2 - Organisation

• Cell


  The basic building block of a living organism
• Tissue


  A group of cells with a similar structure and function working together. For example, muscular tissue contracts to bring about movement.
• Organ


  A collection of tissues working together to perform a specific function. For example, the stomach contains glandular, muscular and epithelial tissues.
• Organ system


  A group of organs working together to perform specific functions. For example, the digestive system contains organs such as the stomach, the small intestine and the large intestine.
• Digestive system


  To digest food and absorb the nutrients obtained from digestion
• Pancreas and salivary gland


  Glands which produce digestive juices containing enzymes
• Stomach


  Produces hydrochloric acid - which kills any bacteria present and provides the optimum acidic pH for the protease enzyme to function
• Small intestine


  The site where soluble food molecules are absorbed into the bloodstream
• Liver


  Produces bile (stored in the gallbladder) which emulsifies lipids and allows the lipase enzyme to work more efficiently
• Large intestine


  Absorbs water from undigested food, producing faeces
• Enzymes


  Act as biological catalysts which speed up the rate of biological reactions (the breakdown of food) without being used up
• Enzyme shape


  Enzymes have a specific active site which is complementary to their substrate
• Metabolism


  The sum of all the reactions in a cell or an organism
• Types of metabolic reactions catalysed by enzymes


  • Building larger molecules from smaller molecules
  • Changing one molecule to another
  • Breaking down larger molecules into smaller molecules
• Lock and key hypothesis


  The shape of the enzyme active site and the substrate are complementary, so can bind together to form an enzyme-substrate complex
• Temperature effect on enzymes


  Up to a certain point, increasing temperature increases enzyme action, as molecules have a higher kinetic energy. Above a certain temperature, the shape of the active site is altered and the enzyme becomes denatured, so it can no longer catalyse the reaction. The optimum temperature is around 37°
• pH effect on enzymes


  The optimum pH for most enzymes is 7 (apart from proteases in the stomach). If the pH is too extreme, the shape of the active site may be altered and the enzyme may no longer work
• Locations of digestive enzymes

  • Carbohydrases: amylase - salivary gland and pancreas; maltase - small intestine
  • Proteases: pepsin - stomach; others - pancreas and small intestine
  • Lipases: pancreas and small intestine
• Role of carbohydrases


  Break down carbohydrates into monosaccharides and disaccharides. Amylase breaks down starch into maltose, and maltase breaks down maltose into glucose
• Role of proteases


  Break down proteins into amino acids
• Role of lipases


  Break down lipids into fatty acids and glycerol
• Use of digestion products


  They are used to build bigger molecules such as carbohydrates and proteins. Glucose is used as a substrate in respiration
• Bile


  Made by the liver and stored in the gallbladder
• Role of bile


  Neutralises the hydrochloric acid secreted by the stomach, and emulsifies lipids to form droplets - this increases the surface area for the lipase enzyme to work on
• Heart


  An organ that pumps blood around the body
• Circulatory system


  Carries oxygen and other useful substances to bodily tissues, and removes waste substances
• Double circulatory system


  1. One pathway carries blood from the heart to the lungs - where the gaseous exchange of oxygen and carbon dioxide takes place

  2. One pathway carries blood from the heart to the tissues
• Right ventricle


  Pumps blood to the lungs
• Left ventricle


  Pumps blood to the body tissues
• Importance of double circulatory system


  It makes the circulatory system more efficient - for example, oxygenated blood can be pumped around the body at a higher pressure by the left ventricle
• Heart chambers


  4 - right atrium, right ventricle, left atrium, left ventricle
• Left ventricle wall


  Thicker to pump blood at a higher pressure around the whole body
• Main blood vessels associated with the heart


  • Aorta (left) - carries oxygenated blood from the heart to the body
  • Pulmonary vein (left) - carries oxygenated blood from the lungs to the heart
  • Vena cava (right) - carries deoxygenated blood from the body to the heart
  • Pulmonary artery (right) - carries deoxygenated blood from the heart to the lungs
• Purpose of heart valves


  Prevent the backflow of blood
• Purpose of coronary arteries


  Supply the heart muscle with oxygenated blood
• Blood flow through the heart


  1. Blood enters the right atrium via the vena cava, and the left atrium via the pulmonary vein

  2. The atria contract, forcing blood into the ventricles and causing valves to shut

  3. After the ventricles contract, blood in the right ventricle is pumped to the lungs, and blood in the left ventricle is pumped to the body
• Purpose of valves in the heart


  Prevent the backflow of blood
• Blood flow through the heart


  1. Blood enters the right atrium via the vena cava, and the left atrium via the pulmonary vein

  2. The atria contract, forcing blood into the ventricles and causing valves to shut

  3. After the ventricles contract, blood in the right ventricle enters the pulmonary artery (to the lungs) and blood in the left ventricle enters the aorta (to the body)
• The approximate value of the natural resting heart rate is 70 beats per minute
• How the heart rate is controlled

  Heart rate is controlled by a group of cells in the right atrium which act as a pacemaker. They release waves of electrical activity which cause the heart muscle to contract.