Biology

• Leaf adaptation for efficient gas exchange

  1. Broad and Thin
  2. Large surface area to volume ratio; no cell far from air
  3. 2. Large number of air spaces within leaf
• Upper epidermis

  Transparent

  • Allows light to pass through
• Palisade Mesophyll

  Lots of chloroplasts

  • For photosynthesis

  Stacked

  • More light can be captured
• Spongy Mesophyll

  Air spaces

  • Allows diffusion to occur more efficently.
• Xylem

  Carries water and minerals
• Phloem


  Carries sucrose
• Mass transport


  Bulk movement of gases or liquids in one direction
• Haemoglobins

  A group of chemically similar molecules found in many different organisms
• Haemoglobin consists of four polypeptide chains

  • 2 alpha 2 beta
• Each polypeptide chain is associated with a prosthetic haem group
• Haem group contains an Fe2+ ion
• Each haemoglobin molecule can carry four oxygen molecules.
• Haemoglobin combines with oxygen to form oxyhaemoglobin.
• Association of oxygen

  Process which haemoglobin binds with oxygen.

  • Occurs in lungs
• Dissociation of oxygen

  Process which oxygen is released from haemoglobin

  • Occurs in lungs for haemoglobin to bind to oxygen again.
• Affinity

  Degree to which one substance combines with another.

  • Haemoglobin affinity changes under different conditions by changing its shape in the presence of certain substances.
• Different species have different types of haemoglobin. 


  Different oxygen transport properties adapted to the environment of each animal
• Haemoglobin is a globular protein
• Four globin subunits are held together by disulphide bonds

  Hydrophobic R groups face inwards

  • Preserve the 3D spherical shape

  Hydrophilic R groups face outwards

  • Maintain solubility
• Reasons why molecules cannot pass through cell-surface membrane through simple diffusion.

  1. Too large
  2. Polar
  3. Hydrophilic
• Production of calibration curves

  1. Make solutions of known concentrations and carry out quantitative tests on each.
  2. Use colorimeter to measure colour value of each solution and plot calibration curve.
  3. Concentration on x-axis, Colorimeter reading on y-axis
  4. Find concentration of sample from calibration curve interpolation.
• Exopeptidase


  Hydrolyses peptide bonds at ends.

  • Removes amino acids at ends
• Endopeptidase


  Hydrolyse internal peptide bonds.

  • Break proteins into shorter chains
  • Increases surface area; number of ends
• Why use a colourimeter

  Improves repeatability of results

  • Quantitative; subjective colour change
  • Standardises method
• Countercurrent Flow

  Blood and water flow in opposite directions

  • Maintains constant concentration gradient
  • Diffusion occurs throughout the lamellae
• Endopeptidases

  Hydrolyse bonds at ends of polypeptides into dipeptides.
• Endoeptidases

  Hydrolyses middle of polypeptide chains into shorter polypeptides
• Digestion

  Hydrolysis of large insoluble molecules into smaller soluble molecules
• Hydrogen bonds

  Form between strongly polar R groups

  • Weakest bonds
  • Most common
• Hydrophobic interactions

  Form between the non-polar (hydrophobic) R groups within the interior of proteins.
• Cell division occurs at the apex