Paper 1 - AQA Biology

• Eukaryotes


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotes


  Cells that lack a nucleus and membrane-bound organelles
• Components of animal and plant cells


  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Components of bacterial cells

  • Cell wall
  • Cell membrane
  • Cytoplasm
  • Single circular strand of DNA and plasmids
• Orders of magnitude


  Used to understand how much bigger or smaller one object is from another
• Prefixes


  • Centi (0.01)
  • Milli (0.001)
  • Micro (0.000,001)
  • Nano (0.000,000,001)
• Structures in animal and plant cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional structures in plant cells

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Structures in bacterial cells


  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Single circular strand of DNA
  • Plasmids
• Sperm cells


  • Streamlined head and long tail to aid swimming
  • Many mitochondria to supply energy
  • Acrosome with digestive enzymes to break down egg cell membrane
• Nerve cells


  • Long axon to transmit impulses
  • Many dendrites for branched connections
  • Mitochondria to supply energy for neurotransmitter production
• Muscle cells


  • Proteins (myosin and actin) that slide over each other to cause contraction
  • Many mitochondria to provide energy
  • Can store glycogen for respiration
• Root hair cells


  • Large surface area for water and mineral ion uptake
  • Large vacuole affects water movement speed
  • Mitochondria provide energy for active transport
• Xylem cells


  • Lignin deposition makes cells hollow and joined to form continuous tubes
  • Lignin spirals help withstand water pressure
• Phloem cells


  • Sieve plates allow movement of substances between cells
  • Companion cells provide energy through their mitochondria
• Cell differentiation


  Process where stem cells switch on/off genes to produce different proteins and acquire specialised structures
• In animals, most cells differentiate early and lose ability, but some like red blood cells are replaced by adult stem cells
• In plants, many cell types retain ability to differentiate throughout life
• Light microscope


  Has two lenses (objective and eyepiece), illuminated from underneath, max magnification x2000, resolving power 200nm
• Electron microscope


  Uses electrons instead of light, can be scanning (3D) or transmission (2D), max magnification x2,000,000, resolving power 10nm (SEM) and 0.2nm (TEM)
• Calculating magnification of light microscope

  Magnification of eyepiece lens x magnification of objective lens
• Calculating size of object

  Size of image / magnification = size of object
• Standard form


  Multiplying a number by a power of 10 to represent very large or small numbers, with the 'number' between 1 and 10
• Components of culture medium


  • Carbohydrates
  • Minerals
  • Proteins
  • Vitamins
• Growing microorganisms in nutrient broth


  Make suspension of bacteria, mix with sterile nutrient broth, stopper with cotton wool, shake regularly
• Growing microorganisms on agar plates


  Spread bacteria suspension on agar plate, seal, incubate, colonies form
• Standard form


  Multiplying a certain number by a power of 10 to make it bigger or smaller, with the 'number' being between 1 and 10
• Standard form examples


  • 1.5 x 10^-5 = 0.000015
  • 3.4 x 10^3 = 3400
• Culturing microorganisms


  Growing many microorganisms in the lab using nutrients
• Components of culture medium


  • Carbohydrates
  • Minerals
  • Proteins
  • Vitamins
• Growing microorganisms in nutrient broth

  1. Make suspension of bacteria

  2. Mix with sterile nutrient broth

  3. Stopper flask with cotton wool

  4. Shake regularly
• Growing microorganisms on agar gel plate


  1. Pour hot sterilised agar jelly into sterilised Petri dish

  2. Allow to cool and set

  3. Inoculate with microorganism using sterilised loop

  4. Tape lid on and incubate
• Reasons for sterilisation steps


  • Prevents contamination with other microorganisms
  • Prevents competition for nutrients and space
  • Prevents introduction of harmful microorganisms
• Reasons for other culturing steps

  • Inoculating loops sterilised to kill unwanted microorganisms
  • Petri dish lid sealed but not completely to allow oxygen
  • Petri dish stored upside down to prevent condensation
  • Incubated at 25°C to prevent growth of harmful bacteria
• Binary fission


  One bacterial cell splitting into two
• Calculating bacterial population growth

  1. Bacteria at beginning x 2^(number of divisions) = bacteria at end

  2. Number of divisions = time left / mean division time
• Inhibition zone


  Clear area around antibiotic disc where bacteria have died
• Testing antibiotic effectiveness


  1. Soak paper discs in antibiotics and place on agar plate with bacteria

  2. Leave plate to incubate

  3. Measure size of inhibition zones
• Calculating cross-sectional areas involves using the formula πr^2
• Chromosomes


  Contain coils of DNA and carry genes