Biology

• Cell division


  Allows the organism to grow and replace old or damaged cells
• Cell division


  1. Cell grows larger

  2. Chromosomes replicate 2 copies

  3. Cell divides into 2 - mitosis
• Mitosis


  • First the 2 sets of chromosomes are pulled to opposite ends of the cell
  • Then the nucleus divides into 2
  • Lastly the cell membranes and cytoplasm divide
• Active transport


  • Substances move from a weaker solution to a more concentrated solution against a concentration gradient
  • Cells have to use energy from respiration for active transport
• Single-celled organisms


  • Have large surface area to volume ratios
• Multicellular organisms


  • Have smaller surface area to volume ratios
  • Have specialised structures for exchanging materials
• Specialised exchange structures


  • Have large surface area
  • Have thin membrane
  • Are ventilated and have good blood supply
• Plant adaptations for material exchange

  • Plant roots are long and thin to absorb water and nutrients quicker
  • Leaves are flat and wide for gas exchange
• Osmosis


  Water diffuses through a partially permeable membrane from an area of higher water concentration to an area of lower water concentration
• Osmosis changes the mass of the cell (potato practical)
• Percentage change in mass


  (Final mass - Original mass) / Original mass x 100
• Plant cells

  • Have a permanent vacuole important for keeping the cells rigid
  • Have a cell wall as well as a cell membrane to provide strength and structure
  • Have chloroplasts with chlorophyll to absorb light for photosynthesis
• Embryonic stem cells

  Cells in the early embryo that have not differentiated and are capable of turning into any type of body cell
• Adult stem cells


  Found in bone marrow and can differentiate into cells found in our blood, but cannot differentiate into anything like embryonic stem cells
• Enzymes


  Biological catalysts produced by living things that are not used up
• Enzymes


  • Amylase
  • Protease
  • Lipase
• Amylase


  Breaks down starches into glucose
• Protease


  Breaks down proteins into amino acids
• Lipase


  Breaks down lipids into fatty acids and glycerol
• Lock and key model

  Enzyme active site fits the substrate like a lock and key
• pH and temperature can denature enzymes
• Food tests


  • Benedict's solution - positive test is brick red
  • Iodine - positive test for starches is blue/black
  • Ethanol - positive test for lipids is milky layer
  • Biuret - positive test for proteins is pink/purple
• Subcellular structures


  Cell membrane, cytoplasm, nucleus, mitochondria, chloroplasts (in plant cells)
• Prokaryotes


  Have a cell membrane and plasmid, no true nucleus
• Eukaryotes


  Have a true nucleus and membrane-bound organelles
• Light microscope


  Can see individual cells and large subcellular structures
• Electron microscope


  Has higher magnification and resolution but is more expensive
• Diffusion


  The movement of particles from an area of high concentration to an area of low concentration down the concentration gradient until equilibrium is reached
• Diffusion is faster for bigger substances, at higher temperatures, and through larger pores in the membrane
• Differentiation


  The process by which a cell changes to become a specialised cell type
• Stem cells


  Undifferentiated cells that can turn into specialised cell types
• Embryonic stem cells


  • Found in early human embryos, can turn into any cell type, but use is controversial
• Adult stem cells


  • Found in bone marrow, can turn into blood cells but not as versatile as embryonic stem cells
• Therapeutic cloning


  Using a patient's own cells to produce stem cells that wouldn't be rejected
• Osmosis


  The movement of water molecules across a partially permeable membrane from an area of high water concentration to an area of low water concentration
• Potato practical - mass increases if water enters, mass decreases if water leaves
• Specialised cells


  • Sperm cells
  • Nerve cells
  • Muscle cells
  • Root hair cells
  • Phloem and xylem cells
• Cell cycle


  1. Cell grows and increases in size

  2. Chromosomes replicate and form X-shaped structures

  3. Mitosis - chromosomes line up, nucleus divides, cell membrane and cytoplasm divide
• Culturing microorganisms


  • Bacteria are grown in a sterile culture medium
  • Petri dishes and equipment must be sterilised to prevent contamination
  • Larger inhibition zones around antibiotic discs indicate more effective antibacterial