1.1 Cell biology

• All living things are made of cells, which can either be prokaryotic or eukaryotic
• Eukaryotic cells


  • Animal cells
  • Plant cells
• Prokaryotic cells


  • Bacterial cells
• Eukaryotic cells

  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Prokaryotic cells


  • Cell wall
  • Cell membrane
  • Cytoplasm
  • Single circular strand of DNA
  • Plasmids
• Organelle


  Structures in a cell that have different functions
• Cells are extremely small, and we can use orders of magnitude to understand how much bigger or smaller one is from another
• Understanding orders of magnitude

  1. 10 times bigger is 10​1​

  2. 1000 times bigger is 10​3​

  3. 10 times smaller is 10​-1​
• Prefixes

  • Centi
  • Milli
  • Micro
  • Nano
• Prefix multipliers

  • Centi: 0.01
  • Milli: 0.001
  • Micro: 0.000, 001
  • Nano: 0.000, 000, 001
• The subcellular structures inside cells all have a specific function
• Bacterial cells are prokaryotic, so do not share as many similarities in the type of organelles as animal and plant cells do
• Animal cell structures and functions

  • Nucleus : control cell activities and contain DNA
  • Cytoplasm: Liquid substance in which chemical reactions occur
  • Cell membrane: Controls what enters and leaves the cell
  • Mitochondria: Where aerobic respiration reactions occur and provide energy to power cell
  • Ribosomes: Where protein synthesis occurs
• Plant cell structures and functions

  • Chloroplasts: Contain chlorophyll to absorb light for photosynthesis to take place
  • Permanent vacuole: Contains cell sap and improves cell’s rigidity
  • Cell wall: Made from cellulose and provides strength to the cell
• Bacterial cell structures

  • Cell wall: Made of a different compound (peptidoglycan)
  • Single circular strand of DNA: Floats in the cytoplasm
  • Plasmids: Small rings of DNA
• Cells specialise by undergoing differentiation
• Differentiation


  Process that involves the cell gaining new sub-cellular structures to be suited to its role
• Cells can either differentiate once early on or have the ability to differentiate their whole life (these are called stem cells)
• Examples of specialised cells in animals


  • Sperm cells
  • Nerve cells
  • Muscle cells
• Sperm cell features

  • Streamlined head and long tail
  • Many mitochondria for energy
  • Acrosome with digestive enzymes to digest cell membrane
• Nerve cell features

  • Long axon to cover more distance
  • Lots of extensions (dendrites) to connect to other cell
  • Nerve endings with many mitochondria
• Muscle cell features

  • Special proteins (myosin and actin)
  • Lots of mitochondria
  • Can store glycogen
• Examples of specialised cells in plants

  • Root hair cells
  • Xylem cells
  • Phloem cells
• Root hair cell features

  • Large surface area for more absorption
  • Large permanent vacuole
  • Mitochondria for active transport
• Xylem cell features

  • Hollow structure due to lignin deposition
  • Joined end-to-end to form a continuous tube
  • Lignin deposited in spirals
• Phloem cell features


  • Cell walls form sieve plates
  • Energy supplied by companion cells' mitochondria
• Stem cells must undergo differentiation to form specialised cells
• In animals, almost all cells differentiate at an early stage and then lose this ability
• In plants, many types of cells retain the ability to differentiate throughout life
• Microscopy


  1. Use microscopes to enlarge images

  2. First cells observed by Robert Hooke in 1665

  3. Light microscope has two lenses

  4. Electron microscope uses electrons to form images
• Calculating size of an object

  Size of image/magnification = size of object
• Bacteria can multiply by binary fission as fast as every 20 minutes
• Microorganisms are very small, so scientists need to grow many of them in the lab using nutrients
• Growing microorganisms on agar gel plate


  1. Pour hot sterilised agar into Petri dish

  2. Cool and set agar

  3. Spread microorganism with inoculating loops

  4. Tape lid and incubate
• Petri dishes and culture media must be sterilised before use
• 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 antibiotics

  2. Place on agar plate

  3. Measure zone of inhibition
• Common calculations


  • Cross-sectional areas of colonies or inhibition zones