Bio Topic 2: Organisation

• Cell:

  • make up all living things.
• Tissue:

  • a group of specialised cells with a similar structure and function.
  • They can be made of more than one type of cell. Examples include muscular tissue or epithelial tissue.
• Organs:

  • are formed from a number of different tissues, working together to produce a specific function.
  • An examples is the stomach, which has muscular tissue and epithelial tissue.
• Organ system:

  • Organs are organised into organ systems, which work together to perform a certain function.
  • The stomach is part of the digestive system, along with organs such as the liver and small intestine.
• The human Digestive system:

  • The digestive system is an organ system, as it is made up of organs working together to perform a certain function.
  • The food you eat is large and insoluble and needs to be broken down in order for it to be in a form that can be absorbed by cells.
• Digestive system


  Made of the following organs:
• Organs of the digestive system

  • Glands (salivary glands and the pancreas)
  • Stomach
  • Small intestine
  • Liver
  • Gall bladder
  • Large intestine
  • Rectum
  • Anus
• Glands (salivary glands and the pancreas)


  • Produce digestive juices containing enzymes which break down food
• Stomach


  • Produces hydrochloric acid to kill bacteria and to provide the optimum pH for the protease enzyme to work
• Small intestine


  • Where soluble molecules are absorbed into the blood
• Liver


  • Produces bile which is stored in the gall bladder, which helps with the digestion of lipids
• Large intestine


  • Absorbs water from undigested food to produce faeces
  • Passes out of your body through the rectum and anus
• Enzymes:

  biological catalysts (a substance that increases the rate of reaction without being used up)

  • Enzymes are present in many reactions so that they can be controlled.
  • They can both break up large molecules and join small ones
  • They are protein molecules and the shape of the enzyme is vital to its function.
  • This is because each enzyme has its own uniquely shaped active site where the substrate binds.
• The Lock and Key Hypothesis (a simplified explanation of how enzymes work):

  1. The shape of the substrate is complementary to the shape of the active site, so when they bond it forms an enzyme-substrate complex
  2. Once bound, the reaction the reaction takes place and the products are released from the surface of the enzyme
• Enzymes

  Require an optimum pH and temperature, because they are proteins
• Optimum temperature


  A range around 37 degrees celsius (body temperature)
• Increase in temperature up to optimum


  Rate of reaction increases
• Temperature above optimum

  Rate of reaction rapidly decreases and eventually the reaction stops
• When the temperature becomes too hot, the bonds in the structure will break
• This changes the shape of the active site, so the substrate can no longer fit in
• Denatured enzyme


  Can no longer work
• Optimum pH


  7 for most enzymes, but some that are produced in acidic conditions, such as the stomach, have a low optimum pH
• If the pH is too high or too low, the forces that hold the amino acid chains that make up the protein will be affected
• This will change the shape of the active site, so the substrate can no longer fit in
• Enzymes

  Vital for breaking down molecules in the digestive system so they can be absorbed into the bloodstream
• Enzymes

  • Released by cells in many different places
  • Specific to a certain type of molecule
• Carbohydrases


  Convert carbohydrates into simple sugars
• Carbohydrases

  • Amylase breaks down starch into maltose
• Amylase is produced in your salivary glands, pancreas and small intestine (most of the starch you eat is digested here)
• Proteases

  Convert proteins into amino acids
• Proteases


  • Pepsin which is produced in the stomach, other forms can be found in pancreas and small intestine
• Lipases


  Convert lipids into fatty acids and glycerol
• Lipases are produced in the pancreas and small intestine
• Digestion

  1. Soluble glucose, amino acids, fatty acids and glycerol pass into the bloodstream

  2. Used to build new carbohydrates, lipids and proteins

  3. Some glucose used in respiration
• There are a number of tests that can be carried out to determine whether a solution is made up of carbohydrate, protein or lipid.

  • Benedict's test for sugars (turns brick red)
  • lodine test for starch (turns blue-black)
  • test for protein (turns purple)
  • Emulsion test for lipids (add ethanol which results in a cloudy layer if a lipid is present)

  OR

  • sudan Ill test for lipids (red layer forms on top)
• Bile:

  • is produced in the liver and stored in the gallbladder. It is then released into the small intestine.

  It has two roles:

  1. It is alkaline to neutralise the hydrochloric acid which comes from the stomach- the enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach.
  2. It breaks down large drops of fat into smaller ones (emulsifies it). The larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids faster.
• Investigating the effect of pH on an enzyme controlled reaction

  1. Carry out a reaction at different pH's

  2. Time how long it takes for the product to form
• Practical involving breakdown of starch to maltose by amylase

  Uses iodine, which turns blue-black in the presence of starch
• Practical procedure

  1. Put a drop of iodine in each well in a spotting tile

  2. Warm a solution of amylase, starch and a buffer solution (this is the independent variable, so is changed each time you repeat the experiment)

  3. At regular points in the experiment, take drops of the solution and place in the wells

  4. The starch is no longer present and has been completely broken down when the iodine solution remains brown as opposed to blue-black

  5. Record the time for this to occur

  6. Calculate the rate from the equation: 1000/time
• The experiment should be repeated at different pH values while controlling all other factors which may affect the rate, such as temperature