The Cell

Topic 2.1: Cell Theory

2.1.1 Cell Theory

•All living things are made of cells.

•Cells are the basic units of life.

•Cells come only from other cells

Since the microscope was introduced biologists have examined the structure of living things. In most cases they have been found to be compose of cells. There are however some strange exceptions to the general cell pattern.

Muscle Cells: very large with many nuclei

•Muscle Cells called fibers can be very long (300mm).

•They are surrounded by a single plasma membrane but they are multi-nucleated.(many nuclei).

•This does not conform to the standard view of a small single nuclei within a cell

Fungal Hyphae: again very large with many nuclei and a continuous cytoplasm

•The tubular system of hyphae form dense networks called mycelium.

•Like muscle cells they are multi-nucleated

•They have cell walls composed of chitin

•The cytoplasm is continuous along the hyphae with no end cell wall or membrane

ProtoctistaProtoctista:a cell capable of all necessary functions

•Single celled organisms have one region of cytoplasm surrounded by a cell membrane.•They can perform all the functions of a differentiated Multicellular organism. •This is an image of an amoeba. A single cell

protoctista capable of all essential functions. What cell organelles can you see?

Acetabularia an extra ordinary large cell!

•This is an example of an algae

•The cells are some 7 cm long!

•This seems to contradict theory about cell size. We would expect a large surface area to volume ratio which facilitates a rapid rate of diffusion.

Bone: so much extra cellular material the basic cell structure seems lost

•There are some cells that secrete material outside of the cell membrane

•The secretions solidify and dominate the structure

•In this example the bone cell has secreted concentric layers of 'bone' largely calcium phosphates.

•The living cell is difficult to distinguish.

A virus is a non-cellular structure•Composed of a protein coat

and containing either the nucleic acid DNA or RNA

•Viruses are the smallest and simplest of the microbes.

•They are a-cellular (not made of cells) and, since they cannot reproduce (or do any of the seven characteristics of life) on their own, they are considered non-living.

•They are in fact more like complex chemicals than simple living organisms.

•Viruses are obligate parasites that can only reproduce inside host cells which get damaged in the process, leading to disease.

•Viruses are thought to have arisen from lengths of DNA that became separated from their cells.

•This is a picture ofBacteriophage viruses.•These are viruses that

infectbacterial rather thaneukaryotic cells•They are an important tool

in genetic engineering•Remember this is a protein structure not a cell

Advantages of using a light microscope•Light microscopy has a resolution of about 200 nm, which is good enough to see cells, but not the details of cell organelles.•Specimens can be seen in color (unlike the monochrome electron micrographs) which includes staining and natural color's.•There is a wide field of view to observe the tissue structure (2mm)•Living specimens can be observed and therefore their movement can be studied

http://www.biology.ualberta.ca/facilities/multimedia/uploads/alberta/microscope.swf

Advantages of the Electron MicroscopeThe electron microscope has greater resolution (detail) and magnification than the light microscope.•Resolution approx = 0.25 nm•Magnifications = x

500,000Rather than shinning light through the specimen the EM takes advantage of the short wavelength of the electron.

Rather than shinning light through the specimen the EM takes advantage of the short wavelength of the electron.

•A beam of electrons is fired from a hot metal wire and focused on the specimen by a series of electromagnets.

•The image is produced by the same principles as a TV screen. Photographs are then produced (electron micrographs)

•The Electron Microscope allows the study of the organelles of cell structure.

There are two kinds of electron microscope.•The transmission electron microscope (TEM)

works much like a light microscope, transmitting a beam of electrons through a thin specimen and then focusing the electrons to form an image on a screen or on film. This is the most common form of electron microscope and has the best resolution.

•The scanning electron microscope (SEM) scans a fine beam of electron onto a specimen and collects the electrons scattered by the surface. This has poorer resolution, but gives excellent 3-dimensional images of surfaces.

Disadvantages of the Electron Microscope:

•Specimens are dead due to preparation technique such as staining, dehydration and placement in a vacuum

•Artifacts (not natural/artificial feature)can be produced in the specimens by the preparation techniques

•No movement can be studies as specimens are dead•Field of view is very small

Light ElectronCheap to purchase (100 –500)

Expensive to buy (over 1,000,000)

Cheap to operate Expensive to produce electron beams

Small and portable Large and requires special rooms

Simple and easy preparations Lengthy and complex preparations

Material rarely distorted by preparation

Preparation distorts material

Vacuum is not required Vacuum is requiredNatural color maintained All images in black and whiteMagnifies objects only up to 2000 times

Magnifies over 500,000 times

Comparison of Size

•In cell Biology it is most important to be able to provide details of the size of structure observed. SI units are used at all times to provide this information.

•The following diagram provides an approximation of the sizes of different structures

MagnificationOn an image of a specimen it is useful to show how muchlarger/smaller the image is than the real specimen. This is called magnification.To calculate magnificationTo calculate magnification• using a ruler measure the size of a large clear feature on

the image•measure the same length on the specimen•convert to the same units of measurement

MagnificationMagnification = length on the image /length on the specimen

Length of the actual specimen = length on the image/Magnification

example

•In this example the image of a Rose leaf the magnification is X 0.83

•This tells us the image is smaller than the real specimen.

•The length of the real specimen = picture length/ 0.83 or 4.2cm/0.82 = 5.0 cm

Scale Bars•A scale bar is a line added to

a drawing, diagram or photograph to show the actual size of the structures.

•The scale bar in the picture allows you quickly to determine the approximate size of a feature.

•The main feature in the micrograph is a nucleus with a dark region called the nucleolus.

•Using the picture estimate the size of the nucleus and its nucleolus.

Surface area : Volume ratio and cell size

• All organisms need to exchange substances such as food, waste, gases and heat with their surroundings. These substances must be exchanged between the organism and its surroundings.

• As the size of a structure increases the surface area to volume ratio decreases.

• Therefore the rate of exchange (diffusion/radiation) decreases.

• This is true for organelles,cells, tissues, organs and organisms.

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

• The exchange depends on the volume of the organism, so the ability to meet the requirements depends on , which is known as the surface area : volume ratio

•As organisms get bigger their volume and surface area both get bigger, but not by the same amount.This can be seen by performing some simple calculations concerning different-sized organisms.

12

3

1 cm1 cm 10 cm10 cm 100 cm100 cm

Assume we have 3 cubes:

With sizes:

What will happen to ratio between V and S.A. as their size increases?

Ratio of V:S.A.

Cube Side Length

Volume (x3)

S.A. (6x2) Ratio (S.A./V)

1 1 cm

2 10 cm

3 100 cm

1 cm3

1 000 cm3

1 000 000 cm3

6 cm2

600 cm2

60 000 cm2

6

0.6

0.06

Conclusions:•As the organism gets bigger its surface area : volume ratio

decreases

Example 2

Cell compartmentalize

Toaster Project

Toaster Project

Toaster Project

Unicellular Organisms• A unicellular organism is a single cell that can carry out all those functions of life that are necessary to survive separately from other cells. They can rely on large SA:Vol ratios for Exchange.• The cell is specialized internally to obtain nutrition; carry out respirationand to reproduce. • As has been already noted some biologists regardsuch organisms as 'acellular'. Such biologist regardcells as inter dependant units and not independent asthese specialized unicellular organisms

All organisms must carry out functions of life.

MOVEMENT – Intracellular and/or extracellularRESPIRATION – Gas exchange. Not always O2 and CO2NUTRITION – Need raw materials, i.e.- food, water,

mineralsEXCRETION – Get rid of waste materialsREPRODUCTION – Ability to produce like organismsIRRATIBILITY – Respond to external stimuli GROWTH – Cells grow larger . . . and don’t forget . . .

‘Mr. Smullen’ also carries out the functions of life!

Multi-cellular Organisms• Multi-cellular organisms are large and have to

specialize parts of their structure to complete the various functions that are characteristic of life.

• Cells within a multi cellular organism specialize their function.

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

• 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.

Tissues, Organs and Organ SystemsCell differentiation leads to higher levels of

organization:During the process of cell specializationA process called differentiation occurs.In the cells of the tissue some genes areexpressed and others are suppressed.1.)1.) A tissue is a group of similar cells

performing a particular function. Simple tissues are composed of one type of cell, while compound tissues are composed of more than one type of cell. Some examples of animal tissues are:

•epithelium (lining tissue)•connective, skeletal•nerve•muscle•blood•glandular.

Some examples of plant tissues are:•epithelium•meristem•epidermis•vascular•leaf•chollenchyma•sclerenchyma•parenchyma.

2.) An organ is a group of physically-linked different tissues working together as a functional unit. For example the stomach is an organ composed of epithelium, muscle, glandular and blood tissues.

3.) A system is a group of organs working together to carry out a specific complex function. Humans have seven main systems: the circulatory, digestive, nervous, respiratory, reproductive, urinary and muscular-skeletal systems.

Evolution: The Blind Watchmaker• What do the components of the

watch do individually?• What do they do when they are

put together in the right way?• This is an example of emergent

properties: the whole is more than the sum of its parts.

• One analogy used for evolution is that of the blind watchmaker.

• Given millions of years and infinite mutations and combinations, it is inevitable that even complex structures will emerge.

• There is no purpose or design to evolution beneficial mutations in a particular environment will allow the organism to survive and reproduce.

Stem Cells Retain the Capacity to divide

• Totipotent: Can become any cell type

• Pluripotent: can become any type except embryonic membrane

• Multipotent: can become a number of different cell types

• Unipotent: Can only become one cell type

• Nullpotent: Cannot divide (red blood cells)

• Differentiation depends on the activation of genes in sequence, often triggered by environmental changes.

• Once a stem cell had differentiated, it can only make more stem cells or the differentiated cell type.

Cell Differentiation: the result of gene expression

Cell Differentiation• All cells in the body carry

the same genes in their nuclei.

• What makes a cell diffeent is which genes are expressed which are turned on or off

• This is triggered by changes and the environment around the cell.

Uses for Stem Cells• In the treatment for lymphoma, bone marrow is destroyed in

chemo or radio therapy. Before this aggressive treatment takes place, stem cells are harvested from the bone marrow and stored.

• These harvested cells can be used to replace damaged bone marrow, producing healthy blood cells in the recovering patient.

Therapeutic Cloning of Stem Cells

• Therapeutic cloning involves the in-vitro culturing of tissues using patient or donor stem cells. It can be used to replace tissues lost in disease, burned skin or even nerve cells.

Topic 2.2Prokaryotic

Cells

Prokaryotic Cells

Prokaryotic Cell: general structure The structural difference

between the Prokaryotes and the Eukaryotes are so significant that some biologist think that these two groups merit the status of Super Kingdoms.

The main distinguishing feature between the Prokaryotes and Eukaryotes is the lack of a true nucleus in the former.

•The general size of a prokaryotic cell is about 1-2 um.•Note the absence of membrane bound organelles

•There is no true nucleus with a nuclear membrane

•The ribosome's are smaller than eukaryotic cells•The slime capsule is used as a means of attachment

to a surface•Only flagellate bacteria have the flagellum•Plasmids are very small circular pieces of DNA that

maybe transferred from one bacteria to another.

Function of Prokaryotic Cell Structures

Structure Function          Cell WallCell Wall Made of murein (not cellulose),

which is a glycoprotein or peptidoglycan (i.e. a protein/carbohydrate complex).

Pili A hair-like structure found on the surface of the membrane. These structures are used to connect bacteria to each other. They may provide a means of transporting materials from one another and maybe involved in reproduction.

Structure Function  Plasma membranePlasma membrane •Controls the entry and exit of

substances, pumping some of them in by active transport.

         MesosomeMesosome •A tightly-folded region of the cell

membrane containing all the membrane-bound proteins required for respiration and photosynthesis. •Can also be associated with the nucleoid. •This is now thought to be an artifact of the electron microscope and not a real structure.

Structure Function  CytoplasmCytoplasm •Contains all the enzymes needed for

all metabolic reactions, since there are no organelles             

 Ribosome'sRibosome's •The smaller (70 S) type are all free in the cytoplasm, not attached to membranes (like RER). They are used in protein synthesis which is part of gene expression.

Naked DNANaked DNA •Nucleoid is the region of the cytoplasm that contains DNA. It is not surrounded by a nuclear membrane. DNA is always circular (i.e. a closed loop), and not associated with any proteins to form chromatin. Sometimes confusingly referred to as the bacterial chromosome

Structure Function Slime CapsuleSlime Capsule •A thick polysaccharide layer

outside of the cell wall, like the glycocalyx of eukaryotes. Used for sticking cells together, as a food reserve, as protection against desiccation and chemicals, and as protection against phagocytosis. In some species the capsules of many cells in a colony fuse together forming a mass of sticky cells called a biofilm. Dental plaque is an example of a biofilm.

Electron Micrograph structure of the prokaryote

• 1. Note the double membrane of this E. coli .

• 2. There is some evidence in the image of pilli which are the surrounding light grey masses.

• 3. In the cytoplasm of the bacterium there are no visible organelles which is consistent with how we expect a prokaryote cell to appear.

• 4. The nucleoid region is not seen well in this particular image.

Prokaryotic MetabolismBacteria have a large range of differentmetabolic reactions at their disposal, far morethan in the eukaryotes, who are confined tojust respiration or photosynthesis. 1. 1. FermentationFermentation:•sometimes these bacteria oxidize organic

molecules like glucose. In many instances they metabolize as far as lactic acid or alcohol molecules making them useful to fermentation industry

2. 2. Photosynthesis Photosynthesis •      Many bacteria are photosynthetic and use the

same process of photosynthesis as plants. These phototrophic bacteria were some of the earliest forms of life on the planet, and their metabolic reactions increased the oxygen content of the atmosphere from 1% to 20%.       

3. 3. Nitrogen FixingNitrogen Fixing•obtain their energy by oxidizing inorganic

compounds like ammonia, nitrite, methane or hydrogen sulphide. These bacteria use a variety of unusual metabolic reactions and many are able to synthesise carbohydrates from carbon dioxide – the chemosynthetic bacteria.

2.2.4 Binary Fission • Prokaryotic cells divide by

binary fission.• This is an asexual

method of reproduction in which a cell divides into two same sized cells.

• The cells are genetically identical and form the basis of a reproductive clone.

(a) Reproduction signal: The cell receives a signal, to initiates the cell division.

(b) Replication of DNA: bacterial cells have a single condensed loop of DNA. This is copied by a process known as semi-conservative replication to produce two copies of the DNA molecule one for each of the daughter cells

(c) Segregation of DNA: One DNA loop will be provided for each of the daughter cells.

(d) Cytokinesis: Cell separation.

Topic 2.3Eukaryotic cells

Eukaryotic cells

The Nucleus• The nucleus is generally a very

conspicuous membrane-bound organelle. It contains most of the genes that control the entire cell.

• It averages ~ 5 um in diameter• It is enclosed by a nuclear envelope• It contains chromosomes/chromatin

Mitochondria

•Mitochondria is the site of aerobic respiration.

•The matrix is the site of the Krebs cycle

•Oxidative phosphorylation occurs on the cristae membrane

•Very active cells usually have a lot of mitochondria e.g. muscle cel

Plasma membrane• Controls what enters and leaves the

cell.Function & structure are covered in more detail in section

Rough Endoplasmic Reticulum

•A complex interconnected network of membrane tubes.

•The surface is covered in ribosomes where proteins are made for secretion

•Unattached ribosomes make proteins for internal use.

Ribosome

•Ribosome size measured in Svedberg (S) units; derived from sedimentation in ultracentrifuge

•Ribosomes made of 40S and 60S subunits, assemble into 80S ribosome

•Contains many enzymes for general metabolism•Compartment in which foodstuffs enter and from

which wastes leave cell

Golgi apparatus•Modification of proteins for secretion

Chloroplast Structure

1. Intermembrane Space- separates the two membranes.

2. Thylakoids- Are flattened sacs inside the chloroplast. They segregate the interior of the chloroplast into 2 compartments:– Thylakoid space– stroma

Thylakoids• Chlorophyll is located in the thylakoid

membrane.• They are stacked together (grana).

Chloroplast Structure Stroma- photosynthetic rxns that convert

chemical energy into sugars. The stroma is a viscous fluid outside the thylakoidsCOCO22 + H + H22O + light O + light C C66HH1212OO66 + O + O22

Vacuole•The vacuole is a

storage area in plants for amino acids and sugars (sap). 

•The tonoplast is a membrane like the plasma membrane it controls what enters and leaves the vacuole

Cell Wall•The cell wall supports plant tissue•Composed of a fully permeable wall of cellulose•Important structure in establishing turgidity

Extracellular component

http://kscience.co.uk/animations/turgor.swf

Prokaryotic vs Eukaryotic cells

Comparison of Plant and Animal Cells

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL2.html

Topic 2.4.1:

Cell Membrane

2.4.1 Fluid mosaic model•Fluid because it can change shape but also because the

phospholipids can change position in the same plane•Mosaic as the membrane has protein molecules embedded and

attached to its surface•This model accounts for the behavior observed in cell membranes.

Like a any good model it also predicts some characteristics.

2.4.2 Phospholipid Properties• The 'head's have large

phosphate group, thus they are hydrophilic and

(attract water) or polar.•The fatty acid tails are

non-charged, hydrophobic and (repel water). This creates a barrier between the internal and external 'water' environments of the cell. The 'tails' effectively create a barrier to the movement of charged molecules

2.4.2 Phospholipid Properties

•The individual phospholipids are attracted through their charges and this gives some stability. They can however move around in this plane

•The stability of the phospholipid can be increased by the presence of cholesterol molecules.

Hydrophilic Hydrophilic ‘ ‘loves water’loves water’

Hydrophobic Hydrophobic ‘ ‘afraid of afraid of

water’water’

Membranes Structure

Integral Proteins•Usually span from one side of the

phospholipid bilayer to the other.•Proteins that span the membrane are

usually involved in transporting substances across the membrane

Peripheral Proteins•These proteins sit on one of the surfaces (peripheral

proteins). They can slide around the membrane very quickly and collide with each other, but can never flip from one side to the other.

•Proteins on the inside surface of plasma membrane are often involved in maintaining the cell's shape, or in cell motility.

•They may also be enzymes, catalysing reactions in the cytoplasm

GlycoproteinsGlycoproteins• Usually involved in cell recognition which is part of the

immune system. They can also acts as receptors in cell signaling such as with hormones. These are extracellular componentsextracellular components

CholesterolCholesterol•Binds together lipid in the plasma membrane reducing its fluidity as conferring structural stability

2.4.3 Membrane Protein Functions

Channel proteinsChannel proteins • These proteins span

the membrane from one side to another. They allow the movement of large molecules across the plasma membrane. Included within this are the passive and active membrane pumps

Receptor proteins

• These proteins (B in diagram) may detect hormones arriving at cells to signal changes in function. They may also be involved in other cell and substance recognition as in the immune system.

Enzymes• Integral in the membrane they may be

enzymes e.g. ATP Synthetase, Maltase

Electron Carries

• Help catalyze chemical reaction an important role in photosynthesis and cell respiration.

Diffusion and Osmosis•The movement of particles is caused by the kinetic

energy possessed by the particle•The direction of movement is random•Observing groups of particles they appear to move

from regions of high concentration to regions of low concentration

•However, most biological diffusion takes place through membranes and involves sources, sinks and diffusion gradients

T1

T2 T3

MembranesMembranesDiffusion is the passive movement of particles

from a region of high concentration to a region of low concentration (down a concentration gradient), until there is an equal distribution.

Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration (high water concentration) to a region of higher solute concentration (low water concentration).

High Concentration

Low Concentration

Diffusion moves down the concentration gradient just like a ball rolling down a hill. It cannot roll uphill without energy.

Passive transportPassive transport across membranes in terms of diffusion.

• Requires no energy• Moves from down the concentration gradient• Some molecules pass through the membrane• Some molecules use channels for facilitated

diffusion

Effects of osmosis on cells:The examples illustrate the problems that organisms will have ifthey live in:

•concentrated solutions (hypertonic)•dilute solutions (hypotonic)

Most organism have a mechanism to deal with these difficulties.These are studied through out the course. How do you maintainisotonic conditions for your tissues?

Animal Cells and Osmotic Pressure

• All cells have thin delicate membranes – animal cells have only plasma membrane

• They respond to differences in external solute concentration and osmotic pressure

• If isotonic (usually 0.9% w/vol NaCl), no change in shape• If hypertonic (high salt) then shrinks• If hypotonic (low salt) then expands and destroy the cell

membrane

Plant Cells and Osmotic Pressure• In plants, hypotonic solutions produce osmotic pressure that

produces turgor pressure– Turgor means “tight or stiff owing to being very full” – Keeps plant upright; in hypertonic conditions plants wilt

Hypotonic solution Hypertonic Hypertonic

Vacuole fills

Vacuole shrinks

Active transport across membranes.• Requires energy, in the form of ATP, or

adenosine triphosphate• Molecules are ‘pumped’ across the membrane

UP the concentration gradient• Pumps fit specific molecules• The pump changes shape when ATP activates it,

this moves the molecule across the membrane

Vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane. The fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis.

Exocytosis the mass movement OUT of the cell by the fusion of a vacuole and the membrane

Endocytosis the mass movement INTO the cell by the membrane ‘pinching’ into a

vacuole

Topic 2.5

Cell Division

Mitosis• Cellular division in eukaryotic cells.• Chromatin is arranged into

chromosomes.• Chromosomes double.• Cell grows in size.• Cells divide.• Is cellular cloning.

Phases of the Cell Cyclethe ‘life cycle’ of a cell.

There are 2 phases:1. Interphase2. M phase (mitotic phase)

a. Prophaseb. Metaphasec. Anaphased. Telophase & cytokinesis

Figure 12.4 The cell cycle

1. Interphase• The non-dividing phase in a cell• Lasts about ~ 90% of the cell cycle.• The cell grows and replicates DNA

preparing for Mitosis.• There are three periods:

3 periods of Interphase1. Go – a cell functioning as normal 2. G1 phase – first growth phase3. S phase- synthesis of DNA4. G2 phase- 2nd growth phase

Mitosis is a reliable process. Only one error occurs

Per 100,000 cell divisions.

2. Mitosis: Prophase• The nucleolus

disappears.• Chromatin

condenses into visible chromosomes.

• There are two sister chromatids held together by a centromere.

• The mitotic spindle forms in the cytoplasm.

Figure 12.3 Chromosome duplication and distribution during mitosis

“Pro”metaphase• The nuclear

envelope disappears.

• Spindle fibers extend from each pole to the cell’s equator.

• Spindle fibers attach to the centromeres.

Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase

Metaphase• Chromosomes

are lined up in the equator (middle) of the cell.

• This is called the metaphase plate.

Figure 12.6 The mitotic spindle at metaphase

Anaphase• Characterized by

movement. It begins when pairs of sister chromatids pull apart.

• Sister chromatids move to opposite poles of the cell.

• Chromosomes look like a “V” as they are pulled.

• At the end of anaphase, the two poles have identical number and types of chromosomes.

Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase; anaphase; telophase and cytokinesis.

Telophase and Cytokinesis

• Microtubules elongate the cell.• Daughter nuclei begin to form at the two

poles.• Nuclear envelopes re-form.• Nucleolus reappears.• Chromatin uncoils.• Cells split their cytoplasm.• It is basically the opposite of prophase.

Figure 12.5x Mitosis

Figure 12.8 Cytokinesis in animal and plant cells

Figure 12-09x Mitosis in an onion root

Role of Mitosis•Growth: Multicellular organisms increase their size

through growth. This growth involves increasing the number of cells through mitosis. These cells will differentiate and specialize their function. 

•Tissue Repair: As tissues are damaged they can recover through replacing damaged or dead cells. This is easily observed in a skin wound. More complex organ regeneration can occur in some species of amphibian. 

•Asexual Reproduction: This the production of offspring from a single parent using mitosis. The offspring are therefore genetically identical to each other and to their “parent”- in other words they are clones. Asexual reproduction is very common in nature, and in addition we humans have developed some new, artificial methods

TumorsThe cancer cells are a mass of cells produced from uncontrolled cell division and can occur in an tissue. These cells disrupt biological order and function. If left unchecked, to bring the whole complex, life sustaining edifice that is thehuman body crashing down' This mass is called a tumor. There are two major types of tumor:

1.Benign Tumors this is a mass of cancerous cells that do

not invade other areas of the body. These are not as dangerous to health but may still require removing to prevent effects on neighboring tissue

2. Malignant Tumors is a mass of cancer cells that may invade surrounding tissues or spread to distant areas of the body. Cancer cells replace normal functioning cells in distant sites:

e.g. replacing blood forming cells in the bone marrow, replacing bones leading to increased calcium levels in the blood, or in the heart muscles so that the heart fails. 1. Image is a normal CT. Images 2, 3 & 4

Are PET scans, Light green/blue areasshow cancer cells