Ch. 7 3 summary

336 views

Published on

Published in: Technology, Education
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
336
On SlideShare
0
From Embeds
0
Number of Embeds
3
Actions
Shares
0
Downloads
0
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Ch. 7 3 summary

  1. 1. 7.3 Cell Transport7.3 Cell Transport
  2. 2. Lesson OverviewLesson Overview Cell TransportCell TransportPassive TransportWhat is passive transport?The movement of materials across thecell membrane without usingcellular energy is called passive transport.
  3. 3. Lesson OverviewLesson Overview Cell TransportCell TransportDiffusionThe cytoplasm of a cell is a solution of many different substancesdissolved in water.In any solution, solute particles tend to move from an area wherethey are more concentrated to an area where they are lessconcentrated.The process by which particles move from anarea of high concentration to an area of lowerconcentration is known as diffusion.Diffusion is the driving force behind the movement of manysubstances across the cell membrane.
  4. 4. Lesson OverviewLesson Overview Cell TransportCell TransportDiffusionSuppose a substance is present in unequalconcentrations on either side of a cellmembrane.
  5. 5. Lesson OverviewLesson Overview Cell TransportCell TransportDiffusionIf the substance can cross the cell membrane, itsparticles will tend to move toward the area where it isless concentrated until it is evenly distributed.
  6. 6. Lesson OverviewLesson Overview Cell TransportCell TransportDiffusionAt that point, the concentration of the substance on bothsides of thecell membrane is the same, and equilibrium is reached.
  7. 7. Lesson OverviewLesson Overview Cell TransportCell TransportDiffusionEven when equilibrium is reached, particles of a solution willcontinue to move across the membrane in both directions.Because almost equal numbers of particles move in each direction,there is no net change in the concentration on either side.
  8. 8. Lesson OverviewLesson Overview Cell TransportCell TransportDiffusionDiffusion depends upon random particle movements.Substances diffuse across membranes without requiringthe cell to use additional energy.The movement of materials across the cell membranewithout using cellular energy is called passive transport.
  9. 9. Lesson OverviewLesson Overview Cell TransportCell TransportFacilitated DiffusionCell membranes have proteins that act as carriers, or channels, making iteasy for certain molecules to cross.Molecules that cannot directly diffuse across themembrane pass through special protein channels in aprocess known as facilitated diffusion.Hundreds of different proteins have been found that allow particularsubstances to cross cell membranes.The movement of molecules by facilitated diffusion does not require anyadditional use of the cell’s energy.
  10. 10. Lesson OverviewLesson Overview Cell TransportCell TransportOsmosis: An Example of FacilitatedDiffusionOsmosis is the diffusion of water through aselectively permeable membrane.Osmosis involves the movement of water molecules froman area of higher concentration to an area of lowerconcentration.
  11. 11. Lesson OverviewLesson Overview Cell TransportCell TransportHow Osmosis WorksIn the experimental setup below, the barrier is permeable to water but not tosugar. This means that water molecules can pass through the barrier, but thesolute, sugar, cannot.
  12. 12. Lesson OverviewLesson Overview Cell TransportCell TransportThere are more sugar molecules on the right side of the barrier than on theleft side. Therefore, the concentration of water is lower on the right, wheremore of the solution is made of sugar.How Osmosis Works
  13. 13. Lesson OverviewLesson Overview Cell TransportCell TransportHow Osmosis WorksThere is a net movement of water into the compartment containing theconcentrated sugar solution.Water will tend to move across the barrier until equilibrium is reached. At thatpoint, the concentrations of water and sugar will be the same on both sides.
  14. 14. Lesson OverviewLesson Overview Cell TransportCell TransportHow Osmosis WorksWhen the concentration is the same on both sides of the membrane, the twosolutions will be isotonic, which means “same strength.”
  15. 15. Lesson OverviewLesson Overview Cell TransportCell TransportHow Osmosis WorksThe more concentrated sugar solution at the start of the experiment washypertonic, or “above strength,” compared to the dilute sugar solution.The dilute sugar solution was hypotonic, or “below strength.”
  16. 16. Lesson OverviewLesson Overview Cell TransportCell TransportOsmotic PressureFor organisms to survive, they must have a way to balance the intake andloss of water.The net movement of water out of or into a cell exerts a force known asosmotic pressure.
  17. 17. Lesson OverviewLesson Overview Cell TransportCell TransportOsmotic PressureBecause the cell is filled with salts, sugars, proteins, and other molecules, itis almost always hypertonic to fresh water.As a result, water tends to move quickly into a cell surrounded by freshwater, causing it to swell. Eventually, the cell may burst.
  18. 18. Lesson OverviewLesson Overview Cell TransportCell TransportOsmotic PressureIn plants, the movement of water into the cell causes the central vacuole toswell, pushing cell contents out against the cell wall.Since most cells in large organisms do not come in contact with fresh water,they are not in danger of bursting.
  19. 19. Lesson OverviewLesson Overview Cell TransportCell TransportOsmotic PressureInstead, the cells are bathed in fluids, such as blood, that are isotonic andhave concentrations of dissolved materials roughly equal to those in thecells.Cells placed in an isotonic solution neither gain nor lose water.
  20. 20. Lesson OverviewLesson Overview Cell TransportCell TransportIn a hypertonic solution, water rushes out of the cell, causing animal cells toshrink and plant cell vacuoles to collapse.Osmotic Pressure
  21. 21. Lesson OverviewLesson Overview Cell TransportCell TransportOsmotic PressureSome cells, such as the eggs laid by fish and frogs, must come into contactwith fresh water. These types of cells tend to lack water channels.As a result, water moves into them so slowly that osmotic pressure does notbecome a problem.
  22. 22. Lesson OverviewLesson Overview Cell TransportCell TransportOsmotic PressureOther cells, including those of plants and bacteria, that come into contactwith fresh water are surrounded by tough cell walls that prevent the cellsfrom expanding, even under tremendous osmotic pressure.
  23. 23. Lesson OverviewLesson Overview Cell TransportCell TransportOsmotic PressureNotice how the plant cell holds its shape in hypotonic solution, while theanimal red blood cell does not.However, the increased osmotic pressure makes such cells extremelyvulnerable to injuries to their cell walls.
  24. 24. Lesson OverviewLesson Overview Cell TransportCell TransportActive TransportWhat is active transport?The movement of materialsagainst a concentrationdifference is known as activetransport. Cells sometimes mustmove materials against aconcentration difference.–Active transport requires energy.
  25. 25. Lesson OverviewLesson Overview Cell TransportCell TransportActive TransportThe active transport ofsmall molecules or ionsacross a cell membraneis generally carried outby transport proteins, orprotein “pumps,” that arefound in the membraneitself.
  26. 26. Lesson OverviewLesson Overview Cell TransportCell TransportActive Transport– Larger molecules andclumps of material canalso be activelytransported across thecell membrane byprocesses known asendocytosis andexocytosis.– The transport of theselarger materialssometimes involveschanges in the shape ofthe cell membrane.
  27. 27. Lesson OverviewLesson Overview Cell TransportCell TransportMolecular TransportSmall molecules and ions arecarried across membranes byproteins in the membrane that actlike pumps.Many cells use such proteins tomove calcium, potassium, andsodium ions across cellmembranes.Changes in protein shape seem toplay an important role in thepumping process.
  28. 28. Lesson OverviewLesson Overview Cell TransportCell TransportMolecular Transport– A considerable portion of the energy used bycells in their daily activities is devoted toproviding the energy to keep this form of activetransport working.– The use of energy in these systems enablescells to concentrate substances in a particularlocation, even when the forces of diffusion mighttend to move these substances in the oppositedirection.
  29. 29. Lesson OverviewLesson Overview Cell TransportCell TransportBulk TransportLarger molecules and even solidclumps of material may betransported by movements ofthe cell membrane known asbulk transport.Bulk transport can take severalforms, depending on the sizeand shape of the material movedinto or out of the cell.
  30. 30. Lesson OverviewLesson Overview Cell TransportCell TransportEndocytosisEndocytosis is theprocess of takingmaterial into the cellby means ofinfoldings, or pockets,of the cell membrane.The pocket that resultsbreaks loose from theouter portion of the cellmembrane and forms avesicle or vacuole withinthe cytoplasm.
  31. 31. Lesson OverviewLesson Overview Cell TransportCell TransportEndocytosis– Large molecules, clumpsof food, and even wholecells can be taken up byendocytosis.– Two examples ofendocytosis arephagocytosis andpinocytosis.
  32. 32. Lesson OverviewLesson Overview Cell TransportCell TransportEndocytosis– In phagocytosis, extensions ofcytoplasm surround a particle andpackage it within a food vacuole. Thecell then engulfs it.– Amoebas use this method for taking in food.– Engulfing material in this way requires aconsiderable amount of energy and, therefore, isa form of active transport.
  33. 33. Lesson OverviewLesson Overview Cell TransportCell TransportEndocytosis–In pinocytosis, cells take up liquid fromthe surrounding environment byforming tiny pockets along the cellmembrane.– The pockets fill with liquid and pinch off to form vacuoleswithin the cell.
  34. 34. Lesson OverviewLesson Overview Cell TransportCell TransportExocytosis• Many cells also release largeamounts of material from thecell, a process known asexocytosis.• During exocytosis,the membrane of thevacuole surroundingthe material fuseswith the cellmembrane, forcingthe contents out ofthe cell.

×