2.1: Cell Theory

1. 2.1: Cell Theory Topic 2: Cells Miss Friedman

2. 2.1.1: Outline cell theory Cell Theory All organisms are composed of one or more cells Cells are the smallest unit of life All cells come from pre-existing cells

3. 2.1.2: Evidence for Cell Theory This theory has been great credibility, largely through the use of the microscope Robert Hooke First described cells in 1665 while observing cork with a microscope he built himself Antonie van Leeuwenhoek Observed first living cells and referred to them as �animalcules� Mathias Scheiden In 1838 stated that plants are made of �independent, separate beings called cells� Theodor Schwann One year later made similar statements about animals Louis Pasteur Showed living organisms would not spontaneously reappear. Only after exposure to pre-existing cells was life able to re-establish itself.

5. 2.1.3: Functions of life All organisms exist in either a unicellular (one cell) or multicellular (many cells) form All organisms carry out all the functions of life. These functions are tied together to produce a functioning living unit Functions of Life Metabolism Growth Reproduction Responses Homeostasis Nutrition

6. Possible Exceptions to Cell Theory Viruses Considered alive because it can reproduce, however cannot do it alone. It needs another organisms (the host). 2. Slime Mold Not always cell division during life cycle. You can only see nuclei floating around in the membrane. 3. Mitochondria & Chloroplasts Have their own genetic material and reproduce independently from the rest of the cell

7. 2.1.4: Comparing size Relative sizes: Molecules (1nm) Cell membrane thickness (10nm) Virus (100nm) Bacteria (1�m) Organelles (less than 10�m) Cells (less than 100�m) Generally plant cells are larger than animal cells

9. 2.1.5: Magnification Magnification = measured length of the image Measured length of the specimen Make sure all units are the same Use scale bar on image to calculate actual length

10. 2.1.6: Limiting cell size Why do cells not grow to larger sizes? Answer! Surface-area to Volume Ratio! Rate of heat and waste production and rate of resource consumption are functions that depend on its volume Most chemical reactions takes place inside the cell and its size affects the rate of these reactions The rate of exchange of substances therefore depends on the organisms surface area that is in contact with the surroundings As the organism gets bigger, their volume and surface area both get bigger, but not by the same amount

12. 2.1.7: Emergent properties of multicellular organisms Emergence is the occurrence of unexpected characteristics or properties in a complex system These properties emerge from the interaction of the �parts� of the system Example Would you be able to predict the behavior of water from what you know about Hydrogen and Oxygen gas?

13. 2.1.8: Differentiation Multicellular organisms are large and have to specialize parts of their structure to complete various functions that are characteristic of life This differentiation process is the result of the expression of specific genes but not others These specific genes produce particular shapes functions and adaptations within a cell In multicellular organisms, specialization is more efficient than the generalized plan when competing for a specific resource

14. 2.1.8: continued Some cells have a diminished ability to reproduce once they become specialized. Nerve and muscle cells are examples of this. Other cells retain the ability to rapidly reproduce throughout their life. Examples of this are epithelial (skin)

15. 2.1.9: Stem Cells Populations of cells within organisms that retain their ability to divide and differentiate into various cell types In plants, meristematic tissue near the roots have the ability to become various types of tissue within the root or stem In the 1980�s scientist found pluripotent or embryonic stem cells in mice

17. 2.1.10: Therapeutic use of stem cells Alzheimer's disease and Parkinson�s are caused by loss of brain cells and it is hoped that implanted stem cells could replace many of these lost brain cells, relieving symptoms Blood stem cells have been routinely introduced into humans to replace the damaged bone marrow of some leukemia patients