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Transcript
CELL STRUCTURE AND FUNCTION (Ch. 7) Cell – basic structural and functional unit of all living organisms. The Cell Theory Anton van Leeuwenhoek (1600s) – used a simple light microscope. He saw living organisms in pond water, milk, etc. Robert Hooke (English – 1600s) – studied cork and oak bark. First to use the word – CELL. Schleiden and Schwann formulated Cell Theory: CELL THEORY: All organisms are composed of one or more cells. The cell is the basic unit of structure and organization of organisms All cells come from preexisting cells. Microscopes: Light microscopes – uses light (1000x actual size) Electron microscopes – uses a beam of electrons instead of light (500,000x actual size). Specimens must be in a vacuum. 1. Scanning Electron Microscope (SEM) – 3-D shape 2. Transmission Electron Microscope (TEM) – study structures within a cell. TWO types of CELLS: 1. Prokaryotes do not have membrane-bound organelles most are unicellular ex. bacteria primitive, small no nucleus 2. Eukaryotes contain membrane-bound organelles most make up multi-cellular organisms contains a nucleus – central organelle that manages all cellular functions larger Cell wall rigid structure located outside the plasma membrane used for additional support and protection ex. plants, fungi and bacteria Composed of cellulose which is porous. It does not select which molecules enter or leave Organelles – small, specialized structures contained within the cell. Each organelle has a specific function. Structure Cell membrane Function Selective permeability Cell Type All Cell wall Support, protection, cellulose, Prokaryotes and thick tough mesh fibers, very Eukaryotes porous (except animal cells) Nucleus Directs activities of other organelles, two membranes Eukaryotes Ribosomes Site of protein synthesis All Cytoplasm Clear gelatinous fluid All Endoplasmic Reticulum Cellular chemical reactions, site of protein synthesis, rough due to ribosomes Eukaryotes Golgi Apparatus Packages proteins in vesicles Eukaryotes (membrane bound structures) Vacuole Storage of food, water, enzymes, waste Large in plant cells, Small or not present in animal cells Lysosome Digests excess or worn out organelles, digests bacteria and viruses Can fuse with vacuoles and digest contents Can digest cells (tadpole’s tail) Converts light energy to chemical energy Eukaryotes Transforms energy Folded membrane – increases surface area and maximizes space for energy production Eukaryotes Chloroplasts Mitochondria Plant cells, some algae, some protists Cytoskeleton Supports and anchors organelles, provides highway system through which materials move All Centrioles Microtubules used for cell division Animal cells and protists Cilia Short hairs on outside of cell used for Locomotion or feeding, Like oars in a rowboat Unicellular Flagella Whip-like tail for locomotion Unicellular The Plasma Membrane – flexible boundary between the cell and its environment. It allows nutrients to enter and waste to leave. Acts to maintain homeostasis (maintaining balance). Selective Permeability – process in which a membrane allows some molecules to pass through while keeping others out. (screen door). Composition of the Plasma Membrane composed of a phospholipid bi-layer – has two layers of phospholipids “tails” of the phospholipid molecule are nonpolar (avoid water) fatty acids “heads” of the phospholipid molecule are polar (attract water) phosphates this creates a barrier that is water-soluble at the outer surface and water in-soluble in the middle so water-soluble molecules will not easily move through the membrane because they are stopped by the water in-soluble layer called “fluid-mosaic model” – proteins move along the membrane transport proteins move needed substances or waste materials through the plasma membrane. cholesterol – prevents the fatty acid “tails” from sticking together proteins and carbohydrates stick out from the surface to identify chemical signals Fluid Mosaic Model: CELLULAR TRANSPORT Diffusion – net movement of particles from an area of higher concentration to an area of lower concentration. This occurs because of brownian motion – the random movement of atoms and molecules. Diffusion occurs until dynamic equilibrium is reached. Diffusion is affected by: temperature (↑ temperature, ↑ diffusion) concentration (↑ concentration, ↑ diffusion) pressure (↑ pressure, ↑ diffusion) Concentration gradient – the difference in concentration across a space. Diffusion occurs until there is no longer a concentration gradient. Osmosis – diffusion of water across a selectively permeable membrane. 1. Isotonic solution – dissolved substances are the same outside the cell as inside the cell. Experiences osmosis but retains shape. 2. Hypotonic solution – concentration of dissolved substances is lower in the solution outside the cell so there is more water outside the cell than inside. Water flows into the cell causing the cell to swell. 3. Hypertonic solution – concentration of dissolved substances is higher in the solution outside the cell so there is less water outside. Water flows out of the cell causing it to shrivel. ex. wilting plants. Passive Transport – requires no energy because movement is within the concentration gradient. Passive transport can occur by: simple diffusion facilitated diffusion – requires transport proteins (channel proteins) to form channels Active Transport – movement of materials through a membrane against the concentration gradient. Requires energy from the cells. carrier protein combines with a specific molecule or ion thus allowing chemical energy to be used to change the shape of the carrier protein Endocytosis - cell surrounds and takes in large molecules. Engulfed and enclosed by a portion of the cell membrane. Exocytosis – reverse of endocytosis. Explulsion of materials from a cell. Uses this method to expel wastes.