1- Cell Biology

• Eukaryotes


  Cells that have a nucleus and membrane-bound organelles
• Prefixes to show multiples of units

  • Centi (0.01)
  • Milli (0.001)
  • Micro (0.000,001)
  • Nano (0.000,000,001)
• 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, but some stem cells retain this ability
• 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, 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
• 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
• Culturing microorganisms


  Growing many microorganisms in the lab using nutrients
• Growing microorganisms in nutrient broth

  1. Make suspension of bacteria

  2. Mix with sterile nutrient broth

  3. Stopper flask with cotton wool

  4. Shake regularly to provide oxygen
• Bacteria can multiply by binary fission every 20 minutes
• Formula to calculate bacterial population growth

  Bacteria at beginning x 2^(number of divisions) = bacteria at end
• Testing antibiotic effectiveness


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

  2. Leave plate to incubate

  3. Measure size of inhibition zone around discs
• Inhibition zone


  Clear area around antibiotic disc where bacteria have died
• Calculating cross-sectional areas involves using the formula πr^2
• Chromosomes


  Contain coils of DNA and carry genes
• Number of chromosomes


  46 in body cells, 23 in gametes
• Cell cycle and mitosis

  1. Interphase: cell growth, organelle increase, DNA replication

  2. Mitosis: chromosomes line up and separate

  3. Cytokinesis: cytoplasm and cell membrane divide to form two daughter cells
• Importance of mitosis


  • Growth and development
  • Replacing damaged cells
  • Asexual reproduction
• Types of stem cells

  • Embryonic
  • Adult (e.g. in bone marrow)
  • Meristems in plants
• Therapeutic cloning


  Producing an embryo with the same genes as the patient to obtain stem cells for treatment
• Substances that can diffuse across cell membranes

  • Small molecules like oxygen, glucose, amino acids, water
  • Large molecules like starch and proteins cannot
• Examples of diffusion in the body

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

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


  The movement of particles from an area of high concentration to an area of low concentration through a permeable membrane
• Where diffusion takes place in the body

  • Oxygen moves through the membranes of alveoli into red blood cells, and is carried to cells across the body for respiration. Carbon dioxide moves from red blood cells into the lungs to be exhaled.
  • Urea moves from liver cells into the blood plasma to be transported to the kidney for excretion
• Factors affecting the rate of diffusion

  • Concentration gradient (difference in concentrations)
  • Temperature
  • Surface area of the membrane
• Surface area to volume ratio

  The size of the surface area of the organism compared to its volume
• If the surface area to volume ratio is large, 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
• Adaptations in multicellular organisms to aid diffusion

  • Lungs: alveoli and capillaries
  • Small intestine: villi
  • Fish gills: gill filaments and gill lamellae
  • Plant roots: root hair cells
  • Plant leaves: stomata and guard cells
• Adaptations to aid diffusion

  • Having a large surface area
  • Having a thin membrane
  • Having an efficient blood supply/being ventilated (in animals)
• Osmosis


  The movement of water from a less concentrated solution to a more concentrated one through a partially permeable membrane
• Isotonic

  When the concentration of the external solution is the same as the internal solution, so there is no net movement of water
• Hypertonic


  When the concentration of the external solution is higher than the internal solution, so water moves out of the cell
• Hypotonic


  When the concentration of the external solution is lower than the internal solution, so water moves into the cell