2.4-nutrition

• Photoautotrophic

  A word to describe an organism that uses light energy to convert simple organic molecules into complex organic ones. Chlorophyll is usually used to absorb green sunlight energy e.g. in green plants such as dandelions, algae and certain bacteria.
• Chemoautotrophic

  A word to describe an organism using energy derived from special methods of respiration (such as oxidation of hydrogen sulphide/sulphur/ferrous ions or nitrates) to convert simple inorganic molecules into complex organic ones, usually in bacteria, e.g. nitrosomonas.
• Saprotrophs

  Another name for saprobionts. They feed on dead/decaying matter through extracellular digestion. This is where enzymes are secreted onto food outside the body, then soluble products of digestion absorbed by diffusion across the cell membrane. This group includes fungi and some bacteria e.g. Clostridium, Mucor, Actinomycete bacteria.
• Saprobionts

  Another name for saprotrophs. They feed on dead/decaying matter through extracellular digestion. This is where enzymes are secreted onto food outside the body, then soluble products of digestion absorbed by diffusion across the cell membrane. This group includes fungi and some bacteria e.g. Clostridium, Mucor, Actinomycete bacteria.
• Heterotrophic Nutrition

  Where complex organic molecules found in other organisms are broken down to release energy, through digestion. This is a feeding method.
• Holozoic (feeder)

  The kind of feeder that processes food as it passes along the gut, a kind of feeding used by herbivores, carnivores and detritivores, the opposite of external digestion. Simple organisms with one type of food have an undifferentiated gut (aphids), whereas advanced organisms with a varied diet such as humans have a divided gut with each part specialised to a function, ingestion, digestion, absorption and egestion.
• Extracellular Digestion

  The breakdown of molecules outside of the feeder's cells, by secreting enzymes onto the food, afterwards the soluble products are absorbed across the cell membrane. This is done by saprotrophs/saprobionts.

  
• Parasite

  An organism that feeds on another organism, the host, which suffers harm and often eventually death. They are highly specialised and show their adaptations to living in/on the host. Examples include Tapeworms, potato blight and Plasmodium (malaria).

  
• Mutualism

  Another name for symbiosis, a close association between members of two different species from which both organisms derive some sort of benefit, for example cellulose digesting bacteria in the gut of herbivores. The bacteria produce enzymes to digest cellulose, and in return bacteria gain digestive products and suitable conditions for growth.

  
• Lumen

  The central cavity of a tubular or other hollow structure in an organism.
• Serosa

  The outermost layer of the gut, tough connective tissue that protects the wall of the gut and reduces friction from other organs in the abdomen as the gut moves during the digestive process.
• Muscle layer

  The second outermost layer of the gut, that cause waves of muscle contractions called peristalsis which propels food along the gut. Behind the food the circular muscles contract and the longitudinal muscles relax.
• Sub-mucosa

  The second innermost layer of the gut, consisting of connective tissue containing blood and lymph vessels to take away absorbed food products as well as nerves that co-ordinate the muscular contractions of peristalsis.
• Mucosa

  The innermost layer that lines the wall of the gut. It secretes mucus which lubricates and protects the layer. In some regions it secretes digestive juices and in others it absorbs digested food.
• Ingestion

  When large food particles are taken into the buccal cavity.
• Mechanical digestion

  The action of teeth, saliva and the tongue on food (mastication), so it may then move into the gut. Further done by the action of stomach and the peristaltic action of muscular layers in the gut wall. The function is to increase surface area of food so enzymes in chemical digestion are more effective.
• Chemical digestion

  The breakdown (with enzymes) of large food molecules to small, soluble molecules. Different regions of the gut have different pH therefore the enzymes found in the different regions have different pH optima.
• Absorption

  The process of small, soluble food molecules moving from the small intestine into the blood stream, which transports them to the cells.
• Egestion

  Also known as elimination, where undigested food moves out of the body as faeces, via the colon, rectum and anus.
• Carbohydrates

  Also known as polysaccharides, long chains of sugars that can be broken down into disaccharides then monosaccharides.
• Polysaccharides

  Also known as carbohydrates, long chains of sugars that can be broken down into disaccharides and then monosaccharides.
• Maltose

  A disaccharide made of two glucose monosaccharides. Broken down in both the buccal cavity and duodenum.

  
• Maltase

  The specific enzyme that hydrolyses maltose to two glucose monomers.

  
• Proteins

  Long chains of amino acids found in meats, dairy products and some veg such as legumes and brussel sprouts. They are generally broken down by endopeptidases and exopeptidases, the general name given to them peptidases.
• Endopeptidase(s)

  Protein breaking enzyme that hydrolyses peptide bonds within the polypeptide chain.
• Exopeptidase(s)

  Protein breaking enzyme that hydrolyses peptide bonds on the ends of shorter polypeptide chains.
• Fats

  Also known as lipids, found in foods such as ice cream, fast food, and oily foods usually associated with unhealthiness due to storage of these in the body. They are hydrolysed by lipase into fatty acids and glycerol, after being emulsified into smaller droplets.

  
• Salivary amylase

  A form of the enzyme that hydrolyses breakdown of starch into glucose, secreted in the mouth to aid mechanical digestion.
• Salivary Mucus

  Secreted in the saliva, that acts as a lubricant and protects the oesophagus wall.
• Salivary Mineral Salts

  The ionic compounds that are secreted in the mouth to maintain a pH of 6.5-7.5, the optimum pH for functioning of salivary amylase.
• Saliva

  The secretion of the mouth, consisting mostly of water but also containing a specific type of amylase, mucus and mineral salts that maintain a pH of 6.5-7.5. It aids with mechanical digestion.
• Peristalsis

  A series of rhythmic contractions that moves the bolus of food down the oesophagus from the mouth.

  
• Buccal Cavity

  Another name for the mouth, the point of entry for food, lined with teeth and containing the tongue. It is the site of mechanical digestion and salivary secretion.
• Oesophagus

  The part of the alimentary canal which connects the throat and the stomach, where peristalsis is most active to move the bolus down.

  
• Alimentary Canal

  The whole passage along which food passes through the body from mouth to anus during digestion.

  
• Goblet Cell

  A cell that secretes mucus, to form a protective layer in the stomach preventing hydrochloric acid and pepsin from breaking down the stomach wall, also aiding movement of food within the stomach. It is alkaline due to the presence of hydrogen carbonate salts.

  
• Stomach Mucus

  Forms a protective layer in the stomach, preventing hydrochloric acid and pepsin from breaking down the stomach wall, also aiding movement of food within the stomach. It is alkaline due to the presence of hydrogen carbonate salts.
• Stomach

  Where the bolus arrives after travelling down the oesophagus, lined with goblet cells, containing hydrochloric acid, pepsin (an endopeptidase), and mucus. It is also the next site of mechanical digestion with churning movements.

  
• Stomach Acid

  Made up of hydrochloric acid, its purpose to kill germs in the food, provide the optimum pH for stomach enzymes, denature incoming proteins and activate peptidases. It causes the stomach to have a pH value of 1-2.
• Pancreas

  The creation site of many enzymes including a specific type of amylase, endo and exopeptidases and lipase. These are released into the duodenum via the pancreatic duct.