adaptions for nutrition

• Nutrition is the process by which organisms obtain energy to maintain life functions and matter to create and maintain structure. Energy and matter are obtained from nutrients.
• There are two main types of nutrition: 

  •  Autotrophic 
  •  Heterotrophic 
•  Organisms which are able to manufacture complex organic compounds from simple inorganic molecules, such as carbon dioxide and water, are called autotrophs.
• Autotrophs are referred to as producers, as they are able to synthesise their own complex organic compounds
• Plants are autotrophic
• Photosynthesis is a process which takes place in the chloroplasts
• Photosynthesis is able to turn simple inorganic compounds like water and carbon dioxide to form complex organic compounds such as sugars and starches.
• Photosynthetic bacteria use a pigment called bacteriochlorophyll, which is simpler than chlorophyll and comes in two forms green and purple.
• Photosynthetic bacteria-The source of energy which drives photosynthesis in autotrophic bacteria is light. These bacteria differ from plants in that the hydrogen needed to reduce carbon dioxide does not come from water, but from hydrogen sulphide. 
• Chemosynthetic bacteria can synthesise organic compounds from inorganic materials in the absence of light
• Chemosynthetic bacteria - They use energy derived from special methods of respiration to synthesise organic food. Hydrogen bacteria can oxidise hydrogen to form water. Nitrifying bacteria are chemosynthetic and are essential in the nitrogen cycle.
• Heterotrophs cannot synthesise their own organic food.
• They have to consume complex organic food material produced by autotrophs. Since they eat organic compounds they are known as consumers.
• Heterotrophs include animals, fungi and bacteria.  
• Holozoic feeders: Includes almost all animals. They take food into their bodies and break it down by the process of digestion. They have a specialised digestive system. Digested material is absorbed into the body tissues and used by the body cells.
•  Animals which feed solely on plant material are called herbivores
• Carnivores feed on other animals
• Omnivores feed on both plant and animal material
• Detritivores are animals which feed on dead and decaying material. 
• Saprophytes: Include all fungi and some bacteria. They feed on dead and decaying matter and do not have a specialised digestive system. They feed by secreting enzymes such as proteases, amylases, lipases and cellulases onto the food material outside the body and then absorb the soluble products across the cell membrane by diffusion. This is known as extracellular digestion.
• Microscopic saprophytes are called decomposers and their activities are essential in the decomposition of dead plant and animal material and the recycling of nutrients, such as nitrogen. 
• Parasites: A parasite lives in or on another living organism and causes harm to the host. The parasite feeds on the host. Some parasites live inside the host, while others live on the surface. They are considered highly specialised organisms and show considerable adaptation. An example is the tapeworm
• Mutualism: This involves a close association between members of two different species, but in this case both derive benefit from the relationship. Cows and sheep feed mainly on grass, a high proportion of which is made up of cellulose cell walls. Herbivores do not secrete cellulase and cannot digest cellulose. Instead they have mutualistic bacteria which live in a specialised region of the gut, called the rumen. These bacteria produce cellulase which benefits the herbivore and the bacteria absorb digested products such as amino acids which allow them to grow and thrive.  
•  Large insoluble organic molecules must be broken down by digestion and absorbed into the body tissues from the digestive system before utilisation in the body cells so digestion and absorption take place in the gut
• The gut is a long, hollow, muscular tube. The gut is organised to allow the movement of its contents in one direction only
•  In simple organisms which feed on only one type of food the gut is undifferentiated.
• In organisms with a varied diet the gut is divided into various parts along its length each part is specialised to carry out particular steps in the processes of mechanical and chemical digestion as well as absorption.
• Nutrition in unicellular organisms such as amoeba have no gut. They engulf food particles or other unicellular organisms using pseudopodia; a food vacuole forms as the pseudopodia fuse together. Lysosomes fuse with the food vacuole, releasing their digestive enzymes. Digestion is carried out intracellularly (inside the cell).  
• Nutrition in multicellular organisms like Hydra has a simple, undifferentiated, sac-like gut. The mouth (in the middle of the tentacles) is the only opening. The inner layer of cells is called the gastrodermis; the gastrodermis secretes digestive enzymes into the lumen of the gut. Digested food is absorbed by the gut wall. Undigested food is egested via the mouth. 
•  Earthworms have a tube-like gut with an opening at both ends; a mouth for ingestion and an anus for egestion. The gut has different regions e.g. an oesophagus, crop, gizzard and intestine, each with a specific function.
• The human gut is highly specialised with distinct regions, each with a specific function. Different regions allow for the digestion of different food substances. In humans the main regions of the gut are the mouth, oesophagus , stomach, small intestine (duodenum and ileum), large intestine and anus.
• small intestine has 2 sections called the duodenum and ileum
• the duoedenum is a section in the small intestine where food will be mixed with bile
• the illeum is a section of the small intestine that digests food and absorbs the nutrients
• the gut wall consists of five tissue layers surrounding the gut cavity   

  • Serosa  
  • Longitudinal muscle  
  • circular muscle  
  • Sub-mucosa  
  • Mucosa 
• The serosa consists of a layer of 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.
•  The muscle layer consists of two layers of muscle running in different directions. longitudinal muscle and circular muscle.
•  Collectively these muscles cause peristalsis which propels food along the gut. Behind the ball of food the circular muscles contract and the longitudinal muscles relax, thus helping move the food along.
• The sub-mucosa consists of connective tissue containing blood and lymph vessels to take away absorbed food as well as nerves that coordinate the muscular contractions involved in the process of peristalsis. 
• The mucosa is the innermost layer and lines the wall of the gut. It secretes mucus which lubricates and protects the mucosa. In some regions of the gut the mucosa secretes digestive juices. In others it absorbs digested food.