Cell Theory - IB Biology PDF

1.1.U1 The cell theory The note blank templates are available here. State the three parts of the cell theory. ◎ The cell is the basic unit of life. ◎ All living things are composed of cells. ◎ Cells come from preexisting cells. 2 The cell is the bas...

1.1.U1 The cell theory The note blank templates are available here. State the three parts of the cell theory. ◎ The cell is the basic unit of life. ◎ All living things are composed of cells. ◎ Cells come from preexisting cells. 2 The cell is the basic unit of life* "Basic" in this context means foundation or starting point; fundamental. Cell = alive Subcellular Components = not alive * ”Life” is an emergent property that arises at the level of the cell. For more about emergent properties, see 1.1.U4. 3  Watch out for the common mistake of saying all things are made of cells, without adding the word "living!" All living things are composed of cells. Is it alive* or was it once alive? Then it is (or once was) made of cells! Viruses are not Bacteria are living Fungus are living Animals are living Plants are living and living and they are and they are made and they are made and they are made they are made of not made of cells. of cells. of cells. of cells. cells. * How do you know if something is alive? There is general consensus around the functional characteristics of life. See 1.1.U2 to learn about these functions in a unicellular organism. 4  Cells come from preexisting cells. Cells can only be formed by division* of preexisting cells. (1.5.U1) Except at the original origin of life, cells do not spontaneously generate (1.5.NOS) * Prokaryotic cells divide by binary fission (1.2.U3) while eukaryotic cells can divide through fission, mitosis (1.6.U1) or meiosis (3.3.U1)! 5 Outline evidence that supports the cell theory. ◎ Repeated observations and experiments support the cell theory. ◎ We have never observed the cell theory not to be true. ○ Subcellular components have never been seen to perform the functions of life whereas full cells have. ○ From the 17th century on, biologists examined tissues from both plants and animals (later from fungi, bacteria and protists) and saw that every specimen contained at least one or more cells. ○ We have observed cells coming from other cells, but never observed spontaneous generation. 6  Outline evidence that supports the cell theory. 1663 1838 Robert Hooke Matthias discovers cells Schleiden realizes all plants are 1855 made of Rudolf cells Virchow 1590 proposed Zacharias that all cells Jansen come from invents the other cells compound microscope 1886 1839 Ernst Abbe 1674 Theodore and Carl Zeiss Anton von Schwann invent the Leeuwenhoek realizes all modern discovers animals compound unicellular are made microscope organisms of cells 1935 The scanning electron NOS: Developments in microscope scientific research follow was invented. improvements in technology 7 Compare the use of the word theory in daily language and scientific language. ◎ In daily use: a theory is a guess, there is doubt. ◎ In scientific use: a theory has been shown to be true through repeated observations and experiments. There is no current doubt*. As of yet, no evidence has been collected that does not support the idea. * This is not to suggest that theories should not be questioned (1.1.A1), might not have exceptions (1.1.NOS1) and might not change with new evidence and technological advancements (1.3.NOS2, D.1.NOS1, 5.4.NOS1 and 8.2.NOS1). 8 Compare the use of the word theory in daily language and scientific language. 9 Compare the use of the word theory in daily language and scientific language. ◎ Well substantiated= lots of evidence ◎ Explanation of the natural world = why natural things are they way they are ◎ Based on a body of facts = not opinion ◎ Repeatedly confirmed = shown over and over and over again ◎ Through observation and experiment = rigorous testing and use of the scientific method ◎ Are not guesses = not a guess 10 Explore more... ◎ In addition to the Cell Theory, other named scientific theories within the scope of the IB Biology course are: ○ Endosymbiosis (1.5.U3) ○ Hydrogen bonding (2.2.NOS1) ○ Semiconservative DNA replication (2.7.S2) ○ Natural selection (5.2.NOS1) ○ Chemiosmosis (8.2.NOS1)