Cell biology

• Eukaryotes


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


  Cells that lack a nucleus and membrane-bound organelles
• 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 (cellulose)
• Structures in bacterial cells

  • Cytoplasm
  • Cell membrane
  • Cell wall (peptidoglycan)
  • Single loop 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
• 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. Used to see tissues and cells.
• 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). Used to see sub-cellular structures
• Calculating magnification of light microscope


  Magnification of eye piece lens x magnification of objective lens
• Components of culture medium


  • Carbohydrates
  • Minerals
  • Proteins
  • Vitamins
• 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 to prevent air contamination

  4. Shake regularly to provide oxygen for growing bacteria
• Culturing microorganisms on agar gel plate

  1. Pour hot sterilised agar jelly into sterilised Petri dish

  2. Allow to cool and set

  3. Use an inoculating loop that's been sterilised by a hot flame to spread the bacteria evenly onto the agar plate

  4. Tape lid on and incubate, stored upside down
• 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
• 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
• There are 23 pairs of chromosomes in each body cell, and 23 chromosomes in each gamete cell
• Cell cycle and mitosis


  1. Interphase: cell grows, organelles increase, DNA replicates

  2. Mitosis: chromosomes line up and are pulled to opposite sides

  3. Cytokinesis: cytoplasm and cell membrane divide to form two daughter cells
• Stem cells


  Undifferentiated cells that can divide to produce more similar cells, some of which can differentiate
• Types of stem cells


  • Embryonic stem cells
  • Adult stem cells
  • Meristems in plants
• Therapeutic cloning


  Producing an embryo with the same genes as the patient, to obtain stem cells that can be grown into needed cells/tissues
• Benefits and problems of stem cell research


  • Benefits: Can replace damaged/diseased body parts, use unwanted embryos, research differentiation
  • Problems: Don't fully understand differentiation, destroying embryos, ethical concerns, risk of contamination, money/time better spent elsewhere
• Substances that can move by diffusion across cell membranes include oxygen, glucose, amino acids, and water, but not starch and proteins
• Examples of diffusion in the body


  • Oxygen and carbon dioxide in gas exchange
  • Urea from liver to blood to kidneys
• Factors affecting rate of diffusion


  • Concentration gradient
  • Temperature
  • Surface area
  • Thickness of membrane
• Diffusion


  The net movement of particles from an area of high concentration to an area of low concentration
• Gas exchange


  The movement of gases like oxygen and carbon dioxide
• Concentration gradient


  The greater the difference in concentration, the faster the rate of diffusion
• How does the surface area of the membrane affect the rate of diffusion

  The greater the surface area, the more space for particles to move through, resulting in a faster rate of diffusion
• Calculating surface area to volume ratio

  1. Find the volume (length x width x height)

  2. Find the surface area (length x width)

  3. Write the ratio in the smallest whole numbers
• Large surface area to volume ratio

  The organism is less likely to require specialised exchange surfaces and a transport system because the rate of diffusion is sufficient in supplying and removing the necessary gases