Nutrition

• Autotrophic


  An organism that produces its own food by manufacturing complex organic compounds from simpler inorganic molecules such as water and carbon dioxide
• Types of autotrophic organisms

  • Photoautotrophic
  • Chemoautotrophic
• Photoautotrophic organism


  An organism which obtains its nutrition through photosynthesis
• Chemoautotrophic organism


  An organism which obtains its nutrition through inorganic molecules, such as sulfur, in the absence of light
• Heterotrophic


  An organism that cannot produce its own food and obtains energy by feeding on organic compounds produced by other organisms
• Saprotroph


  An organism that feeds by extracellular digestion, e.g. fungi
• Extracellular digestion by saprotrophs

  1. Release enzymes which catalyse the breakdown of dead plant and animal material into simpler organic matter

  2. Absorb the products of digestion
• Holozoic


  Describes a heterotrophic organism that internally digests food substances
• Processes of holozoic nutrition

  • Ingestion
  • Digestion
  • Absorption
  • Assimilation
  • Egestion
• Ingestion


  The process by which organisms take food into their bodies
• Digestion


  The processes by which large, insoluble molecules are broken down into smaller, soluble molecules that can be absorbed across cell membranes
• Types of digestion


  • Mechanical digestion
  • Chemical digestion
• Mechanical digestion


  Type of digestion that involves physically breaking down food material into smaller pieces to increase the total surface area for chemical digestion
• Chemical digestion


  A type of digestion that involves breaking down large, insoluble molecules into smaller, soluble molecules using enzymes
• Assimilation


  The synthesis of biological compounds from absorbed simpler molecules
• Absorption


  The movement of useful substances into the bloodstream
• Egestion


  The removal of undigested waste material from the body
• How unicellular organisms obtain nutrients

  1. Ingestion via phagocytosis

  2. Intracellular digestion (using hydrolytic enzymes) breaks down large, insoluble molecules into smaller, soluble molecules

  3. Products of digestion pass into the cytoplasm by diffusion and active transport

  4. Undigested material removed by exocytosis
• Hydra


  A small, multicellular, freshwater organism of the phylum Cnidaria
• Structure of Hydra


  • Basic, undifferentiated sac-like gut
  • Single opening, surrounded by tentacles, that serves as a mouth and an anus
  • Single gut cavity (known as the enteron)
• Digestion in Hydra


  1. Hydrolytic enzymes secreted into the enteron by the endodermis

  2. Extracellular digestion partially digests food molecules

  3. Partially digested food transported, via phagocytosis, into endodermal cells where intracellular digestion takes place

  4. Undigested material egested from the enteron via the single opening
• Gut shape in more complex organisms

  Tube-like with two openings, a mouth for ingestion and anus for egestion
• Human gut adaptation


  Adapted to an omnivorous diet consisting of plant and animal material
• Layers of the gut wall

  • Epithelium
  • Mucosa
  • Submucosa
  • Muscle layer
  • Serosa
• Epithelium


  A single layer of cells that line the gut wall
• Mucosa layer


  • Mucous membrane lining the gut wall
  • Contains glands that secrete digestive enzymes, mucus, and an acid or alkaline liquid that provides an optimum pH
• Submucosa layer


  • Layer of connective tissue below the mucous membrane
  • Contains blood vessels and lymph for the transport of digestion product and glands that secrete an alkaline fluid
• Muscle layer


  A layer of circular and longitudinal muscles beneath the submucosa
• Action of circular and longitudinal muscles in peristalsis

  The contraction of the circular muscle behind the bolus of food and the relaxation of the longitudinal muscle in front forces food down the gut
• Serosa


  The tough, protective layer that surrounds the gut
• Buccal cavity


  The oral cavity through which food enters the body
• Types of digestion in the buccal cavity

  • Mechanical digestion
  • Chemical digestion of starch
• pH range of the buccal cavity

  pH 6.5 to 7.5
• Function of the teeth

  To mechanically break down food
• Types of digestion in the buccal cavity

  • Mechanical digestion
  • Chemical digestion of starch
• Function of the teeth

  Crush and grind food into smaller pieces, increasing its surface area
• Tongue


  A muscular organ in the buccal cavity that is vital in the chewing and swallowing of food
• Function of salivary glands

  Secrete amylase, mineral ions and mucus into the buccal cavity
• Function of the oesophagus


  Carries food from the buccal cavity to the stomach by peristalsis
• Processes in the stomach

  Mechanical digestion (mixing and grinding) and chemical digestion of protein