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The discovery of cells › Cells All living things are composed of cells. Cells are the smallest unit that can carry on the processes of life. Beginning in the 17th century naturalists were able to use microscopes to study objects too small to be seen by the naked eye. › Robert Hooke Studied nature using an early light microscope. Looked at thin slice of cork from the bark of a cork oak tree Saw little boxes, cubbies or cells Anton Van Leeuwenhoek › First person to observe living cells › Made microscopes that were simple and tiny, but he ground the lenses so precisely that the magnification was 10 times that of Hooke’s instruments. › He discovered protists or one celled organisms. Although Hooke and Leeuwenhoek were the first to observe cells, their observations were not realized until 150 years later. 1838 Matthias Schleiden concluded that all plants were composed of cells. 1839 Theodor Schwann concluded that animals were composed of cells. Rudolph Virchow noted that all cells come from other cells. These three observations were combined to create the CELL THEORY. 3 ESSENTIAL PARTS All living organisms are composed of one or more cells. Cells are the basic unit of structure and function in an organism. Cells come only from the reproduction of existing cells. Cells within different organisms and within the same organism are very different and diverse in terms of shape size, and internal organization. › Shape Diversity in shapes reflects the different functions of cells. Diversity in shapes reflects the different functions of cells. Cell shape can be simple to complex. https://www.youtube.com/w atch?v=wuXSEOKNxN8 The size of a cell is limited by the relationship of the cell’s outer surface area to its volume or its surface area – to – volume ratio. As cells grow its volume increase much faster than its surface area. Important because the materials needed by a cell and the waste produced by the cell must pass into and out of the cell through its surface. › If a cell were to become very large, the volume would increase much more that the surface area. Therefore the surface area would not allow materials to enter or exit the cell quickly enough to meet the cell’s needs. As a result most cells are microscopic in size. › Cells have three basic features that are common to all types. › Outer boundary Cells outer boundary is called the plasma membrane or the cell membrane. Covers the cells surface and acts as a barrier between the inside and outside of a cell. All materials enter and exit through the plasma membrane. › Interior substance The region of the cell that is within the plasma membrane and that includes the fluid, the cytoskeleton, and all of the other organelles except the nucleus is called the cytoplasm. The part of the cytoplasm that includes molecules and small particles, such as ribosomes, but not membrane bound organelles is the cytosol. Cells carry coded information in the form of DNA for regulating function and reproduction. DNA is some cells moves freely inside while others have DNA in a organelle called the nucleus. Most of the functions of the eukaryotic cell are controlled by the nucleus. Often the biggest structure in the cell. Maintains shape with the help of a protein skeleton called the nuclear matrix or nuclear envelope. Nuclues Prokaryotes › Organisms that lack a membrane-bound nucleus and membrane bound organelle. › Although prokaryotic cells do not have a nucleus, their genetic information – in the form of DNA – is concentrated in a part of the cell called the nucleoid. › Prokaryotes are divided into 2 domains: Bacteria and Archaea. Bacteria includes organisms that are similar to the first life-forms. Eukaryotes › Organisms made up of one or more cells that have a nucleus and membrane-bound organelles. › Have a variety of subcellular structures called organelles. Organelles are well defined, intracellular bodies that perform specific functions for a cell. Many organelles are surrounded by membranes. Generally much larger than prokaryotes Over time cells began to form groups that function together. Some retained the ability to live outside a group. Others became dependent on each other for survival. Colonies › A colonial organism is a collection of genetically identical cells that live together in a connected group. › They are not truly multi-cellular because few cell activities are coordinated. True multicellularity › As organisms evolved, cells became more specialized and eventually › › › › › could not survive independently. Groups of cells took on specific roles or functions within the organism. Groups of cells and their products that carry out specific functions are called tissues. Groups of tissues that perform a particular function or job within an organism are celled organs. An organ system is a group of organs that accomplish related tasks. An organism is a collective of organ systems that carry out the processes of life.