biology paper 1 and 2

• 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
  • Examples: plant and animal cells
• Prokaryotic cells


  • Don't have a nucleus, DNA is in a ring called a plasmid
• Subcellular 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 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 that 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 occurs
  • Rate also affected by pH
• Enzyme activity practical


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


  Movement of molecules/particles from high to low concentration, passive process
• 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 percentage change in mass

  5. Plot against sugar concentration, x-axis crossing is no change (same concentration inside)
• Active transport


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


  • Mitosis
  • Meiosis
• Mitosis


  • Genetic material duplicated, number of organelles doubled
  • Nucleus breaks down, chromosomes pulled to opposite sides
  • New nuclei form, resulting in two identical cells
• Cell specialisation


  Cells take on specific functions e.g. nerve, muscle, root hair
• 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 through sensory and relay neurons

  3. Signal crosses synapses using neurotransmitters

  4. Signal goes to brain for conscious decision

  5. Signal travels back to effector (muscle) via relay and motor neurons
• 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, coordination)
  • Medulla oblongata (unconscious actions)
• MRI scans


  Safely show brain activity
• Eyes


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

  1. Chromosomes duplicated

  2. Homologous chromosomes pair up and swap genes

  3. Cell divides twice to produce 4 haploid gametes
• Asexual reproduction produces genetically identical offspring (clones)
• 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 the resulting protein doesn't function properly