1. Topic 2 - Cells

2. 2.1.1 Outline the cell theory.
Include the following:
Living organisms are composed of cells.
Cells are the smallest unit of life.
Cells only come from other cells.

3. Important Cell Scientists
Robert Hooke
Anton van Leeuwenhoek
Schleiden and Schwann
N.B. Cell discovery improved along with improvements in microscope technology.

4. 2.1.2 Discuss Cell Theory All living things are made of cells
TOK
2.1.2 Discuss Cell Theory All living things are made of cells
Some cells do not conform to cell theory
Biology is, by nature, variable so there will always be irregularities to any “theory”
Does this mean the theory is wrong?
Or should we accept the “most regular observation”?
Where do we draw the line?

5. 2.1.2 Discuss Cell Theory All living things are made of cells
TOK
2.1.2 Discuss Cell Theory All living things are made of cells
For example: Muscle cells
One membrane but…
Multi-nucleated
Long fibres

6. 2.1.2 Discuss Cell Theory All living things are made of cells
TOK
2.1.2 Discuss Cell Theory All living things are made of cells
For example: Fungal cells
Continuous cytoplasm
Multi-nucleated
Mycelium of Hyphae
No end cell wall

7. 2.1.2 Discuss Cell Theory All living things are made of cells
TOK
2.1.2 Discuss Cell Theory All living things are made of cells
Protoctista
One cell does everything!
Acellular? Non-cellular?
What cell organelles can you see?

8. 2.1.2 Discuss Cell Theory Cells are the smallest unit of life
TOK
2.1.2 Discuss Cell Theory Cells are the smallest unit of life
Only cells can carry out all life processes
Organelles need other organelles
Mitochondria (where respiration happens)
Can replicate
Can carry out metabolism
Used to be autonomous structures???

9. 2.1.2 Discuss Cell Theory Cells only come from other cells
TOK
2.1.2 Discuss Cell Theory Cells only come from other cells
Cell division = Mitosis
Common ancestor?
All organisms are related??
Inanimate matter cannot assemble itself into living forms.

10. 2.1.3 Unicellular organisms
State that unicellular organisms carry out all the functions of life.

11. 2.1.3 Unicellular organisms
All unicellular organisms are able to carry out all the processes which are characteristic of living things such as:
Metabolism
Response
Homeostasis
Growth
Reproduction
Nutrition

12. 2.1.4 Relative sizes in Biology
1m divided by 1000 = 1mm (10-3 m)
1 mm divided by 1000 = 1 μm (10-6 m)
1 μm divided by 1000 = 1nm (10-9 m)

13. 2.1.4 Relative sizes in Biology
Rely on microscope technology – usually dependable!
TOK – can we believe in something we have not seen directly? Is there any difference between knowledge gained directly from your own senses and that which has been gained by the use of technology??

14. 2.1.4 Relative sizes in Biology
Rely on microscope technology – usually dependable!
Artefacts
Shrinking
Resolution of microscope (when image becomes too blurred to distinguish 2 different objects)
Changes due to slide preparation
Distortion??? Misinterpretation???

15. 2.1.4 Relative sizes in Biology
Relative sizes: 1. Molecules (1nm). 2. Cell membrane thickness (10nm). 3. Virus (100nm). 4. Bacteria (1 μm). 5. Organelles (less 10 μm). 6. Cells (<100 μm). 7. Generally plant cells are larger than animal cells.

16. 2.1.4 Relative sizes in Biology

17. 2.1.5 Magnification
The number of times larger an image is than the object
Magnification = size of image/your diagram
size of object/ microscope specimen
Sizes MUST be the same unit!!

18. 2.1.5 Magnification
E.g. An image measures 50mm and the object measures 5 μm.
The size of the image should be converted to μm.
Size of image = 50mm = μm
Magnification = = 5

19. 2.1.5 Magnification
If you know the magnification and the size of the image you can work out the size of the actual object:
Size of actual object = Size of image/your diagram
magnification

20. 2.1.5 Magnification Scale bars Shows length of bar in real image
All other measurements are made relative to this scale bar.

21. 2.1.5 Magnification Practical Investigation
Make a scale drawing of one cell from one of the slides the slide set. Work out the magnification of your image and label as many parts as you can.
Sharp pencil
At least half a page
Clear
Labelled

22. 2.1.6 Surface area: Volume ratio
As organisms get bigger both their volume and surface area get bigger
However the increase is not by the same amount.

23. 2.1.6 Surface area: Volume ratio
Volume x 8
Surface area x 4
Surface area x ?
Each side is 2cm long
Volume =
Surface area =
Each side is 1cm long
Volume =
Surface area =

24. 2.1.6 Surface area: Volume ratio
Consequences for organisms:
All organisms need to exchange substances with surroundings by diffusion and osmosis
e.g. ??
They can only do this through their surface
why?
The amount of exchange needed depends on the organism’s volume
But the rate of exchange depends on what?

25. 2.1.6 Surface area: Volume ratio
Therefore, diffusion/osmosis decreases as the organism gets bigger.
Trying to balance the rate of exchange and the needs of the organism becomes a deciding factor in the size of the organism.
So the ability to meet the requirements of a cell depends on the
Volume : Surface area ratio

26. 2.1.6 Surface area: Volume ratio
Each side is 2cm long
Volume =
Surface area =
Ratio =
Each side is 1cm long
Volume =
Surface area =
Ratio =

27. 2.1.6 Surface area: Volume ratio
The bigger the organism, the smaller the surface area to volume ratio. So the less surface area there is (for diffusion) for every unit of volume.

28. Experiment: Is bigger better?
You will be assessed on your manipulative skills (how well you carry out the experiment).
You will be assessed on your data collection and processing skills.
You will also be assessed on your conclusion.

29. Biological Consequences
The African Elephant kg
3 – 4 m high
5.4 – 7.3m long
Has a small surface area : Volume ratio
Makes heat faster than it can lose heat????
Look at the ears…..

30. Biological Consequences
The Pygmy shrew
Approximately 60mm from tip of nose to base of tail.
The tail is around 40mm long
4 g in total weight
Has a large surface area : Volume ratio
Loses heat faster than it can make heat????
Look at the eating habits…

31. TOK Emergent Properties The whole is greater than the sum of the parts
Combining together parts produces something with new properties.
E.g. a light bulb. Wire, glass, electricity and metal or something that gives out light?
This works consistently well for Physics but not so well in Biology.

32. TOK Emergent Properties
We can take the parts of the light bulb and figure out how it would work from all the properties of said light bulb. It is predictable because there is little variation within the component parts.
When looking at Biological systems (like your body), we need to be aware of the problems of variation. You cannot look at the parts and predict the outcome of the whole.

33. TOK Emergent Properties
Combining cells together to make tissues, organs and systems and assuming you know what the organism will be like is not viable.
Only when the organism is looked at as a whole can we see the full picture.

34. TOK Emergent Properties
Therefore, if life itself is an emergent property, at what point does life end or begin?
If it is more than just a load of organs working at the same time in the same place, should life support machines have been invented?
When is “alive” actually “dead”?
And who decides??

35. Differentiation of Cells
Multicellular organisms need to specialise their cells
Why?
What are the benefits? (Why don’t all cells do all things?)
Specialise = Differentiation
Differentiated cells only express certain genes of the genome. E.g. muscle cells only express muscle genes.

36. Differentiation of Cells
Differentiation = Survival.
Embryology – how cells become specialised from the first fertilised egg.
First few cells of cell division after fertilisation are not specialised = STEM CELLS
Stem cells can be induced to express certain genes (using growth factors) and so differentiate along different pathways.

37. LOOK AT THIS ANIMATION TO SEE HOW STEM CELLS ARE HARVESTED.
LOOK AT THIS ANIMATION TO SEE HOW STEM CELLS ARE HARVESTED.

38. Stem Cells Ethical issues Where do we get the stem cells from?
IVF treatment
Abortions
Therapeutic cloning?
Should we “play God” by creating new cells or organisms?
Going back to emergent properties, when does a life begin? Is it ethical to destroy what would have been a human life?
Therapeutic cloning - Essentially, a patient would clone an embryo of himself and use the stem cells from his own embryo to replace diseased cells in his body. Banned in US (or nearly banned) but ok in the UK! 38

39. Stem Cells
The biological and medical possibilities for stem cells are astronomical.
Fast-forward to the end of the 21st Century: surgeons can create new organs to order, regrow crippled spines and hearts and reverse the damage of Parkinson's disease or diabetes with ease. Immune rejection and waiting lists for replacement organs are consigned to history. (New Scientist)

40. Therapeutic cloning

41. Therapeutic Cloning Skin cell from patient Egg cell
Remove nucleus and discard
Remove nucleus and keep
Put patient nucleus into empty egg cell
Allow egg cell to divide
After 1 week the cells form a blastocyst

42. Therapeutic Cloning Stem cells are taken from the inner cell mass
The stem cells can be used to make tissue that is exactly the same as the tissue in the patient (because it contains the same DNA)
This tissue or organs can then be put back into the patient

43. Good websites
New Scientist special report on stem cells.
The basics

44. Stem Cells and Internationalism
Stem cell research has depended on the work of teams of scientists in many countries, who share results and so speed up the rate of progress.
However, ethical concerns about the procedures have led to restrictions on research in some countries.
National governments are influenced by local, cultural and religious traditions, which vary greatly, and these, therefore, have an impact on the work of scientists.