BIOLOGY P1

• 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
• Magnification


  Image size / object size
• Can measure cell size by dividing image size by magnification
• Cell types


  • Eukaryotic cells
  • Prokaryotic cells
• Eukaryotic cells


  • Have a nucleus containing DNA
  • Examples: plant and animal cells
• 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)
  • Permanent 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
• Chloroplasts


  Contain chlorophyll, where photosynthesis takes place (plant cells)
• Permanent 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
• Practical on enzyme activity: mix amylase with starch at different temperatures or pH, time how long it takes to break down starch
• Food tests


  Iodine turns black with starch, Benedict's solution turns orange with sugars, Biuret's reagent turns purple with proteins, cold ethanol goes cloudy with lipids
• Diffusion


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


  Diffusion of water across a semi-permeable membrane
• Practical on osmosis: weigh potato/vegetable cylinders in different sugar solutions, calculate percentage change in mass
• Active transport


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


  • Diploid cells (23 pairs of chromosomes)
  • Haploid cells (23 chromosomes)
• Mitosis


  1. Genetic material duplicated

  2. Nucleus breaks down

  3. Chromosomes pulled to opposite sides

  4. New nuclei form
• Cell specialisation


  Cells take on specific functions e.g. nerve, muscle, root hair
• Stem cells


  Unspecialised cells that can develop into different cell types
• Stem cells can be used to treat conditions like diabetes and paralysis
• Cloning plants can prevent extinction or produce crops with specific characteristics
• 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 synapse using neurotransmitter

  4. Signal travels to brain

  5. Brain sends signal back to effector
• 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
• Eyes


  • Accommodation - lens changes shape to focus light
  • Pupil changes size to control light intensity
  • Cornea, lens, retina with rods and cones
• Meiosis


  1. Chromosomes copied

  2. Homologous chromosomes pair up and swap genes

  3. Cell divides twice to form 4 haploid cells
• Advantage of sexual reproduction is increased variation, advantage of asexual is only one parent needed
• Genome


  All the genetic material in an organism
• Gene


  Section of DNA that codes for a specific protein