Modes of nutrition

• Autotrophic - Synthesis of complex organic chemicals from inorganic substances using an energy source.
• Photoautotrophic - formation of organic molecules from inorganic molecules using light energy
• Chemoautotrophic - uses chemical energy, from chemicals such as hydrogen sulfide, to combine inorganic substances into complex organic chemicals
• Heterotrophic - an organism that consumes ready-made complex organic material (its food)
• Saprophytes - organism that feeds on dead or decaying matter by extracellular digestion and absorption of the products of digestion
• Holozoic - the internal digestion of food, involving ingestion, digestion and egestion
• Parasitic - an organism that obtains nutrients from another living organism, its host, to which it causes harm
• How do unicellular organisms gain nutrition?

  Holozoic nutrition. They obtain nutrients via diffusion, facilitated diffusion and active transport across the cell surface membrane. Larger molecules (microbes) are absorbed via endocytosis into food vacuoles. Products are absorbed into cytoplasm and indigestible remains are egested via exocytosis.
• How do simple multicellular organisms e.g. Hydra gain nutrition?

  Extends its tentacles, discharges stinging cells to paralyse prey.

  The tentacles move prey through the mouth to hollow body cavity;

  Endodermal cells secrete protease and lipase and prey is digested extracellularly;

  The products of digestion are absorbed into the cells and indigestible remains egested through the mouth.
• Fully explain saprotrophic nutrition:

  • feed on dead or decaying matter
  • no specialised digestive system
  • extend branching hyphae into the food material and secrete digestive enzymes from the tip of the hypha
  • Enzymes include proteases, lipases, amylases and cellulases
  • Soluble products of digestion are absorbed via diffusion and active transport
• Decomposer - microscopic saprotrophs involved in decaying leaf litter and recycling nutrients
• Saprotrophic - the external digestion of food, involving the secretion of enzymes onto food