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2/17/2017 • They learned many things about cells. Understanding Cells – There are two major types of cells, prokaryotic cells and eukaryotic cells. • English scientist Robert Hooke first identified cells over 300 years ago while looking at cork under a microscope he built. – All cells have DNA, a cell membrane to protect them, and are filled with a jelly-like substance called cytoplasm. • He saw honeycomb-like openings. They reminded him of small rooms, so he called them cells. – Some cells have special structures that do specific jobs, called organelles. – Plant and animal cells have different structures Understanding Cells Prokaryotic Cells • After Hooke’s discovery, other scientists began to use better microscopes to identify different structures in the cells of plants and animals. • Over time, they developed cell theory. Cell theory includes three principles. • Prokaryotic Cells are very simple and very abundant cells. • They were the first cells to evolve. • They are mostly bacteria. • All have a hard cell wall. Prokaryotic Cells Getty Images • They do not store their DNA in a nucleus (an area in the center that holds DNA) • They do not have organelles (cell organs) • They are unicellular. • All have a hard cell wall on the outside for protection. 1 2/17/2017 Prokaryotic Cells • Some have flagella (whip-like tails used for movement) Understanding Cells (cont.) How did scientists’ understanding of cells develop? Eukaryotic Cells • Eukaryotic Cells are any cell that is not a bacteria. • They are more complex that prokaryotic cells. • They can be unicellular or multicellular. Eukaryotic Cells • They store their DNA in a nucleus (an area in the center that holds DNA) • They have organelles (cell organs) • All have a hard cell wall on the outside for protection. 2