Chapter 1 Section 2

 Cells were discovered in 1665 by Robert Hooke.  He observed them by looking at a thin slice of cork.

 He saw hundreds of Little boxes and called them cells, which means “little rooms.”  Hooke believed that cells were only found in plants.

 In 1673, Anton van Leeuwenhoek observed pond water and scum and saw small creatures he named animalcules, which means “little animals.”

 He also observed blood from different animals and teeth scrapings.  He was also the first person to see bacteria, a unicellular organism.

 It took nearly two centuries after Hooke’s discovery of cells that anyone realized, cells are present in all living things.  Matthew Schleiden, a German scientist who studied animals also stated that they are made of cells.

 Schleiden wrote the first two parts of what is known as the Cell Theory.  In 1858, a German doctor, Rudolf Virchow wrote the third part of the Cell Theory.

 All organisms are composed of one or more cells.  The cell is the basic unit of life in all living things.  All cells come from existing cells.

 Cells come in different shapes, sizes, and perform different functions but they share many similarities. Cell Membrane Hereditary Material Cytoplasm and Organelles Small size

 All cells are surrounded by a cell membrane.  This membrane acts as a barrier between the inside and outside of the cell.  It controls the passage of materials into and out of the cell.

 When new cells are made, they receive a copy of the hereditary material of the original cells.  DNA

 All cells have organelles, chemicals and structures that enable it to live, grow, and reproduce.  The chemicals and structures of a cell are surrounded by fluid called the cytoplasm.

 Almost all cells are too small to be seen with the naked eye and must be observed under high power of a microscope.

 A cell’s outer wall (surface area) needs to be able to accommodate its inner activities (volume).  If a cell gets too large, its surface will have too few openings to allow enough materials into and out of it.

 A single cell as big as us would have an incredibly small surface-to-volume ratio.  The cell would not survive because its outer surface would be too small to allow in the materials it would need.  Multicellular organisms grow by producing more small cells, not by getting larger.

 Multicellular organisms have cells that specialize in a particular area and do a particular job.  These cells can form tissues and organs with different functions.

 Prokaryotic Cells  No membrane-covered nucleus, free floating DNA  Eukaryotic Cells  Membrane-covered nucleus that contains DNA

 These cells are also called bacteria and are the world’s smallest cells.  Their DNA is one long, circular strand.  They do not have any membrane-covered organelles.  Most bacteria are covered by a hard cell wall outside a softer cell membrane.  These cells were probably the first types of cells on Earth.

 These cells are more complex than prokaryotic cells and about 10 times larger.  These cells first appeared about 2 billion years ago.  All living things that are not bacteria are made of one or more eukaryotic cells (plants, animals, fungi, and protists.)  They have a nucleus and several membrane-covered organelles.

Prokaryotic Cells Eukaryotic Cells *No nucleus*Nucleus *No membrane *Membrane-covered organelles *Circular DNA*Linear DNA *Bacteria*All other cells