Biology

• Eukaryotes


  Cells that have a nucleus and membrane-bound organelles
• Components of animal and plant cells

  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Additional structures in plant cells

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Specialised animal cells


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


  • Root hair cells
  • Xylem cells
  • Phloem cells
• In animals, most cells differentiate early and lose ability to differentiate further. Cell division mostly happens to repair/replace damaged cells.
• 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 size of object

  Size of image / magnification = size of object
• Standard form


  A way to represent very large or small numbers by multiplying a number between 1 and 10 by a power of 10
• 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
• 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
• Growing microorganisms on agar gel plate


  1. Pour hot sterilised agar jelly into sterilised Petri dish

  2. Allow to cool and set

  3. Inoculate with microorganism using sterilised loop

  4. Seal plate and incubate
• Reasons for incubating at 25°C


  • Prevents growth of bacteria harmful to humans
• Testing antibiotic effectiveness


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

  2. Leave plate to incubate for 2 days

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


  Clear area around antibiotic disc where bacteria have died
• Chromosomes


  Contain coils of DNA and carry 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 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
• 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
• Problems of stem cell research

  • Difficulty controlling differentiation
  • Destruction of embryos
  • Religious/ethical objections
  • Risk of viral contamination
  • Money and time could be better spent elsewhere
• Diffusion


  The spreading out of particles in a solution or gas, resulting in net movement from higher to lower concentration
• Examples of diffusion in the body

  • Oxygen and carbon dioxide in the lungs
  • 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
• Oxygen and water can move through cell membranes by diffusion, but starch and proteins cannot
• Where diffusion takes place in the body

  • Oxygen moves from alveoli into red blood cells, and carbon dioxide moves from red blood cells into the lungs
  • Urea moves from liver cells into 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
• Single-celled organisms can use diffusion to transport molecules into their body from the air because they have a relatively large surface area to volume ratio
• Multicellular organisms cannot rely on diffusion alone due to their small surface area to volume ratio, so they have adaptations to allow molecules to be transported in and out of cells
• Adaptations to increase surface area for diffusion

  • Lungs: alveoli
  • Small intestine: villi
  • Fish gills: lamellae
  • Leaves: flattened shape and air spaces
• Osmosis


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


  Isotonic: concentration of external solution is the same as internal

  Hypertonic: concentration of external solution is higher than internal

  Hypotonic: concentration of external solution is lower than internal
• Osmosis in animals


  If external solution is more dilute, cells will burst. If external solution is more concentrated, cells will shrivel.
• Osmosis in plants


  If external solution is more dilute, water will move into the cell and vacuole, causing turgor pressure. If external solution is less dilute, water will move out and the cell will become soft and eventually die.
• Experiment: Effect of sugar solutions on plant tissue

  Place potato tubers in different concentrations of sugar solution

  Measure change in mass to determine if external solution is more or less concentrated than potato