B2: Organisation

• Levels of organisation in organisms

  • Cell
  • Tissue
  • Organ
  • Organ system
• Cell


  Smallest structural and functional unit of an organism, eg. muscle cell
• Tissue


  Group of cells with a similar structure and function, eg. muscle tissue
• Organ


  Group of tissues performing specific functions, eg. stomach
• Organ system


  Group of organs performing specific functions, eg. digestive system

  
• The nucleus of a cell is not an organ
• Food does not pass through the liver and pancreas in the digestive system
• - Levels of organisation

  1. Neurone (cell)

  2. Nerve (tissue)

  3. Brain (organ)

  4. Nervous system (organ system)

  5. Dog (organism)
• Digestion


  Breaking down large, insoluble molecules in food into smaller, soluble molecules that can be absorbed into blood
• Enzyme


  A type of protein molecule that acts as a biological catalyst, speeding up reactions in organisms without being used up or changed
• How enzymes work (lock and key theory)

  1. Substrate fits into / binds to enzyme active site

  2. Chemical reaction occurs (eg. bonds in substrate broken)

  3. Products released from unchanged enzyme
• Why each enzyme can only catalyse a specific reaction

  Each enzyme has an active site with a specific (3D) shape that only a substrate molecule with a complementary shape can bind to
• Metabolism


  The sum of all the reactions in a cell or the body, catalysed by different enzymes
• Enzymes involved in digestion

  • Lipase (breaks down lipids)
  • Carbohydrase (breaks down carbohydrates)
  • Protease (breaks down proteins)
• Where enzymes are produced and act

  Lipase - produced in pancreas & small intestine, acts in small intestine

  Carbohydrase - produced in salivary glands, pancreas & small intestine, acts in mouth & small intestine

  Protease - produced in stomach, pancreas & small intestine, acts in stomach & small intestine
• What the products of digestion are used for

  • Fatty acids & glycerol - to build new lipids (fats)

  Simple sugars (eg. glucose) - to build new carbohydrates, some used for respiration

  Amino acids - to build new proteins
• Where bile is produced, stored and released

  Produced - liver

  Stored - gall bladder

  Released into - small intestine
• Role of bile in digestion

  1. Neutralises hydrochloric acid from stomach to create optimum conditions for small intestine enzymes

  2. Emulsifies lipids (fat) by converting larger lipid droplets into smaller droplets to increase surface area for lipase enzyme to work on
• Enzyme denaturation


  Active site changes shape (eg. due to too high temp. or too high / low pH) so substrate no longer binds / fits and reaction can no longer be catalysed
• How temperature affects enzyme activity

  As temperature increases up to an optimum, rate of reaction increases (molecules gain kinetic energy so more frequent enzyme-substrate collisions)

  As temperature increases above optimum, rate of reaction decreases to 0 (enzymes denature so substrate no longer fits)
• How pH affects enzyme activity

  Enzyme activity is at a maximum at an optimum pH

  As pH is increased above or decreased below this, enzyme activity decreases (above / below optimum pH enzymes denature so substrate no longer fits)
• Enzymes are not cells
• Some enzymes also join molecules together to make larger molecules, not just break them down
• Bile is not an enzyme, it is a substance produced by the liver that helps the enzyme lipase
• Enzymes are not living, so they cannot die. At high temperatures they can denature, meaning their active site changes shape
• How amylase breaks down starch

  Starch / substrate binds to active site (of enzyme)

  Shape of active site and substrate are complementary

  A chemical reaction occurs to produce smaller molecules OR bonds between the (starch) molecules are broken to produce smaller molecules
• Why a person with a tumour blocking the tube from the gall bladder would have difficulty digesting fat

  No / less bile reaches the small intestine

  So less / no emulsification of fat

  So smaller surface area for lipase to break down fat

  pH of small intestine not neutralised

  So lipase is not at its optimum pH to break down fat
• How pancreatic cancer may cause weight loss

  Reduced / no enzyme production from pancreas

  Food is not broken down / digested fully

  Eg. less glucose absorbed, so less glucose available for respiration so more fat used up

  Eg. fewer fatty acids absorbed, so fewer fatty acids available so less fat is stored
• Test for sugars (carbohydrates)

  Grind up food and add Benedict's reagent

  Heat (above 65oC) in a water bath

  Sugar turns solution (from blue to) orange/brick red
• Test for starch (carbohydrates)


  Grind up food and add iodine solution

  Starch turns solution (from orange / brown to) blue-black
• Test for lipids (fats)


  Grind up food and add ethanol, then add water

  Fat turns solution milky / cloudy white
• Test for proteins


  Grind up food and add Biuret reagent

  Protein turns solution (from blue to) purple / lilac
• Safety precautions for practical

  Wear goggles to protect eyes

  Clean up spills immediately as Biuret is an irritant / corrosive / poisonous
• Method to compare sugar content of sausages


  Grind up each sausage and add to test tubes with water

  Add same mass of each sausage

  Add same volume of Benedict's solution to each test tube

  Place test tubes in a heated water bath for same length of time

  Record colour change - green / yellow / orange / brown / red if sugar present (or blue if no sugar present)

  The closer the colour to red, the more sugar present
• Variables in practical on effect of pH on amylase

  • Independent - pH of buffer solution

  Dependent - time for no starch to be detected (so time taken for amylase to break down starch)

  Control - volume & concentration of amylase and starch solution, temperature of water bath etc.
• Method to investigate effect of pH on amylase

  Set up test tubes with different pH solutions and a set volume of starch solution

  Put in water bath at 30oC, leave for 10 mins

  Set up spotting tiles with 1 drop of iodine solution in each well

  Add a set volume & concentration of amylase to one of test tubes, start stopwatch / timer

  Remove a drop of amylase-starch mixture every 30 seconds and place into a spotting tile to test for starch (blue-black)

  Record time when no starch is detected (no longer turns blue-black)

  Repeat for each pH buffer solution
• How to get more accurate optimum pH

  Use smaller pH intervals
• How to get more accurate time

  Remove a drop of mixture every 10 seconds
• How to extend investigation to test effect of different factor

  Keep pH constant

  But change named factor eg. temperature / starch concentration AND test a range of values of named factor
• Measuring starch concentration every 30 secs is a better method than subjective observations