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
  • Branched dendrites to form connections
  • Mitochondria to supply energy for neurotransmitter production
• Muscle cells


  • Proteins (myosin and actin) that slide over each other to cause contraction
  • Lots of 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


  • Hollow tubes with lignin deposits to withstand water pressure
  • Lignin deposited in spirals for structural support
• 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 become specialised cells
• In animals, most cells differentiate early and lose ability to differentiate further
• 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


  Expressing very large or small numbers by multiplying by a power of 10, 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
• Standard form


  Multiplying a certain number by a power of 10 to make it bigger or smaller
• To be able to compare the size of numbers while using standard form, the 'number' which being multiplied by a power of 10 needs to be between 1 and 10
• Standard form


  • 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 solution

  1. Make suspension of bacteria

  2. Mix with sterile nutrient broth

  3. Stopper flask with cotton wool

  4. Shake regularly to provide oxygen
• Growing microorganisms on agar gel plate


  1. Pour hot sterilised agar jelly into sterilised Petri dish

  2. Leave to cool and set

  3. Dip inoculating loops in microorganism solution and spread over agar

  4. Tape lid on and incubate for a few days
• Petri dishes and culture media must be sterilised before use, often done by an autoclave or UV light
• If this sterilisation step does not take place, they are likely to be contaminated with other microorganisms
• Inoculating loops must be sterilised by passing them through a flame
• The lid of the Petri dish should be sealed (but not completely) with tape
• The Petri dish should be stored upside down
• The culture should be incubated at 25 degrees
• Binary fission


  One cell splitting into two
• Calculating number of bacteria after a certain time

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

  2. To calculate number of divisions, divide time by mean division time