The Cell: The Basic Unit of Life

What is a Theory?? After scientists accumulate sufficient data, postulates are made to produce a theory. After scientists accumulate sufficient data, postulates are made to produce a theory. Theories help us to explain natural processes. (Ex. Cells and their functions or states of matter) Theories help us to explain natural processes. (Ex. Cells and their functions or states of matter)

Can a Theory be Discarded?? Yes!! Yes!! Contradicting information may cause the theory to be rejected or discarded after some time. Contradicting information may cause the theory to be rejected or discarded after some time. As time progresses, new information is revealed and modifications need to be made to existing theories. As time progresses, new information is revealed and modifications need to be made to existing theories.

The Cell Theory. Through out the 1600’s, 1700’s, and 1800’s, scientists began to discover the world of microorganisms. Through out the 1600’s, 1700’s, and 1800’s, scientists began to discover the world of microorganisms. The discovery of the microscope facilitated this movement. The discovery of the microscope facilitated this movement. Collectively, the discoveries were brought together to formulate the cell theory. Collectively, the discoveries were brought together to formulate the cell theory.

Who were the major contributors??  Zacharias Janssen (1590) – Discovered the first compound microscope by putting together 2 lenses.

 Robert Hooke (1665) – Described cells by observing cork through a compound microscope.

 Anton van Leeuwenhoek (1674) – Using a single lens microscope, he observed the first living cells. He called these living cells “animalcules”.  Also, the first to observe blood and sperm cells.

 Mathias Schleiden (1838) – Schleiden was a botanist. He studied plant cells and described what he saw. Plants were made of cells with special features and structures.

 Theodor Shwann (1839) – Studied animal cells and found similar observations as those from Schleiden.

 Louis Pasteur (1860’s) – He sterilized chicken broth. His experimentation demonstrated that new cells do not spontaneously regenerate unless you place existing unicellular organisms in the broth.

The Cell Theory States: All life forms are made from one or more cells All life forms are made from one or more cells The cell is the basic unit of life. The cell is the basic unit of life. Cells only come from pre-existing cells Cells only come from pre-existing cells The activity of an organism depends on the total activity of its independent cells. The activity of an organism depends on the total activity of its independent cells.

Cells are the basic unit of life!! Regardless if we have unicellular or multicellular organisms, all organisms need to carry out the same life functions: Metabolism Growth Reproduction Response Homeostasis Nutrition

Multicellular organisms grow and differentiate to include many different components. Multicellular organisms grow and differentiate to include many different components. Ex. Cells differentiate to form different organs (heart, kidneys, liver…) Ex. Cells differentiate to form different organs (heart, kidneys, liver…) Differentiation occurs to allow different systems to exist. ( ex. Respiratory, digestive and circulatory system) Differentiation occurs to allow different systems to exist. ( ex. Respiratory, digestive and circulatory system) Together, all cells in a multicellular organism will differentiate to produce complex systems that interact and work together to sustain life. Together, all cells in a multicellular organism will differentiate to produce complex systems that interact and work together to sustain life.

How do cells know what path to take during differentiation?? Cells differentiate into their specific role based on their genes that are expressed. Cells differentiate into their specific role based on their genes that are expressed. Not all genes are expressed. Not all genes are expressed.

Cells grow in volume and mass Inside of the cell is growing in volume (metabolism and other reactions are taking place here.) Cell membrane is growing in surface area (controls the substances moving into the cell for chemical processes) Over time, the cell membrane cannot compensate for the volumetric growth of the inside – Cell division is required to maintain efficient function. In order to be efficient at the life functions listed above, cells need to maintain a proper volume : surface area ratio.

The Surface area is increasing by squaring the radius where as the volume is increasing by cubing the radius of the sphere.