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What is homeostasis? Why is the ability to maintain homeostasis important? What are some things that the human body must regulate? How does the body regulate these things? What are some things that cells must regulate? water, salt, ions, glucose, temperature, carbon dioxide, oxygen,… How is a cell able to do this? nucleus monitors activities and the cell membrane controls what enters and exits the cell Cells… Homeostasis and Transport Chapter 7.4 organisms, both simple and complex must maintain homeostasis individual cells must also maintain homeostasis cells maintain homeostasis by regulating what gets into and out of the cell the cell part that is of great importance in maintaining homeostasis is … THE CELL MEMBRANE Cell Membrane Structure 1. two layers of (phospho-) lipids ◦ ◦ called lipid bilayer forms a barrier between external and internal environment of the cell (both which are watery) 2. scattered proteins 3. some carbohydrates MOVEMENT OF MOLECULES all molecules are in constant, random motion – BROWNIAN MOVEMENT as a result of the random motion of molecules, molecules tend to …. move into areas where they are less concentrated TRANSPORT PROCESSES (or Transport Mechanisms or Transport Systems) are ways in which substances get into and out of cells 2 main categories: PASSIVE TRANSPORT ACTIVE TRANSPORT Passive Transport Processes movement of molecules from an area of greater concentration to an area of lesser concentration requires no energy (ATP) from the cell movement is with the gradient example: rolling a boulder down a hill types - diffusion; osmosis; facilitated diffusion Diffusion (type of passive transport)… movement of a substance from area of greater concentration to lesser concentration Osmosis (type of passive transport)…. movement of water from greater concentration to lesser concentration through a semipermeable membrane Water is essential to life and to living things !!!!! In living things water is usually not pure, but is found as part of a solution. a SOLUTION contains: solute – substance being dissolved solvent – substance doing the dissolving (in living things the solvent is usually water) solutions can be described as…. hypertonic, hypotonic, or isotonic Hypertonic describes a solution that contains a greater concentration of solutes (than the solution it is compared to) in this diagram, colored dots = solute white space = water the solution outside the cell is hypertonic as compared to the solution inside If osmosis occurs, what will happen to the water? If osmosis occurs, what will happen to the cell? Hypotonic describes a solution that contains a lower concentration of solutes (than the solution it is compared to) the solution outside the cell is hypotonic as compared to the solution inside If osmosis occurs, what will happen to the water? If osmosis occurs, what will happen to the cell? Isotonic describes a solution whose solute concentration is the same both inside and outside of the cell the solution outside the cell is isotonic as compared to the solution inside If osmosis occurs, what will happen to the water? If osmosis occurs, what will happen to the cell? Let’s Practice cell A – 20% starch, 80% water cell B – 15% starch, 85% water cell C – 10% starch, 90% water cell D – 25% starch, 75% water What is the solute in these cells? What is the solvent in these cells? Which cell is hypotonic to the others? Which cell is hypertonic to the others? When comparing cells…. A and B, which is hypertonic? A and D, which is hypertonic? C and D, which is hypotonic? Let’s Practice some more…. cell cell cell cell A – 20% starch, 80% water B – 15% starch, 85% water C – 10% starch, 90% water D – 25% starch, 75% water In which direction would water flow… between cells A and B? between cells A and D? between cells B and C? between cells C and A? Which cell has the greatest solute concentration? Which cell has the greatest solvent concentration? Cytolysis “cyte” = cell “lyse” = burst If a cell is placed in a hypotonic solution it may burst or lyse. Why? Some cells have evolved adaptations to prevent cytolysis. What type of solution is this red blood cell in ? before during after Adaptations of Cells Some unicellular organisms have contractile vacuoles to collect and pump out excess water. Plant cells don’t undergo cytolysis because of the rigid cell wall. Turgor Pressure (osmotic) pressure within a plant cell due to the movement of water into the cell Plants rely on hypotonic environments to get water into them and into their vacuoles. If plants are in a hypertonic environment they will wilt (known as plasmolysis). Facilitated Diffusion (passive transport) “assisted diffusion” carrier proteins (in the cell membrane) will assist the movement of some molecules across the membrane Active Transport Processes movement of molecules from an area of lesser concentration to greater concentration movement is against the gradient requires energy (ATP) from the cell example: rolling a boulder up a hill types – pump mechanism; endocytosis; exocytosis Pump Mechanism (also known as a Cell Membrane Pump) active transport process in which small molecules are moved from a region of lower concentration to greater concentration (against a gradient) with the assistance of proteins in the cell membrane Endocytosis (active transport) process by which cells ingest fluid, macromolecules, or large particles, including other cells (viruses and bacteria) * the cell membrane folds around the particle and forms a pouch (called a vesicle) Endocytosis (active transport) 2 types: Pinocytosis: transport of solutes or fluids into the cell Phagocytosis: transport of large particles or whole cells into the cell many unicellular organisms feed by phagocytosis Exocytosis (active transport) reverse of endocytosis a vesicle within the cell fuses with the cell membrane and releases its contents outside the cell Endocytosis & Exocytosis Review Transport Mechanisms Interactive Tutor