Biology paper 1

• 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 (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


  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
  • Rate also affected by pH
• Enzyme activity practical

  1. Mix enzyme with substrate

  2. Measure time for reaction to complete at different temperatures or pH

  3. Plot graph to find optimum temperature or pH
• 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/particles from high to low concentration, down concentration gradient, 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 graph to find concentration with no change (same as inside potato)
• Active transport


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


  • Contains DNA stored in chromosomes
  • Humans have 23 pairs (diploid)
  • Gametes have 23 (haploid)
• 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 specialization


  Cells specialize depending on their function
• Stem cells


  Unspecialized cells that can differentiate into various cell types
• Cloning plants can prevent extinction or produce crops with specific characteristics
• 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 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 and measure distance fallen before caught

  2. Repeat multiple times and take average

  3. Can introduce independent variable like 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 - lens changes shape to focus light
  • Pupil changes size based on light intensity
  • Cornea, lens, retina with rods and cones
• Meiosis


  1. Chromosomes copied and paired

  2. 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