Adaptations to different diets

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  • Adaptations to different diets
    • Differences in dentition
      • Herbivores
        • Tough plant material must thoroughly ground up food before it is swallowed
        • Grazers (e.g. cows and sheep) have small, flat top incisors on lower jaw only and cuts against a horny pad on upper jaw
        • The canine teeth are not present or indistinguishable from the incisors
        • The diastema (a gap) between front teeth and premolars. Allows tongue to move freshly-cut grass to the large grinding surfaces of the molars
        • The horizontal jaw movement is a circular grinding motion
        • Molars interlock in a W M arrangement
        • Teeth continuously growing due to open, unrestricted roots
      • Carnivores
        • Teeth for catching/killing prey, cutting or crushing bones and for tearing meat
        • The sharp incisors grip and tear flesh from the bone
        • Large canine teeth curved and pointed for seizing/killing prey and tearing flesh
        • Powerful , well developed jaw muscles to enable gripping prey finmly and help in crushing bone
        • The vertical jaw movement allowing the jaw to open widely for capturing and killing prey
        • Carnassials (specialised cheek teeth), with cisor -like shearing action for cutting flesh
        • The premolars and molars are for cutting an  crushing
      • In total, adult humans have 32 teeth
        • 8 incisors for biting and cutting
          • 4 canines for biting and cutting
            • 10 premolars and molars for chewing, crushing and grinding
              • Our teeth are not particularly specialised as we are omnivores - we eat both plant and animal material
    • Herbivore Digestion
      • Herbivorous mammals have a diet that consists of cellulose
        • But mammals don't produce the enzyme cellulase to break down cellulose
          • Instead, these animals have evolved a symbiotic relationship with bacteria which do produce cellulose; this relationship is called mutualism
      • Mutualism: 'A close association between organisms of two different species, where both organisms benefit from the relationship'
      • Herbivores can be divided into ruminants and non-ruminants
        • Ruminants (Fore-gut digesters)
          • A ruminant is an animal with a specialised stomach (rumen) in which mutualistic bacteria live
          • Ruminants have a stomach made up of 4 chambers
            • Three of these chambers are formed by the oesophagus and one is the true stomach
              • The region of the gut occupied by the bacteria is kept seperate from the main digestive region so that;
                • Food can be kept there long enough for bacteria to digest the cellulose
                • The bacteria are isolated from the cow's own digestive juices so that they are in the optimum pH for their activities and they are not killed by extremes of pH
          • 1. Mouth
            • Grass chopped by teeth, mixed with saliva to form cud and then swallowed
          • 2. Rumen
            • Cud is mixed with cellulose digesting bacteria to produce glucose
              • This is fermented to form organic acids that are absorbed into the blood to provide energy for the cow
                • Waste products - carbon dioxide and methane - are passed out
          • 3. Reticulum
            • The cud arrives here before being regurgitated into the mouth and chewed again
          • 4. Omasum
            • The cud passes here to reabsorb water
          • 5. Abomasum
            • This functions like a 'normal' stomach and protein is digested
          • 6. Small intestine
            • Protein and lipid digestion followed by absorption
        • Non ruminants (Hind-gut digesters)
          • In non ruminant herbivores e.g. rabbits, the caecum is enlarged to provide a region for mutualistic micro-organisms to break down cellulose
            • As the digestion of cellulose to glucose occurs after the ileum, the glucose can't be absorbed
              • Hind gut digesters get round this by re-eating the faeces and absorbing the glucose 'second time around'
        • Ruminant v Non ruminant
          • Ruminants are more efficient than non ruminants as the rumen contains a greater variety of mutualistic bacteria than the caecum
            • Ruminants are therefore able to achieve a more complete breakdown of cellulose and consequently absorb more glucose
          • Carnivores have a short gut because protein is easy to digest. Herbivores have a long gut because cellulose is difficult to digest


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