Nutrition

• Autotrophic nutrition

  Organisms synthesise simple inorganic molecules into complex organic molecules which requires energy.
• Types of autotrophic nutrition

  • Photoautotrophs
  • Chemoautotrophs
• Photoautotrophs 


  Plants and green algae use light energy for photosynthesis to convert simple inorganic molecules into complex organic molecules.
• Chemoautotrophs 


  Bacteria in hydrothermal vents use energy released in chemical reactions during chemosynthesis to convert simple inorganic molecules into complex organic molecules.
• Heterotrophic nutrition

  Organisms gain complex organic molecules from other organisms.
• Name 4 types of heterotrophic nutrition

  1. Holozoic
  2. Saprotrophic
  3. Mutualistic
  4. Parasitic
• Holozoic nutrition

  • Internal digestion involving enzymes

  Key stages

  1. Ingestion: food taken in
  2. Digestion: food broken down
  3. Absorption: nutrients move into blood
  4. Assimilation: nutrients are used
  5. Egestion: removal of undigested food
• Saprotrophic nutrition

  • External digestion where enzymes are secreted from the ends of hyphae onto food
  • Small soluble substances are absorbed by facilitated diffusion or active transport as hyphae provide a short diffision pathway
• Parasitic nutrition

  Is an association between 2 species where the parasite gains nutrients from the host while causing harm to the host.
• Mutualistic nutrition 


  Is an association between 2 species where both organisms benefit nutritionally.
• 2 examples of holozoic nutrition

  • Amoeba
  • Hydra
• Holozoic nutrition: Amoeba

  • Intracellular digestion
  • Pseudopodia are temporary extensions to the cytoplasm
  • Food is ingested by endocytosis
  • When the amoeba engulfs it's prey, it is digested by vesicles containing digestive enzymes which fuse with the food vacuole
  • Absorption is when small molecules are moved through the food vacuoles membrane into the cytoplasm
• Holozoic nutrition: Hydra

  • Ingestion occurs when the tentacles extend and discharge stinging cells to paralyse prey. Prey is moved through the mouth into the body cavity
  • Extracellular digestion is when some endodermal cells secrete lipase and protease
  • Intracellular digestion is when the products are digestion are absorbed into cells where other endodermal cells engulf and digest food within food vacuoles
  • Indigestible food is egested through the mouth
• Levels of gut structure

  Lumen

  Mucosa

  Submucosa

  Inner circular muscle

  Outer longitudinal muscle

  Serosa
• Mucosa

  • Goblet cells secrete mucus for lubrication and to prevent autodigestion
  • Made of epithelium which lines the gut and can be adapted for absorption
• Submucosa

  • Has capillaries to proved the mucose with blood, transport absorbed nutrients and to maintain concentration gradients
  • Has nerve fibres which coordinate contractions of the muscle layer for peristalsis
• Muscle layer

  • Made of circular and longitudinal muscle
  • Smooth muscle
  • Muscle is responsible for peristalsis
  • Some parts of the circular muscle thickens to form sphincters
• Serosa

  • Made of tough connective tissue
  • Reduces friction with other organs
• Sphincters are thickened parts of circular muscle which control the movement of food from one place in the gut to another.
• Peristalsis is the wave of muscular contraction that moves food down the oesophagus. Circular muscle contracts behind the bolus and longitudinal muscle contracts in front.
• Autodigestion is the breakdown of proteins by enzymes in the stomach and small intestine wall.
• Digestion - Mouth

  • Food is ingested
  • Mechanical digestion breaks food up by chewing
  • Food is mixed with saliva which contains amylase, mucus, lysozyme, and hydrogen carbonates
• Why is food chewed?

  • To increase the surface of area for amylase
  • Make it easier to swallow
• Why does saliva contain mucus?

  • To bind food together
  • For lubrication
  • Aids peristalsis
• Why does saliva contain amylase?

  To break starch down into maltose
• Why does saliva contain lysozyme?

  Digestive enzymes defend against pathogens.
• Why does saliva contain hydrogen carbonates?

  To provide the optimum pH for amylase
• Digestion - Oesophagus

  • Secretes mucus for lubrication
  • Peristalsis moves food towards the stomach due to a thicker muscular layer
• Digestion - Stomach

  • Gastric glands secrete gastric juices
  • Gastric glands contain goblet cells, oxyntic cells and chief cells
  • Had oblique muscle to provide stronger contractions
  • Rugae allows the stomach wall to stretch
  • Protein digestion occurs
• Chyme is the mixture of partially digested food and gastric juices that leave the stomach
• Why do gastric glands have goblet cells?

  • To secrete mucus for lubrication and to prevent autodigestion
• Why do gastric glands have chief cells?

  • To secrete pepsinogen which is an inactive precursor of pepsin to prevent autodigestion.
• Why do gastric glands have oxyntic cells?

  • Secrete hydrochloric acid to reduce the pH for pepsin, kill pathogens and to activate pepsinogen
• Rugae


  Are folds in the stomach wall to allow it to stretch and expand
• Pepsinogen is an inactive precursor of pepsin which is secreted by chief cells and is activated by hydrogen ions from hydrochloric acid. This helps to reduce autodigestion of the stomach wall.
• Exopeptidases are enzymes that hydrolyse peptide bonds on the ends of polypeptide chains to form amino acids.
• Endopeptidases are enzymes that hydrolyse peptide bonds within a polypeptide chain to form shorter dipeptides and amino acids.
• Protein digestion is best whenthere is a mixture of endopeptidases and exopeptidases because endopeptidases create more ends for exopeptidases to work on.
• Types of endopeptidases

  • Pepsin
  • Trypsin
• Digestion - Duodenum

  • Main site of digestion
  • Receives secretions from 3 places: Pancreas, liver and Brunners glands