Organisation

• Cells are the basic building blocks that make up all living organisms


  specialised cells carry out a particular function- differentiation

  differentiation occurs during the development of multicellular organisms
• specialised cells form tissues, which form organs, which form organ systems


  large multicellular organisms have different organ systems inside them for exchanging and transporting materials
• a tissue is


  a group of similar cells that work together to perform a specific function

  it can include more than one type of cell- muscular tissue
• Tissues are organised into organs


  An organ is a group of different tissues that work together to perform a certain function- stomach
• an organ system is a group of organs working together to perform a particular function


  the digestive system breaks down and absorbs food
• enzymes are catalysts produced by living things- act as biological catalysts


  a catalyst is a substance which increases the speed of a reaction, without being changed or used up in the reaction
• Chemical reactions involve things being split apart or joined together


  Every enzyme has an active site with a unique shape that fits onto the substance involved in a reaction

  they only catalyse one specific reaction
• for an enzyme to work the substance has to fit into its active site


  if the substrate doesn't match the enzyme's active site, then the reaction won't be catalysed
• Lock and key theory

  enzymes have a specific active site that binds to a specific substrate
• Enzymes need the right temperature


  Changing the temperature, changes the rate of a reaction

  A higher temperature increases the reaction at first

  If it gets too hot, the bonds holding the enzyme together break, changing the shape of an enzyme's active site

  The substrate won't fit anymore so the enzyme has been denatured
• All enzymes have an optimum temperature
• Enzymes need the right pH


  If the pH is too high or too low, the pH interferes with the bonds holding the enzyme together

  This changes the shape of the active site and denatures the enzyme

  All enzymes have an optimum pH they work best at
• Investigate the effect of pH on enzyme activity

  Place a drop of iodine into every well of a spotting tile

  Using a bunsen burner heat a beaker of water to 35C

  Add amylase solution and buffer solution to a boiling tube

  Add starch solution + mix contents

  Record how long it takes the amylase to break down the starch(the iodine will remain browny orange)
• rate of reaction


  1000/time
• Digestive enzymes break down big molecules

  Starch, proteins, and fats are big molecules

  They are too big to pass through the walls of the digestive system so digestive enzymes break these substances down into smaller ones

  The smaller, soluble molecules can pass easily into the bloodstream
• AMYLASE breaks down STARCH into MALTOSE


  amylase is made in the salivary glands, the pancreas, and the small intestine
• PROTEINS are broken down by PROTEASE into AMINO ACIDS


  protease is made in three places, the stomach, the pancreas, and the small intestine
• LIPIDS are broken down by LIPASE into GLYCEROL and FATTY ACIDS


  lipases are made in two places, the pancreas, and the small intestine
• Bile neutralises the stomach acid


  Bile is produced in the liver and stored in the gall bladder before being released into the small intestine

  The hydrochloric acid in the stomach makes the pH too acidic for the enzymes in the small intestine to work properly

  Bile is alkaline- it neutralises the acid and makes the conditions alkaline

  The enzymes in the small intestine work best in alkaline conditions
• Bile emulsifies fat


  Bile breaks fat down into tiny droplets

  This gives it a larger surface area for the enzyme lipase to work on, making its digestion quicker
• The digestive system is made up of


  the mouth, the gullet (oesophagus), the stomach, the liver, the gall bladder, the pancreas, the large intestine, the small intestine, and the rectum
• the salivary glands


  produce the AMYLASE enzyme in the saliva
• gullet (oesophagus)


  connects the mouth with the stomach
• stomach


  pummels the food with its muscular walls

  produces the PROTEASE enzyme- pepsin

  produces hydrochloric acid- to kill bacteria, to give the right pH for the protease enzyme to work
• Liver


  where bile is produced
• gall bladder


  where bile is stored, before being released into the small intestine
• pancreas


  produces PROTEASE, AMYLASE, and LIPASE enzymes- releases these into the small intestine
• large intestine


  where excess water is absorbed from the food
• small intestine


  produces PROTEASE, AMYLASE, and LIPASE enzymes to complete digestion

  digested food is absorbed out of the digestive system into the blood
• rectum


  where faeces is stored before being excreted through the anus
• Benedict's test for SUGARS


  Prepare a food sample and transfer 5cm3 to a test tube

  Prepare a water bath at 75C

  Add some benedict's solution to the test tube using a pipette

  Place the test tube in the water bath and leave for 5 minutes

  If the food contains sugar it will turn from a normal BLUE to a GREEN, YELLOW, or BRICK RED depending on how much sugar the food contains
• Iodine solution to test for STARCH


  Make a food sample and transfer 5cm3 to a test tube

  Add a few drops of iodine solution and gently shake to mix the contents

  If the sample contains starch, the solution will change from BROWNY-ORANGE to BLACK or BLUE
• Biuret test for PROTEINS


  Prepare a food sample and transfer 2cm3 to a test tube

  Add 2cm3 of biuret solution to the sample and gently mix by shaking the contents

  If the food contains protein, it will change from BLUE to LILAC
• Sudan III test for LIPIDS


  Prepare a sample of food and transfer 5cm3 to a test tube

  Use a pipette to transfer 3 drops of sudan III stain solution to the tube and shake it

  If the sample contains lipids, the mixture will split into two layers- the top layer will be BRIGHT RED
• the lungs are in the thorax


  the thorax is the top part of the body

  the lungs are separated from the lower half of the body by the diaphragm

  the lungs are protected by the ribcage
• the air breathed enters the trachea


  the trachea splits into two tubes called bronchi

  the bronchi split into smaller tubes called bronchioles

  the bronchioles end at small bags called alveoli, where gaseous exchange takes place
• Alveoli carry out gaseous exchange


  the blood passing next to the alveoli contains lots of carbon dioxide and little oxygen

  this means oxygen diffuses out of the alveoli and into the blood

  carbon dioxide diffuses out of the blood and into the alveoli to be breathed out
• when the blood reaches body cells oxygen is released


  oxygen diffuses into the body cells where the concentration is low

  carbon dioxide diffuses out of the body cells, where the concentration is high and into the blood, to be carried back to the lungs
• double circulatory system


  made of the pulmonary circuit- containing the lungs, and the pulmonary artery and vein

  and the systemic circuit- made of the heart, the rest of the veins and arteries, and the body
• The heart pumps blood around the body


  the walls of the heart are mostly made up of muscular tissue

  the heart has valves to prevent the backflow of blood and maximise efficency

  the heart uses four chambers to pump blood around- the left and right atrium, and the left and right ventricle