Adaptations for Nutrition

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  • Adaptations for Nutrition
    • 'Nutrition is the process by which organisms obtain nutrients to provide energy to maintain life functions and matter to create and maintain structure'
    • Organisms are divided into;
      • Autotrophs (Producers)
        • Synthesise complex organic compounds from simple inorganic molecules using a source of energy
          • There are two types of autotrophs;
            • Photoautotrphs
              • Convert carbon dioxide and water into glucose using light energy from the sun during photosynthesis
                • Include green plants, fungi and some bacteria
            • Chemoautotrophs
              • Use energy derived from special methods of respiration to build up organic molecules
                • Include some bacteria
      • Heterotrophs (Consumers)
        • Organisms that feed on complex organic molecules produced by autotrophs
          • These tend to be large, insoluble molecules such as polysaccharides e.g. starch and proteins which cannot pass into the plasma membrane
            • Includes animals, fungi, some protocists and bacteria
        • There are three types of heterotrophs;
          • Holozoic Feeders
            • Take food into the body and break it down by digestion. They have a specialised digestive system. Includes most animals
            • Types of Holozoic Feeders;
              • Herbivores - Feed on Plants
              • Carnivores - Feed on other animals
              • Detrivores - Feed on dead and decaying material
          • Saphrophytic Feeders
            • Digest food outside their body
              • Feed on dead and decaying matter
                • Have simple digestive systems
                  • Includes some fungi and bacteria
            • Saphrophytic digestion
              • Enzymes are secreted onto dead organic matter outside the body
                • The enzymes hydrolyse the bonds in the organic matter e.g. protein/carbs to make smaller soluble molecules e.g. amino acids/glucose
                  • These smaller molecules are absorbed across the cell membrane by diffusion
                    • Microscopic saphrophytes are called decomposers. Their activities are important in the decomposition of leaf litter and the recycling of valuable nutrients like nitrogen
          • Parasites
            • Live on or in another organism (host) and obtain nourishment at the expense of the host
              • No digestive system
                • Highly specialised and can adapt to ways of life
            • E.g. Tapeworm
    • Digestion
      • Organic molecules must be broken down by digestion and absorbed into the body tissues from the digestive system before they can be used in the body cells
        • Digestion and absorption take place in the gut
          • In simple organisms, feeding on only one type of food, the gut is undifferentiated
            • In advanced organisms with a varied diet, the gut is divided into various parts along it's length and each part is specialised according to it's function
      • Stages
        • Humans, like most animals, use holozoic nutrition which consist of these stages
          • Ingestion: Taking food into the body through the mouth
            • Peristalsis: Muscular contraction of the gut wall to move food along the gut. Cellulose fibre provides bulk and stimulates peristalsis
              • Digestion: Breaking down large, insoluble food molecules into smaller, soluble molecules. This is done by both mechanical and chemical action
                • Absorption: The passage of food through gut wall into the blood
                  • Egestion: The elimination of food that cannot be digested e.g. cellulose cell walls of plants
    • Human digestive system
      • Consists of the alimentary canal which is muscular tube with lands extending from the mouth to the anus
        • In adults it is up to 10m long and is divided into distinct parts that have been adapted to carry out different functions
      • Regions of the Gut
        • Mouth: Chemical and Mechanical Digestion
          • Mechanical digestion of food begins in the mouth when food is chewed using the teeth
            • This makes the food easier to swallow and increases it's surface area for enzyme ction
          • Chemical digestion also occurs in the mouth
            • As it is chewed, the food is mixed with saliva from the salivary glands
              • Saliva is a watery secretion containing mucus and amylase together with some mineral ions which help keep the pH of the mouth slightly alkaline (pH 6.5-7.5) the optimum pH for amylase
                • Amylase breaks down starch into maltose. After chewing, the food is rolled into a ball (bolus) by the tongue and swallowed. The mucus lubricates it's passage down the oesophagus
        • The Oesophagus
          • Once inside the oesophagus, the bolus of food is pushed down to the stomach by a wave of contraction called peristalsis
            • Behind the bolus, the muscles lining the walls of the gut work in antagonistic pairs
              • The circular muscles contract and the longitudinal muscles relax, pushing food along in front of the wave of contraction
                • Peristalsis continues throughout the length of the gut
                  • Goblet cells in the mucosa secrete mucus for lubrication
        • The Stomach
          • Stores food for up to 4 hours
          • Main functions;
            • Mechanical Digestion - There are three layers of muscle that churn the food into liquid chyme
            • Chemical Digestion -of proteins begins
          • Gastric juices secrete endopeptidase enzymes that hydrolyse proteins to polypeptides
            • Hydrochloric acid provides the acidic conditions for the enzyme to work (pH2) and kills bacteria in food
              • Mucus protects the stomach lining from digestive enzymes and acid Lubricates food to assist movement in stomach
        • The small intestine
          • Divided into:
            • Duodenum - The first 20cm and main site of digestion
              • Relaxation of the muscle at the base of the stomach allows small amounts of the partially digested food into the duodenum a little at a time
                • The duodenum recieves; bile from the liver and pancreatic juice from the pancreas
                  • The walls of the duodenum also contain brunners glands that secrete;
                    • Alkaline Juices - keeps the contents of the small intestine at the correct pH for enzyme action
                    • Mucus - lubricates and protects
                  • Bile
                    • Secreted by the liver and stored in the gall bladder
                      • Enters the duodenum via the bile duct
                        • Contains bile salts which emulsify lipids into smaller droplets, increasing the surface area for pancreatic lipase action
                          • They also neutralise HCl from the stomach, making the pH of the small intestine slightly alkaline
                  • Pancreatic Juices
                    • Secreted by the exocrine glands in the pancreas. Enters the duodenum via the pancreatic duct
                      • Contains the digestive enzymes;
                        • Amylase - Hydrolyse remaining starch into maltose
                        • Lipase - Hydrolyse lipids into fatty acids and glycerol
                        • Endopeptidases - Hydrolyse proteins to polypeptides
                        • Maltase - Hydrolyses maltose into glucose
                        • Exopeptidases - Hydrolyse short chains of polypeptides into amino acids
            • The Ileum - Up to 6m long and forms the majority of the small intestine. Main site of absorption
              • Some digestion also takes place;
                • Maltase - Hydrolyses maltose into glucose
                • Endopeptidases - Hydrolyse proteins to polypeptides
                • Exopeptidases - Hydrolyse short chains of polypeptides to amino acids
              • Increases diffusion by;
                • Large surface area
                  • It is very long
                  • It is highly folded
                  • The mucosa forms fingerlike projections called villi
                  • On the ends of the villi the individual epithelial cells also have finger like projections called microvilli
                • A short diffusion pathway
                  • The epithelium is one cell thick
                • A steep diffusion gradient
                  • Blood capillaried - These remove glucose and amino acids, keeping their concentration low
                  • Lacteals - (part of the lymph system) which remove faty acids, glycerol and monoglycerides, keeping their concentration low

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