Digestion

• Types of nutrition


  • Autotrophic
  • Heterotrophic
• Autotrophic


  Make own food
• Photoautotrophic


  • Use light energy to perform photosynthesis
  • Examples include green plants, Protoctista and some bacteria
• Chemoautotrophic


  • Use energy from chemical reactions
  • Examples include some prokaryotes
• Heterotrophic


  Consume complex organic molecules produced by autotrophs
• Saprotrophic


  • Feed on dead or decaying matter by secreting enzymes extracellularly and then absorbing the products
  • Example: Rhizopus (bread mould)
• Parasitic


  • Obtain nutrition from another living organism called the host over a long period of time, whilst causing it harm
  • Endoparasites live within the host's body, e.g. tapeworm, Taenia
  • Ectoparasites live on the surface, eg human head louse, Pediculus
• Holozoic


  • Form of nutrition used by most animals where they ingest and then digest food, absorbing nutrients
  • They possess a specialised digestive system
  • Examples include herbivores (plant material), carnivores (animal material), omnivores (plant and animal material) and detritivores (dead or decaying material)
• Digestion in the gut

  1. Ingestion - taking food into contact with the digestive system

  2. Digestion - results in smaller molecules, begins with mechanical breakdown of large food pieces by enzymes

  3. Absorption - passage of nutrients into the blood

  4. Egestion - elimination of undigested material
• Protoctista such as amoeba are holozoic heterotrophs. They absorb nutrients directly through their cell membrane by diffusion, ingesting larger molecules by endocytosis and fluids by pinocytosis into food vacuoles. Lysosomes fuse with the vacuoles and release digestive enzymes. Nutrients are absorbed through the membrane of the food vacuole and waste is egested by exocytosis.
• Some larger organisms have a single body opening; e.g. Hydra, which ingests prey through the mouth and the digested products move into the body cavity. More developed organisms possess a tube gut, ingesting at one end and egesting at the other.