organisation

• cells are the basic building blocks of all living organisms
• tissues are a group of cells with a similar structure and function
• organs are aggregations of tissues performing specific functions
• organs are organised into organ systems which work together to form organisms
• the human digestive system is an example of an organ system in which several organs work together to digest and absorb food. In the digestive system, large insoluble molecules are broken down into smaller, soluble molecules which can be absorbed by the body
• the salivary gland and pancreas produce digestive juices containing enzymes which break down large insoluble food molecules
• the stomach produces hydrochloric acid to kill bacteria and provides the optimum pH for the protease enzyme to work
• the small intestine is where soluble molecules are released and absorbed into the blood
• the liver produces bile (which is stored in the gall bladder), and bile neutralises and emulsifies lipids
• the large intestine absorbs water from undigested food, and faeces is left behind. Faeces is ejected out the body through the rectum and anus
• enzymes are proteins that are biological catalysts
• the shape of the enzymes active site is vital to its function, this is because the enzymes active site and its substrate are complimentary in shape
• lock-and-key theory:

  1. a specific enzyme and its specific substrate are complimentary in shape like a lock and key.
  2. the substrate fits or 'locks' into the enzymes active site forming an enzyme-substrate complex
  3. the chemical reaction takes place in the active site, and the substrate is broken down into small, soluble molecules
  4. products are released, and then the enzyme can be reused to break down another substrate
• enzymes work fastest at their optimum temperature (in the human body is around 37 degrees celsius), and the temperature increasing beyond the optimum temperature will cause the bonds between the amino acids to break, and the active site of the enzyme will change, so its complimentary substrate cannot bind to the active site. At this point the enzyme is denatured
• at too low a temperature, an enzyme won't have enough energy to bind with a substrate, and form an enzyme-substrate complex.
• the optimum pH for most enzymes is 7
• if the pH is too high or low, the enzyme denatures, and the shape of the active site changes
• amylase:

  • breaks starch down into glucose (carbohydrase breaks carbohydrates into simple sugars)
  • produced in -> salivary glands, the pancreas and the small intestine
• enzymes catalyse specific reactions in living organisms due to the shape of their active site.
• protease:

  • breaks down proteins into amino acids
  • produce in -> the stomach, small intestine and pancreas
• lipase:

  • breaks down lipids into fatty acids and glycerol
  • produced in -> the pancreas and small intestine
• the products of digestion are carried in the bloodstream and are used to build new carbohydrates, lipids and proteins. Some glucose is used in respiration
• bile:

  • bile is made in the liver and stored in the gall-bladder
  • it is alkaline to neutralise hydrochloric acid from the stomach, bringing it to the optimum pH for lipase and amylase
  • it also emulsifies lipids to form small droplets which increases the surface area
  • the alkaline conditions and large surface area increase the rate of fat breakdown by lipase
• test for starch:

  • add iodine
  • if colour changes from a brown-orange to a blue-black, starch is present
• test for proteins:

  • grind up food in a pestle and mortar
  • add distilled water
  • add Biuret's solution
  • if it goes from blue to a lilac purple, proteins are present
• test for sugars:

  • grind up food in a pestle and mortar
  • add distilled water
  • add Benedict's reagent and heat in a water bath
  • if it goes from blue to green or green-yellow, there is a low amount of sugars
  • if it goes from blue to brick-red, quantity of sugars is high
• the heart is an organ that pumps blood around the body through a double circulatory system
• the right side of the heart receives deoxygenated blood from the body and pumps it to the lungs where oxygen diffuses into the blood from the alveoli and carbon dioxide diffuses out (gas exchange takes place)
• the left side of the heart receives oxygenated blood from the lungs and pumps it around the body, so cells can get oxygen and substances needed to respire
• pathway of blood:

  1. deoxygenated blood enters the heart via the vena cava into the right atrium
  2. blood flows through valves into the right ventricle
  3. the right ventricle contracts, and the blood is pumped to the lungs through the pulmonary artery where gas exchange occurs and the blood becomes oxygenated
  4. oxygenated blood returns to the heart via the pulmonary vein, to the left atrium
  5. blood flows the the left ventricle
  6. the left ventricle contracts where the blood is pumped around the body through the aorta
• adaptations of the heart - valves:

  • valves prevent back flow
• adaptations of the heart - coronary artery:

  • coronary artery provides the heart with oxygenated blood
  • the heart needs a constant supply of oxygen for aerobic respiration to release energy to allow continued muscle contract (which pumps blood) and oxygen is needed for the heart muscle and cells to stay alive
• adaptations of the heart - heart muscle:

  • the heart muscle is made of a special type of cardiac muscle which does not fatigue like skeletal muscle
• adaptations of the heart - ventricles:

  • the walls of ventricles are thicker and stronger so they can generate a high enough pressure for the blood to be able to flow
  • the walls of the left ventricle is much thicker than the walls of the right ventricle as left has to pump blood all around the body, whilst the right ventricle just has to pump the blood to the lungs
• the natural resting heart rate is controlled by a group of cells located in the right atrium that acts as a pacemaker
• artificial pacemakers are electrical devices used to correct irregularities in the heart rate
• pacemakers (natural and artificial) coordinate the contraction of the heart muscles
• artery -> transport blood away from the heart:

  • narrow lumen to maintain blood pressure
  • thick muscular walls to withstand a high blood pressure
  • elastic fibres allow the arteries to stretch and cope with the high blood pressure
• veins -> transport blood to the heart:

  • wide lumen to keep blood flowing (blood is usually at a low pressure)
  • valves to stop back flow and keep blood moving in the right direction towards the heart
• capillaries -> allows blood to flow close enough to cells that substances can diffuse between them:

  • one cell thick to create a short diffusion pathway
  • permeable walls so substances can move in and out, between the cells and capillaries