Digestive system

• Digestive System


  • Main structures: Oral cavity, pharynx, esophagus, stomach, intestines, liver, pancreas, rectum and anus
  • Main functions: Converts ingested matter into molecules and ions that can be absorbed into body, eliminates undigested matter, helps regulate water content
• Biological molecules


  Organic molecules: carbohydrates (for energy), proteins (for bodily functions), nucleic acids (for instructions & information), lipids (for energy, signalling & membranes)
• Polymer


  Long molecule consisting of many similar building blocks called monomers
• Macromolecule


  Complex and large polymers, including many carbohydrates, proteins, and nucleic acids. Lipids are not large enough to be classed as macromolecules or polymers.
• Polymerisation


  Polymers are assembled from monomers by dehydration synthesis reactions
• Depolymerisation


  Breakdown of polymers into monomers occurs by hydrolysis, where water is added to break down a polymer
• Carbohydrate polymers


  • Maltose, sucrose, lactose
• Carbohydrates


  • Glycogen (animal muscles), cellulose & starch (plant cells), chitin (arthropods' exoskeleton)
• Lipids


  • Phospholipids (cell membrane)
• Proteins


  • Enzymes (e.g. alcohol dehydrogenase)
• Nucleic acids


  • DNA and RNA (nucleus)
• Triglycerides


  Constructed from glycerol and three fatty acids, serve as energy reserves in animals, help insulate and waterproof
• Saturated fatty acids


  Have maximum hydrogen atoms, no double bonds, may contribute to cardiovascular disease
• Unsaturated fatty acids


  Have one or more double bonds, essential fatty acids like omega-3 may provide protection against cardiovascular disease
• Proteins


  Polymers made from polypeptide chains of amino acid monomers, have diverse structures and functions
• Amino acids


  Have amino group, carboxyl group, and differing side chains (R groups) that give them different properties

  
• Protein structures


  Primary, secondary, tertiary, quaternary
• Nucleic acids


  Polymers called polynucleotides, made of nucleotides consisting of nitrogenous base, pentose sugar, and phosphate group
• Categories of feeding habits

  • Herbivores
  • Carnivores
  • Omnivores
  • Opportunistic feeders
• Purpose of feeding


  Provide chemical energy for cellular processes, organic building blocks for macromolecules, essential nutrients
• Essential nutrients


  Materials an animal cannot assemble from simpler organic molecules, must be obtained from diet
• Classes of essential nutrients

  • Essential amino acids
  • Essential fatty acids
  • Vitamins
  • Minerals
• Essential amino acids


  Amino acids that must be obtained from food in preassembled form, "complete" proteins have all essential amino acids
• Essential fatty acids


  Certain unsaturated fatty acids that must be obtained from diet, include monounsaturated and polyunsaturated omega-3 fatty acids
• Vitamins


  Organic molecules required in diet in small amounts, categorised as fat-soluble or water-soluble
• Minerals


  Simple inorganic nutrients usually required in small amounts, ingesting large amounts can upset homeostatic balance
• Essential fatty acids


  Obtained from the diet and include certain unsaturated fatty acids
• Essential fatty acids


  • Monounsaturated fatty acids in olive oil, most nuts, avocados, peanut butter, etc.
  • Polyunsaturated omega-3 fatty acids, linoleic acid from linseed oil & other oils, fish, etc.
• Deficiencies in fatty acids are rare because their sources (e.g., seeds, grains & vegetables) are in abundance
• Vitamins

  Organic molecules required in the diet in very small amounts
• Thirteen vitamins are essential for humans
• Vitamins

  Categorised as either fat-soluble or water-soluble
• Minerals


  Simple inorganic nutrients, usually required in small amounts
• Ingesting large amounts of some minerals can upset homeostatic balance (e.g., salt)
• Ingestion


  The act of eating or feeding
• Feeding strategies


  • Suspension (filter) feeders
  • Substrate feeders
  • Fluid feeders
  • Bulk feeders
• Suspension (filter) feeders


  • Humpback whale
• Substrate feeders


  • Leaf miner caterpillar
  • Maggots (fly larvae) on KFC meat
• Fluid feeders


  • Hummingbird sucking flower nectar
  • Mosquito sucking blood
• Bulk feeders


  • Blue heron & Fish
  • Rock python & Gazelle