Copyright Pearson Prentice Hall 7-3 Cell Boundaries 7-3 Cell Boundaries Photo Credit: © Quest/Science Photo Library/Photo Researchers, Inc. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 7-3 Cell Boundaries All cells are surrounded by a thin, flexible barrier known as the cell membrane. Many cells also produce a strong supporting layer around the membrane known as a cell wall. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cell Membrane Cell Membrane The cell membrane regulates what enters and leaves the cell and also provides protection and support. Copyright Pearson Prentice Hall

Functions of a cell membrane Isolate the cytoplasm from the external environment Regulate the exchange of substances Communicate with other cells Identification The membrane is selectively permeable (also called semipermeable )  Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cell Membrane Cell Membrane Outside of cell Carbohydrate chains Proteins Cell membrane The cell membrane regulates what enters and leaves the cell. Inside of cell (cytoplasm) Protein channel Lipid bilayer Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cholesterol - stiffens the membrane by connecting phospholipids Glycolipids - signal molecules Glycoproteins - have an attached chain of sugar (antibodies) Proteins embedded in membrane serve different functions Channel Proteins - form small openings for molecules to diffuse through Carrier Proteins- binding site on protein surface "grabs" certain molecules and pulls them into the cell, Receptor Proteins - molecular triggers that set off cell responses Cell Recognition Proteins - ID tags, to identify cells to the body's immune system Enzymatic Proteins - carry out metabolic reactions Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cell Walls What is the main function of the cell wall? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cells walls provide support and protection Most are made from carbohydrates and protein Cellulose Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Cell Walls Cell Wall Cell walls are found in plants, algae, fungi, and many prokaryotes. Copyright Pearson Prentice Hall

Diffusing through Cell Boundaries Copyright Pearson Prentice Hall

Diffusion Through Cell Boundaries Cells must regulate the movement of molecules from the liquid on the outside of the membrane to the liquid on the other side. The process of moving molecules or particles is called diffusion (movement of particles from high to low concentration) Copyright Pearson Prentice Hall

Diffusion Through Cell Boundaries What happens during diffusion? Copyright Pearson Prentice Hall

Diffusion Through Cell Boundaries Diffusion is the process by which molecules of a substance move from areas of higher concentration to areas of lower concentration. Diffusion does not require the cell to use energy. Copyright Pearson Prentice Hall

Diffusion Move from HIGH to LOW concentration diffusion of water passive transport no energy needed diffusion of water diffusion osmosis

Simple Diffusion Move from HIGH to LOW fat fat fat inside cell fat fat Which way will fat move? inside cell fat fat fat LOW HIGH fat outside cell fat fat fat fat fat fat fat

Facilitated Diffusion Glucose molecules Facilitated Diffusion During facilitated diffusion, molecules, such as glucose, that cannot diffuse across the cell membrane’s lipid bilayer on their own move through protein channels instead. Protein channel Copyright Pearson Prentice Hall

Facilitated Diffusion Move from HIGH to LOW through a channel sugar sugar sugar sugar inside cell sugar sugar LOW Which way will sugar move? HIGH outside cell sugar sugar sugar sugar sugar sugar sugar

Simple vs. facilitated diffusion simple diffusion facilitated diffusion lipid inside cell outside cell inside cell outside cell H2O protein channel H2O

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Copyright Pearson Prentice Hall Osmosis What is osmosis? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Osmosis Osmosis Osmosis is the diffusion of water through a selectively permeable membrane. Copyright Pearson Prentice Hall

Selectively permeable membrane Osmosis How Osmosis Works Dilute sugar solution (Water more concentrated) Concentrated sugar solution (Water less concentrated) Sugar molecules Osmosis is the diffusion of water through a selectively permeable membrane. In the first beaker, water is more concentrated on the right side of the membrane. As a result, the water diffuses (as shown in the second beaker) to the area of lower concentration. Movement of water Selectively permeable membrane Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Water tends to diffuse from a highly concentrated region to a less concentrated region. If you compare two solutions, three terms can be used to describe the concentrations: Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Osmosis hypertonic a hypotonic solution has a lower concentration of solutes outside the cell than inside the cell. In an attempt to balance the concentrations of solutes inside and outside the cell, water will rush into the cell, and can cause it to burst Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall hypotonic a hypotonic solution has a lower concentration of solutes outside the cell than inside the cell. In an attempt to balance the concentrations of solutes inside and outside the cell, water will rush into the cell, and can cause it to burst. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall isotonic Equal concentrations on the inside and outside of the cell Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Osmosis Osmotic Pressure  Osmosis exerts a pressure known as osmotic pressure on the hypertonic side of a selectively permeable membrane. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Active Transport Active Transport Sometimes cells move materials in the opposite direction from which the materials would normally move (Low to High concentration) —that is against a concentration difference. This process is known as active transport. Active transport requires energy. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Active Transport Molecular Transport In active transport, small molecules and ions are carried across membranes by proteins in the membrane. Energy use in these systems enables cells to concentrate substances in a particular location, even when diffusion might move them in the opposite direction. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Active Transport Molecular Transport Molecule to be carried Active Transport Active transport of particles against a concentration difference requires transport proteins and energy. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Active Transport Endocytosis and Exocytosis  Endocytosis is the process of taking material into the cell. Two examples of endocytosis are: Phagocytosis – solid material pinocytosis-liquid material During exocytosis, materials are forced out of the cell. Copyright Pearson Prentice Hall

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Copyright Pearson Prentice Hall osmosis Copyright Pearson Prentice Hall