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Cell Boundaries and Transport Objectives • Explain the role of the cell membrane in supporting cell functions • Draw and label the parts of the cell membrane • Compare and contrast active and passive transport • Describe how tonicity is a measure of the osmotic pressure gradient (Isotonic, Hypertonic and Hypotonic) About Cell Membranes • All cells have a cell membrane • Functions: a.Controls what enters and exits the cell to maintain an internal balance called homeostasis b.Provides protection and support for the cell TEM picture of a real cell membrane. Why do cells need to control what enters and exits? • Plasma membrane – boundary between the cell and its environment • Homeostasis – maintaining the cells environment • Cells need to bring in nutrients, get rid of wastes, and keep harmful molecules out • The plasma membrane also supports the cytoplasm, recognizes foreign material, and communicates with other cells. Structure of cell membranes • The cell membrane is primarily composed of a mix of proteins and lipids. – Lipids help to give membranes their flexibility – Proteins monitor and maintain the cell's chemical climate and assist in the transfer of molecules across the membrane. About Cell Membranes (continued) • Structure of cell membrane Lipid Bilayer -2 layers of phospholipids a.Phosphate head is polar (water loving) b.Fatty acid tails are nonpolar (water fearing) c.Proteins embedded in membrane Phospholipid Lipid Bilayer Polar heads Fluid Mosaic love water Model of the & dissolve. cell membrane Non-polar tails hide from water. Other Components • Cholesterol – stabilizes phospholipids, keeps fatty acid tails from sticking together • Cell-Surface Markers – chain of sugars attached to proteins (glycoproteins) that identifies each cell type • Receptor Proteins – bind with substances outside of cell causing changes in the cell • Enzymes – catalyze chemical reactions • Transport Proteins – help movement of substances into and out of the cell About Cell Membranes (continued) • 4. Cell membranes have pores (holes) in it a. Selectively permeable: Allows some molecules in and keeps other molecules out b. The structure helps it be selective! Pores Structure of the Cell Membrane Outside of cell Proteins Lipid Bilayer Transport Protein Animations of membrane Go to structure Section: Phospholipids Inside of cell (cytoplasm) Cell Boundaries: Cell Wall Plants, algae, fungi and many prokaryotes have this additional barrier outside their plasma membrane. It provides additional protection and support for the cell. The wall is made of carbohydrate and protein fibers like cellulose. Cellulose is the principle component of wood and paper! Which of the four organic compounds does a book belong to? Cell Limitations – A solution is a mixture of 2 or more substances – The liquid doing the dissolving is the solvent (usually water) – The solid being dissolved is the solute – The concentration is the amount of solute in the solution Types of Cellular Transport •Animations of Active Transport & Passive Transport • Weeee!! ! Passive Transport cell doesn’t use energy 1. Diffusion 2. Facilitated Diffusion 3. Osmosis • high low Active Transport cell does use energy 1. Protein Pumps 2. Endocytosis 3. Exocytosis This is gonna be hard work!! high low Passive Transport • • • cell uses no energy molecules move randomly Molecules spread out from an area of high concentration to an area of low concentration. • (HighLow) Three types 3 Types of Passive Transport 1. Diffusion 2. Facilitative Diffusion – diffusion with the help of transport proteins 3. Osmosis – diffusion of water Passive Transport: 1. Diffusion Simple Diffusion Animation 1. Diffusion: random movement of particles from an area of high concentration to an area of low concentration. (High to Low) • Diffusion continues until all molecules are evenly spaced (equilibrium is reached)-Note: molecules will still move around but stay spread out. http://bio.winona.edu/berg/Free.htm Examples of diffusion in your body • Diffusion occurs throughout the human body – Absorption of food in digestive system (stomach, intestines) – Absorption of nutrients from food into cells – Diffusion of oxygen through the cornea in eyes – Medicine from pills are absorbed into the lining of the stomach and then into the bloodstream (both processes of diffusion) Passive Transport: 2. Facilitated Diffusion A 2. Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane a.Transport Proteins are specific – they “select” only certain molecules to cross the membrane b.Transports larger or charged molecules Facilitated diffusion (Channel Protein) Carrier Protein B Diffusion (Lipid Bilayer) Passive Transport: 2. Facilitated Diffusion Glucose molecules Cellular Transport From aHigh Concentration High • Channel Proteins animations Cell Membrane Low Concentration Through a Go to Section: Transport Protein Protein channel Low Passive Transport: 3. Osmosis Osmosis animation • 3.Osmosis: diffusion of water through a selectively permeable membrane • Water moves from high to low concentrations •Water moves freely through pores. •Solute (green) to large to move across. The diffusion of solvent molecules, such as water, is known as osmosis water glucose Solvent molecules e.g. water Solute molecules e.g.glucose Water is the solvent used in nature Osmotic concentration relates to the amount of dissolved solutes in a solution high osmotic concentration (concentrated) low osmotic concentration (dilute) Insoluble molecules do not affect the osmotic concentration Partially permeable membranes only let water and very small molecules through A partially permeable membrane results in an uneven distribution across the membrane Low osmotic concentration: A dilute solution with a high water potential High osmotic concentration: A concentrated solution with a low water potential Which way will osmosis occur? water glucose NET osmosis high osmotic concentration low osmotic concentration partially permeable membrane Active Transport •cell uses energy (ATP) to actively move molecules to where they are needed •Carrier proteins in the cell membrane •Movement from an area of low concentration to an area of high concentration . Against the concentration gradient •Low High concentration Three Types Types of Active Transport 1. Protein Pumps transport proteins that require energy to do work •Example: Sodium / Potassium Pumps are important in nerve responses. Sodium Potassium Pumps (Active Transport using proteins) Protein changes shape to move molecules: this requires energy! Active Transport • Shape of carrier protein is complimentary to molecule they carry • Binding • Molecule transported across membrane • 1 way flow-molecule can only fit into carrier protein on 1 side of membrane Other two types of Active Transport: Bulk Transport-Moving large amounts • Moving large quantities- in & out: Endocytosis- & Exocytosis • Fusing & pinching off of membranes • Used to form vesicles & to move vesicles around the cell •Examples: • Hormones e.g. insulin released into blood by pancreatic cells • Plant cells-vesicles carry materials to make cell wall • WBC engulfing foreign invaders & fusion with lysosomes Types of Active Transport 2. Endocytosis: taking bulky material into a cell • Uses energy • Cell membrane in-folds around food particle • “cell eating” • forms food vacuole & digests food • This is how white blood cells eat bacteria! Types of Active Transport 3. Exocytosis: Forces material out of cell in bulk • membrane surrounding the material fuses with cell membrane • Cell changes shape – requires energy • EX: Hormones or wastes released from cell Endocytosis & Exocytosis animations Review: Active vs. Passive Transport Active Passive Energy needed? YES, in the form of ATP Energy needed? No When If diffusion cannot meet needs of cell/is not quick enough When To transport molecules across cell membrane high-low conc. Tonicity • Tonicity is a measure of the osmotic pressure gradient (as defined by the water potential of the two solutions) of two solutions separated by a semipermeable membrane. • Tonicity is influenced only by solutes that cannot cross the membrane, as only these exert an osmotic pressure. – Solutes able to freely cross the membrane do not affect tonicity because they will always be in equal concentrations on both sides of the membrane. http://www.youtube.com/watch?v=6MWl3DCa2uM Homeostasis • Defined as one of the fundamental characteristics of all living systems • It is the tendency of an organism to maintain a stable, constant internal environment • Maintained by various organ systems in the body – An organ system is a group of organs that works together to perform a common function Effects of Osmosis on Life • Osmosis- diffusion of water through a selectively permeable membrane • Water is so small and there is so much of it the cell can’t control it’s movement through the cell membrane. Osmosis and Plant Cells Plant cells placed in solutions with different water concentrations: Lower water concentration outside cell Water leaves the cell by osmosis. Cell membrane pulls away from cell wall. The cell is described as being plasmolysed. Same water concentration outside cell Water constantly enters and leaves the cell. Higher water concentration outside cell Water enters the cell by osmosis. Cell membrane pushes against the cell wall. The cell is described as being turgid. Osmosis and Animal Cells Animal cells placed in solutions with different water concentrations: Lower water concentration outside cell Same water concentration outside cell Higher water concentration outside cell Water Water leaves the cell by osmosis. Animal cells shrink. Water constantly enters and leaves the cell. Water enters the cell by osmosis. Cell expands and can burst, this is known as lysis. Unlike plant cells, animal cells do not have a strong cell wall to protect them. • Hypotonic Solution Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Hypotonic: The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water) Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)! Hypotonic solutions have a lower osmotic concentration than the cytoplasm of the cell external solution blood cell NET osmosis into the cell Can cause animal cells to burst • Hypertonic Solution Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Hypertonic: The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water) shrinks Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)! Hypertonic solutions have a higher osmotic concentration than the cytoplasm of the cell external solution blood cell NET osmosis out of the cell Causes animal cells to shrink • Isotonic Solution Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Isotonic: The concentration of solutes in the solution is equal to the concentration of solutes inside the cell. Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium) Isotonic solutions have the same osmotic concentration as the cytoplasm of the cell external solution blood cell No NET osmosis Review: Diffusion and Osmosis – Isotonic – concentration of solute is the same both in and out of cell, water movement is equal – Hypertonic – concentration of solute is greater outside the cell, water moves to the outside of cell to balance out (possibly resulting in cell shriveling) – Hypotonic - concentration of solute is lower outside the cell, water moves into the cell to balance out (possibly resulting in cell explosion) Blood cells in animals are isotonic and have roughly the same amount of dissolved materials inside the cell as surrounding the cell Plant cells have cell walls that prevent the cell from swelling and bursting when in contact with water Respiration and Diffusion • Respiration depends heavily on both the circulatory system and the process of diffusion. • The passage of air into your lungs comes in through the nasal cavity trachea branching system of bronchial tubes in each lung alveoli • The alveoli are lined with capillaries so that O2 you breathe in can enter the bloodstream and CO2 waste can leave the blood stream. • Like most animals, your lungs are lined with moist mucus providing a wet environment for gas exchange Diffusion and Osmosis… a review • Why does the CO2 leave the blood stream and O2 enter?... Diffusion • Diffusion is a form of passive transport (no energy required) in which substances flow from an area of high concentration to an area of low concentration. Substances such as O2 and CO2, are small enough to pass through the walls of the capillaries. • A specific type of diffusion is osmosis, or the movement of water from high to low concentration due to a change in conditions Diffusion and osmosis in the kidney • The main function of the kidneys is to filter our blood and remove waste as urine. Both kidneys do the same job. Blood is taken to the kidneys by the renal artery and when it is cleaned, it is returned to the heart by the renal vein. The urine is taken to the bladder by the ureters. Diffusion and Osmosis in the kidney • Maintaining water balance in the kidney can be inhibited by a diuretic, a substance that causes the kidneys to allow excess water loss. A very common diuretic is caffeine. – Diuretics block the production of the hormone vasopressin, an anti-diuretic hormone (ADH). When the blood has a high concentration of sodium ions, the hypothalamus and pituitary gland (both in the brain) triggers the release of ADH which would tell the kidneys to reabsorb more water to help rehydrate the body. This is an example of maintaining homeostasis with the endocrine system. The endocrine system is made up of glands and cells that release chemical messengers called hormones, directly into the blood stream. What type of solution are these cells in? A B C Hypertonic Isotonic Hypotonic How Organisms Deal with Osmotic Pressure • Paramecium (protist) removing excess water video •Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called tugor pressure. •A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding. •Salt water fish pump salt out of their specialized gills so they do not dehydrate. •Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.