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Download Key Terms Prokaryote Nucleus Organelle Cytoplasm Eukaryote Cell
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Transcript
Biology B4.a B4.c (part 1 only) Key Terms Prokaryote Nucleus Organelle Cytoplasm Eukaryote Cell (plasma) membrane Cell wall Virus Unicellular Multicellular The Classification of Living Things There are lots of different types of living things on our planet. Every living thing on the planet can be classified into two groups based on the cells that make them up. Cells are the basic units of life, and all living things are composed of cells. Although all cells have some things in common, each cell type also has unique characteristics that make them easy to identify. Let’s focus on these unique characteristics. Prokaryotes Our first cell type is called a prokaryotic cell or prokaryote (pro-kar-e-oat). These cells are unique because they are only found in the smallest organisms on the planet, bacteria. Scientists believe that these bacterial cells (prokaryotes) were the very first life forms on Earth. That means that these cells have been on the planet longer than any other living thing. These prokaryotic cells are very simple and small-they are made of only one cell (unicellular). Prokaryotes do not have any membrane-bound organelles (cell parts). That means that bacteria don’t have a nucleus (PRO-NO). Their DNA just floats around in the cytoplasm (the fluid inside the cell). Look at the example of a prokaryote below Eukaryotes If bacteria are the only living examples of prokaryotes, everything other living thing on the planet must be composed of eukaryotic cells. Eukaryotes (U-kar-e-oats) are much bigger than prokaryotic cells. Some eukaryotic cells are even large enough to be seen without a microscope! Eukaryotic cells are complex. They have lots of different compartments inside of them called membrane-bound organelles. These are located in the cytoplasm. The most important organelle Biology B4.a B4.c (part 1 only) in a eukaryotic cell is its nucleus, which holds its DNA. This is the control center of the cell. This means eukaryotes can grow much larger than prokaryotic cells, and control lots of unique cellular activities all at once. Eukaryotes also have a cell membrane. Some, like plants, have a cell wall, but animal cells do not. All multicellular (made of more than one cell) organisms are eukaryotes, including you! You are EU-karyote! Look at the example of a eukaryotic cell below. It is much more complex than the prokaryote above. This is an animal cell—it does not have a cell wall. Viruses Viruses are not generally considered to be alive because they are not cells. We study them in Biology because they are found in living organisms. Viruses have DNA (or sometimes RNA), but do not have a cell membrane, or any organelles. They also do not have cytoplasm. They are very small (smaller than prokaryotes even). Look at the examples of different virus shapes. Biology B4.a B4.c (part 1 only) Use the facts from the reading to complete this chart. QUESTION PROKARYOTES EUKARYOTES VIRUSES Does it have a nucleus? Does it have membrane-bound organelles? Does it have a cell membrane? Does it have DNA? Is it small, smallest or biggest in size of the three? Imagine in the future that you are an astrobiologist (astrobiologists are scientists who look for life in space) on a mission to another planet. You have discovered something that may or may not be alive, may or may not be prokaryotic or eukaryotic. 1. What information could you gather and analyze about its structure to determine the answer? 2. How can you justify (support) your answer? Use the information from your chart and the reading to complete the Venn Diagram. Biology B4.a B4.c (part 1 only) Comparing and Contrasting Prokaryotes and Eukaryotes PROKARYOTES BOTH EUKARYOTES