IB Diploma Biology HL & SL

What is Cell Theory?

Aristotle (384 – 322BC)

What level of complexity is necessary for life?

An idea of hierarchy of structure developed:

With the development of the microscope:

1850’s Schwann - Proposed cell theory with Schleiden. (All made of identical cells. Cells are the basis of all tissues.)

The concept of ‘Cell Theory’

1600’s Jansen - Invented compound microscope

1660’s Hooke - Examines cork with improved compound microscope

1680’s Von Leeuwenhoek - Observes unicellular organisms and nuclei

1830’s Schleiden - Says all plants made of cells

1890’s Virchow - Omnis cellula e cellula: every cell originates from another cell.

THE ORGANISMAL THEORY

The counter argument to the cell theory developed during the later part of the C19th.

THE CELL THEORY THE ORGANISMAL THEORY

1. Multicellular organisms develop from a single fertilised germ cell (the zygote).

1. Some organisms (e.g. Fungi) are not divided into cellular compartments = non-cellular. Plants have plasmodesmata = cytoplasmic bridges between neighbouring cells.

2. The basic components of the cell (viz. nucleus, mitochondria etc) are repeated in every cell, even free living unicellular organisms.

2. Certain cells lack the basic components (e.g. mature red blood cells have no nucleus). Cells in multicellular organisms are highly specialised. Unicellular organisms have a cytoplasm that is not subdivided into cells and should therefore be considered as acellular.

3. Cells can be taken from organisms and cultured away from the body. In primitive multicellular animals (e.g. sponges) and most plants whole new individuals can be cultured from isolated cells. This power of regeneration is called totipotence.

3. Remove cells from complete multicellular organisms requires elaborate life support systems to keep them alive.

  4. Homeostatic control and co-ordination is required to maintain the whole organism whether it is unicellular or multicellular.

Cell Theory Concepts:

All living things are made from cells

Cells are the smallest unit of life

All cells come from pre-existing cells

TOK: *What is a theory?

*Where do theories come from?

*Should it be abandoned if it cannot

explain thing fully?

All metabolic activities occur in cells

All cells contain genetic information which is passed on

The 7 signs of life

ovement

espiration (metabolism)

ensitivity (response)

rowth

eproduction

xcretion (homeostasis)

utrition

A unicellular Amoeba is a highly organised animal.It carries out all the processes of a living thing.

However, it could never be as advanced as a multicellular organism like a cat or fish!

Why? –because each cell in a multicellular organism is adapted and specialised. Each cell carries out the processes of life, but each helps the other to survive.

In this way one multicellular organism is much better at surviving than millions of separate individual cells.

amoeba.mov

Emergent Properties of Cells

Cells are specialised, to carry out specific functions. Together they can work as an effective team. Although each cell contains a full compliment of diploid (2n) DNA, each only reads (expresses) certain genes in the code. That way different cells have the information to develop and become specialised.

Embryonic stem cells (germ cells) do not read specific information. They are the first cells to develop After fertilisation. They are able to divide continually and turn into any type of cell/tissue/organ.

TOK: Ethics of stem cell research

Stem Cells

Stem cell research and therapy has recently been seen by science as one of the breakthrough Technologies of the 21 century.

Research- what is Stem Cell therapy? what is special about Stem Cells? how are they currently used? how could they be used in the future? what ethical/medical debates are there?

1.  Specimens can be alive2.  Faster –slides and usage3.  Cheaper4.  Easier to maintain5.  Smaller6.  More colourful7. Small and portable8. Not affected by magnetic fields9. True colours can be seen

Advantages of light microscopes

1.      Higher resolution2.      Far greater magnification

Advantages of electron microscopes

Title: Onion epidermal cells, iodine stained.

X ________ magnification

The real size of one cell is ...

Title: Human cheek cells, methylene blue stained.

X ________ magnification

The real size of one cell is ...

Calculating linear magnification

Actual size = 15µmApparent size = cm

Calculate the magnification. Show working out clearly.

Stage micrometers and Eyepiece graticules

Cell wall No cell wall

Sometimes chloroplasts Never chloroplasts

Large central vacuole No large vacuole

Starch storage Glycogen storage

Resolution Vs. Magnification

On telescopes, binoculars, glasses.Means how many more times biggeran object is (_____x). Eg magnify thelength of your pen x5- how big?

How clear an object can be seen.Maximum resolution with a lightmicroscope= x1500. Why?The wavelength of light is 400-700nm. The smallest thingseen must block light, so must be at least ½ the wavelength= 200nm.

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

Cells:100 micrometres

Organelles: 10 micrometres

Bacteria: 1 micrometre

Viruses: 100 nm

Membrane thickness:10 nm

Eg Human liver cell

Cytoskeleton Network of fibers which help organize the internal arrangement within cells.Three basic types of fibers compose cytoskeleton:

Actin Filaments Thinnest fibers ~7nM Formed from protein Actin Microtubules Largest component of cytoskeleton ~25 nM Formed from protein Tubulin Intermediate filaments Intermediate in size and can vary Form from several proteins inluding vimentin & keratin

CELLS EUKARYOTE CELL ULTRASTRUCTURESummary of the major cell organelles:

ORGANELLE MAIN FUNCTIONS DIMENSIONS

Nucleus Cell division, protein synthesis

10 µm diameter

Mitochondrion Respiration pathways 1.0 to 12.5 µm

Chloroplast Photosynthetic pathways 5 to 10 µm diameter

Lysosome Digestion, recycling & isolation

0.5 to 3.0 µm diameter

Golgi apparatus Secretion, reprocessing, lysosome synthesis

Cisternae: 0.5µm thick, l-3µm diameter

Endoplasmic Reticulum (ER) Support, Golgi apparatus synthesis.

26 to 56 nm thick

Ribosome Protein synthesis 20 nm diameter

Escherichea coli (E.coli) bacteria

Reproducing by b____________ f____________.

Ekaryotic Prokaryotic

DNA linked with proteins (histones) DNA not linked with proteins- naked

DNA plasmid loose in cytoplasm

DNA in cytoplasm enclosed in membrane

Mitochondria No mitochondria

Organelles enclosed in membranes No specialised organelles with membranes

Large 80S ribosomes

Mitosos and meiosis

Smaller 70S ribosomes

Binary fission

Glycoproteins

Used as a marker to identify cells (antigens). Help stick specific cellsTogether in tissues. Recognition of certain molecules moving into the cell.

Cell wall

Helps keep cell shape, helps hold plant up against gravity andprevents excessive water uptake by osmosis.

Fungal cell walls are made of chitin, while plant cell walls are made of The carbohydrate cellulose. Consist of a primary cell wall made first and a woody secondary cell wallin some plants.

Why do cells only get so big? Surface Area of cube / cm2 Volume of cube /cm3

1cm

Does the ratio of surface area to volume stay the same??

NO!The sa:vol ratio decreases,meaning that a cell finds it more difficult to exchange nutrients and resources asit gets larger. This limits cell

size to about 200 micrometres.

Loxodonta africana (African elephant).This is the largest land living mammals. The adult African elephants can reach a length of 18-24 feet and a height of 10-13 feet. They weigh in at 8,800-15,500 pounds. Maximumsize is reached at around 25 years of age. According to the calculations above the elephantshould have a small surface are to volume ratio in comparison to smaller animals.Heat exchange ought to be quite slow which would be a problem for an animal living in a warm region.

The elephant has evolved large ears to increase the surface area for heat exchange allowing the elephant to remain cool.

Small organisms have the opposite problem of a rapid rate of exchange with the environment.

Sorex minutus (pygmy shrew)

Size: Approximately 60mms from tip of nose to base of tail. The tail is around 40mms long.Mass: 4 grams.This shrew looses body heat so fast that it consumes food at a furious rate simply to produce heat from respiration. I understand that this particular species needs to eat every two hours to stay alive.

A. Separates the cytoplasm of the cell from its environmentB. Protects the cell & controls what enters and leavesC. Cell membranes are selectively permeable only allowing certain materials to enter or leaveD. Composed of a lipid bilayer made of phospholipid molecules

A phospholipid molecule

What do membranes do?

Hydrophilic-

Hydrophobic-

Water loving properties. Forms a boundaryor vesicle between 2 water layers.

Water hating properties. Forms a vesicle around non-water solvent chemicals.

The hydrophilic head of a phospholipid is polar& composed of aglycerol & phosphate group and points to the aqueous cytoplasm and external environment

When phospholipids are placed in water, they line up on the water’s surface with their heads sticking into the water & their tails pointing upward from the surface.

The two hydrophobic tails are nonpolar point toward each other in the center of the membrane & are composed of two fatty acids

The inside of the cell or cytoplasm is an aqueous or watery environment& so is the outside of the cell. Phospholipid "heads" point toward the water.

The cell membrane is constantly breaking down & being reformed inside living cells.

Small molecules such as CO2, H2O, & O2 can easily pass through the phospholipids Fluid Mosaic model: Singer and Nicolson 1972

Fluidity of the membrane

Lipids move laterally in a membrane Unsaturated hydrocarbon tail of phospholipids

have kinks that keep the molecules from packing together, enhancing membrane fluidity.

Cholesterol reduces membrane fluidity by reducing phospholipid movement at moderate temperatures but it also hinders solidification at low temperatures.

Membrane Proteins

Some proteins called peripheral proteins are attached to the external & internal surface of the cell membrane. Integral proteins or transmembrane proteins are embedded & extend across the entire cell membrane. These are exposed to both the inside of the cell & the exterior environment.

Cell membrane proteins help move materials into & out of the cell, help change the density Of the membrane and aid in recognition & chemical reactions.

Some integral proteins called channel proteins have holes or pores through them so certain substances can cross the cell membrane.

Channel proteins help move ions (charged particles) such as Na+, Ca+, & K+ across the cell membrane.

Transmembrane proteins bind to a substance on one side of the membrane & carry it to the other side. e.g. glucose

Glycoproteins help change the density/fluidity of the membrane- helping movement (pseudopodia) and support, aid sticking to other cells (adhesion) and cell recognition.

Membrane Proteins

Protein type Function

Integral proteins Hormone binding site

Immobilised enzymes

Protein pore Passive and facilitated transport

Carrier protein Active transport

Glycoproteins Cell & molecule recognition

Movement into and out of cells

Chemicals move into and out of cells in a number of ways

1). Osmosis & diffusion2). Passive & facilitated diffusion3). Active transport4). Bulk transport using vesicles

Diffusion into and out of cells

Osmosis- water movement.

Cells are surrounded by a m________. This is p________permeable, as it has pores in it. Very small, soluble molecules can move in/out freely using their k______ energy.

Larger molecules (like_______ and ________) cannot pass.The amount of water on either side of the membrane makesa difference. Water will move to try to balance the concentration on either side. This is w______ potential.

http://www.ias.ac.in/initiat/sci_ed/resources/chemistry/osmosis3.gif

Diffusion = the passive movement of particles from a regionof higher concentration to a region of lower concentration.

Osmosis = the passive movement of water molecules, acrossa partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.

Plasmolysis in cells- the role of the cell wall and homeostasis.

Animals Plants

Internally Assessed Practical:experiment to assess concentration of cytoplasm in potato cells using osmosis.

Diffusion: from high to low concentration across membrane. Uses energy of molecules.

Osmosis: diffusion ofwater molecules.

Active transport: selective movement againstconcentration gradient at protein pumps.Uses ATP from mitochondria.

Facilitated diffusion: through selective protein pores.Uses energy of molecules.

Bulk transport: solids and liquidsby vesicles at membrane.Uses ATP from mitochondria.

Simple diffusion: traveling directly through the membrane if they are small and uncharged, thus avoiding repulsion bythe hydrophobic, non-polar tails of phospholipids in the middle of the membrane.

Facilitated diffusion: traveling through special transport proteins, if they match the shape and charge requirements to fit through the channels provided by the transport proteins.

Against the concentration gradient: Moves substance from an area where it is in lower concentration to an area where it is in higher concentration.

Protein pumps: Integral protein pumps embedded within membranes. Specific to molecule transported.

Requires energy: Usually provided by ATP. Often by phosphorylating the protein pump as ATP is hydrolyzed.

Protein Pumps and ATP

Using Vesicles- bulk transportProtein synthesis: rER produces proteins which travel through the lumen of the ER

Transport in vesicles: Membranes produced by the rER flows in the form of transport vesicles to the Golgi, carrying proteins within the vesicles

Modification: Golgi apparatus modifies proteins produced in rER

Transport to membrane: Golgi pinches off vesicles that contain modified proteins and travel to plasma membrane

Exocytosis: Vesicles then fuse with plasma membrane, releasing their contents

STEM CELLS

A stem cell is able to divide but has not yet expressed genes to specialise to a particular function.Under the right conditions stem cells can be induced to express particular genes and differentiateinto a particular type of cell.

Stem cells can be obtained from a variety of different places including the blastocyte. Adults still posses stem cells in some organs but much less so than a child. Even the placenta can be a useful source of stem cells.

Use of Stem Cell TherapyNon-Hodgkins Lymphoma is a cancerous disease of the lymphatic system. Outline of the disease.

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.

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 but in time the adapt to this treatment so that radiation and chemotherapy are often used together.

6. Post radiation/ chemotherapy the patients health blood tissues is also destroyed.

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

.

2. Embryonic Stem cell therapy this animation is an excellent introduction to the use of embryonic stem cell for therapies.

3. Therapeutic cloning . This is a method of obtaining ES cells from someone who has already been born. These stem cells can be used to treat the individual without generating an immune response. The human body recognizes and attacks foreign cells, including stem cells. This is a serious barrier to stem cell therapy.

1. The patient requires the replacement of some diseased tissue. First we obtain a health cell from the same patient.2. At the same time we require a human egg cell. This is mainly as the cell retains the tendency to divide unlike the sample tissue from the patient.3. The nucleus is removed from the egg and discarded. The cell body itself is retained.4. The nucleus of the patients cell is removed and retained. The cell body of the patients cell is discarded.

5. The nucleus from the patients cell is transferred to the enucleated cell body. 6. The cells then stimulated to divide forming a clone. 7. The cell mass forms a blastocyst. 8. The inner cell mass becomes a source of totipotent stem cells. Totipotent means they are capable of being stimulated to become one of any type of cell. 9. Cells are stimulated using differentiation factors to become the type of cell required for therapy. 10. Therapy would require the transfer of the new healthy cell to the patient. In therapeutic cloning these cells have the same immune system identity as the patient therefore there is not immune rejection problem

Other uses of Stem Cells