Topic 2: Cells


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This is all you need to know for topic 2 if you're an IB student testing out of SL Biology!

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Topic 2: Cells

  1. 1. Topic 2Cells
  2. 2. Introducing Cells• Consist of cytoplasm• Enclosed in a plasma membrane• Usually controlled by a single nucleas
  3. 3. Unicellular Organisms• Single cell that carries out all the functionsof life:– Metabolism (chemical reactions inside thecell)– Response (reacting to stimuli)– Homeostasis (controlling internal conditions)– Growth (increasing in size)– Reproduction (producing offspring)– Nutrition (obtaining food)
  4. 4. Multicellular Organisms• Consist of many cells that are specializedfor one specific function• Differentiation: cells become specialized tocarry out one process efficiently• Emergent properties: the whole organismis more than the sum of its parts due to thecomplex interactions between cells
  5. 5. The Cell Theory• Living organisms are composed of cells• Cells are the smallest units of life• Cells can only be made from pre-existingcells
  6. 6. Differentiation• Differentiation: cells develop in differentways to carry out different functions• The cells need different genes to developin different ways– each cell has all of the genes available• Once a pathway of development hasbegun in a cell, it is usually fixed
  7. 7. Stem Cells• Stem cells: cells that have the capacity toself-renew by cell division and todifferentiate• Human embryos consist entirely of stemcells early on• Interest in stem cells are due to theirpotential for tissue repair and for treating avariety of degenerative conditions– i.e. Parkinson’s disease
  8. 8. Therapeutic Use of Stem Cells• Stems Cells can be used therapeuticly– Blood from an umbilical cord contains stemcells– Red blood cells are taken from the cord bloodand the remaining fluid is then tested– Cord blood is matched to the patient’s tissuetype– Cord blood is introduced into the patient’sblood system• Used for leukemia patients
  9. 9. Limitations to Cell Size• Cells have a maximum size– If a cell was too large its surface area tovolume ratio would be too small• The rate at which materials enter/leavecell depends on the surface area• The rate at which materials areused/produced depends on the volume
  10. 10. Units for Size Measurements• 1 meter (m) = 1,000 millimeters (mm)• 1 millimeter (mm) = 1,000 micrometer (µm)• 1 micrometers (µm) = 1,000 nanometers (nm)
  11. 11. Calculating Magnification• To calculate magnification:1. Choose an obvious length and measure it on thedrawing2. Measure the same length on the actualspecimen3. Convert the units4. Divide the drawing length by actual specimen’slength• Magnification = size of image ÷ size of object
  12. 12. Scale Bars• Scale bar: Line added to a micrograph ordrawing to help show the actual size of thestructures
  13. 13. Ultrastructure of Cells• Two types of cells: prokaryotic andeukaryotic• Prokaryotic cells have existed longer• Prokaryotic cells reproduce by binaryfission: dividing in two
  14. 14. Functions of Parts of a ProkaryoticCellStructure FunctionCell Wall Protective outer layer from external danger and bursting frominternal pressures.PlasmaMembraneControls entry and exit of substances. Uses pumps for activetransport.Cytoplasm Contains enzymes to catalyze metabolism reactions. ContainsDNA in the nucleoid.Pili Hair-like structures protecting the cell walls that allow bacteria toadhere and share informationFlagella Protein structures that project from the cell wall that rotate andcause locomotionRibosomes Synthesize proteins by translating messenger RNA.Nucleoid Contains naked DNA (the genetic information of the cell)
  15. 15. Comparing Prokaryotic andEukaryotic CellsFeature Prokaryotic Cells Eukaryotic CellsType of geneticmaterialNaked loop of DNA Chromosomes consisting ofstrands of DNA associated with aprotein.Location ofgeneticmaterialIn the cytoplasm within thenucleoid regionIn the nucleus inside the nuclearenvelopeMitochondria Not present Always presentRibosomes 70s (smaller size) 80s (larger size)InternalMembranesFew or none present Many present: endoplasmicreticulum, Golgi apparatus,lysosomes
  16. 16. Comparing Plant and AnimalEukaryotic CellsFeature Animal PlantCell wall No cell wall, only plasmamembraneBoth cell wall andplasma membraneChloroplasts Not present Present in cells thatphotosynthesizePolysaccharides Glycogen is used as astorage compoundStarch is used as astorage compoundVacuole Not usually present; fewand temporaryLarge vacuole oftenpresentShape Able to change shape;usually roundedFixed shape; usuallyrectangular
  17. 17. Fluid Mosaic Model of a BiologicalMembrane
  18. 18. Phospholipids• Phosphate heads are hydrophilic– They are attracted to water• Lipid tails are hydrophobic– They are not attracted to water, but areattracted to each other• Phospholipids form double layers withhydrophilic heads facing outward and lipidtails facing inward• Very stable, yet fluid
  19. 19. Fluidity of Membranes• Phospholipids in membranes are in a fluidstate• Allows membranes to change shape• Allows vesicles to be pinched off from orfuse with the membrane
  20. 20. Functions of Membrane Proteins• Hormone bonding sites• Protein pumps for Active Transport• Channels for Passive Transport• Cell-to-cell communication and celladhesion• Enzymes
  21. 21. Diffusion• Diffusion: the passive movement ofparticles from a region of higherconcentration to a region of lowerconcentration, as a result of the randommotion of particles• Can occur across semi-permeablemembranes if there is a concentrationgraident
  22. 22. Simple and Facilitated Diffusion• Partially permeable membranes: allow somesubstances to diffuse through, but not others• Simple diffusion: when substances movebetween the phospholipid molecules in themembrane• Facilitated diffusion: substances that areunable to pass between phospholipids aremoved through using specific channelproteins• Both processes do not need to use energy
  23. 23. Osmosis• Solvent: liquid in which particles dissolve• Solutes: dissolved particles in solvent• Osmosis: passive movement of watermolecules from a region of lower soluteconcentration to a region of higher soluteconcentration, across a partiallypermeable membrane
  24. 24. Pump Proteins and ActiveTransport1. Particle enters pump from the side of lowerconcentration2. Particle binds to a specific site on the proteinpump3. Energy from ATP changes the shape of thepump4. The change in shape allows the particle tobe released on the side of higherconcentration5. Pump returns to its original shape
  25. 25. Endocytosis and Exocytosis• Endocytosis: enters the cell1. Part of membrane is pulled inwards2. Fluid becomes enclosed when a vesicle ispinched off3. Vesicles can then move inside the cell• Exocytosis: exits the cell1. Vesicles fuse with the plasma membrane2. Contents of vesicle are expelled3. Membrane flattens out again
  26. 26. Extracellular Components• Extracellular components: componentsproduced by cells that are placed outsidethe plasma membrane using exocytosis• Examples:– Plant cell wall– Glycoproteins• Carbohydrate attached to a protein in plasmamembrane
  27. 27. Interphase• Interphase is the longest phase of cellcycle of Eukaryotes• Interphase has 3 stages:1. G1: period of growth, DNA transcription,protein synthesis2. S phase: period during which all DNA in thenucleas is replicated3. G2: period in which the cell prepares fordivision
  28. 28. Mitosis• Mitosis: process that divides nucleus into twogenetically identical nuclei• Mitosis is used during growth, embryonicdevelopment, repairing tissues, produceasexually• Mitosis has four phases:1. Prophase2. Metaphase3. Anaphase4. Telophase• Ends with cytokinesis
  29. 29. Prophase• Spindle microtubules grow• Move to extend from each pole to theequator• Chromsomes supercoil to become shorterand fatter• Each chromosome are made up ofidentical chromatids held together by acentromere
  30. 30. Metaphase• The nuclear membrane brakes downcontaining the chromosomes• Chromosomes move to the equator• Spindle microtubules attach to eachcentromere (on opposite sides of thecentromeres)
  31. 31. Anaphase• The centromeres divide and the twocromatids have become chromosomes• Spindle microtubules pull the geneticallyidentical chromosomes to opposite poles
  32. 32. Telophase• Chromsomes reach the poles and nuclearmembranes form around them• Spindle microtubules break down withinthe membranes• Chromosomes uncoil and are no longerindividually visible• Two cells are formed with geneticallyidentical nuclei
  33. 33. Cytokinesis• The process of dividing the cytoplasm toform two cells at the end of mitosis
  34. 34. Tumors• The genes in a cell change and so thenormal control of mitosis fails• Repeated uncontrolled divisions produce amass of cells• These cells are called a tumor– Can happen in any organ or tissue– Can spread to other parts of body– Cancer: diseases caused by tumors