw in his microscope ‘cells’?
3.
Name two ways that living things can vary?
4.
What occurs in every living organism?
5.
What is the control centre of the cell called?
6.
Where does cork come from?
Answers :
 The Dutch optician, Zacharias Jansen. Or The Englishman,
Robert Hooke.
 Hooke called them cells because he thought they looked like
‘monk’s cells’ (rooms).
 Size and shape.
 All the processes, such as metabolism, response, growth,
reproduction, homeostasis and nutrition.
 The bark of trees.
2. The Cell Theory Debate
• When there is evidence to disprove a theory
scientists have to start doubting the theory.
• This is particularly difficult to do when the theory
has obvious uses, and if the theory has been
accepted for a long time.
• Cell theory is an example of a theory where it can be
applied to nearly all organisms but with a few specific
exceptions.
Should we abandon the theory?
Task:
 Make a four slide presentation
 a) What are the key points of ‘cell theory’?
 b) Describe the evidence that supports it?
 c) What examples of cells are there which
don't support it and how. (ie; fungal hyphae,
skeletal muscles, amoeba)
 d) Explain whether we should keep the cell
theory or change it?
Use the information in the following slide and from
your text book to help you do this. (15 minute)
A brief history
2. Discuss the current
evidence that supports
the cell theory.
 Through the process of scientific
investigation much evidence has been
collected to support the cell theory.
Living things have been examined and
all have been found to consist of cells
thus far.
 However, like much of science there
are some exceptions to the rule and
while they do not disprove the cell
theory they do not fit into our idea of
cells as small box-like structures with
the same organelles inside each cell.
2. Discuss the current
evidence that supports the
cell theory.
 The following are exceptions to the
general cell structure you have been
taught:
 Skeletal muscles have muscle fibres
which have a membrane but contain
hundreds of nuclei and fungi have hyphae
with similar thread-like structures.
 Some tissues contain extra-cellular
material like bones and teeth. Some
unicellular organisms such as amoeba
have a region of cytoplasm surrounded by
a membrane and the cytoplasm has to
carry out all vital functions.
2. Discuss the current
evidence that supports the
cell theory.
 Despite these exceptions most living
tissues are composed of cells. Cells
can be removed from an organism and
survive whereas smaller parts cannot so
this is evidence that supports the theory
that cells are the smallest unit of life.
 The evidence for support of the last
statement of the cell theory has shown up
in biology experiments that disprove the
idea of spontaneous generation. The only
exception to this would be when life first
appeared on the Earth’s surface.
3. List the functions of life that must
be carried out by all unicellular
organisms.
 Unicellular organisms consist of only one cell
and that one cell must carry out all life
functions for that organism.
 This includes metabolism, homeostasis,
growth, obtaining food and other nutrients
(nutrition), excreting wastes (excretion),
respiration and reproduction.
Poster……………
Discuss the functions of life in
Paramecium
Discuss the functions of life in a named
unicellular photosynthetic organism.
metabolism, homeostasis, growth,
(nutrition (excretion), respiration
and reproduction.
Paramecium
 Homeostasis: contractile vacuole fill up with water and expel
I through the plasma membrane to manage the water content
 Reproduction: The nucleus can divide to support cell division
by mitosis, reproduction is often asexual
 Metabolism: most metabolic pathways happen in the
cytoplasm
 Growth: after consuming and assimilating biomass from food
the paramecium will get larger until it divides.
 Response: the wave action of the cilia moves the paramecium
in response to changes in the environment, e.g. towards food.
 Excretion: the plasma membrane control the entry and exit
of substances including expulsion of metabolic waste
 Nutrition: food vacuoles contain organisms the parameium
has consumed
4. Explain the connection between surface area of
a cell and its ability to exchange materials
with its outside environment.
 Once cells reach a
certain size they stop
growing and divide.
 If a cell grew too
large it would have
many problems
because its surface
area to volume ratio
would become too
small.
 As the size of an
object increases the
ratio between surface
are and volume
decreases.
4. Explain the connection between surface area of a cell and its
ability to exchange materials with its outside environment.
 In cells, the rate at which materials can enter or
leave a cell depends on the surface area of that cell
while the rate at which those materials can be used
or produced depends on the volume of that cell. If
cells become too large it becomes inefficient at
exchanging materials with its environment.
5. Define Emergent Properties.
 Emergent properties can be defined as properties
where the whole is more than the sum of their parts.
 In other words, multicellular organisms can achieve
more than the sum of what each cell could
accomplish individually.
Multicellular organisms
are capable of completing
functions that individual
cells could not undertake this is due to the
interaction between cells
producing new functions.
Extension: Emergent Properties and
Reductionism
 Here is the problem in Biology……….
 If individual parts of an organism do not work by themselves, how can we study
them as we cannot pull them apart.
 Biological reductionism is an attempt at describing an organism by describing the
characteristics of its most basic components. A reductionist perspective is that
any organism can be described as a sum of its parts, and so it is important to
find the building blocks of life in order to describe any organism.
This perspective is limited and is becoming less and less attractive to scientists.
A systems approach to science, which focuses on the function and interactions
of different biological objects, is much more inclusive and a more accurate
representation of biological entities.
Reductionism has been pursued in the efforts to decode the human genome, but,
according to Sverdlov (2006), reductionist efforts do not address the main
question of biology, "What is life?"
6. Distinguish between multicellular and unicellular
organisms using the concept of emergent
properties.
 Multicellular organisms show emergent
properties when the cells work together
to achieve more than what one cell on
its own can achieve (unicellular).
 A good example of emergent properties in
a multicellular organism would be the
human brain. On their own, individual
neurons (nerve cells) are not capable of
thought but it is the interactions of all
neurons that allow the brain to think.
7.Define differentiation.
 Differentiation is a
process that occurs in
the cells of
multicellular organisms
where cells develop in
different ways and
become specialized for
one particular function.
8. Explain how cells in multicellular organisms
differentiate by expressing some of their genes
but not others.
The process of differentiation is directed by
the genes of the cells. All the cells contain
the same genes but the cell only uses the
ones it needs to follow its path of
development. In other words all cells have
genes they turn on and others they leave
inactive.
For example, the cells in your toes contain the
genetic information in the form of genes to
make the pigment colors for your eyes but
the cell does not express those genes.
9. Define stem cells.
 Stem cells are
unspecialized cells that
have the ability to divide
or self renew by cell
division and to
differentiate.
 Sources of stem cells
are human embryos,
umbilical cord of a new
born baby, and some can
be found in the adult
body mostly in the bone
marrow.
10. Outline one therapeutic
use of stem cells.
 Stem cells can be used in therapeutic ways
because they are different from other cells
in two main ways:
They are unspecialized or what is known as
totipotent because they can become any
type of cell due to the fact that they have
not differentiated yet.
Stem cells are self-sustaining and they can
perform mitotic cell division for long
periods of time.
10. Outline one therapeutic
use of stem cells.
 Using stem cells to treat disease and repair
tissues is often referred to as cell therapy.
 We have been performing one type of cell
therapy, bone marrow transplants, for over
40 years.
 People who have leukemia can receive a bone
marrow transplant which replaces their
diseased bone marrow with healthy marrow
and this will hopefully cure their disease.
10. Outline one therapeutic
use of stem cells.
 Cell therapy is being used to create new
skin grafts for burn victims. It is also
being used to grow new corneas for
people suffering from failing eyesight.
 In order for any stem cell treatment to be
effective, the stem cells must become
part of the body and function well. In
other words, if they are meant to be new
blood cells they must be able to carry out
that job for the therapy to work.
Research
 Research STARGARDTS DISEASE and briefly explain how
stem cells are used.
 Produce a cartoon using boxes to explain explain this.
Pick a Side
 Ethics of the therapeutic use of stem cells from specially
created embryos, from the umbilical cord blood of a newborn baby and from an adult’s own tissues.
 Research ethics of stem cell use and be prepared to debate
one side of the argument.
11. Use the handout given to you in class to calculate the size
of the nucleus in the electron micrograph photo below.
 Magnification of image =
20 000x
 Size of nucleus with
ruler = 40mm
 Real size =
=
size of nucleus
magnification
40 000
20 000
= 2 μm
Relative sizes of molecules, cell membrane
thickness, viruses, bacteria, organelles and cells.
Eukaryotic cell
10 – 100 µm
= 10 – 100 x 10-6 m
Prokaryotic cell
1 – 5 µm
= 1 – 5 x 10-6 m
Nucleus
10 – 20 µm
= 10 – 20 x 10-6 m
Chloroplast
2 – 10 µm
= 2 – 10 x 10-6 m
Mitochondrion
0.5 – 5 µm
= 0.5 – 5 x 10-6 m
Bacteria
1 – 4 µm
= 1 x 10-6 m
Large virus (HIV)
100 nm
= 100 x 10-9 m
Ribosome
25 nm
= 25 x 10-9 m
Cell membrane
7.5 nm thick
= 7.5 x 10-9 m
DNA double helix
2 nm diameter
= 2 x 10-9 m
Hydrogen atom
0.1 nm
= 0.1 x 10-9 m