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B9-10 Cell Membranes

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  • 1. Unit B 9 & 10: Cell Biology (Transport Across Cell Membrane) Authored by Michelle Choma ©
    • Students who have fully met the prescribed learning outcomes (PLO’s) are able to:
    • B9. Analyze the structure and function of the cell membrane.
        • apply knowledge of organic molecules – including phospholipids, proteins, glycoproteins, glycolipids, carbohydrates, and cholesterol – to explain the structure and function of the fluid-mosaic membrane model.
  • 2. Analyze the structure and function of the cell membrane. (continued)
        • identify the hydrophobic and hydrophilic regions of the phospholipid bilayer.
        • explain why the cell membrane is described as “selectively permeable”.
        • describe passive transport processes including diffusion, osmosis, and facilitated transport.
        • explain factors that affect the rate of diffusion across a cell membrane (e.g., temperature, size of molecule, charge of molecule, concentration gradient, pressure gradient).
        • predict the effects of hypertonic, isotonic, and hypertonic environments on osmosis in animal cells.
  • 3. And a little bit more….
      • describe active transport processes including active transport, endocytosis (Phagocytosis and pinocytosis), and exocytosis.
      • compare specific transport processes – including diffusion, osmosis, facilitated transport, active transport, endocytosis and exocytosis – in terms of:
          • concentration gradient
          • use of channel or carrier protein
          • use of energy
          • types/sizes of molecules transported
      • devise an experiment using the scientific method (e.g. to investigate the tonicity of cells). Spud Lab!
  • 4. B10. Explain why cells divide when they reach a particular surface area-to-volume ratio.
    • differentiate between cells that have a high or low surface area-to-volume ratio.
    • demonstrate an understanding of the significance of surface-area-to-volume ratio in cell size.
      • Short one eh!?
  • 5. Web Sites for Cell Transport
    • http:// www.coolschool.ca/content/available_courses.php (Unit 04) Scroll to Lesson 01 – Lesson 08 (‘U04L01 – L08’)
    • http://highered.mcgraw-hill.com/sites/0072421975/student_view0/chapter4/ (Mader’s Student Edition Website Support for Chapter 4; Animations, quizzes, flashcards, Thinking Scientifically etc.)
    • http://www.mhhe.com/biosci/genbio/espv2/data/cells/003/index.html (Essential Study Partner: CM & Cell Transport)
    • http://www.ibiblio.org/virtualcell/textbook/chapter3/cms1.htm (Cell membrane structure text & animation)
  • 6. More websites
    • http://sps.k12.ar.us/massengale/biology%20class%20notes2.htm (A terrific site with animations, self-quiz, notes etc. Click on the various notes for Effect of Solutions on Cells, Web Tutorials on Passive & Active Transport, Scientific Method, and Designing an Experiment )
    • http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm (Animation of Cell Transport)
    • http://curriculum.calstatela.edu/courses/builders/lessons/less/les4/cellsize.html (Limits to Cell Size)
  • 7. And a few more
    • http://science.nhmccd.edu/biol/bio1int.htm
    • http://sps.k12.ar.us/massengale/pwpt_biology.htm
    • (Terrific power points on Scientific Method and Identifying Controls & Variables )
    • www.emc.maricopa.edu/.../BioBooktransp.html
    • http://fig.cox.miami.edu/~cmallery/150/memb/membrane s.htm
    • http://www.citruscollege.edu/apps/pub.asp?Q=808&T=Tutoring%20Services&B=4
  • 8. B9 - Cell Membrane Structure
    • Introduction
    • The ‘fluid-mosaic model’ is a model that describes the structures of the CM, i.e. a fluid lipid layer in a mosaic made up of many different types of molecules. Cell membranes include a flexible bilayer of phospholipids interspersed with large protein molecules that aid in membrane transport and cholesterol for rigidity.
  • 9.  
  • 10.  
  • 11.  
  • 12.  
  • 13.  
  • 14. 1.) Phospholipid bilayer
    • Make up the basic structural unit of the cell membrane.
    • Contains a charged polar head ( hydrophilic /‘H 2 O- loving’) and non-polar , fat-soluble tails ( hydrophobic /‘H 2 O-fearing’).
    • Fluid-like consistency.
  • 15. Phospholipid bilayer
    • Functions
    • Allows lipid-soluble molecules such as alcohol, O 2 , CO 2 and lipid soluble molecules, i.e. lipids, steroids, (and vitamins A & E) to pass through the phospholipid bilayer.
    • Provides flexibility and fluidity thus allowing vesicles to form.
    • Prevents non-lipid soluble molecules , e.g. water, ions, amino acids and monosaccharides to pass through.
  • 16. Note: Lack of permeability to ions sets up membrane potential (See C11: Nerve transmission).
  • 17. 2.) Proteins
    • Form a “mosaic” pattern/scattered throughout the phospholipid bilayer.
    • Largely determine the cell membrane’s functions.
    • Embedded in cell membrane and on the surfaces; 3 o structures act as carriers, pumps, channels, receptors and cell recognition proteins.
  • 18. Proteins
    • Functions
    • Some act as carriers bringing amino acids , ions , and glucose in/out, e.g. Na+/K+ pump in nerve transmission; protein carriers bringing in glucose for RBC’s; or concentrating molecules/ions inside or outside of cell, e.g. nerve cells actively pumping Na+ & K+ or thyroid cells concentrating iodine.
  • 19.  
  • 20. Some have channels/gates/pores to allow passage of H 2 O, dissolved ions, and small molecules.
  • 21. Some are receptors that a specific molecule can bind to, e.g. hormones such as insulin, thyroxin, aldosterone, estrogen, testosterone etc. or neurotransmitters such as acetylcholine (ACh), norepinephrine (NE). http://www.mhhe.com/biosci/genbio/espv2/data/cells/003/index.html
  • 22. 3.) Glycoproteins and Glycolipids
    • Attached to outside of cell membrane
    • * NOT found on intra-cellular membranes (e.g. mitochondria, ER, Golgi, etc.)
    • Made up of carbohydrate-chains attached to a phospholipid head or a protein.
    • Function : - Serves as recognition sites allowing organisms to recognize foreign cells/molecules.
  • 23. 4.) Cholesterol
    • Abundant lipids found wedged between the phospholipids.
    • Function : - Stiffen CM and provides more flexibility.
  • 24.  
  • 25. Note: Cytoskeleton (Recall Unit B1) is an internal framework of protein fibres that gives the cytoplasm strength and flexibility and provides movement of organelles. Some protein filaments attaches to the integral proteins of the CM. Attachment of the Cytoskeleton
  • 26.  
  • 27.  
  • 28. Summary of Cell Membrane Structures and Functions Amino acids Allows/selects certain molecules in/out of cell through channels/gates/pores . E.g. H 2 O, O 2 , CO 2 , ions. Carries molecules selectively in/out of cell by carriers. E.g. Na + , K + , C 6 H 12 O 6 , áá’s, HCO 3 - , Ca 2+ . Proteins Unit molecules Functions Molecules
  • 29. Protein Function Cont
    • Catalyzes reactions on cell surface by enzymatic proteins. E.g. Enzymes for ATP metabolism or breakdown of ATP for Na+ transport.
    • Provides receptor sites by receptor proteins. E.g. Hormones having the same shape as receptor proteins to bind to it.
  • 30. Backbone of 4 fused C-H rings Stiffen CM and provide flexibility Cholesterol Chains of carbohydrates attached to lipid or protein (a) Used in cell identification . (b) Glycoproteins can form a carbohydrate coat that envelops the cell membrane (glycocalyx). Glycolipids and Glycoproteins 2 fatty acids (saturated/ unsaturated) & 1 glycerol, N and phosphate group (a) Allows for diffusion of lipid soluble molecules. E.g. O 2 , CO 2 , and alcohol. (b) Allows for flexibility & fluidity of cell membrane. E.g. Vesicle formation. (c) Excludes H 2 O and ions. (d) Acts as a boundary keeping organelles within the cell. Phospholipids
  • 31. B9 – Selectively Permeable Cell Membrane
    • Cell membrane is described as selectively permeable because it allows only certain molecules or ions to pass through it, i.e. it limits what can move across.
  • 32. *Functions of Cell Membrane
    • Regulates the exit/entrance of molecules/ions via pinocytosis/phagocytosis/endocytosis/exocytosis.
    • Regulates the exit/entrance of molecules/ions via diffusion/facilitated transport/active transport/osmosis.
    • Used in cell identification via glycoproteins and glycolipids.
    • Catalyzes reactions on the cell surface via enzymatic proteins.
    • Provides receptor sites via receptor proteins for certain molecules.
    • Acts as a cell boundary keeping the organelles within the cell.
  • 33. B9 – Entrance/Exit of Molecules
    • Introduction: Terms to know
    • Solvent - the dissolving agent, usually H 2 O.
    • Solute - molecules, ions dissolved in the solvent.
    • Concentration - # of molecules in a given unit of volume.
    • Gradient - the physical difference between two regions which cause molecules to move from one region to the other and tends to equalize the difference.
    • Concentration gradient - the difference in solute concentration between two regions resulting in molecular movement.
    • Osmotic pressure - pressure generated by H 2 O moving by osmosis into or out of a cell.
  • 34. Note---ie. Pay Attention!!
    • Osmotic pressure always moves water toward the hypertonic side (the side containing the least amount of water) of a membrane.
  • 35.  
  • 36. Some more terms….
    • Hydrostatic pressure – pressure exerted by the weight of H 2 O/fluid pushing against a surface, e.g. capillary.
    • Tonicity - total solute concentration of the solution outside the cell; causes the cell to gain or lose H 2 O.
    • Turgor (‘to swell’)- the rigid state of a cell (especially plants) caused by osmotic pressure of the cytoplasm against the cell wall or membrane.
  • 37. There are two main categories of transport across selectively permeable membranes:
    • 1.) Passive transport
    • Movement of molecules from [high] to [low] (along a concentration gradient).
    • Does not require energy; some use specific CM proteins; does not use vesicles; involves movement of small molecules, water (osmosis), ions, C 6 H 12 O 6 , amino acids, fatty acids.
  • 38.  
  • 39. Second type of transport
    • 2.) Active transport
    • Movement of molecules from [low] to [high] and energy (ATP) is required (against a concentration gradient).
    • Requires energy; uses carrier or receptor proteins; can use vesicle formation; involves movement of small & large molecules, ions, cells, microorganisms.
  • 40.  
  • 41. Passive Transport
    • Materials/molecules can move by 3 processes:
      • (a) Diffusion .
      • (b) Facilitated transport/diffusion .
      • (c) Osmosis .
  • 42. Diffusion
  • 43. Osmosis
  • 44. examples of lab equipment which demonstrate diffusion and osmosis, i.e. the osmometer and U-tube apparatus .
  • 45.  
  • 46.  
  • 47.  
  • 48.  
  • 49.  
  • 50. Diffusion
    • Net movement of molecules/ions from an area of [ high ] to [ low ].
    • Requires no energy and molecules must be lipid soluble .
    • Large molecules, proteins, polysaccharides, nucleic acids, and charged ions cannot diffuse across.
    • Small, uncharged molecules (CO 2 , O2) can enter easily, e.g. O 2 and CO 2 diffuse across membranes of alveoli (See C10); H 2 O as well via channel proteins/ “ aquaporins ” (osmosis).
  • 51. Diffusion Continued
    • C 6 H 12 O 6 , amino acids, fatty acids and ions diffuse via CM proteins, e.g. neurotransmitters (NT’s) diffusing across the synaptic cleft during nerve impulses/synapse OR
    • Ca 2+ diffusing across the presynaptic membrane during nerve impulses/synapse (See C11); monomers diffusing into epithelial cells of villi (See C1).
  • 52. Animations
    • http://www.coolschool.ca/lor/BI12/unit4/U04L03/diffusion.swf
    • http://highered.mcgraw-hill.com/sites/0072421975/student_view0/chapter4/animations__english_.html (Diffusion)
    • http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm
  • 53.  
  • 54. Facilitated Transport/Diffusion
    • Net movement of molecules from an area of [ high ] to [ low ] using carrier proteins to get across the cell membrane.
    • Requires no ATP .
    • Involves protein carriers that are highly specific to the substance and transports it at a faster rate .
    • E.g. C 6 H 12 O 6 , sucrose, amino acids and ions insoluble in the lipid bilayer can be transported along a concentration gradient across the cell membrane using a carrier protein to enter quickly.
  • 55.  
  • 56. Osmosis (See diagrams and worksheet)
    • Net diffusion of H 2 O only from [high] to [low] across a cell membrane via CM proteins (channel proteins/“ aquaporins ”).
    • OR
    • Net diffusion of H 2 O from an area of [lower solute] to [higher solute] across a cell membrane via CM proteins (channel proteins/“ aquaporins ”).
  • 57.  
  • 58.  
  • 59. Animations
    • http://www.phschool.com/science/biology_place/labbench/lab1/osmosis.html
    • http://www.coolschool.ca/lor/BI12/unit4/U04L03/osmosis.swf
    • http://www.coolschool.ca/lor/BI12/unit4/U04L06/rbc.html (interactive RBC)
    • http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm
  • 60.  
  • 61. Osmosis
    • There are three conditions of tonicity/osmosis:
      • i) Isotonic (“equal solute and H 2 0”)
      • ii) Hypotonic (“less solute, more H 2 0”)
      • iii) Hypertonic (“more solute, less H 2 0”)
  • 62. Isotonic If the concentration of solute (salt) is equal on both sides, water will move back in forth but it won't have any result on the overall amount of water on either side. " ISO " means the same.
  • 63. Hypotonic " HYPO " means less. There are less solute (salt) molecules outside the cell, which causes water to move into the cell by osmosis (high to low). The cell will gain water & grow larger. In plant cells, the central vacuole will fill and the plant becomes stiff and rigid, i.e. turgor. The cell wall keeps the plant from bursting. In human animal cells, the cell is in danger of lysis or bursting.
  • 64. Hypertonic
  • 65. Hypertonic
    • " HYPER " means more. There are more solute (salt) molecules outside the cell, which causes the water to leave the cell by osmosis (high to low).
    • In plant cells, the central vacuole loses water; the cells shrink, i.e. plasmolysis causing wilting.
    • In animal cells, the cells also shrink. In both cases, the cell may die.
    • It is dangerous to drink sea water. People marooned at sea will speed up dehydration (and death) by drinking sea water. This is also why "salting fields" was a common tactic during war, it would kill the crops, thus causing food shortages.
  • 66. Isotonic:
    • iso – equal tonicity – solute
    • The solution has the same/equal [solute] as the [solute] inside the cell.
    • This results in the cell not gaining or losing H 2 O.
  • 67. Isotonic 95% H 2 0 5% salt 95% H 2 O 5% salt Isotonic Solution 95% H 2 O 5% salt H 2 O moves in/out of red blood cells (RBC) at equal rates and the shape remains as biconcave.
  • 68. Hypotonic:
    • hypo – less tonicity – solute
    • The solution has a lower [solute] than the [solute] inside the cell.
    • This results in the movement of water (osmosis) INTO the cell causing it to swell and burst causing lysis .
  • 69. Hypotonic
    • H 2 O moves into the RBC by osmosis, causing it to swell and lysis to occur.
    95% H 2 0 5% salt 98% H 2 O 2% salt Hypotonic Solution
  • 70.  
  • 71. Example of a RBC placed in a hypotonic solution . RBC shape in the beginning of the experiment? After 2 minutes?
  • 72. Hypertonic:
    • hyper – more tonicity – solute
    • The solution has a highe r [solute] than the [solute] inside the cell.
    • This results in the movement of water (osmosis) OUT of the cell causing it to shrivel or in the case of RBC’s, crenation occurs; in plant cells, plasmolysis occurs.
  • 73. Hypertonic H 2 O moves OUT of the RBC’s by osmosis causing it to shrivel and undergo crenation .
  • 74. Hypertonic
    • In plant cells , H 2 O moves OUT of the cytoplasm by osmosis causing the cell membrane to pull away from the cell wall. This is termed plasmolysis .
  • 75.  
  • 76. Active Transport
    • Movement of molecules from an area of [low] to [high] (against [gradient]) using ATP and a protein carrier in cell membrane.
  • 77.  
  • 78. Active Transport Cont.
    • E.g. Thyroid gland cells accumulates iodine from the blood against a [gradient] OR cells in intestine absorbing C 6 H 12 O 6 and concentrating in the blood against a [gradient] OR amino acids entering the blood from specific cells of the nephron OR cells of the nephron absorbing Na+ from the filtrate.
  • 79. Active Transport
    • Proteins involved are often called pumps *.
    • E.g. Na+/K+ pumps in neurons. Protein ‘pumps’ Na+ across cell membrane against [gradient] and also moves K+ across cell membrane against [gradient], and thus maintains the resting potential and recovery during nerve transmission (See C11).
  • 80.  
  • 81. Animations:
    • http://www.coolschool.ca/lor/BI12/unit4/U04L03/active
    • %20transport_jeffedit.swf
    • http://highered.mcgraw-hill.com/sites/0072421975/student_view0/chapter4/animations__english_.html (Na+/K+ pump)
  • 82.  
  • 83. More on Active Transport
    • Active transport also involves the movement of materials into/out of the cell using ATP, BUT do not cross through the lipid bilayer. Instead, portions of the lipid bilayer membrane engulf items being moved into or fuse with a membrane-bound sac to get out of the cell.
    • ATP energy is used to alter the shape of the membrane surface.
  • 84. Two types
    • There are two types of this style of active transport:
      • (a) Endo cytosis (in)
      • (b) Exo cytosis (out)
  • 85.  
  • 86.  
  • 87. Cellular Activity/Process?
  • 88. A. Endocytosis:
    • (‘endo’ = within; ‘cytosis’ = cell)
    • Movement of particles/macromolecules into the cell. The cell membrane invaginates around the particles, pinches off forming a membrane-bound vesicle; requires ATP .
      • E.g. Removal of worn out red blood cells from blood, or invading microbes etc. or cholesterol synthesized in the liver are packaged as LDL’s (low density lipoproteins + cholesterol/’bad cholesterol’), get released into the blood and then re-enter body cells by endocytosis .
  • 89. Animation:
    • http://www.coolschool.ca/lor/BI12/unit4/U04L05/endocytosis_final.html
    • http://highered.mcgraw-hill.com/sites/0072421975/student_view0/chapter4/animations__english_.html (Animation of Endocytosis & Exocytosis )
  • 90. Endocytosis
    • There are two types based on the materials enclosed:
      • Pinocytosis and Phagocytosis .
  • 91.  
  • 92.  
  • 93. Phagocytosis (“cell eating”)
    • Movement of cells , organelles ,
    • microorganisms , or solids into the cell by the cell membrane invaginating, pinching off forming a vesicle/vacuole enclosing the large particle.
      • E.g. Liver cells engulfing worn out red blood cells; white blood cells/macrophages/neutrophils engulfing bacteria.
  • 94.  
  • 95. ii) Pinocytosis (“cell drinking”)
    • Movement of molecules in solution into the cell by the cell membrane invaginating, pinching off forming a vesicle enclosing the liquid and dissolved molecules.
      • E.g. Small intestine epithelial cells engulfing fat droplets; body cells engulfing polypeptide molecules.
  • 96. B. Exocytosis:
    • (‘exo’ = exit; ‘cytosis’ = cell)
    • Movement of macromolecules out the cell. Membrane-bound vesicles move to the cell membrane, fuse and discharges the molecules; requires ATP .
      • E.g. Secretory vesicle containing insulin (hormone) OR a protein from Golgi apparatus fusing with the cell membrane OR salivary amyl ase made in salivary glands act in the mouth and pancreatic enzymes act in the small intestine OR neuron cells secreting noradrenaline (neurotransmitter) into the synaptic cleft (See C11).
  • 97.  
  • 98.  
  • 99.  
  • 100.  
  • 101. Ions, sugars, and amino acids. Carrier protein and ATP energy towards higher concentration active Active Transport Water 0nly. Concentration gradient, channel proteins optional towards lower concentration passive Osmosis Water, glucose, and amino acids. Concentration gradient, plus channel or carrier proteins towards lower concentration passive Facilitated Diffusion Water, gases (0 2 and CO 2 ), and steroid hormones. Concentration gradient towards lower concentration passive Diffusion   Examples Conditions Direction of Movement Type of Transport Name Comparison of the ways molecules move into & out of cells.
  • 102. B9 - Factors Which Affect Movement of Molecules
    • 1.) Temperature
      • -Increase of temperature increases the speed of molecules/molecular movement.
      • -Decrease of temperature decreases the speed of molecules/molecular movement.
    • 2.) Molecular size/mass
      • Larger molecules move slower because of molecular weight.
  • 103. More factors
    • 3.) Chemical Composition
      • E.g. Chemically, lipid soluble molecules are able to pass through the phosopholipid bilayer while other non-lipid molecules are unable to pass through easily.
    • 4.) Concentration/tonicity
      • Molecules tend to distribute themselves equally over time when there is a difference between 2 regions/sides of the membrane (concentration gradient).
      • Decreasing [gradient], decreases the rate of diffusion and vice versa.
    • 5.) Viscosity
      • The “thicker” the fluid, the slower the molecules can pass through.
  • 104. And Some More
    • 6.) Pressure
      • E.g. Blood pressure, atmospheric pressure or osmotic pressure can “force” the movement of molecules as a result of the gradient/differences.
    • 7.) Specific Hormonal Effects
      • E.g. ADH (anti-diuretic hormone) affects water reabsorption in kidney cells; thyroxin effects oxygen uptake in body cells; insulin causes liver and muscle cells to become permeable to glucose.
  • 105. And some more factors
    • 8.) Number of Protein Pores, Carriers
      • The greater number of protein pores and carriers allows faster and more numerous molecular movements.
    • 9.) Chemical and Physical Properties of CM
      • Permeability of molecules is affected by the hydrophobic and hydrophilic properties of the phospholipid bilayer and the scattered proteins.
    • 10.) Electrical Charge
      • Ions or molecules with a charge cannot pass through the lipid bilayer by diffusion. Other mechanisms involving protein carriers and ATP energy are required, e.g. the Na+/K+ ion pump transport mechanism.
  • 106. Summary of Passive VS Active
    • Passive Transport
    • (a) Diffusion of CO 2 , O 2 , glycerol, fatty acids, steroid hormones from an area of [high] outside the cell to an area of [low] inside the cell
    • Active Transport -Na+/K+ pumps on nerve cells.
    • C 6 H 12 O 6 & amino acids from intestines enters the blood.
    • C 6 H 12 O 6 & amino acids from kidney nephrons enters the blood.
    • Iodine from blood & concentrates in thyroid gland
  • 107. More comparison
    • Passive
    • (b) Osmosis of H 2 0, from [high] to [low].
    • (c) Facilitated transport of C 6 H 12 O 6 & amino acids entering quickly from [high] to [low] using protein carriers.
    • No ATP.
    • Some use protein carriers, channel proteins
    • Moves with the [gradient].
    • Movement of lipid soluble molecules, gases, & H 2 0.
    • Active
    • Endo/exocytosis of macromolecules using vesicles.
    • Phago/pinocytosis using vesicles.-
    • Requires ATP to form vesicle.
    • Uses protein carriers.
    • Moves against the [gradient] & requires ATP.
    • Movement of ions, large molecules, cells, molecules in fluid via vesicles.
  • 108. Devise an Experiment Using the Scientific Method and Interpreting Data and Graphs
    • See provincial diagrams, data, graphs, “Potato lab”, class worksheets AND web link resources.
    • Note: The Potato Lab/Solute Concentration of Potato Cells will be performed over 1.5 days and a lab report (includes data sheet, graphs, questions & conclusion) will be evaluated. It is expected that you review the Scientific Method in order to understand the sequential steps of this controlled experiment. See text…..p. 10-13.
    • Demonstrating your comprehension of Experimental Design is covered in detail in A1. This is a new unit! You can preview this at:
    • http://www.bced.gov.bc.ca/exams/specs/grade12/bi/07_experimental_design.pdf
  • 109. Terms to know for Experimental Design and the Potato Lab include:
    • conclusion dependent variable independent variable control group experimental group procedure
    • control hypothesis sample size validity reliability experimental variable
    • http://www.coolschool.ca/lor/BI11/unit1/U01L04.htm
    • (Review of Scientific Method)
  • 110. Experimental Design Terms to Clarify
    • Sample Size
      • The specific number of the group or groups (plants, animals, bacteria etc.) being studied. Generally, the larger the sample size, the more reliable the study results , and the more likely it is that the results can be applied to larger groups of people.
    • Independent variable
      • When a variable is manipulated by an experimenter.
      • (graph this on the X-axis)
  • 111. Dependent variable
    • The experiment observes the effect of the independent variable, i.e how a variable changed or responded to the independent variable.
    • (graph this on the Y-axis)
    • In general the independent variable is manipulated by the experimenter & its effects on the dependent variable are measured.
  • 112. Control Group or a “control”
    • The group that does not include the variable being tested (all other factors remain the same; are unchanged or controlled) and is used as a comparison with the experimental group.
  • 113. Example
    • A. Your Observation!
    • A study indicates that antioxidants found in blueberries may slow down the process of aging. Wow!
    • B. Hypothesis? (An educated guess/possible answer to the observation)
    • If…………………………….then…………
  • 114. Example cont.
    • In this study, 19-month old rats (equivalent to 60-year old humans) were fed either a standard diet or a diet supplemented by either blueberry, strawberry, or spinach powder. After eight weeks, the rats were given memory and motor tests. Although all supplemented rats showed improvement, those supplemented with blueberry powder showed the most notable improvement.
  • 115. Testing
    • C. Test the hypothesis by designing an experiment! It will support or reject the hypothesis.
    • For a valid and reliable experiment it must include an experimental group testing one variable or factor, control group , sample size , collect data , repeatable ….
  • 116.
    • What is the independent variable (manipulated/changed variable)?
      • (diet: blueberries or no blueberries)
    • What are the dependent variable(s) ? (measured variable)
      • (memory test and motor skills test)
    • Control group? Experimental group?
    • Sample Size?
  • 117. And Finally
    • D. Conclusion?
    • E. Repeat the experiment to validate your experiment & collect similar data.
  • 118. B10 - Cell Size and Surface Area to Volume Relationship
    • Cells are roughly cuboidal or spherical in shape and are limited in size by the ratio between surface area and volume (SA/V) ; cells divide when they reach a certain surface area-to-volume ratio.
    • The volume of a cell is related to the amount of chemical activity within the cell and the surface area of the cell limits the exchange of nutrients, gases and waste products with its environment.
  • 119. SA/Volume Ratio
    • The following diagram shows how increasing
    • cell size affects the SA/V . As a cell grows larger, its rate of producing wastes and requiring nutrients increases faster than the surface area through which molecules must exit and enter. Volume increases by the cube, while surface area increases by the square. As a cell grows larger, its surface area becomes too small to maintain life functions. Cells remain small and therefore maintain a large surface-area-to volume ratio
  • 120. SA/Volume
    • Note: As the cell increases in size, the SA/V ratio decreases (the V ↑ faster than the SA, i.e. cubed function vs. squared function). There is less surface (CM) to meet the needs of the volume (chemical activity within the cytoplasm & organelles). If chemical reactions within the cytoplasm cannot be supplied with nutrients or remove wastes, the cell will die OR it can divide into two cells and thus obtain a favourable, i.e. large SA/V ratio .
  • 121.
    • The important point is that the surface area to the volume ratio gets smaller as the cell gets larger .
  • 122.
    • In summary, increasing cell size results in a decrease in the SA/V ratio for the cell. This reduction in the SA/V ratio combined with the increased distance to the cell center makes diffusion of materials into & out of the cell less efficient.
  • 123.
    • Note: Some cells have unique shapes & structures to overcome SA/V ratio. E.g. intestinal epithelial cells on villi contain microvilli (a “brush border”) to ↑ SA for diffusion of nutrients; RBC’s are biconcave shape to ↑ SA/V ratio for more efficient gas diffusion (See C1 and C6).