OCR 21st Century Science - Biology B456

B4 - The Processes of Life

• Cell structure and function
  • Animal cell
    • Nucleus - contains DNA, the instructions for proteins
    • Cytoplasm - gel substance where proteins like enzymes are made, anaerobic respiration occurs here
    • Cell membrane - holds cell together and controls what goes in and out
    • Mitochondria - enzymes needed for aerobic respiration found here
  • Plant cells
    • Rigid cell wall - made of cellulose, supports and strengthens cell
    • Vacuole - contains cell sap, weak solution of sugar and salts
    • Chloroplasts - contain chlorophyll, place where photosynthesis occurs
  • Yeast - single cell microorganisms; nucles, cytoplasm, mitochondria, membrane, cell wall
  • Bacteria - no nucleus or mitochondria; cell membrane + wall, cytoplasm, circular DNA
• Enzymes
  • Proteins that speed up chemical reactions
  • Have an 'active site' where the substrate (molecule changed) attaches to
  • At too high temp, bonds in the enzyme break, changing the shape of the active site
  • pH can also denature enzymes and prevent them from working
• Aerobic respiration
  • A series of chemical reactions that release energy by breaking down food molecules
  • This energy is used for movement, active transport + synthesis of large molecules
  • Aerobic respiration needs oxygen, releases more energy than anaerobic
  • C6H12H6 + 6O2 --> 6C02 + 6H2O + energy released
• Anaerobic respiration
  • Respiration without oxygen
  • Happens in humans during vigorous excercise; plants when roots become waterlogged
  • Glucose --> Lactic acid + energy released (animal cells/some bacteria)
  • Glucose --> Ethanol + carbon dioxide + energy released (plant cells/yeast)
  • Fermenting plant and animal waste gives biogas; yeast ferments hydrocarbons in flour making CO2, causing it to rise; yeast ferment sugar to form alcohol
  • Fermentation - microorganisms breaking down sugar as they respire anaerobically
• Photosynthesis
  • Series of chemical reactions that use sunlight to produce food (glucose)
  • Chlorophyll absorbs sunlight and uses the energy to convert the CO2 and H20 into glucose
  • 6CO2 + 6H2O --> C6H12O6 + 6O2
  • Glucose is used for respiration; making amino acids when combined with nitrogen
• Rate of photosynthesis
  • Light and CO2 increase rate up to a point, after which temp is limiting factor - enzymes denature at around 45 degrees
• Investigating photosynthesis
  • Transect - measure between two fixed points, move along and colect data you want
  • Light meter - measures levels of light
  • Quadrat - 10x10 grid, used for percentage cover
  • ID Key - series of questions narrowing down options until identification
• Diffusion, osmosis and active transport
  • Diffusion - the passive overall movement of particles from an area of high concentration to an area of low concentration
  • Osmosis - the overall movement of water particles across a partially permeable membrane from an area of low concentration to and area of high concentration
  • Active transport - overall movement of chemicals across a cell membrane from a region of low to high concentration using energy released by respiration

B5 - Growth and Development

• DNA - making proteins
  • Structure
    • Double helix - two strands coiled…