1.1 Introduction to Cells

Essential idea: The evolution of multicellular organismsallowed cell specialization and cell replacement.

The background image shows totipotent stem cells. These unspecialised cell will be divideand some will become the cells that form heart muscle, neurones in the brain andlymphocytes in the blood. These three types of specialised human cells are structurally verydifferent and perform certain functions much more efficiently than an unspecialised cell, suchas the embryonic cells above, could. Another advantage that multicellular organisms have over unicellular organisms is thatsevere damage to a cell does not mean the end of an organism. Stem cell persist through thelife of a multi-cellular organism, this enables organisms to digest severely damaged cells andreplace them, i.e. wounds can be healed.

Understandings Statement Guidance1.1.U

1According to the cell theory, living organisms arecomposed of cells.

1.1.U2

Organisms consisting of only one cell carry outall functions of life in that cell.

Students are expected to be able to nameand briefly explain these functions of life:nutrition, metabolism, growth, response,excretion, homeostasis and reproduction.

1.1.U3

Surface area to volume ratio is important in thelimitation of cell size.

1.1.U4

Multicellular organisms have properties thatemerge from the interaction of their cellularcomponents.

1.1.U5

Specialized tissues can develop by celldifferentiation in multicellular organisms.

1.1.U6

Differentiation involves the expression of somegenes and not others in a cell’s genome.

1.1.U7

The capacity of stem cells to divide anddifferentiate along different pathways isnecessary in embryonic development and alsomakes stem cells suitable for therapeutic uses.

Applications and Skills

Statement Guidance1.1.A1 Questioning the cell theory using atypical

examples, including striated muscle, giant algaeand aseptate fungal hyphae.

1.1.A2 Investigation of functions of life in Parameciumand one named photosynthetic unicellularorganism.

Chlorella or Scenedesmus are suitablephotosynthetic unicells, but Euglena shouldbe avoided as it can feed heterotrophically.

1.1.A3 Use of stem cells to treat Stargardt’s disease andone other named condition.

1.1.A4 Ethics of the therapeutic use of stem cells fromspecially created embryos, from the umbilicalcord blood of a new-born baby and from anadult’s own tissues.

1.1.S1 Use of a light microscope to investigate thestructure of cells and tissues, with drawing ofcells. Calculation of the magnification of drawingsand the actual size of structures andultrastructures shown in drawings ormicrographs. (Practical 1)

Scale bars are useful as a way of indicatingactual sizes in drawings and micrographs.

1.1.S1 Use of a light microscope to investigate the structure of cellsand tissues, with drawing of cells. Calculation of the magnificationof drawings and the actual size of structures and ultrastructuresshown in drawings or micrographs. (Practical 1)

Virtual microscope: http://www.udel.edu/biology/ketcham/microscope/scope.html

Learn about Microscopes: http://www.wisc-online.com/objects/ViewObject.aspx?ID=BIO905

Microscopes are best learn through experience thebelow links are primarily for those without access toa microscope.

Source: https://microbewiki.kenyon.edu/index.php/Dinoflagellata

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1.1.U1 According to the cell theory, livingorganisms are composed of cells.Cell theory states that:• All living things are composed of cells (or cell products)• The cell is the smallest unit of life• Cells only arise from pre-existing cells

Source: http://www.engr.uconn.edu/alarm/research?id=63

1.1.U1 According to the cell theory, livingorganisms are composed of cells.

Longitudinal section of a root tip of Maize (Zea mays)by Science and Plants for Schools on Flickr (CC) http://flic.kr/p/bNNM6M

All living thingsare composed ofcells (or cellproducts)

1.1.U1 According to the cell theory, livingorganisms are composed of cells.The cell is the smallest unitof life

Specialized structures within cells(organelles) carry out differentfunctions. Organelles cannotsurvive alone. This micrograph of a Parameciumshows the 2 contractile vacuoles,the oral groove with the formationof a new food vacuole at its end,and the overall surrounding cilia.

Source: http://www.dr-ralf-wagner.de/

1.1.U1 According to the cell theory, livingorganisms are composed of cells.Cells only arise from pre-existingcells:• Cells multiply through division• All life evolved from simpler

ancestors• Mitosis results in genetically identical

diploid daughter cells• Meiosis generates haploid gametes

(sex cells)

4-cell stage of a sea biscuit by Bruno Vellutini on Flickr(CC) http://flic.kr/p/daWnnS

1.1.A1 Questioning the cell theory using atypical examples,including striated muscle, giant algae and aseptate fungal hyphae.

striated muscle• challenges the idea

that a cell has onenucleus

• Muscle cells havemore than onenucleus per cell

• Muscle Cells calledfibres can be verylong (300mm)

• They are surroundedby a single plasmamembrane but theyare multi-nucleated Source: http://en.wikipedia.org/wiki/File:Skeletal_striated_muscle.jpg

1.1.A1 Questioning the cell theory using atypical examples,including striated muscle, giant algae and aseptate fungal hyphae.

aseptate fungalhyphae• challenges the idea that

a cell is a single unit.• Fungal hyphae are

again very large withmany nuclei and acontinuous cytoplasm

• The tubular system ofhyphae form densenetworks calledmycelium

• Like muscle cells theyare multi-nucleated Source: http://www.apsnet.org/edcenter/intropp/pathogengroups/pages/introfungi.aspx

1.1.A1 Questioning the cell theory using atypical examples,including striated muscle, giant algae and aseptate fungal hyphae.

giant algae(Acetabularia)• Acetabularia is a

single-celledorganism thatchallenges boththe idea that cellsmust be simple instructure and smallin size

• Gigantic in size (5– 100mm) Source: http://deptsec.ku.edu/~ifaaku/jpg/Inouye/Inouye_01.html

1.1.U2 Organisms consisting of only one cellcarry out all functions of life in that cell.

You probably know:• Movement• Reproduction• Sensitivity• Homeostasis• Growth• Respiration• Excretion• Nutrition

In this course the functions are refined:• Metabolism - the web of all the enzyme-

catalysed reactions in a cell or organism,e.g. respiration

• Response - Living things can respond to andinteract with the environment

• Homeostasis - The maintenance andregulation of internal cell conditions, e.g.water and pH

• Growth - Living things can grow or changesize / shape

• Excretion – the removal of metabolic waste• Reproduction - Living things produce

offspring, either sexually or asexually• Nutrition – feeding by either the synthesis

of organic molecules (e.g. photosynthesis)

1.1.U2 Organisms consisting of only one cellcarry out all functions of life in that cell.

Remembering the functions of lifeAn easy way to remember Metabolism, Response, Homeostasis, Growth,Reproduction, Excretion and Nutrition is: “MR H GREN” (each letter is a function of life)

Source: http://www.dr-ralf-wagner.de/

1.1.A2 Investigation of functions of life inParamecium and one named photosyntheticunicellular organism.How does this paramecium show the functions of life?

Source: http://umanitoba.ca/Biology/BIOL1030/Lab1/biolab1_3.html#Ciliophora

1.1.A2 Investigation of functions of life inParamecium and one named photosyntheticunicellular organism.

Source: http://umanitoba.ca/Biology/BIOL1030/Lab1/biolab1_3.html#Ciliophora

Homeostasis – contractile vacuole fill upwith water and expel I through the plasmamembrane to manage the water content

Reproduction – Thenucleus can divide tosupport cell division bymitosis, reproduction isoften asexual

Metabolism –mostmetabolicpathwayshappen in thecytoplasm

Growth – after consumingand assimilating biomassfrom food the parameciumwill get larger until itdivides.

Response – thewave action ofthe cilia movestheparamecium inresponse tochanges in theenvironment,e.g. towardsfood.

Excretion – the plasmamembrane control the entryand exit of substancesincluding expulsion ofmetabolic waste

Nutrition – foodvacuoles containorganisms the parameiumhas consumed

1.1.A2 Investigation of functions of life inParamecium and one named photosyntheticunicellular organism.

How does this algae show the functions of life?

Source: http://www.algae.info/Algaecomplete.aspx

1.1.A2 Investigation of functions of life inParamecium and one named photosyntheticunicellular organism.

Source: http://www.algae.info/Algaecomplete.aspx

Homeostasis –contractilevacuole fill upwith water andexpel I throughthe plasmamembrane tomanage the watercontent

Reproduction – The nucleus can divideto support cell division, by mitosis (thesecells are undergoing cytokinesis)

Metabolism –mostmetabolicpathwayshappen in thecytoplasm

Growth – after consuming and assimilatingbiomass from food the algae will get larger untilit divides.

Response – thewave action ofthe cilia movesthe algae inresponse tochanges in theenvironment,e.g. towardslight.

Excretion – the plasmamembrane control theentry and exit ofsubstances including thedifussion out of wasteoxygen

Nutrition –photosynthesis happensinside thechloroplaststo provide thealgae withfood

1.1.U3 Surface area to volume ratio isimportant in the limitation of cell size.

1.1.U3 Surface area to volume ratio isimportant in the limitation of cell size.

1.1.U3 Surface area to volume ratio isimportant in the limitation of cell size.

1.1.U3 Surface area to volume ratio isimportant in the limitation of cell size.

The cell must consequently dividein order to restore a viable SA:Volratio and survive.• A represents a small single

celled organism• B a large single celled

organism• C multicellular organism

Cells and tissues specialisedfor gas or material exchangewill increase their surfacearea to optimise the transferof materials, e.g. microvilli(below) in the small intestine A B C

1.1.U3 Surface area to volume ratio isimportant in the limitation of cell size.In summary:• The rate of metabolism of a cell is a function of its mass / volume• The rate of material exchange in and out of a cell is a function of its

surface area• As the cell grows, volume increases faster than surface area (leading

to a decreased SA:Vol ratio)• If the metabolic rate is greater than the rate of exchange of vital

materials and wastes, the cell will eventually die• Hence the cell must consequently divide in order to restore a viable

SA:Vol ratio and survive• Cells and tissues specialised for gas or material exchange (e.g.

alveoli) will increase their surface area to optimise the transfer ofmaterials

Extension: Can you think of any exceptions? See if you can find

1.1.U4 Multicellular organisms have properties that emergefrom the interaction of their cellular components.

Emergent properties arise from the interaction of componentparts. The whole is greater than the sum of its parts. Multicellularorganisms are capable of completing functions that individualcells could not undertake - this is due to the interaction betweencells producing new functions.

1.1.U4 Multicellular organisms have properties that emergefrom the interaction of their cellular components.

Science traditionally has been taken a reductionist approach tosolving problems and developing theories. Systems Biology usesinductive thinking as it is realised the importance of emergentproperties, whether it be the interaction of genes, enzymesworking together in a metabolic pathway, or cells formingtissues, different tissues forming organs, in turn forming organsystems and then the organism itself. At each level emergentproperties arise.

1.1.U4 Multicellular organisms have properties that emergefrom the interaction of their cellular components.

As a model consider the electric light bulb. The bulb is the system and iscomposed of a filament made of tungsten, a metal cup, and a glass container.We can study the parts individually how they function and the properties theyposses. These would be the properties of :• Tungsten• Metal cup• Glass container When studied individually they do not allowthe prediction of the properties of the lightbulb. Only when we combine them to form thebulb can these properties be determined. Thereis nothing supernatural about the emergentproperties rather it is simply the combinationof the parts that results in new propertiesemerging.

Source: http://en.wikipedia.org/wiki/File:Gluehlampe_01_KMJ.jpg

1.1.U6 Differentiation involves the expression of somegenes and not others in a cell’s genome.

• All (diploid) cells of an individualorganisms share an identical genome- each cell contains the entire set ofgenetic instructions for that organism

• BUT not all genes are expressed(activated) in all cells

• In (totipotent) embryonic stem cellsthe entire genome is active

• Newly formed cells receive signalswhich deactivate (or more rarelyactivate) genes, e.g. a skin cell doesnot need to be able to producehaemoglobin (the pigment in redblood cells that carries oxygen)

Screenshot from this excellent tutorial: http://www.ns.umich.edu/stemcells/022706_Intro.html

1.1.U6 Differentiation involves the expression of somegenes and not others in a cell’s genome.

• Extension: Active genes are usuallypackaged in an expanded andaccessible form (euchromatin), whileinactive genes are mainly packagedin a condensed form(heterochromatin)

• The fewer active genes a cellpossesses the more specialised it willbecome

• As a result of gene expression celldifferentiation begins: the cell’smetabolism and shape changes tocarry out a specialised function.

Screenshot from this excellent tutorial: http://www.ns.umich.edu/stemcells/022706_Intro.html

1.1.U5 Specialized tissues can develop by celldifferentiation in multicellular organisms.

• In humans 220 distincthighly specialised celltypes have beenrecognised

• All specialised cells andthe organs constructedfrom them have developedas a result ofdifferentiation

Source: http://images.wisegeek.com/types-of-human-cells.jpg

1.1.U7 The capacity of stem cells to divide and differentiate alongdifferent pathways is necessary in embryonic development and alsomakes stem cells suitable for therapeutic uses.

Stem cells areunspecialised cellsthat can:• Can continuously

divide andreplicate

• Have the capacityto differentiateinto specialisedcell types

Totipotent

Image from: http://en.wikipedia.org/wiki/Stem_cell

1.1.U7 The capacity of stem cells to divide and differentiate alongdifferent pathways is necessary in embryonic development and alsomakes stem cells suitable for therapeutic uses.

Learn about stem cells using the tutorials

A Stem CellStory

http://ns.umich.edu/stemcells/022706_Intro.html

http://www.youtube.com/watch?v=2-3J6JGN-_Y

http://learn.genetics.utah.edu/content/stemcells/scintro/

1.1.U7 Use of stem cells to treat Stargardt’s disease and one othernamed condition.

Stargardt's macular dystrophy

Theproblem

• Affects around one in 10,000 children• Recessive genetic (inherited) condition• The mutation causes an active transport protein on photoreceptor cells

to malfunction• The photoreceptor cells degenerate• the production of a dysfunctional protein that cannot perform energy

transport• that causes progressive, and eventually total, loss of central vision

Thetreatment

• Embryonic stem cells are treated to divide and differntiate to becomeretinal cells

• The retinal cells are injected into the retina• The retinal cells attach to the retina and become functional• Central vision improves as a result of more functional retinal cells

The future • This treatment is still in at the stage of limited clinical trials, but willlikely be in usage in the future

1.1.U7 Use of stem cells to treat Stargardt’s disease and one othernamed condition.

Learn about stem cell therapies using thetutorials

http://media.hhmi.org/biointeractive/click/Stem_Cell_Therapies/01.html

1.1.U7 Use of stem cells to treat Stargardt’s disease and one othernamed condition.

Leukemia

Theproblem

• Cancer of the blood or bone marrow, resulting in abnormally highlevels of poorly-functioning white blood cells.

Thetreatment

• Hematopoetic Stem Cells (HSCs) are harvested from bone marrow,peripheral blood or umbilical cord blood

• Chemotherapy and radiotherapy used to destroy the diseased whiteblood cells

• New white blood cells need to be replaced with healthy cells.• HSCs are transplanted back into the bone marrow• HSCs differentiate to form new healthy white blood cells

Thebenefit

• The use of a patient’s own HSCs means there is far less risk ofimmune rejection than with a traditional bone marrow transplant.

1.1.A4 Ethics of the therapeutic use of stem cells from speciallycreated embryos, from the umbilical cord blood of a new-born babyand from an adult’s own tissues.

Comparison of stem cell sources

Embryo Cord blood Adult

Ease of extraction Can be obtainedfrom excess embryosgenerated by IVFprograms.

Easily obtained andstored. Thoughlimited quantitiesavailable

Difficult to obtain asthere are very fewand are buried deepin tissues

Ethics of theextraction

Can only beobtained bydestruction of anembryo

Umbilical cord isremoved at birth anddiscarded whether ornot stem cells areharvested

Adult patient cangive permission forcells to be extracted

Growth potential Almost unlimited Reduced potential (compared to embryoniccells)

Tumor risk Higher risk ofdevelopment

Lower risk of development

1.1.A4 Ethics of the therapeutic use of stem cells from speciallycreated embryos, from the umbilical cord blood of a new-born babyand from an adult’s own tissues.

Comparison of stem cell sources

Embryo Cord blood Adult

Differentiation Can differentiate intoany cell type

Limited capacity todifferentiate (withoutinducement onlynaturally divide intoblood cells)

Limited capacity todifferentiate(dependent on thesource tissue)

Genetic damage Less chance of genetic damage than adultcells

Due to accumulationof mutations throughthe life of the adultgenetic damage canoccur

Compatibility Stem cells are notgenetically identicalto the patient

Fully compatible with the patient as the stemcells are genetically identical

1.1.A4 Ethics of the therapeutic use of stem cells from speciallycreated embryos, from the umbilical cord blood of a new-born babyand from an adult’s own tissues.

Arguments for Therapeutic Cloning• Stem cell research may pave the way for future discoveries

and beneficial technologies that would not have occurred iftheir use had been banned

• May be used to cure serious diseases or disabilities with celltherapy (replacing bad cells with good ones)

• Transplants are less likely to be rejected as they are cellswhich are genetically identical to the parent

• Transplants do not require the death of another human• Stem cells can be taken from embryos that have stopped

developing and would have died anyway (e.g. abortions)• Cells are taken at a stage when the embryo has no nervous

system and can arguably feel no pain• Stem cells can be created without the need for fertilisation and

1.1.A4 Ethics of the therapeutic use of stem cells from speciallycreated embryos, from the umbilical cord blood of a new-born babyand from an adult’s own tissues.

Arguments Against Therapeutic Cloning• Involves the creation and destruction of human

embryos (at what point do we afford the right tolife?)

• Embryonic stem cells are capable of continueddivision and may develop into cancerous cells andcause tumors

• More embryos are generally produced than areneeded, so excess embryos are killed

• With additional cost and effort, alternativetechnologies may fulfill similar roles (e.g. nuclearreprogramming of differentiated cell lines)

1.1.A4 Ethics of the therapeutic use of stem cells from speciallycreated embryos, from the umbilical cord blood of a new-born babyand from an adult’s own tissues.

1.1.A4 Ethics of the therapeutic use of stem cells from speciallycreated embryos, from the umbilical cord blood of a new-born babyand from an adult’s own tissues.

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Bibliography / Acknowledgments

Jason de Nys