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Membrane Structure and Membrane Proteins Presenter: Mrs. Knopke FUHS Science Dept.

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Presentation on theme: "Membrane Structure and Membrane Proteins Presenter: Mrs. Knopke FUHS Science Dept."— Presentation transcript:

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2 Membrane Structure and Membrane Proteins Presenter: Mrs. Knopke FUHS Science Dept.

3 Fluid Mosaic Model of a Biological Membrane

4 Summary Section 2 – pages Water Plasma Membrane

5 Phospholipids: Hydrophobic Molecules fatty acid tails are sheltered from waterHydrophobic Molecules fatty acid tails are sheltered from water Hydrophilic molecules phosphate groups interact with water.Hydrophilic molecules phosphate groups interact with water.

6 Summary Section 2 – pages Structure of the Plasma Membrane The plasma membrane is composed of two layers of phospholipids back- to-back. The plasma membrane is composed of two layers of phospholipids back- to-back. Phospholipids are lipids with a phosphate attached to them.

7 Phospholipid Bi-layer The molecules in the bilayer are arranged such that the hydrophobic fatty acid tails are sheltered from water while the hydrophilic phosphate groups interact with water.The molecules in the bilayer are arranged such that the hydrophobic fatty acid tails are sheltered from water while the hydrophilic phosphate groups interact with water.

8 Summary Section 2 – pages The lipids in a plasma membrane have a glycerol backbone, two fatty acid chains, and a phosphate group. The lipids in a plasma membrane have a glycerol backbone, two fatty acid chains, and a phosphate group. Glycerol Backbone Two Fatty Acid Chains Phosphate Group

9 Summary Section 2 – pages Makeup of the phospholipid bilayer The phosphate group is critical for the formation and function of the plasma membrane. The phosphate group is critical for the formation and function of the plasma membrane. Phosphate Group

10 Summary Section 2 – pages Makeup of the phospholipid bilayer The fluid mosaic model The fluid mosaic model

11 Fluidity of Membranes Phospholipids in membranes are in a fluid state.Phospholipids in membranes are in a fluid state.

12 Summary Section 2 – pages Other components of the plasma membrane: Cholesterol plays the important role of preventing the fatty acid chains of the phospholipids from sticking together. Cholesterol Molecule

13 Membrane fluidity is influenced by temperature and by its constituents.Membrane fluidity is influenced by temperature and by its constituents. As temperatures cool, it maintains fluidity by preventing tight packing.As temperatures cool, it maintains fluidity by preventing tight packing. Membranes rich in unsaturated fatty acids are more fluid that those dominated by saturated fatty acids because the kinks in the unsaturated fatty acid tails prevent tight packing. Membranes rich in unsaturated fatty acids are more fluid that those dominated by saturated fatty acids because the kinks in the unsaturated fatty acid tails prevent tight packing. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.4b

14 The steroid cholesterol is wedged between phospholipid molecules in the plasma membrane of animals cells.The steroid cholesterol is wedged between phospholipid molecules in the plasma membrane of animals cells. At warm temperatures, it restrains the movement of phospholipids and reduces fluidity.At warm temperatures, it restrains the movement of phospholipids and reduces fluidity. At cool temperatures, it maintains fluidity by preventing tight packing.At cool temperatures, it maintains fluidity by preventing tight packing. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.4c

15 Membrane molecules are held in place by relativelyMembrane molecules are held in place by relatively weak hydrophobic interactions.weak hydrophobic interactions. Most of the lipids and some proteins can drift laterally in the plane of the membrane, but rarely flip-flop from one layer to the other.Most of the lipids and some proteins can drift laterally in the plane of the membrane, but rarely flip-flop from one layer to the other. Membranes are fluid Membranes are fluid Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.4a

16 Membrane Proteins and the Fluid Mosaic Model Some electron micrographs show the positionof proteins within membranes.Some electron micrographs show the positionof proteins within membranes. The proteins are seen to be dotted over the membraneThe proteins are seen to be dotted over the membrane This gives the membranes the appearance of a mosaic.This gives the membranes the appearance of a mosaic. Because the protein molecules float in the fluid phospholipid bilayer.Because the protein molecules float in the fluid phospholipid bilayer.

17 A specialized preparation technique, freeze-fracture, splits a membrane along the middle of the phospholid bilayer prior to electron microscopy.A specialized preparation technique, freeze-fracture, splits a membrane along the middle of the phospholid bilayer prior to electron microscopy. This shows protein particles interspersed with a smooth matrix, supporting the fluid mosaic model.This shows protein particles interspersed with a smooth matrix, supporting the fluid mosaic model. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.3

18 To work properly with active enzymes and appropriate permeability, membrane must be fluid, about as fluid as salad oil.To work properly with active enzymes and appropriate permeability, membrane must be fluid, about as fluid as salad oil. Cells can alter the lipid composition of membranes to compensate for changes in fluidity caused by changing temperatures.Cells can alter the lipid composition of membranes to compensate for changes in fluidity caused by changing temperatures. –For example, cold-adapted organisms, such as winter wheat, increase the percentage of unsaturated phospholipids in the autumn. – This allows these organisms to prevent their membranes from solidifying during winter. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

19 Summary Section 2 – pages Other components of the plasma membrane: Transport proteins allow needed substances or waste materials to move through the plasma membrane. Transport proteins allow needed substances or waste materials to move through the plasma membrane. Click image to view movie.

20 Proteins determine most of the membrane’s specific functions.Proteins determine most of the membrane’s specific functions. The plasma membrane and the membranes of the various organelles each have unique collections of proteins.The plasma membrane and the membranes of the various organelles each have unique collections of proteins. There are two populations of membrane proteins.There are two populations of membrane proteins. –Peripheral proteins are not embedded in the lipid bilayer at all. –Instead, they are loosely bounded to the surface of the protein, often connected to the other population of membrane proteins. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

21 –Integral proteins penetrate the hydrophobic core of the lipid bilayer, often completely spanning the membrane (a transmembrane protein). –Where they contact the core, they have hydrophobic regions with with nonpolar amino acids, often coiled into alpha helices. Where they are in contact with the aqueous environment, they have hydrophilic regions of amino acids.Where they are in contact with the aqueous environment, they have hydrophilic regions of amino acids. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.7

22 Membranes have distinctive inside and outside faces.Membranes have distinctive inside and outside faces. –The two layers may differ in lipid composition, and proteins in the membrane have a clear direction. –The outer surface also has carbohydrates. –This asymmetrical orientation begins during synthesis of new membrane in the endoplasmic reticulum. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.8

23 The proteins in the plasma membrane may provide a variety of major cell functions.The proteins in the plasma membrane may provide a variety of major cell functions. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.9

24 The membrane plays the key role in cell-cell recognition.The membrane plays the key role in cell-cell recognition. –Cell-cell recognition is the ability of a cell to distinguish one type of neighboring cell from another. –This attribute is important in cell sorting and organization as tissues and organs in development. –It is also the basis for rejection of foreign cells by the immune system. –Cells recognize other cells by keying on surface molecules, often carbohydrates, on the plasma membrane. Membrane carbohydrates are important for cell- cell recognition

25 Fluid Mosaic Model of a Biological Membrane

26 Membrane carbohydrates are usually branched oligosaccharides with fewer than 15 sugar units.Membrane carbohydrates are usually branched oligosaccharides with fewer than 15 sugar units. They may be covalently bonded either to lipids, forming glycolipids, or, more commonly, to proteins, forming glycoproteins.They may be covalently bonded either to lipids, forming glycolipids, or, more commonly, to proteins, forming glycoproteins. The oligosaccharides on the external side of the plasma membrane vary from species to species,The oligosaccharides on the external side of the plasma membrane vary from species to species, individual to individual, and even from cell type to cell type within the same individual. individual to individual, and even from cell type to cell type within the same individual. –This variation marks each cell type as distinct. –The four human blood groups (A, B, AB, and O) differ in the external carbohydrates on red blood cells. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

27 Section 2 Check Which of the following best describes the plasma membrane's mechanism in maintaining homeostasis? Which of the following best describes the plasma membrane's mechanism in maintaining homeostasis? Question 1 A. protein synthesis B. selective permeability C. fluid composition D. structural protein attachment CA: Biology/Life Sciences 1a

28 Section 2 Check The answer is B. Selective permeability is the process in which the membrane allows some molecules to pass through, while keeping others out. CA: Biology/Life Sciences 1a

29 Section 2 Check Describe the structure of the plasma membrane. Describe the structure of the plasma membrane. Question 2 CA: Biology/Life Sciences 1a

30 Section 2 Check The plasma membrane is composed of a phospholipid bilayer, which has two layers of phospholipids back-to- back. The polar heads of phospholipid molecules contain phosphate groups and face outward. The plasma membrane is composed of a phospholipid bilayer, which has two layers of phospholipids back-to- back. The polar heads of phospholipid molecules contain phosphate groups and face outward. CA: Biology/Life Sciences 1a

31 Section 2 Check Why is the phosphate group of a phospholipid important to the plasma membrane? Why is the phosphate group of a phospholipid important to the plasma membrane? Question 3 Polar head (includes phosphate group) Nonpolar tails (fatty acids) Phospholipid molecule CA: Biology/Life Sciences 1a

32 Section 2 Check When phospholipid molecules form a bilayer, the phosphate groups lie to the outside. Because phosphate groups are polar, they allow the cell membrane to interact with its watery (polar) environments inside and outside the cell. Polar head (includes phosphate group) Nonpolar tails (fatty acids) Phospholipid molecule CA: Biology/Life Sciences 1a

33 Section 2 Check Explain why the model of the plasma membrane is called the fluid mosaic model. Explain why the model of the plasma membrane is called the fluid mosaic model. Question 4 CA: Biology/Life Sciences 1a

34 Section 2 Check It is fluid because the phospholipid molecules move within the membrane. Proteins in the membrane that move among the phospholipids create the mosaic pattern. CA: Biology/Life Sciences 1a

35 Summary Section 2 – pages Early observations: Bownian motion In 1827, Scottish scientist Robert Brown used a microscope to observe pollen grains suspended in water. He noticed that the grains moved constantly in little jerks, as if being struck by invisible objects. This motion is now called Brownian motion. Today we know that Brown was observing evidence of the random motion of atoms and molecules.

36 Kinetic Energy Heat is kinetic energy while temperature is a measure of the average kinetic energy per particleHeat is kinetic energy while temperature is a measure of the average kinetic energy per particle E k = ½ MV 2E k = ½ MV 2 where E k = kinetic energy M= mass of the particle and V= the velocity of the particle.where E k = kinetic energy M= mass of the particle and V= the velocity of the particle.

37 Brownian motion Heat motion of small particles in waterHeat motion of small particles in water

38 Summary Section 2 – pages The process of diffusion Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. Diffusion results because of the random movement of particles (Brownian motion). Three key factors —concentration, temperature, and pressure—affect the rate of diffusion.

39 Terms CONCENTRAION of molecules in a fluid is the number of molecules of solute in a given unit of volumeCONCENTRAION of molecules in a fluid is the number of molecules of solute in a given unit of volume GRADIENT is the physical difference between two regions of space such that molecules tend to move from one region to the other. Ex. = pressure, concentration, and electrical chargeGRADIENT is the physical difference between two regions of space such that molecules tend to move from one region to the other. Ex. = pressure, concentration, and electrical charge

40 Summary Section 2 – pages The results of diffusion When a cell is in dynamic equilibrium with its environment, materials move into and out of the cell at equal rates. As a result, there is no net change in concentration inside or outside the cell. Material moving out of cell equals material moving into cell

41 Summary Section 2 – pages Diffusion in living systems The difference in concentration of a substance across space is called a concentration gradient. Ions and molecules diffuse from an area of higher concentration to an area of lower concentration, moving with the gradient. Dynamic equilibrium occurs when there is no longer a concentration gradient.

42 Diffusion - the movement of particles from an area of high concentration to an area of low concentration

43 Factors that affect speed of diffusion Molecular MassMolecular Mass Type of medium in which diffusion is occurringType of medium in which diffusion is occurring TemperatureTemperature Steepness of the concentration gradientSteepness of the concentration gradient

44 Section 8.1 Summary – pages The diffusion of water across a selectively permeable membrane is called osmosis.The diffusion of water across a selectively permeable membrane is called osmosis. Osmosis: Diffusion of Water Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within a cell.Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within a cell.

45 In which direction will water flow?

46 Tonicity

47 Section 8.1 Summary – pages Unequal distribution of particles, called a concentration gradient, is one factor that controls osmosis.Unequal distribution of particles, called a concentration gradient, is one factor that controls osmosis. What controls osmosis? Before Osmosis After Osmosis Water molecule Sugar molecule Selectively permeable membrane

48 An animal cell immersed in an isotonic environment experiences no net movement of water across its plasma membrane.An animal cell immersed in an isotonic environment experiences no net movement of water across its plasma membrane. Water flows across the membrane, but at the same rate in both directions.Water flows across the membrane, but at the same rate in both directions. –The volume the cell is no net movement of water across its plasma membrane. Cell survival depends on balancing water uptake and loss Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

49 Section 8.1 Summary – pages Most cells whether in multicellular or unicellular organisms, are subject to osmosis because they are surrounded by water solutions.Most cells whether in multicellular or unicellular organisms, are subject to osmosis because they are surrounded by water solutions. Cells in an isotonic solution H2OH2O H2OH2O Water Molecule Dissolved Molecule

50 The same cell is a hypertonic environment will loose water, shrivel, and probably die.The same cell is a hypertonic environment will loose water, shrivel, and probably die. A cell in a hypotonic solution will gain water, swell, and burst.A cell in a hypotonic solution will gain water, swell, and burst. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.12

51 For a cell living in an isotonic environment (for example, many marine invertebrates) osmosis is not a problem.For a cell living in an isotonic environment (for example, many marine invertebrates) osmosis is not a problem. –Similarly, the cells of most land animals are bathed in an extracellular fluid that is isotonic to the cells. Organisms without rigid walls have osmotic problems in either a hypertonic or hypotonic environment and must have adaptations for osmoregulation to maintain their internal environment.Organisms without rigid walls have osmotic problems in either a hypertonic or hypotonic environment and must have adaptations for osmoregulation to maintain their internal environment. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

52 Section 8.1 Summary – pages Cells in an isotonic solution In an isotonic solution, the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell.In an isotonic solution, the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell. H2OH2O H2OH2O Water Molecule Dissolved Molecule

53 Section 8.1 Summary – pages Cells in an isotonic solution In an isotonic solution, water molecules move into and out of the cell at the same rate, and cells retain their normal shape.In an isotonic solution, water molecules move into and out of the cell at the same rate, and cells retain their normal shape. H2OH2O H2OH2O Water Molecule Dissolved Molecule

54 Section 8.1 Summary – pages Cells in an isotonic solution A plant cell has its normal shape and pressure in an isotonic solution.A plant cell has its normal shape and pressure in an isotonic solution.

55 For example, Paramecium, a protist, is hypertonic when compared to the pond water in which it lives.For example, Paramecium, a protist, is hypertonic when compared to the pond water in which it lives. –In spite of a cell membrane that is less permeable to water than other cells, water still continually enters the Paramecium cell. –To solve this problem, Paramecium have a specialized organelle, the contractile vacuole, that functions as a bilge pump to force water out of the cell. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.13

56 The cells of plants, prokaryotes, fungi, and some protists have walls that contribute to the cell’s water balance.The cells of plants, prokaryotes, fungi, and some protists have walls that contribute to the cell’s water balance. An animal cell in a hypotonic solution will swell until the elastic wall opposes further uptake.An animal cell in a hypotonic solution will swell until the elastic wall opposes further uptake. –At this point the cell is turgid, a healthy state for most plant cells. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.12

57 Section 8.1 Summary – pages Cells in a hypotonic solution In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell.In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell. H2OH2O H2OH2O Water Molecule Dissolved Molecule

58 Section 8.1 Summary – pages Cells in a hypotonic solution Plant cells swell beyond their normal size as pressure increases.Plant cells swell beyond their normal size as pressure increases.

59 Turgid cells contribute to the mechanical support of the plant.Turgid cells contribute to the mechanical support of the plant. If a cell and its surroundings are isotonic, there is no movement of water into the cell and the cell flaccid and the plant may wilt.If a cell and its surroundings are isotonic, there is no movement of water into the cell and the cell flaccid and the plant may wilt. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.12

60 Section 8.1 Summary – pages Cells in a hypertonic solution In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink.In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink. H2OH2O H2OH2O Water Molecule Dissolved Molecule

61 In a hypertonic solution, a cell wall has no advantages.In a hypertonic solution, a cell wall has no advantages. As the plant cell looses water, its volume shrinks.As the plant cell looses water, its volume shrinks. Eventually, the plasma membrane pulls away from the wall.Eventually, the plasma membrane pulls away from the wall. This plasmolysis is usually lethal.This plasmolysis is usually lethal. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.12

62 Section 8.1 Summary – pages Cells in a hypertonic solution Plant cells lose pressure as the plasma membrane shrinks away from the cell wall.Plant cells lose pressure as the plasma membrane shrinks away from the cell wall.

63 Turgor Pressure Turgor pressure occurs when the central vacuole fills and applies pressure to the cell wall.Turgor pressure occurs when the central vacuole fills and applies pressure to the cell wall.

64 Section 8.1 Summary – pages Passive Transport When a cell uses no energy to move particles across a membrane passive transport occurs.When a cell uses no energy to move particles across a membrane passive transport occurs. Concentration gradient Plasma membrane

65 Section 8.1 Summary – pages Passive Transport by proteins Passive transport of materials across the membrane using transport proteins is called facilitated diffusion.Passive transport of materials across the membrane using transport proteins is called facilitated diffusion. Plasma membrane Channel proteins Concentration gradient

66 Section 8.1 Summary – pages Passive Transport by proteins Some transport proteins, called channel proteins, form channels that allow specific molecules to flow through.Some transport proteins, called channel proteins, form channels that allow specific molecules to flow through. Plasma membrane Channel proteins Concentration gradient

67 Section 8.1 Summary – pages Passive transport by proteins The movement is with the concentration gradient, and requires no energy input from the cell.The movement is with the concentration gradient, and requires no energy input from the cell. Concentration gradient Plasma membrane Step 1Step 2 Carrier proteins

68 Section 8.1 Summary – pages Passive transport by proteins Carrier proteins change shape to allow a substance to pass through the plasma membrane.Carrier proteins change shape to allow a substance to pass through the plasma membrane. Concentration gradient Plasma membrane Step 1Step 2 Carrier proteins

69 Section 8.1 Summary – pages Passive transport by proteins In facilitated diffusion by carrier protein, the movement is with the concentration gradient and requires no energy input from the cell.In facilitated diffusion by carrier protein, the movement is with the concentration gradient and requires no energy input from the cell. Plasma membrane Step 1Step 2 Carrier proteins Concentration gradient

70 Section 8.1 Summary – pages Active Transport Movement of materials through a membrane against a concentration gradient is called active transport and requires energy from the cell.Movement of materials through a membrane against a concentration gradient is called active transport and requires energy from the cell. Plasma membrane Concentration gradient Carrier proteins Cellular energy Step 1Step 2

71 Section 8.1 Summary – pages How active transport occurs In active transport, a transport protein called a carrier protein first binds with a particle of the substance to be transported.In active transport, a transport protein called a carrier protein first binds with a particle of the substance to be transported. Plasma membrane Concentration gradient Carrier proteins Cellular energy Step 1Step 2

72 Section 8.1 Summary – pages How active transport occurs Click image to view movie.

73 Section 8.1 Summary – pages How active transport occurs Each type of carrier protein has a shape that fits a specific molecule or ion.Each type of carrier protein has a shape that fits a specific molecule or ion. Plasma membrane Concentration gradient Carrier proteins Cellular energy Step 1Step 2

74 Section 8.1 Summary – pages How active transport occurs When the proper molecule binds with the protein, chemical energy allows the cell to change the shape of the carrier protein so that the particle to be moved is released on the other side of the membrane.When the proper molecule binds with the protein, chemical energy allows the cell to change the shape of the carrier protein so that the particle to be moved is released on the other side of the membrane. Step 1Step 2 Carrier proteins Cellular energy Plasma membrane Concentration gradient

75 Section 8.1 Summary – pages How active transport occurs Once the particle is released, the protein’s original shape is restored.Once the particle is released, the protein’s original shape is restored. Step 1Step 2 Carrier proteins Cellular energy Plasma membrane Concentration gradient Active transport allows particle movement into or out of a cell against a concentration gradient.Active transport allows particle movement into or out of a cell against a concentration gradient.

76 Section 8.1 Summary – pages How active transport occurs Click image to view movie.

77 Section 8.1 Summary – pages Transport of Large Particles Endocytosis is a process by which a cell surrounds and takes in material from its environment.Endocytosis is a process by which a cell surrounds and takes in material from its environment. Endocytosis Exocytosis Digestion Nucleus Wastes

78 Section 8.1 Summary – pages Transport of Large Particles The material is engulfed and enclosed by a portion of the cell’s plasma membrane.The material is engulfed and enclosed by a portion of the cell’s plasma membrane. Exocytosis Digestion Nucleus Wastes Endocytosis

79 Section 8.1 Summary – pages Transport of Large Particles The resulting vacuole with its contents moves to the inside of the cell.The resulting vacuole with its contents moves to the inside of the cell. Exocytosis Digestion Nucleus Wastes Endocytosis

80 Section 8.1 Summary – pages Transport of Large Particles Exocytosis is the expulsion or secretion of materials from a cell.Exocytosis is the expulsion or secretion of materials from a cell. Endocytosis Exocytosis Digestion Nucleus Wastes

81 Section 8.1 Summary – pages Transport of Large Particles Endocytosis and exocytosis both move masses of material and both require energy.Endocytosis and exocytosis both move masses of material and both require energy. EndocytosisExocytosis Digestion Nucleus Wastes

82 Section 1 Check Question 1 B. endocytosis A. active transport The diffusion of water across a selectively permeable membrane is called __________. The diffusion of water across a selectively permeable membrane is called __________. Water molecule Sugar molecule Selectively permeable membrane CA: Biology/Life Sciences 1a

83 Section 1 Check Question 1 D. osmosis C. exocytosis The diffusion of water across a selectively permeable membrane is called __________. The diffusion of water across a selectively permeable membrane is called __________. Water molecule Sugar molecule Selectively permeable membrane CA: Biology/Life Sciences 1a

84 Section 1 Check The answer is D, osmosis. Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within the cell. Water molecule Sugar molecule Selectively permeable membrane Before osmosisAfter osmosis CA: Biology/Life Sciences 1a

85 Section 1 Check What is the expected result of having an animal cell in a hypertonic solution? What is the expected result of having an animal cell in a hypertonic solution? Question 2 D. The cell retains its normal shape. C. The cell swells up. A. The cell shrivels up. B. The plasma membrane shrinks away from the cell wall. the cell wall. CA: Biology/Life Sciences 1a

86 Section 1 Check The answer is A. In a hypertonic solution, cells experience osmosis of water out of the cell. Animal cells shrivel because of decreased pressure in the cells. H2OH2O H2OH2O Water molecule Sugar molecule CA: Biology/Life Sciences 1a

87 Section 1 Check A grocer mists the celery display with water to keep it looking fresh. What type of solution is the celery now in? A grocer mists the celery display with water to keep it looking fresh. What type of solution is the celery now in? Question 3 D. exotonic C. hypertonic B. hypotonic A. isotonic CA: Biology/Life Sciences 1a, 1j

88 Section 1 Check The answer is B. Plant cells contain a rigid cell wall and do not burst even in a hypotonic solution. CA: Biology/Life Sciences 1a, 1j

89 Plasma membrane Section 1 Check Transport of materials across the plasma membrane that does not require energy from the cell but does use transport proteins is called __________. Transport of materials across the plasma membrane that does not require energy from the cell but does use transport proteins is called __________. Question 4 B. simple diffusion A. osmosis Concentration gradient Channel proteins CA: Biology/Life Sciences 1a

90 Section 1 Check Transport of materials across the plasma membrane that does not require energy from the cell but does use transport proteins is called __________. Transport of materials across the plasma membrane that does not require energy from the cell but does use transport proteins is called __________. Question 4 D. active transport C. facilitated diffusion Plasma membrane Concentration gradient Channel proteins CA: Biology/Life Sciences 1a

91 Section 1 Check The answer is C. Facilitated diffusion is a type of passive transport and requires no energy from the cell. Plasma membrane Concentration gradient Channel proteins CA: Biology/Life Sciences 1a


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