Topic 2 - Cells

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.

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

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?

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

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

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?

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???

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.

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

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

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)

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??

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???

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.

2.1.4 Relative sizes in Biology

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!!

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 = 50 000 μm Magnification = 50 000 = 10 000 5

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

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

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

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.

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 =

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?

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

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 =

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.

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.

Biological Consequences The African Elephant 4000 - 6800 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…..

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…

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.

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.

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.

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??

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.

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.

LOOK AT THIS ANIMATION TO SEE HOW STEM CELLS ARE HARVESTED. http://www.dnalc.org/stemcells.html LOOK AT THIS ANIMATION TO SEE HOW STEM CELLS ARE HARVESTED.

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

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)

Therapeutic cloning

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

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

Good websites http://www.newscientist.com/channel/sex/stem-cells New Scientist special report on stem cells. http://www.college.ucla.edu/webproject/micro7/studentprojects7/TrinhF01/Table%20of%20Contents.htm The basics

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.