Essential idea: The evolution of multicellular organisms allowed cell specialization and cell replacement

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 TheoryOutline Cell Theory

Assessment StatementAssessment Statement

Outline Cell theory

Cell TheoryCell Theory

KEY CONCEPT Cells are the basic unit of life.


All living All living things are things are made of cells. made of cells.

Cells are the smallest Cells are the smallest unit of life.unit of life.

Existing cells Existing cells have have come come from other from other cellscells. .


How did the below scientist contribute to Cell How did the below scientist contribute to Cell Theory???Theory???

Evidence for Cell TheoryEvidence for Cell Theory

Assessment StateAssessment State

Discuss the evidence for Cell TheoryDiscuss the evidence for Cell Theory


a. All living things are made of cellsa. All living things are made of cells:When :When living things are observed under the living things are observed under the microscope they microscope they consistentlyconsistently appear to be appear to be composed of cells.composed of cells.


b. Cells are the smallest unit of life.b. Cells are the smallest unit of life.The cell is the smallest unit of organisation that can show all The cell is the smallest unit of organisation that can show all the the characteristics of living processes, including:characteristics of living processes, including:

MetabolismMetabolism ResponseResponse SensitivitySensitivity GrowthGrowth ReproductionReproduction NutritionNutrition DNADNA RespireRespire

Organelles often require the cooperation of other organelles for their Organelles often require the cooperation of other organelles for their successful function.successful function.


c. Cells come only from other cellsc. Cells come only from other cells..o Cells carry out a form of Cells carry out a form of cell division cell division to form new cells. to form new cells.

This process of cell replication in eukaryotes is called This process of cell replication in eukaryotes is called MitosisMitosis and in prokaryotes is called bi and in prokaryotes is called binary fissionnary fission. .

o This aspect of cell theory suggests that all cells therefore This aspect of cell theory suggests that all cells therefore have a have a common ancestorcommon ancestor, the original ancestral cell form , the original ancestral cell form which all other cells have arisen by descent. (origin of which all other cells have arisen by descent. (origin of cellular life).cellular life).

o This relationship of common ancestor suggest that This relationship of common ancestor suggest that all all organisms are related.organisms are related.

Limitations of Cell TheoryLimitations of Cell Theory

Questioning Cell Theory.Questioning Cell Theory.

Using atypical examples: Discuss problem in Using atypical examples: Discuss problem in Cell Theory:Cell Theory:

• Striated Muscles ExampleStriated Muscles Example• Giant Algae ExampleGiant Algae Example• Fungal Hyphae ExampleFungal Hyphae Example

Functions of LifeFunctions of Life


State that unicellular organisms carry out all the function of life

Functions of LifeFunctions of Life

Organisms are able to carry out all the processes which are Organisms are able to carry out all the processes which are characteristic of living things such as:characteristic of living things such as:

• a. a. metabolismmetabolism which includes respiration the synthesis of which includes respiration the synthesis of ATP. ATP.

• b. b. responseresponse to a change in the environment to a change in the environment • c. c. homeostasihomeostasiss the maintenance and regulation of internal the maintenance and regulation of internal

cell conditions. cell conditions. • d. d. growthgrowth which for a unicellular organism means an which for a unicellular organism means an

increase in cell size and volume. increase in cell size and volume. • e. e. reproductionreproduction which for the unicellular organism is largely which for the unicellular organism is largely

asexual through cell division to form a clone.asexual through cell division to form a clone.• f. f. nutritionnutrition which means either the synthesis of organic which means either the synthesis of organic

molecules or the absorption of organic matter.molecules or the absorption of organic matter.

Relative Sizes Relative Sizes

Assessment StatementsAssessment Statements

Compare relative sizes of molecules, cell membrane thickness, eukaryotes, viruses, bacteria and cells using the appropriate SI units

Relative Sizes Relative Sizes

Relative sizesRelative sizes:1. molecules (1nm). 2. cell membrane thickness (10nm).3. :1. molecules (1nm). 2. cell membrane thickness (10nm).3. virus (100nm).4. bacteria (1um).5. organelles (less 10um).6. cells virus (100nm).4. bacteria (1um).5. organelles (less 10um).6. cells (<100 um).7. generally plant cells are larger than animal cells.(<100 um).7. generally plant cells are larger than animal cells.

Relative Sizes Relative Sizes • Molecules of Biological significance are around 1 nm in size where as the cell Molecules of Biological significance are around 1 nm in size where as the cell

membrane is about ten times thicker at 10nm.membrane is about ten times thicker at 10nm.• Where as a virus is ten times larger again at around 100nm.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 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 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. where as a eukaryotic plant cell is ten times larger again at around 100 um.

MagnificationMagnification


Calculate Linear Magnification of drawings and the actual size of specimens in images of know magnification

Units used in magnification calculationsUnits used in magnification calculations

Calculate Magnification of Specimen in DrawingCalculate Magnification of Specimen in Drawing

CalculateCalculate MagnificationMagnification

==Length of specimen in Length of specimen in

drawing/ photo (measured)drawing/ photo (measured)

Actual length of specimen Actual length of specimen (estimated)(estimated)

Explain how you would estimate Explain how you would estimate the size of cell A.the size of cell A.

A

30 μm

Estimate the actual size of cell A.Estimate the actual size of cell A.

A

30 μm

Use actual length and measured length to calculateUse actual length and measured length to calculateLinear magnificationLinear magnification

A

30 μm





Summary of Magnification CalculationsSummary of Magnification Calculations

Estimate Size of Amoeba Estimate Size of Amoeba in mm & μmin mm & μm

a. mm

μmm.

Calculate MagnificationCalculate Magnification

Actual length mm = .

Measure length in photo mm= .





Estimate the size of the Daphnia Estimate the size of the Daphnia in mm & μmin mm & μm

e. mm

μmm.

Calculate MagnificationCalculate Magnification

Actual length mm = .

Measure length in photo mm= .





Calculate Actual sizeCalculate Actual size

If a drawing of a cell has a magnification of If a drawing of a cell has a magnification of 10X, and the length of the drawing is 20 10X, and the length of the drawing is 20 mm. What is the actual length of the the mm. What is the actual length of the the cell?cell?





MagnificationMagnification


If the magnification of If the magnification of the drawing is the drawing is 25Xwhat is the actual 25Xwhat is the actual length of this length of this drawing?drawing?

Calculating Actual LengthCalculating Actual Length

Calculating Actual SizeCalculating Actual Size



Cell SizeCell Size

Assessment Statement:Assessment Statement:• Explain the importance of the surface area Explain the importance of the surface area

to volume ratio as a factor of limiting cell to volume ratio as a factor of limiting cell size. size.

Why are cells so small?Why are cells so small?

Surface area to volume ratioSurface area to volume ratio• As cell size increases, As cell size increases, volume increase faster volume increase faster

than surface areathan surface area

• Surface area to volume Surface area to volume ratio decrease ratio decrease as cell as cell increasesincreases

• Thus less Thus less cytoplasmcytoplasm has contact with has contact with plasma plasma membranemembrane to exchange material with its to exchange material with its environment.environment.

Cell SizeCell Size

Cells need a Cells need a large surface area to volume large surface area to volume ratioratio for three reasons: for three reasons:

1.1. Get rid of wasteGet rid of waste more quickly more quickly

2.2. Absorb materials from environmentAbsorb materials from environment more quicklymore quickly

3.3. Get rid of internal heat and Get rid of internal heat and absorb heat absorb heat from the environment more quicklyfrom the environment more quickly. .

Cell Size SummaryCell Size Summary

The The smaller the cellsmaller the cell the more easily it can the more easily it can get get rid of wasterid of waste to, and to, and absorb nutrientsabsorb nutrients from, from, its environment.its environment.

LE 6-7LE 6-7

Total surface area(height x width xnumber of sides xnumber of boxes)

6

125 125

150 750

1

11

5

1.2 66

Total volume(height x width x lengthX number of boxes)

Surface-to-volumeratio(surface area volume)

Surface area increases whileTotal volume remains constantCompare the Surface area

of the solid box to the box made of a lot of small

boxes

Surface Area to Volume RatioSurface Area to Volume Ratio

The rate of exchange of substances therefore depends on the organism's The rate of exchange of substances therefore depends on the organism's surface area that is in contact with the surroundings. surface area that is in contact with the surroundings.

Reason: as organisms get bigger their volume and surface area both get Reason: as organisms get bigger their volume and surface area both get bigger, but not by the same amount. The volume increases as the bigger, but not by the same amount. The volume increases as the cube but the area of the surface only increases by the square.cube but the area of the surface only increases by the square.

Surface Area to Volume RatioSurface Area to Volume Ratio

Conclusions:Conclusions: As the organism gets bigger its surface area : volume ratio decreases As the organism gets bigger its surface area : volume ratio decreases This rule is a limiting factor for cell size.This rule is a limiting factor for cell size. As the cell gets bigger the ratio decreasesAs the cell gets bigger the ratio decreases If the ratio decreases the rate of exchange decreasesIf the ratio decreases the rate of exchange decreases

Example: gas exchange of oxygen for respirationExample: gas exchange of oxygen for respiration.. A cell which respires aerobically demands oxygen for the process.A cell which respires aerobically demands oxygen for the process. Oxygen is obtained form the surrounding environment such as water or blood Oxygen is obtained form the surrounding environment such as water or blood

(depends on the cell).(depends on the cell). Oxygen diffuses across the cell membrane.Oxygen diffuses across the cell membrane. More membrane more diffusion (Surface area= increases by the More membrane more diffusion (Surface area= increases by the 22). ). Bigger cell (Volume = increases by the Bigger cell (Volume = increases by the 33).). However the ratio of surface areaHowever the ratio of surface area22 : volume : volume 33 is decreasing is decreasing Therefore the volume of oxygen obtained for each unit of cell volume is actually Therefore the volume of oxygen obtained for each unit of cell volume is actually

decreasingdecreasing Cells must not get too big because they cannot obtain sufficient oxygen to Cells must not get too big because they cannot obtain sufficient oxygen to

satisfy the demands of the cell. satisfy the demands of the cell.

why cells are small (reasoning):why cells are small (reasoning):

Size as a limiting Factors for cell because:Size as a limiting Factors for cell because: A big cell needs more oxygen than a little cellA big cell needs more oxygen than a little cell Big cells need to have more oxygen diffusion across the cell Big cells need to have more oxygen diffusion across the cell

membrane.membrane. But the big cell has relatively small surface area compared to its But the big cell has relatively small surface area compared to its

volume i.e. the surface area: volume ratio is small.volume i.e. the surface area: volume ratio is small. What ever other benefits a cell might gain from being big, it cannot What ever other benefits a cell might gain from being big, it cannot

become larger than is limited by the rate of gas exchange.become larger than is limited by the rate of gas exchange. This reasoning can be applied to nutrients and to waste, anything that This reasoning can be applied to nutrients and to waste, anything that

is exchanged across the cell surface.is exchanged across the cell surface. Try preparing a reason why size is a limiting factor for:Try preparing a reason why size is a limiting factor for: Obtaining nutrient (glucose) Obtaining nutrient (glucose) Excretion of waste molecules ( urea, ammonia, carbon dioxide)Excretion of waste molecules ( urea, ammonia, carbon dioxide)..

Emergent PropertiesEmergent Properties

Assessment Statement:Assessment Statement:

State that multicellular organisms show State that multicellular organisms show Emergent PropertiesEmergent Properties


''Emergent properties Emergent properties arise from the arise from the interaction of the component parts; the interaction of the component parts; the whole is greater than the sum of the parts'.whole is greater than the sum of the parts'.


EmergenceEmergence is the occurrence of unexpected is the occurrence of unexpected characteristics or properties in a complex system. characteristics or properties in a complex system.

These properties emerge from the interaction of These properties emerge from the interaction of the ‘parts’ of the system.the ‘parts’ of the system.

Remember that biology insists on a population Remember that biology insists on a population thinking so that we know the interacting ‘parts’ thinking so that we know the interacting ‘parts’ vary in themselves and therefore their ‘emerging’ vary in themselves and therefore their ‘emerging’ properties can only be generalized. properties can only be generalized.


Multicellular and DifferentiationMulticellular and Differentiation


Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others.


Rather than all cells carrying out all functions, Rather than all cells carrying out all functions, tissuestissues and and organs specialize organs specialize to particular to particular functions. functions.

These organs and systems are then integrated to These organs and systems are then integrated to give the give the whole organism whole organism (with its emergent (with its emergent properties).properties).

Differentiation: Differentiation: Cells within a multi-cellular Cells within a multi-cellular organism specialize their function.organism specialize their function.

Specialized cells have switched on Specialized cells have switched on particular particular genes (expressed) that genes (expressed) that correlate to these correlate to these specialist functions.specialist functions.


These These specific gene specific gene expressions produce expressions produce particular particular shapes, functionsshapes, functions and and adaptations adaptations within a cell.within a cell.Therefore a Therefore a muscle cell muscle cell will expresswill express muscle muscle genes genes but but NOT NOT those genes which are for nerve those genes which are for nerve cells.cells.


What is the benefit of differentiation and What is the benefit of differentiation and specialization of tissues rather than all tissues specialization of tissues rather than all tissues carrying out all functions?carrying out all functions?

In a multi cellular organism specialization is more efficient In a multi cellular organism specialization is more efficient than the generalized plan when competing for a specific than the generalized plan when competing for a specific resource. Consider the role of water transport through the resource. Consider the role of water transport through the plant:plant: In higher plants we have specialization to for a tubular system called the xylem. 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 This is more efficient way of water transport than simply been passed by the mass

movement of water from cell to cell. movement of water from cell to cell. In the xylem water can be moved very efficiently from underground to the canopy of 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.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 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 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.therefore limited in size and therefore cannot compete with larger species.


Watch the below animation and then in your own words 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







Stem CellsStem Cells

State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways

What is a Stem Cell?What is a Stem Cell?

Unspecialized cellsUnspecialized cells

Able to self-renew without Able to self-renew without differentiating for extended differentiating for extended periods of timeperiods of time

Ability to differentiate into Ability to differentiate into specialized cellsspecialized cells

Embryonic and adult stem cells Embryonic and adult stem cells are derived from different are derived from different sources.sources. TIME 2001

Human blastocyst showing inner cell mass and

trophectoderm

Photo: Mr. J. Conaghan

What is an Embryonic Stem Cell?What is an Embryonic Stem Cell?

Fusion of nuclei

First cell division

Only cells between the nuclei fusion and blastocyst stages are considered true

stem cells.

Blastocyst (~5-6 days old): a “pre-embryo” ball of cells which has not implanted in

the uterus.

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.

Placenta cellStem cell

Embryonic Stem Cells are Derived from BlastocystsEmbryonic Stem Cells are Derived from Blastocysts

Fusion of nuclei

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 CellsAdult Stem Cells

Have two characteristics:Have two characteristics:• They can make identical copies of themselves for the They can make identical copies of themselves for the

lifetime of the organism.lifetime of the organism.• They can give rise to differentiated mature cells with They can give rise to differentiated mature cells with

specific morphologies (shapes and functions).specific morphologies (shapes and functions).

Adult stem cells are rare—and appear to help with Adult stem cells are rare—and appear to help with homeostasis.homeostasis.

Stem cells have been found in the brain and spinal Stem cells have been found in the brain and spinal cord, dental pulp, blood vessels, skeletal muscle, cord, dental pulp, blood vessels, skeletal muscle, the digestive system, the cornea and retina, and the digestive system, the cornea and retina, and the liver and pancreas.the liver and pancreas.

Stem CellsStem Cells

A stem cell retains the capacity to divide and has A stem cell retains the capacity to divide and has the ability to the ability to differentiate differentiate along different pathways. along different pathways.

A stem cell is able to divide but has A stem cell is able to divide but has NOTNOT yet yet expressed genes expressed genes to specialize to a particular to specialize to a particular function. Under the right conditions stem cells can function. Under the right conditions stem cells can be be induced to express particular genes induced to express particular genes and and differentiate into a particular type of celldifferentiate into a particular type of cell . .

Embryonic Stem Cells Can Become Embryonic Stem Cells Can Become Any Tissue in the BodyAny Tissue in the Body

Blastocyst

Cultured laboratory stem

cells

Scientific manipulations entice stem cells to become specialized tissues (blood, muscle,

neuron, etc.).

Blood cellsMuscle cells

Neuron (brain) cells


Stems CellsStems Cells

Uses of Stem CellsUses of Stem Cells


OutlineOutline one use of stem cells (6 Points) one use of stem cells (6 Points)

• Summarize. Summarize.

Question 3Question 3Outline one therapeutic use of stem cells (6 points). Outline one therapeutic use of stem cells (6 points). Award [4 max] for any of the following general statements: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 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;differentiate along different paths into all types of cells / are pluripotent / totipotent;stem cells are derived from blastocysts / human embryos, left over from IVF / stem cells are derived from blastocysts / human embryos, left over from IVF / placenta / umbilical cord / some adult tissues;placenta / umbilical cord / some adult tissues;new techniques / technologies rely on replacing diseased / dysfunctional cells with new techniques / technologies rely on replacing diseased / dysfunctional cells with healthy / functioning ones;healthy / functioning ones;need to identify desired type of stem cell and grow in culture / special solutions / need to identify desired type of stem cell and grow in culture / special solutions / controlled conditions;controlled conditions;develop biochemical solution that will cause cells to differentiate into desired cell develop biochemical solution that will cause cells to differentiate into desired cell type;type;develop means of implanting / integrating cells into patient’s own tissues so that develop means of implanting / integrating cells into patient’s own tissues so that they function with the body’s natural cells;they function with the body’s natural cells;danger of rejection of cells therefore need to suppress immune system;danger of rejection of cells therefore need to suppress immune system;must make sure new cells do not become overgrown / develop into cancerous must make sure new cells do not become overgrown / develop into cancerous tumourstumours;;Award [2 max] for a specific example ie: [1] for type of cells and [1] for proposed use:Award [2 max] for a specific example ie: [1] for type of cells and [1] for proposed use:egeg retinal cells retinal cells; replace dead cells in retina to cure presently incurable diseases such as glaucoma ; replace dead cells in retina to cure presently incurable diseases such as glaucoma and macular degeneration;and macular degeneration;egeg graft new skin cells; graft new skin cells;to treat serious burn victims; to treat serious burn victims; egeg nerve tissue; nerve tissue; help repair catastrophic spinal injuries / help victims of paralysisregain movement;help repair catastrophic spinal injuries / help victims of paralysisregain movement;

What Diseases Could Be Impacted What Diseases Could Be Impacted by Stem Cell Research? by Stem Cell Research?

More than 100 million Americans suffer from diseases which might be More than 100 million Americans suffer from diseases which might be alleviated by stem cell transplantation technologies.alleviated by stem cell transplantation technologies.

Examples include cardiovascular disease, autoimmune disease, diabetes, Examples include cardiovascular disease, autoimmune disease, diabetes, osteoporosis, cancer, Alzheimerosteoporosis, cancer, Alzheimer’’s disease and Parkinsons disease and Parkinson’’s disease.s disease.

Stem cell treatment could potentially help patients with severe burns, Stem cell treatment could potentially help patients with severe burns, spinal cord injuries, or birth defects. spinal cord injuries, or birth defects.

Types of ResearchTypes of Research• TransplantationTransplantation• Therapeutic delivery systemsTherapeutic delivery systems• Developmental studiesDevelopmental studies

Science (2000) 287:1423.

Uses of Stem CellsUses of Stem Cells

Non-Hodgkins Lymphoma is a cancerous disease of the lymphatic system. Non-Hodgkins Lymphoma is a cancerous disease of the lymphatic system.

1. patient requires heavy does of radiation and or chemotherapy. This will 1. patient requires heavy does of radiation and or chemotherapy. This will destroy health blood tissue as well as the diseased tissue.destroy health blood tissue as well as the diseased tissue.

2. Blood is filtered for the presence of peripheral stem cells. Cells in the 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 general circulation that can still differentiate into different types of blood cell otherwise known as stem cells.cell otherwise known as stem cells.

3. Bone marrow can be removed before treatment.3. Bone marrow can be removed before treatment.

4. Chemotherapy supplies toxic drugs to kill the cancerous cells.4. Chemotherapy supplies toxic drugs to kill the cancerous cells.

5. Radiation can be used to kill the cancerous cells. In time however the 5. Radiation can be used to kill the cancerous cells. In time however the cancerous cells adapt to this treatment so that radiation and cancerous cells adapt to this treatment so that radiation and chemotherapy are often used together.chemotherapy are often used together.

6. Post radiation/ chemotherapy means that the patients health blood 6. Post radiation/ chemotherapy means that the patients health blood tissues is also destroyed by the treatment.tissues is also destroyed by the treatment.

7. 7. Healthy stem cells Healthy stem cells or marrow cells can be transplanted back to produce or marrow cells can be transplanted back to produce blood cells againblood cells again

Animation of Stem CellsAnimation of Stem Cells

Watch the Below Animation and then address Watch the Below Animation and then address the sunsequent assessment statements :the sunsequent assessment statements :

http://www.sumanasinc.com/webcontent/animations/content/stemcells.htmlAssessment Statements: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.

http://www.sumanasinc.com/webcontent/animations/content/stemcells.html

http://www.sumanasinc.com/webcontent/animations/content/stemcells.html

Documents

Essential idea: The evolution of multicellular organisms allowed cell specialization and cell replacement