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• 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 where DNA is found
• Prokaryotic cells


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


  • Cell membrane
  • Cell wall (in plant cells and bacteria)
  • Cytoplasm
  • Mitochondria
  • Ribosomes
  • Chloroplasts (in plant cells)
  • Permanent vacuole (in plant cells)
  • Enzymes
• Cell membrane


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


  Provides rigid structure (in 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 (in plant cells)
• Permanent vacuole


  Stores sap (in 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 active site changes shape and enzyme denatures
• Enzyme activity experiment


  1. Mix enzyme with substrate

  2. Measure time taken for all substrate to be broken down

  3. Plot time against temperature or pH

  4. Optimum is lowest point on curve
• Food tests


  • Iodine turns black in presence of starch
  • Benedict's solution turns orange in presence of sugars
  • Biuret reagent turns purple in presence of proteins
  • Cold ethanol goes cloudy in presence of lipids
• Diffusion


  Movement of molecules or particles from high to low concentration, down concentration gradient, passive
• Osmosis


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


  1. Cut equal sized cylinders from potato

  2. Weigh and place in varying sugar solutions

  3. Reweigh after a day

  4. Calculate percentage change in mass

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


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


  • Nerve cells
  • Muscle cells
  • Root hair cells
  • Xylem cells
  • Phloem cells
  • Stem cells
• Stem cells


  Unspecialised cells that can differentiate into various 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 synapse using neurotransmitter

  4. Signal travels to brain

  5. Brain makes decision

  6. Signal travels back to effector (e.g. muscle) through relay and motor neurons
• Reflex arc


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

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


  Safely show brain activity
• Eye accommodation


  1. Ciliary muscles relax and suspensory ligaments tighten to focus on distant objects

  2. Ciliary muscles contract and suspensory ligaments slacken to focus on near objects
• Pupil


  Changes size depending on light intensity
• Meiosis


  1. Chromosomes duplicate

  2. Homologous chromosomes pair up and swap genes

  3. Cell divides twice to form 4 haploid cells
• Asexual reproduction produces genetically identical offspring (clones)
• Advantages of sexual reproduction include increased variation in offspring
• Genome


  All the genetic material in an organism
• Gene


  Section of DNA that codes for a specific protein
• Genotype


  Genetic code stored in DNA
• Phenotype


  How the genetic code is expressed in an organism's characteristics
• Harmful mutations can change a gene so much that the resulting protein doesn't function properly