The Cell

History and Early Contributions Robert Hooke (1665) – first to see cells  Used an early microscope to look at a slice of cork and saw tiny chambers  Gave cells their name Anton van Leeuwenhoek (1674) – observed living cells in pond water  Called them “animalcules”

Cont’d Matthias Schleiden (1838) – botanist; concluded all plants composed of cells Theodor Schwann (1839) – concluded all animals composed of cells Rudolf Virchow (1855) – proposed new cells produced from existing cells

The Cell Theory All of the previous findings, once confirmed by other biologists, are put together to form the cell theory The cell theory states:  All living things are composed of one or more cells  Cells are the basic unit of life (structure and function)  All cells arise from pre-existing cells

Cells Can come in a variety of shapes and sizes Can perform various functions depending on specific structure All cells have three common characteristics  Surrounded by cell membrane  Genetic Material (DNA and RNA)  Cytoplasm

Two main cell types: 1.Prokaryotes – cells that do not contain a nucleus “pro” means “before”, believed to be the first cells DNA free in “nucleoid” region Generally smaller and simpler No membrane bound organelles Includes bacteria

2. Eukaryotes – cells that contain a nucleus or nuclei  Generally larger and more complex  DNA is separated from the rest of the cell (in the nucleus)  Usually contain highly specialized structures (organelles) and internal membranes  Great variety and specialization  Includes plants, animals, protists, and fungi

Plant Cell

Animal Cell

Special Organelles Chloroplast and mitochondria contain their own DNA, ribosomes, and can reproduce on their own It is suggested that these organelles are descendants of ancient prokaryotes Endosymbiotic theory – eukaryotic cells evolved from the engulfing of bacteria cells by other prokaryotes, thus creating additional parts