Modes of Nutrition

• Modes of nutrition for organisms

  • Autotrophic
  • Heterotrophic
• Autotrophic organisms


  Can synthesize their own complex materials, meaning they make their own food
• Heterotrophic organisms


  Cannot synthesize their own complex materials and must obtain nutrition from other organisms
• Types of autotrophic nutrition

  • Photoautotrophic
  • Chemoautotrophic
• Photoautotrophs


  • Use light energy to make their own food
  • Require chlorophyll, which gives them their green pigment
  • Examples include green plants, algae, phytoplankton, and cyanobacteria
• Chemoautotrophs


  • Use inorganic chemicals like hydrogen sulfide, ferrous ions, and ammonia to synthesize organic materials
  • Found in extreme environments
  • Include nitrogen-fixing bacteria and bacteria in cow stomachs
• Types of heterotrophic nutrition

  • Saprotrophic
  • Parasitism
  • Holozoic
• Saprotrophic nutrition


  • Illustrated by fungi that rely on extracellular digestion
  • Fungi grow hyphae that secrete extracellular enzymes for digestion outside their bodies, allowing nutrient absorption
• Parasitism


  • Exemplified by tapeworms in the human intestine
  • Adapted to avoid digestion by hosts
  • Have hooks and suckers for attachment
  • Secrete enzyme inhibitors and mucus to prevent digestion
• Life cycle of a tapeworm

  1. Eggs released in feces

  2. Ingested by a secondary host like a cow

  3. Larvae burrow through the cow's gut wall

  4. Develop into cysts in the muscle

  5. Ingested by humans through undercooked meat

  6. Grow inside the human intestine
• Ectoparasite head louse


  • Feeds on blood from the scalp
  • Holds onto hair with claws
  • Lays eggs at the base of hair
• Holozoic nutrition


  • Involves internal digestion
  • Seen in single-celled amoebas that ingest food through phagocytosis, digest with hydrolytic enzymes, absorb nutrients, assimilate food for energy, and expel waste
• Mutualism involves beneficial relationships between organisms