The digestive track

Key words:  diffusion, enzymes, enzyme specificity, surface area:volume ratio, blind sac, open tube
 
 

  1. Digestion
    1. physical break-up of food
      1. chewing, crops
    2. chemical processing of three main macromolecule types
      1. breaking macromolecules into component parts
      2. each requires particular set of enzymes
      3. carbohydrates (amylase)-> sugars
        1. examples: starch, sugar
      4. proteins (protease)-> amino acids
      5. fats (lipase)->glycerol and free fatty acids
  2. Digestion occurs in all heterotrophic organisms
    1. Intracellular digestion
      1. macromolecules taken up via endocytosis
      2. examples: amoebae, Paramicium, some sponges
    2. Extra cellular digestion
      1. macromolecules digested outside of cells
        1. component parts absorbed via active transport, diffusion
      2. advantage: keep digestive enzymes outside of cell
      3. disadvantage: surface area: volume limitations
    3. some example digestive tracks
      1. evolutionary trend towards increased complexity
Study questions
1. Bacterial symbionts are found in the digestive tracks of many organisms (including humans) .  Thinking about the metabolic diversity of bacteria, why do you think these particular ones are thought of as being mutually beneficial (symbiotic) rather than parasitic?

2.  Few organisms can digest cellulose, the cell wall material of plants:  some fungi and some bacteria can.  However, many grazing animals such as cattle, iguanas and termites eat diets very high in cellulose.  What symbiotic organisms might you expect to find in their guts?

3.  Compare three examples of gut systems, emphasizing the structural adaptations that increase nutrient absorption.

4.  What is the importance of diffusion in digestion?  Absorption?

5.  Digestive enzymes are usually produced in inactive forms and loaded into membrane-bound packets until exocytosis.  Following exocytosis they are activated in the stomach or intestinal lumen.  Why does this make sense?

6.  Contrast extracellular and intracellular digestion.  Which involves endocytosis?  Which involves absorption?  Which takes place in your digestive track?

Answers