TOPIC 2: CELLS.

2.1: CELL THEORY

2.1.1. and 2.1.2. Cell Theory

Robert HookeLiving organisms are composed of cells

Cells are the smallest unit of life

Cells come from pre-existing cells

2.1.3: Unicellular Organisms

Paramecium. sp

Euglena. sp

STATE: Unicellular organisms carry out all the functions of life

metabolism e.g. cellular respirationresponsehomeostasisgrowthreproductionnutrition

Evidence for the Cell Theory

• Can’t be proven “true”– Require us to examine

every single cell….which is impossible!

• Evidence comes form observations and experimentation.

• When Separated cells’ individual parts can not sustain life.– “The whole is greater than the sum of

the parts.”

• The first cells are believed to come from self-replicating molecules.– Inorganic Organic

Onion CellOnion Cell Stained with Iodine

x40 Magnification

How big is an onion cell?

Size Matters!

Size Matters!

Size Matters!

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

1nm

A molecule

http://mendosa.com/glucose_molecule.jpg

10nm

A molecule

http://www.biolibogy.com/images/structure_of_plasma_membrane.JPG

Glucose (1nm)

A virus – the T bacteriophage

http://oceanworld.tamu.edu/resources/oceanography-book/Images/BacteriophageCartoon.jpg

10nm

100nm

E.coli (bacteria cell)

Bacteriophage (virus)

100nm0.1µm

1000nm1µm

http://bio1903.nicerweb.com/doc/class/bio1903/Locked/media/ch18/18_01T4PhageEColi_LP.jpg

http://www.cic-caracas.org/departments/science/images/08eukaryote.jpg

Bacteria (1µm) Organelle (10µm)

Eukaryote Cell (100µm)

2.1.4: Relative sizes

• In the last sequence of slides every thing increased by a magnitude of 10x each time. The IB requires you to remember the sizes.

• Make up a mnemonic to help you to remember the order!

• My Mom Visits Bieber Outside Concerts.• My Money Vanishes Beautifully On Cars.• My Most Valued subject is Bio, Obviously!

Cool!

1 nm molecules 10 nm membrane thickness 100 nm virus

1 µm bacteria(up to) 10 µm organelles(up to) 100 µm cells

1mm = 1,000 µm1 µm = 1,000 nm

http://learn.genetics.utah.edu/content/begin/cells/scale/

Cheek Cell

Magnification of Your DrawingHow Much Bigger is it?

Drawing Size / Real Size

Drawing size 10 cmReal Size 100 µm (work out from field of view)

Convert units 100 µm = 0.01 cm

10cm/0.01cm= 1,000 Magnification

2.1.5: Scale bar

15 µm

Why are cells so small?

• Nutrients and wastes move across a cell surface by diffusion.

• The chemical reactions that take place is known as the cell’s metabolism

• Substances must be absorbed by the cell and waste products must be removed.

• The rate at which this occurs is determined by the surface area of the cell.

• As size of an object increases the ratio between the surface area and volume decreases.

• Rate materials enter and leave the cell depends on surface area• Rate materials are used or produced depends on the volume

Why is this important?

• The surface area relates to how much material can enter a cell at a time.

The bigger the area is the more material can enter in an amount of time

• The volume relates to how much material is needed at a time.

The bigger the volume is the more material isneeded to maintain it for an amount of time.

Lets look at Surface areas and volumes………

• Fill in the table below:

a

a

a Size of side (a)

Surface area of the box (a x a x 6)

Volume of the box(a x a x a)

Surface area to volume ratio

1 6 1 6 : 1

2

3

4

5

6

7

Size of side (a)

Surface area of the box (a x a x 6)

Volume of the box(a x a x a)

Surface area to volume ratio

1 6 1 6 : 1

2 24 8

3 54 27

4 96 64

5 150 125

6 216 216

7 294 343

Size of side (a)

Surface area of the box (a x a x 6)

Volume of the box(a x a x a)

Surface area to volume ratio

1 6 1 6 : 1

2 24 8 3 : 1

3 54 27 2 : 1

4 96 64 1.5 : 1

5 150 125 1.2 : 1

6 216 216 1 : 1

7 294 343 0.9 : 1

• What trend did you notice?

– What happened to the area as side size increased?The area increased much faster than the side size.

– What happened to the volume?The volume increased much faster than the side size

– Which one (area or volume) increased the fastest?

• Assume that a volume of 1 needs 1 lot of material to sustain it….And an area of 1 can provide 1 lot of material:

• Look at cell size where a=1. Is it able to supply its needs?

• Look at cell size where a=6. Is it able to supply its needs?

• What about a=7?

Area = 6 Volume =1 ….It can provide 6x as much material than it needs

Area = 216 Volume =216 ….It can just provide as much material than it needs

aa

a

• If the cell gets too large and the ratio of Surface Area to Volume decreases it can’t take in the essential materials or excrete the waste fast enough….. So it must divide.

• The same idea is relevant for heat and waste needing to be given out by an organism.

Can you think of some organisms that have to deal with this problem?

1. Elephant – a very big organism produces lots of heat. How does it get rid of all the heat with a relatively low SA : Vol ratio?

– Find out about elephant ears.

2. The Shrew – A very small organism with a relatively large SA : Vol ratio. How does it manage to stay warm in winter?

– Find out about changes in metabolism.

2.1.6: Surface area : volume

2.1.6: Surface area:volume

2.1.7: Multicellular Organisms

STATE: Multi-cellular organisms show emergent properties

2.1.8: Multicellular Organisms• All cells in an individual contain the

same genetic information• At an early stage of embryonic

development, cells differentiate and become specialized to perform specific function.

• Some genes are turned on while others are not turned on to produce specific cells e.g. in muscle cells, muscle genes get turned on while liver genes get turned off.

•

2.1.9: Stem cellsSTATE: Stem cells retain the capacity to divide and have the ability to differentiate along different pathways

2.1.10: Therapeutic stem cells

For more than 30 years, bone marrow stem cells have been used to treat cancer patients with conditions like leukemia and lymphoma. During chemotherapy, most of the leukemia cells are killed as are the bone marrow stem cells needed as a patient recovers. However, if stem cells are removed before chemotherapy, and then re-injected after treatment is completed, the stem cells in the bone marrow are able to produce large amounts of red and white blood cells, to keep the body healthy and to help fight infections.

2.2: PROKARYOTIC CELLS

2.2.1, 2.2.2: Ultrastructure of E.coli

Mesosome

Plasmid

2.2.3: Electron micrograph of E.coli

2.2.4: Binary fission

2.3: EUKARYOTIC CELLS

2.3.1, 2.3.2: Liver cell

2.3.3: Electron micrograph of liver cell (rat)

Glycogen

2.3.4: Prokaryotic VS Eukaryotic cell

FEATURE Prokaryotic cell Eukaryotic cell

DNA Naked DNA DNA associated with proteins

Ribosomes 70s 80s

DNA DNA inside the cytoplasm

DNA enclosed by a membrane

Mitochondria no yes

Internal membranes

no yes

2.3.5: Plant VS Animal cell

1. Plant cells have large vacuoles and animal cells do not have large vacuoles.

2. Plant cells have a cell wall and animal cells do not have a cell wall.3. Plant cells (may) have chloroplasts and animals do not have chloroplasts.4. Plant cells store excess glucose as starch and animal cells store excess

glucose as glycogen.

2.3.6: Extracellular components• The plant cell wall maintains

cell shape, prevents excessive water uptake, and hold the whole plant up against the force of gravity.

• Animal cells secrete glycoproteins that form the extracellular matrix. This functions in support, adhesion and movement.

Glycoproteins

2.4: MEMBRANES

2.4.1: Membrane Structure

2.4.2: Hydrophobic/hydrophilic

2.4.3: Membrane ProteinsHormone binding sitesImmobilized enzymesCell adhesionCell to cell communicationChannels for passive transportPumps for active transport

Simple diffusion

2.4.4: Diffusion

2.4.4: Osmosis

2.4.5: Passive Transport

2.4.5: Passive Transport

2.4.6: Active Transport

2.4.7: Vesicle Transport

2.4.8: Endo/Exocytosis

2.5: CELL DIVISION

2.5.1: Cell Cycle

Cytokinesis starting

2.5.2: STATE: Tumours (cancer) cells are the result of uncontrolled cell division and these can occur in any organ or tissue

2.5.3: STATE: Interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and / or chloroplasts

Mitosis is division of the nucleus in which one parent nucleus divides into two daughter nuclei each having the same number of chromosomes as the parent nucleus.

2.5.4 and 2.5.5: Mitosis

Supercoiling of chromosomesNuclear membrane breaks downSpindle microtubles extend from pole to equator

Microtubules attach to centromere Chromosomes line along equator of cell

Centromere splits and sister Chromatids (now chromosomes) move to opposite poles

Reformation of nuclear membrane around chromosomesChromosomes uncoil

STATE: Growth, embyonic development, tissue repair and asexual reproduction involve mitosis