Cell Function

• Simple Diffusion

  The passive net movement of a substance from a region with a high concentration to a region with a low concentration until equilibrium is reached
• Osmosis


  The passive net diffusion of solvent molecules through a semipermeable membrane from a region with a low solute concentration to a region with a high solute concentration until equilibrium is reached (e.g. water molecules)
• Facilitated diffusion


  The passive movement of molecules (too large, polar, or charged) across a membrane down a concentration gradient via a specific integral proteins (e.g. channel or carrier protein)
• Active transport


  The movement of materials across a membrane against their concentration gradient, via a specific carrier protein.

  Requires energy
• Bulk transport


  Involves the movement of materials, too large to pass through a carrier or channel protein, in membrane-bound vesicles that fuse within the cell membrane
• Exocytosis


  Process by which the contents of a cell vacuole are released to the exterior by the fusion of the vacuole membrane with the cell membrane. This is possible because of the fluid nature of the cell membrane
• Endocytosis


  Process by which the cell membrane changes shape to surround a particle and engulf it
• Phagocytosis


  ("cell eating") when material being engulfed is solid
• Pinocytosis


  ("cell drinking") when material being engulfed is fluid
• Energy


  The ability to perform work. Can be in the form of chemical energy, light energy, heat energy, and kinetic (movement) energy.

  Energy use examples

  • synthesis
  • growth, repair, maintenance
  • active transport
• ATP (Adenosine triphosphate)


  Energy storage molecule
• Photosynthesis


  Series of reactions in the chloroplast which allow plants, algae, and some protists to produce glucose from carbon dioxide and water using light energy trapped by chlorophyll.

  1. Light-dependent
  2. Light-independent
• Chloroplast


  A plastid found in photosynthetic cells of green plants, in which photosynthesis takes place
• Light-dependent stage


  First stage. Occurs in the grana where light energy from the sun splits water molecules into oxygen (waste) and hydrogen. ATP is also formed.

  • Requires light

  Light + Water → Oxygen + Hydrogen Ions + ATP
• Light-independent stage


  Second stage. Occurs in the stroma where carbon dioxide and hydrogen ions (split from water molecules in light-dependent stage) combine to form glucose

  • Does not directly require light

  carbon dioxide + hydrogen ions -- ATP --> glucose
• Cellular respiration


  A series of chemical cellular reactions that convert biochemical energy from glucose to chemical energy in ATP

  1. Glycolysis

  2. Krebs cycle

  3. Electron transport
• Enzyme


  A protein that acts as a catalyst; speeding up a chemical reaction while itself, remaining unchanged
• Substrate


  Reactant that binds to active site of enzyme, substances that result are called the 'product'
• Activation energy


  The minimum energy required to start a chemical reaction
• The lock & key model


  Suggests that the geometric shape of a substrate exactly fits the active site of the enzyme
• The induced fit model

  Suggest that shapes and charges of the substrate and enzyme are a very close, but not exact fit
• Passive transport


  The movement of materials across a membrane with their concentration gradient. Requires no energy.
• Adenosine triphosphate (ATP)

  Energy storage molecule. Three phosphates attached to adenosine.

  When third phosphate broken --> energy released, becomes Adenosine diphosphate (ADP)
• Concentration gradient


  Movement from a high to low area of concentration
• Channel proteins


  Type of integral protein that is open on both sides to control the transport of small ions and molecules

  E.g. Aquaporin channel protein for water molecules
• Carrier protein


  Type of integral protein that is open on one side and changes shape to fit particle, to control the enter/exit of large ions and molecules e.g. sugars
• Integral proteins

  Embedded within membrane for channelling and transport of materials.

  • Carrier proteins
  • Channel proteins
  • Aquaporin
• Aquaporin


  Type of channel protein channel where water molecules pass through. Where Osmosis occurs.
• Isotonic solution


  Solute concentration equal to cytoplasm
• Hypotonic solution


  Lower solute concentration (water>solute) than cytoplasm.

  Osmosis: water moves in and cell swells
• Hypertonic solution

  Higher solute concentration (water<solute) than cytoplasm.

  Osmosis: water moves out and cell shrinks
• Osmosis in animal cells

  Hypotonic: No cell wall to stop water, cell will burst and die
• Osmosis in plant cells

  Hypertonic: Vacuoles fill with water and cell swells

  Hypotonic: Water leaves, vacuoles and cell shrinks --> plasmolysis
• Osmotic pressure


  Pressure created by water moving across the membrane.

  More water = higher pressure
• Plasmolysis


  Process by which cells lose water in a hypertonic solution, causing the cytoplasm to shrink away from the cell wall.
• What effects the speed of diffusion?

  Temperature (high temp. speeds up) and concentration gradient (steeper = faster)
• Characteristics of a molecule that can affect diffusion

  • size
  • polarity: polar molecules are harder to cross
  • charge: charged molecules (ions) are harder
  • solubility: lipid-soluble molecules are easier
• Anaerobic respiration


  Requires no oxygen e.g. fermentation
• Aerobic respiration


  Requires oxygen
• Photosynthesis word equation

  Carbon dioxide + water -- light energy + chlorophyll --> Glucose + oxygen