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7.3 Cell Transport Passive Transport Passive Transport is the movement of materials across the cell membrane _______________using ____________ ____________________. There are three forms of passive transports: _______________, Facilitated Diffusion and _________________. Passive Transport Every living cell exists in a _______________environment. One of the most important functions of the cell _________________ is to keep the cell’s internal conditions relatively constant. It does this by regulating the movement of _______________________ from __________ side of the cell membrane to the ________________ side. Diffusion (Passive Transport) The cytoplasm of a cell is a_______________ of many different substances dissolved in water. In any ______________ (water and sugar), __________ particles (sugar) tend to move from an area where they are more concentrated to an area where they are less concentrated. The process by which _____________ (sugars) move from an area of _________concentration to an area of ___________ concentration is known as ______________. ____________________ is the driving force behind the movement of many substances across the cell membrane. Diffusion (Passive Transport) Suppose a substance is present in _____________ concentrations on either side of a cell membrane. There is a higher concentration of ______________ (sugar) on one side of the membrane than on the other. Diffusion (Passive Transport) If the substance can cross the cell membrane, its particles will tend to move toward the area where it is ___________ concentrated until it is evenly distributed. Diffusion causes a net movement of ____________ particles (sugar) from the side of the membrane with the ______________ solute (sugar) concentration to the side with the _____________ solute (sugar) concentration. Diffusion (Passive Transport) At that point, the concentration of the substance on both sides of the cell membrane is the same, and ________________ is reached. Once equilibrium is reached, solute (sugar) particles continue to diffuse across the cell membrane in ______________ directions but at approximately equal rates, so there is no __________ change in solute (sugar) concentration. Diffusion (Passive Transport) Diffusion depends upon ___________ particle movements. Substances diffuse across membranes _______________ requiring the cell to use additional ____________________. The movement of materials across the cell membrane _____________ using cellular ______________ is called ________________ transport. Facilitated Diffusion (Passive Transport) Cell membranes have __________________ that act as _________________, or channels, making it easy for certain molecules to cross. Molecules that cannot directly diffuse across the membrane pass through special ________________channels in a process known as __________________ diffusion. ____________________ of different proteins have been found that allow particular substances to cross cell membranes. The movement of molecules by ___________________ diffusion does not require any additional use of the cell’s energy. Osmosis: An Example of Facilitated Diffusion The inside of a cell’s lipid bilayer is ____________________—or “waterhating.” Because of this, water molecules have a _______________ time passing through the cell membrane. Many cells contain water channel proteins, known as ________________, that allow water to pass right through them. Without ___________________, water would diffuse in and out of cells very ______________. The movement of___________ through cell membranes by facilitated diffusion is an extremely important biological process—the process of _____________. Osmosis: An Example of Facilitated Diffusion (Passive Transport) __________________ is the diffusion of water through a selectively permeable membrane. ____________involves the movement of water molecules from an area of ____________ concentration to an area of _______________ concentration. A Look at Osmosis: How Osmosis Works In the experimental setup below, the barrier is ______________ to water but not to sugar. This means that ___________ molecules can pass through the barrier, but the solute, ___________, cannot. How Osmosis Works There are ___________ sugar molecules on the right side of the barrier than on the left side. Therefore, the concentration of water is lower on the ___________, where more of the solution is made of sugar. How Osmosis Works There is a _______ movement of water into the compartment containing the concentrated sugar solution. Water will tend to move across the barrier until ____________ is reached. At that point, the concentrations of water and sugar will be the _____________ on both sides. How Osmosis Works When the _________________ is the same on both sides of the membrane, the two solutions will be ________________, which means “same strength.” How Osmosis Works The more concentrated sugar solution at the start of the experiment was _____________, or “above strength,” compared to the dilute sugar solution. The dilute sugar solution was ___________________, or “below strength.” Osmotic Pressure For organisms to survive, they must have a way to balance the _______ and _________ of water. The _______ movement of water out of or into a cell exerts a force known as osmotic __________. Osmotic Pressure Because the cell is filled with salts, sugars, proteins, and other molecules, a cell placed in freshwater, would be placed in a ___________ solution. As a result, water tends to move quickly into a cell surrounded by fresh water, causing it to _________. Eventually, the cell may ______________. Osmotic Pressure In plants, the movement of water into the cell causes the central __________ to swell, pushing cell contents out against the _____________wall. Since most cells in large organisms do not come in contact with fresh water, they are not in danger of bursting. Osmotic Pressure Instead, the cells are bathed in fluids, such as __________, that are ___________and have concentrations of dissolved materials roughly equal to those in the cells. Cells placed in an isotonic solution neither _________ nor lose water. Osmotic Pressure In a hypertonic solution, water rushes _____________ of the cell, causing animal cells to shrink and plant cell vacuoles to collapse. Active Transport Cells sometimes must move materials ___________a concentration difference. The movement of material against a ______________ difference is known as _____________ transport. Active transport requires ______________. Active Transport The active transport of small molecules or ions across a cell membrane is generally carried out by _____________proteins, or protein “pumps,” that are found in the membrane itself. Active Transport (molecular transport) Small molecules and ions are carried across membranes by ________ in the membrane that act like ____________. Many cells use such proteins to move calcium, ______________, and sodium ions across cell membranes. Changes in protein __________ seem to play an important role in the pumping process. Active Transport (Molecular Transport) A considerable portion of the ____________ used by cells in their daily activities is devoted to providing the ____________ to keep this form of active transport working. The use of energy in these systems enables cells to concentrate substances in a particular location, even when the forces of __________ might tend to move these substances in the opposite direction. Active Transport Larger molecules and clumps of material can also be actively transported across the cell membrane by processes known as _____________________and ___________________. The transport of these larger materials sometimes involves changes in the ___________ of the cell membrane. Bulk Transport Larger molecules and even solid clumps of material may be transported by movements of the cell membrane known as bulk transport. Bulk transport can take several forms, depending on the size and shape of the material moved into or out of the cell. Endocytosis _______________ is the process of taking material into the cell by means of infoldings, or ___________________, of the cell membrane. The pocket that results breaks loose from the outer portion of the cell membrane and forms a vesicle or vacuole within the cytoplasm. Exocytosis Many cells also _____________ large amounts of material from the cell, a process known as ______________________. During __________________, the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell. A Look at Endocytosis and Exocytosis: