bio paper 1

• All life consists of cells
• Light microscope


  Can see cells and maybe the 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 where DNA is found
  • Examples: plant and animal cells
• Prokaryotic cells


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


  • 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 that makes up the cell, where most chemical reactions take place
• Mitochondria


  Where respiration takes place, releasing energy for the cell
• Ribosomes


  Where proteins are assembled or synthesized
• Chloroplasts


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


  Permanent structure in plant cells, stores sap
• 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
• Enzyme activity practical


  1. Mix enzyme with substrate

  2. Measure time for reaction to complete

  3. Plot time against temperature or pH

  4. Optimum is lowest point on curve
• Food tests


  • Iodine turns black for starch
  • Benedict's solution turns orange for sugars
  • Biuret reagent turns purple for proteins
  • Ethanol goes cloudy 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 potato cylinders

  2. Weigh and place in sugar solutions

  3. Reweigh after a day

  4. Calculate % change in mass

  5. Plot against concentration, x-axis crossing is no change
• Active transport


  Using energy to move substances against a concentration gradient
• Diploid cells


  Have 23 pairs of chromosomes
• Haploid cells


  Have 23 single chromosomes
• Mitosis


  1. Genetic material duplicated

  2. Nucleus breaks down

  3. Chromosomes pulled to opposite sides

  4. New nuclei form, resulting in two identical cells
• Cell specialisation


  Cells specialize depending on their function
• Stem cells


  Unspecialized cells that can differentiate into different cell types
• Parts of the nervous system

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


  1. Receptor detects stimulus

  2. Electrical signal travels to spine through sensory and relay neurons

  3. Signal crosses synapses using neurotransmitters

  4. Signal goes to brain

  5. Brain sends signal back through motor neurons to effector
• Reflex arc


  Signal bypasses brain and goes straight from spine to effector
• Glands


  Produce specific chemicals the body needs
• Reaction time practical


  1. Drop ruler, measure distance fallen before caught

  2. Repeat multiple times, calculate average

  3. Introduce independent variable (stimulant or depressant)
• 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
• Pupil


  Changes size depending on light intensity
• Cornea


  Transparent outer layer of eye with slight lensing effect
• Retina


  Back of eye with rods and cones
• Meiosis


  1. Chromosomes copied and paired up

  2. Cell divides twice to make 4 haploid cells