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


  A way to understand how much bigger or smaller one object is compared to another
• Prefixes to show multiples of units

  • 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
• Cell specialisation


  The process where cells gain new sub-cellular structures to be suited to their role
• Specialised animal cells


  • Sperm cells
  • Nerve cells
  • Muscle cells
• Specialised plant cells


  • Root hair cells
  • Xylem cells
  • Phloem cells
• Cell differentiation


  The process where stem cells switch on/off genes to produce different proteins and acquire new sub-cellular structures
• In animals, most cells differentiate early and lose ability to differentiate further. Cell division mostly happens to repair/replace damaged cells.
• In plants, many cell types retain ability to differentiate throughout life. They only differentiate when they reach final position in plant.
• Light microscope


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


  Uses electrons instead of light, two types (scanning and transmission), 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


  A way to represent very large or small numbers by multiplying by a power of 10, with the 'number' between 1 and 10
• Culture medium


  Contains carbohydrates, minerals, proteins and vitamins to grow microorganisms
• Growing microorganisms in nutrient broth solution

  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


  • Microorganisms are very small, so scientists need to grow many of them in the lab using nutrients
• Components of culture medium


  • Carbohydrates for energy
  • Minerals
  • Proteins
  • Vitamins
• Growing microorganisms in the lab

  1. In nutrient broth solution

  2. On an agar gel plate
• Making an agar gel plate involves pouring hot sterilised agar jelly into a sterilised Petri dish, letting it cool and set, then inoculating with a microorganism and incubating
• Sterilisation


  Petri dishes and culture media must be sterilised before use, often by autoclave or UV light, to prevent contamination
• Inoculating loops


  Wire loops used to transfer microorganisms, which must be sterilised by passing through a flame
• Sealing Petri dish


  Lid should be sealed but not completely, to prevent airborne contamination while allowing oxygen entry
• Storing Petri dish


  Upside down to prevent condensation from lid disrupting growth
• Incubation temperature


  25 degrees, to prevent growth of bacteria harmful to humans
• Testing antibiotic effectiveness


  Soak paper discs in antibiotics, place on agar plate with bacteria, measure inhibition zone after incubation
• Calculating cross-sectional areas of colonies or inhibition zones involves using the formula πr^2, where r is the radius
• Chromosomes


  Contain coils of DNA, with each chromosome carrying many genes
• There are 23 pairs of chromosomes in each body cell, and 23 chromosomes in each gamete cell
• Cell cycle and mitosis

  1. Interphase (cell growth, organelle increase, DNA replication)

  2. Mitosis (chromosome alignment and separation)

  3. Cytokinesis (daughter cell formation)
• Importance of mitosis


  • Growth and development, replacing damaged cells, asexual reproduction