Topic 1: Cell 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


  • 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
• Culture medium


  Contains carbohydrates, minerals, proteins and vitamins to grow microorganisms
• 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
• 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 sterilisation 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
• Testing effectiveness of antibiotics

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

  2. Leave plate at 25 degrees for 2 days

  3. Measure zone of inhibition - bigger zone means more bacteria killed, so more effective antibiotic
• To calculate cross-sectional areas (of colonies or inhibition zones), use the formula πr²
• Chromosomes


  Contain coils of DNA, each chromosome carries many genes
• There are 23 pairs of chromosomes in each cell of the body, resulting in 46 chromosomes in total