An Outline of the Cell Theory

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Chapter 2 IB Biology
2.1 Cell Theory
2.1.1 Outline the cell theory (2).
All organisms are composed of one or more cells
Cells are the smallest units of life
All cells come from preexisting cells
TOK: cell theory replaces the former ideas of spontaneous generation or abiogenesis in which inanimate matter assembles itself into living forms •Exception: muscle cells- more than 1 nucleus, very long; (fungal cells) hyphae roots- not a single unit; protoctista- not specialized to single function; subcellular things like organelles 2.1.2 Discuss the evidence for the cell theory (3).

Robert Hooke first described cells in 1665 while observing cork with a microscope he built. Coined the term “cell” •Antoine van Leeuwenhoek observed the 1st living cells and referred to them as animalcules. “microscope” •In 1838, botanist Mathias Schleiden stated that plants are made of independent separate being called cells. Later, Theoder Schwann made a similar statement about animals. •The 2nd principle continues to gain support because we have not been able to find any living entity that is not made of at least one cell. •Louis Pasteur in the 1860s performed experiments to support the last principle. After sterilizing chicken broth by boiling, Pasteur showed that living organisms would not ‘spontaneously’ reappear. “biogenesis” •Only after exposure to preexisting cells was life able to re-establish itself in the chicken broth. •Eukaryotes- mitosis; prokaryotes- binary fission; thus all cells have a common ancestor- original ancestral form 2.1.3 State that unicellular organisms carry out all the functions of life (1). •Functions include:

Metabolism- chemical reactions that occur within an organism •Growth- may be limited but is always evident in some way •Reproduction- hereditary molecules that can be passed to offspring •Response- to environment is imperative to survival

Homeostasis- maintain a constant internal environment ex: temp •Nutrition- provide a source of compounds with many chemical bonds which can be broken to provide the organism with the NRG and the nutrients necessary to maintain life CHNOPS 2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit (3). •Cells- 100 micrometers (plant)

Organelles- < 10 micrometers
Bacteria- 1 micrometer
Viruses- 100 nanometers
Membranes- 10 nanometers thick
Molecules- 1 nanometer
Animal cell- 10 micrometers
cm = 10-2 m
mm = 10-3 m
um = 10-6 m
nm = 10-9 m
A = 10-10 m
2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification (2). •Magnification = size of image divided by the size of specimen •Magnification = measured length / scale bar level

Actual size = measured length / magnification
2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size (3). •In the cell, the rate of heat and waste production and rate of resource consumption are functions that depend of its volume. •Most of the chemical reactions occur in the interior of the cell and its size affects the rate of these reactions. •The surface of the cell, the membrane, controls what materials move in and out of the cell. •Cells with more surface are per unit volume are able to move materials in and out of the cell, for each unit volume of the cell. •As the width of the object increases, the surface area also increases but at a much slower rate than the volume. •This means that a large cell has less surface area to bring in needed materials and to rid the cell of waste than a small cell. •Because of this, cells are limited to the size they can attain and still be able to carry out the functions of life. Large animals have more cells not larger ones. •A large surface area to volume ratio means the cell can act more efficiently: for every unit of volume that requires nutrients...
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