Biology

• All life consists of cells
• Light microscope


  • Can see cells and nucleus, but not subcellular structures
• Electron microscope


  • Can see finer details and subcellular structures, has better resolving power and higher resolution
• Calculating cell size


  1. Measure image size

  2. Divide by magnification
• Cell types


  • Eukaryotic cells
  • Prokaryotic cells
• Eukaryotic cells


  • Have a nucleus containing DNA
• Prokaryotic cells


  • Don't have a nucleus, DNA is in a ring called a plasmid
• Cell structures


  • Cell membrane
  • Cell wall (plant cells and bacteria)
  • Cytoplasm
  • Mitochondria
  • Ribosomes
  • Chloroplasts (plant cells)
  • Vacuole (plant cells)
  • Enzymes
• Cell membrane


  Keeps everything inside the cell, semi-permeable
• Cell wall


  Provides rigid structure (plant cells and bacteria)
• Cytoplasm


  Liquid in which most chemical reactions take place
• Mitochondria


  Where respiration takes place, releasing energy
• Ribosomes


  Where proteins are assembled or synthesized
• Chloroplasts


  Contain chlorophyll, where photosynthesis takes place (plant cells)
• Vacuole


  Stores sap (plant cells)
• Enzymes


  Biological catalysts that break down larger molecules into smaller ones
• Enzymes


  • Specific, work on a lock and key principle
  • Rate of activity increases with temperature until denaturation
  • Have an optimum pH and temperature
• Enzyme activity practical


  1. Mix enzyme and substrate

  2. Take samples at intervals

  3. Test for presence of substrate

  4. Plot time taken for substrate to be broken down against temperature or pH

  5. Optimum is at lowest point on graph
• Food tests


  • Iodine test for starch
  • Benedict's solution for sugars
  • Biuret reagent for proteins
  • Ethanol for lipids
• Diffusion


  Movement of molecules/particles from high to low concentration, passive
• Osmosis


  Diffusion of water across a semi-permeable membrane
• Osmosis practical


  1. Cut equal cylinders from potato

  2. Weigh and place in sugar solutions

  3. Reweigh after a day

  4. Calculate percentage change in mass

  5. Plot against sugar concentration, point of no change is osmotic concentration
• Active transport


  Using energy to move substances against a concentration gradient
• Cell division


  • Mitosis
  • Meiosis
• Mitosis


  • Genetic material duplicated, cell divides to form two identical cells
• Meiosis


  • Genetic material halved, four genetically different cells produced
• Cell specialisation


  Cells take on specific functions
• Stem cells


  Unspecialised cells that can develop into different cell types
• Nervous system


  • Central nervous system (brain and spinal cord)
  • Peripheral nervous system (nerves)
• Nerve impulse transmission


  1. Receptor detects stimulus

  2. Electrical signal travels to spine

  3. Signal crosses synapses using neurotransmitters

  4. Signal goes to brain

  5. Brain sends signal back to effector (e.g. muscle)
• Reflex arc


  Electrical signal bypasses brain and goes straight from spine to effector
• Parts of the brain

  • Cerebral cortex (higher functions)
  • Cerebellum (motor skills, balance)
  • Medulla oblongata (unconscious actions)
• MRI scans


  Safely show brain activity
• Eye accommodation


  Ciliary muscles relax/contract, suspensory ligaments tighten/slacken, lens becomes thinner/thicker to focus light
• Pupil


  Changes size to control light intensity
• Cornea


  Transparent outer layer that refracts light
• Retina


  Contains rods (light intensity) and cones (colour)
• Meiosis


  1. Chromosomes duplicate

  2. Homologous chromosomes pair up and swap genes

  3. Cell divides twice to produce 4 haploid cells
• Asexual reproduction


  Produces genetically identical offspring
• Sexual reproduction


  Produces genetically varied offspring