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Cell Structure & Function History: 1665 - Robert Hooke viewed thin slices of cork and called the hollow boxes cells 1674 - Anton van Leeuwenhoek observed living cells in water 1838 - Matthias Schleiden concludes that all plants are made up of cells 1839 - Theodor Schwann concludes that all animals are made up of cells 1855 - Rudolph Virchow concludes that all cells reproduce 1970 - Lynn Margulis proposes endosymbiont hypothesis that some cell parts may have once been cells themselves Cell Theory 1. all living things are made of cells 2. cells are the basic unit of structure and function in living things 3. new cells come from pre-existing cells There are 2 types of cells Prokaryotic Eukaryotic Characteristics of prokaryotes: All are bacteria No organized nucleus No organelles Small ribosomes Characteristics of eukaryotes: Typical cells of: plants animals fungus protists Have an organized nucleus and many small organelles Cell parts: Cell (plasma) membrane controls what goes in or out Cell wall provides support Cytoplasm (cytosol) liquid containing cell parts Nucleus control center containing Chromosomes genetic material Nucleolus makes ribosomes Cilia short fibers for movement Flagella long strands for movement Cell organelles: Ribosomes site of protein synthesis Mitochondria produce energy Golgi apparatus modify and package proteins Lysosomes contain digestive enzymes Peroxisomes contain special enzymes Endoplasmic reticulum (ER) membrane transport system site of product synthesis Vacuoles storage units Centrioles help in cell reproduction Plastids specialized storage units amyloplasts store starch chloroplasts store chlorophyll chromoplasts store pigments Cytoskeleton fibers for support microtubules microfilaments Levels of organization: unicellular multicellular tissue - organ organ system – organism CELL MEMBRANES Cell membranes help maintain Homeostasis. Some substances cross the membrane with no energy required by the cell. This is called passive transport. Small molecules like O2, H2O, CO2 can move in and out freely, Large molecules like proteins and carbohydrates cannot. The cell membrane is semi-permeable or selectively permeable . Diffusion across a membrane is passive transport. Diffusion is movement from high to low concentration. The difference in concentration across a membrane is called a concentration gradient. Diffusion is driven by kinetic energy. Kinetic energy keeps molecules in constant motion. The rate of diffusion depends on: Temperature Molecular size Type of molecule Molecules diffuse faster at higher temperatures. Small molecules diffuse faster than large molecules. Diffusion always occurs down a concentration gradient. Diffusion occurs until there is equal concentration. When there is no concentration gradient, there is equilibrium, but molecules continue to move. Diffusion of water across a membrane is called osmosis. Diffusion of water down a gradient does not require energy. Cytoplasm is mostly water that contains dissolved solutes. Concentrated solutions have many solute particles and less water. Water moves from areas of low solute concentration to areas of high solute concentration. There are three types of solution based on concentration : Hypertonic Isotonic Hypotonic Hypertonic Solute concentration outside the cell is high (like salt water). Water diffuses out of the cell and the cell contents shrink. Called plasmolysis in animal cells In plant cells it results in wilting Isotonic Solute concentration is the same inside and outside the cell and water moves in and out of the cell at the same rate. The cell remains normal. Animal cells do best here. Plant cells remain normal. Hypotonic Solute concentration is greater inside the cell. Water diffuses into the cell. The cell contents swell and the cell may rupture. In animal cells it is called lysis. In plant cells, the result is turgidity. Plants do best here. Most animal cells exist in isotonic environments. Cells in fresh water are in hypotonic solution. They must pump water out using contractile vacuoles. Plant cells have a cell wall that prevents them from bursting. Facilitated diffusion Faster than simple diffusion, it is considered passive transport. It uses carrier proteins that can change shape. It helps move certain solutes like glucose across the membrane. Facilitated diffusion may also use channel proteins that can form open paths through the membrane or have gated channels that open and close in response to concentration. Osmosis occurs through aquaporins Active transport Requires energy from ATP. Moves substances against or up A concentration gradient. It may involve membrane proteins. It is used to move ions like Na+, Ca++, or K+ across the membrane. Bulk transport Moves large complex molecules across the cell membrane Endocytosis moves large quantities of substances into the cell. phagocytosis moves solid particles into the cell, pinocytosis moves fluid drops into the cell. Exocytosis Used to remove large particles from the cell such as waste, mucus, and cell products like insulin