organisation

• a tissue is a group of cells with a similar structure and function
• an organ is a group of tissues working together for a specific function. Eg the stomach. The stomach contains muscle tissue and glandular tissue )which release enzymes)
• organs are grouped into organ systems which work together to form organisms.
• food contains 3 main nutrients:

  • carbohydrates (starch)
  • protein
  • lipids (fats) all of these are large molecules. They are too large to be absorbed into the bloodstream. So they have to be digested.
• during digestion, large food molecules are broken down into small molecules by enzymes. The small molecules can then be absorbed into the bloodstream.
• The digestive system: part 1

  • mouth - chew food. Enzymes in the saliva begin to digest starch into smaller sugar molecules.
  • oesophagus - the food then passes down the oesophagus into the stomach.
  • stomach - enzymes begin the digestion of proteins. The stomach also contains hydrochloric acid which helps the enzymes to digest proteins. The food spends several hours in the stomach. The churning from the stomach muscles, turns the food into a fluid increasing the surface area for enzymes to digest.
• The digestive system: part 2

  • small intestine - fluid passes into here. Chemicals are released into the small intestine from the:
  • pancreas - releases enzymes which continue the digestion of starch and protein. They also start the digestion of lipids
  • liver - releases bile which helps to speed up the digestion of lipids. Bile also neutralises the acid released from the stomach.
• The digestive system: part 3

  • small intestine - the fluid now makes its way down the rest of the small intestine. The walls of the small intestine release enzymes to continue the digestion of protein and lipids. In the small intestine, the small food molecules produced by digestion are absorbed into the bloodstream either by diffusion or active transport.
  • large intestine - the fluid makes its way through the large intestine, where water is absorbed into the bloodstream
  • finally the faeces is released from the body.
• the order of the digestive system:

  • mouth
  • oesophagus
  • stomach
  • small intestine (liver and pancreas release chemicals)
  • large intestine
  • exit the body
• in the digestive system, large molecules are digested into smaller molecules and then the products of digestion are absorbed into the bloodstream
• the products of digestion are then used by the body to build new carbohydrates, lipids and proteins.
• some of the glucose produced in digestion, is used in respiration
• enzymes catalyse (speed up) chemical reactions.
• enzymes are large protein molecules and they have a groove on their surface called the active site. The active site is where the substrate attaches to. The substrate is the molecules the enzyme breaks down.

  
• the substrate molecules fits perfectly into the active site of the enzyme. The enzyme now breaks down the substrate into the products. The enzyme cannot break down substrates that don't fit into the active site.
• enzymes are specific. The substrate must fit perfectly into the active site (the lock and key theory)
• Enzymes are proteins that function as biological catalysts. So, they are molecules that speed up a chemical reaction without being changed by the reaction.
• proteins are broken down by enzymes called proteases. These are found in the stomach, pancreatic fluids and the small intestine.
• proteins are long chains of chemicals called amino acids
• When we digest proteins, the protease enzymes convert the protein back to the individual amino acids, which are then absorbed into the bloodstream. When the amino acids are then absorbed by the body cells, they are joined together in a different order to make human proteins.
• starch consists of a chain of glucose molecules.
• starch is a carbohydrate
• carbohydrates are broken down by enzymes called carbohydrases. In the case of starch this is called amylase.
• starch is broken down by amylase.
• when carbohydrates like starch are digested, we produce simple sugars.
• amylase is found in the saliva and pancreatic fluid.
• a lipid molecules consists of a molecule of glycerol attached to three molecules of fatty acids
• lipid molecules are digested by the enzyme lipase. This produces glycerol and fatty acids.
• lipase is found in the pancreatic fluid and small intestine.
• • proteins - long chains of amino acids - digested by protease which is found in the stomach, pancreatic fluids and small intestine.
  • starch - carbohydrate - a chain of glucose molecules - digested by amylase which is found in the saliva and pancreatic fluid.
  • lipids - fats - glycerol attached to 3 molecules of fatty acids - digested by lipase which is found in the pancreatic fluid and the small intestine.
• bile is made in the liver and it is stored in the gall bladder
• bile helps to speed up the digestion of lipids but it is not an enzyme
• bile converts large lipid droplets into smaller ones. Scientists say that bile emulsifies the lipid, this massively increases the surface area of the lipid droplets, this increases the rate if lipid breakdown by lipase.
• bile emulsifies lipid
• bile is also alkaline. This allows it to neutralise stomach acid, creating alkaline conditions in the small intestine. This increases the rate of lipid digestion by lipase.
• as we increase the temperature, the activity of the enzyme increases (the reaction gets faster). As the temperature increases, the enzyme and substrate are moving faster so there are more collisions per second between the substrate and the active site. At a certain temperature, the enzyme is working at the fastest possible rate. That's called the optimum temperature. At this point there is the maximum frequency of successful collisions between the substrate and the active site.
• for most human enzymes the optimum temperature is 37 degrees celsius. Which is human body temperature.
• as we increase the temperature past the optimum, then the activity of the enzyme rapidly decreases to zero (the enzyme stops working). That's because at high temperatures, the enzyme molecule vibrates and the shape of the active site changes. Now the substrate no longer fits perfectly into the active site. The active site is now denatured. The enzyme can no longer catalyse the reaction
• the enzyme has an optimum pH, where the activity is maximum. If we make the pH more acidic or more alkaline then the activity drops to zero. That's because the active site denatures if the conditions are too acidic or alkaline.
• each enzyme has a specific optimum pH.