Essential idea:
The evolution of multicellular organisms
allowed cell specialization and cell
replacement.
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)
Outline Cell Theory
Assessment Statement
Outline Cell theory
Cell Theory
KEY CONCEPT Cells are the basic unit of life.
Outline Cell Theory

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
All living things are
made of cells.
Cells are the smallest
unit of life.
Existing cells have
come from other
cells.
Outline Cell Theory

How did the below scientist contribute to Cell
Theory???
Evidence for Cell Theory
Assessment State
Discuss the evidence for Cell Theory
Evidence for Cell Theory
a. All living things are made of
cells: When living things are observed
under the microscope they consistently
appear to be composed of cells.
Evidence for Cell Theory
b. Cells are the smallest unit of life.
The cell is the smallest unit of organisation that can show all the
characteristics of living processes, including:

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Metabolism
Response
Sensitivity
Growth
Reproduction
Nutrition
DNA
Respire
Organelles
often require the cooperation of other organelles for their
successful function.
Evidence for Cell Theory
c. Cells come only from other cells.
o Cells carry out a form of cell division to form new cells.
This process of cell replication in eukaryotes is called
Mitosis and in prokaryotes is called binary fission.
o This aspect of cell theory suggests that all cells therefore
have a common ancestor, the original ancestral cell form
which all other cells have arisen by descent. (origin of
cellular life).
o This relationship of common ancestor suggest that all
organisms are related.
Limitations of Cell Theory
Questioning Cell Theory.
Using atypical examples: Discuss problem in
Cell Theory:
• Striated Muscles Example
• Giant Algae Example
• Fungal Hyphae Example
Functions of Life
Assessment Statement
State that unicellular organisms carry out all
the function of life
Functions of Life
Organisms are able to carry out all the processes which are
characteristic of living things such as:
• a. metabolism which includes respiration the synthesis of
ATP.
• b. response to a change in the environment
• c. homeostasis the maintenance and regulation of internal
cell conditions.
• d. growth which for a unicellular organism means an
increase in cell size and volume.
• e. reproduction which for the unicellular organism is
largely asexual through cell division to form a clone.
• f. nutrition which means either the synthesis of organic
molecules or the absorption of organic matter.
Relative Sizes
Assessment Statements
Compare relative sizes of molecules, cell
membrane thickness, eukaryotes, viruses,
bacteria and cells using the appropriate SI
units
Relative Sizes
Relative sizes: 1. molecules (1nm). 2. cell membrane thickness
(10nm). 3. virus (100nm). 4. bacteria (1um). 5. organelles (less
10um). 6. cells (<100 um). 7. generally plant cells are larger than
animal cells.
Relative Sizes
•
•
•
•
•
Molecules of Biological significance are around 1 nm in size where as the cell
membrane is about ten times thicker at 10nm.
Where as a virus is ten times larger again at around 100nm.
where as a bacteria is ten times larger again at around 1 um.
where as a eukaryotic animal cell is is ten time larger again at around 10 um.
where as a eukaryotic plant cell is ten times larger again at around 100 um.
Magnification
Assessment Statement
Calculate Linear Magnification of drawings
and the actual size of specimens in images
of know magnification
Units used in magnification calculations
Calculate Magnification of Specimen in Drawing
Calculate
Magnification
=
Length of specimen in
drawing/ photo (measured)
Actual length of specimen
(estimated)
Explain how you would estimate
the size of cell A.
30 μm
A
Estimate the actual size of cell A.
30 μm
A
Use actual length and measured length to calculate
Linear magnification
Calculate
Magnification
=
Length of specimen in
drawing/ photo (measured)
Actual length of specimen
(estimated)
30 μm
A
Summary of Magnification Calculations
Estimate Size of Amoeba
in mm & μm
a.
mm
μm.
Calculate Magnification
Actual length mm =
Measure length in photo mm=
Calculate
Magnification
=
.
.
Length of specimen in
drawing/ photo (measured)
Actual length of specimen
(estimated)
Estimate the size of the Daphnia
in mm & μm
e.
mm
μm.
Calculate Magnification
Actual length mm =
.
Measure length in photo mm=
Calculate
Magnification
=
Length of specimen in
drawing/ photo (measured)
Actual length of specimen
(estimated)
.
Calculate Actual size
If a drawing of a cell has a magnification of
10X, and the length of the drawing is 20
mm. What is the actual length of the the
cell?
Actual length of specimen
(estimated)=
Calculate
Magnification
Length of specimen in
drawing/ photo (measured)
Actual length of specimen
Magnification
(estimated)
Calculating Actual Length
If the magnification of
the drawing is
25Xwhat is the actual
length of this
drawing?
Calculating Actual Size
Calculating Actual Size
Calculating Actual Size
Cell Size
Assessment Statement:
• Explain the importance of the surface area
to volume ratio as a factor of limiting cell
size.
Why are cells so small?
Surface area to volume ratio
•
As cell size increases, volume increase faster
than surface area
•
Surface area to volume ratio decrease as cell
increases
•
Thus less cytoplasm has contact with plasma
membrane to exchange material with its
environment.
Cell Size
Cells need a large surface area to volume
ratio for three reasons:
1.
2.
3.
Get rid of waste more quickly
Absorb materials from environment
more quickly
Get rid of internal heat and absorb heat
from the environment more quickly.
Cell Size Summary
The smaller the cell the more easily it can
get rid of waste to, and absorb nutrients
from, its environment.
LE 6-7
Surface area increases while
Total volume remains constant
Compare the Surface area
of the solid box to the box
made of a lot of small
boxes
5
1
1
Total surface area
(height x width x
number of sides x
number of boxes)
6
150
750
Total volume
(height x width x length
X number of boxes)
1
125
125
Surface-to-volume
ratio
(surface area  volume)
6
1.2
6
Surface Area to Volume Ratio
The rate of exchange of substances therefore depends on the organism's
surface area that is in contact with the surroundings.
Reason: as organisms get bigger their volume and surface area both get
bigger, but not by the same amount. The volume increases as the cube
but the area of the surface only increases by the square.
Surface Area to Volume Ratio
Conclusions:
 As the organism gets bigger its surface area : volume ratio decreases
 This rule is a limiting factor for cell size.
 As the cell gets bigger the ratio decreases
 If the ratio decreases the rate of exchange decreases
Example: gas exchange of oxygen for respiration.
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
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
A cell which respires aerobically demands oxygen for the process.
Oxygen is obtained form the surrounding environment such as water or blood
(depends on the cell).
Oxygen diffuses across the cell membrane.
More membrane more diffusion (Surface area= increases by the 2).
Bigger cell (Volume = increases by the 3).
However the ratio of surface area2 : volume 3 is decreasing
Therefore the volume of oxygen obtained for each unit of cell volume is
actually decreasing
Cells must not get too big because they cannot obtain sufficient oxygen to
satisfy the demands of the cell.
why cells are small (reasoning):
Size as a limiting Factors for cell because:

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
A big cell needs more oxygen than a little cell
Big cells need to have more oxygen diffusion across the cell
membrane.
But the big cell has relatively small surface area compared to its
volume i.e. the surface area: volume ratio is small.
What ever other benefits a cell might gain from being big, it cannot
become larger than is limited by the rate of gas exchange.
This reasoning can be applied to nutrients and to waste, anything that
is exchanged across the cell surface.
Try preparing a reason why size is a limiting factor for:
Obtaining nutrient (glucose)
Excretion of waste molecules ( urea, ammonia, carbon dioxide).
Emergent Properties
Assessment Statement:
State that multicellular organisms show
Emergent Properties
Emergent Properties
'Emergent properties arise from the
interaction of the component parts; the
whole is greater than the sum of the parts'.
Emergent Properties

Emergence is the occurrence of unexpected
characteristics or properties in a complex system.
 These properties emerge from the interaction of
the ‘parts’ of the system.
 Remember that biology insists on a population
thinking so that we know the interacting ‘parts’
vary in themselves and therefore their ‘emerging’
properties can only be generalized.
Emergent Properties
Multicellular and Differentiation
Assessment Statement
Explain that cells in multicellular organisms
differentiate to carry out specialized
functions by expressing some of their genes
but not others.
Multicellular and Differentiation

Rather than all cells carrying out all functions,
tissues and organs specialize to particular
functions.
 These organs and systems are then integrated to
give the whole organism (with its emergent
properties).
 Differentiation: Cells within a multi-cellular
organism specialize their function.
 Specialized cells have switched on particular
genes (expressed) that correlate to these
specialist functions.
Multicellular and Differentiation

These specific gene expressions produce
particular shapes, functions and adaptations
within a cell.
 Therefore a muscle cell will express muscle
genes but NOT those genes which are for nerve
cells.
Multicellular and Differentiation
What is the benefit of differentiation and
specialization of tissues rather than all tissues
carrying out all functions?

In a multi cellular organism specialization is more efficient
than the generalized plan when competing for a specific
resource. Consider the role of water transport through the
plant:
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

In higher plants we have specialization to for a tubular system called the xylem.
This is more efficient way of water transport than simply been passed by the mass
movement of water from cell to cell.
In the xylem water can be moved very efficiently from underground to the canopy
of the highest trees at very little cost to the plant.
If there is no specialized tissue for carrying water then the plant would rely on the
movement of water by mass flow of diffusion which is very slow. The plant is
therefore limited in size and therefore cannot compete with larger species.
Multicellular and Differentiation
Watch the below animation and then in your own words explain that cells in multicellular
organisms differentiate to carry out specialized functions by expressing some of their
genes but not others
http://outreach.mcb.harvard.edu/animations/preloaderStemCells.swf
Multicellular and Differentiation
Multicellular and Differentiation
Stem Cells
State that stem cells retain the capacity to
divide and have the ability to differentiate
along different pathways
What is a Stem Cell?
Unspecialized cells
Able to self-renew without
differentiating for extended
periods of time
Ability to differentiate into
specialized cells
Embryonic and adult stem cells
are derived from different
sources.
Human blastocyst
showing inner
cell mass and
trophectoderm
TIME 2001
Photo: Mr. J. Conaghan
What is an Embryonic Stem Cell?
Placenta cell
Fusion
of nuclei
Stem cell
First cell
division
Blastocyst (~5-6 days old):
a “pre-embryo” ball of cells which
has not implanted in the uterus.
Only cells between the nuclei
fusion and blastocyst stages are
considered true stem cells.
Stem cells are harvested
from the inner cell mass.
By the latter stages
of development in the
fetus, cells already have
“decided” which
tissues they are
to become.
Embryonic Stem Cells are Derived from Blastocysts
Placenta cell
Fusion
of nuclei
Stem cell
First cell
division
Blastocyst
(~5-6 days old)
Stem cells are harvested
from the inner cell mass.
Undifferentiated
stem cells are
cultured (grown)
in the laboratory.
Adult Stem Cells
Have two characteristics:
They can make identical copies of themselves
for the lifetime of the organism.
• They can give rise to differentiated mature cells
with specific morphologies (shapes and
functions).
•
Adult stem cells are rare—and appear to help
with homeostasis.
Stem cells have been found in the brain and
spinal cord, dental pulp, blood vessels,
skeletal muscle, the digestive system, the
cornea and retina, and the liver and
Stem Cells

A stem cell retains the capacity to divide and has
the ability to differentiate along different pathways.
 A stem cell is able to divide but has NOT yet
expressed genes to specialize to a particular
function. Under the right conditions stem cells can
be induced to express particular genes and
differentiate into a particular type of cell.
Embryonic Stem Cells Can Become
Any Tissue in the Body
Placenta cell
Blastocyst
Cultured laboratory
stem cells
Stem cell
Scientific manipulations entice stem cells to become
specialized tissues (blood, muscle, neuron, etc.).
Blood cells
Muscle cells
Neuron (brain)
cells
Stems Cells
Uses of Stem Cells
Assessment Statement
Outline one use of stem cells (6 Points)
•
Summarize.
Question 3
Outline one therapeutic use of stem cells (6 points).
Award [4 max] for any of the following general statements:
stem cells are cells that retain the capacity to divide and have the ability to
differentiate along different paths into all types of cells / are pluripotent / totipotent;
stem cells are derived from blastocysts / human embryos, left over from IVF /
placenta / umbilical cord / some adult tissues;
new techniques / technologies rely on replacing diseased / dysfunctional cells with
healthy / functioning ones;
need to identify desired type of stem cell and grow in culture / special solutions /
controlled conditions;
develop biochemical solution that will cause cells to differentiate into desired cell
type;
develop means of implanting / integrating cells into patient’s own tissues so that
they function with the body’s natural cells;
danger of rejection of cells therefore need to suppress immune system;
must make sure new cells do not become overgrown / develop into cancerous
tumours;
Award [2 max] for a specific example ie: [1] for type of cells and [1] for proposed use:
eg retinal cells; replace dead cells in retina to cure presently incurable diseases such as glaucoma
and macular degeneration;
eg graft new skin cells;
to treat serious burn victims;
eg nerve tissue;
help repair catastrophic spinal injuries / help victims of paralysisregain movement;
What Diseases Could Be Impacted
by Stem Cell Research?
More than 100 million Americans suffer from diseases which might be
alleviated by stem cell transplantation technologies.
Examples include cardiovascular disease, autoimmune disease, diabetes,
osteoporosis, cancer, Alzheimer’s disease and Parkinson’s disease.
Stem cell treatment could potentially help patients with severe burns,
spinal cord injuries, or birth defects.
Types of Research
• Transplantation
• Therapeutic delivery systems
• Developmental studies
Science (2000) 287:1423.
Uses of Stem Cells
Non-Hodgkins Lymphoma is a cancerous disease of the lymphatic
system.
1. patient requires heavy does of radiation and or chemotherapy. This will
destroy health blood tissue as well as the diseased tissue.
2. Blood is filtered for the presence of peripheral stem cells. Cells in the
general circulation that can still differentiate into different types of blood
cell otherwise known as stem cells.
3. Bone marrow can be removed before treatment.
4. Chemotherapy supplies toxic drugs to kill the cancerous cells.
5. Radiation can be used to kill the cancerous cells. In time however the
cancerous cells adapt to this treatment so that radiation and
chemotherapy are often used together.
6. Post radiation/ chemotherapy means that the patients health blood
tissues is also destroyed by the treatment.
7. Healthy stem cells or marrow cells can be transplanted back to
produce blood cells again
Animation of Stem Cells
Watch the Below Animation and then address
the sunsequent assessment statements :
http://www.sumanasinc.com/webcontent/anim
ations/content/stemcells.html
Assessment Statements:
State that stem cells retain the capacity to divide and
have the ability to differentiate along different
pathways
Outline one therapeutic use of stem cells.